Precipitation hardening type martensitic stainless steel for pressing plate, and solid solution material and aging treatment material thereof

Abstract

Provided are: a precipitation-hardening martensitic stainless steel for a platen, which has high hardness and excellent flatness; a solid solution material for the stainless steel; and an aging-treated material for the stainless steel. The precipitation hardening martensitic stainless steel for a press plate has a prescribed component composition in which MA, which is defined by MA = [Ni] + 0.65 * [Mn] + 0.23 * [Si] + 0.62 * [Cr] + 0.25 * [Mo] + 0.35 * [Cu] + 30.6 * ([C] + [N])-16.5, is in the range of 1.0-4.5, and H, which is defined by H = [Cu] + 0.6 * [Ni] + 1.8 * [Si] + 3.8 * [Ti] + 1.8 * [Nb]-0.9 * [Mn]-13.8 * ([C] + [N]), is in the range of 5.0 or more. The solid solution material has a two-phase structure of a martensite phase and a retained austenite phase, the amount of the retained austenite phase being 0.2-8% by volume, and the hardness being less than 380 HV. The aging-treated material has a hardness of 450 HV or more.

Description

Technical Field

[0001] The present invention relates to precipitation-hardened martensitic stainless steel capable of providing a pressed plate having high hardness and excellent flatness, and its solution-treated material and aging-treated material. Background Art

[0002] Precipitation-hardening martensitic stainless steel such as SUS630, which can achieve high strength by precipitating an ε-Cu phase by adding Cu, is used for press plates used for producing laminates such as multilayer printed wiring boards by press forming.

[0003] For example, Patent Document 1 discloses a precipitation hardening martensitic stainless steel in which, in addition to the ε-Cu phase, Ti and Si are added to control the Ni 16 Ti6Si7 intermetallic compound phase (G phase) is distributed in the grains, thus maintaining high strength and toughness. The G phase precipitated by aging heat treatment, that is, Ni 16 Since X in X6Si7 can be substituted not only with Ti but also with Fe, Mn, and Nb, the component composition after adjusting the amount of Nb is particularly clarified.

[0004] Patent Document 2 discloses a method for manufacturing a pressed plate and a steel material thereof. In this method, austenitic stainless steel containing 1.0 to 4.0% Si by mass and having a high austenite ratio is subjected to necessary shape correction and then aging treatment, thereby increasing the surface hardness to 430 HV or higher through strain aging. This method points out that it is difficult to fully flatten a steel plate composed of hard stainless steel with a surface hardness of 400 HV or higher by simply performing shape correction through tempering or a tension tempering mill. Furthermore, when using martensitic stainless steel, flatness cannot be ensured during the quenching or tempering process. Furthermore, it is suggested that austenitic stainless steel with a low martensite content and a high austenite ratio should be used.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2021-134395

[0008] Patent Document 2: Japanese Patent Application Laid-Open No. 2008-297601 Summary of the Invention

[0009] However, in precipitation-hardening martensitic stainless steels such as SUS630, a predetermined hardness (strength) is achieved by performing an aging treatment at approximately 500°C after solution treatment at 1000°C or higher. In other words, precipitation-hardening martensitic stainless steels for press plates are required to have a hardness sufficient to allow shape correction after solution treatment, while also being able to increase their strength to a sufficient hardness during the subsequent aging treatment.

[0010] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a precipitation-hardened martensitic stainless steel capable of providing a pressed plate having high hardness and excellent flatness, and a solution-treated material thereof and an aging-treated material thereof.

[0011] The precipitation hardening martensitic stainless steel for a press plate of the present invention is characterized by containing, in mass%, C: 0.01-0.07%, Si: 0.05-2.25%, Mn: 0.5-5.0%, Ni: 4.5-10.0%, Cr: 10.0-17.0%, Mo: 0.1-1.50%, Cu: 0.30-5.0%, Al: 0.001-0.100%, N: 0.001-0.020%, Ti: 0.15-0.55%, Nb: 0.15-0.45%, Co: 0.03-0.80%, P: 0.04% or less, S: 0.0020% or less, and the remainder The present invention is a composition composed of Fe and inevitable impurities, and in the composition, when the mass% of element M is set to [M], MA defined by MA=[Ni]+0.65×[Mn]+0.23×[Si]+0.62×[Cr]+0.25×[Mo]+0.35×[Cu]+30.6×([C]+[N])-16.5 is in the range of 1.0 to 4.5, and H defined by H=[Cu]+0.6×[Ni]+1.8×[Si]+3.8×[Ti]+1.8×[Nb]-0.9×[Mn]-13.8×([C]+[N]) is in the range of 5.0 or more.

[0012] According to this feature, a pressed plate having high hardness and excellent flatness can be obtained through solution treatment and aging treatment.

