EP3034642B1 - Rostfreier martensitischer stahl mit ausgezeichneter verschleissfestigkeit und korrosionsbeständigkeit und verfahren zur herstellung davon - Google Patents

Rostfreier martensitischer stahl mit ausgezeichneter verschleissfestigkeit und korrosionsbeständigkeit und verfahren zur herstellung davon Download PDF

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EP3034642B1
EP3034642B1 EP14835747.8A EP14835747A EP3034642B1 EP 3034642 B1 EP3034642 B1 EP 3034642B1 EP 14835747 A EP14835747 A EP 14835747A EP 3034642 B1 EP3034642 B1 EP 3034642B1
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amount
hot
steel
stainless steel
corrosion resistance
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EP3034642A4 (de
EP3034642A1 (de
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Shinichi Teraoka
Shunji Sakamoto
Eiichiro Ishimaru
Keiichi Oomura
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Nippon Steel Stainless Steel Corp
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Nippon Steel and Sumikin Stainless Steel Corp
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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
    • 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
    • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
    • C21D1/18—Hardening; Quenching with or without subsequent tempering
    • C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
    • 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
    • C21D6/002—Heat treatment of ferrous alloys containing Cr
    • 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
    • C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
    • 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
    • C22C38/008—Ferrous alloys, e.g. steel alloys containing tin
    • 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
    • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
    • 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
    • C22C38/40—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
    • C22C38/44—Ferrous alloys, e.g. steel alloys containing chromium with nickel with molybdenum or tungsten
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/46—Ferrous alloys, e.g. steel alloys containing chromium with nickel with vanadium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/48—Ferrous alloys, e.g. steel alloys containing chromium with nickel with niobium or tantalum
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/50—Ferrous alloys, e.g. steel alloys containing chromium with nickel with titanium or zirconium
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C38/00—Ferrous alloys, e.g. steel alloys
    • C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
    • C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
    • C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
    • C—CHEMISTRY; METALLURGY
    • 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 having excellent corrosion resistance after quenching or after quenching and tempering, and a method for producing the same.
  • the present invention relates to martensitic stainless steel whch is used to produce edged tools such as knives and scissors, loom components, tools, and the like, and has excellent corrosion resistance when having predetermined hardness, and to a method for producing the same.
  • SUS420J1 steel and SUS420J2 steel are generally used for western tableware knives (table knives), scissors, loom components, and tools such as calipers, and SUS440A steel is used for western kitchen knives, fruit knives, and the like requiring higher hardness.
  • SUS410 steel is generally used for structural members such as disc brakes for a motorcycle and reinforcing bars.
  • plating, paint, or rustproofing oil for rustproofing it is difficult to use plating, paint, or rustproofing oil for rustproofing, and steel needs to have strong abrasion resistance and high hardness, and thus martensitic stainless steel is used.
  • martensitic stainless steel is classified depending on the amount of C and the amount of Cr into SUS410 containing 0.15% or less of C and 11.5% to 13.5% of Cr, SUS420J1 containing 0.16% to 0.25% of C and 12% to 14% of Cr, SUS420J2 containing 0.26% to 0.40% of C and 12% to 14% of Cr, and SUS440A containing 0.60% to 0.75% of C and 16% to 18% of Cr.
  • SUS410 steel is used in a quenched state
  • SUS420 steel is used in a state in which the steel is tempered after being quenched and thus has improved toughness.
  • the corrosion resistance of stainless steel is evaluated on the basis of components, and it is known that the corrosion resistance is improved by addition of Cr, Mo, and N.
  • PTL 1 describes martensitic stainless steel having excellent corrosion resistance and high hardness which contains less than 0.15% of C, 12.0% to 18.5% of Cr, and 0.40% to 0.80% of N.
  • Nitrogen is an inexpensive element that is not only effective for improving corrosion resistance but also broadens an austenite range, but causes problems in that nitrogen which exceeds the solid solubility limit during melting and casting produces gas bubbles and sound ingot cannot be obtained.
  • the solid solubility limit of nitrogen varies depending on components other than nitrogen or atmospheric pressure of an atmosphere. Cr and C are components having a large influence on the solid solubility limit of nitrogen.
