WO2021124511A1 - High-hardness and high–corrosion resistance martensitic steel having excellent cold workability and production method for same - Google Patents

High-hardness and high–corrosion resistance martensitic steel having excellent cold workability and production method for same Download PDF

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WO2021124511A1
WO2021124511A1 PCT/JP2019/049821 JP2019049821W WO2021124511A1 WO 2021124511 A1 WO2021124511 A1 WO 2021124511A1 JP 2019049821 W JP2019049821 W JP 2019049821W WO 2021124511 A1 WO2021124511 A1 WO 2021124511A1
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stainless steel
martensitic stainless
softening
hardness
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PCT/JP2019/049821
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French (fr)
Japanese (ja)
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光司 高野
雅之 東城
富美夫 札軒
規介 田中
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日鉄ステンレス株式会社
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Priority to KR1020227019630A priority Critical patent/KR20220097991A/en
Priority to JP2020531682A priority patent/JP6821097B1/en
Priority to PCT/JP2019/049821 priority patent/WO2021124511A1/en
Priority to CN201980103114.XA priority patent/CN114829636B/en
Publication of WO2021124511A1 publication Critical patent/WO2021124511A1/en

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    • 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
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • 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
    • C21D6/00—Heat treatment of ferrous alloys
    • 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
    • C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat 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
    • C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
    • C21D8/06—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of rods or wires
    • 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
    • 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
    • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
    • 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
    • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
    • 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
    • C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
    • 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
    • C22C38/42—Ferrous alloys, e.g. steel alloys containing chromium with nickel with copper
    • 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
    • C22C38/52—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
    • C22C38/60—Ferrous alloys, e.g. steel alloys containing lead, selenium, tellurium, or antimony, or more than 0.04% by weight of sulfur
    • 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
    • C21D2211/008—Martensite

Definitions

  • the present invention relates to martensitic stainless steel for cold-working parts, which has excellent softening properties and is capable of strong cold-working, and has high hardness and high corrosion resistance, and a method for manufacturing the same.
  • Patent Documents 1 to 4 These high-hardness, high-corrosion-resistant martensitic stainless steel parts, especially large automobile parts, are molded into a complicated shape by cold working such as cold forging. For this reason, the steel is softened by softening and annealing before cold working, and then cold working is performed, and then quenching is performed after cold working to obtain high hardness and high corrosion resistant martensitic stainless steel. In the martensitic stainless steel after quenching, the higher the C content in the steel, the higher the hardness of the steel can be obtained.
  • the hardness of stainless steel after softening and annealing increases as the C content in the steel increases.
  • the stainless steel after softening and annealing is in a softened state having an Hv hardness of (60C + 170) or less, preferably (60C + 160) or less, depending on the amount of C (mass%). Is desired.
  • Patent Document 5 proposes a component design and a softening annealing technique for improving cold forging property, but the softening has not been achieved to the level required for the present invention.
  • Japanese Patent No. 3340225 Japanese Patent No. 4252145 Japanese Unexamined Patent Publication No. 2016-50320 Japanese Patent No. 3587330 Japanese Patent No. 3328791
  • the problem to be solved by the present invention is to reduce the cost of martensitic stainless steel for high hardness and high corrosion resistance, which has significantly improved softening properties, as a material for cold working or cold forged parts of complicated shapes, and a method for producing the same. Is to provide to.
  • the steel structure is composed of ferrite and carbide, and is not a martensite structure.
  • the stainless steel of the present invention is cold-worked and then hardened and the final product has a martensitic structure, the stainless steel of the present invention is referred to as a martensitic stainless steel.
  • the present inventors have determined the size and composition of oxides, which are secondary deoxidizing products, in martensitic stainless steels for high corrosion resistance and high hardness whose components have been adjusted. It was found that by controlling and controlling the dispersed state of fine carbonitride by softening and annealing at high temperature, the hardness is softened to Hv hardness of (60C + 170) or less and the cold workability is remarkably improved. Further, it is more preferable to control the fine deoxidized product composition that does not pin the dislocations and grain boundaries to the Al-containing system.
  • the present invention has been made based on the above findings, and the gist thereof is as follows.
  • C More than 0.15% 0.70% or less Si: 2.0% or less, Mn: 1.5% or less, S: less than 0.01%, P: 0.05% or less, Ni: 1.5% or less, Cr: 10.5 to 16.0%, Mo: 0.9-3.0%, N: 0.14% or less, Al: 0.008 to 1.0%, O: Contains 0.001 to 0.008%, It has a chemical component consisting of the balance Fe and impurities, C + N / 2: 0.16 to 0.70%, In addition, there are 10 or more carbonitrides of 1.0 ⁇ m or more in 1600 ⁇ m 2 , the average diameter size of the oxide is 1 to 5 ⁇ m, and the Hv hardness is represented by the formula (a).
  • Nb 0.1% or less
  • Ti 0.1% or less
  • V 0.2% or less
  • Ta The martensitic stainless steel of the present invention, which comprises one or more of 0.2% or less.
  • Mg 0.01% or less
  • Ca 0.01% or less
  • Hf 0.01% or less
  • REM The martensitic stainless steel of the present invention, which comprises one or more of 0.01% or less.
  • the martensitic stainless steel of the present invention, wherein the average Al concentration of the oxide is 15 to 40% by mass.
  • strong cold forging (cold working) or near net forming can be performed on a complicated part shape, and the effect of significantly reducing the part cost by cold forging (cold working) for automobiles and the like can be exhibited. It is possible to provide a softened annealed material of martensitic stainless steel having high hardness and high corrosion resistance.
  • the metallographic structure when 13Cr-2Mo-0.2C-0.1N steel is softened and annealed by a known method is shown.
  • the metallographic structure when 13Cr-2Mo-0.2C-0.1N steel is softened and annealed by the method of the present invention is shown.
  • the martensitic stainless steel for high hardness and high corrosion resistance which is the object of the present invention and has excellent cold workability, is a stainless steel softened by softening and annealing the steel, and the steel structure is ferrite and carbonitride. Consists of.
  • the softened stainless steel of the present invention is used as a material for cold working, and then quenching is carried out to increase the hardness, and the final product is obtained.
  • the component composition of the present invention described later most of the steel has a martensitic structure by quenching, and martensitic stainless steel can be obtained. Specifically, it is a steel in which about 80% or more of the structure becomes a martensite structure by quenching treatment from 1000 to 1200 ° C.
  • C is limited to more than 0.15% and C + N / 2 is limited to more than 0.16%. This is to ensure hardness after quenching. However, if C is contained in an amount of more than 0.70% and C + N / 2 is contained in an amount of more than 0.70, the cold workability is deteriorated due to coarse carbides and fine nitrides.
  • the preferred range of C which stably obtains a quenching hardness of 500 Hv or more and exerts a softening effect, is 0.16 to 0.40%, and the preferable range of C + N / 2 is 0.18 to 0.45%. ..
  • N can be contained in order to ensure the corrosion resistance of the product in addition to the quenching hardness described above. However, if N is contained in excess of 0.14%, casting becomes difficult due to the formation of blow holes, and even if casting is possible, coarse carbonitride is formed in the steel and cold workability deteriorates, so the upper limit is 0. .14%.
  • the preferred range is 0.02 to 0.11%. More preferably, it is 0.04 to 0.10%.
  • Si is an element that deteriorates cold workability due to solid solution strengthening of the ferrite structure during softening and annealing and fine dispersion of carbonitride, so the content is limited to 2.0% or less. Preferably, it is 0.7% or less.
  • the Si content is preferably 0.01% or more. Si may not be contained.
  • the content of Mn is limited to 1.5% or less because it increases the strength after softening and annealing and deteriorates the cold workability.
  • the Mn content is preferably 0.01% or more. Mn may not be contained.
  • the content of S is limited to less than 0.01% because it forms sulfide and deteriorates cold workability. It is preferably 0.007% or less.
  • the content of P is limited to 0.05% or less because it segregates at grain boundaries and deteriorates cold workability.
  • Ni is an element that improves the toughness and corrosion resistance of martensitic stainless steel products, so it may be contained. However, if it is contained in excess of 1.5%, the hardness after softening and annealing does not soften below the Hv hardness of (60C + 170), and the cold workability deteriorates. Therefore, it is limited to 1.5% or less. Preferably, it is 1.3% or less.
  • the Ni content is preferably 0.01% or more. Ni does not have to be contained.
  • Cr is a basic element for obtaining the function of high corrosion resistance of stainless steel, and contains 10.5% or more. However, if it is contained in an amount of more than 16.0%, the high hardness of the product, which is a feature of the present invention, cannot be obtained after quenching, and cold workability can be ensured by the conventional technique. Therefore, it is limited to 16.0% or less.
  • the preferred Cr range is 11.0 to 15.0%.
  • Mo is included to obtain highly corrosion-resistant martensitic stainless steel. It should be noted that it is an element that inhibits the coarsening of the carbonitride during softening annealing and makes it difficult to soften the material, and is limited to 0.9% or more at which the effect of the soft and highly cold workability of the present invention becomes clear. .. If it is less than 0.9%, cold workability can be ensured by a known softening and annealing method, the effectiveness of the present invention becomes unclear, and corrosion resistance is insufficient. On the other hand, if it is excessively contained in excess of 3.0%, it becomes difficult to soften even by the method of the present invention, the carbonitride does not become coarse during annealing, and the cold workability deteriorates. Therefore, it is limited to 3.0% or less. The preferred range is 1.0 to 2.5%.
  • Al is an element effective in reducing deoxidation products by deoxidation and suppressing decomposition and miniaturization, so it is contained in an amount of 0.008% or more. However, even if it is added in excess of 1.0%, not only the deoxidizing effect is saturated but also coarse oxides are generated, which significantly deteriorates cold workability. Therefore, the upper limit is limited to 1.0%. Preferably, it is 0.01 to 0.2%.
  • O greatly affects the composition and size of fine deoxidizing products (oxides) in Al-containing steel. Controlling the solidification rate and O content, which will be described later, prevents the average diameter of the deoxidized product of the product from becoming excessively coarse, exceeding 5 ⁇ m, and makes it substantially harmless to cold-rolled cracks. In addition, it suppresses the decomposition and miniaturization of oxides to a size of less than 1 ⁇ m during hot rolling. Therefore, O in steel is controlled to 0.001 to 0.008%.
  • O is T.I. Means O. If O is less than 0.001%, industrial implementation becomes difficult, and if it is contained in excess of 0.008%, coarse oxides are generated and cold workability is lowered. Preferably, it is 0.001 to 0.006%.
  • the distribution of carbon nitride in the martensitic stainless steel (after softening and annealing) of the present invention affects the softening behavior (softening characteristics after softening and annealing) of the martensitic stainless steel during softening and annealing. If the carbonitride in the steel after softening annealing is finely dispersed, it is difficult to perform cold working by pinning the movement of dislocations and grain boundaries in the cold working after softening annealing.
  • FIG. 1 shows the metallographic structure when 13Cr-2Mo-0.2C-0.1N steel is softened and annealed by a known method (low temperature annealing at 650 ° C.-4h). Submicron rod-shaped carbides are precipitated at the interface of the lath martensite structure, and even after being softened and annealed, the Hv hardness is 305, which is inferior in cold workability.
  • FIG. 2 shows an example of steel softened and annealed by the method of the present invention described later.
  • 1600 .mu.m carbonitride or more sizes 2 ⁇ m in 2 is 10 or more.
  • the carbonitride size indicates (major axis + minor axis) / 2 of the carbonitride.
  • a steel having the suitable steel composition of the present invention and having 10 or more carbonitrides of 1.0 ⁇ m or more in 1600 ⁇ m 2 can be obtained by performing softening annealing using the suitable softening annealing conditions described later. It can be realized.
  • the size of the oxide which is a secondary deoxidizing product produced during solidification of the martensitic stainless steel of the present invention (after softening and annealing), is the softening behavior of the martensitic stainless steel during softening and annealing (softness after softening and annealing). If the average diameter size of this oxide is reduced to less than 1 ⁇ m, it will be difficult to perform cold working by pinning dislocations and movements of grain boundaries in cold working after softening annealing. , Hv ⁇ (60C + 170) softening characteristics cannot be obtained either.
  • the average diameter size of the oxide exceeds 5 ⁇ m, it becomes the starting point of cracking during cold working, so that the cold workability deteriorates. It is preferably 2 to 4 ⁇ m.
  • the size of the oxide as the secondary deoxidizing product indicates the secondary deoxidizing product (major axis + minor axis) / 2 2
  • the average size indicates the average value of 30 arbitrarily sampled pieces. ..
