Patent Application
20190040491
The disclosure relates generally to thermally treated metallic materials and to related methods and systems for the thermal treatment of metals and alloys.
In the thermal treatment of metallic materials such as pure metals, alloys, intermetallics and metallic glasses, a variety of thermal and/or thermomechanical processes are used to provide desired combinations of microstructure, mechanical properties, physical properties and/or surface finishes. Particularly, metallic materials can be thermally treated and/or thermomechanically treated to produce recrystallization of the metallic material's microstructure, stress relief of a metallic material article and/or desired second phase morphology within a host matrix. Such thermal treatments typically include heating of a metallic material article to an elevated temperature, holding the metallic material article at the elevated temperature for a desired length of time and then cooling the metallic material article. In some processes, a controlled heating rate employed to heat the metallic component article to the elevated temperature and/or cooling a controlled cooling rate to cool the metallic material article is desired.
Current thermal treatment of metallic material articles, particularly in commercial thermal treatment processers, use large heating furnaces, long cooling (runout) tables which require large amounts energy to provide sufficient heat and cooling liquid to provide sufficient cooling rates. In addition, rapidly quenching metallic material articles from the elevated temperature to a desired lower temperature can be a problematic when attempting to move metallic material articles from a heated furnace (heating zone) to a quench station (cooling zone). Accordingly, apparatuses and methods that provide thermal treatments to metallic material articles while reducing energy consumption and increasing ease of movement between heating zones and cooling zones would be desirable.
This disclosure relates, in part, to thermally treated metallic material articles, and to methods, processes, and systems that thermally treat metallic material articles. In various embodiments, the process and method of the current disclosure heats and/or cools an article formed from a metallic material (article), the article supported with gas during the heating and/or cooling. The article is heated by transferring thermal energy from a heat source to the article across a heating gap between the heat source and the article such that more than 20% of the thermal energy leaving the heat source crosses the heating gap and is received by the article. The article is heated to and held at a desired elevated temperature for a desired amount of time. Thereafter, the article is allowed to cool. In embodiments, the article is allowed to air cool. In other embodiments, the article is cooled by transferring thermal energy from the article to a heat sink across a cooling gap between the article and the heat sink such that more than 20% of the thermal energy leaving the heated article crosses the cooling gap and is received by the heat sink. In embodiments, the article is supported with gas during heating and more than half of the thermal energy leaving the heat source crosses the heating gap is received by the article. The article can also be supported with gas during cooling and more than half of the thermal energy leaving the article crosses the cooling gap is received by the heat sink. The heating gap or the cooling gap can have an average thickness between an outer surface of the heat source and the article or the article and an outer surface of the heat sink surface, respectively, that is less than 10 millimeters (mm), 5 mm, 2 mm 1 mm, 800 micrometers (μm), 600 μm, 400 μm, or 200 μm. In embodiments, a heat transfer rate from the heat source to the article during heating, or from the article to the heat sink during cooling, is greater than 50 kilowatts per square meter (kW/m2), greater than 100 kW/m2, greater than 150 kW/m2, greater than 200 kW/m2, greater than 250 kW/m2, greater than 300 kW/m2, greater than 350 kW/m2, greater than 450 kW/m2, greater than 550 kW/m2, greater than 650 kW/m2, greater than 750 kW/m2, greater than 1000 kW/m2, or greater than 1200 kW/m2 for the area of the outer surface of the heat source, or for the area of the outer surface of the article, respectively.
The article can be in the form of a sheet, a cylindrical rod, a hexagonal rod, and the like. When the article is in the form of a sheet, the article has a length, a width, and a thickness. In embodiments, the thickness of the sheet is less than 3 mm, less than 2 mm, less than 1.5 mm, less than 1.0 mm, less than 0.5 mm, less than about 0.25 mm, less than about 0.1 mm, less than 0.08 mm, less than 0.06 mm, or less than 0.04 mm. At least one of the width and the length are greater than five times the thickness of the sheet. When the article is in the form of a rod, the rod has an average diameter and a length. In embodiments, the diameter of the rod is less than 10 mm, less than 9 mm, less than 8 mm, less than 7 mm, less than 6 mm, less than 5 mm, less than 4 mm, less than 3 mm, less than 2 mm, less than 1 mm, less than 0.8 mm, less than 0.6 mm, less than 0.4 mm, less than 0.2 mm or less than 0.1 mm.
The heating gap or cooling gap can be a gas gap with a gap area and a total mass flow rate of gas into the gas gap is greater than 0 and less than 2 k/gCp per square meter of gap area where k is the thermal conductivity of a gas within the gas gap evaluated in the direction of heat conduction, g is the distance between the heated article and the heat sink surface, and Cp is the specific heat capacity of the gas within the gas gap.
The metallic material can be a pure metal or an alloy and the pure metal or alloy can be polycrystalline, single crystal, or metallic glass. The pure metal can be a commercial pure metal such as commercial pure aluminum (Al), copper (Cu), chromium (Cr), nickel (Ni), niobium (Nb), iron (Fe), magnesium (Mg), molybdenum (Mo), silver (Ag), tantalum (Ta), titanium (Ti), tungsten (W) zirconium (Zr), gold (Au), platinum (Pt) or any other commercially available pure metal. The alloy can be an Al-base alloy, a Cu-base alloy, a Cr-base alloy, a Ni-base alloy, a Nb-base alloy, an Fe-base alloy, a Mg-base alloy, a Mo-base alloy, a Ag-base alloy, a Ta-base alloy, a Ti-base alloy, a W-base alloy, a Zr-base alloy, a Au-base alloy or another known alloy.