[0013] The present invention also relates to a solution-hardened martensitic stainless steel material for a press plate, characterized in that it contains, by mass%, C: 0.01-0.07%, Si: 0.05-2.25%, Mn: 0.5-5.0%, Ni: 4.5-10.0%, Cr: 10.0-17.0%, Mo: 0.1-1.50%, Cu: 0.30-5.0%, Al: 0.001-0.100%, N: 0.001-0.020%, Ti: 0.15-0.55%, Nb: 0.15-0.45%, and Co: 0.03-0.80%. %, P: less than 0.04%, S: less than 0.0020%, and the remainder consisting of a component consisting of Fe and inevitable impurities, in which, when the mass% of the element M is defined as [M], H defined by H=[Cu]+0.6×[Ni]+1.8×[Si]+3.8×[Ti]+1.8×[Nb]-0.9×[Mn]-13.8×([C]+[N]) is in the range of 5.0 or more, and the material has a dual-phase structure of a martensite phase+retained austenite phase, the amount of the retained austenite phase is 0.2 to 8% by volume, and the material has a hardness of less than 380 HV.

[0014] According to this feature, shape correction is easily performed, and high hardness is imparted by aging treatment, so that a press plate having high hardness and excellent flatness can be obtained.

[0015] The above invention may also be characterized in that, in the composition, when the mass percentage of the element M is represented by [M], MA, defined by MA = [Ni] + 0.65 × [Mn] + 0.23 × [Si] + 0.62 × [Cr] + 0.25 × [Mo] + 0.35 × [Cu] + 30.6 × ([C] + [N]) - 16.5, is in the range of 1.0 to 4.5. This feature facilitates shape correction, and, by imparting high hardness through aging treatment, a pressed plate having high hardness and excellent flatness can be obtained.

[0016] The aging treatment material of the precipitation hardening martensitic stainless steel for press plates according to the present invention is characterized by containing, in mass%, C: 0.01-0.07%, Si: 0.05-2.25%, Mn: 0.5-5.0%, Ni: 4.5-10.0%, Cr: 10.0-17.0%, Mo: 0.1-1.50%, Cu: 0.30-5.0%, Al: 0.001-0.100%, N: 0.001-0.020%, Ti: 0.15-0.55%, Nb: 0.15-0.4 5%, Co: 0.03-0.80%, P: less than 0.04%, S: less than 0.0020%, and the remainder is composed of a component consisting of Fe and inevitable impurities. In this component composition, when the mass% of element M is set to [M], MA defined by MA=[Ni]+0.65×[Mn]+0.23×[Si]+0.62×[Cr]+0.25×[Mo]+0.35×[Cu]+30.6×([C]+[N])-16.5 is in the range of 1.0 to 4.5, and has a hardness of more than 450HV.

[0017] According to this feature, a press plate having high hardness and excellent flatness can be obtained.

[0018] The present invention may also be characterized in that, in the composition, when the mass percentage of the element M is defined as [M], H, defined by H = [Cu] + 0.6 × [Ni] + 1.8 × [Si] + 3.8 × [Ti] + 1.8 × [Nb] - 0.9 × [Mn] - 13.8 × ([C] + [N]), is in a range of 5.0 or greater. This feature enables a pressed plate having high hardness and excellent flatness to be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a table showing the composition of the steel used in the test.

[0020] Figure 2 This is a table showing the test results. DETAILED DESCRIPTION

[0021] As described above, precipitation-hardening martensitic stainless steel for press plates requires a low hardness after solution treatment, while also being able to achieve sufficient hardness through aging. To achieve this hardness, the inventors conducted extensive research on the effects of the simultaneous addition of Nb and Co. They discovered that by adjusting the steel composition so that an austenite phase remains after solution treatment, the desired hardness can be achieved both after solution treatment and after aging. The following composition is a possible example of such a steel.

[0022] That is, the precipitation-hardening martensitic stainless steel for the press plate involved in this embodiment has a composition containing both Nb and Co, and containing, in terms of mass%, C: 0.01~0.07%, Si: 0.05~2.25%, Mn: 0.5~5.0%, Ni: 4.5~10.0%, Cr: 10.0~17.0%, Mo: 0.1~1.50%, Cu: 0.30~5.0%, Al: 0.001~0.100%, N: 0.001~0.020%, Ti: 0.15~0.55%, Nb: 0.15~0.45%, Co: 0.03~0.80%, P: less than 0.04%, and S: less than 0.0020%.

[0023] Furthermore, in this component composition, when the mass % of element M is set to [M], MA defined by MA = [Ni] + 0.65×[Mn] + 0.23×[Si] + 0.62×[Cr] + 0.25×[Mo] + 0.35×[Cu] + 30.6×([C] + [N]) - 16.5 is in the range of 1.0 to 4.5, and H defined by H = [Cu] + 0.6×[Ni] + 1.8×[Si] + 3.8×[Ti] + 1.8×[Nb] - 0.9×[Mn] - 13.8×([C] + [N]) is in the range of 5.0 or more.

