Patent Application
20190382875
This application deals with a new class of advanced high strength steel alloys with ductility characteristics such as high impact toughness and improved resistance to penetration, crack initiation and crack propagation.
Toughness as an engineering property can be thought of as the work energy needed to cause failure in a material. The higher the work required to cause failure by a method, the higher the toughness of the material. Toughness in materials is becoming increasingly important across many sectors, especially where tough materials can be used to improve safety. In the automotive industry, relatively high toughness materials are seeing use in so-called crumple zones to reduce the energy that enters the passenger compartment during a collision. Using relatively high toughness materials, gauge thicknesses can be reduced in automobiles in parts where energy absorption is needed to protect passengers, increasing fuel efficiency without compromising safety. These relatively high toughness materials can also be used for road barriers to keep out-of-control vehicles from leaving the roadway or entering the opposing traffic by absorbing energy from the vehicle and safely stopping it. The automotive industry is not alone in the need for relatively high toughness materials, however. The safety of cargo transported overland by rail and on waterways by ships can also be improved with relatively high toughness materials. In recent years, several high-profile incidents where cargo vessels were damaged during collisions or derailments have occurred that have resulted in significant loss of life, property, and cargo. New regulations have been introduced to lessen the probability and impact of such events, and the use of relatively high toughness materials to ensure improved cargo containment is one option available. By increasing the toughness of materials for these shipping containers, cargo can be kept inside the container during such an event and will reduce environmental impact and loss of life or property damage that could result from wayward cargo. Relatively high toughness materials therefore provide many industries the opportunity to improve fuel and cargo efficiency while maintaining or improving safety.
Advanced High Strength Steels (AHSS's) are those classes of materials whose mechanical properties are superior to the conventional steels. Conventional mild steel has a relatively simple ferritic microstructure; it typically has relatively low carbon content and minimal alloying elements, is readily formed, and is especially sought for its ductility. Widely produced and used, mild steel often serves as a baseline for comparison of other materials. Conventional low- to high-strength steels include IF (interstitial free), BH (bake hardened), and HSLA (high-strength low-alloy). These steels generally have a yield strength of less than 550 MPa and ductility that decreases with increased strength. Higher strength steels are more complex and include such grades as dual phase (DP), complex phase (CP) and transformation induced plasticity (TRIP) steels. The development of advanced high strengths steel has been a challenge since increased strength often results in reduced ductility, cold formability, and toughness.
Toughness can be measured by a variety of methods, with each method characterizing a material response to a specific condition. Methods to characterize toughness include tensile testing, bulk fracture testing, and Charpy impact testing including V-notched and un-notched specimen geometries. Tensile testing is one of the most widely used methods for mechanical properties evaluation and generally performed by applying load to a sample with a reduced section by a moving crosshead until the sample fails. The displacement rate of the crosshead in tensile testing is generally kept constant or near constant, resulting in a relatively narrow range of strain rates throughout the test. Tensile testing can provide a measure of toughness by calculating the integral of the engineering stress −engineering strain curve and is related to the work required to break the sample in tension and estimated by multiplying the ultimate tensile strength by the total elongation (strength-ductility product). Toughness requirements are unique for each application and a selection of testing method depends on where the application is likely to see failure in a manner similar to particular test condition.
A method to achieve a strength/ductility characteristic in a metal comprising:
a. supplying a metal alloy comprising at least 70 atomic percent Fe, at least 9.0 atomic percent Mn, at least 0.4 atomic percent Al, and at least two elements selected from Cr, Si or C, melting and cooling at a rate of ≤250 K/s to a thickness of 25.0 mm to 500.0 mm;
b. processing said alloy into sheet by heating and reducing said thickness to form to a thickness of 1.5 mm to 8.0 mm wherein the sheet exhibits an ultimate tensile strength (TS) of 650 MPa to 1500 MPa, a yield strength (YS) at 0.2% offset of 200 MPa to 1,000 MPa and an elongation (E) from 10% to 70%, wherein the alloy further indicates a strength ductility product (TS×E) in the range of 15,000 MPa % to 75,000 MPa %.