  • martensitic stainless steel such as SUS420J1 or SUS420J2 is cast at atmospheric pressure
  • the amount of nitrogen solved therein is generally reported to be approximately 0.1%. Therefore, in PTL 1, 0.40% or more of nitrogen is solution heat-treated using a pressure casting method.
  • the pressure casting method cannot be easily applied to continuous casting and exhibits poor productivity, and thus this method is not suitable for mass production.
  • PTL 2 discloses martensitic stainless steel containing 0.15% to 0.50% of C, 0.05% to 3.0% of Cu, 0.05% to 3.0% of Ni, 13.0% to 20.0% of Cr, 0.2% to 4.0% of Mo, 0.30% to 0.80% of N, or the like.
  • the amount of N solved therein is increased and the nitrogen-blowing is suppressed by actively adding Mo, Ni, or the like to martensitic stainless steel.
  • This method is considered to improve blowholes during pressure casting, but pressure casting is essential in this method. Thus, continuous casting is difficult, and the problem of poor productivity is not solved.
  • addition of Ni, Mo, or the like causes an increase in raw material costs.
  • PTL 3 A technique for improving the corrosion resistance of martensitic stainless steel without performing the pressure casting method or adding a large amount of Mo, Ni, or the like is disclosed in PTL 3.
  • 0.03% to 0.25% of C, 0.03% to 0.15% of Sn, and 0.01% to 0.08% of N are added to martensitic stainless steel, and quenched and tempered hardness (hardness after quenching and tempering is performed) is set in a range of 300 HV to 600 HV, thereby obtaining an effect of Sn improving corrosion resistance.
  • EN1.4034 contains 0.43% to 0.50% of C, 12.5% to 14.5% of Cr, 1% or less of Si, 1% or less of Mn, 0.04% or less of P, and 0.015% or less of S.
  • EN1.411 contains 0.48% to 0.60% of C, 13.0% to 15.0% of Cr, 0.50% to 0.80% of Mo, 0.15% or less of V, 1% or less of Si, 1% or less of Mn, 0.04% or less of P, and 0.015% or less of S.
  • Stainless steel having a higher value of the pitting resistance equivalent has more favorable corrosion resistance.
  • corrosion resistance refers to corrosion resistance to an environment of a neutral aqueous solution of a chloride, and as an evaluation method, for example, methods of pitting potential measurement for stainless steels regulated by JIS G 0577:2014, methods of salt spray testing regulated by JIS Z 2371:2000, or the like, can be used.
  • sensitization refers to a phenomenon in which, in a case in which a stainless steel material is welded or the like, Cr carbides are precipitated due to the welding temperature history of the stainless steel material, Cr-depleted zones are generated in the matrix around the carbides, and consequently, corrosion resistance is impaired. It is known that, in a welded portion of SUS430 or in a case in which SUS304 is used for a long period of time at a temperature in a range of 650°C to 700°C, sensitization occurs.
  • martensitic stainless steel While the sensitization phenomenon in martensitic stainless steel is not well known, it is assumed that martensitic stainless steel is also sensitized from the fact that, when a commercially available knife is subjected to a salt spray test, significant rust is observed. Martensitic stainless steel has property of self-hardening, and, even with air hardening, as-quenched hardness comparable with that obtainable through water quenching can be obtained. Thus, in many cases, martensitic stainless steel is quenched with a slow cooling rate. Accordingly, it is assumed that Cr carbides are precipitated in a cooling step with a slow cooling rate and sensitization occurs.
  • the present invention has been made in consideration of the above-described circumstances, and an object of the present invention is to provide martensitic stainless steel having excellent corrosion resistance at low cost.
  • the present inventors investigated precipitation of carbonitrides or a solution treatment phenomenon. As a result, it was found that addition of a small amount of Sn and addition of an appropriate amount of N to the amount of C suppress the sensitization phenomenon in martensitic stainless steel and improve corrosion resistance. In addition, it was also found that the solution treatment during hardening heating is accelerated, higher as-quenched hardness can be obtained with heating at a relatively lower temperature for a shorter period of time than those for steel of the related art, and tempered toughness is also improved.
