Austenitic alloy material, exhaust parts and exhaust gas purification device

Abstract

Provided are an austenitic alloy material, an exhaust part, and an exhaust gas purification device that exhibit excellent thermal fatigue properties even in a relatively low-temperature environment. [Solution] The chemical composition, in mass%, is C: 0.200% or less, Si: less than 4.00%, Mn: 2.00% or less, P: 0.050% or less, S: 0.0050% or less, Ni: 5.00 to 50.00%, Cr: 12.00 to 30.00%, Cu: more than 0% and 3.00% or less, Mo: more than 0% and 4.00% or less, V: more than 0% and 1.00% or less, Al: 1.000% or less, Ti: 1.500% or less, N: 0.400% or less, optionally added elements, balance: Fe and impurities, and the KAM measured using electron backscatter diffraction. M , G.O.S. M and HAGB M The value of [KAM M ×GOS M / HAGB M An austenitic alloy material that satisfies the following requirements.

Description

[Technical Field]

[0001] The present invention relates to an austenitic alloy material, an exhaust part, and an exhaust gas purification device. [Background technology]

[0002] Exhaust components such as exhaust manifolds, converters, front pipes, and center pipes of automobiles are exposed to high-temperature environments due to the high-temperature exhaust gases emitted from the engine passing through them. For this reason, austenitic stainless steel, which has excellent thermal fatigue properties, is often used as a material for exhaust system components. For example, Patent Document 1 evaluates the thermal fatigue of austenitic stainless steel when the lower limit temperature is 200°C and the upper limit temperature is 950°C, as well as the high-temperature high-cycle fatigue limit at 800°C. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-160493 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, from the viewpoint of environmental protection, vehicles such as automobiles, agricultural machinery, and construction machinery have begun to be equipped with devices that purify exhaust gases. In addition, hydrogen engines have been attracting attention as one of the measures toward a carbon-neutral society. Vehicles using hydrogen engines also require NO x Therefore, the installation of an exhaust gas purification device is required.

[0005] The temperature of exhaust gas passing through an exhaust gas purification device is about 300 to 600°C, which is lower than the temperature of exhaust gas passing through an exhaust manifold, etc., located upstream. However, as in Patent Document 1, only thermal fatigue properties in high-temperature environments have been studied up until now, and sufficient research has not been conducted on thermal fatigue properties in relatively low-temperature environments of about 300 to 600°C.

[0006] As a result of investigations carried out by the present inventors, it was found that in a relatively low temperature environment of about 300 to 600°C, thermal fatigue damage specific to this temperature range can occur.

[0007] The present invention aims to solve the above problems and to provide an austenitic alloy material, an exhaust part, and an exhaust gas purification device that exhibit excellent thermal fatigue properties even in a relatively low-temperature environment. [Means for solving the problem]

[0008] The present invention has been made to solve the above-mentioned problems, and is summarized as the following austenitic alloy material, exhaust part, and exhaust gas purification device.

[0009] (1) Chemical composition, in mass%, C: 0.200% or less, Si: less than 4.00% Mn: 2.00% or less, P: 0.050% or less, S: 0.0050% or less, Ni: 5.00~50.00%, Cr: 12.00~30.00%, Cu: more than 0% and less than 3.00%, Mo: more than 0% and less than 4.00%, V: more than 0% and less than 1.00%, Al: 1.000% or less, Ti: 1.500% or less, N: 0.400% or less, Nb: 0 to 1.000%, B: 0~0.0100%, Co: 0-3.00%, W: 0~3.00%, Sn: 0 to 1.00% Zr: 0 to 0.30% REM: 0~0.200%, Ca: 0 to 0.0100%, Mg: 0 to 0.0100%, Sb: 0 to 0.500% Ga: 0 to 0.300%, Ta: 0 to 1.000%, Hf: 0 to 1.000%, Bi: 0 to 0.020% The balance is Fe and impurities. KAM measured using electron backscatter diffraction M , G.O.S. M and HAGB M The value of satisfies the following formula (i): Austenitic alloy material. KAM M ×GOS M / HAGB M ≦0.05 (i) However, KAM in the above formula M is the ratio of the number of measurement points where the KAM value is within 1-2° to the total number of measurement points, and GOS M is the average value of the GOS obtained for each grain, and M is the ratio of the length of grain boundaries with a relative misorientation of 15° or more to the total length of grain boundaries.

[0010] (2) The chemical composition is in mass%: Nb: 0.001 to 1.000%, B: 0.0002~0.0100%, Co: 0.01 to 3.00%, W: 0.01 to 3.00%, Sn: 0.01 to 1.00%, Zr: 0.01 to 0.30%, REM: 0.001~0.200%, Ca: 0.0005 to 0.0100%, Mg: 0.0002 to 0.0100%, Sb: 0.0002 to 0.500%, Ga: 0.0002 to 0.300%, Ta: 0.0002 to 1.000%, Hf: 0.0002 to 1.000%, and Bi: 0.0002 to 0.020%, Contains one or more selected from The austenitic alloy material according to (1) above.

[0011] (3) A thermal fatigue life of 10,000 cycles or more measured by a thermal fatigue test in which heating and cooling are repeated continuously under the conditions of a maximum temperature of 400°C, a minimum temperature of 200°C, a holding time at the maximum temperature of 30 seconds, and a restraint rate of 100%. The austenitic alloy material according to (1) or (2) above.

[0012] (4) The fatigue limit at 400°C is 150 MPa or more. The austenitic alloy material according to (1) or (2) above.