A method to achieve a strength/ductility characteristic in a metal comprising:
a. supplying a metal alloy comprising at least 70 atomic percent Fe, at least 9.0 atomic percent Mn, at least 0.4 atomic percent Al, and at least two elements selected from Cr, Si or C, melting and cooling at a rate of ≤250 K/s to a thickness of 25.0 mm to 500.0 mm;
b. processing said alloy into sheet by heating and reducing said thickness to form to a thickness of 1.5 mm to 8.0 mm;
c. processing said alloy into sheet by reducing said thickness without heating to form to a thickness of 0.5 mm to 3.0 mm wherein the sheet is annealed and exhibits an ultimate tensile strength (TS) of 650 MPa to 1500 MPa, a yield strength (YS) at 0.2% offset of 200 MPa to 1000 MPa and an elongation (E) from 10.0% to 90.0%, wherein the alloy further indicates a strength ductility product (TS×E) in the range of 10,000 MPa % to 80,000 MPa %.
The detailed description below may be better understood with reference to the accompanying FIG.s which are provided for illustrative purposes and are not to be considered as limiting any aspect of this invention.
Alloys herein can be produced by different methods of casting including but not limited to continuous casting, thin slab casting, thick slab, and bloom casting at 25.0 to 500.0 mm in thickness with achievement of advanced property combinations by subsequent post-processing. After casting hot rolling is applied to produce thickness ranges from 1.5 to 8.0 mm. Cold rolling may be additionally applied to the hot rolled sheet to produce thickness ranges from 0.5 to 3.0 mm. Annealing may or may not be applied to produced hot rolled and/or cold rolled sheet or plate.
Step 2 in
Step 2 in
Step 3 in
Sheet toughness produced from
Bulk fracture testing has been developed to test material toughness to simulate material performance under specific collision-like loading events. It characterizes a resistance to crack initiation. The bulk fracture sample is dynamically loaded perpendicular to the thickness of the material. The sample ends are held fixed in place during the test. This load deforms the sample out of plane until the sample fails by a plastic instability (necking in ductile metals), similar to failure by tensile loading. Preferably, the sheet material herein produced via the method in
Charpy impact testing is preferably performed by the dynamic loading of a sample by a swinging hammer starting from a known height and distance from the center of rotation. The ends of the samples in Charpy impact testing are free and the loading of the sample is similar to a three-point bend test. The total energy of the moving hammer is known and the energy lost in the impact event with the sample can be measured by the rotation angle of the hammer after impact. In Charpy V-notch testing the sample has a pre-machined stress concentration point at the V-notch tip which helps encourage crack nucleation. In this test, the hammer strikes the side opposite the machined notch. Charpy V-notch impact testing measures the work required to plastically deform the sample as well as crack nucleation and propagation. Preferably, the sheet material herein produced via the method in
The chemical composition of the alloys herein is shown in Table 1, which provides the preferred atomic ratios utilized.
With regards to the above, and as can be seen from Table 1, preferably, when Fe is present at a level of greater than or equal to 70 at. % with Mn and Al, at least two elements are selected from Cr, Si, or C, and optionally, Ni and/or Cu to provide a formulation of elements that totals 100 atomic percent. More preferably, the alloys herein can be described as comprising, consisting essentially of, or consisting of the following elements at the indicated atomic percent: Fe (70 to 80 at. %), Mn (9.0 to 17.0 at. %), Al (0.4 to 6.7 at. %), at least two elements selected from Cr, Si, or C in the following ranges, Cr (0.2 to 6.3 at. %), Si (0.3 to 6.3 at. %), and C (0.3 to 2.7 at. %), and optionally Ni (0.3 to 3.5 at. %) and/or Cu (0.2 to 2.5 at. %). The level of impurities of other elements is in the range of 0 to 5,000 ppm, or 0 to 4000 ppm, or 0 to 3000 ppm, or 0 to 2000 ppm, or 0 to 1000 ppm. In a more preferred embodiment, the alloys herein are substantially free of nickel and copper, meaning that nickel and copper are present only as potential impurities, such as at a level of 0 to 5000 ppm, or 0 to 4000 ppm, or 0 to 3000 ppm, or 0 to 2000 ppm, or 0 to 1000 ppm.
