WO2021044889A1 - Tôle d'acier inoxydable martensitique et élément en acier inoxydable martensitique - Google Patents

Tôle d'acier inoxydable martensitique et élément en acier inoxydable martensitique Download PDF

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WO2021044889A1
WO2021044889A1 PCT/JP2020/031886 JP2020031886W WO2021044889A1 WO 2021044889 A1 WO2021044889 A1 WO 2021044889A1 JP 2020031886 W JP2020031886 W JP 2020031886W WO 2021044889 A1 WO2021044889 A1 WO 2021044889A1
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stainless steel
martensitic stainless
steel sheet
corrosion resistance
quenching
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Japanese (ja)
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井上 宜治
山田 義仁
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日鉄ステンレス株式会社
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Priority to JP2021543703A priority Critical patent/JP7167354B2/ja
Priority to KR1020227002677A priority patent/KR102670275B1/ko
Priority to EP20859662.7A priority patent/EP4026920A1/fr
Priority to CN202080054736.0A priority patent/CN114174546B/zh
Publication of WO2021044889A1 publication Critical patent/WO2021044889A1/fr

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    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
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    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
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    • C21D8/00Modifying the physical properties by deformation combined with, or followed by, heat treatment
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    • C21D2211/00Microstructure comprising significant phases
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    • C21D2211/00Microstructure comprising significant phases
    • C21D2211/008Martensite