  • the present inventors performed a number of studies regarding corrosion resistance of high-carbon martensitic stainless steel after quenching. As a result, the present inventors found that corrosion resistance after quenching is significantly poorer than the corrosion resistance of ordinary stainless steel commensurate with the amount of Cr and performed various studies regarding a method for improving corrosion resistance. In addition, the present inventors performed detailed studies regarding precipitation of carbonitrides during annealing of high-carbon martensitic stainless steel, the growth process of the carbonitrides, and a process of solution treatment of carbonitrides during hardening heating. As a result, it was found that addition of a small amount of Sn had a significant influence on behavior regarding the precipitation, growth, and solution treatment of carbonitrides.
  • Sn is an element that easily segregates in crystal grain boundaries or interfaces between precipitates and a matrix.
  • a material in which carbonitrides are precipitated in a cooling process of quenching and which is easily sensitized such as high-carbon martensitic stainless steel
  • Sn segregates in the interface between the carbonitrides and the matrix in a hardening cooling process.
  • the segregated Sn inhibits the precipitation and growth of the carbonitrides, formation of Cr-depleted zones is delayed, and sensitization is suppressed, and thus corrosion resistance is improved.
  • Sn is an element that deteriorates the hot workability of the base material and also degrades high-temperature aging embrittlement characteristics (makes steel easily embrittled when the steel is used at a high temperature for a long period of time).
  • there is an optimal range for the amount of Sn added An effect of suppressing sensitization is obtained when the amount of Sn added is 0.005% or higher.
  • addition of more than 0.10% of Sn degrades the hot workability of high-carbon martensitic stainless steel and causes not only cracks during hot-rolling but also aging embrittlement. Therefore, it is necessary to set the additive amount of Sn to 0.1% or less.
  • the present embodiment describes the optical component balance of martensitic stainless steel in the above-described uses.
  • the reasons for limiting individual components will be described below.
  • the unit “%” for the amounts of individual elements indicates “mass%” unless particularly otherwise described.
  • C is an element that dominates as-quenched hardness (hardness after quenching).
  • the amount of C is desirably set in a range of 0.42% to 0.48%.
  • Si is required for deoxidization during melting and refining and is also effective for suppressing generation of oxide scales during a hardening thermal treatment (hardening heating). Therefore, the amount of Si is set to 0.25% or higher. However, Si narrows the austenite single-phase region temperature and impairs quenching stability. Therefore, the amount of Si is set to 0.60% or lower. In order to reduce the proportion of defects generated by oxide-based inclusions, the amount of Si is desirably set to 0.30% or higher. In addition, since Si narrows the austenite single-phase region temperature and impairs quenching stability, the amount of Si is desirably set to 0.50% or lower.
  • Mn is an austenite-stabilizing element, while Mn accelerates generation of oxide scales during a hardening thermal treatment (hardening heating) and increases the subsequent polishing load. Therefore, the upper limit of the amount of Mn is set to 2.0%. When degradation of corrosion resistance due to coarsening of sulfide-based inclusions such as MnS is taken into account, the amount of Mn is desirably set to 1.0% or lower. In addition, since Mn is also included in other alloy raw materials, and it is difficult to further reduce the amount of Mn, the amount of Mn is preferably set to 0.10% or higher.
  • P is an element included as an impurity in hot metal or an alloy such as ferrochromium which is a raw material. Since P is a harmful element to the toughness of a hot-rolled and annealed plate and to the toughness thereof after quenching, the amount of P is set to 0.035% or lower. P is also an element that degrades workability, and thus the amount of P is desirably set to 0.030% or lower. In addition, an excess decrease in the amount of P creates a necessity of a high-purity raw material for producing steel, which leads to an increase in costs. Therefore, the lower limit of the amount of P is preferably set to 0.010%.
  • the amount of S is an element only a small amount of which is solution heat-treated in an austenite phase, and which segregates in grain boundaries and thus accelerates degradation of hot workability.