[0013] (5) A thermal fatigue test was conducted in which heating and cooling were repeated repeatedly under the conditions of a maximum temperature of 400°C, a minimum temperature of 200°C, a holding time at the maximum temperature of 30 seconds, and a restraint rate of 100%. The KAM was measured using electron backscatter diffraction on the test specimen after it had reached the end of its thermal fatigue life. S , G.O.S. S and HAGB S The value satisfies the following formula (ii): The austenitic alloy material according to (1) or (2) above. KAM S ×GOS S / HAGB S ≦4.0 (ii) However, KAM in the above formula S is the ratio of the number of measurement points where the KAM value is within 1-2° to the total number of measurement points, and GOS S is the average value of the GOS obtained for each grain, and Sis the ratio of the length of grain boundaries with a relative misorientation of 15° or more to the total length of grain boundaries.

[0014] (6) Used in exhaust components or exhaust gas purification devices; An austenitic alloy material according to any one of (1) to (5) above.

[0015] (7) An exhaust part using the austenitic alloy material according to any one of (1) to (5) above.

[0016] (8) An exhaust gas purification device using the austenitic alloy material according to any one of (1) to (5) above. [Effects of the Invention]

[0017] According to the present invention, it is possible to obtain an austenitic alloy material, an exhaust part, and an exhaust gas purification device that exhibit excellent thermal fatigue properties even in a relatively low-temperature environment. DETAILED DESCRIPTION OF THE INVENTION

[0018] The present inventors have investigated methods for improving the thermal fatigue properties of austenitic alloy materials in a relatively low temperature environment, and have obtained the following findings.

[0019] (a) It has been believed that the higher the temperature of the usage environment, the stronger the effect of thermal strain, making thermal fatigue damage more likely to occur. However, as a result of investigations by the present inventors, it has been found that, unlike high-temperature environments exceeding 600°C, in relatively low-temperature environments of 300 to 600°C, the effects of processing strain in addition to thermal strain make thermal fatigue damage more likely to occur due to a more complex mechanism.

[0020] (b) As a result of further investigations, the inventors have found that in austenitic alloy materials, by controlling the chemical composition and forming a recrystallized structure, the thermal fatigue properties can be improved not only in high temperature environments but also in relatively low temperature environments.

[0021] (c) In order to make the metal structure of an austenitic alloy material a recrystallized structure, it is effective to optimize the annealing conditions after cold rolling. Specifically, it is necessary to increase the heating rate and cooling rate during annealing and to keep the maximum temperature within a specified range.

[0022] An embodiment of the present invention has been made based on the above findings. Each requirement of this embodiment will be described in detail below.

[0023] 1.Chemical composition The reasons for limiting the content of each element are as follows: In the following description, "%" in the content means "% by mass."

[0024] C: 0.200% or less Carbon (C) is an austenite-forming element and also has the effect of improving high-temperature strength. However, excessive C content not only leads to excessive work hardening and deterioration of workability, but also deteriorates corrosion resistance, thermal fatigue life, and high-cycle fatigue strength due to the formation of Cr carbides. Therefore, the C content is 0.200% or less. The C content is preferably 0.150% or less, more preferably 0.100% or less, and even more preferably 0.050% or less. To achieve the above effects, the C content is preferably 0.005% or more, more preferably 0.008% or more, and even more preferably 0.010% or more.

[0025] Si: Less than 4.00% Silicon (Si) is added as a deoxidizing element and has the effect of improving high-temperature strength. However, excessive addition not only deteriorates workability but also reduces the thermal fatigue life and fatigue limit. Therefore, the Si content is less than 4.00%. The Si content is preferably 3.5% or less, more preferably 2.50% or less, even more preferably 1.50% or less, and even more preferably 0.80% or less. To achieve the above effects, the Si content is preferably 0.10% or more, more preferably 0.20% or more, and even more preferably 0.30% or more.

[0026] Mn: 2.00% or less Manganese (Mn) is an austenite-forming element and also has the effect of improving high-temperature strength. However, excessive Mn content forms MnS, resulting in a decrease in corrosion resistance and oxidation resistance. Therefore, the Mn content is 2.00% or less. The Mn content is preferably 1.80% or less, more preferably 1.50% or less, and even more preferably 1.20% or less. To achieve the above effects, the Mn content is preferably 0.10% or more, more preferably 0.30% or more, and even more preferably 0.50% or more.

[0027] P:0.050% or less P (phosphorus) is an element that is mixed in as an impurity and reduces hot workability and toughness. Therefore, the P content is 0.050% or less. The P content is preferably 0.045% or less, and more preferably 0.040% or less. It is preferable to reduce the P content as much as possible, but excessive reduction of P increases refining costs. Therefore, the P content is preferably 0.005% or more, and more preferably 0.010% or more.

[0028] S: 0.0050% or less S (sulfur) is an element that is mixed in as an impurity and reduces hot workability and corrosion resistance. Therefore, the S content is 0.0050% or less. The S content is preferably 0.0045% or less, and more preferably 0.0040% or less. It is preferable to reduce the S content as much as possible, but excessive reduction of S increases refining costs. Therefore, the S content is preferably 0.0001% or more, and more preferably 0.0005% or more.

[0029] Ni: 5.00~50.00% Ni (nickel) is an austenite-forming element and also has the effect of improving corrosion resistance and oxidation resistance. Therefore, the Ni content is 5.00% or more. The Ni content is preferably 5.50% or more, more preferably 6.00% or more, and even more preferably 6.50% or more. However, excessive Ni content not only deteriorates workability but also reduces the thermal fatigue life and fatigue limit. Therefore, the Ni content is 50.00% or less. The Ni content is preferably 35.00% or less, preferably 20.00% or less, preferably 18.00% or less, more preferably 15.00% or less, and even more preferably 13.00% or less.