Definitions

  • the present invention relates to a martensitic stainless steel sheet and a martensitic stainless steel member having excellent corrosion resistance after quenching. More specifically, the present invention relates to martensitic stainless steel having excellent corrosion resistance even when air-cooled and hardened, which is used for manufacturing Western tableware knives, looms, tools, disc brakes and the like.
  • Martensitic stainless steel sheets such as SUS420J1 and SUS420J2 steel are generally used for tools such as Western tableware knives (table knives), scissors, weaving machines, and calipers. In such applications, it is difficult to use plating, painting, and rust preventive oil, and the material itself is required to have rust resistance. It is also important that it does not wear easily, and high hardness is required.
  • the manufacturing process of Western tableware knives, etc. is usually made by die-cutting from a steel plate, heating, quenching, and then polishing to make a knife.
  • the quenching process is often performed by air cooling, which also depends on the characteristics of the martensitic stainless steel sheet, which has excellent quenching properties.
  • Patent Document 1 discloses a martensitic stainless steel that is air-cooled and has excellent corrosion resistance during quenching.
  • N is added up to about 0.06% as an element for improving corrosion resistance.
  • Patent Document 2 discloses a steel to which N is further added.
  • Patent Document 3 discloses a steel in which N is further increased by using special equipment.
  • the present inventors first investigated the rusting condition of the table knife in detail. As a result, it was clarified that the rusting site starts from the end face of the steel sheet, more specifically, the central part of the thickness of the steel sheet. Furthermore, the formation of a ⁇ ferrite phase ( ⁇ Fe phase) due to macrosegregation was confirmed, and the grain boundaries of this ⁇ Fe became the accumulation sites of carbides, and the carbides melted by heating during quenching, and then grain boundaries during cooling. It was found that the mechanism of quenching is that precipitation occurs, resulting in sensitization and intergranular corrosion. It was also found that the rusting depends on the cooling rate during quenching.
  • the cooling rate varies greatly depending on the quenching equipment, but when evaluated by the average cooling rate from the quenching temperature to 600 ° C, which is the temperature at which carbide precipitation is almost completed, the cooling rate exceeds 100 ° C / s in water quenching.
  • the cooling rate is only about 5 ° C / s, and carbide precipitation cannot be suppressed and quenching is unlikely to occur. It turns out that is likely to occur.
  • a martensitic stainless steel sheet having a ⁇ p of 120 or more represented by the following formula (1) When the martensitic stainless steel sheet is held at 1050 ° C. for 30 minutes, then air-cooled and quenched, and tempered at 150 ° C. for 30 minutes, the area of ⁇ ferrite ( ⁇ Fe) present in the center of the plate thickness in the plate thickness cross section.
  • ⁇ p 420C + 470N + 30Ni + 7Mn + 9Cu-11.5Cr-11.5Si-12Mo-23V-47Nb-52Al + 189 ... Equation (1)
  • the element symbol in the formula (1) means the content (mass%) of the element.
  • the ⁇ p represented by the following formula (1) is 120 or more, and Further, a martensitic stainless steel member characterized in that the area ratio of ⁇ ferrite ( ⁇ Fe) existing in the central portion of the plate thickness in the plate thickness cross section is 0.1 to 1%.
  • ⁇ p 420C + 470N + 30Ni + 7Mn + 9Cu-11.5Cr-11.5Si-12Mo-23V-47Nb-52Al + 189 ... Equation (1)
  • the element symbol in the formula (1) means the content (mass%) of the element.
  • the martensitic stainless steel sheet of the present invention has excellent corrosion resistance, especially end face corrosion resistance, while maintaining sufficient hardness to withstand use for martensitic stainless steel applications such as table knives and other Western tableware. Therefore, when it is used as a martensitic stainless steel member such as a Western tableware knife, it can be expected to have an effect of improving corrosion resistance and prolonging the product life.
  • C is an element that determines the quenching hardness together with N, and is required to be 0.100% or more in order to obtain the hardness required for a Western tableware knife. It is preferably 0.110% or more, and 0.120% or more.
  • the quenching hardness becomes larger than necessary, the load during polishing increases, and the toughness also decreases.
  • Cr carbides are likely to precipitate during air-cooling quenching and the corrosion resistance is likely to be impaired, so the content is set to 0.170% or less. It is preferably 0.155% or less.
  • Si 0.25 to 0.60% Since Si is necessary for deoxidation in steelmaking and is also effective in suppressing the formation of oxide scale after quenching heat treatment, it is contained in an amount of 0.25% or more. If it is less than 0.25%, an oxidation scale is excessively generated, which increases the final polishing load. However, excessive addition suppresses austenite production and impairs hardenability, so the content is set to 0.60% or less.
  • Mn 0.10 to 0.60%
  • Mn is an austenite-stabilizing element and is necessary for ensuring hardness and the amount of martensite during quenching. Therefore, it is contained in an amount of 0.10% or more. However, in order to promote the formation of oxide scale during quenching and increase the subsequent polishing load, the content is set to 0.60% or less. Further, if it is added excessively, a large amount of MnS is generated and the corrosion resistance is also lowered.
  • P 0.035% or less
  • P is an element contained as an impurity in alloys such as hot metal and ferrochrome, which are raw materials. Since it is an element harmful to the toughness of the steel sheet after hot spreading annealing and quenching, its content shall be 0.035% or less. Excessive addition reduces hot workability and corrosion resistance.
  • S 0.015% or less S has a small solid solubility in the austenite phase and segregates at the grain boundaries to promote a decrease in hot workability. Therefore, the content is set to 0.015% or less. Further, if it is added excessively, a large amount of MnS is generated and the corrosion resistance is also lowered.
  • Cr 11.0 to 15.0% Cr is required at least 11.0% or more in order to maintain corrosion resistance as a Western tableware knife. On the other hand, since it also has the effect of narrowing the stable temperature of austenite, it should be 15.0% or less. Preferably, it is 12.0% or more. The upper limit is preferably 14.0% or less. The range is preferably 12.0 to 14.0%.
  • Ni 0.05 to 0.60% Like Mn, Ni is an austenite-stable element and is necessary for securing hardness and the amount of martensite during quenching. It also has the effect of improving corrosion resistance. Therefore, it is contained in an amount of 0.05% or more. However, since Ni is more expensive than other elements, it should be 0.60% or less.