  • the distinction between the primary deoxidizing product and the secondary deoxidizing product is that a coarse product having a size of more than 15 ⁇ m produced in molten steel is judged to be a primary deoxidizing product and is 15 ⁇ m or less. Is determined as a secondary deoxidizing product that crystallizes over the entire surface during solidification.
  • the average diameter size of the oxide can be set to 1 to 5 ⁇ m by having the suitable steel composition of the present invention, particularly setting the Al content within the range of the present invention, and optimizing the solidification conditions described later. it can.
  • Hv hardness represented by equation (a)
  • Hv hardness of the stainless steel (after softening and annealing) of the present invention is described below in order to be softer than known techniques and cold-worked into a complicated shape to exert a remarkable effect. It is limited to the Hv hardness represented by the formula a). Further, when the Hv hardness is Hv ⁇ (60C + 160), cold forging of a large part having a complicated shape becomes possible, and the industrial and economic effect is dramatically increased. Therefore, it is preferably (60C + 160) or less. Hv hardness or less. Hv ⁇ 60C + 170 ⁇ ⁇ ⁇ ⁇ (a) C: C content (mass%)
  • the deoxidized product is thermally stabilized, and decomposition and miniaturization to a size of less than 1 ⁇ m during hot rolling are suppressed.
  • the average composition in the oxide is a value obtained by converting in mass% including O excluding the S element in the non-metal inclusions.
  • the stainless steel of the present invention is composed of chemical components composed of Fe and impurities other than the elements described above. Further, in addition to the above-mentioned component composition, the following elements may be selectively contained in place of a part of Fe.
  • Cu may be contained as necessary in order to improve the corrosion resistance of the product. However, even if the content exceeds 1.5%, the effect is saturated and the cold workability is deteriorated, so the content is set to 1.5% or less. Preferably, it is 0.35% or less.
  • Co and W may be contained as necessary in order to improve the toughness and corrosion resistance of the product. However, even if each content exceeds 1.5%, the effect is saturated and the cold workability is deteriorated, so the content is set to 1.5% or less. Preferably, it is 1.0% or less.
  • the content B may be contained as necessary in order to improve the toughness of the product.
  • the content is set to 0.01% or less. Preferably, it is 0.006% or less.
  • Sn and Sb may be contained as necessary in order to improve the corrosion resistance of the product.
  • the content is set to 0.3% or less. Preferably, it is 0.1% or less.
  • Nb and Ti may be contained as necessary in order to improve the toughness and corrosion resistance of the product.
  • the content is 0.1% or less.
  • it is 0.06% or less.
  • V and Ta may be contained as necessary in order to improve the toughness and corrosion resistance of the product.
  • the content is 0.2% or less.
  • it is 0.1% or less.
  • Mg, Ca, Hf, and REM may be contained as necessary because they increase the thermodynamic stability of the deoxidized product and are effective in softening during softening and annealing. However, even if each is added in excess of 0.01%, the effect is saturated, and conversely, coarse oxides are generated and cold workability is deteriorated. Therefore, the content is set to 0.01% or less. To do. Preferably, it is 0.005% or less.
  • REM rare earth element
  • Y yttrium
  • 15 elements lanthanoids from lanthanum (La) to lutetium (Lu), according to a general definition. It may be contained alone or as a mixture.
  • typical impurities include Zn, Bi, Pb, Ge, Se, Ag, Se, Te, etc., and usually, as impurities in the steel manufacturing process, 0. Mix in the range of about 1%.
  • typical optional additive elements are specified in (3) to (5) above, even elements not described in the present specification do not impair the effects of the present invention. Can be contained in.
  • the retention heat treatment time is shorter than 1 h, the carbon nitride size becomes fine and softening cannot be expected. On the contrary, if it is longer than 48 h, the effect is saturated and the economic rationality is lost industrially. Therefore, the retention heat treatment time is limited to 1 to 48 hours. The preferred range is 2 to 10 hours.
  • the retention heat treatment temperature becomes lower than 870 ° C or (T-120) ° C, the carbide size becomes fine and softening cannot be expected. On the contrary, the retention heat treatment is performed at a temperature higher than (T-20) ° C. Then, it becomes a film-like grain boundary carbide, and the cold workability deteriorates.
  • the preferred range of the retention heat treatment temperature is 900 ° C. or higher and 30 to 100 ° C. lower than T.
  • the slow cooling end temperature if the slow cooling is not performed to (T-250) ° C, softening cannot be expected due to the miniaturization of the carbonitride and the formation of a hard martensite structure. Therefore, it is preferable to slowly cool to a temperature lower than (T-250) ° C.
  • the cooling rate does not have to be specified at a temperature lower than (T-250) ° C.
  • the carbide size and dispersion state are determined by the above-mentioned softening annealing method of the present invention, the effect is continued even if the conventional annealing method is applied after the annealing method of the present invention, and therefore, it may be combined with the conventional annealing method. ..
  • Oxides which are fine secondary deoxidizing products in steel, are formed during solidification.
  • the oxide is thermodynamically unstable, it is decomposed and refined by thermal processing such as hot rolling, and dislocations and movements of grain boundaries are pinned during softening annealing to inhibit softening.
  • the average cooling rate during casting is set in the range of 5 to 500 ° C / s, so that the average of secondary deoxidized products generated during solidification It can be softened by suppressing decomposition and miniaturization when the size is 1 ⁇ m or more and 5 ⁇ m or less.
  • the average cooling rate is slower than 5 ° C./s, the deoxidized product becomes coarser than 5 ⁇ m, the softening effect of the present invention becomes unclear, and the cold workability also deteriorates.
  • the average cooling rate is higher than 500 ° C./s, the Al concentration of the secondary deoxidizing product decreases to 15% or less, becomes thermodynamically unstable, and decomposition / miniaturization to less than 1 ⁇ m progresses. , It becomes difficult to promote the softening of the material. Therefore, in order to obtain a fine thermodynamically stable oxide size that is easily softened as defined in the present invention, it is necessary to solidify at an average cooling rate of 5 to 500 ° C./s. It is preferably 10 ° C./s or more and less than 400 ° C./s.
  • Example 1 Steels having the chemical compositions shown in Tables 1 to 3 were melted at about 1600 ° C. in a 150 kg vacuum melting furnace, and then cast into a mold. The amount of O was changed depending on the amount of deoxidizing elements added such as Al, Si, and Mn and the time from the addition of the deoxidizing elements to the molten steel to the delivery time to the mold. By using various sizes ( ⁇ 20 to ⁇ 250 mm) and materials (iron-based, magnesia-based, silica-based) as the mold, the average cooling rate during solidification was changed.
  • the average cooling rate during solidification is the average value obtained by measuring the secondary dendrite arm spacing: ⁇ in the 1/4 part of the cross section and the central part of the slab of the SUS304 sample melted and solidified under the same conditions.
  • the steel bar was embedded in the central cross section in the longitudinal direction and polished, and the Hv hardness of 1/4 of the cross section diameter and the central portion was measured with a load of 1 kg and evaluated by the average value. Tables 4 to 6 It was shown to. In the table, the value of the right side (60C + 170) of the equation (a) is shown on the right side of Hv.
  • the cold workability was determined by preparing a compression test piece with a diameter of 8 mm and a height of 12 mm, performing end face compression processing at a strain rate of 10 / s in the height direction, and determining whether cold compression processing was possible without cracking. ..
  • the cold workability of the steel material depends on the amount of C (mass%), and the higher the amount of C, the lower the cold workability. Therefore, the limit workability is defined as the formula for the amount of C. "B” if cold compression processing is possible at the limit processing rate of (85-50C)%, "X” if cracks occur, and cold compression processing at the limit processing rate of (90-50C)% Was evaluated as "A” if possible. All of the steels of the present invention were B or A, and showed excellent cold workability.
  • the processing rate is (12-H) / 12 ⁇ 100 (%), and H is the thickness (mm) of the test piece after cold compression processing.
  • the dispersed state of the carbonitride was evaluated by SEM / EDS after etching the embedded polished surface with aqua regia. "B” if the 1600 .mu.m carbonitride or more in diameter 1 ⁇ m size during 2 is 10 or more, "A” if the carbonitride above diameter 2 ⁇ m size in 1600 .mu.m 2 is 10 or more, the rest " It was evaluated by "X”. In the steel of the present invention, all of them were B or A, and showed a dispersed state of the carbonitride that contributed to excellent cold workability. The diameter of the size is calculated by (major axis + minor axis) / 2.
  • the carbonitride is a precipitate mainly composed of Cr, Fe, C and N in EDS analysis.
  • the average size of the oxide and the composition of the oxide were evaluated using a material hardened by air cooling from 1150 ° C. in order to eliminate the influence of the carbonitride.
  • a steel material whose surface layer is # 500 polished is electrolyzed (100 mV constant voltage) in a non-aqueous solution (3% maleic acid + 1% tetramethylammonium cloid + residual methanol) to dissolve the matrix, filtered with a filter, and oxidized. The thing was extracted. Then, for the oxides remaining on the filter, the diameter sizes of 30 oxides were arbitrarily measured by SEM / EDS to calculate the average diameter size.
  • Oxide means a non-metal inclusion mainly composed of O and Al, Mn, Si, Fe, Cr, Ti and the like in EDS analysis.
  • the diameter size is calculated by (major axis + minor axis) / 2.
  • those having a size of 15 ⁇ m or less were regarded as secondary deoxidation products and used for determining the oxide size.
  • composition analysis was carried out by arbitrarily selecting 20 oxides. The composition of the oxide was also analyzed for the hot forged material in the same manner, and it was confirmed that the state of the oxide did not change during the main quenching treatment.
  • non-metal inclusions mainly composed of O and Al, Mn, Si, Fe, Cr, Ti, etc. are used as oxides, and the total excluding S is converted to 100% to calculate the mass% of Al. did.
  • the martensitic stainless steel of the present invention is used for high hardness and high corrosion resistance, and is required to have high hardness and high corrosion resistance at the stage of quenching after cold working to make a final product.
  • Hv hardness was evaluated for the high hardness characteristics. After cold working, air-cooled quenching was performed from a temperature of T + 50 ° C., and Hv hardness was evaluated. If it is Hv500 or higher, the requirements of the present invention can be satisfied. In the examples, when the Hv was less than 500 after quenching, "insufficient quenching hardness" was described in the remarks column of Table 6.
  • Examples of the present invention in Tables 4 and 5 are 1 to 63.
  • the Hv hardness was (60C + 170) or less, and in most cases, the preferable Hv hardness (60C + 160) or less was obtained.
  • the cold workability all of the steels of the present invention were B or A, indicating a dispersed state of the carbonitride that contributes to excellent cold workability.
  • Inventive Examples 1 to 3, 7 to 15, 17 to 50, 52 have an Al content of 0.01 to 0.2% and an O content of 0.001 to 0.006 in a preferable range for softening. It showed a contributing oxide state.
  • the average Al concentration of an oxide having a size of 1 to 5 ⁇ m is in a preferable range of 15 to 40% by mass.
  • Comparative Examples 1 to 22 shown in Table 6 the component composition of the steel deviates from the present invention, or the solidification rate deviates from the preferable conditions of the present invention, and the distribution state of the carbonitride and the average oxide size are present. It can be seen that the specified range of the invention is not satisfied and the required characteristics are not satisfied.
  • the solidification cooling rate was high, and in Comparative Example 19, Al was too small, and the average diameter size of the oxide was too small in each case, so that Hv was high and cold workability was poor. there were.
  • Comparative Examples 2, 4 and 6 the solidification cooling rate was slow and the average diameter size of the oxide was excessive, so that the cold workability was poor.
  • Example 2 Next, the influence of the manufacturing method of the softened annealed material was investigated.
  • the ⁇ 14 mm steel bar of the hot forged material of the steel C of the present invention produced above was softened and annealed under various conditions, and the influence of the manufacturing method on the softening, cold workability and the state of the carbonitride was investigated. Since the state of the fine oxide does not change during softening and annealing, the oxide was not investigated in this example.
  • Table 7 shows the manufacturing method and survey results of the softened annealed material.
  • Invention Examples 7, 53 to 63 the dispersed state of the carbonitride contributing to the excellent cold workability was shown, and the cold forging property was excellent.
  • Invention Example 63 as described in the remarks in Table 5, "additional softening annealing", after the softening annealing under the conditions of the present invention, after the conventional 850 ° C.-2h retention, up to 700 ° C. at 30 ° C./h. This is an example in which soft annealing is applied to slowly cool and degas. The quality is good and the effects of the present invention are inherited.

