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• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
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  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D6/00—Heat treatment of ferrous alloys
  • C21D6/004—Heat treatment of ferrous alloys containing Cr and Ni
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  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D8/00—Modifying the physical properties of ferrous metals or ferrous alloys by deformation combined with, or followed by, heat treatment
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  • C22C30/04—Alloys containing less than 50% by weight of each constituent containing tin or lead
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  • C22C—ALLOYS
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  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
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  • C22C—ALLOYS
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  • C22C38/004—Very low carbon steels, i.e. having a carbon content of less than 0,01%
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  • C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
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  • C22C—ALLOYS
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  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
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  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
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  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
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  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
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  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
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  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/52—Ferrous alloys, e.g. steel alloys containing chromium with nickel with cobalt
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/54—Ferrous alloys, e.g. steel alloys containing chromium with nickel with boron
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
  • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
  • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
  • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
  • C23C8/24—Nitriding
  • C23C8/26—Nitriding of ferrous surfaces
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
  • C23C8/80—After-treatment
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/001—Austenite

Definitions

• Austenitic stainless steel materials are excellent in strength and corrosion resistance, and are used for various applications. For this reason, for example, as disclosed in Patent Document 1, austenitic stainless steel materials with enhanced wear resistance have been developed.
• Patent Document 1 JP5-222512A
• Patent Document 1 discloses an austenitic stainless steel material which is subjected to a heat treatment in a nitrogen atmosphere (hereinafter, also referred to as "nitridation treatment") to harden the surface and thereby improve its properties.
• nitridation treatment is sometimes performed, for example, after a certain amount of processing has been performed, in order to make it difficult for scratches to occur during transportation and the like.
• microcracks small cracks occur from the hardened surface (hereinafter, referred to simply as "microcracks") in the austenitic stainless steel material. Such microcracks are undesirable in terms of the appearance and performance of the product.
• an austenitic stainless steel material is required to have weldability.
• the weldability may decrease. In other words, it is generally difficult to both suppress microcracks and also improve weldability.
• an austenitic stainless steel material in which microcracks are suppressed and which has good weldability even when subjected to processing before and after nitridation treatment is obtained.
• the present inventors have conducted various studies directed at improving weldability while suppressing the microcracks described above, and obtained the findings described in (a) to (c) below.
• C carbon
• C has an effect of improving strength.
• C has an effect of suppressing formation of a nitridation layer. Therefore, the content of C is 0.010% or more.
• the content of C is preferably 0.020% or more, and more preferably is 0.030% or more.
• the content of C is 0.15% or less.
• the content of C is preferably 0.12% or less, and more preferably is 0.10% or less.
• Si silicon is an element that has a deoxidizing effect. In addition, Si has an effect of suppressing formation of a nitridation layer. Therefore, the content of Si is 0.10% or more.
• the content of Si is preferably 0.12% or more, more preferably is 0.15% or more, and further preferably is 0.20% or more. However, if Si is excessively contained, weldability will decrease. Therefore, the content of Si is 2.00% or less.
• the content of Si is preferably 1.70% or less, more preferably is 1.40% or less, and further preferably is 1.00% or less.
• P phosphorus
• P is an impurity element contained in the steel. P reduces mechanical properties such as strength and toughness. Therefore, the content of P is 0.060% or less.
• the content of P is preferably 0.050% or less. Although it is preferable to reduce the content of P as much as possible, excessive reduction of P will increase the refining cost. Therefore, the content of P is preferably 0.005% or more.
• S sulfur is an impurity element contained in the steel. S reduces mechanical properties such as strength and toughness. Therefore, the content of S is 0.010% or less. The content of S is preferably 0.0050% or less. Although it is preferable to reduce the content of S as much as possible, excessive reduction of S will increase the refining cost. Therefore, the content of S is preferably 0.0001% or more.