[0030] Cr: 12.00~30.00% Cr (chromium) has the effect of improving corrosion resistance and oxidation resistance. Therefore, the Cr content is 12.00% or more. The Cr content is preferably 13.00% or more, more preferably 14.00% or more, and even more preferably 15.00% or more. However, excessive Cr content not only deteriorates workability but also reduces the thermal fatigue life and fatigue limit. Therefore, the Cr content is 30.00% or less. The Cr content is preferably 28.00% or less, more preferably 25.00% or less, and even more preferably 20.00% or less.

[0031] Cu: more than 0% and less than 3.00% Copper (Cu) is an austenite-forming element and also has the effect of improving corrosion resistance and oxidation resistance. Cu also has the effect of improving high-temperature strength and thermal fatigue properties through precipitation strengthening. Therefore, the Cu content is greater than 0%. The Cu content is preferably 0.05% or more, more preferably 0.10% or more, and even more preferably 0.15% or more. However, excessive Cu content generates coarse precipitates, which actually degrades acid resistance and thermal fatigue properties. Therefore, the Cu content is 3.00% or less. The Cu content is preferably 2.50% or less, more preferably 2.00% or less, and even more preferably 1.00% or less.

[0032] Mo: More than 0% and less than 4.00% Mo (molybdenum) not only improves corrosion resistance and oxidation resistance, but also has the effect of improving high-temperature strength and thermal fatigue properties through solid-solution strengthening. Therefore, the Mo content is greater than 0%. The Mo content is preferably 0.01% or more, more preferably 0.05% or more, and even more preferably 0.10% or more. However, Mo is expensive, and excessive Mo content reduces workability, thermal fatigue life, and fatigue limit. Therefore, the Mo content is 4.00% or less. The Mo content is preferably 3.50% or less, more preferably 2.50% or less, and even more preferably 2.20% or less.

[0033] V: More than 0% and less than 1.00% V (vanadium) has the effect of improving corrosion resistance. Furthermore, V forms carbides and nitrides, improving high-temperature strength and thermal fatigue properties. Therefore, the V content is greater than 0%. The V content is preferably 0.005% or more, more preferably 0.01% or more, and even more preferably 0.02% or more. However, excessive V content reduces workability, thermal fatigue life, and fatigue limit. Therefore, the V content is 1.00% or less. The V content is preferably 0.80% or less, more preferably 0.50% or less, and even more preferably 0.20% or less.

[0034] Al: 1.000% or less Aluminum (Al) acts as a deoxidizing element and has the effect of improving inclusion cleanliness. However, excessive content of Al reduces workability, thermal fatigue life, and fatigue limit. Therefore, the Al content is 1.000% or less. The Al content is preferably 0.700% or less, more preferably 0.300% or less, even more preferably 0.100% or less, and even more preferably 0.010% or less. To achieve the above effects, the Al content is preferably 0.0005% or more, more preferably 0.001% or more, preferably 0.002% or more, and even more preferably 0.100% or more.

[0035] Ti:1.500% or less Titanium (Ti) combines with carbon, nitrogen, and sulfur to improve corrosion resistance. However, excessive Ti content not only reduces manufacturability due to the formation of coarse Ti carbonitrides, but also reduces workability, thermal fatigue life, and fatigue limit. Therefore, the Ti content is 1.500% or less. The Ti content is preferably 0.700% or less, more preferably 0.300% or less, more preferably 0.100% or less, more preferably 0.040% or less, more preferably 0.030% or less, even more preferably 0.020% or less, and even more preferably 0.010% or less. To achieve the above effects, the Ti content is preferably 0.0005% or more, more preferably 0.001% or more, more preferably 0.002% or more, preferably 0.100% or more, and even more preferably 0.500% or more.

[0036] N: 0.400% or less N (nitrogen) is an austenite-forming element and also has the effect of improving high-temperature strength. However, excessive content of N not only deteriorates workability but also reduces the thermal fatigue life and fatigue limit. Therefore, the N content is 0.400% or less. The N content is preferably 0.200% or less, more preferably 0.100% or less, and even more preferably 0.050% or less. To achieve the above effects, the N content is preferably 0.001% or more, more preferably 0.005% or more, and even more preferably 0.010% or more.

[0037] In addition to the above elements, one or more elements selected from Nb, B, Co, W, Sn, Zr, REM, Ca, Mg, Sb, Ga, Ta, Hf, and Bi may be contained within the ranges shown below. The reasons for limiting each element will be explained below.

[0038] Nb: 0 to 1.000% Nb (niobium) has the effect of improving high-temperature strength and thermal fatigue properties through solid solution strengthening, so it may be added as needed. However, excessive addition of Nb deteriorates hot workability. Therefore, the Nb content is 1.000% or less. The Nb content is preferably 0.900% or less, more preferably 0.400% or less, more preferably 0.300% or less, and even more preferably 0.150% or less. To achieve the above effects, the Nb content is preferably 0.001% or more, more preferably 0.005% or more, and even more preferably 0.010% or more.

[0039] B: 0 to 0.0100% Boron (B) has the effect of improving corrosion resistance and high-temperature strength, and may be added as needed. However, excessive addition of B reduces cleanliness due to the formation of boron carbides. Therefore, the B content is 0.0100% or less. The B content is preferably 0.0080% or less, more preferably 0.0060% or less, and even more preferably 0.0050% or less. To achieve the above effects, the B content is preferably 0.0001% or more, more preferably 0.0002% or more, and even more preferably 0.0005% or more.