  • the amount of S exceeds 0.010%, the influence of the above-described action becomes significant, and thus the amount of S is set to 0.010% or lower.
  • a decrease in the amount of S decreases the amount of sulfide-based inclusions generated and improves corrosion resistance, while a desulfurization load for decreasing the amount of S is increased (a step and a facility for desulfurization become necessary), and production costs are increased. Therefore, the lower limit of the amount of S is preferably set to 0.001%.
  • the amount of S is preferably in a range of 0.001% to 0.008%.
  • the amount of Cr needs to be at least 11.0% in order to maintain corrosion resistance required for principal uses of martensitic stainless steel.
  • the upper limit of the amount of Cr is set to 15.5%.
  • the range of the amount of Cr is preferably set in a range of 12.0% to 14.0%.
  • Ni is an austenite-stabilizing element like Mn.
  • C, N, Mn, and the like are removed from the surface layer portion through decarburization, denitrification, or oxidization, and there are cases in which ferrite is generated in the surface layer.
  • Ni is highly resistant to oxidization, there are no cases in which C, N, Mn, and the like are removed from the surface layer.
  • Ni is highly effective for stabilizing an austenite phase. This effect begins to appear at an amount of Ni of 0.01%, and thus the amount of Ni is set to 0.01% or higher. However, since Ni is an expensive raw material, the amount of Ni is set to 0.60% or lower.
  • the upper limit of the amount of Ni is desirably set to 0.30%.
  • the lower limit of the amount of Ni is desirably set to 0.05%.
  • the amount of Cu is preferably set to 0.20% or lower.
  • the amount of Cu is preferably set to 0.01% or higher.
  • V 0.10% or lower
  • V is inevitably mixed into steel from ferrochromium which is an alloy raw material. Since V has a strong action of narrowing the austenite single-phase region temperature, the amount of V is set to 0.10% or lower. In addition, V is an element highly capable of forming a carbide, and in Cr carbonitrides including a V-based carbide as a nucleus, there is a tendency that solution treatment of the Cr carbonitrides is delayed. Therefore, the amount of V is preferably set to 0.08% or lower. In addition, since it is difficult to decrease the amount of V mixed into steel as an inevitable impurity, the lower limit of the amount of V is preferably set to 0.01%. When productivity or the production cost is collectively taken into account, the amount of V is preferably set in a range of 0.03% to 0.07%.
  • Mo is an element effective for improving corrosion resistance.
  • Mo is an element stabilizing a ferrite phase, and there are problems in that addition of Mo narrows the hardening heating temperature range and non-transformed ferrite is generated after the quenching.
  • Mo enhances tempering softening resistance (suppresses softening by means of tempering), addition of Mo deteriorates productivity. For example, the annealing time of a hot-rolled plate is extended. Therefore, the upper limit of the amount of Mo is set to 0.10%. While being an expensive element, Mo is not effective for suppressing sensitization and for common uses, does not easily produce an effect of improving corrosion resistance commensurate with costs. Therefore, the amount of Mo is preferably set to 0.05% or lower. In addition, since it is difficult to avoid Mo mixed into steel from a raw material, the amount of Mo is preferably set to 0.01% or higher.
  • Al is an effective element for deoxidization.
  • Al increases the basicity of slags, precipitates CaS as water-soluble inclusions in steel, and degrades corrosion resistance. Therefore, the upper limit of the amount of Al is set to 0.03%.
  • the amount of Al is preferably set to 0.01% or lower.
  • the amount of Al is preferably set to 0.003% or higher.
  • N has an effect of increasing as-quenched hardness like C.
  • N improves corrosion resistance by means of the following two actions.
  • the first one is an action of strengthening a passivation film and the second one is an action of suppressing the precipitation of Cr carbides (suppressing the generation and growth of Cr-depleted zones).
  • the amount of N is set to 0.01% or higher.
  • addition of excess N generates blowholes during casting at atmospheric pressure, and thus the amount of N is set to 0.05% or lower.
  • the optical range of the amount of N varies depending on the amount of Sn added.
  • the amount of N is preferably set to 0.025% or higher.
  • the amount of N is preferably set to 0.035% or lower.