Abstract

A soft-annealed material of a high-hardness and high–corrosion resistance martensitic steel that has excellent cold workability. The soft-annealed material has a chemical composition that contains, by mass%, 0.15%–0.70% of C, no more than 2.0% of Si, no more than 1.5% of Mn, less than 0.01% of S, no more than 0.05% of P, no more than 1.5% of Ni, 10.5%–16.0% of Cr, 0.9%–3.0% of Mo, no more than 0.14% of N, 0.008%–1.0% of Al, and 0.001%–0.008% of O, the remainder being Fe and impurities, and C+N/2 being 0.14%–0.70%. There are at least 10 carbonitride particles of at least 1 μm per 1600 μm2, the average oxide particle diameter is 1–5 μm, and the Hv hardness is no more than (60C+170).

Description

冷間加工性に優れる高硬度・高耐食性用途のマルテンサイト系ステンレス鋼及びその製造方法Martensitic stainless steel for high hardness and corrosion resistance with excellent cold workability and its manufacturing method
　本発明は、冷間加工用の部品に関して、軟化特性に優れて強冷間加工が可能な高硬度・高耐食部品用のマルテンサイト系ステンレス鋼及びその製造方法に関するものである。 The present invention relates to martensitic stainless steel for cold-working parts, which has excellent softening properties and is capable of strong cold-working, and has high hardness and high corrosion resistance, and a method for manufacturing the same.
　近年、高硬度・高耐食マルテンサイト系ステンレス鋼のニーズが高く、自動車部品やねじ締結部品等の多くに使用されている（特許文献１～４）。これら高硬度・高耐食マルテンサイト系ステンレス鋼部品、特に、大型の自動車部品等において、複雑形状に冷間鍛造等の冷間加工によって成型される。このため、冷間加工前に軟化焼鈍を行って鋼を軟質化した上で冷間加工を行い、冷間加工後に焼き入れを行い、高硬度・高耐食マルテンサイト系ステンレス鋼となる。焼入れ後のマルテンサイト系ステンレス鋼において、鋼中のＣ含有量が高いほど高硬度の鋼を得ることができる。同様に、軟化焼鈍後のステンレス鋼においても、鋼中のＣ含有量が高いほど硬度が高くなることが知られている。そのような状況の中、軟化焼鈍後のステンレス鋼において、Ｃ量（質量％）に依存して（６０Ｃ＋１７０）以下のＨｖ硬さ、好ましくは（６０Ｃ＋１６０）以下のＨｖ硬さの軟化状態であることが望まれる。 In recent years, there has been a strong need for martensitic stainless steel with high hardness and high corrosion resistance, and it is used in many automobile parts, screw fastening parts, etc. (Patent Documents 1 to 4). These high-hardness, high-corrosion-resistant martensitic stainless steel parts, especially large automobile parts, are molded into a complicated shape by cold working such as cold forging. For this reason, the steel is softened by softening and annealing before cold working, and then cold working is performed, and then quenching is performed after cold working to obtain high hardness and high corrosion resistant martensitic stainless steel. In the martensitic stainless steel after quenching, the higher the C content in the steel, the higher the hardness of the steel can be obtained. Similarly, it is known that the hardness of stainless steel after softening and annealing increases as the C content in the steel increases. Under such circumstances, the stainless steel after softening and annealing is in a softened state having an Hv hardness of (60C + 170) or less, preferably (60C + 160) or less, depending on the amount of C (mass%). Is desired.
　しかしながら、高硬度・高耐食マルテンサイト系ステンレス鋼には、Ｃ，Ｎ，Ｍｏ，Ｎｉ等合金元素が多く添加されているため、軟化焼鈍で十分に軟質化して優れた冷間加工性（冷間鍛造性）を確保することが難しい。例えば、特許文献５には冷間鍛造性を向上させるための成分設計と軟化焼鈍技術が提案されているが、本発明に求められる水準まで軟質化できていない。 However, since a large amount of alloying elements such as C, N, Mo, and Ni are added to the high hardness and high corrosion resistant martensitic stainless steel, it is sufficiently softened by softening and annealing and has excellent cold workability (cold). It is difficult to secure forgeability). For example, Patent Document 5 proposes a component design and a softening annealing technique for improving cold forging property, but the softening has not been achieved to the level required for the present invention.
　このように従来の技術では、高硬度・高耐食マルテンサイト系ステンレス鋼を軟化焼鈍で十分に軟質化させて複雑形状へ冷間加工（冷間鍛造）することができない。 As described above, with the conventional technology, it is not possible to sufficiently soften high hardness and high corrosion resistant martensitic stainless steel by soft annealing and cold work (cold forging) into a complicated shape.
特許第３３４０２２５号公報Japanese Patent No. 3340225 特許第４２５２１４５号公報Japanese Patent No. 4252145 特開２０１６－５０３２０号公報Japanese Unexamined Patent Publication No. 2016-50320 特許第３５８７３３０号公報Japanese Patent No. 3587330 特許第３３２８７９１号公報Japanese Patent No. 3328791
　本発明の解決すべき課題は、複雑形状の冷間加工、もしくは冷間鍛造部品用素材として、軟質化特性を著しく改善した高硬度・高耐食性用途のマルテンサイト系ステンレス鋼及びその製造方法を安価に提供することである。なお、本発明が対象とする、軟化焼鈍後のステンレス鋼においては、鋼組織はフェライトと炭化物からなり、マルテンサイト組織ではない。一方、本発明のステンレス鋼を冷間加工した後に焼き入れを行い、最終製品はマルテンサイト組織を有していることから、本発明のステンレス鋼をマルテンサイト系ステンレス鋼と呼ぶこととする。 The problem to be solved by the present invention is to reduce the cost of martensitic stainless steel for high hardness and high corrosion resistance, which has significantly improved softening properties, as a material for cold working or cold forged parts of complicated shapes, and a method for producing the same. Is to provide to. In the stainless steel after softening and annealing, which is the subject of the present invention, the steel structure is composed of ferrite and carbide, and is not a martensite structure. On the other hand, since the stainless steel of the present invention is cold-worked and then hardened and the final product has a martensitic structure, the stainless steel of the present invention is referred to as a martensitic stainless steel.
　本発明者等は、上記課題を解決するために種々検討した結果、成分調整された高耐食高硬度用途のマルテンサイト系ステンレス鋼において、２次脱酸生成物である酸化物のサイズと組成を制御し、且つ、高温の軟化焼鈍により微細な炭窒化物の分散状態を制御することで、（６０Ｃ＋１７０）以下のＨｖ硬さまで軟質化して冷間加工性が著しく向上する知見を得た。また、転位や結晶粒界をピン止めしないような微細な脱酸生成物組成をＡｌ含有系に制御するとより好ましい。 As a result of various studies to solve the above problems, the present inventors have determined the size and composition of oxides, which are secondary deoxidizing products, in martensitic stainless steels for high corrosion resistance and high hardness whose components have been adjusted. It was found that by controlling and controlling the dispersed state of fine carbonitride by softening and annealing at high temperature, the hardness is softened to Hv hardness of (60C + 170) or less and the cold workability is remarkably improved. Further, it is more preferable to control the fine deoxidized product composition that does not pin the dislocations and grain boundaries to the Al-containing system.
　本発明は、上記知見に基づいてなされたものであり、その要旨とするところは以下の通りである。
（１）質量％で、
Ｃ：０．１５％超０．７０％以下
Ｓｉ：２．０％以下、
Ｍｎ：１．５％以下、
Ｓ：０．０１％未満、
Ｐ：０．０５％以下、
Ｎｉ：１．５％以下、
Ｃｒ：１０．５～１６．０％、
Ｍｏ：０．９～３．０％、
Ｎ：０．１４％以下、
Ａｌ：０．００８～１．０％、
Ｏ：０．００１～０．００８％を含有し、
残部Ｆｅおよび不純物からなる化学成分を有し、
Ｃ＋Ｎ／２：０．１６～０．７０％であり、
かつ、１．０μｍ以上の炭窒化物が１６００μｍ２中に１０個以上であり、酸化物の平均直径サイズが１～５μｍであり、（ａ）式で示されるＨｖ硬さであることを特徴とするマルテンサイト系ステンレス鋼。
　Ｈｖ≦６０Ｃ＋１７０　　　・・・・・・・・・・・・・・・・・・・（ａ）
　　Ｃ：Ｃ含有量（質量％）
（２）前記Ｆｅの一部に替えて、更に質量％で、
Ｃｕ：１．５％以下、
Ｗ：１．５％以下、
Ｃｏ：１．５％以下
Ｂ：０．０１％以下、
Ｓｎ：０．３％以下、
Ｓｂ：０．３％以下の内、１種類以上を含有することを特徴とする本発明のマルテンサイト系ステンレス鋼。
（３）前記Ｆｅの一部に替えて、更に質量％で、
Ｎｂ：０．１％以下、
Ｔｉ：０．１％以下、
Ｖ：０．２％以下、
Ｔａ：０．２％以下の内、１種類以上を含有することを特徴とする本発明のマルテンサイト系ステンレス鋼。
（４）前記Ｆｅの一部に替えて、更に質量％で、
Ｍｇ：０．０１％以下、
Ｃａ：０．０１％以下、
Ｈｆ：０．０１％以下、
ＲＥＭ：０．０１％以下の内、１種類以上を含有することを特徴とする本発明のマルテンサイト系ステンレス鋼。
（５）酸化物の平均Ａｌ濃度が１５～４０質量％であることを特徴とする本発明のマルテンサイト系ステンレス鋼。 The present invention has been made based on the above findings, and the gist thereof is as follows.
(1) By mass%
C: More than 0.15% 0.70% or less Si: 2.0% or less,
Mn: 1.5% or less,
S: less than 0.01%,
P: 0.05% or less,
Ni: 1.5% or less,
Cr: 10.5 to 16.0%,
Mo: 0.9-3.0%,
N: 0.14% or less,
Al: 0.008 to 1.0%,
O: Contains 0.001 to 0.008%,
It has a chemical component consisting of the balance Fe and impurities,
C + N / 2: 0.16 to 0.70%,
In addition, there are 10 or more carbonitrides of 1.0 μm or more in 1600 μm 2 , the average diameter size of the oxide is 1 to 5 μm, and the Hv hardness is represented by the formula (a). Martensitic stainless steel.
Hv ≦ 60C + 170 ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ (A)
C: C content (mass%)
(2) Instead of a part of the Fe, the mass% is further increased.
Cu: 1.5% or less,
W: 1.5% or less,
Co: 1.5% or less B: 0.01% or less,
Sn: 0.3% or less,
Sb: The martensitic stainless steel of the present invention, which comprises one or more of 0.3% or less.
(3) Instead of a part of the Fe, the mass% is further increased.
Nb: 0.1% or less,
Ti: 0.1% or less,
V: 0.2% or less,
Ta: The martensitic stainless steel of the present invention, which comprises one or more of 0.2% or less.
(4) Instead of a part of the Fe, further by mass%,
Mg: 0.01% or less,
Ca: 0.01% or less,
Hf: 0.01% or less,
REM: The martensitic stainless steel of the present invention, which comprises one or more of 0.01% or less.
(5) The martensitic stainless steel of the present invention, wherein the average Al concentration of the oxide is 15 to 40% by mass.
（６）軟化焼鈍処理として、
８７０℃よりも高く、Ｃ濃度と下記（ｂ）式で表される炭化物の固溶温度：Ｔよりも２０～１２０℃低い温度範囲で１～４８ｈの熱処理を施し、引き続き平均６０℃／ｈ以下の冷却速度でＴよりも２５０℃低い温度まで除冷することを特徴とする本発明のマルテンサイト系ステンレス鋼の製造方法。
　　　ｌｏｇ（Ｃ）　＝　－６１００／（Ｔ＋２７３）　＋　４　・・・・・（ｂ）
（ｂ）式で「Ｃ」はＣ濃度（質量％）、「Ｔ」は炭化物の固溶温度（℃）を意味する。
（７）鋳造時の凝固時の平均冷却速度が５～５００℃／ｓであることを特徴とする本発明のマルテンサイト系ステンレス鋼の製造方法。 (6) As a softening annealing treatment
Heat treatment is performed for 1 to 48 h in a temperature range higher than 870 ° C., C concentration and solid solution temperature of carbide represented by the following formula (b): 20 to 120 ° C. lower than T, and the average is 60 ° C./h or less. The method for producing a martensitic stainless steel of the present invention, which comprises cooling to a temperature 250 ° C. lower than T at the cooling rate of.
log (C) = -6100 / (T + 273) + 4 ... (b)
In the formula (b), "C" means the C concentration (mass%), and "T" means the solid solution temperature (° C.) of the carbide.
