Patent Application
20120168044
The present invention relates to heat-resistant components for use in chemical processing apparatuses used mainly for causing chemical reactions for a feedstock through high-temperature chemical treatment, such as in petroleum refineries that heat and fractionate petroleum, and in heating and synthesizing apparatuses that synthesize desired compounds through chemical reactions caused by heating a feedstock.
From the safety standpoint, heat-resistant components used in portions in contact with a feedstock in the high-temperature chemical treatment by a chemical processing apparatus (hereinafter, referred to as “heat-resistant component for a chemical processing apparatus”) require long-hour durability. Examples of such heat-resistant components for a chemical processing apparatus include valves, pipes, pressure vessels, and flanges. Generally, chemically stable ferritic high Cr-steel with sufficient strength is used as the material of the heat-resistant components.
In recent years, high heating temperatures of 650° C. and higher are desired for improving heat efficiency and synthesis techniques. It is difficult, however, to meet such demands with the performance of the conventional heat-resistant components.
The devices used in high temperatures are designed according to the allowable stress formulated based on the creep strength, because the creep strength of ferritic high Cr-steel greatly drops at high temperatures above 650° C.
On the other hand, Ni-based superalloy is known as a heat-resistant material, as described in Patent Document 1. However, it is not known whether the Ni-based superalloy is applicable to heat-resistant components for a chemical processing apparatus.
Problems that the Invention is to Solve
Under these circumstances, it is an object of the present invention to provide a heat-resistant component for a chemical processing apparatus, and a producing process thereof with which safety can be ensured even at high temperatures of 650° C. and higher.
In order to solve the foregoing problems, the present invention provides a heat-resistant component for a chemical processing apparatus that performs a high-temperature chemical treatment for a feedstock at 650° C. or higher, characterized in that the heat-resistant component is formed from a ferritic Cr-steel of a chemical composition that mainly includes, in % by mass,
Cr: 13 to 30%,
Ni: 1×10−1 to 2.5%,
C: 1×10−3 to 1×10−1%, and
N: 1×10−3 to 1×10−1%,
wherein the ferritic Cr-steel allows for inclusion of an additional component and unavoidable impurities, includes Fe as the remaining part, and forms a ferrite phase.
It is preferable in the heat-resistant component for a chemical processing apparatus that Ni is added in an amount that satisfies the relationship Ni>10(C+N), where Ni, C, and N each represent the amount of each component added (in % by mass), when C is added in 1×10−2% by mass or more and/or Ni is added in 1×10.2% by mass or more.
It is preferable in the heat-resistant component for a chemical processing apparatus that the ferrite phase is 70 volume % or more.
It is preferable in the heat-resistant component for a chemical processing apparatus that the additional component is one or more of the following in % by mass,
Mo: 5×10−1 to 5%,
W: 5×10−1 to 1×10%,
V: 5×10−2 to 4×10−1%,
Nb: 1×10−2 to 1×10−1%,
Co: 1×10−1 to 1×10%, and
B: 2×10−3 to 4×10−3%, and
that at least one of carbide, nitride, and intermetallic compound is precipitated in crystal grains.
It is preferable in the heat-resistant component for a chemical processing apparatus that Mo and W are added in amounts that satisfy the relationship Mo+0.5W 3.0% by mass, where Mo and W each represent the amount of each component added (in % by mass).
The present invention also provides a heat-resistant component for a chemical processing apparatus that performs a high-temperature chemical treatment for a feedstock at 650° C. or higher,
characterized in that the heat-resistant component is formed from a ferritic Cr-steel that contains Cr in an amount of from 13% by mass to 30% by mass, wherein the ferritic Cr-steel has a creep rate of 1×10−5/h or less at 700° C. under stress of 100 MPa, and an oxidation weight gain of 10 mg/cm2 or less after being maintained in a 650° C. water vapor for 1,000 h.
The present invention also provides a process for producing a heat-resistant component for a chemical processing apparatus, the process including hot working the ferritic Cr-steel of the foregoing chemical composition in a temperature range of 850 to 1,200° C., forming the ferritic Cr-steel into a component shape, subjecting the steel to an annealing treatment in a temperature range of 1,000 to 1,250° C., and cooling the steel to 400° C. or less at a cooling rate of 100° C./min or higher.
A heat-resistant component for a chemical processing apparatus and a producing process thereof according to the present invention realize a chemical processing apparatus that can perform the conventionally difficult high-temperature operation at 650° C. or higher temperatures. The material of the heat-resistant component for a chemical processing apparatus is ferritic Cr-steel, a material belonging to the commonly used ferritic high Cr-steels. The heat-resistant component is thus highly practical. The invention is therefore applicable to various techniques, including the current production techniques and quality management techniques, and is very convenient because hardly any additional limitations are imposed.