  • Sn is a segregated element which is concentrated in not only crystal grain boundaries in the matrix but also interfaces between precipitates and the matrix. Thus, Sn suppresses the growth and coarsening of the precipitates. Therefore, addition of Sn suppresses sensitization in a hardening cooling step, and thus an effect of improving corrosion resistance is obtained. Since this effect can be reliably obtained by setting the amount of Sn to 0.005%, the lower limit of the amount of Sn is set to 0.005%.
  • the solid solubility limit of Sn in an austenite phase is low, and, in plain carbon steel, Sn causes cracks during hot-rolling or defects.
  • the amount of Sn is desirably decreased as much as possible.
  • Sn has a relatively large solid solubility limit, and thus, in certain types of ferritic stainless steel, similar to Cr or Mo, 0.1% or more of Sn is added thereto in order to strengthen a passivation film by actively adding Sn to steel.
  • martensitic stainless steel is austenite in a producing process thereof or during hardening heating.
  • Sn degrades hot workability, and, when steel is used in a high-temperature environment, aging embrittlement occurs. Therefore, there is an optimal range for the amount of Sn added.
  • the limit amount of Sn at which hot workability and high-temperature aging embrittlement characteristics are not deteriorated varies depending on the types of steel. In high-carbon martensitic stainless steel, the upper limit of the amount of Sn is 0.1%.
  • the amount of Sn is preferably set to 0.01% or higher.
  • Sn and N have an effect of suppressing sensitization caused by precipitation of Cr carbides in a hardening cooling process. However, this effect varies depending on the amount of C and thus is not consistent.
  • the present inventors studied the optimal balance between Sn, C, and N in high-carbon martensitic stainless steel having an as-quenched hardness of higher than 550 HV.
  • hot-rolled plates having a plate thickness of 6 mm were produced in a laboratory using steels in which 13.3% Cr-0.4% Si-0.5% Mn-0.027% P-0.001% S-0.005% Al-0.05% V-0.02% Mo-0.02% Cu steel was used as a base composition, the amount of C was changed in a range of 0.40% to 0.50%, the amount of N was changed in a range of 0.01% to 0.05%, and the amount of Sn was changed in a range of 0.000% to 0.20%, respectively.
  • hot-rolled plates were produced by heating ingots having a thickness of 100 mm at 1240°C and then hot-rolling the ingots to a plate thickness of 6 mm.
  • the hot-rolled plates were box-annealed at 850°C for four hours, thereby obtaining hot-rolled and annealed plates. These hot-rolled and annealed plates were held at 1050°C for 10 minutes, and then were air-hardened (air cooling, slow cooling), and the surfaces thereof were polished using a grain size #600 (JIS R 6001:1998 (corresponding to ISO 8486-1:1996 and ISO 8486-2:1996)). On each of the samples obtained as described above, a salt spray test regulated by JIS Z 2371:2000 (based on ISO 9227:1990) was performed for 24 hours, and the degree of rust was visually evaluated.
  • FIG. 1 the horizontal axis indicates the S value of Expression (1), and the vertical axis sequentially indicates A (PASS), B (FAIL), and C (FAIL) from the bottom. It was found that samples satisfying Expression (1) were evaluated as PASS in terms of corrosion resistance.
  • individual element names in the expression such as C, N, and Sn represent amounts (mass%) of the respective elements.
  • the S value may be lower than 2.0, and the effects are saturated even when the S value exceeds 4.25.
  • the high-carbon martensitic stainless steel according to the present embodiment preferably includes one or more of Nb: 0.005% to 0.05%, Ti: 0.005% to 0.05%, Zr: 0.005% to 0.05%, and B: 0.0005% to 0.0030%.
  • Nb 0.005% to 0.05%
  • Ti 0.005% to 0.05%
  • Zr 0.005% to 0.05%
  • B 0.0005% to 0.0030%.