In embodiments, the article is made from an Al-base alloy and the Al-base alloy article is solution heat treated, quenched and aged in order to provide a precipitation strengthened (also known as precipitation hardened or age hardened) article with reduced residual stresses. In addition, the Al-base alloy article can be subjected cold working and then heated by the heat source such that recrystallization of the cold worked Al-base alloy article microstructure occurs. The recrystallized Al-base alloy article can be controllably cooled to prevent undesired grain growth of the recrystallized Al-base alloy article microstructure.
In embodiments, the article is made from a Cu-base alloy article and the Cu-base alloy article is solution heat treated, quenched and aged in order to provide a precipitation strengthened article with reduced residual stresses. In addition, the Cu-base alloy article can be subjected cold working and then heated by the heat source such that recrystallization of the cold worked Cu-base alloy article microstructure occurs. The recrystallized Cu-base alloy article can be controllably cooled to prevent undesired grain growth of the recrystallized Cu-base alloy article microstructure.
In embodiments, the article is made from an Fe-base alloy and the Fe-base alloy article is solution annealed such that the microstructure of the Fe-base alloy is completely austenite and then cooled to provide a microstructure with ferrite and a desired amount of pearlite, including no pearlite. In other embodiments, the Fe-base alloy article is solution annealed such that the microstructure of the Fe-base alloy is completely austenite and then cooled to provide a microstructure with ferrite and a desired amount of bainite and/or martensite. The solution annealed Fe-base alloy article can be cooled such retained austenite can be present in the Fe-base alloy article's microstructure. The Fe-base alloy article can be subjected cold working and then heated by the heat source such that recrystallization of the cold worked Fe-base alloy article microstructure occurs. The recrystallized Fe-base alloy article can be controllably cooled to prevent undesired grain growth of the recrystallized Fe-base alloy article microstructure.
In embodiments, the article is made from a Ni-base alloy and the Ni-base alloy article is solution annealed such that the microstructure of the Ni-base alloy is completely austenitic (face centered cubic—FCC) and then cooled to provide a microstructure with desired second phase precipitates. Such second phases precipitates can include Ni3Al (gamma prime) precipitates, carbide precipitates, nitride precipitates and/or carbonitride precipitates. The Ni-base alloy article can be subjected cold working and then heated by the heat source such that recrystallization of the cold worked Ni-base alloy article microstructure occurs. The recrystallized Ni-base alloy article can be controllably cooled to prevent undesired grain growth of the recrystallized Ni-base alloy article microstructure. The article can be made from other types of alloys and heat treated and cooled to provide a desired article microstructure. It should be appreciated that the microstructure of an alloy article is closely linked to the article's mechanical properties. Accordingly, an alloy article can be heated treated and cooled to provide a desired combination of strength and ductility.
The process can include heating of the metallic material article in a heating zone configured to chemically alter a surface region of the article. For example, the heating zone can include chemical vapor deposition (CVD) equipment and/or plasma deposition equipment that can chemically alter the surface region of the article. The surface region of the article can be chemically altered such as by coating with, impregnation and/or diffusion of elements such as nitrogen (nitriding), boron (boriding), carbon (carburizing), and combinations thereof.
Additional features and advantages will be set forth in the detailed description that follows, and, in part, will be readily apparent to those skilled in the art from the description or recognized by practicing the embodiments as described in the written description and claims hereof, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary, and are intended to provide an overview or framework to understand the nature and character of the claims.
The accompanying drawings are included to provide a further understanding and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiments, and together with the description serve to explain principles and the operation of the various embodiments.
Applicant has recognized a need for improvements in thermal treatment of metallic materials, both in methods and systems for thermally treating metallic materials and the resulting thermally treated metallic materials themselves. For example, thin sheets of metallic materials are useful for a number of applications, including use in heat exchangers, aerospace applications, cookware, cutlery, heat treating equipment, alternative energy components, and building materials. Metallic materials, the term herein including pure metals, alloys, intermetallics, and metallic glasses, can be processed to have a wide range of microstructures and mechanical properties. Metallic materials, particularly alloys, can provide high strength and excellent ductility compared to ceramics and glasses. In addition, metallic materials are typically electrically conductive and are used in electrical applications.
Traditional thermal treatment of metallic materials typically includes placing a metallic material article (article) in a furnace at an elevated temperature for a given amount of time and then removing the article form the furnace and cooled. In the event that the article has been subjected to cold working, the thermal treatment of the article can result in recrystallization of the article's microstructure. The thermal treatment of the article can also reduce residual stress within the article without recrystallization of the article's microstructure. When the article is made from a metal or alloy that has a high temperature phase and a different low temperature phase, e.g. iron or steel with an austenitic high temperature phase (γ) and a ferritic low temperature phase (α) thermal treatment of the article can provide an article microstructure with the ferritic low temperature phase and additional metastable phases. In addition, heating and controlled cooling of the article can provide a desired density and spatial location of the one or more metastable phases. However, traditional thermal treatment of articles typically involves large furnaces that use significant amounts of energy for heating. Additionally, such furnaces may provide a reducing atmosphere for thermal treatment of the articles and this use large amounts of reducing gases such as hydrogen gas.
Therefore, a need exists for systems and methods for thermally treating articles that significantly reduce energy and/or reducing gas requirements. Specifically, processes and systems discussed herein thermally treat articles with a reduced energy consumption of at least 50% compared to traditional thermal treating systems. When a reducing gas is used during thermal treatment of a given type of classification of articles, the methods and systems described herein reduce the amount of reducing gas needed by more than 50% compared to traditional thermal treating systems.