• N nickel is an element that stabilizes austenite. Further, N has an effect of improving strength. In addition, N has an effect of suppressing formation of a nitridation layer. Therefore, the content of Ni is 16.0% or more. The content of Ni is preferably 16.5% or more, more preferably is 17.0% or more, and further preferably is 18.0% or more. However, if Ni is excessively contained, weldability and hot workability will decrease. Therefore, the content of Ni is 25.0% or less. The content of Ni is preferably 24.8% or less, more preferably is 24.5% or less, and further preferably is 24.0% or less.
• Cr Cr (chromium) has an effect of increasing corrosion resistance. Therefore, the content of Cr is 20.0% or more.
• the content of Cr is preferably 21.0% or more, more preferably is 21.5% or more, and further preferably is 22.0% or more. However, if Cr is excessively contained, weldability will decrease. Therefore, the content of Cr is 29.0% or less.
• the content of Cr is preferably 28.0% or less, more preferably is 27.5% or less, and further preferably is 27.0% or less.
• Mo mobdenum
• the content of Mo is 0.08% or more.
• the content of Mo is preferably 0.10% or more, more preferably is 0.12% or more, and further preferably is 0.15% or more.
• the content of Mo is 1.0% or less.
• the content of Mo is preferably 0.95% or less, more preferably is 0.90% or less, and further preferably is 0.85% or less.
• Sn (tin) has an effect of increasing corrosion resistance. Further, Sn also has an effect of increasing weldability. Therefore, the content of Sn is 0.001% or more.
• the content of Sn is preferably 0.0015% or more, more preferably is 0.002% or more, and further preferably is 0.003% or more. However, if Sn is excessively contained, hot workability will decrease. Therefore, the content of Sn is 0.080% or less.
• the content of Sn is preferably 0.075% or less, more preferably is 0.070% or less, and further preferably is 0.060% or less.
• N nitrogen
• the content of N is preferably 0.015% or more, more preferably is 0.020% or more, and further preferably is 0.030% or more.
• the content of N is 0.15% or less.
• the content of N is preferably 0.14% or less, more preferably is 0.13% or less, and further preferably is 0.12% or less.
• Co is an important element in a steel plate of the present embodiment, and has an effect of suppressing formation of a nitridation layer. Therefore, the content of Co is 0.001% or more.
• the content of Co is preferably 0.005% or more, more preferably is 0.01% or more, and further preferably is 0.02% or more. However, if Co is excessively contained, the production cost will increase. Therefore, the content of Co is 1.50% or less.
• the content of Co is preferably 1.30% or less, more preferably is 1.00% or less, and further preferably is 0.80% or less.
• the chemical composition may also contain Nb within the range described below in lieu of a part of Fe. The reason for limiting the element is described below.
• Nb (niobium) forms carbo-nitrides and has an effect of increasing corrosion resistance. Therefore, Nb may be contained as necessary. However, if Nb is excessively contained, mechanical properties such as toughness will decrease. Therefore, the content of Nb is 0.20% or less.
• the content of Nb is preferably 0.15% or less, and more preferably is 0.10% or less.
• the content of Nb is preferably 0.001% or more, more preferably is 0.005% or more, further preferably is 0.010% or more, and further preferably is 0.015% or more.
• the chemical composition may also contain one or more kinds of element selected from Cu, V, Ti, Al, and B within the ranges described below in lieu of a part of Fe. The reasons for limiting each element are described below.
• Cu copper stabilizes austenite and has an effect of improving strength. Therefore, Cu may be contained as necessary. However, if the content of Cu is excessive, hot workability will decrease. Therefore, the content of Cu is 1.0% or less.
• the content of Cu is preferably 0.80% or less, and more preferably is 0.60% or less. On the other hand, in order to obtain the aforementioned advantageous effect, the content of Cu is preferably 0.001% or more.
• V 0.30% or less
• V vanadium
• V vanadium
• the content of V is preferably 0.25% or less, and more preferably is 0.20% or less.
• the content of V is preferably 0.001% or more.