(7) The method for producing a martensitic stainless steel of the present invention, wherein the average cooling rate during solidification during casting is 5 to 500 ° C./s.
　本発明によれば、複雑部品形状に強冷間鍛造（冷間加工）もしくはニアネット成形が可能となり、自動車用等の冷間鍛造（冷間加工）による部品コストの大幅な低減効果を発揮できる高硬度・高耐食性マルテンサイト系ステンレス鋼の軟化焼鈍材を提供できる。 According to the present invention, strong cold forging (cold working) or near net forming can be performed on a complicated part shape, and the effect of significantly reducing the part cost by cold forging (cold working) for automobiles and the like can be exhibited. It is possible to provide a softened annealed material of martensitic stainless steel having high hardness and high corrosion resistance.
１３Ｃｒ－２Ｍｏ－０．２Ｃ－０．１Ｎ系鋼を公知の方法で軟化焼鈍した場合の金属組織を示す。The metallographic structure when 13Cr-2Mo-0.2C-0.1N steel is softened and annealed by a known method is shown. １３Ｃｒ－２Ｍｏ－０．２Ｃ－０．１Ｎ系鋼を本発明の方法で軟化焼鈍した場合の金属組織を示す。The metallographic structure when 13Cr-2Mo-0.2C-0.1N steel is softened and annealed by the method of the present invention is shown.
　以下に本発明の各要件について説明する。なお、以下の説明における（％）は特に断りがない限り、質量（％）である。 Each requirement of the present invention will be described below. In the following description, (%) is mass (%) unless otherwise specified.
　本発明が対象とする、冷間加工性に優れる高硬度・高耐食性用途のマルテンサイト系ステンレス鋼は、鋼を軟化焼鈍することで軟質化したステンレス鋼であり、鋼組織はフェライトと炭窒化物からなる。軟質化した本発明のステンレス鋼を素材として冷間加工を行い、その後に焼き入れ処理を行って高硬度化し、最終製品とする。なお、後述の本発明の成分組成を含有することにより、焼き入れ処理により大半がマルテンサイト組織となり、マルテンサイト系ステンレス鋼とすることができる。具体的には、１０００～１２００℃からの焼き入れ処理で組織の約８割以上がマルテンサイト組織になる鋼である。 The martensitic stainless steel for high hardness and high corrosion resistance, which is the object of the present invention and has excellent cold workability, is a stainless steel softened by softening and annealing the steel, and the steel structure is ferrite and carbonitride. Consists of. The softened stainless steel of the present invention is used as a material for cold working, and then quenching is carried out to increase the hardness, and the final product is obtained. By containing the component composition of the present invention described later, most of the steel has a martensitic structure by quenching, and martensitic stainless steel can be obtained. Specifically, it is a steel in which about 80% or more of the structure becomes a martensite structure by quenching treatment from 1000 to 1200 ° C.
　《鋼の必須成分組成》
　本発明の軟質による冷間加工性向上の効果は、製品の焼入れ処理後の硬さで５００Ｈｖ以上になる高硬度・高耐食マルテンサイト系ステンレス鋼で著しく発揮される。最高焼入れで５００Ｈｖ未満の鋼については従来の技術で冷間加工性を十分に確保でき本発明の効果が不明瞭になる。そのため、焼入れ硬さを支配するＣ，Ｎ，Ｃ＋Ｎ／２の含有量を限定し、本発明の効果が明瞭な範囲を規定する。 << Essential composition of steel >>
The effect of improving cold workability due to the softness of the present invention is remarkably exhibited in high hardness and high corrosion resistant martensitic stainless steel having a hardness of 500 Hv or more after quenching of the product. For steels with a maximum quenching of less than 500 Hv, the cold workability can be sufficiently ensured by the conventional technique, and the effect of the present invention becomes unclear. Therefore, the content of C, N, C + N / 2, which controls the quenching hardness, is limited, and the range in which the effect of the present invention is clear is defined.
　Ｃを０．１５％超、Ｃ＋Ｎ／２を０．１６％超に限定する。焼入れ後の硬度確保のためである。しかしながら、Ｃを０．７０％超、Ｃ＋Ｎ／２を０．７０超含有させると粗大な炭化物や微細な窒化物により冷間加工性が劣化するため、上限を該値に規定する。５００Ｈｖ以上の焼入れ硬さを安定的に得て、軟質化効果が発揮するＣの好ましい範囲は０．１６～０．４０％、Ｃ＋Ｎ／２の好ましい範囲は０．１８～０．４５％である。 C is limited to more than 0.15% and C + N / 2 is limited to more than 0.16%. This is to ensure hardness after quenching. However, if C is contained in an amount of more than 0.70% and C + N / 2 is contained in an amount of more than 0.70, the cold workability is deteriorated due to coarse carbides and fine nitrides. The preferred range of C, which stably obtains a quenching hardness of 500 Hv or more and exerts a softening effect, is 0.16 to 0.40%, and the preferable range of C + N / 2 is 0.18 to 0.45%. ..
　Ｎは上述した焼入れ硬さに加えて製品の耐食性の確保のために含有させることができる。しかしながら、Ｎを０．１４％超含有させるとブローホールの生成のため鋳造が困難となり、鋳造できても鋼中に粗大な炭窒化物が生成し、冷間加工性が劣化するため上限を０．１４％にする。好ましい範囲は０．０２～０．１１％である。更に好ましくは、０．０４～０．１０％である。 N can be contained in order to ensure the corrosion resistance of the product in addition to the quenching hardness described above. However, if N is contained in excess of 0.14%, casting becomes difficult due to the formation of blow holes, and even if casting is possible, coarse carbonitride is formed in the steel and cold workability deteriorates, so the upper limit is 0. .14%. The preferred range is 0.02 to 0.11%. More preferably, it is 0.04 to 0.10%.
　Ｓｉは、軟化焼鈍時のフェライト組織の固溶強化、及び炭窒化物の微細分散により冷間加工性を劣化させる元素であるため、含有量を２．０％以下に限定する。好ましくは、０．７％以下である。Ｓｉ含有量を０．０１％以上とすると好ましい。Ｓｉは含有しなくても良い。 Si is an element that deteriorates cold workability due to solid solution strengthening of the ferrite structure during softening and annealing and fine dispersion of carbonitride, so the content is limited to 2.0% or less. Preferably, it is 0.7% or less. The Si content is preferably 0.01% or more. Si may not be contained.
　Ｍｎは、軟化焼鈍後の強度を上昇させて冷間加工性を劣化させるため、含有量を１．５％以下に限定する。Ｍｎ含有量を０．０１％以上とすると好ましい。Ｍｎは含有しなくても良い。 The content of Mn is limited to 1.5% or less because it increases the strength after softening and annealing and deteriorates the cold workability. The Mn content is preferably 0.01% or more. Mn may not be contained.
　Ｓは、硫化物を形成して冷間加工性を劣化させるため、含有量を０．０１％未満に限定する。好ましくは０．００７％以下である。 The content of S is limited to less than 0.01% because it forms sulfide and deteriorates cold workability. It is preferably 0.007% or less.
　Ｐは、粒界偏析して冷間加工性を劣化させるため、含有量を０．０５％以下に限定する。 The content of P is limited to 0.05% or less because it segregates at grain boundaries and deteriorates cold workability.
　Ｎｉは、マルテンサイト系ステンレス鋼の製品の靭性、耐食性を向上させる元素であるため、含有させてもよい。しかしながら、１．５％を超えて含有させると軟化焼鈍後の硬度が（６０Ｃ＋１７０）のＨｖ硬さ以下に軟質化せずに冷間加工性が劣化する。そのため、１．５％以下に限定する。好ましくは、１．３％以下である。Ｎｉ含有量を０．０１％以上とすると好ましい。Ｎｉは含有しなくても良い。 Ni is an element that improves the toughness and corrosion resistance of martensitic stainless steel products, so it may be contained. However, if it is contained in excess of 1.5%, the hardness after softening and annealing does not soften below the Hv hardness of (60C + 170), and the cold workability deteriorates. Therefore, it is limited to 1.5% or less. Preferably, it is 1.3% or less. The Ni content is preferably 0.01% or more. Ni does not have to be contained.
　Ｃｒは、ステンレス鋼の高耐食性の機能を得るための基本元素であり、１０．５％以上を含有させる。しかしながら、１６．０％を超えて含有させると、焼入れ後に本発明の特徴である高硬度の製品硬さを得ることができず、また、従来の技術で冷間加工性を確保できる。そのため、１６．０％以下に限定する。好ましいＣｒの範囲は、１１．０～１５．０％である。 Cr is a basic element for obtaining the function of high corrosion resistance of stainless steel, and contains 10.5% or more. However, if it is contained in an amount of more than 16.0%, the high hardness of the product, which is a feature of the present invention, cannot be obtained after quenching, and cold workability can be ensured by the conventional technique. Therefore, it is limited to 16.0% or less. The preferred Cr range is 11.0 to 15.0%.
　Ｍｏは、高耐食性マルテンサイト系ステンレス鋼を得るため含有させる。なお、軟化焼鈍時に炭窒化物の粗大化を阻害して、素材を軟化し難くする元素であり、本発明の軟質・高冷間加工性の効果が明瞭になる０．９％以上に限定する。０．９％未満では公知の軟化焼鈍方法で冷間加工性が確保でき、本発明の有効性が明瞭でなくなるとともに耐食性が不足する。一方、３．０％を超えて過度に含有させると本発明の手法でも軟化し難くなり、焼鈍時に炭窒化物が粗大化せず、冷間加工性が劣化する。そのため、３．０％以下に限定する。好ましい範囲は、１．０～２．５％である。 Mo is included to obtain highly corrosion-resistant martensitic stainless steel. It should be noted that it is an element that inhibits the coarsening of the carbonitride during softening annealing and makes it difficult to soften the material, and is limited to 0.9% or more at which the effect of the soft and highly cold workability of the present invention becomes clear. .. If it is less than 0.9%, cold workability can be ensured by a known softening and annealing method, the effectiveness of the present invention becomes unclear, and corrosion resistance is insufficient. On the other hand, if it is excessively contained in excess of 3.0%, it becomes difficult to soften even by the method of the present invention, the carbonitride does not become coarse during annealing, and the cold workability deteriorates. Therefore, it is limited to 3.0% or less. The preferred range is 1.0 to 2.5%.
　Ａｌは、脱酸で脱酸生成物を低減させて、分解・微細化を抑制するのに有効な元素であるため０．００８％以上含有させる。しかしながら、１．０％を超えて添加しても脱酸効果は飽和するばかりか粗大な酸化物が生成して冷間加工性を著しく劣化させる。そのため、上限を１．０％に限定する。好ましくは、０．０１～０．２％である。 Al is an element effective in reducing deoxidation products by deoxidation and suppressing decomposition and miniaturization, so it is contained in an amount of 0.008% or more. However, even if it is added in excess of 1.0%, not only the deoxidizing effect is saturated but also coarse oxides are generated, which significantly deteriorates cold workability. Therefore, the upper limit is limited to 1.0%. Preferably, it is 0.01 to 0.2%.
　Ｏは、Ａｌ含有鋼での微細な脱酸生成物（酸化物）の組成やサイズに大きく影響を与える。後述する凝固速度を制御すると共にＯ含有量を制御すると、製品の脱酸生成物の平均直径が５μｍ超と過度に粗大化することを防止して冷間加工割れに対して実質的に無害化し、且つ、熱間圧延時に酸化物が１μｍ未満サイズに分解・微細化することを抑制する。そのため、鋼中のＯを０．００１～０．００８％に制御する。ＯはＴ．Ｏを意味する。Ｏが０．００１％未満の場合、工業的な実施が困難となり、０．００８％を超えて含有させると粗大な酸化物が生成するため冷間加工性が低下していく。好ましくは、０．００１～０．００６％である。 O greatly affects the composition and size of fine deoxidizing products (oxides) in Al-containing steel. Controlling the solidification rate and O content, which will be described later, prevents the average diameter of the deoxidized product of the product from becoming excessively coarse, exceeding 5 μm, and makes it substantially harmless to cold-rolled cracks. In addition, it suppresses the decomposition and miniaturization of oxides to a size of less than 1 μm during hot rolling. Therefore, O in steel is controlled to 0.001 to 0.008%. O is T.I. Means O. If O is less than 0.001%, industrial implementation becomes difficult, and if it is contained in excess of 0.008%, coarse oxides are generated and cold workability is lowered. Preferably, it is 0.001 to 0.006%.