The processes and systems described herein thermally treat an article by heating and/or cooling the article while it is supported with gas. In some embodiments the gas can be a moving and, in further embodiments, capable of moving the article. The article can be heated by transferring thermal energy from a heat source to the article across a heating gap between the heat source and the article such that more than 20% of the thermal energy leaving the heat source crosses the heating gap and can be received by the article. Also, the article can be cooled by transferring thermal energy from the article to a heat sink across a cooling gap between the article and the heat sink such that more than 20% of the thermal energy leaving the article crosses the cooling gap and can be received by the heat sink. In embodiments, more than 50% of the thermal energy leaving the heat source or the article crosses the heating gap or the cooling gap, respectively, and can be received by the article component or the heat sink, respectively. The heating gap or the cooling gap can have an average thickness between an outer surface of the heat source and the article or between the article and an outer surface of the heat sink that can be less than 200 microns, less than 180 microns, less than 160 microns, less than 140 microns, less than 120 microns, less than 100 microns, less than 80 microns, less than 60 microns, less than 40 microns or less than 20 microns. A heat transfer rate from the heat source to the article during heating or from the article to the heat sink during cooling can be greater than 50 kilowatts per square meter (kW/m2), greater than 100 kW/m2, greater than 150 kW/m2, greater than 200 kW/m2, greater than 250 kW/m2, greater than 300 kW/m2, greater than 350 kW/m2, greater than 450 kW/m2, greater than 550 kW/m2, greater than 650 kW/m2, greater than 750 kW/m2, greater than 1000 kW/m2, or greater than 1200 kW/m2 for the area of the outer surface of the heat source, or for the area of the outer surface of the article, respectively.
The article can be in the form of a sheet, a cylindrical rod, a hexagonal rod, and the like. When the article is in the form of a sheet, the article has a length, a width, and a thickness. In embodiments, the thickness of the sheet can be less than 3 mm, less than 2 mm, less than 1.5 mm, less than 1.0 mm, less than 0.5 mm, less than about 0.25 mm, less than about 0.1 mm, less than 0.08 mm, less than 0.06 mm, or less than 0.04 mm. At least one of the width and the length are greater than five times the thickness of the sheet. When the article is in the form of a rod, the rod has an average diameter and a length. In embodiments, the diameter of the rod can be less than 10 mm, less than 9 mm, less than 8 mm, less than 7 mm, less than 6 mm, less than 5 mm, less than 4 mm, less than 3 mm, less than 2 mm, less than 1 mm, less than 0.8 mm, less than 0.6 mm, less than 0.4 mm, less than 0.2 mm or less than 0.1 mm.
The heating gap or cooling gap can be a gas gap with a gap area and the total mass flow rate of gas into the gas gap can be greater than zero and less than 2 k/gCp per square meter of gap area, where k is the thermal conductivity of a gas within the gas gap evaluated in the direction of heat conduction, g is the distance between the heat source and the article or between the article and the heat sink surface, and Cp is the specific heat capacity of the gas within the gas gap.
The metallic material can be a pure metal or an alloy and the pure metal or alloy can be polycrystalline, single crystal, or metallic glass. The pure metal can be a commercial pure metal such as commercial pure aluminum (Al), copper (Cu), chromium (Cr), nickel (Ni), niobium (Nb), iron (Fe), magnesium (Mg), molybdenum (Mo), silver (Ag), tantalum (Ta), titanium (Ti), tungsten (W) zirconium (Zr), gold (Au), platinum (Pt) or any other commercially available pure metal. The alloy can be an Al-base alloy, a Cu-base alloy, a Cr-base alloy, a Ni-base alloy, a Nb-base alloy, an Fe-base alloy, a Mg-base alloy, a Mo-base alloy, a Ag-base alloy, a Ta-base alloy, a Ti-base alloy, a W-base alloy, a Zr-base alloy, a Au-base alloy or another known alloy.
In embodiments, the article can be made from an Al-base alloy and the Al-base alloy article can be solution heat treated and quenched in order to provide a precipitation strengthened (also known as precipitation hardened or age hardened) article with reduced residual stresses. In addition, the Al-base alloy article can be subjected cold working and then heated by the heat source such that recrystallization of the cold worked Al-base alloy article microstructure occurs. The recrystallized Al-base alloy article can be controllably cooled to prevent undesired grain growth of the recrystallized Al-base alloy article microstructure.
In embodiments, the article can be made from a Cu-base alloy article and the Cu-base alloy article can be solution heat treated, quenched and aged in order to provide a precipitation strengthened article with reduced residual stresses. In addition, the Cu-base alloy article can be subjected cold working and then heated by the heat source such that recrystallization of the cold worked Cu-base alloy article microstructure occurs. The recrystallized Cu-base alloy article can be controllably cooled to prevent undesired grain growth of the recrystallized Cu-base alloy article microstructure.
In embodiments, the article can be made from an Fe-base alloy and the Fe-base alloy article can be solution annealed such that the microstructure of the Fe-base alloy can be completely austenite and then cooled to provide a microstructure with ferrite and a desired amount of pearlite, including no pearlite. In other embodiments, the Fe-base alloy article can be solution annealed such that the microstructure of the Fe-base alloy can be completely austenite and then cooled to provide a microstructure with ferrite and a desired amount of bainite and/or martensite. The solution annealed Fe-base alloy article can be cooled such retained austenite can be present in the Fe-base alloy article's microstructure. The Fe-base alloy article can be subjected cold working and then heated by the heat source such that recrystallization of the cold worked Fe-base alloy article microstructure occurs. The recrystallized Fe-base alloy article can be controllably cooled to prevent undesired grain growth of the recrystallized Fe-base alloy article microstructure. For the purposes of the present disclosure, the term “solution annealed” refers to a thermal treatment that produces a solid solution of alloy elements in a high temperature matrix phase. It should be appreciated that the high temperature matrix phase can be the same phase as a low temperature matrix phase, e.g. face centered cubic (FCC) austenite for Ni-base alloys, or can be a different phase from the low temperature phase, e.g. FCC austenite versus BCC ferrite for Fe-base alloys.