The ferritic Cr-steel used for a heat-resistant component for a chemical processing apparatus of the present invention is a material that has excellent high temperature strength, heat resistance, oxidation resistance, and high toughness even at high temperatures above 650° C. (here and below, the temperature is represented in units of 50° C.), and that can withstand use under high temperature and high pressure for extended time periods while undergoing only a limited decrease in strength.
The ferritic Cr-steel used for the heat-resistant component for a chemical processing apparatus is produced by hot working a ferritic Cr-steel ingot in a temperature range of 850 to 1,200° C. and forming the ferritic Cr-steel into a predetermined shape, and then subjecting the steel to an annealing treatment in a temperature range of 1,000 to 1,250° C., and cooling the steel to 400° C. or less at a cooling rate of 100° C./min or higher.
The hot working temperature such as in hot forging is 850 to 1,200° C., preferably 950 to 1,150° C., more preferably 1,000 to 1,100° C. Above the upper limit temperature, an abrupt decrease in ductility may occur. Below the lower limit temperature, deformation resistance increases, which may lead to processing defects such as cracking.
The temperature of the annealing treatment is 1,000 to 1,250° C., preferably 1,000 to 1,200° C., more preferably 1,050 to 1,150° C. Above the upper limit temperature, serious coarsening of crystal grains may occur, which can be detrimental to various properties of the steel, including toughness, ductility, and weldability. Below the lower limit temperature, it may not be possible to completely melt the steel and to exhibit a sufficient strength.
Temperatures of 400° C. and higher may cause precipitation of a second phase in the process of cooling from the annealing temperature, because of the fast precipitation rate of second-phase compounds such as carbides, nitrides, and intermetallic compounds. In order to control such precipitation of the second phase, the cooling rate of the cooling to 400° C. or less following the annealing treatment is 100° C./min or higher, preferably 120° C./min or higher, more preferably 150° C./min or higher. Below the lower limit, a coarse second phase may precipitate at the crystal grain boundary during the cooling process, and it becomes difficult to disperse and precipitate a fine second phase in the crystal grains. In this case, sufficient strength may not be developed because of the failure to effectively control the precipitation state of the second phase for strength improvement.
The ferritic Cr-steel produced as above has a minimum creep rate of 1.0×10−4/h or less at 700° C. under stress of 100 MPa. A minimum creep rate exceeding the upper limit causes creep deformation during high-temperature use. This may lead to an early loss of functionality in components such as valves that require high dimension accuracy, or may encourage corrosion or oxidation.
Further, the ferritic Cr-steel has a creep rupture time of preferably 1,000 hr or more at 750° C. under stress of 80 MPa, 5,000 hr or more at 750° C. under stress of 50 MPa, and 10,000 hr or more at 750° C. under stress of 30 MPa. A creep rupture time below the lower limit shortens the creep rupture lifetime that depends on the load generated during the operation of the chemical processing apparatus, and may thus present difficulties in ensuring a sufficient creep rupture lifetime in practical applications.
Further, the ferritic Cr-steel has a sufficiently small oxidation weight gain of 10 mg/cm2 or less after being maintained in a 650° C. water vapor for 1,000 h. The ferritic Cr-steel thus excels in high-temperature oxidation resistance, and can ensure safety at high temperatures of 650° C. and higher. Oxidative degradation becomes likely and performance becomes unstable with an oxidation weight gain in excess of this upper limit.
Increasing the additive amount of Cr generally improves not only the oxidation resistance but the corrosion resistance of iron and steel materials. Thus, the ferritic Cr-steel with excellent oxidation resistance also excels in corrosion resistance.
The ferritic Cr-steel has a linear expansion coefficient of 15×10−6 or less in a temperature range of from room temperature to 850° C. Above the upper limit, the amounts of thermal expansion and contraction at the start-up and stopping of the chemical processing apparatus increase, and it becomes difficult to produce heat-resistant components with high dimension accuracy.
The ferritic Cr-steel in the form of, for example, a steel ingot to be subjected to hot working is a ferritic Cr-steel, or a ferritic high Cr-steel as it is called, whose chemical composition is adjusted to include the components below (here and below, % means % by mass).
C needs to be added in at least 1×10−3% to improve creep strength. The upper limit of the C additive amount is 1×10−1%, because the excess addition lowers toughness. When C is added in 1×10−2% or more, it is preferable that Ni>10 (C+N), where Ni, C, and N each represent the additive amount of each component (in % by mass).