[0040] Co: 0-3.00% Co (cobalt) has the effect of improving corrosion resistance and high-temperature strength, so it may be added as needed. However, excessive addition leads to a decrease in toughness and an increase in manufacturing costs. Therefore, the Co content is 3.00% or less. The Co content is preferably 1.00% or less, more preferably 0.50% or less, more preferably 0.40% or less, and even more preferably 0.30% or less. To achieve the above effects, the Co content is preferably 0.005% or more, more preferably 0.01% or more, and even more preferably 0.02% or more.

[0041] W: 0~3.00% W (tungsten) has the effect of improving high-temperature strength through solid solution strengthening. It also has the effect of improving corrosion resistance. Therefore, it may be added as needed. However, excessive addition of W leads to a decrease in toughness and an increase in manufacturing costs. Therefore, the W content is 3.00% or less. The W content is preferably 2.50% or less, more preferably 2.00% or less, and even more preferably 1.50% or less. To achieve the above effects, the W content is preferably 0.01% or more, more preferably 0.03% or more, and even more preferably 0.05% or more.

[0042] Sn: 0 to 1.00% Sn (tin) has the effect of improving corrosion resistance and high-temperature strength, so it may be added as needed. However, excessive addition may cause slab cracking during manufacturing. Therefore, the Sn content is 1.00% or less. The Sn content is preferably 0.80% or less, more preferably 0.50% or less, and even more preferably 0.30% or less. To achieve the above effects, the Sn content is preferably 0.005% or more, more preferably 0.01% or more, and even more preferably 0.02% or more.

[0043] Zr: 0 to 0.30% Zr (zirconium) combines with C or N to form carbides or nitrides, improving high-temperature strength and oxidation resistance, and may be added as needed. However, excessive addition reduces manufacturability and increases manufacturing costs. Therefore, the Zr content is 0.30% or less. The Zr content is preferably 0.25% or less, more preferably 0.20% or less, and even more preferably 0.15% or less. To achieve the above effects, the Zr content is preferably 0.01% or more, more preferably 0.03% or more, and even more preferably 0.05% or more.

[0044] REM: 0 to 0.200% REM (rare earth elements) have the effect of improving oxidation resistance and may be added as needed. However, excessive addition of REM results in the formation of REM-containing sulfides, which reduces corrosion resistance. Therefore, the REM content is 0.200% or less. The REM content is preferably 0.160% or less, more preferably 0.130% or less, and even more preferably 0.100% or less. To achieve the above effects, the REM content is preferably 0.001% or more, more preferably 0.002% or more, and even more preferably 0.003% or more.

[0045] REM refers to a total of 17 elements, including Sc, Y, and lanthanides, and the REM content above refers to the total content of these elements. In industry, REM is often added in the form of misch metal.

[0046] Ca: 0 to 0.0100% Ca (calcium) acts on desulfurization, improves inclusion cleanliness, and has the effect of improving corrosion resistance, so it may be added as needed. However, excessive addition of Ca causes the formation of water-soluble inclusions (CaS), which reduces corrosion resistance. Therefore, the Ca content is 0.0100% or less. The Ca content is preferably 0.0080% or less, more preferably 0.0060% or less, and even more preferably 0.0050% or less. To achieve the above effects, the Ca content is preferably 0.0001% or more, more preferably 0.0003% or more, even more preferably 0.0005% or more, and even more preferably 0.0007% or more.

[0047] Mg: 0 to 0.0100% Magnesium (Mg) acts as a deoxidizing element, improving inclusion cleanliness and corrosion resistance, and may be added as needed. However, excessive Mg content actually reduces corrosion resistance. Therefore, the Mg content is 0.0010% or less. The Mg content is preferably 0.0080% or less, more preferably 0.0060% or less, and even more preferably 0.0050% or less. To achieve the above effects, the Mg content is preferably 0.0001% or more, more preferably 0.0003% or more, even more preferably 0.0005% or more, and even more preferably 0.0007% or more.

[0048] Sb: 0 to 0.500% Sb (antimony) has the effect of improving high-temperature strength and may be added as needed. However, excessive addition of Sb leads to a decrease in toughness and an increase in manufacturing costs. Therefore, the Sb content is 0.500% or less. The Sb content is preferably 0.400% or less, more preferably 0.300% or less, and even more preferably 0.200% or less. To achieve the above effects, the Sb content is preferably 0.0001% or more, more preferably 0.0002% or more, and even more preferably 0.0005% or more.

[0049] Ga: 0 to 0.300% Ga (gallium) has the effect of improving corrosion resistance and may be contained as necessary. However, excessive inclusion of Ga reduces manufacturability and increases manufacturing costs. Therefore, the Ga content is 0.300% or less. The Ga content is preferably 0.280% or less, more preferably 0.250% or less, and even more preferably 0.200% or less. To achieve the above effects, the Ga content is preferably 0.0001% or more, more preferably 0.0002% or more, and even more preferably 0.0005% or more.

[0050] Ta: 0 to 1.000% Ta (tantalum) has the effect of improving high-temperature strength and may be added as needed. However, excessive addition increases manufacturing costs. Therefore, the Ta content is 1.000% or less. The Ta content is preferably 0.700% or less, more preferably 0.400% or less, and even more preferably 0.100% or less. To achieve the above effects, the Ta content is preferably 0.0001% or more, more preferably 0.0002% or more, and even more preferably 0.0005% or more.