  • Nb has an action of making Cr carbonitrides finer and accelerating solution treatment during hardening heating by being precipitated during hot rolling in a form of fine Nb(C, N) and acting as a precipitation nucleus of the Cr carbonitrides. Therefore, Nb is preferably added to steel as necessary. Since this effect is developed when 0.005% or more of Nb is added to steel, the lower limit of the amount of Nb is preferably set to 0.005%. However, when excess Nb is added to steel, there are cases in which, in a temperature region higher than heating temperature for hot rolling, coarse Nb(C, N) is precipitated, and defects resulting from inclusions are generated. Therefore, the upper limit of the amount of Nb is preferably set to 0.05%. The amount of Nb is more preferably set in a range of 0.01% to 0.03%.
  • Ti has an action of making Cr carbonitrides finer and accelerating solution treatment during hardening heating by being precipitated during hot rolling in a form of fine Ti(C, N) and acting as a precipitation nucleus of the Cr carbonitrides. Therefore, Ti is preferably added to steel as necessary. Since this effect is developed when 0.005% or more of Ti is added to steel, the lower limit of the amount of Ti is preferably set to 0.005%. However, when excess Ti is added to steel, there are cases in which, in a temperature region higher than heating temperature for hot rolling, coarse TiN is precipitated, and defects resulting from inclusions are generated. Therefore, the upper limit of the amount of Ti is preferably set to 0.05%. The amount of Ti is more preferably set in a range of 0.01% to 0.03%.
  • Zr has an action of making Cr carbonitrides finer and accelerating solution treatment during hardening heating by being precipitated during hot rolling in a form of fine Zr(C, N) and acting as a precipitation nucleus of the Cr carbonitrides. Therefore, Zr is preferably added to steel as necessary. Since this effect is developed when 0.005% or more of Zr is added to steel, the lower limit of the amount of Zr is preferably set to 0.005%. However, when excess Zr is added to steel, there are cases in which, in a temperature region higher than heating temperature for hot rolling, coarse Zr(C, N) is precipitated, and defects resulting from inclusions are generated. Therefore, the upper limit of the amount of Zr is preferably set to 0.05%. The amount of Zr is more preferably set in a range of 0.01% to 0.03%.
  • B Since B improves high-temperature ductility during hot rolling and suppresses a decrease in yield caused by edge cracks in a hot-rolled plate, B may be added to steel as necessary.
  • the lower limit of the amount of B is desirably set to 0.0005%.
  • the upper limit of the amount of B is set to 0.0030%.
  • the amount of B is more desirably set in a range of 0.0008% to 0.0015%.
  • the martensitic stainless steel according to the present embodiment is preferably produced by casting steel having the above-described composition, hot-rolling the obtained ingot so as to obtain a hot-rolled plate, coiling the hot-rolled plate, tempering (annealing) the coiled hot-rolled plate, and quenching the tempered hot-rolled plate.
  • the heating temperature during the hot rolling is set in a range of 1140°C to 1240°C
  • the coiling temperature is set in a range of 700°C to 840°C
  • the hot-rolled plate is annealed using a batch furnace at a temperature in a range of 700°C to 900°C for four hours or longer.
  • the heating temperature for the hot rolling is higher than 1240°C, a ⁇ single phase turns into a two-phase region of ⁇ + ⁇ . Cr, Si, and the like are concentrated in the ⁇ phase, C, N, Ni, and the like negatively segregate in the ⁇ phase, and the ⁇ phase inhibits formation of the ⁇ single phase during quenching. Therefore, hardenability is impaired.
  • the heating temperature for the hot rolling is lower than 1 140°C, a soaking time as a diffusion time for eliminating the segregation (solidification segregation) needs to be two hours or longer, and thus the productivity of hot rolling is significantly impaired, which is not preferable.
  • the finishing temperature (temperature during finishing rolling) of the hot rolling is set to 800°C or higher.
  • the coiling temperature is set in a range of 700°C to 900°C.
  • the metallographic structures become significantly different between the coolest portion and the hottest portion in a coil, this structural difference is not eliminated even after the coiled hot-rolled plate is annealed, and the material qualities become inconsistent in the coil, which is not preferable.
  • the coiling temperature is set to 700°C or higher, during the cooling of the coil, the carbide is precipitated and coarsened, and the hot-rolled plate is softened.