• Ti titanium
• Ti has an effect of improving the strength of the steel by forming carbo-nitrides. Therefore, Ti may be contained as necessary. However, if the content of Ti is excessive, toughness will decrease. Therefore, the content of Ti is 0.020% or less.
• the content of Ti is preferably 0.015% or less, and more preferably is 0.010% or less. On the other hand, in order to obtain the aforementioned advantageous effect, the content of Ti is preferably 0.001% or more.
• W tungsten
• W dissolves in the parent phase and has an effect of improving the strength of the steel. Therefore, W may be contained as necessary. However, if the content of W is excessive, hot workability will decrease. Therefore, the content of W is 0.10% or less.
• the content of W is preferably 0.08% or less, and more preferably is 0.05% or less. On the other hand, in order to obtain the aforementioned advantageous effect, the content of W is preferably 0.001% or more.
• Al is an element that has a deoxidizing effect. Therefore, Al may be contained as necessary. However, if the content of Al is excessive, inclusions will excessively form and productivity will decrease. Therefore, the content of Al is 0.050% or less.
• the content of Al is preferably 0.040% or less, and more preferably is 0.030% or less. On the other hand, in order to obtain the aforementioned advantageous effect, the content of Al is preferably 0.001% or more.
• B (boron) forms intermetallic compounds at grain boundaries, and has an effect of increasing grain boundary strength. Therefore, B may be contained as necessary. However, if the content of B is excessive, hot workability will decrease. Therefore, the content of B is to be 0.050% or less.
• the content of B is preferably 0.040% or less, and more preferably is 0.030% or less. On the other hand, in order to obtain the aforementioned advantageous effect, the content of B is preferably 0.0001% or more.
• the balance is Fe and impurities.
• impurities refers to components which, during industrial production of the steel, are mixed in from raw material such as ore or scrap or due to various causes during the production process, and which are allowed within a range that does not adversely affect the present embodiment.
• Fl calculated by Formula (i) below is 7.5 to 20.0.
• F 1 16.0 + 8.0 C + 2.4 Si ⁇ 0.5 Mn + 0.3 Ni ⁇ 0.9 Cr ⁇ 3.1 Mo + 119 N + 2.0 Co
• each symbol of an element in the above formula represents the content (mass%) of a corresponding element contained in the austenitic stainless steel material, and is assigned a value of 0 if the corresponding element is not contained.
• nitridation layer in which nitrogen is concentrated at the surface of the steel material grows too thick due to nitridation treatment, microcracks will form. Therefore, it is effective to cause nitrides, for example, CrN and the like, to form in order to reduce the thickness of the nitridation layer.
• nitrides for example, CrN and the like
• the above Formula (i) is an experimentally obtained relational expression with respect to C, Si, Mn, Ni, Cr, Mo, N, and Co, which are elements which affect the formation of nitrides
• F1 is an index of the likelihood of microcracks occurring in a case where processing is performed before and after nitridation treatment.
• F1 is 7.5 or more.
• Fl is preferably 7.6 or more, more preferably is 7.7 or more, and further preferably is 7.8 or more.
• F1 is 20.0 or less.
• F1 is preferably 19.0 or less, more preferably is 18.0 or less, and further preferably is 17.0 or less.
• Formula (ii) is an experimentally obtained formula. That is, Formula (ii) is a relational expression with respect to C, Si, Mn, Cr, Mo, Sn, and Nb which mutually affect weldability. If F2 is more than 320.0, weldability will decrease and cracks will easily occur after welding. Therefore, F2 is 320.0 or less. F2 is preferably 319.0 or less, more preferably is 318.0 or less, and further preferably is 317.0 or less. Note that, although a lower limit of F2 is not particularly limited, F2 will be 213.0 or more based on the ranges of the contents of the elements constituting Formula (ii).
• the thickness of the aforementioned Cr depleted zone is to be measured by the following method.
• a field emission electron probe microanalyzer FE-EPMA
• FE-EPMA field emission electron probe microanalyzer
• the measurement is to be performed under conditions of an acceleration voltage of 15 kV and an analysis diameter of 0.1 ⁇ m.