The alloys herein were processed into a laboratory sheet by processing of laboratory slabs. Laboratory alloy processing is developed to mimic closely the commercial sheet production by continuous casting and include hot rolling and cold rolling. Annealing might be applied depending on targeted properties. Produced sheet can be used in hot rolled (hot band), cold rolled, annealed or partially annealed states.
Alloys were weighed out into 3,000 to 3,400 gram charges according to the atomic ratios in Table 1 using commercially available ferroadditive powders and a base steel feedstock with known chemistry. Impurities can be present at various levels depending on the feedstock used. Impurity elements would commonly include the following elements; Co, N, P, Ti, Mo, W, Ga, Ge, Sb, Nb, Zr, O, Sn, Ca, B, and S which if present would be in the range from 0 to 5,000 ppm (parts per million) (0 to 0.5 wt %) at the expense of the desired elements noted previously. Preferably, the level of impurities is controlled to fall in the range of 0 to 3,000 ppm (0.3 wt %).
Charges were loaded into a zirconia coated silica crucible which was placed into an Indutherm VTC800V vacuum tilt casting machine. The machine then evacuated the casting and melting chambers and flushed with argon to atmospheric pressure twice prior to casting to prevent oxidation of the melt. The melt was heated with a 14 kHz RF induction coil until fully molten, approximately from 5 to 7 minutes depending on the alloy composition and charge mass. After the last solids were observed to melt it was allowed to heat for an additional 30 to 45 seconds to provide superheat and ensure melt homogeneity. The casting machine then evacuated the chamber and tilted the crucible and poured the melt into a water-cooled copper die. The melt was allowed to cool under vacuum for 200 seconds before the chamber was filled with argon to atmospheric pressure.
A sample of between 50 and 150 mg from each alloy herein was taken in the as-cast condition. This sample was heated to an initial ramp temperature between 900° C. and 1300° C. depending on alloy chemistry, at a rate of 40° C./min. Temperature was then increased at 10° C./min to a max temperature between 1425° C. and 1510° C. (maximum temperature limit for the used DSC equipment) depending on alloy chemistry. Once this maximum temperature was achieved, the sample was cooled at a rate of 10° C./min back to the initial ramp temperature before being reheated at 10° C./min to the maximum temperature. Differential Scanning calorimetry (DSC) measurements were taken using a Netzsch Pegasus 404 DSC through all four stages of the experiment, and this data was used to determine the solidus and liquidus temperatures of each alloy, which are in a range from 1325 to 1510° C. as listed in Table 2. Depending on the alloy's chemistry, liquidus-solidus gap varies from 38 to 139° C. Thermal analysis provides information on maximum temperature for the following hot rolling processes that varies depending on alloy chemistry.
The density of the alloys herein was measured on samples from hot rolled material using the Archimedes method in a specially constructed balance allowing weighing in both air and distilled water. The density of each alloy is tabulated in Table 3 and was found to be in the range from 7.35 to 7.90 g/cm3. The accuracy of this technique is ±0.01 g/cm3.
The alloys herein were preferably processed into a laboratory hot band by hot rolling of laboratory slabs at high temperatures. Laboratory alloy processing is developed to simulate the hot band production from slabs produced by continuous casting. Industrial hot rolling is performed by heating a slab in a tunnel furnace to a target temperature, then passing it through either a reversing mill or a multi-stand mill or a combination of both to reach the target gauge. During rolling on either mill type, the temperature of the slab is steadily decreasing due to heat loss to the air and to the work rolls, so the final hot band is formed at a reduced temperature. This is simulated in the laboratory by heating in a tunnel furnace to between 1100° C. and 1250° C., then hot rolling. The laboratory mill is slower than industrial mills causing greater loss of heat during each hot rolling pass, so the slab is reheated for 4 minutes between passes to reduce the drop in temperature. The final temperature at target gauge when exiting the laboratory mill commonly is in the range from 800° C. to 1,000° C., depending on furnace temperature and final thickness.