In embodiments, the article can be made from a Ni-base alloy and the Ni-base alloy article can be solution annealed such that the microstructure of the Ni-base alloy can be completely austenitic (face centered cubic—FCC) and then cooled to provide a microstructure with desired second phase precipitates. Such second phases precipitates can include Ni3Al (gamma prime) precipitates, carbide precipitates, nitride precipitates and/or carbonitride precipitates. The Ni-base alloy article can be subjected cold working and then heated by the heat source such that recrystallization of the cold worked Ni-base alloy article microstructure occurs. The recrystallized Ni-base alloy article can be controllably cooled to prevent undesired grain growth of the recrystallized Ni-base alloy article microstructure. The article can be made from other types of alloys and heat treated and cooled to provide a desired article microstructure. It should be appreciated that the microstructure of an alloy article can be closely linked to the article's mechanical properties. Accordingly, an alloy article can be heated treated and cooled to provide a desired combination of strength and ductility.
The process can include heating of the metallic material article in a heating zone configured to chemically alter a surface region of the article. For example, the heating zone can include chemical vapor deposition (CVD) equipment and/or plasma deposition equipment that can chemically alter the surface region of the article. The surface region of the article can be chemically altered such as by coating with, impregnation and/or diffusion of elements such as nitrogen (nitriding), boron (boriding), carbon (carburizing), and combinations thereof.
By way of example,
In some embodiments, heating the article in the hot zone may be done predominantly via conduction of heat from a heat sink through a thin gas barrier. The conductive heating processes used in the hot zone can be similar to, but the reverse of the cooling processes described herein (e.g., pushing heat into the article). As shown in
In some embodiments, the heat sources and/or the surfaces thereof may be segmented. In some embodiments, the heat sources may be porous, and in such embodiments, the apertures through which the gas for gas bearings 312 can be delivered are the pores of the porous heat sinks. The plurality of apertures 314b, a gas source and the channel gap 316a may be in fluid communication. In some embodiments, the gas flows through the apertures 314b to form gas cushions, layers or bearings in the channel gap 316a. The gas cushions of some embodiments prevent the sheet 400a from contacting the heat source 314 surfaces. The gas also serves as the gas through which the sheet 400a can be heated by conduction more than by convection.
In some embodiments, the gas flowed through the apertures 314b heats the heat sources 314. In some embodiments, the gas flowed through the apertures both facilitates heat conduction, from the heat source 314, across the gap 316a, into the sheet 400a, and also heats the heat sources 314. In some instances, a separate gas or liquid may be used to heat the heat sources 314. For instance, the heat sources 314 may include passages (not shown), for flowing a heating gas or liquid therethrough to heat the heat sources 314. The passages can be enclosed.
Where two heat sources are used (i.e., a first heat source and the second heat source), one or more gas sources may be used to provide a gas to the channel gap 316a. The gas sources may include the same gas as one another or different gases. The channel gap 316a may, therefore, include one gas, a mixture of gases from different gas sources, or the same gas source. Exemplary gases include air, nitrogen, carbon dioxide, helium or other noble gases, hydrogen and various combinations thereof. The gas may be described by its thermal conductivity when it enters the channel 316 just before it begins to conductively heat the sheet 400a. In some instances, the gas may have a thermal conductivity of about (e.g., plus or minus 1%) 0.02 W/(m·K) or greater, about 0.025 W/(m·K) or greater, about 0.03 W/(m·K) or greater, about 0.035 W/(m·K) or greater, about 0.04 W/(m·K) or greater, about 0.045 W/(m·K) or greater, about 0.05 W/(m·K) or greater, about 0.06 W/(m·K) or greater, about 0.07 W/(m·K) or greater, about 0.08 W/(m·K) or greater, about 0.09 W/(m·K) or greater, about 0.1 W/(m·K) or greater, about 0.15 W/(m·K) or greater, or about 0.2 W/(m·K) or greater).
The processes and systems described herein allow for high heat transfer rates which, as discussed above, allow for rapid and controlled heating within sheet, and allow for rapid, localized and controlled heating of outer surface regions of thin sheet. Using air as the gas, with gaps between the sheet and the heat sinks, heat transfer rates as high as 50 kilowatts per square meter (kW/m2), greater than 100 kW/m2, greater than 150 kW/m2, greater than 200 kW/m2, greater than 250 kW/m2, greater than 300 kW/m2, greater than 350 kW/m2, greater than 450 kW/m2, greater than 550 kW/m2, greater than 650 kW/m2, greater than 750 kW/m2, greater than 1000 kW/m2, or greater than 1200 kW/m2 or more are possible through conduction alone. Using helium or hydrogen, heat transfer rates of 5000 kW/m2 or more can be achieved. Accordingly, the cold zone 330 can provide cooling rates that equate to furnace cooling, air cooling and/or water quenching (1000-4000 kW/m2) of articles thermally treated in the thermal treatment system 300.
In some embodiments, gaps 316a, between the hot zone gas bearings 312 and the sheet 400a, may be relatively large, on the order of 0.05″ (1.27 mm) to 0.125″ (3.175 mm) or greater, since the sheet 400a may be heated up relatively slowly and thermal radiation from the hot gas bearings 312 into the sheet 400a can be adequate for this purpose. In other embodiments, hot zone gap size may be as small as 150 microns per side or 500 microns per side. Smaller gaps may be advantageous, in some embodiments, because they enable the bearings to have better “stiffness”—i.e., ability to centralize the sheet and therefore flatten it while it is in its softened state. In some embodiments, the process may re-form the sheets flattening them—in the initial heating step, for example via the pressure supplied by the gas bearings 312. In some embodiments, the top and bottom hot zone bearings may be on actuators, allowing for changing the gap width in a continuous manner or, alternatively, allowing the sheet to be brought into the hot zone when the gap is large and then compressing the gap to flatten the sheet while it is still soft.