　《１．０μｍ以上の炭窒化物が１６００μｍ２中に１０個以上》
　本発明のマルテンサイト系ステンレス鋼（軟化焼鈍後）の炭窒化物の分布は、マルテンサイト系ステンレス鋼の軟化焼鈍時の軟化挙動（軟化焼鈍後の軟質化特性）に影響を与える。軟化焼鈍後の鋼中の炭窒化物が微細分散していると、軟化焼鈍後の冷間加工において、転位や結晶粒界の動きをピンニングして冷間加工し難い。炭窒化物サイズは大きい方がよく、１６００μｍ２中に１．０μｍ以上の炭窒化物個数が１０個以上であれば、１．０μｍ未満の微細な炭窒化物が減少するため、Ｈｖ≦（６０Ｃ＋１７０）の軟質化特性が得られる。
　図１に、１３Ｃｒ－２Ｍｏ－０．２Ｃ－０．１Ｎ系鋼を公知の方法（６５０℃－４ｈの低温焼鈍）で軟化焼鈍した場合の金属組織を示す。ラスマルテンサイト組織の界面にサブミクロンの棒状炭化物が析出しており、軟化焼鈍して軟質化した後もＨｖ硬さで３０５あり、冷間加工性に劣る。一方、後述の本発明の方法で軟化焼鈍した鋼の例を図２に示す。図２において、１６００μｍ２中に１．０μｍサイズ以上の炭窒化物が１０個以上あり、Ｈｖ≦６０Ｃ＋１７０まで軟質化している。
　炭窒化物サイズは大きい方がよく、１６００μｍ２中に１μｍ以上のサイズの炭窒化物個数が１０個以上で軟質化特性が得られている。好ましくは、１６００μｍ２中に２μｍ以上のサイズ以上の炭窒化物が１０個以上である。ここで炭窒化物サイズとは、炭窒化物の（長径＋短径）／２を示す。 << 10 or more carbonitrides of 1.0 μm or more in 1600 μm 2 >>
The distribution of carbon nitride in the martensitic stainless steel (after softening and annealing) of the present invention affects the softening behavior (softening characteristics after softening and annealing) of the martensitic stainless steel during softening and annealing. If the carbonitride in the steel after softening annealing is finely dispersed, it is difficult to perform cold working by pinning the movement of dislocations and grain boundaries in the cold working after softening annealing. The larger the size of the carbonitride is, the better, and if the number of carbonitrides of 1.0 μm or more is 10 or more in 1600 μm 2 , fine carbonitrides of less than 1.0 μm are reduced, so Hv ≦ (60C + 170). ) Softening characteristics can be obtained.
FIG. 1 shows the metallographic structure when 13Cr-2Mo-0.2C-0.1N steel is softened and annealed by a known method (low temperature annealing at 650 ° C.-4h). Submicron rod-shaped carbides are precipitated at the interface of the lath martensite structure, and even after being softened and annealed, the Hv hardness is 305, which is inferior in cold workability. On the other hand, FIG. 2 shows an example of steel softened and annealed by the method of the present invention described later. In FIG. 2, there are 10 or more carbonitrides having a size of 1.0 μm or more in 1600 μm 2, which are softened to Hv ≦ 60C + 170.
The larger the size of the carbonitride, the better, and the number of carbonitrides having a size of 1 μm or more in 1600 μm 2 is 10 or more, and the softening property is obtained. Preferably, 1600 .mu.m carbonitride or more sizes 2μm in 2 is 10 or more. Here, the carbonitride size indicates (major axis + minor axis) / 2 of the carbonitride.
　前記本発明の好適な鋼成分組成を有するとともに、後述する好適な軟化焼鈍条件を用いて軟化焼鈍を行うことにより、１．０μｍ以上の炭窒化物が１６００μｍ２中に１０個以上となる鋼を実現することができる。 A steel having the suitable steel composition of the present invention and having 10 or more carbonitrides of 1.0 μm or more in 1600 μm 2 can be obtained by performing softening annealing using the suitable softening annealing conditions described later. It can be realized.
　《酸化物の平均直径サイズが１～５μｍ》
　本発明のマルテンサイト系ステンレス鋼（軟化焼鈍後）の凝固時に生成する２次脱酸生成物である酸化物のサイズは、マルテンサイト系ステンレス鋼の軟化焼鈍時の軟化挙動（軟化焼鈍後の軟質化特性）に影響を与え、この酸化物の平均直径サイズが１μｍ未満に微細化していると、軟化焼鈍後の冷間加工において、転位や結晶粒界の動きをピンニングして冷間加工し難く、Ｈｖ≦（６０Ｃ＋１７０）の軟質化特性も得られない。酸化物サイズが大きい方がよく、平均直径サイズが１μｍ以上であれば軟質化特性が得られる。一方、酸化物の平均直径サイズが５μｍ超になると冷間加工時の割れの起点となるため冷間加工性が劣化する。好ましくは２～４μｍである。ここで２次脱酸生成物である酸化物のサイズとは、２次脱酸生成物の（長径＋短径）／２を示し、平均サイズとは任意にサンプリングした３０個の平均値を示す。酸化物の評価において、１次脱酸生成物と２次脱酸生成物との区別は、溶鋼中で生成する１５μｍ超のサイズの粗大なものを１次脱酸生成物と判定し、１５μｍ以下のサイズを凝固中に全面に晶出する２次脱酸生成物として判定する。 << Average diameter size of oxide is 1-5 μm >>
The size of the oxide, which is a secondary deoxidizing product produced during solidification of the martensitic stainless steel of the present invention (after softening and annealing), is the softening behavior of the martensitic stainless steel during softening and annealing (softness after softening and annealing). If the average diameter size of this oxide is reduced to less than 1 μm, it will be difficult to perform cold working by pinning dislocations and movements of grain boundaries in cold working after softening annealing. , Hv ≦ (60C + 170) softening characteristics cannot be obtained either. The larger the oxide size, the better, and if the average diameter size is 1 μm or more, softening characteristics can be obtained. On the other hand, when the average diameter size of the oxide exceeds 5 μm, it becomes the starting point of cracking during cold working, so that the cold workability deteriorates. It is preferably 2 to 4 μm. Here, the size of the oxide as the secondary deoxidizing product indicates the secondary deoxidizing product (major axis + minor axis) / 2, and the average size indicates the average value of 30 arbitrarily sampled pieces. .. In the evaluation of oxides, the distinction between the primary deoxidizing product and the secondary deoxidizing product is that a coarse product having a size of more than 15 μm produced in molten steel is judged to be a primary deoxidizing product and is 15 μm or less. Is determined as a secondary deoxidizing product that crystallizes over the entire surface during solidification.
　前記本発明の好適な鋼成分組成を有し、特にＡｌ含有量を本発明範囲とするとともに、後述する凝固条件を好適化することにより、酸化物の平均直径サイズを１～５μｍとすることができる。 The average diameter size of the oxide can be set to 1 to 5 μm by having the suitable steel composition of the present invention, particularly setting the Al content within the range of the present invention, and optimizing the solidification conditions described later. it can.
　《（ａ）式で示されるＨｖ硬さ》
　以上詳述したように、公知技術よりも軟質化して複雑形状へ冷間加工して効果が著しく発揮されるためには、本発明のステンレス鋼（軟化焼鈍後）のＨｖ硬さについて、下記（ａ）式で示されるＨｖ硬さに限定する。更に、Ｈｖ≦（６０Ｃ＋１６０）のＨｖ硬さになると、複雑形状の大型部品への冷間鍛造も可能となり、飛躍的に工業的・経済的な効果が大きくなるため、好ましくは、（６０Ｃ＋１６０）以下のＨｖ硬さ以下である。
　　　Ｈｖ≦６０Ｃ＋１７０　　　・・・・・・・・・・・・・・・・（ａ）
　　　Ｃ：Ｃ含有量（質量％） << Hv hardness represented by equation (a) >>
As described in detail above, the Hv hardness of the stainless steel (after softening and annealing) of the present invention is described below in order to be softer than known techniques and cold-worked into a complicated shape to exert a remarkable effect. It is limited to the Hv hardness represented by the formula a). Further, when the Hv hardness is Hv ≦ (60C + 160), cold forging of a large part having a complicated shape becomes possible, and the industrial and economic effect is dramatically increased. Therefore, it is preferably (60C + 160) or less. Hv hardness or less.
Hv ≦ 60C + 170 ・ ・ ・ ・ ・ (a)
C: C content (mass%)
　《酸化物の平均Ａｌ濃度》
　脱酸生成物は熱間圧延時に分解・微細化するため軟化焼鈍時の素材の軟質化を抑制する。そのため、脱酸元素であるＡｌ量、さらにＯ量や凝固速度の調整によって脱酸生成物の組成を制御することで、脱酸生成物の熱間圧延時の分解・微細化を抑制でき、転位や結晶粒界をピン止めせずに冷間加工割れを誘発しないサイズに安定的に制御することができ、軟質化を促進することができるので好ましい。具体的には、酸化物の平均Ａｌ濃度を１５～４０質量％とすることにより、脱酸生成物を熱的に安定化して、熱間圧延時の１μｍ未満サイズへの分解・微細化の抑制に寄与する。
　酸化物中の平均組成とは、非金属介在物中のＳ元素を除いてＯを含めて質量％で換算して求めた値である。Ａｌ含有の熱力学的に安定（熱間圧延時に分解して微細化しない）な脱酸生成物を生成させることにより、軟化焼鈍後の冷間加工時に、転位や結晶粒界の動きをピンニングし難くするので、軟化焼鈍時の軟質化促進に有効である。 << Average Al concentration of oxide >>
Since the deoxidized product decomposes and becomes finer during hot rolling, it suppresses the softening of the material during softening and annealing. Therefore, by controlling the composition of the deoxidized product by adjusting the amount of Al, which is a deoxidizing element, the amount of O, and the solidification rate, it is possible to suppress the decomposition and refinement of the deoxidized product during hot rolling, and dislocations. It is preferable because it can be stably controlled to a size that does not induce cold rolling cracks without pinning the grain boundaries and can promote softening. Specifically, by setting the average Al concentration of the oxide to 15 to 40% by mass, the deoxidized product is thermally stabilized, and decomposition and miniaturization to a size of less than 1 μm during hot rolling are suppressed. Contribute to.
The average composition in the oxide is a value obtained by converting in mass% including O excluding the S element in the non-metal inclusions. By generating an Al-containing thermodynamically stable deoxidizing product (which does not decompose and become finer during hot rolling), dislocations and grain boundary movements are pinned during cold working after softening annealing. Since it makes it difficult, it is effective in promoting softening during softening annealing.
　《選択的含有成分》
　本発明のステンレス鋼は、上述してきた元素以外は、Ｆｅおよび不純物からなる化学成分から構成される。さらに、前記成分組成に加え、Ｆｅの一部に替えて、選択的に以下に示す元素を含有しても良い。 << Selective ingredients >>
The stainless steel of the present invention is composed of chemical components composed of Fe and impurities other than the elements described above. Further, in addition to the above-mentioned component composition, the following elements may be selectively contained in place of a part of Fe.
　Ｃｕは、製品の耐食性を向上させるため、必要に応じて含有させてもよい。しかしながら、１．５％を超えて含有させても、その効果は飽和し、冷間加工性を劣化させるため、含有量は１．５％以下とする。好ましくは、０．３５％以下である。 Cu may be contained as necessary in order to improve the corrosion resistance of the product. However, even if the content exceeds 1.5%, the effect is saturated and the cold workability is deteriorated, so the content is set to 1.5% or less. Preferably, it is 0.35% or less.
　Ｃｏ，Ｗは、製品の靭性や耐食性を向上させるため、必要に応じて含有させてもよい。しかしながら、それぞれ１．５％を超えて含有させても、その効果は飽和し、冷間加工性を劣化させるため、含有量は１．５％以下とする。好ましくは、１．０％以下である。 Co and W may be contained as necessary in order to improve the toughness and corrosion resistance of the product. However, even if each content exceeds 1.5%, the effect is saturated and the cold workability is deteriorated, so the content is set to 1.5% or less. Preferably, it is 1.0% or less.