Prior to hot rolling, laboratory slabs were preheated in a Lucifer EHS3GT-B18 furnace. The furnace set point varies between 1100° C. to 1250° C., depending on alloy melting point and point in the hot rolling process, with the initial temperatures set higher to facilitate higher reductions, and later temperatures set lower to minimize surface oxidation on the hot band. The slabs were allowed to soak for 40 minutes prior to hot rolling to ensure they reach the target temperature and then pushed out of the tunnel furnace into a Fenn Model 061 2 high rolling mill. The 50 mm casts were hot rolled for 5 to 10 passes though the mill before being allowed to air cool. Final thickness ranges after hot rolling are preferably from 1.5 mm to 8.0 mm with variable reduction per pass ranging from 20% to 50%.
Tensile testing results for hot band with thickness from 1.8 to 2.7 mm are listed in Table 4. Two to four specimens were tested for each alloy. The ultimate tensile strength values of the annealed sheet from alloys herein are in a range from 732 to 1434 MPa, the yield strength at 0.2% offset (a parallel line is drawn on the initial stress strain curve and the resulting point of intersection is measured at the 0.2% offset) varies from 405 to 771 MPa, the total elongation recorded in the range from 17.2 to 69.5%, strength ductility product toughness, i.e. the ultimate tensile strength times the total elongation, varies from 17,500 to 71,100 MPa %, and a Modulus of toughness which is calculated in a range from 152 to 580 N/mm2. Note that the Modulus of Toughness represents the numerical integration of the stress-strain curve area under tensile stress-strain curve from no applied strain all the way up to failure. The Table 4 properties correspond to Step 2 in
Alloys with chemistries listed in Table 1 were laboratory cast into ingots with 50 mm thickness. The ingots then were hot rolled at the temperature in a range between 1100° C. and 1250° C. and afterward the hot rolled material (i.e. hot band) was media blasted prior to cold rolling to remove surface oxides which could become embedded during the rolling process. Final thickness after cold rolling are preferably from 0.5 mm to 3.0 mm with variable reduction per pass ranging from 10% to 50%.
For this specific study, hot rolling was done to produce sheet in a range from 1.9 mm to 2.3 mm which was cold rolled using a Fenn Model 061 2 high rolling mill to a thickness range from 1.1 to 1.4 mm with reductions from 10% to 40%. Once the final gauge thickness was reached, tensile samples were cut from the laboratory sheet by wire-EDM. An example of tensile specimen before testing and its dimensions are shown in
Tensile properties were measured on an Instron mechanical testing frame (Model 3369), utilizing Instron's Bluehill control and analysis software. All tests were run at ambient temperature in displacement control at a constant displacement rate of 0.036 mm/s.
Tensile properties of sheet material with thickness from 1.1 to 1.4 mm from alloys herein after annealing at 850° C. for 10 min are listed in Table 5. The ultimate tensile strength values of the annealed sheet from alloys herein are in a range from 717 to 1414 MPa, the yield strength at 0.2% offset varies from 273 to 838 MPa, the total elongation recorded in the range from 20.8 to 78.9%, strength ductility product toughness varies from 20,500 to 77,100 MPa %, and area under tensile stress-strain curve is calculated in a range from 135 to 677 N/mm2. Note that the Table 5 properties correspond to Step 2 in
Tensile properties of sheet material with thickness from 1.1 to 1.4 mm from alloys herein after annealing at 950° C. for 6 hr are listed in Table 6. The ultimate tensile strength values of the annealed sheet from alloys herein are in a range from 679 to 1418 MPa, the yield strength at 0.2% offset varies from 209 to 588 MPa, the total elongation recorded in the range from 12.0 to 88.2%, strength ductility product toughness varies from 11,000 to 76,200 MPa %, and area under tensile stress-strain curve is calculated in a range from 101 to 663 N/mm2. Note that the Table 6 properties correspond to Step 2 in
Materials toughness was measured by Charpy V-notch testing and bulk fracture testing. Charpy V-notch and bulk fracture samples were machined by wire EDM from cold rolled sheet. Charpy V-notch samples are machined in an L-T orientation (sample length in rolling direction, notch in transverse direction), while bulk fracture samples are machined in L-N orientation (length in rolling direction, striking direction is normal to rolled surface). The samples were then annealed either at 850° C. for 10 minutes in argon/air atmosphere or at 950° C. for 6 hours in hydrogen atmosphere.