  • Cu 0.010 to 0.50%
  • Cu is an austenite-stable element like Mn and Ni, and is an element that improves corrosion resistance. Although it is an element that cannot be avoided from scrap during steelmaking, it is contained in an amount of 0.010% or more in order to improve corrosion resistance. On the other hand, excessive content reduces hot workability and the like, so the content should be 0.50% or less. Although it is cheaper than Ni, it is relatively expensive, so its addition is an element that we want to keep as low as possible.
  • V 0.010 to 0.10%
  • V is an element that is often inevitably mixed with ferrochrome or the like, which is an alloy element. The reduction is difficult and contains 0.010% or more. However, since excessive content narrows the austenite formation temperature range, it was set to 0.10% or less. Further, if it is added in an excessive amount, VN is formed and N is immobilized, which causes a decrease in hardness and a decrease in corrosion resistance, which is not preferable.
  • Al 0.05% or less Al is an effective element for deoxidation, but its content is 0.05 because excessive content produces CaS, which is a soluble inclusion, during heat spreading and reduces corrosion resistance. % Or less. Al may not be contained.
  • N 0.060 to 0.090%
  • N is an element that determines quenching hardness together with C, and is an important element in the present invention that improves corrosion resistance. Therefore, in the present invention, the content is 0.060% or more. 0.065% or more is preferable. However, if N is excessively contained, bubble defects are likely to occur in the slab and the production cost is increased in the secondary refining by VOD or the like, so the content is set to 0.090% or less. Preferably, it is 0.085% or less.
  • C + 1 / 2N 0.130 to 0.190%
  • the elements that determine the hardness of the martensite phase in steel are C and N, the sum of which contributes to the hardness. According to the study of the present inventor, the contribution of N to hardness is half that of C, and it is necessary that C + 1 / 2N is 0.130% or more in order to obtain the hardness required for a Western tableware knife. .. It is preferably 0.150% or more. On the other hand, if C + 1 / 2N is excessive, the quenching hardness is excessively increased, and the toughness of the intermediate material (slab or the like) in the product or manufacturing process is impaired. It is preferably 0.180% or less, and may be 0.175% or less.
  • ⁇ p may be adjusted to 130 or more, or 140 or more. In the present invention, it may be 170 or less, and may be 150 or less.
  • the steel sheet and steel member of the present invention have a steel composition in which the balance is composed of Fe and impurities.
  • elements of Mo, Nb, Ti and Sn, Bi are added in place of a part of Fe in order to improve rust resistance and corrosion resistance. it can.
  • Mo 0.01-1.0% Mo is an element that improves corrosion resistance, and its effect is exhibited by adding 0.01% or more. However, Mo is also an expensive element, and even if it is added excessively, the effect is not clear, and the upper limit is 1.0%.
  • Ti 0.005 to 0.050%
  • Ti is an element that suppresses sensitization and deterioration of corrosion resistance due to precipitation of chromium carbonitride in stainless steel by forming carbonitride. The effect is expressed at 0.005% or more. However, excessive addition destabilizes the martensite phase and reduces the hardness, so the upper limit is 0.050%.
  • Nb 0.005 to 0.050%
  • Nb is an element that suppresses sensitization and deterioration of corrosion resistance due to precipitation of chromium carbonitride in stainless steel by forming carbonitride. The effect is expressed at 0.005% or more. However, excessive addition destabilizes the martensite phase and reduces the hardness, so the upper limit is 0.050%.
  • Sn 0.01% to 0.10% Sn is an element effective for improving corrosion resistance after quenching, preferably 0.01% or more, and preferably 0.05% or more if necessary. However, excessive addition is preferably 0.10% or less because it promotes ear cracking during hot spreading.
  • Bi 0.01% to 0.20% Bi is an element that improves corrosion resistance. Although the mechanism has not been clarified, it is considered that the addition of Bi has the effect of miniaturizing MnS, which tends to be the starting point of rusting, and thus reduces the probability of becoming the starting point of rusting. It is effective when added at 0.01% or more. Even if more than 0.20% is added, the effect is only saturated, so the upper limit is set to 0.20%.
  • ⁇ ferrite phase ratio of steel plate and steel member The present inventors have found that ⁇ ferrite ( ⁇ Fe) existing in the central portion of the thickness of the steel sheet has a great influence on the end face corrosion resistance of the steel sheet.
  • ⁇ ferrite ⁇ Fe
  • the grain boundary between ⁇ Fe and the matrix phase ( ⁇ phase) becomes a precipitation site of Cr carbide during cooling, causing sharpening in the vicinity of the precipitated Cr carbide, and end face corrosion resistance. I think it will reduce.
  • N improves the end face corrosion resistance is that it also has an effect of suppressing the precipitation of Cr carbides. Therefore, in the present invention, it is effective to suppress ⁇ Fe in steel as well as N content.
  • the steel sheet of the present invention is subjected to quenching / tempering treatment and then ⁇ Fe. Evaluate the quantity.
  • the quenching conditions for evaluation are heating to 1050 ° C., holding for 30 minutes, and then air cooling, and the tempering conditions are 150 ° C. and 30 minutes.
  • the quenching method is air cooling. After quenching and tempering the steel sheet under the above evaluation conditions, good end face corrosion resistance can be obtained if ⁇ Fe is 1% or less when evaluated by the abundance area ratio in the plate thickness cross section. If it is less than 0.1%, excellent corrosion resistance is exhibited regardless of the present invention, but it is not preferable because long-term heat treatment is required to reduce ⁇ Fe and the cost increases. Further, if it exceeds 1%, the improvement of corrosion resistance is not sufficient even with the present invention, and the hardness is also insufficient, which is not preferable. A more preferable upper limit is 0.5%. The range is preferably 0.1% to 0.5%.
  • ⁇ Manufacturing method of steel sheet> As the method for producing the steel sheet of the present invention, a conventional method is used. A slab with adjusted components is obtained by melting and casting, which is hot-rolled, then box-annealed, shot, and pickled to obtain a product.
  • the slab is preheated.
  • heating at 1100 to 1150 ° C. is preferably set to a soaking time of 1 hour or more and 50 hours or less.