　Ｂは、製品の靭性を向上させるため、必要に応じて含有させてもよい。しかしながら、０．０１％を超えて含有させても、その効果は飽和するし、逆に粗大なボライドを生成して冷間加工性を劣化させるため、含有量は０．０１％以下とする。好ましくは、０．００６％以下である。 B may be contained as necessary in order to improve the toughness of the product. However, even if the content exceeds 0.01%, the effect is saturated, and conversely, coarse boride is generated and the cold workability is deteriorated. Therefore, the content is set to 0.01% or less. Preferably, it is 0.006% or less.
　Ｓｎ，Ｓｂは、製品の耐食性を向上させるため、必要に応じて含有させてもよい。しかしながら、それぞれ０．３％を超えて含有させても、その効果は飽和するし、熱間製造性が著しく劣化させるため、含有量は０．３％以下とする。好ましくは、０．１％以下である。 Sn and Sb may be contained as necessary in order to improve the corrosion resistance of the product. However, even if each content exceeds 0.3%, the effect is saturated and the hot manufacturability is significantly deteriorated. Therefore, the content is set to 0.3% or less. Preferably, it is 0.1% or less.
　Ｎｂ，Ｔｉは、製品の靭性や耐食性を向上させるため、必要に応じて含有させてもよい。しかしながら、それぞれ０．１％を超えて含有させても、その効果は飽和するし、逆に粗大な炭窒化物を生成して冷間加工性が劣化させるため、含有量は０．１％以下とする。好ましくは、０．０６％以下である。 Nb and Ti may be contained as necessary in order to improve the toughness and corrosion resistance of the product. However, even if each content exceeds 0.1%, the effect is saturated, and conversely, coarse carbonitride is generated and the cold workability is deteriorated. Therefore, the content is 0.1% or less. And. Preferably, it is 0.06% or less.
　Ｖ，Ｔａは、製品の靭性や耐食性を向上させるため、必要に応じて含有させてもよい。しかしながら、それぞれ０．２％を超えて含有させても、その効果は飽和するし、逆に粗大な炭窒化物を生成して冷間加工性が劣化させるため、含有量は０．２％以下とする。好ましくは、０．１％以下である。 V and Ta may be contained as necessary in order to improve the toughness and corrosion resistance of the product. However, even if each content exceeds 0.2%, the effect is saturated, and conversely, coarse carbonitride is generated and the cold workability is deteriorated, so that the content is 0.2% or less. And. Preferably, it is 0.1% or less.
　Ｍｇ，Ｃａ，Ｈｆ，ＲＥＭは、脱酸生成物の熱力学的な安定度を増加して軟化焼鈍時の軟質化に効果があるため、必要に応じて含有させてもよい。しかしながら、それぞれ０．０１％を超えて添加しても、その効果は飽和するし、逆に粗大な酸化物を生成して冷間加工性を劣化させるため、含有量を０．０１％以下とする。好ましくは、０．００５％以下である。
　ＲＥＭ（希土類元素）は、一般的な定義に従い、スカンジウム（Ｓｃ）、イットリウム（Ｙ）の２元素と、ランタン（Ｌａ）からルテチウム（Ｌｕ）までの１５元素（ランタノイド）の総称を指す。単独で含有させてもよいし、混合物であってもよい。 Mg, Ca, Hf, and REM may be contained as necessary because they increase the thermodynamic stability of the deoxidized product and are effective in softening during softening and annealing. However, even if each is added in excess of 0.01%, the effect is saturated, and conversely, coarse oxides are generated and cold workability is deteriorated. Therefore, the content is set to 0.01% or less. To do. Preferably, it is 0.005% or less.
REM (rare earth element) is a general term for two elements, scandium (Sc) and yttrium (Y), and 15 elements (lanthanoids) from lanthanum (La) to lutetium (Lu), according to a general definition. It may be contained alone or as a mixture.
　本発明のステンレス鋼が含有する不純物について、代表的な不純物としては、Ｚｎ，Ｂｉ，Ｐｂ，Ｇｅ，Ｓｅ，Ａｇ，Ｓｅ，Ｔｅ等が挙げられ、通常、鉄鋼の製造プロセスで不純物として、０．１％程度の範囲で混入する。
　また、任意添加元素について、代表的なものを上記（３）～（５）で規定しているが、本明細書中に記載されていない元素であっても、本発明の効果を損なわない範囲で含有させることができる。 Regarding the impurities contained in the stainless steel of the present invention, typical impurities include Zn, Bi, Pb, Ge, Se, Ag, Se, Te, etc., and usually, as impurities in the steel manufacturing process, 0. Mix in the range of about 1%.
In addition, although typical optional additive elements are specified in (3) to (5) above, even elements not described in the present specification do not impair the effects of the present invention. Can be contained in.
　《マルテンサイト系ステンレス鋼の製造方法》
　次に、本発明のマルテンサイト系ステンレス鋼の製造方法について説明する。
　第一に、軟化焼鈍処理条件について説明する。
　前記のように、１．０μｍ以上の炭窒化物が１６００μｍ２中に１０個以上となる鋼として軟質化するためには、前記本発明の好適な鋼成分組成を有するとともに、軟化焼鈍処理として、８７０℃以上の高温で、かつ、（ｂ）式で計算される炭化物の固溶温度：Ｔよりも２０～１２０℃低い温度範囲で１～４８ｈの保定熱処理を施し、引き続き平均６０℃／ｈ以下の冷却速度で徐冷することが好ましい。保定熱処理時間が１ｈよりも短いと炭素窒化物サイズが微細となり、軟質化が期待できず、逆に４８ｈよりも長いと効果は飽和するし、工業的に経済合理性を失う。そのため、保定熱処理時間を１～４８ｈに限定する。好ましい範囲は、２～１０ｈである。なお、（ｂ）式でＣ量による炭化物の固溶温度を計算できる。
　ｌｏｇ（Ｃ）＝―６１００／（Ｔ＋２７３）＋４　・・・・・（ｂ）
（ｂ）式で「Ｃ」はＣ濃度（質量％）、「Ｔ」は炭化物の固溶温度（℃）を意味する。 << Manufacturing method of martensitic stainless steel >>
Next, the method for producing the martensitic stainless steel of the present invention will be described.
First, the softening and annealing treatment conditions will be described.
As described above, in order to soften the carbonitride of 1.0 μm or more into 10 or more steels in 1600 μm 2 , it has the suitable steel component composition of the present invention and is used as a softening annealing treatment. Solid solution temperature of carbide calculated by Eq. (B) at a high temperature of 870 ° C or higher: 1 to 48 h of retention heat treatment is performed in a temperature range 20 to 120 ° C lower than T, and the average is 60 ° C / h or less. It is preferable to slowly cool at the cooling rate of. If the retention heat treatment time is shorter than 1 h, the carbon nitride size becomes fine and softening cannot be expected. On the contrary, if it is longer than 48 h, the effect is saturated and the economic rationality is lost industrially. Therefore, the retention heat treatment time is limited to 1 to 48 hours. The preferred range is 2 to 10 hours. In addition, the solid solution temperature of the carbide can be calculated by the amount of C by the formula (b).
log (C) = -6100 / (T + 273) +4 ... (b)
In the formula (b), "C" means the C concentration (mass%), and "T" means the solid solution temperature (° C.) of the carbide.
　保定熱処理温度が８７０℃もしくは（Ｔ－１２０）℃よりも低温になると炭窒化物サイズが微細になり、軟質化が期待できず、逆に（Ｔ－２０）℃よりも高温で保定熱処理を実施するとフィルム状の粒界炭化物となり、冷間加工性が劣化する。なお、保定熱処理温度の好ましい範囲は、９００℃以上で、かつ、Ｔよりも３０～１００℃低い温度である。 When the retention heat treatment temperature becomes lower than 870 ° C or (T-120) ° C, the carbide size becomes fine and softening cannot be expected. On the contrary, the retention heat treatment is performed at a temperature higher than (T-20) ° C. Then, it becomes a film-like grain boundary carbide, and the cold workability deteriorates. The preferred range of the retention heat treatment temperature is 900 ° C. or higher and 30 to 100 ° C. lower than T.
　保定熱処理温度からの徐冷の冷却速度について、平均６０℃／ｈを超える冷却速度で徐冷すると、炭窒化物が微細となり、軟質化が期待できない。 Regarding the cooling rate of slow cooling from the retention heat treatment temperature, if slow cooling is performed at a cooling rate exceeding 60 ° C./h on average, the carbonitride becomes fine and softening cannot be expected.
　徐冷終了温度について、（Ｔ－２５０）℃まで徐冷しなかった場合、炭窒化物の微細化や硬質なマルテンサイト組織の生成により軟質化が期待できない。そのため、（Ｔ－２５０）℃よりも低い温度まで徐冷することが好ましい。なお、（Ｔ－２５０）℃よりも低い温度では特に冷却速度は規定しなくともよい。 Regarding the slow cooling end temperature, if the slow cooling is not performed to (T-250) ° C, softening cannot be expected due to the miniaturization of the carbonitride and the formation of a hard martensite structure. Therefore, it is preferable to slowly cool to a temperature lower than (T-250) ° C. The cooling rate does not have to be specified at a temperature lower than (T-250) ° C.
　上記の本発明の軟化焼鈍方法で炭化物サイズ、分散状態が決まるため、本発明の焼鈍方法の後に従来の焼鈍方法を適用しても効果は継続されるので、従来の焼鈍方法と組み合わせてもよい。 Since the carbide size and dispersion state are determined by the above-mentioned softening annealing method of the present invention, the effect is continued even if the conventional annealing method is applied after the annealing method of the present invention, and therefore, it may be combined with the conventional annealing method. ..
　次に、本発明のマルテンサイト系ステンレス鋼の製造方法のうち、鋳造時の製造条件について説明する。
　鋼中の微細な２次脱酸生成物である酸化物は凝固時に生成する。酸化物が熱力学的に不安定な場合、熱間圧延等の熱加工で分解・微細化が進み、軟化焼鈍時に転位や結晶粒界の動きをピンニングして軟化を阻害する。マルテンサイト系ステンレス鋼の場合、Ａｌ，Ｏ含有量の適正制御に加え、鋳造時の平均冷却速度を５～５００℃／ｓの範囲とすることにより、凝固時に生じる２次脱酸生成物の平均サイズが１μｍ以上５μｍ以下となって分解・微細化を抑制することによって軟質化することができる。一方、平均冷却速度が５℃／ｓよりも遅くなると脱酸生成物が５μｍを超えて粗大化し、本発明の軟質化効果が不明瞭となるばかりか、冷間加工性も劣化する。一方、５００℃／ｓよりも平均冷却速度が大きいと２次脱酸生成物のＡｌ濃度が１５％以下に低下して熱力学的に不安定となって１μｍ未満への分解・微細化が進み、素材の軟質化を促進し難くなる。そのため、本発明で規定する軟質化し易い微細な熱力学的に安定な酸化物のサイズを得るには５～５００℃／ｓの平均冷却速度で凝固させることが必要になる。好ましくは１０℃／ｓ以上、４００℃／ｓ未満である。 Next, among the methods for producing martensitic stainless steel of the present invention, the production conditions at the time of casting will be described.
Oxides, which are fine secondary deoxidizing products in steel, are formed during solidification. When the oxide is thermodynamically unstable, it is decomposed and refined by thermal processing such as hot rolling, and dislocations and movements of grain boundaries are pinned during softening annealing to inhibit softening. In the case of martensitic stainless steel, in addition to proper control of Al and O contents, the average cooling rate during casting is set in the range of 5 to 500 ° C / s, so that the average of secondary deoxidized products generated during solidification It can be softened by suppressing decomposition and miniaturization when the size is 1 μm or more and 5 μm or less. On the other hand, when the average cooling rate is slower than 5 ° C./s, the deoxidized product becomes coarser than 5 μm, the softening effect of the present invention becomes unclear, and the cold workability also deteriorates. On the other hand, if the average cooling rate is higher than 500 ° C./s, the Al concentration of the secondary deoxidizing product decreases to 15% or less, becomes thermodynamically unstable, and decomposition / miniaturization to less than 1 μm progresses. , It becomes difficult to promote the softening of the material. Therefore, in order to obtain a fine thermodynamically stable oxide size that is easily softened as defined in the present invention, it is necessary to solidify at an average cooling rate of 5 to 500 ° C./s. It is preferably 10 ° C./s or more and less than 400 ° C./s.
　以上説明した本発明によれば、軟質化特性を有して複雑形状に強冷間加工できる高硬度・高耐食性マルテンサイト系ステンレス鋼の軟化焼鈍材を安価に提供できる。 According to the present invention described above, it is possible to inexpensively provide a softened annealed material of high hardness and high corrosion resistance martensitic stainless steel which has softening characteristics and can be strongly cold-worked into a complicated shape.