Process temperatures in the hot and/or cool zone are dependent on a number of factors, including sheet composition, sheet thickness, sheet properties (CTE, etc.), and desired level of thermal treatment (e.g. stress reliving, solution annealing, etc.). Generally, the starting process temperature may be any value between the ambient temperature and the melting point of the sheet. For low carbon steel, for example, system 300 heats the sheet 400a to a temperature between about (e.g., plus or minus 1%) 780 to about 820° C. For age-hardenable aluminum alloys, for example, system 300 heats the sheet to a solution anneal temperature of about 530° C., an annealing temperature of about 410° C. and/or an aging precipitation heat treatment temperature of about 175° C. For solution strengthened nickel alloys, for example, system 300 heats the sheet to a solution anneal temperature of about 1150° C. For age-hardenable nickel alloys, for example, system 300 heats the sheet to a solution anneal temperature of about 1080° C., to a first age-hardening treatment temperature of about 995° C., to a second age-hardening treatment temperature of about 845° C. and to a third age-hardening treatment temperature of about 760° C. Between the first age-hardening treatment temperature to the a second age-hardening treatment temperature, and from the a second age-hardening treatment temperature to the third age-hardening treatment temperature, the sheet can be cooled at one or more desired cooling rates such that furnace cooling, air cooling, water quenching, or some cooling rate between cooling rates associate with furnace cooling, air cooling or water quenching, can be provided to the sheet. Furthermore, the sheet can be moved back and forth between the hot zone 310 and the cold zone 330 in order to provide desired heating and cooling cycles for the sheet.
The sheet 400a can be heated to its desired starting thermal treatment temperature (e.g., a solution anneal temperature), and it can then moved from the hot zone 310 to the cold zone 330 for controlled cooling using any suitable means. In some embodiments, moving the sheet 400a from the hot zone 310 to the cold zone 330 may be accomplished by, for example (1) tilting the entire assembly such that gravity acting on the sheet forces it to move to the cold zone, (2) blocking off the gas flow from the leftmost exit of the hot zone 310 (the sides are enclosed in this embodiment), thereby forcing all of the gas emanating from all of the gas bearings to exit from the rightmost exit of the cold zone, causing fluid forces to be exerted on the sheet 400a and causing it to move to the cold zone 330, or (3) by a combination of (1) and (2)).
The transition gas bearings 320 may be supplied with gas by transition bearing plenums 328. The solid material thickness behind the surfaces of the transition gas bearings 320 may be thin, of low thermal mass and/or low thermal conductivity, allowing for reduced heat conduction from the hot zone 310 to the cold zone 330. The transition gas bearings 320 may serve as a thermal break or transition between the two zones 310 and 330 and may serve to transition from the larger gaps 316a of the hot zone down to small gaps 336 of the cold zone 330. Further, the low thermal mass and/or low thermal conductivity of transition gas bearings 320 limit(s) the amount of heat transfer and therefore cooling experienced by sheet 400a while passing past transition gas bearings 320.
Once the sheet 400a (hot zone) moves into the cold zone 330 and into the channel 330a, the sheet 400b (cold zone) can be stopped from exiting the right side exit by a mechanical stop or any other suitable blocking mechanism, shown as stop gate 341. Once the sheet 400b cools sufficiently, the stop gate 341 may be moved, unblocking cold zone channel 330a, and then the sheet 400b may be removed from the system 300. If desired, the sheet 400b may be left in the cold zone 330 until somewhere near room temperature or below before removal.
As noted above, within hot zone 310, sheet 400a can be heated to a desired temperature and the cold zone 330 includes a channel 330a for receiving heated sheet 400a through an opening 330b, conveying the sheet 400a into the cold zone 330, and cooling the sheet 400b in the cold zone 330. In one or more embodiments, the channel 330a includes a conveyance system that may include gas bearings, roller wheels, conveyor belt, or other means to physically transport the sheet through the cold zone. As shown in
As shown in
In some embodiments, the heat sinks and/or the surfaces thereof may be segmented. As noted above, in some embodiments, the heat sinks may be porous, and in such embodiments, the apertures through which the gas for gas bearings 332 can be delivered are the pores of the porous heat sinks. The plurality of apertures 332b, a gas source and the channel gap 330a may be in fluid communication. In some embodiments, the gas flows through the apertures 331a to form gas cushions, layers or bearings in the channel gap 330a. The gas cushions of some embodiments prevent the sheet 400b from contacting the heat sink 331 surfaces. The gas also serves as the gas through which the sheet 400b can be cooled by conduction more than by convection.
In some embodiments, the gas flowed through the apertures 331a cools the heat sinks. In some embodiments, the gas flowed through the apertures both facilitates heat conduction, from the sheet, across the gap, into the heat sinks, and also cools the heat sinks 331. In some instances, a separate gas or liquid may be used to cool the heat sinks 331. For instance, the heat sinks 331 may include passages 334, for flowing a cooling gas or liquid therethrough to cool the heat sinks 331. The passages 334 can be enclosed.