  • coiling temperature is higher than 900°C, thick oxide scales are formed on the surface, and problems such as degradation of corrosion resistance due to formation of a decarbonized phase or poor polishing properties after quenching are caused, which is not desirable.
  • the annealing conditions of the hot-rolled plate in order to improve workability before quenching, it is necessary to soften the hot-rolled plate by means of annealing. In a continuous annealing furnace, it is not possible to ensure a sufficient annealing time for softening. Thus, it is desirable to hold the hot-rolled plate in a temperature region of 700°C to 900°C for four hours or longer using a batch furnace. When the temperature is lower than 700°C or higher than 900°C, the hot-rolled plate is not sufficiently softened.
  • the hot-rolled plate when the hot-rolled plate is annealed at a temperature higher than 900°C for a long period of time, due to the influence of an atmosphere gas, nitrification or decarburization of the surface layer causes an inconsistent metallographic structure of the surface layer or a change in material qualities, which is not preferable.
  • the inconsistent temperature in the coil causes a change in material qualities in the coil.
  • the hot-rolled plate turns into a hot-rolled product by being pickled after the annealing, but a part of the annealed hot-rolled plate turns into a cold-rolled product by being cold-rolled and annealed.
  • the product As a hardening thermal treatment (hardening heating) of the product, the product is held at a temperature region of 950°C to 1100°C for 5 seconds to 10 minutes in a nitrogen atmosphere. After that, the product is quenched by air hardening. At a heating temperature of lower than 950°C, solution treatment of the carbonitrides becomes insufficient, and thus the target as-quenched hardness cannot be obtained.
  • the heating temperature is set to 950°C or higher, it becomes possible to solution-treat the carbonitrides, and a metallographic structure mainly including austenite can be obtained.
  • the heating temperature increases, delta ferrite is precipitated in an austenite matrix, and corrosion resistance or hardenability is impaired.
  • the heating time is desirably set to 1100°C or lower.
  • the time needs to be five seconds or longer in order to accelerate the solution treatment.
  • the time is shorter than five seconds, the amount of the solution heat-treated C and N is small, and sufficient hardness cannot be obtained.
  • the cooling rate of quenching is preferably in a range of 3°C/sec to 100°C/sec.
  • the finishing temperature was set to 900°C, and the hot-rolled plates were coiled at 800°C.
  • the coiled hot-rolled plates were, subsequently, held at 850°C for four hours and then were cooled in the furnace, thereby being tempered.
  • Hot-rolled plates having a crack with a deepness of 1 mm or more on the end surface were determined as FAIL since edge cracks were generated therein. The results are shown in the note column of Tables 3 and 4. Edge cracks having a deepness of less than1 mm were determined as slightly edge cracks.
  • the hardness after annealing (after tempering) was measured using a method described in JIS Z 2245:2011 (based on ISO 6508-1:2005). Hot-rolled plates having a hardness after annealing of higher than 92 HRB were determined as FAIL since the plates were hard. The results are shown in the note column of Tables 3 and 4.
  • the tempered hot-rolled plates were, subsequently, held at 1050°C in a thermal treatment furnace having a nitrogen atmosphere for 10 minutes, were ejected from the furnace, and then were air-hardened, thereby obtaining quenched steel plates.
  • the as-quenched hardness and the corrosion resistance were evaluated by the following method. The results are shown in Table 3 and 4.
  • a test specimen (No. 40) was oil-quenched, thereby obtaining a quenched steel plate.
  • numerical values outside the ranges regulated by the present embodiment were underlined. [Table 1] Classification Steel No.
  • each of the quenched specimens was polished using a milling machine so as to be flattened, was polished using sandpaper, and then was buffed, thereby being mirror-finished.
  • the salt spray test regulated by JIS Z 2371:2000 was performed, and the presence or absence of rust was evaluated. Specimens having no rust were determined as PASS. Specimens having defects on the finished surface were determined as FAIL.
  • the hardness after quenching was 550 Hv or higher, and rust was not generated due to addition of Sn in the salt spray test after the air hardening. This fact shows that the steel of the present invention has excellent corrosion resistance in a practical environment.