[0051] Hf: 0 to 1.000% Hf (hafnium) has the effect of improving high-temperature strength and may be added as needed. However, excessive addition increases manufacturing costs. Therefore, the Hf content is 1.000% or less. The Hf content is preferably 0.700% or less, more preferably 0.400% or less, and even more preferably 0.100% or less. To achieve the above effects, the Hf content is preferably 0.0001% or more, more preferably 0.0002% or more, and even more preferably 0.0005% or more.

[0052] Bi: 0 to 0.020% Bi (bismuth) has the effect of improving high-temperature strength and may be added as needed. However, excessive addition increases manufacturing costs. Therefore, the Bi content is 0.020% or less. The Bi content is preferably 0.017% or less, more preferably 0.014% or less, and even more preferably 0.010% or less. To achieve the above effects, the Bi content is preferably 0.0001% or more, more preferably 0.0002% or more, and even more preferably 0.0005% or more.

[0053] In the chemical composition of this embodiment, the balance is Fe and impurities. Here, "impurities" refer to components that are mixed in due to various factors in raw materials such as ores and scraps, or in the manufacturing process, when industrially producing an austenitic alloy, and are acceptable within a range that does not adversely affect this embodiment.

[0054] 2.Metal structure As described above, in order to improve the thermal fatigue properties in a relatively low temperature environment, the metal structure of the austenitic alloy material is made to have an appropriate recrystallization completed structure. In this embodiment, the KAM measured using the electron backscattering diffraction pattern (EBSD) method is used. M , G.O.S. M and HAGB MWhen the value of satisfies the following formula (i), it is determined that the recrystallization-completed structure is appropriate. KAM M ×GOS M / HAGB M ≦0.05 (i) However, KAM in the above formula M is the ratio of the number of measurement points where the KAM value is within 1-2° to the total number of measurement points, and GOS M is the average value of the GOS obtained for each grain, and M is the ratio of the length of grain boundaries with a relative misorientation of 15° or more to the total length of grain boundaries.

[0055] The value of the left side of the above formula (i) is preferably 0.04 or less, more preferably 0.03 or less, and even more preferably 0.02 or less. The lower the value of the left side of the above formula (i), the better, so the lower limit is 0.

[0056] KAM M , G.O.S. M and HAGB M The value of is measured by the following procedure. A test piece 10 mm long and 5 mm wide is cut out from the austenitic alloy material, and the cross section (L cross section) parallel to the rolling direction and plate thickness direction is used as the observation surface. Mechanical polishing and mechanochemical polishing using colloidal silica suspension, etc. are performed to remove surface strain. After obtaining a mirror-like observation surface, observation and measurement are performed using a field emission-scanning electron microscope (FE-SEM) equipped with an EBSD measurement device. Then, analysis is performed using OIM (Orientation Imaging Microscopy) to determine the KAM. M , G.O.S. M and HAGB M The software used is "OIM Analysis" manufactured by TSL. The measurement range is the area from the center of the plate thickness to 1 / 4 of the plate thickness, with one field of view of 500 μm. 2 Measurements are performed in 10 fields of view at a measurement magnification of 200x and a measurement interval of 1.5 μm.

[0057] As mentioned above, KAM M is the ratio of the number of measurement points where the KAM value is within the range of 1 to 2 degrees to the total number of measurement points. The KAM value means the average value of the crystal orientation difference between the measurement point in question and its surrounding measurement points. If recrystallization does not progress sufficiently and strain remains, the KAM M The value of becomes larger.

[0058] Also, GOS M is the average value of the GOS value obtained for each grain in all grains included in the observation field. The GOS value means the average value of the misorientation between any point and other points within the same grain. If there is a lot of bending and / or twisting within the grain, the GOS M The value of becomes larger.

[0059] Furthermore, HAGB M is the ratio of the length of grain boundaries with a relative misorientation of 15° or more to the length of all grain boundaries. M represents the proportion of high-angle grain boundaries. Note that boundaries with a relative misorientation of 2° or more are considered to be grain boundaries. The smaller the residual strain, the greater the likelihood of HAGB. M The value of becomes larger.

[0060] As mentioned above, the more recrystallization progresses, the more KAM M and G.O.S. M The value of HAGB becomes smaller. M The value of KAM becomes large. M ×GOS M / HAGB M It was found that by setting the value calculated as below a predetermined value, it is possible to suppress the occurrence of thermal fatigue damage even in a relatively low temperature environment where processing strain is imparted in addition to thermal strain.

[0061] 3.Applications The austenitic alloy material of this embodiment includes austenitic alloy plates and austenitic alloy pipes. Furthermore, because the austenitic alloy material of this embodiment has excellent thermal fatigue properties, it can be suitably used as exhaust parts for automobiles and the like. Examples of exhaust parts include exhaust manifolds, center pipes, front pipes, converter peripheral parts, mufflers, turbocharger housings, and internal precision parts (e.g., back plates, oil deflectors, compressor wheels, nozzle mounts, nozzle plates, nozzle vanes, drive rings, drive levers, etc.). In addition to vehicles such as automobiles and motorcycles, the material can also be used in parts used in high-temperature environments, such as various boilers (e.g., incinerator boilers, next-generation boilers, sheath heaters, combustion burners, etc.), chemical plants (e.g., ethylene plants, hydrogen production plants, polysilicon production plants, steel plants, reduction iron-making facilities, nuclear power plants, thermal power plants, solar thermal power plants, oil mining plants, oil refineries, etc.), and fuel cell systems. The fuel for the fuel cell system may be any of city gas, LP gas, hydrogen, ammonia, and the like.