Where two heat sinks are used (i.e., a first heat sink and the second heat sink), one or more gas sources may be used to provide a gas to the channel gap 330a. The gas sources may include the same gas as one another or different gases. The channel gap 330a may, therefore, include one gas, a mixture of gases from different gas sources, or the same gas source. Exemplary gases include air, nitrogen, carbon dioxide, helium or other noble gases, hydrogen and various combinations thereof. In embodiments, the gas can be hydrogen and the thermal treatment system 300 serves as a bright anneal furnace, i.e. a furnace that anneals the sheet in a reducing environment which prevents oxidation of the sheet surface and reduces most oxides present on the sheet surface, thereby providing an annealed sheet with a “bright” surface. The quick transfer of the sheet 400a from the hot zone 310 to the cold zone 330 can provide a rapid cooling rate, e.g. equivalent to water quenching, to the sheet 400b. It should be appreciated that such a “water quench” type of cooling provides cooling rates currently not available for current bright anneal furnaces.
The gas may be described by its thermal conductivity when it enters the channel 330a just before it begins to conductively cool the sheet 400b. In some instances, the gas may have a thermal conductivity of about (e.g., plus or minus 1%) 0.02 W/(m·K) or greater, about 0.025 W/(m·K) or greater, about 0.03 W/(m·K) or greater, about 0.035 W/(m·K) or greater, about 0.04 W/(m·K) or greater, about 0.045 W/(m·K) or greater, about 0.05 W/(m·K) or greater, about 0.06 W/(m·K) or greater, about 0.07 W/(m·K) or greater, about 0.08 W/(m·K) or greater, about 0.09 W/(m·K) or greater, about 0.1 W/(m·K) or greater, about 0.15 W/(m·K) or greater, or about 0.2 W/(m·K) or greater).
The processes and systems described herein allow for high heat transfer rates which, as discussed above, allow for a strengthening degree of temperature differential to form within even a very thin sheet. Using air as the gas, with gaps between the sheet and the heat sinks, heat transfer rates as high as 50, 100, 150, 200, 250, 300 350, 450, 550, 650, 750, 1000, and 1200 kW/m2 or more are possible through conduction alone. Using helium or hydrogen, heat transfer rates of 5000 kW/m2 or more can be achieved.
The heat sinks 331 of one or more embodiments may be stationary or may be movable to modify the thickness of the channel gap 330a. The thickness of the sheet 400b may be in a range from about 0.4 times the thickness to about 0.6 times the thickness of channel gap 300a, which is defined as the distance between the opposing surfaces of the heat sinks 331 (e.g., upper and lower surface of heat sinks 331 in the arrangement of
In some embodiments, the channel gap in the hot zone 310 and/or the cold zone 330 may have a thickness such that when sheet 400a or 400b is being conveyed through or located within the channel 316a or 330a, the distance between the major surfaces of the sheet 400a or 400b and the heat source surface or heat sink surface (e.g., the gap size discussed above) can be about (e.g., plus or minus 1%) 100 μm or greater (e.g., in the range from about 100 μm to about 200 μm, from about 100 μm to about 190 μm, from about 100 μm to about 180 μm, from about 100 μm to about 170 μm, from about 100 μm to about 160 μm, from about 100 μm to about 150 μm, from about 110 μm to about 200 μm, from about 120 μm to about 200 μm, from about 130 μm to about 200 μm, or from about 140 μm to about 200 μm). In some embodiments, the channel gap may have a thickness such that when sheet 400a or 400b is being conveyed through the channel 316 or 330a, the distance between the sheet and the heat source surface or heat sink surface (the gap or gaps 316a or 330a) can be about (e.g., plus or minus 1%) 100 μm or less (e.g., in the range from about 10 μm to about 100 μm, from about 20 μm to about 100 μm, from about 30 μm to about 100 μm, from about 40 μm to about 100 μm, from about 10 μm to about 90 μm, from about 10 μm to about 80 μm, from about 10 μm to about 70 μm, from about 10 μm to about 60 μm, or from about 10 μm to about 50 μm). The total thickness of the channel gap 316a or 330a can be dependent on the thickness of the sheet 400a or 400b, but can be generally characterized as 2 times the distance between the heat source surface or heat sink surface and the sheet, plus the thickness of the sheet. In some embodiments, the distance or gaps 316a or 330a between the sheet and the heat sources or heat sinks may not be equal. In such embodiments, the total thickness of the channel gap 316a or 330a may be characterized as the sum of the distances between the sheet and each heat source surface or the sheet and each heat sink surface, plus the thickness of the sheet.
In some instances, the total thickness of the channel gap 316a or 330a may be less than about (e.g., plus or minus 1%) 2500 μm (e.g., in the range from about 120 μm to about 2500 μm, about 150 μm to about 2500 μm, about 200 μm to about 2500 μm, about 300 μm to about 2500 μm, about 400 μm to about 2500 μm, about 500 μm to about 2500 μm, about 600 μm to about 2500 μm, about 700 μm to about 2500 μm, about 800 μm to about 2500 μm, about 900 μm to about 2500 μm, about 1000 μm to about 2500 μm, about 120 μm to about 2250 μm, about 120 μm to about 2000 μm, about 120 μm to about 1800 μm, about 120 μm to about 1600 μm, about 120 μm to about 1500 μm, about 120 μm to about 1400 μm, about 120 μm to about 1300 μm, about 120 μm to about 1200 μm, or about 120 μm to about 1000 μm). In some instances, the total thickness of the channel gap may be about 2500 μm or more (e.g., in the range from about 2500 μm to about 10,000 μm, about 2500 μm to about 9,000 μm, about 2500 μm to about 8,000 μm, about 2500 μm to about 7,000 μm, about 2500 μm to about 6,000 μm, about 2500 μm to about 5,000 μm, about 2500 μm to about 4,000 μm, about 2750 μm to about 10,000 μm, about 3000 μm to about 10,000 μm, about 3500 μm to about 10,000 μm, about 4000 μm to about 10,000 μm, about 4500 μm to about 10,000 μm, or about 5000 μm to about 10,000 μm).