  • the corrosion resistance, the as-quenched hardness, and the toughness before quenching were insufficient or other characteristics (the raw material costs and the hot workability) were poor.
  • the comparative steels were determined as FAIL in terms of productivity, qualities, and/or costs. That is, for Nos.
  • the present invention it is possible to produce martensitic stainless steel having high hardness and excellent corrosion resistance at low cost with favorable productivity without adding a large amount of an expensive element such as Mo. Therefore, the present invention contributes to significant improvement of the producing costs and qualities of stainless steel for table knives, stainless kitchen knives, tools, and disc brakes for a motorcycle.

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Claims (2)

  1. Martensitischer Edelstahl mit ausgezeichneter Korrosionsbeständigkeit, bestehend aus: ausgedrückt in Massen-%,
    C: 0,40% bis 0,50%;
    Si: 0,25% bis 0,60%;
    Mn: 2,0% oder weniger;
    P: 0,035% oder weniger;
    S: 0,010% oder weniger;
    Cr: 11,0% bis 15,5%;
    Ni: 0,01% bis 0,60%;
    Cu: 0,50% oder weniger;
    Mo: 0,10% oder weniger;
    Sn: 0,005% bis 0,10%;
    V: 0,10% oder weniger;
    Al: 0,03% oder weniger;
    N: 0,01% bis 0,05%; und
    gegebenenfalls eines oder mehrere von:
    Nb: 0,005% bis 0,05%;
    Ti: 0,005% bis 0,05%;
    Zr: 0,005% bis 0,05%; und
    B: 0,0005% bis 0,0030%, und
    einem Rest, der Fe und unvermeidbare Verunreinigungen enthält,
    wobei die Mengen von C, N und Sn Ausdruck (1) erfüllen: S − Wert = 16 × Sn / C + 2 × N / C ≥ 0,40
    Figure imgb0004
     wobei C, N und Sn im oben genannten Ausdruck jeweils Mengen davon (in Massen-%) darstellen.
  2. Ein Verfahren zur Herstellung von martensitischem Edelstahl, umfassend:
    Gießen eines Stahls mit einer Zusammensetzung des martensitischen Edelstahls gemäß Anspruch 1, um einen Block zu erhalten;
    Erwärmen des erhaltenen Blocks bei einer Temperatur in einem Bereich von 1140°C bis 1240°C und anschließendem Warmwalzen des erwärmten Blocks, um eine warmgewalzte Platte zu erhalten;
    Aufrollen der erhaltenen warmgewalzten Platte;
    Tempern der aufgerollten warmgewalzten Platte bei einer Temperatur im Bereich von 700°C bis 900°C für vier Stunden; und
    Halten der Temperatur der getemperten warmgewalzten Platte in einem Bereich von 950°C bis 1100°C für 5 Sekunden bis 10 Minuten in einer Stickstoffatmosphäre und anschließendem Quenchen der warmgewalzten Platte, wobei das Quenchen Lufthärten ist, eine Endtemperatur des Warmwalzens 800°C oder höher ist und eine Aufrolltemperatur der warmgewalzten Platte in einem Bereich von 700°C bis 900°C liegt.
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JP6635890B2 (ja) * 2016-07-15 2020-01-29 日鉄ステンレス株式会社 製造性と耐食性に優れた刃物用マルテンサイト系ステンレス鋼板
CN107287533B (zh) * 2017-05-02 2018-10-16 山东太阳耐磨件有限公司 铲刀制备方法及铲刀
CN108441781B (zh) * 2018-02-28 2020-05-08 河钢股份有限公司承德分公司 一种高强耐腐蚀钢筋及其热处理方法
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CN112899571B (zh) * 2021-01-19 2022-03-08 山东钢铁股份有限公司 一种耐疲劳耐腐蚀锻压用圆钢及其制备方法
KR20230148843A (ko) * 2021-03-11 2023-10-25 닛테츠 스테인레스 가부시키가이샤 내식성이 우수한 마르텐사이트계 스테인리스 강판 및 그 제조 방법, 그리고 마르텐사이트계 스테인리스 칼날 제품
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