[0062] Furthermore, the austenitic alloy material of this embodiment exhibits excellent thermal fatigue properties, particularly in a relatively low-temperature environment of 300 to 600°C, and is therefore suitable for use as a component of an exhaust gas purification device mounted on a vehicle. Examples of exhaust gas purification devices include EGR-C (EGR cooler), urea SCR system, DPF (diesel particulate filter), GPF (gasoline particulate filter), and three-way catalyst. The vehicle fuel may be any of gasoline, diesel oil, hydrogen, ammonia, synthetic fuel such as e-fuel, and biofuel such as bioethanol and biodiesel.

[0063] 4.Characteristics The austenitic alloy material of this embodiment has a high thermal fatigue life and fatigue limit not only in a high-temperature environment exceeding 600° C. but also in a relatively low-temperature environment of 300 to 600° C. In this embodiment, the thermal fatigue life and fatigue limit can be evaluated by the following methods, respectively.

[0064] <Thermal fatigue life> A tubular test piece having a diameter of 38.1 mm and a test section thickness of 1.0 mm was prepared from an austenitic alloy material. Using the obtained test piece, a thermal fatigue test was conducted in which heating and cooling were continuously repeated at maximum temperatures of 400°C and 800°C, a minimum temperature of 200°C, a holding time at the maximum temperature of 30 s, and a restraint ratio of 100%. During the thermal fatigue test, the change in tensile stress over time for each heating and cooling cycle was measured, and the number of cycles at which a through crack was confirmed in the test piece was defined as the thermal fatigue life. In this embodiment, if the thermal fatigue life at the maximum temperature of 400°C is 10,000 cycles or more, it is determined that the test piece has a long thermal fatigue life in a relatively low-temperature environment. Similarly, if the thermal fatigue life at the maximum temperature of 800°C is 100 cycles or more, it is determined that the test piece has a long thermal fatigue life in a high-temperature environment.

[0065] <Fatigue limit> Plate-shaped test pieces with a total length of 90 mm, a grip width of 30 mm, a test width of 20 mm, and a thickness of 2 mm are taken from the austenitic alloy material. Using the obtained test pieces, the test was carried out at temperatures of 400°C and 800°C, with a cycle rate of 1700 cpm, fully reversed swings, and a maximum test stop count of 1 x 10 7 The fatigue limit is measured using a Schenck type plane bending fatigue tester equipped with a tubular electric furnace under the test conditions of 1 x 10 cycles. 7 The fatigue limit is the average value of the maximum amplitude stress at which the specimen did not break even after reaching 100 cycles and the minimum amplitude stress at which the specimen broke. In this embodiment, if the fatigue limit at 400°C is 150 MPa or more, the specimen is judged to have a high fatigue limit in a relatively low-temperature environment. Similarly, if the fatigue limit at 800°C is 80 MPa, the specimen is judged to have a high fatigue limit in a high-temperature environment.

[0066] <Tissue stability> In the austenitic alloy material of this embodiment, since the stability of the metal structure is excellent, it is possible to maintain an appropriate recrystallized structure even after the above-mentioned thermal fatigue test is performed. Specifically, in the test piece after reaching the end of the thermal fatigue life, the KAM measured using EBSD S , G.O.S. S and HAGB S It is preferable that the value of satisfies the following formula (ii). As a result, the thermal fatigue properties are further improved. In this embodiment, the stability of the metal structure is evaluated by the following method. KAM S ×GOS S / HAGB S ≦4.0 (ii) However, KAM in the above formula S is the ratio of the number of measurement points where the KAM value is within 1-2° to the total number of measurement points, and GOS S is the average value of the GOS obtained for each grain, and S is the ratio of the length of grain boundaries with a relative misorientation of 15° or more to the total length of grain boundaries.

[0067] A tubular test piece with a diameter of 38.1 mm and a test section thickness of 1.0 mm is prepared from an austenitic alloy material. Using the obtained test piece, a thermal fatigue test is performed in which heating and cooling are repeated repeatedly under conditions of a maximum temperature of 400°C, a minimum temperature of 200°C, a holding time at the maximum temperature of 30 seconds, and a restraint rate of 100% until the thermal fatigue life described above is reached. After the thermal fatigue test, a measurement test piece is then taken from the test piece so that the L-section becomes the observation surface, and mechanical polishing and mechanical chemical polishing using colloidal silica suspension, etc. are performed to remove surface strain. EBSD measurements are then performed, and KAM is performed. S , G.O.S. S and HAGB S The value of KAM is calculated. S , G.O.S. S and HAGB S are the KAMs mentioned above. M , G.O.S. M and HAGB MSince it is the same indicator as the above and can be measured using the same method, details will be omitted.

[0068] 5. Manufacturing method A preferred method for producing the austenitic alloy material of this embodiment will now be described. The austenitic alloy material of this embodiment can be stably produced, for example, by the following production method.

[0069] As described above, in order to make the metal structure of an austenitic alloy material a recrystallization-completed structure, it is important to optimize the annealing conditions after cold rolling. Therefore, general conditions may be used for the processes up to the cold rolling process. In the following explanation, a steel plate manufacturing process will be described as an example, but general conditions may also be used for manufacturing steel pipes.

[0070] Stainless steel having the above chemical composition is melted and produced into billets such as slabs. Next, the billets are heated to a predetermined temperature and hot rolled (hot rolling process). The heating temperature in hot rolling is preferably in the range of 1000 to 1300°C, and the rolling reduction is preferably 40% or more. This is because by setting the heating temperature and rolling reduction in the above ranges during hot rolling, it becomes easier to control the plate thickness to the desired value.