　＜実施例１＞
　１５０ｋｇの真空溶解炉にて表１～表３に示す化学組成の鋼を約１６００℃で溶解した後、鋳型に鋳造した。なお、Ａｌ，Ｓｉ，Ｍｎ等の脱酸元素添加量と脱酸元素の溶鋼への投入から鋳型への出鋼時間でＯ量を変化させた。鋳型として、各種サイズ（φ２０～φ２５０ｍｍ）、材質（鉄系，マグネシア系，シリカ系）のものを用いることにより、凝固時の平均冷却速度を変化させた。なお、凝固時の平均冷却速度は、同じ条件で溶解・凝固させたＳＵＳ３０４のサンプルの鋳片の断面の１／４部および中央部の２次デンドライトアーム間隔：λを測定し、その平均値で平均冷却速度（℃／ｓ）＝（１１０／λ）２．２を見積もった。
　その後、１２００℃加熱後に熱間鍛造して直径１４ｍｍの棒鋼に熱間加工し、常温まで空冷した。その後、軟化焼鈍を行うに際し、表４～表６に示す各温度で５ｈの保定熱処理を施し、２０℃／ｈで６５０℃まで徐冷した。そして、軟質化状況、冷間加工性および炭窒化物や微細酸化物の状態に及ぼす成分の影響について調査した。表４～表６に製造条件および評価結果について示す。 <Example 1>
Steels having the chemical compositions shown in Tables 1 to 3 were melted at about 1600 ° C. in a 150 kg vacuum melting furnace, and then cast into a mold. The amount of O was changed depending on the amount of deoxidizing elements added such as Al, Si, and Mn and the time from the addition of the deoxidizing elements to the molten steel to the delivery time to the mold. By using various sizes (φ20 to φ250 mm) and materials (iron-based, magnesia-based, silica-based) as the mold, the average cooling rate during solidification was changed. The average cooling rate during solidification is the average value obtained by measuring the secondary dendrite arm spacing: λ in the 1/4 part of the cross section and the central part of the slab of the SUS304 sample melted and solidified under the same conditions. The average cooling rate (° C./s) = (110 / λ) 2.2 was estimated.
Then, after heating at 1200 ° C., it was hot forged, hot-worked into a steel bar having a diameter of 14 mm, and air-cooled to room temperature. Then, when the softening annealing was performed, a retention heat treatment for 5 hours was performed at each temperature shown in Tables 4 to 6, and the temperature was gradually cooled to 650 ° C. at 20 ° C./h. Then, the effects of the components on the softening condition, cold workability, and the state of carbonitrides and fine oxides were investigated. Tables 4 to 6 show the manufacturing conditions and evaluation results.
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000001
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000002
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000003
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000004
Figure JPOXMLDOC01-appb-T000005
Figure JPOXMLDOC01-appb-T000005
Figure JPOXMLDOC01-appb-T000006
Figure JPOXMLDOC01-appb-T000006
　軟質化について、前記棒鋼を長手方向中心断面に埋め込み研磨し、荷重１ｋｇで断面の直径の１／４部および中心部のＨｖ硬さを測定し、その平均値で評価し、表４～表６に示した。表中、Ｈｖの右隣に（ａ）式右辺（６０Ｃ＋１７０）の値を示している。 For softening, the steel bar was embedded in the central cross section in the longitudinal direction and polished, and the Hv hardness of 1/4 of the cross section diameter and the central portion was measured with a load of 1 kg and evaluated by the average value. Tables 4 to 6 It was shown to. In the table, the value of the right side (60C + 170) of the equation (a) is shown on the right side of Hv.
　冷間加工性は、φ８ｍｍ，高さ１２ｍｍの圧縮試験片を作成し、高さ方向に１０／ｓの歪み速度で端面圧縮加工を施し、割れなく冷間圧縮加工が可能か否かで判断した。なお、鋼材の冷間加工性はＣ量（質量％）に依存し、Ｃ量が高いほど冷間加工性が低下する性質があるため、限界加工率をＣ量の式として規定する。（８５－５０Ｃ）％の限界加工率で冷間圧縮加工が可能であれば「Ｂ」、割れが発生した場合を「Ｘ」、さらに（９０－５０Ｃ）％の限界加工率で冷間圧縮加工が可能であれば「Ａ」で評価した。本発明鋼では全てＢまたはＡであり、優れた冷間加工性を示していた。なお、加工率とは、（１２－Ｈ）／１２×１００（％）であり、Ｈは冷間圧縮加工後の試験片の厚さ（ｍｍ）である。 The cold workability was determined by preparing a compression test piece with a diameter of 8 mm and a height of 12 mm, performing end face compression processing at a strain rate of 10 / s in the height direction, and determining whether cold compression processing was possible without cracking. .. The cold workability of the steel material depends on the amount of C (mass%), and the higher the amount of C, the lower the cold workability. Therefore, the limit workability is defined as the formula for the amount of C. "B" if cold compression processing is possible at the limit processing rate of (85-50C)%, "X" if cracks occur, and cold compression processing at the limit processing rate of (90-50C)% Was evaluated as "A" if possible. All of the steels of the present invention were B or A, and showed excellent cold workability. The processing rate is (12-H) / 12 × 100 (%), and H is the thickness (mm) of the test piece after cold compression processing.
　炭窒化物の分散状態は、埋め込み研磨面を王水にてエッチングし、ＳＥＭ・ＥＤＳにて評価した。１６００μｍ２中に直径１μｍサイズ以上の炭窒化物が１０個以上ある場合を「Ｂ」、１６００μｍ２中に直径２μｍサイズ以上の炭窒化物が１０個以上ある場合を「Ａ」、それ以外を「Ｘ」で評価した。本発明鋼では全てＢまたはＡであり、優れた冷間加工性に資する炭窒化物の分散状態を示していた。なお、サイズの直径とは（長径＋短径）／２で計算される。炭窒化物とはＥＤＳ分析にてＣｒ、Ｆｅ、Ｃ、Ｎを主体とする析出物である。 The dispersed state of the carbonitride was evaluated by SEM / EDS after etching the embedded polished surface with aqua regia. "B" if the 1600 .mu.m carbonitride or more in diameter 1μm size during 2 is 10 or more, "A" if the carbonitride above diameter 2μm size in 1600 .mu.m 2 is 10 or more, the rest " It was evaluated by "X". In the steel of the present invention, all of them were B or A, and showed a dispersed state of the carbonitride that contributed to excellent cold workability. The diameter of the size is calculated by (major axis + minor axis) / 2. The carbonitride is a precipitate mainly composed of Cr, Fe, C and N in EDS analysis.
　酸化物の平均サイズおよび酸化物の組成の評価については、炭窒化物の影響を除くため１１５０℃から空冷の焼入れ処理した材料を用いて評価した。表層を＃５００研磨した鋼材を非水溶液中（３％のマレイン酸＋１％のテトラメチルアンモニウムクロイド＋残部メタノール）で電解（１００ｍＶ定電圧）して、マトリックスを溶解し、フィルターでろ過して、酸化物を抽出した。その後、フィルター上に残った酸化物について、ＳＥＭ・ＥＤＳにて、任意に３０個の酸化物の直径サイズを測定して平均直径サイズを算出した。酸化物とはＥＤＳ分析にてＯとＡｌ，Ｍｎ，Ｓｉ，Ｆｅ，Ｃｒ，Ｔｉ等の組成が主体の非金属介在物を意味する。直径のサイズとは（長径＋短径）／２で計算される。観察される介在物のうち１５μｍ以下のサイズのものを、２次脱酸生成物であるとして上記酸化物サイズの判定に用いた。
　また、任意に２０個の酸化物を選定して組成分析を実施した。なお、熱間鍛造材についても同様に酸化物の組成分析を実施し、本焼入れ処理で酸化物の状態が変化していないことを確認している。ＥＤＳ分析にてＯとＡｌ，Ｍｎ，Ｓｉ，Ｆｅ，Ｃｒ，Ｔｉ等の組成が主体の非金属介在物を酸化物とし、Ｓを除いたものの合計を１００％換算し、Ａｌの質量％を算出した。 The average size of the oxide and the composition of the oxide were evaluated using a material hardened by air cooling from 1150 ° C. in order to eliminate the influence of the carbonitride. A steel material whose surface layer is # 500 polished is electrolyzed (100 mV constant voltage) in a non-aqueous solution (3% maleic acid + 1% tetramethylammonium cloid + residual methanol) to dissolve the matrix, filtered with a filter, and oxidized. The thing was extracted. Then, for the oxides remaining on the filter, the diameter sizes of 30 oxides were arbitrarily measured by SEM / EDS to calculate the average diameter size. Oxide means a non-metal inclusion mainly composed of O and Al, Mn, Si, Fe, Cr, Ti and the like in EDS analysis. The diameter size is calculated by (major axis + minor axis) / 2. Among the observed inclusions, those having a size of 15 μm or less were regarded as secondary deoxidation products and used for determining the oxide size.
In addition, composition analysis was carried out by arbitrarily selecting 20 oxides. The composition of the oxide was also analyzed for the hot forged material in the same manner, and it was confirmed that the state of the oxide did not change during the main quenching treatment. In EDS analysis, non-metal inclusions mainly composed of O and Al, Mn, Si, Fe, Cr, Ti, etc. are used as oxides, and the total excluding S is converted to 100% to calculate the mass% of Al. did.
　粗大な酸化物の評価について、前記の埋め込み研磨材を光学顕微鏡にて観察し、長径が３０μｍ以上の粗大な酸化物がある場合、表６の備考欄に「粗大酸化物」と記載した。 Regarding the evaluation of coarse oxides, the above-mentioned embedded abrasive was observed with an optical microscope, and when there was a coarse oxide having a major axis of 30 μm or more, it was described as “coarse oxide” in the remarks column of Table 6.
　本発明のマルテンサイト系ステンレス鋼は、高硬度・高耐食性用途であり、冷間加工後に焼き入れ処理を施して最終製品とした段階で、高硬度・高耐食性を具備していることが要求される。
　高硬度特性については、冷間加工後にＴ＋５０℃の温度から空冷の焼き入れを行い、Ｈｖ硬さ評価を行った。Ｈｖ５００以上であれば本発明の要件を具備しえいる。実施例において、焼き入れ後にＨｖ５００未満の場合に表６の備考欄に「焼き入れ硬さ不足」と記載した。
　耐食性特性については、冷間加工後にＴ＋５０℃の温度から空冷の焼き入れを行い、表面を＃５００研磨後にＪＩＳの中性塩水噴霧試験で２４ｈの塩水噴霧で耐食性評価を行い、赤錆が発生しなければ良好な耐食性を具備している。実施例において、赤錆びが発生した場合（端部除く）に表６の備考欄に「耐食性不足」と記載した。 The martensitic stainless steel of the present invention is used for high hardness and high corrosion resistance, and is required to have high hardness and high corrosion resistance at the stage of quenching after cold working to make a final product. To.
For the high hardness characteristics, after cold working, air-cooled quenching was performed from a temperature of T + 50 ° C., and Hv hardness was evaluated. If it is Hv500 or higher, the requirements of the present invention can be satisfied. In the examples, when the Hv was less than 500 after quenching, "insufficient quenching hardness" was described in the remarks column of Table 6.
Regarding the corrosion resistance characteristics, after cold working, air-cooling quenching is performed from a temperature of T + 50 ° C., and after polishing the surface with # 500, corrosion resistance is evaluated by spraying salt water for 24 hours in the JIS neutral salt spray test, and red rust must occur. It has good corrosion resistance. In the examples, when red rust occurred (excluding the end portion), "insufficient corrosion resistance" was described in the remarks column of Table 6.
　表４、表５の本発明例は１～６３である。製品の硬さについて、本発明例ではＨｖ硬さで（６０Ｃ＋１７０）以下が得られており、また、大半で好ましいＨｖ硬さである（６０Ｃ＋１６０）以下が得られた。冷間加工性について、本発明鋼では全てＢまたはＡであり、優れた冷間加工性に資する炭窒化物の分散状態を示していた。 Examples of the present invention in Tables 4 and 5 are 1 to 63. Regarding the hardness of the product, in the example of the present invention, the Hv hardness was (60C + 170) or less, and in most cases, the preferable Hv hardness (60C + 160) or less was obtained. Regarding the cold workability, all of the steels of the present invention were B or A, indicating a dispersed state of the carbonitride that contributes to excellent cold workability.