The geometry of Charpy V-notch samples were cut in accordance with ASTM E23-12c (10 mm×55 mm×thickness with a centered 45° V-notch of 0.25 mm radius, 2 mm in depth with a surface finish Ra of less than 2.0 μm on notch and strike face). An example of the Charpy V-notch specimen before testing and its schematic illustration are shown in
Testing results are shown in Table 7. Absorbed energy values during Charpy V-notch testing of alloys herein are in a range from 0.7 to 26.1 J in cold rolled and annealed sheet with thickness from 1.1 to 1.4 mm. Thickness normalized values of the Charpy V-notched toughness vary from 0.5 to 21.8 J/mm. Note that the Table 7 properties correspond to Step 2 in
Bulk fracture samples have 45 mm long by 2 mm wide parallel region between two wedge shaped grips designed to be clamped into a cutout in the anvil. An example of the specimen before testing and its schematic illustration are shown in
Testing results are shown in Table 8. Absorbed energy values during bulk fracture testing of alloys herein are in a range from 5.8 to 75.2 J for the cold rolled and annealed sheet with thickness of 1.1 to 1.4 mm. Thickness normalized values of bulk fracture toughness vary from 4.1 to 53.7 J/mm. Note that the Table 8 properties correspond to Step 2 in
Charpy V-notch specimens (
This Case Example demonstrates that alloys herein show high toughness with a resistance to failure even in the presence of a notch.
Specimens from Alloy 7, Alloy 9, Alloy 19, and Alloy 20 after Charpy V-notch testing in cold rolled and annealed (850° C. for 10 min) state described in the Main Body section of this application were used for SEM analysis of the fracture surface. The Charpy V-notch testing results for these specific specimens from selected alloys are listed in Table 10. Fractured specimens from each alloy were mounted and analyzed by using a Zeiss MA-10 Scanning Electron Microscope (SEM). Micrographs of the fracture surface in tested specimens are shown in
This Case Example demonstrates that alloys herein undergo a ductile fracture during V-notch impact testing.
Specimens from Alloy 7, Alloy 9, Alloy 19, and Alloy 20 after bulk fracture testing in cold rolled and annealed (850° C. for 10 min) state described in the Main Body section of this application were used for SEM analysis of the fracture surface. The bulk fracture testing results for these specific specimens from selected alloys are listed in Table 11. Fractured specimens from each alloy were mounted and analyzed by using a Zeiss MA-10 Scanning Electron Microscope (SEM). Micrographs of the fracture surface are shown in
This Case Example demonstrates that alloys herein undergo a ductile fracture during bulk fracture impact testing.
As indicated from Tables 8 and 11, the normalized bulk fracture toughness range is from 4.1 to 53.7 J/mm. From the existing data the entire range of properties expected for the alloys herein according to the methodology in
Slabs with thickness of 50 mm were laboratory cast from the Alloy 7 and Alloy 9 according to the atomic ratios provided in Table 1 and laboratory processed by hot rolling to thickness of 5 and 7 mm and by subsequent cold rolling to thicknesses of 1.2 and 2.5 mm. At each listed thickness, Charpy un-notched specimens were cut from the material. Specimens that were cut from the cold rolled sheet (i.e. the 1.2 mm and 2.5 mm samples) were subsequently annealed at 950° C. for 6 hr as described in the Main Body section of the current application.
Charpy testing was done by using the Instron SI-1B Pendulum Impact Tester in accordance with the methodology described in the Main Body section of the current application. None of the tested specimens broke during the testing but bent and slip through the anvil. The recorded toughness, which corresponds to the work required to bend specimen and push it through the anvil is listed in Table 12 for both alloys. Examples of unbroken specimens after testing are shown in
This Case Example demonstrates high toughness of alloys herein that do not break in a case of impact testing of un-notched specimens.