It is essential that Cr is added in 13% or more. In actual practice, Cr is added in preferably 13.5% or more to ensure a 70 volume % or more of the ferrite phase, and to improve oxidation resistance. The upper limit of Cr additive amount is 30%, because a Cr additive amount in excess of 30% notably lowers toughness.
N needs to be added in at least 1×10−3% to improve creep strength. The upper limit of N additive amount is 1×10−1%, because the excess addition lowers toughness. When N is added in 1×10−2% or more, it is preferable that Ni>10 (C+N), as with the case of C.
Ni needs to be added in at least 1×10−1% to improve toughness. When C and/or N are added in 1×10″2% or more, it is preferable that the Ni additive amount satisfy Ni>10 (C+N) to ensure toughness, as above. The upper limit of Ni additive amount is 2.5%, because the excess addition lowers the percentage volume of the ferrite phase.
As presented in Table 2 below, comparative steels 7 and 8 with the Ni additive amount satisfying Ni≦10 (C+N) (Ni, C, and N each represent the additive amount of each component (in % by mass)) have small Charpy impact values, regardless of the cooling rate. On the other hand, the water-cooled materials of the steels 1 to 4 of the present invention satisfying the relationship Ni>10 (C+N) have sufficiently greater Charpy impact values than those of the comparative steels 7 and 8.
The ferritic Cr-steel can be reinforced with the controlled precipitation of at least one of carbide, nitride, and intermetallic compound, specifically, by the fine dispersion and precipitation within the crystal grains. This is effective for improving creep strength. To this end, the ferritic Cr-steel allows for addition of the components below in its chemical composition, in addition to the foregoing components.
Mo is a chemical component effective for precipitating an intermetallic compound, and can improve creep strength. Mo may be added in 5×10−1% or more. The upper limit of Mo additive amount is preferably 5%, because the excess addition may lower toughness.
As with Mo, W is a chemical component effective for precipitating an intermetallic compound, and can improve creep strength. W may be added in 5×10−1% or more. The upper limit of W additive amount is preferably 1×10%, because the excess addition may lower toughness.
Note that Mo and W may be added to satisfy the relationship Mo+0.5W 3.0% (Mo and W each represent the additive amount (in % by mass)), so as to ensure a sufficient amount of intermetallic compound precipitation.
V forms carbides or nitrides effective for improving creep strength. V maybe added in 5×10−2% or more. The upper limit of V additive amount is preferably 4×10−1%, because the excess addition is not necessarily effective for the formation of carbides and nitrides.
As with V, Nb forms carbides or nitrides effective for improving creep strength. Nb may be added in 1×10−2% or more. The upper limit of Nb additive amount is preferably 1×10−1%, because the excess addition is not necessarily effective for the formation of carbides and nitrides.
Co is a component effective for miniaturizing the precipitated carbide, nitride, and intermetallic compound, and for improving creep strength. Co may be added in 1×10−1% or more. The upper limit of Co additive amount is preferably 1×10%, because the excess addition may lower the percentage volume of the ferrite phase.
B is a component effective for miniaturizing and stabilizing the precipitates, and for strengthening the grain boundary. B may be added in 2×10−3% or more. The upper limit of B additive amount is preferably 4×10−3%, because the excess addition may lead to formation of boron nitride, and may not be necessarily effective for improving creep strength.
Mn is a component effective as a deoxidant. Mn may be added in 5×10−2% or more. The upper limit of Mn additive amount is preferably 8×10−1%, because the excess addition is detrimental to strength and toughness.
Si is a component effective as a deoxidant. Si may be added in 5×10−2% or more. The upper limit of Si additive amount is preferably 5×10−1%, because the excess addition accelerates the coarsening of the precipitates and lowers strength.
The remaining parts of the ferritic Cr-steel chemical composition are Fe and unavoidable impurities.
Preferably, the ferritic Cr-steel forms at least 70 volume % of the ferrite phase to improve creep strength. A tempered martensite structure with 70 volume % or more of the ferrite phase is unstable at high temperatures, whereas the ferrite phase has high structure stability at high temperatures. As presented in Table 2, furnace cooling of the steels 2 to 4 of the present invention makes the percentage volume of the ferrite phase less than 70% because of the slow cooling rate following the annealing treatment. However, the percentage volume of the ferrite phase becomes 70% or more when the cooling rate down to 400° C. or less is 100° C/min or higher in water cooling. Thus, as represented in
Further, as presented in
Examples are described below.