  • the heating temperature exceeds 1150 ° C.
  • the two phases ( ⁇ + ⁇ ) become stable and the amount of ⁇ Fe rapidly increases, which is not preferable.
  • the rapidly increased ⁇ Fe remains in a large amount even in the subsequent process, which causes a decrease in hardness.
  • ⁇ Fe does not decrease even if it is heated for a long time, which is not preferable.
  • the amount of ⁇ Fe is smaller than that in the case of exceeding 1150 ° C., the hardness may be maintained depending on the post-process. Further, if it is less than 1 hour, the amount of ⁇ Fe becomes too large, which is not preferable, and if it exceeds 50 hours, the cost becomes high, which is not preferable.
  • This preheating is performed as slab heating before hot rolling, and hot rolling may be performed as it is.
  • the obtained steel sheet is punched, hardened, tempered, and polished to prepare a member. After punching, forging is performed and the shape is adjusted.
  • the following are preferable conditions for quenching and tempering.
  • the quenching temperature is preferably 1000 to 1150 ° C. If it is less than 1000 ° C, the austenite phase is small at high temperature and the hardness after quenching becomes low, which is not preferable. If it is more than 1150 ° C, the ⁇ phase and the stable austenite phase increase, and the hardness also increases in this case. It is not preferable because it decreases.
  • the holding time during quenching is preferably 1 minute to 1 hour.
  • the cooling rate at the time of quenching is an average cooling rate from the quenching temperature to 600 ° C., preferably 1 ° C./sec or more. If it is less than this, the hardness is lowered, which is not preferable. By air-cooling the quenching, the preferable cooling rate can be realized.
  • the tempering is preferably 100 ° C to 250 ° C. If the temperature is lower than 100 ° C, the effect of tempering is poor, and if the temperature exceeds 250 ° C, the decrease in hardness becomes too large, which is not preferable.
  • the steels having the composition shown in Tables 1 and 2 were melted and cast into a slab having a thickness of 250 mm.
  • these slabs were heat-treated at 1150 ° C. for 40 hours as preheating, and the amount of ⁇ Fe was set within a certain range.
  • the A2 steel was preheated at 1175 ° C. for 40 hours and at 950 ° C. for 40 hours to obtain A2'steel and A2'steel, respectively.
  • the hot-rolled steel sheet was annealed by box annealing.
  • the maximum heating temperature was set to a temperature range of 800 ° C. or higher and 900 ° C. or lower.
  • the scale on the surface of the steel sheet after annealing was removed by shot blasting and pickled.
  • Example 1 In order to evaluate the obtained steel sheet, a sample for evaluation was cut out from the steel sheet, and the sample was heated to 1050 ° C. for 30 minutes as a quenching / tempering process, held for 30 minutes, and then air-cooled at 150 ° C. for 30 minutes. It was tempered. After that, each evaluation of ⁇ Fe amount measurement, hardness measurement, and end face corrosion resistance was performed. The results obtained are shown in Table 3.
  • ⁇ Fe The amount of ⁇ Fe was measured by mirror-polishing and etching the end face of the sample to reveal the structure.
  • ⁇ Fe can be expressed in aqua regia or the like as the etching solution, but it is preferable to use a reagent called the improved Murakami reagent described in Non-Patent Document 1 because ⁇ Fe is deeply etched in brown, and evaluation is performed using this. did.
  • a typical example is shown in FIG.
  • the tissue revealed by the improved Murakami reagent is examined under a microscope, a photograph of ⁇ Fe is taken from the total thickness of a certain width (2 mm in this example), the ⁇ Fe area is obtained from the image analysis, and then the area ratio ( ⁇ Fe area ( ⁇ Fe area ( ⁇ Fe area)). mm 2 ) / 2 mm ⁇ total thickness (mm) ⁇ 100 (%)) was calculated.
  • its value needs to be 0.1 to 1%. Further, it is preferably 0.1% to 0.5%.
  • ⁇ Fe area ratio 0.1 to 1% was regarded as pass (A), and more than that was regarded as fail (X).
  • the surface hardness is evaluated by the Rockwell hardness tester C scale in accordance with JIS Z2245, and 50 or more is passed (A), and the others are rejected (Failure). X).
  • the end face corrosion resistance After polishing the sample surface and end face with # 600, the end face is used as the evaluation surface and the salt spray test is performed for 24 hours (JIS Z 2371 "salt spray test method") to determine the rusting point. I counted. A score of 2 or less was regarded as a pass (A), and a score exceeding that score was a failure (X). In particular, those with zero rusting points were regarded as passing (S). Even if the salt spray test was carried out for 24 hours or more, rust did not develop further, so the end face corrosion resistance was judged based on the results for 24 hours.
  • All of the steel sheets of the present invention are excellent not only in end face corrosion resistance but also in other properties, and are preferable as steel sheets for Western tableware knives.
  • the comparative steel has inferior end face corrosion resistance or inferior other characteristics, and it is clear that it is not preferable as a steel plate for Western tableware knives.
  • Example 2 Using the member cut out from the obtained steel sheet, quenching and tempering were performed under the conditions shown in Table 4 to obtain a steel member. Quenching was performed by heating at 1050 to 1150 ° C., and then cooling was performed by controlling the cooling rate from the quenching temperature to 600 ° C. to the cooling rate shown in Table 4. Further, a tempering treatment for 1 to 2 hours was carried out at 150 to 250 ° C. to obtain a steel member. Further, A2'steel and A2'steel were also treated in the same manner.
  • Table 4 shows the ⁇ Fe amount measurement, hardness measurement, and end face corrosion resistance evaluation of the obtained steel member together with the heat treatment conditions.
  • the evaluation method and evaluation criteria were the same as in Example 1.
  • All of the steel members of the present invention are excellent not only in end face corrosion resistance but also in other characteristics, and are preferable as steel members for Western tableware knives.
  • the comparative steel has inferior end face corrosion resistance or inferior other characteristics, and it is clear that it is not preferable as a steel member for Western tableware knives.
  • the present invention it is possible to produce a martensitic stainless steel member having excellent end face corrosion resistance after air-cooling and quenching with high productivity, and the corrosion resistance of a Western tableware knife produced by using the martensitic stainless steel member is improved, and industrially. , Very useful.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Crystallography & Structural Chemistry (AREA)
  • Heat Treatment Of Sheet Steel (AREA)
  • Heat Treatment Of Steel (AREA)