The apertures 331a in the heat sink 331 may be positioned to be perpendicular to the heat sink surface or may be positioned at an angle of 20 degrees or less, such as about (e.g., plus or minus 1%) 15 degrees or less, about 10 degrees or less or about 5 degrees or less) from perpendicular to the heat sink surface.
In some embodiments, the material behind the heat sink (cold gas bearing 332) surfaces can be any suitable material having high heat transfer rates, including metals (e.g., stainless steel, copper, aluminum), ceramics, carbon, etc. This material may be relatively thick compared to the material behind the surfaces of the transition gas bearings 320, as shown in
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Apparatus setup—As detailed above, the apparatus comprises three zones—a hot zone, a transition zone, and a cold zone. The gaps between the top and bottom thermal bearings in the hot zone and cold zone are set to desired spacings. Gas flow rates in the hot zone, transition zone, and quench zone are set to ensure centering of the article on the gas-bearing. The hot zone can be pre-heated to a desired temperature To where the article will be held a predetermined and desired amount of time before being transferred to the cold zone and cooled. The temperature T0 is determined by metallic material of the article being thermally treated and the specific thermal treatment being performed on the article. The time to equilibration is dependent at least on the thickness of the article. For example, for sheets of approximately 1.1 mm or less, equilibration occurs in approximately 10 seconds. For 3 mm sheets, equilibration occurs in approximately 10 seconds to 30 seconds. For thicker sheets, up to approximately 6 mm, the equilibration time may be on the order of 60 seconds. Once the article has equilibrated to T0, it can be held at To for a desired amount of time and then transferred through the transition zone on gas bearings and into the cooling or quench zone. The article cools at a desired cooling rate to a temperature below To (TL)and may or may not be held in the cold zone at TL for an extended period of time before exiting the cold zone. The article can be maintained in the cold zone for any period of time from 1 second, 10 seconds, 1 minute, several minutes, 1 hour, several hours or more, depending on the thermal treatment desired and/or the desired temperature of the article at removal.
A variety of different alloys can be thermally treated with the thermal treatment system disclosed herein. Examples of such alloys and microstructures and mechanical properties that can be obtained are provided.
A 6061 wrought aluminum sheet having a chemical composition in weight percent of 0.15 Mn, 0.4-0.8 Si, 0.15-0.35 Cr, 0.15-0.4 Cu, 0.7 Fe, 0.25 Zn, 0.8-1.2 Mg, 0.15 Ti, with the remainder being Al and other incidental impurities was provided as thin sheet having a thickness of 1 mm. The thin sheet was annealed in the hot zone at 775° F. for 2 hours followed by controlled cooling at 50° F. per hour down to 500° F., followed by air cooling. The material was subjected to an age hardening heat treatment at 350° F. for 8 hours followed by air cooling in order to produce the T6 temper. Mechanical properties of the 6061 aluminum sheet with the T6 temper showed an average tensile strength of 45,000 psi, yield strength of 40,000 psi, shear strength of 31,000 psi, elongation to failure of 12%, and a Brinell hardness of 95.
A cold rolled steel alloy sheet having a thickness of 0.5 mm and a chemical composition within the range and weight percent of 0.085-0.11 C, 1.4-2.0 Mn, 0.09-0.21 Mo, 0.02-0.05 Al, 0.16-0.5 Si, 0.13-0.5 Cr, 0.016 max Ti, 0.06 max Ni, 0.003 max S, 0.015 max P, 0.006 max N, and with the balance being iron and incidental metal impurities can be processed through the metal thermal treatment system 300 and subjected to an intercritical annealing in the hot zone at temperatures between 760-800° C. Thereafter, the intercritically annealed steel alloy sheet can be rapidly cooled to a temperature of less than 450° C. in the cold zone. The rapidly cooled sheet has a ferrite-martensite microstructure with less than 6 volume percent bainite, a 0.2% yield strength of at least 330 MPa, a tensile strength of at least 590 MPa, a total elongation to failure of at least 18%, and a uniform elongation of at least 10%.
Although Co-base and Ni-base solid-solution strengthened alloys employ second phase precipitates such as Cr-carbides, W-carbides, etc., to assist in high temperature strengthening of the material, the primary strengthening mechanism can be the addition and alloying of various elements within the Co or Ni matrix to provide “solid solution strengthening.”
One Co-base and two Ni-base solid-solution strengthened alloys having the following nominal chemical compositions (wt %) can be processed through the metal thermal treatment system 300.
Cobalt Alloy (C1): 10 Ni, 20 Cr, 15 W, 3 max Fe 1.5 Mn, 0.4 max Si, 0.10 C with the balance Co (approximately 51 et %) and incidental impurities (commercially available as HAYNES® 25 alloy).
First Nickel Alloy (N1): 22 Cr, 14 W, 2 Mo, 3 max Fe, 5 max Co, 0.5 Mn, 0.4 Si, 0.3 Al, 0.10 C, 0.02 La, 0.015 max B, with the balance Ni (approximately 57 wt %) and incidental impurities (commercially available as HAYNES® 230® alloy).
Second Nickel Alloy (N2): 22 Cr 18 Fe 9 Mo 1.5 Co 0.6 W 0.10 C 1 max Mn 1 max Si 0.008 B with the balance Ni (approximately 47 wt %) and incidental impurities (commercially available as HAYNES® Hastelloy® X alloy).