In the following Examples, a round bar was assumed to be a component, and various properties were measured. As noted above, the heat-resistant component for a chemical processing apparatus of the present invention is a heat-resistant component used in portions in contact with a feedstock in the high-temperature chemical treatment in a chemical processing apparatus, and may be, for example, a valve, a pipe, a pressure vessel, or a flange. It would be easily anticipated and understood that the heat-resistant component for a chemical processing apparatus produced from the ferritic Cr-steel has properties comparable to those of the ferritic Cr-steel used as the material.
The round bars of steels 1 to 8 with the chemical compositions presented in Table 1 (steels 1 to 6 of the present invention, and comparative steels 7 and 8) were each prepared from a 10-kg steel ingot subjected to 850 to 1,150° C. hot forging to have a diameter of 15 mm. After 1,200° C. annealing treatment, each specimen was cooled by furnace cooling or water cooling.
Note that Table 1 also presents the chemical compositions of the existing ferritic heat-resistant steels (steels 9 to 15; comparative steels).
Table 1 also presents steel 16 (comparative steel). The chemical composition of comparative steel 16 is such that Ni and Cr are added in amounts below the lower limits for the steels of the present invention.
These test pieces were subjected to a Charpy impact test at 100° C. The results are presented in Table 2.
Impact value was smaller in comparative steels 7 and 8 in which Ni was added in small amounts outside the range for the steels of the present invention, regardless of the cooling rate after the annealing treatment. In contrast, the steels 1 to 4 of the present invention had greater impact values of 300 J/cm2 or more than the furnace cooled materials and comparative steels 7 and 8 in water cooling with a high cooling rate, though the values were small in furnace cooling that involves a lower cooling rate.
It was confirmed that the required cooling rate conditions include an annealing treatment within a temperature range of 1,000 to 1,250° C., and the subsequent cooling to 400° C—a temperature that essentially does not allow for precipitation of carbides, nitrides, and intermetallic compounds—at a high cooling rate that can suppress the precipitation of these components, specifically at 100° C/min or higher.
It can be seen that the steels 1 to 4 of the present invention have higher creep strengths than comparative steels 9 to 15 in which Cr is added in less than 13% by mass, and in which the percentage volume of the ferrite phase is less than 70%.
Table 4 represents the measured data used to create
It can be seen that the creep rates of the steels 2 and 4 of the present invention are only about 1/1,000 of the creep rates of comparative steels 9 to 11, and that the creep rupture times are at least about 100 times longer.
Table 5 represents the minimum creep rates obtained from
The steel 4 of the present invention did not rupture during the course of testing. The creep rates of the steels 2 and 4 of the present invention were only 1/100 or less of the creep rates of comparative steels 9 and 13, and the creep rupture times were at least about 100 times longer.
Table 6 represents the measured data used to create
The steels 2 and 4 of the present invention did not rupture during the course of testing under stresses of 50 MPa and 30 MPa. Further, the steels 2 and 4 of the present invention tested under stresses of 80 to 50 MPa had creep rupture times at least about 100 times longer than the rupture times of comparative steels 9 to 15. It can also be seen that the creep rupture times are longer than those of the austenite heat-resistant steel (steel No. X; SUS316) presented in Table 7. Further, it can be seen that, even under stress of 30 MPa, the steels 2 and 4 of the present invention have creep rupture times comparable to that of SUS316.
Tables 7 and 8 represent the measured data used to create FIG. 5. Table 7 represents the creep rupture time (h) of the austenite steel SUS316 (steel No. X) at 750° C. Table 8 represents the mean values for the steel No. X presented in Table 7, along with the creep rupture times (h) of the steels 2 and 4 of the present invention, comparative steels 9 to 15, and X measured at 750° C.
Table 9 represents the measured data used to create
The steels 2 and 4 of the present invention were heated from room temperature to 1,000° C. at a rate of 1,000° C/h, and the thermal expansion was measured to determine a linear expansion coefficient at each temperature. The linear expansion coefficients of the practical heat-resistant materials are values specified in the boiler and pressure vessel specifications of the American Society of Mechanical Engineers (ASME).
Table 10 represents the measured data used to create
The present invention realizes a heat-resistant component for a chemical processing apparatus with which safety can be ensured even at high temperatures of 650° C. and higher. The invention enables a high-temperature operation of a chemical processing apparatus at high temperatures of 650° C. and higher. The material of the heat-resistant component for a chemical processing apparatus is ferritic Cr-steel, and thus the heat-resistant component is highly practical. The invention is applicable to various techniques, including the current production techniques and quality management techniques, and is very convenient because hardly any additional limitations are imposed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-149579 | Jun 2009 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2010/059450 | 6/3/2010 | WO | 00 | 1/31/2012 |