Abstract

La présente invention concerne une tôle d'acier inoxydable martensitique et un élément en acier inoxydable martensitique, qui sont utilisés dans la fabrication de couteaux de table occidentaux, de métiers à tisser, d'outils, de freins à disques, etc. et qui présentent une excellente résistance à la corrosion même après avoir été trempés par refroidissement à l'air. La tôle d'acier inoxydable martensitique contient, en % en masse, de 0,100 à 0,170 % de C, de 0,30 à 0,60 % de Si, de 0,10 à 0,60 % de Mn, de 11,0 à 15,0 % de Cr, de 0,05 à 0,60 % de Ni, de 0,010 à 0,50 % de Cu, de 0,010 à 0,10 % de V, une proportion inférieure ou égale à 0,05 % d'Al, de 0,060 à 0,090 % de N et de 0,130 à 0,190 % de C + 1/2N et présente un γp d'au moins 120 tel que représenté par l'équation (1), dans laquelle, après trempe et revenu de la tôle d'acier inoxydable martensitique, le rapport surfacique de la ferrite δ (δFe) présente dans la partie centrale de l'épaisseur de la tôle d'acier est de 0,1 à 1 % dans une section transversale dans le sens de l'épaisseur de la tôle.
PCT/JP2020/031886 2019-09-03 2020-08-24 Tôle d'acier inoxydable martensitique et élément en acier inoxydable martensitique WO2021044889A1 (fr)

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JP2021543703A JP7167354B2 (ja) 2019-09-03 2020-08-24 マルテンサイト系ステンレス鋼板およびマルテンサイト系ステンレス鋼部材
KR1020227002677A KR102670275B1 (ko) 2019-09-03 2020-08-24 마르텐사이트계 스테인리스 강판 및 마르텐사이트계 스테인리스강 부재
EP20859662.7A EP4026920A1 (fr) 2019-09-03 2020-08-24 Tôle d'acier inoxydable martensitique et élément en acier inoxydable martensitique
CN202080054736.0A CN114174546B (zh) 2019-09-03 2020-08-24 马氏体系不锈钢钢板及马氏体系不锈钢钢构件

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KR20220024982A (ko) 2022-03-03
TW202118882A (zh) 2021-05-16
CN114174546A (zh) 2022-03-11
TWI737475B (zh) 2021-08-21
EP4026920A1 (fr) 2022-07-13
CN114174546B (zh) 2022-08-30
JPWO2021044889A1 (fr) 2021-03-11

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