Typical solution annealing temperatures provided by the thermal treatment system 300 for the C1 and N1-N2 alloys are shown in Table 1 below. Such solid-solution-strengthened alloys are typically supplied in the solution annealed condition with microstructures of primary carbides dispersed in a single phase matrix. The microstructure can be free of primary carbides at grain boundaries and provides an optimum combination for room temperature fabricability and elevated temperature properties once the material can be put into service. Heat treatments performed at temperatures below the solution heat treating temperature range provided by the thermal treatment system 300 are known as mill annealing or stress relief thermal treatments (see Table 1 below). Mill annealing treatments are employed for restoring formed, partially fabricated, or otherwise as-worked alloy material to a condition where additional deformation or welding of the material can be performed. Such treatments may also be used to produce structures in finished raw materials which are optimum for specific forming operations. For example, mill annealing thermal treatments provided by the thermal treatment system 300 can be used to produce a microstructure with a fine grain size for deep drawing applications. Mill annealing of the solid-solution-strengthened alloys by the thermal treatment system 300 can also be used to relief stress and yet avoid article distortion that can occur at full solution annealing temperatures. However, it should be appreciated that the gas bearings of the thermal treatment system 300 support the solid-solution-strengthened alloys during annealing and thus can actually impose and ensure a final shape is maintained during the higher temperature solution annealing thermal treatments. Use of a mill annealing heat treatment typically results in precipitation of secondary carbides on grain boundaries of material originally supplied in the solution-annealed condition, and will not normally restore the material to the as-received condition.
When the solid-solution-strengthened are in the cold or warm-worked condition, i.e. after cold working of the material, application of a mill anneal or solution heat thermal treatment by the thermal treatment system 300 typically alters the microstructure of the article. The amount of prior cold work in the article influences the resulting microstructure and mechanical properties of the article. The results for several combinations of prior cold work and annealing temperature upon the microstructure response for sheet of the alloys noted above are shown below in Table 2.
Currently available commercial annealing furnaces for such alloys have temperature tolerances of +/−15° C. with tolerances of +/−10° C. obtainable with specialized equipment. However with the very small gap between the heat sources and the metallic material article in the thermal treatment system 300, temperature tolerances can be maintained within +/−8° C., and, in some embodiments, between +/−6° C., +/−4° C., +/−3° C., +/−2° C., or +/−1° C. at annealing temperatures up to 1200° C. Accordingly, greater temperature control provides increased microstructure and mechanical property control of articles thermally treated with embodiments of the thermal treatment system disclosed herein.
Two Ni-base age-hardenable (also known as precipitation hardenable or precipitation strengthenable) alloys having the following nominal chemical compositions (wt %) can be processed through the metal thermal treatment system 300.
First Ni-base age-hardenable alloy (NiAH1): 13.5 Co, 2 max Fe, 19 Cr, 4.3 Mo, 1.5 Al, 3 Ti, 0.08 C, 0.1 max Mn, 0.15 max Si, 0.006 B, 0.1 Cu, 0.05 Zr, with balance Ni (approximately 58 wt %) and incidental impurities (commercially available as HAYNES® Waspaloy alloy).
Second Ni-base age-hardenable alloy (NiAH2): 16 Cr, 8 Fe, 2.5 Ti, 1 Nb, 0.8 Al, 1 max Co, 0.35 max Mn, 0.35 max Sai, 0.08 max C, with balance Ni (approximately 70 wt %) and incidental impurities (commercially available as INCONEL® X-750 alloy and HAYNES® X-750 alloy).
Ni-base age-hardenable alloys derive most of their strength from thermal treatments that result in a range of second phase precipitates in the microstructure. The predominant precipitate is Ni3Al (gamma prime). Thermal treatment of such alloys to provide the precipitation hardened microstructure requires a number of heating and cooling steps. For example, a typical heat treatment for the NiAH1 alloy to provide the precipitation hardened microstructure includes solution annealing the material at 1080° C. for 30 minutes followed by a water quench. Then the material is subjected to a first precipitation thermal treatment at 995° C. for 2 hours followed by air cooling to room temperature, then a second precipitation thermal treatment at 845° C. for 4 hours followed by air cooling to room temperature, and then a third precipitation thermal treatment at 760° C. for 16 hours followed air cooling to room temperature. The resulting precipitation hardened microstructure for the NiAH1 provides excellent mechanical properties up to temperatures approximately 700° C. as shown in Table 3 (tensile test properties) and Table 4 (stress-rupture properties) below.
For another example, a typical heat treatment for the NiAH2 alloy to provide the precipitation hardened microstructure includes solution annealing the material at 1040° C. followed by a first precipitation thermal treatment at 730° C. for 8 hours followed by furnace cooling to a second precipitation thermal treatment at 620° C. for 8 hours followed by air cooling to room temperature. The resulting precipitation hardened microstructure for the NiAH2 provides excellent mechanical properties up to temperatures approximately 700° C. as shown in Tables 5 and 6 below.
Other aspects and advantages will be apparent from a review of the specification as a whole, the appended claims and Appendix A.
The construction and arrangements of the metallic materials as shown in the various exemplary embodiments, are illustrative only. Although only a few embodiments have been described in detail in this disclosure, many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes, and proportions of the various elements, values of parameters, mounting arrangements, use of materials, orientations) without materially departing from the novel teachings and advantages of the subject matter described herein. Some elements shown as integrally formed may be constructed of multiple parts or elements, the position of elements may be reversed or otherwise varied, and the nature or number of discrete elements or positions may be altered or varied. The order or sequence of any process, logical algorithm, or method steps may be varied or re-sequenced according to alternative embodiments. Other substitutions, modifications, changes and omissions may also be made in the design, operating conditions and arrangement of the various exemplary embodiments without departing from the scope of the present inventive technology.
This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Ser. No. 62/288,695 filed on Jan. 29, 2016, the content of which is relied upon and incorporated herein by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2017/015283 | 1/27/2017 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62288695 | Jan 2016 | US |