Laboratory slabs from Alloy 7 and Alloy 9 were cast according to the atomic compositions provided in Table 1. Materials were produced at a range of thicknesses for Charpy V-notch impact testing by hot rolling, cold rolling, and annealing as previously described. The approximate thicknesses produced for testing are 1.2 mm, 2.5 mm, 5 mm, and 7 mm. For samples at thickness >2.5 mm, material was cast and hot rolled only, whereas for samples with 1.2 mm and 2.5 mm thicknesses the material was cast, hot rolled, cold rolled, and then annealed at 950° C. for 6 hr as described in the Main Body section of the current application. Charpy V-Notch specimens were cut by wire EDM from the sheet material with each thickness.
Charpy testing was done by using the Instron SI-1B Pendulum Impact Tester in accordance with the methodology described in the Main Body section of the current application. Three specimens were tested at each thickness for each alloy. The measured Charpy V-notch impact energy for Alloy 7 and Alloy 9 are provided in Table 13 and Table 14, respectively. The Charpy V-notch toughness for alloys herein was measured in a range from 16.3 to 104.4 J. Thickness normalized values of the Charpy V-notched toughness vary from 12.5 to 15.6 J/mm. Note that the Table 13 and Table 14 properties correspond to sheet produced to Step 2 in both
This Case Example demonstrates the trend in Charpy V-notch toughness of the alloys herein as a function of sheet thickness. Note that for alloys herein, the measured Charpy V-notch toughness increases with increasing thickness.
As indicated from Tables 7, 10, 13, and 14, the normalized Charpy V-notched toughness range is from 0.5 to 21.8 J/mm. From the existing data the entire range of properties expected for the alloys here-in according to the methodology in
Slabs with thickness of 50 mm were laboratory cast from selected alloys listed in Table 16 according to the atomic ratios provided in Table 1 and laboratory processed by hot rolling. Prior to hot rolling, laboratory slabs were preheated in a Lucifer EHS3GT-B18 furnace. The furnace set point varies between 1100° C. to 1250° C., depending on alloy melting point and point in the hot rolling process, with the initial temperatures set higher to facilitate higher reductions, and later temperatures set lower to minimize surface oxidation on the hot band. The slabs were allowed to soak for 40 minutes prior to hot rolling to ensure they reach the target temperature and then pushed out of the tunnel furnace into a Fenn Model 061 2 high rolling mill. The 50 mm casts were hot rolled for 5 to 10 passes though the mill before being allowed to air cool. Final thickness of the hot band materials was from 1.8 to 2.2 mm. Specimens for Charpy V-notch testing and bulk fracture testing were cut by wire EDM from the hot band for each alloy. Charpy V-notch testing and bulk fracture testing were done using the same procedures described in the Main Body section of the current application. For each alloy, two to three specimens were tested by each method.
Charpy V-notch and bulk fracture testing results are shown in Table 15 and Table 16, respectively. Absorbed energy representing Charpy V-notch toughness of the alloys herein is in a range from 11.9 to 23.7 J for samples with thickness from 1.8 to 2.2 mm. Thickness normalized values of the Charpy V-notched toughness vary from 6.6 to 11.9 J/mm. Note that the Table 15 properties correspond sheet produced in Step 2 in
As indicated from Tables 13, 14, and 15, the normalized Charpy V-notched toughness range is from 6.6 to 15.2 J/mm. From the existing data the entire range of properties expected for the alloys here-in according to the methodology in
This Case Example demonstrates Charpy V-notch toughness of the alloys herein in a hot rolled condition (hot band) with a thickness more than 1.4 mm and less than or equal to 5 mm.
Slabs with thickness of 50 mm were laboratory cast from selected alloys listed in Table 17 according to the atomic ratios provided in Table 1 and laboratory processed by hot rolling, cold rolling and annealing at 850° C. for 10 min as described in the current application. Final thickness of the cold rolled and annealed sheet was from 1.1 to 1.4 mm. Strips with 100 mm width and approximately 300 mm length were cut from the produced sheet from alloys herein.