• a region where the Cr concentration is 0.9 times or less for the content of Cr in the aforementioned austenitic stainless steel material is defined as a Cr depleted zone.
• the shape of the austenitic stainless steel material of the present embodiment is not particularly limited.
• the austenitic stainless steel material may be a steel plate, or may be a steel bar or wire rod.
• the austenitic stainless steel material of the present embodiment is suitable for use in applications in which processing such as drawing is performed after nitridation treatment.
• the austenitic stainless steel material of the present embodiment can be stably produced, for example, by the following production method.
• the hot working is, for example, hot forging, hot extrusion, hot rolling or the like.
• the shape may be, for example, a steel plate, a steel bar, a wire rod or the like. Note that, the conditions of the hot working are not particularly limited and may be adjusted as necessary. After the hot working, cold working may be performed as necessary.
• the cold working is, for example, cold drawing or cold rolling.
• a heat treatment is performed.
• Well-known conditions can be used as the heat treatment conditions.
• the steel material may be heated to a temperature range of 1060 to 1350°C, and thereafter rapidly cooled.
• An atmosphere furnace is generally used when performing the heat treatment.
• Steel types A to S having the chemical compositions shown in Table 1 were melted in a laboratory and subjected to hot forging to produce steel materials with a thickness of 20 mm. Thereafter, hot rolling was performed to a predetermined thickness to produce steel plates (austenitic stainless steel materials) of 1.25 mm and 7 mm in thickness.
• the obtained steel plates were then subjected to a heat treatment in which the steel plates were heated to a temperature of 1060°C or more in an atmosphere furnace described in Table 2, followed by rapid cooling. For some of the steel plates, the thickness of a Cr depleted zone was measured in the as heat treatment condition. Thereafter, for steel type N which had been subjected to heat treatment using an atmosphere furnace, a descaling treatment was performed by pickling. Further, for all of the steel materials, evaluation of the occurrence of microcracks and evaluation of weldability were carried out by the methods described below.
• microcracks The occurrence of microcracks was evaluated by a tensile test, and a subsequent structural observation and the like. Specifically, based on JIS Z 2241: 2022, a No. 5 test coupon specified in JIS was taken from each 1.25-mm thick steel plate. Strain was introduced into the test coupon by performing cold working so that the cold reduction ratio was 30% using a tensile testing machine. Thereafter, nitridation treatment was performed in which the test coupon was held at a heat treatment temperature of 1040°C for a heat treatment time of 30 minutes in a 100% nitrogen atmosphere, and then cooled with gas.
• a tensile test was performed once more, and strain was introduced into the tensile test coupon by cold working so that the cold reduction ratio was 25%. At such time, strain was introduced in a manner so that the tensile test coupon did not rupture, and thereafter the surface of the test coupon was observed with a scanning microscope to check for the presence or absence of microcracks. At that time, the observation magnification was set to 500 ⁇ , and the number of visual fields was set to five visual fields. The number of visual fields in which cracks were observed is shown in Table 2. In the present Example, if the number of visual fields in which cracks were observed among the five visual fields was one or less, it was determined that the test coupon was acceptable.
• Trans-Varestraint test refers to a test to examine cracking (solidification cracking) that occurs in a weld metal during welding.
• GTAW Gas Tungsten Arc Welding
• the maximum length of the occurred cracks was measured. The results are shown in Table 2. In the present Example, if the maximum length of the cracks was 1.00 mm or less, it was determined that the resistance to weld crack susceptibility was good. On the other hand, if the maximum length of the cracks was more than 1.00 mm, it was determined that the resistance to weld crack susceptibility was failed.
• the content of N was low and, furthermore, the value of F1 was less than the specified value, and consequently the thickness of the nitridation layer was excessive and microcracks occurred.
• the content of Cr was excessive, the value of F1 was less than the specified value and, in addition, the value of F2 was more than the specified value. As a result, microcracks occurred, and the weld crack resistance was inferior.

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