　発明例１～３、７～１５，１７～５０、５２は、Ａｌ含有量が０．０１～０．２％、Ｏ含有量が０．００１～０．００６の好適範囲にあり、軟質化に資する酸化物状態を示していた。また、１～５μｍサイズの酸化物の平均Ａｌ濃度は１５～４０質量％の好適範囲にある。 Inventive Examples 1 to 3, 7 to 15, 17 to 50, 52 have an Al content of 0.01 to 0.2% and an O content of 0.001 to 0.006 in a preferable range for softening. It showed a contributing oxide state. The average Al concentration of an oxide having a size of 1 to 5 μm is in a preferable range of 15 to 40% by mass.
　一方、表６に示す比較例１～２２では、鋼の成分組成が本発明から外れ、あるいは凝固速度が本発明の好適条件から外れており、炭窒化物の分布状態、酸化物平均サイズが本発明の規定範囲を満たしておらず、所要の特性を満足していないことがわかる。
　比較例１、３、５は凝固冷却速度が速く、比較例１９はＡｌが過少であり、いずれも酸化物の平均直径サイズが過小であるため、Ｈｖが高くなり、冷間加工性が不良であった。比較例２、４、６は凝固冷却速度が遅く、酸化物の平均直径サイズが過大であるため、冷間加工性が不良であった。
　比較例８～１０、１３、１７、１８、２１は、それぞれＣ、Ｓｉ、Ｍｎ、Ｎｉ、Ｍｏ、Ａｌ、Ｃ＋Ｎ／２が過多であり、Ｈｖが高くなり、冷間加工性が不良であった。加えて比較例９、１７は炭窒化物の分散状態も不良であった。
　比較例７はＣが過少であり、比較例１５はＣｒが過多であり、焼入れ硬さ不足となった。比較例１４はＣｒが過少であり、比較例１６はＭｏが過少であり、耐食性不足となった。
　比較例１８はＡｌが過多であり、比較例２２はＯが過多であり、粗大な酸化物が形成されるとともに、冷間加工性が不良であった。 On the other hand, in Comparative Examples 1 to 22 shown in Table 6, the component composition of the steel deviates from the present invention, or the solidification rate deviates from the preferable conditions of the present invention, and the distribution state of the carbonitride and the average oxide size are present. It can be seen that the specified range of the invention is not satisfied and the required characteristics are not satisfied.
In Comparative Examples 1, 3 and 5, the solidification cooling rate was high, and in Comparative Example 19, Al was too small, and the average diameter size of the oxide was too small in each case, so that Hv was high and cold workability was poor. there were. In Comparative Examples 2, 4 and 6, the solidification cooling rate was slow and the average diameter size of the oxide was excessive, so that the cold workability was poor.
In Comparative Examples 8 to 10, 13, 17, 18, and 21, C, Si, Mn, Ni, Mo, Al, and C + N / 2, respectively, were excessive, Hv was high, and cold workability was poor. .. In addition, in Comparative Examples 9 and 17, the dispersed state of the carbonitride was also poor.
In Comparative Example 7, C was too small, and in Comparative Example 15, Cr was too much, resulting in insufficient quenching hardness. In Comparative Example 14, Cr was too small, and in Comparative Example 16, Mo was too small, resulting in insufficient corrosion resistance.
In Comparative Example 18, Al was excessive, and in Comparative Example 22, O was excessive, coarse oxides were formed, and cold workability was poor.
　＜実施例２＞
　次に、軟化焼鈍材の製造方法の影響を調査した。前述で製造した本発明鋼Ｃの熱間鍛造材のφ１４ｍｍ棒鋼について、種々の条件で軟化焼鈍を施し、軟質化、冷間加工性および炭窒化物の状態に及ぼす製造方法の影響について調査した。なお、軟化焼鈍時には微細酸化物の状態は変化しないため本実施例では酸化物の調査は実施していない。表７に軟化焼鈍材の製造方法と調査結果を示す。 <Example 2>
Next, the influence of the manufacturing method of the softened annealed material was investigated. The φ14 mm steel bar of the hot forged material of the steel C of the present invention produced above was softened and annealed under various conditions, and the influence of the manufacturing method on the softening, cold workability and the state of the carbonitride was investigated. Since the state of the fine oxide does not change during softening and annealing, the oxide was not investigated in this example. Table 7 shows the manufacturing method and survey results of the softened annealed material.
Figure JPOXMLDOC01-appb-T000007
Figure JPOXMLDOC01-appb-T000007
　発明例７、５３～６３ではいずれも優れた冷間加工性に資する炭窒化物の分散状態を示し、冷間鍛造性に優れていた。発明例６３では、表５の備考に「軟化焼鈍追加」と記載したように、本発明条件での軟化焼鈍を実施した後に、従来の８５０℃－２ｈ保定後、３０℃／ｈで７００℃まで徐冷して脱炉する軟化焼鈍を付与している例である。品質は良好であり、本発明の効果が引き継がれている。 In Invention Examples 7, 53 to 63, the dispersed state of the carbonitride contributing to the excellent cold workability was shown, and the cold forging property was excellent. In Invention Example 63, as described in the remarks in Table 5, "additional softening annealing", after the softening annealing under the conditions of the present invention, after the conventional 850 ° C.-2h retention, up to 700 ° C. at 30 ° C./h. This is an example in which soft annealing is applied to slowly cool and degas. The quality is good and the effects of the present invention are inherited.
　一方、比較例２２～２６では、軟化焼鈍条件が本発明の規定範囲を満たしておらず、本発明の炭窒化物の分散状態やＨｖ硬さ、優れた冷間加工性を満足していないことがわかる。 On the other hand, in Comparative Examples 22 to 26, the softening and annealing conditions did not satisfy the specified range of the present invention, and did not satisfy the dispersed state, Hv hardness, and excellent cold workability of the carbonitride of the present invention. I understand.
　以上の各実施例から明らかなように、本発明により、冷間加工性に優れる高硬度・高耐食用途のマルテンサイト系ステンレス鋼の軟化焼鈍材を安定的に提供することができ、冷間加工で大量生産することで部品の製造コストを大幅に低減でき、産業上極めて有用である。 As is clear from each of the above examples, according to the present invention, it is possible to stably provide a softened annealed material of martensitic stainless steel for high hardness and high corrosion resistance, which is excellent in cold workability, and cold working. Mass production in stainless steel can significantly reduce the manufacturing cost of parts, which is extremely useful in industry.

Claims (7)

  1. 　質量％で、
    Ｃ：０．１５～０．７０％
    Ｓｉ：２．０％以下、
    Ｍｎ：１．５％以下、
    Ｓ：０．０１％未満、
    Ｐ：０．０５％以下、
    Ｎｉ：１．５％以下、
    Ｃｒ：１０．５～１６．０％、
    Ｍｏ：０．９～３．０％、
    Ｎ：０．０１～０．１４％、
    Ａｌ：０．００８～１．０％、
    Ｏ：０．００１～０．００８％を含有し、
    残部Ｆｅおよび不純物からなる化学成分を有し、
    Ｃ＋Ｎ／２：０．１６～０．７０％であり、
    かつ、１．０μｍ以上の炭窒化物が１６００μｍ２中に１０個以上であり、酸化物の平均直径サイズが１～５μｍであり、（ａ）式で示されるＨｖ硬さであることを特徴とするマルテンサイト系ステンレス鋼。
    　　　Ｈｖ≦６０Ｃ＋１７０　　　・・・・・・・・・・・・・・・・（ａ）
    　　　Ｃ：Ｃ含有量（質量％）     By mass%
    C: 0.15 to 0.70%
    Si: 2.0% or less,
    Mn: 1.5% or less,
    S: less than 0.01%,
    P: 0.05% or less,
    Ni: 1.5% or less,
    Cr: 10.5 to 16.0%,
    Mo: 0.9-3.0%,
    N: 0.01-0.14%,
    Al: 0.008 to 1.0%,
    O: Contains 0.001 to 0.008%,
    It has a chemical component consisting of the balance Fe and impurities,
    C + N / 2: 0.16 to 0.70%,
    In addition, there are 10 or more carbonitrides of 1.0 μm or more in 1600 μm 2 , the average diameter size of the oxide is 1 to 5 μm, and the Hv hardness is represented by the formula (a). Martensitic stainless steel.
    Hv ≦ 60C + 170 ・ ・ ・ ・ ・ (a)
    C: C content (mass%)
  2. 　前記Ｆｅの一部に替えて、更に質量％で、
    Ｃｕ：１．５％以下、
    Ｗ：１．５％以下、
    Ｃｏ：１．５％以下
    Ｂ：０．０１％以下、
    Ｓｎ：０．３％以下、
    Ｓｂ：０．３％以下の内、１種類以上を含有することを特徴とする請求項１に記載のマルテンサイト系ステンレス鋼。     Instead of a part of the Fe, by mass%,
    Cu: 1.5% or less,
    W: 1.5% or less,
    Co: 1.5% or less B: 0.01% or less,
    Sn: 0.3% or less,
    The martensitic stainless steel according to claim 1, wherein Sb: contains one or more of 0.3% or less.
  3. 　前記Ｆｅの一部に替えて、更に質量％で、
    Ｎｂ：０．１％以下、
    Ｔｉ：０．１％以下、
    Ｖ：０．２％以下、
    Ｔａ：０．２％以下の内、１種類以上を含有することを特徴とする請求項１または請求項２に記載のマルテンサイト系ステンレス鋼。     Instead of a part of the Fe, by mass%,
    Nb: 0.1% or less,
    Ti: 0.1% or less,
    V: 0.2% or less,
    Ta: The martensitic stainless steel according to claim 1 or 2, wherein the martensitic stainless steel contains one or more of 0.2% or less.
  4. 　前記Ｆｅの一部に替えて、更に質量％で、
    Ｍｇ：０．０１％以下、
    Ｃａ：０．０１％以下、
    Ｈｆ：０．０１％以下、
    ＲＥＭ：０．０１％以下の内、１種類以上を含有することを特徴とする請求項１～請求項３のいずれか１項に記載のマルテンサイト系ステンレス鋼。     Instead of a part of the Fe, by mass%,
    Mg: 0.01% or less,
    Ca: 0.01% or less,
    Hf: 0.01% or less,
    REM: The martensitic stainless steel according to any one of claims 1 to 3, wherein the martensitic stainless steel contains one or more of 0.01% or less.
  5. 　酸化物の平均Ａｌ濃度が１５～４０質量％であることを特徴とする請求項１～請求項４のいずれか１項に記載のマルテンサイト系ステンレス鋼。 The martensitic stainless steel according to any one of claims 1 to 4, wherein the average Al concentration of the oxide is 15 to 40% by mass.
  6. 　軟化焼鈍処理として、
    ８７０℃よりも高く、Ｃ濃度と下記（ｂ）式で表される炭化物の固溶温度：Ｔよりも２０～１２０℃低い温度範囲で１～４８ｈの熱処理を施し、引き続き平均６０℃／ｈ以下の冷却速度でＴよりも２５０℃低い温度まで除冷することを特徴とする請求項１～請求項５のいずれか１項に記載のマルテンサイト系ステンレス鋼の製造方法。
    　　　ｌｏｇ（Ｃ）　＝　－６１００／（Ｔ＋２７３）　＋　４　・・・・・（ｂ）
    （ｂ）式で「Ｃ」はＣ濃度（質量％）、「Ｔ」は炭化物の固溶温度（℃）を意味する。     As a softening annealing treatment
    Heat treatment is performed for 1 to 48 h in a temperature range higher than 870 ° C., C concentration and solid solution temperature of carbide represented by the following formula (b): 20 to 120 ° C. lower than T, and the average is 60 ° C./h or less. The method for producing martensitic stainless steel according to any one of claims 1 to 5, wherein the cold is cooled to a temperature 250 ° C. lower than T at the cooling rate of.
    log (C) = -6100 / (T + 273) + 4 ... (b)
    In the formula (b), "C" means the C concentration (mass%), and "T" means the solid solution temperature (° C.) of the carbide.
  7. 　鋳造時の凝固時の平均冷却速度が５～５００℃／ｓであることを特徴とする請求項１～請求項６のいずれか１項に記載のマルテンサイト系ステンレス鋼の製造方法。 The method for producing martensitic stainless steel according to any one of claims 1 to 6, wherein the average cooling rate during solidification during casting is 5 to 500 ° C./s.
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WO2024018520A1 (en) * 2022-07-19 2024-01-25 日鉄ステンレス株式会社 High strength stainless steel wire and spring

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