The material being drop impact tested was clamped between two steel plates. The plate under the sample has a 50 mm diameter hole centered about the point of impact. The plate above is a square frame to prevent the material from buckling during testing. The impactor utilized for the testing was made from hardened steel having 12.7 mm in diameter with a 3.18 mm radius as shown in
This Case Example demonstrates drop impact toughness of the alloys herein in a cold rolled and annealed state with a sheet thickness equal or more than 0.5 mm and less or equal to 1.4 mm.
As indicated from Table 17, the normalized drop impact toughness range is from 90.0 to 232.5 J/mm. From the existing data the entire range of properties expected for the alloys here-in according to the methodology in
A slab of Alloy 24 was cast according to the atomic ratios provided in Table 1 and laboratory processed by hot rolling. Prior to hot rolling, the slab was preheated in a Lucifer EHS3GT-B18 furnace. The slab was allowed to soak for 40 minutes prior to hot rolling to ensure that the slab reached the target temperature. The slab was pushed out of the furnace into a Fenn Model 061 2-high rolling mill. The 50 mm slab was then hot rolled to a final thickness of approximately 4 mm. Specimens for bulk fracture testing were cut by wire-EDM from the hot band. Bulk fracture testing was performed according to the procedures described in the Main Body section of this application.
The measured bulk fracture energy is provided in Table 19. All tested samples broke and subsequently stopped the hammer. Absorbed energy for the bulk fracture specimens were all measured at 119 J. Note that these measured values are slightly less than the maximum 120 J energy for the test. An image of a tested 4 mm thick bulk fracture sample is provided in
This Case Example demonstrates that for the alloys herein, bulk fracture toughness at ≥4 mm thickness is at the limit measurable by current test equipment. The measured bulk fracture toughness is almost equal to the maximum energy that can be imparted by the hammer, thereby resulting in inaccurate measurements.
As indicated from Tables 16 and 19, the normalized bulk fracture toughness range is from 8.2 to 46.5 J/mm. Note that due to experimental capacity limitations, the maximum thickness which could be tested in this laboratory system is −4 mm. From the existing data the entire range of properties expected for the alloys herein according to the methodology in
A slab of Alloy 24 was cast according to the atomic ratios provided in Table 1 and laboratory processed by hot rolling. Prior to hot rolling, the slab was preheated in a Lucifer EHS3GT-B18 furnace. The slab was allowed to soak for 40 minutes prior to hot rolling to ensure that the slab reached the target temperature. The slab was pushed out of the furnace into a Fenn Model 061 2-high rolling mill. The 50 mm slab was then hot rolled to a final thickness of approximately 4 mm. Drop impact testing was performed according to the procedures described in the Main Body section of this application. Total impact energy of 432 J was used which is the maximum available with this test fixture.
An image of a tested 4 mm thick drop impact sample is provided in
Slabs were cast from alloys listed in Table 20 according to the atomic ratios provided in Table 1 and laboratory processed by hot rolling. Prior to hot rolling, the slab was preheated in a Lucifer EHS3GT-B18 furnace. The slab was allowed to soak for 40 minutes prior to hot rolling to ensure that the slab reached the target temperature. The slab was pushed out of the furnace into a Fenn Model 061 2-high rolling mill. The 50 mm slab was then hot rolled to a final thickness from 2.0 to 3.2 mm. Strips with 100 mm width and approximately 300 mm length were cut from the produced sheet from alloys herein.
The material being drop impact tested was clamped between two steel plates. The plate under the sample has a 50 mm diameter hole centered about the point of impact. The plate above is a square frame to prevent the material from buckling during testing. The impactor utilized for the testing was made from hardened steel having 12.7 mm in diameter with a 3.18 mm radius as shown in
This Case Example demonstrates drop impact toughness of the alloys herein in a hot rolled state with a sheet thickness equal or more than 2.0 mm and less or equal to 3.2 mm.
As indicated from Case Examples 9 and 10, the normalized drop impact toughness range is from 80 to 154 J/mm. The maximum thickness which could be tested was ˜4 mm. From the existing data the entire range of properties expected for the alloys herein according to the methodology in
This application claims the benefit of U.S. Provisional Application 62/684,869 filed Jun. 14, 2018 which is fully incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62684869 | Jun 2018 | US |