[0071] After hot rolling, annealing may be performed to adjust the structure, if necessary. The annealing conditions are not particularly limited, but for example, the annealing temperature is preferably in the range of 900 to 1300°C. The annealing time is preferably in the range of 0.5 to 15 minutes. The annealing atmosphere may be air. After hot rolling, or if annealing is performed after hot rolling, pickling is performed after annealing to remove scale. The pickling conditions are also not particularly limited, and may be performed in accordance with conventional methods.

[0072] Subsequently, the obtained hot-rolled sheet is subjected to cold rolling to obtain a cold-rolled sheet. The conditions for this are not particularly limited, but a cold rolling reduction ratio of 40% or more is preferable. Cold rolling may be performed multiple times. Intermediate annealing may also be performed between cold rolling steps. The conditions for intermediate annealing are not particularly limited, but it is preferable to perform the annealing for 10 seconds to 10 minutes in a temperature range of 900 to 1200°C.

[0073] The obtained cold-rolled sheet is subjected to cold-rolled sheet annealing. The annealing conditions are important for obtaining a recrystallized structure. Specifically, the sheet is heated at a rate of 10°C / s or more, held at a temperature range of 950 to 1200°C for 10 to 200 seconds, and then cooled at a rate of 20°C / s or more. Recrystallization can be promoted by increasing the heating rate and cooling rate during annealing. Furthermore, a recrystallized structure can be obtained by setting the maximum temperature to 950°C or higher. Furthermore, in order to reduce the value of the left side of the above-mentioned equation (i), it is preferable that the maximum temperature be low within the above-mentioned range. Specifically, in order to set the value of the left side of equation (i) to 0.03 or less, it is preferable that the maximum temperature be 1150°C or less.

[0074] After annealing, pickling may be performed according to a conventional method, if necessary. After pickling, shape and material adjustment may be performed using temper rolling, a tension leveler, etc. Here, the heating rate refers to the average heating rate from 400°C to the annealing temperature, and the cooling rate refers to the average cooling rate from the annealing temperature to 400°C.

[0075] EXAMPLES The austenitic alloy material according to the present invention will be described in more detail below with reference to examples, but the present embodiment is not limited to these examples. [Example]

[0076] A 45 kg ingot was produced by melting an alloy having the chemical composition shown in Table 1 in a vacuum melting furnace, and a block measuring 90 mm in length, 150 mm in width, and 40 mm in thickness was cut out. The resulting block was heated to 1250 ° C, hot-rolled to a thickness of 10 mm, and then subjected to hot-rolled sheet annealing by heating at 1150 ° C for 60 s, followed by pickling. It was then cold-rolled to produce a cold-rolled sheet having a thickness of 2.0 mm. After cold rolling, the cold-rolled sheet was annealed under the conditions shown in Table 2 and then pickled to obtain an austenitic alloy sheet. Note that the heating rate in Table 2 refers to the average heating rate from 400 ° C to the annealing temperature, and the cooling rate refers to the average cooling rate from the annealing temperature to 400 ° C.

[0077] [Table 1]

[0078] [Table 2]

[0079] The obtained austenitic alloy sheets were subjected to the following evaluation tests.

[0080] <Organizational Evaluation> A test piece 10 mm long and 5 mm wide was cut out from the austenitic alloy plate, and the L-section was used as the observation surface. Mechanical polishing and mechanical-chemical polishing using colloidal silica suspension were performed to remove surface strain. After obtaining a mirror-like observation surface, observation and measurement were performed using an FE-SEM equipped with an EBSD measurement device, and analysis was performed using an OIM, and the KAM was obtained. M , G.O.S. M and HAGB M The software used was "OIM Analysis" manufactured by TSL. The measurement range was the area from the center of the plate thickness to 1 / 4 of the plate thickness, with one field of view of 500 μm. 2 Measurements were carried out in 10 fields of view at a measurement magnification of 200x and a measurement interval of 1.5 μm.

[0081] <Thermal fatigue life> Tubular test pieces with a diameter of 38.1 mm and a test section thickness of 1.0 mm were prepared from the austenitic alloy plate. Using the obtained test pieces, thermal fatigue tests were conducted in which continuous heating and cooling were repeated at maximum temperatures of 400°C and 800°C, minimum temperatures of 200°C, a holding time at the maximum temperature of 30 s, and a restraint ratio of 100%. The number of cycles at which a through crack was confirmed in the test piece was defined as the thermal fatigue life. In this example, if the thermal fatigue life at the maximum temperature of 400°C was 10,000 cycles or more, it was determined that the test piece had a long thermal fatigue life in a relatively low-temperature environment, and if the thermal fatigue life at the maximum temperature of 800°C was 100 cycles or more, it was determined that the test piece had a long thermal fatigue life in a high-temperature environment.

[0082] <Fatigue limit> Plate-shaped test pieces with a total length of 90 mm, a grip width of 30 mm, a test width of 20 mm, and a thickness of 2 mm were taken from the austenitic alloy plate. Using the obtained test pieces, the test was carried out at temperatures of 400°C and 800°C, with a cycle rate of 1700 cpm, fully reversed swings, and a maximum test stop count of 1 × 10 7 The test was carried out using a Schenck type plane bending fatigue tester equipped with a tubular electric furnace under the test conditions of 1 × 10 cycles. 7 The fatigue limit was defined as the average value of the maximum amplitude stress at which the specimen did not break even after reaching the fatigue limit of 1000 cycles and the minimum amplitude stress at which the specimen broke. In this example, if the fatigue limit at 400°C was 150 MPa or more, the specimen was judged to have a high fatigue limit in a relatively low-temperature environment, and if the fatigue limit at 800°C was 80 MPa or more, the specimen was judged to have a high fatigue limit in a high-temperature environment.

[0083] <Elongation at break> JIS No. 13B test pieces specified in JIS Z 2241: 2022 were prepared from the austenitic alloy plates, and tensile tests were performed using the test pieces in accordance with JIS Z 2241: 2022 to measure the breaking elongation. In this example, if the breaking elongation was 45% or more, it was determined that the alloy had high workability.

[0084] <Tissue stability> A tubular test piece with a diameter of 38.1 mm and a test section thickness of 1.0 mm was prepared from the austenitic alloy plate. Using the obtained test piece, a thermal fatigue test was conducted in which heating and cooling were repeated continuously under conditions of a maximum temperature of 400°C, a minimum temperature of 200°C, a holding time at the maximum temperature of 30 seconds, and a restraint ratio of 100%. After the thermal fatigue test, a measurement test piece was taken from the test piece so that the L-section was the observation surface, and mechanical polishing and mechanical-chemical polishing using colloidal silica suspension, etc. were performed to remove surface strain. Then, measurements were performed using EBSD, and KAM was performed. S , G.O.S. S and HAGB S The value of was calculated.

[0085] The results are shown in Table 2.

[0086] As shown in Table 2, Test Nos. 1 to 12, which satisfied all of the requirements of the present invention, were excellent in all of workability, thermal fatigue life, and fatigue limit. In contrast, Test Nos. 13 to 24, which did not satisfy formula (i) due to inappropriate chemical composition or manufacturing conditions, resulted in poor workability, thermal fatigue life, and fatigue limit. [Industrial Applicability]

[0087] According to the present invention, it is possible to obtain an austenitic alloy material, an exhaust part, and an exhaust gas purification device that exhibit excellent thermal fatigue properties even in a relatively low-temperature environment.

Claims

1. The chemical composition, in mass%, is C: 0.200% or less, Si: less than 4.00% Mn: 2.00% or less, P: 0.050% or less, S: 0.0050% or less, Ni: 5.00 to 50.00%, Cr: 12.00-30.00%, Cu: more than 0% and 3.00% or less, Mo: more than 0% but not more than 4.00%, V: more than 0% and less than 1.00%, Al: 1.000% or less, Ti: 1.500% or less, N: 0.400% or less, Nb: 0 to 1.000%, B: 0 to 0.0100%, Co: 0-3.00%, W: 0-3.00%, Sn: 0-1.00%, Zr: 0 to 0.30%, REM: 0-0.200%, Ca: 0-0.0100%, Mg: 0 to 0.0100%, Sb: 0 to 0.500%, Ga: 0-0.300%, Ta: 0-1.000%, Hf: 0-1.000%, Bi: 0 to 0.020%, The balance is Fe and impurities. KAM measured using electron backscatter diffraction Ｍ , G.O.S. Ｍ and HAGB Ｍ The value satisfies the following formula (i): Austenitic alloy material. KAM Ｍ ×193 Ｍ / HAGB Ｍ ≦0005 ・・・(i) However, KAM in the above formula Ｍ is the ratio of the number of measurement points where the KAM value is within the range of 1 to 2° to the total number of measurement points, and GOS Ｍ is the average value of the GOS value obtained for each grain, and HAGB Ｍ is the ratio of the length of grain boundaries with a relative misorientation of 15° or more to the length of all grain boundaries.

2. The chemical composition is, in mass %, Nb: 0.001-1.000%, B: 0.0002 to 0.0100%, Co: 0.01 to 3.00%, W: 0.01-3.00%, Sn: 0.01-1.00%, Zr: 0.01 to 0.30%, REM: 0.001-0.200%, Ca: 0.0005-0.0100%, Mg: 0.0002 to 0.0100%, Sb: 0.0002 to 0.500%, Ga: 0.0002-0.300%, Ta: 0.0002-1.000%, Hf: 0.0002 to 1.000%, and Bi: 0.0002-0.020%, Contains one or more selected from The austenitic alloy material according to claim 1.

3. The thermal fatigue life measured by a thermal fatigue test in which heating and cooling are repeated continuously under the conditions of a maximum temperature of 400°C, a minimum temperature of 200°C, a holding time at the maximum temperature of 30 seconds, and a constraint rate of 100%, is 10,000 cycles or more. The austenitic alloy material according to claim 1.

4. The fatigue limit at 400 ° C is 150 MPa or more. The austenitic alloy material according to claim 1.

5. The KAM measured by electron backscatter diffraction method on the test piece after conducting a thermal fatigue test in which heating and cooling were repeated continuously under the conditions of a maximum temperature of 400°C, a minimum temperature of 200°C, a holding time at the maximum temperature of 30 seconds, and a constraint rate of 100%. Ｓ , G.O.S. Ｓ and HAGB Ｓ The value satisfies the following formula (ii): The austenitic alloy material according to claim 1. KAM Ｓ ×193 Ｓ / HAGB Ｓ ≦4.0 ・・・(ii) However, KAM in the above formula Ｓ is the ratio of the number of measurement points where the KAM value is within the range of 1 to 2° to the total number of measurement points, and GOS Ｓ is the average value of the GOS value obtained for each grain, and HAGB Ｓ is the ratio of the length of grain boundaries with a relative misorientation of 15° or more to the length of all grain boundaries.

6. Used in exhaust components or exhaust gas purification devices, The austenitic alloy material according to any one of claims 1 to 5.

7. An exhaust part made of the austenitic alloy material according to any one of claims 1 to 5.

8. An exhaust gas purification device using the austenitic alloy material according to any one of claims 1 to 5.

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