[0024] Here, it is found that in the composition containing only a small amount of Co while containing Nb, the hardness difference before and after aging treatment can be made large enough, and the hardness before aging treatment, that is, after solution treatment, can be stabilized to a hardness that can correct the shape. Co is a stabilizing element of the austenite phase, but the value of MA is an index of the stabilization of the austenite phase relative to the small amount of Co. By making the value of MA within the above range, the amount of retained austenite (retained γ phase) after solution treatment can be kept at an appropriate amount, so that the hardness after solution treatment is low, thereby being able to obtain excellent flatness by correcting the shape of the sheet. However, relatively speaking, compared to the G phase, Co is more contained in the ε-Cu phase, thereby affecting the precipitation morphology of the compound. The value of H is an index of the hardness obtained after aging treatment, but the range of the value of H is determined in consideration of the precipitation morphology of the compound added relative to the small amount of Co. By making the value of H within the above range, it is possible to obtain sufficient hardness from the hardness that can correct the shape by aging treatment. That is, by containing only a small amount of Co, the mechanical strength of the base material composed of the martensite phase can be improved, and the mechanical strength of the aged material can be maintained at a high level despite the residual austenite phase.

[0025] The material after solution treatment is required to have a dual-phase structure of martensite and retained austenite, with the retained austenite content being 0.2 to 8% by volume and the hardness being less than 380 HV. To obtain such a solutionized material, the MA value is within the aforementioned range of 1.0 to 4.5, preferably 1.2 to 3.5, and more preferably 1.4 to 2.5.

[0026] Furthermore, as an aging-treated material, a hardness of 450 HV or higher is required. To obtain such an aging-treated material, the H value is within the aforementioned range of 5.0 or higher, preferably 6.0 to 15.0, and more preferably 7.0 to 12.0. Furthermore, the upper limit of the H value is preferably set to prevent embrittlement of the steel during production.

[0027] The press plate of this embodiment can be manufactured as follows. First, the steel with the aforementioned composition is cast and hot-rolled, followed by cold-rolling to obtain a strip steel material of a predetermined thickness. The resulting strip steel material is solution-treated, and during cooling, the austenite phase is partially retained and transformed into martensite. During the solution treatment, a predetermined temperature within the range of, for example, 1000-1150°C is maintained, followed by water cooling. This produces a solution-treated material of precipitation-hardening martensitic stainless steel for the press plate.

[0028] Next, the strip steel material, which has become a solutionized material, undergoes shape correction. For example, a tension leveler can be suitably used for shape correction. By presetting the hardness of the solutionized material to less than 380 HV, the burden on the manufacturing process during shape correction can be reduced. For example, excellent flatness can be achieved simply by using a tension leveler for shape correction.

[0029] Finally, the steel sheet is aged to achieve the desired hardness. During the aging treatment, for example, the steel sheet can be held at 400-600°C for 30 minutes to 10 hours. This allows the hardness after aging to reach the aforementioned 450 HV or higher. This produces an aged material of precipitation-hardened martensitic stainless steel for press plates.

[0030] As described above, a press plate having high hardness and excellent flatness can be obtained.

[0031] [Tests of solution treated and aging treated materials]

[0032] Next, the results of producing plate materials and conducting hardness and other tests on a plurality of precipitation-hardening martensitic stainless steels will be described.

[0033] about Figure 120 kg steel ingots were cast from the steel compositions shown in Examples 1 to 11 and Comparative Examples 1 to 8, respectively. These ingots were hot forged to produce forged plates, which were then cold rolled to produce 1.6 mm thick steel plates. The resulting steel plates were solution treated at 1050°C for 2.5 minutes and then cooled to form solution-treated steel. Furthermore, a portion of the solution-treated steel was shape-corrected and aged to produce aged steel.

[0034] like Figure 2 As shown, the Vickers hardness (solution hardness) of the obtained solutionized material was measured, and the amount of retained γ phase was further measured. The amount of retained γ phase was measured using FE-SEM (field emission electron microscope; JSM-7001F manufactured by JEOL Ltd.) and EBSD (electron backscatter diffraction). In addition, the flatness of the solutionized material after shape correction was measured. Flatness is determined by bringing a 2m ruler into contact with the steel plate placed on the platform from above and judging it based on the maximum value of the distance between the upper surface of the steel plate and the lower surface of the ruler. When the distance is less than 1mm, it is judged as "excellent" and recorded as "◎". Similarly, when it exceeds 1mm and is less than 3mm, it is judged as "good" and recorded as "○", when it exceeds 3mm and is less than 5mm, it is judged as "acceptable" and recorded as "△", and when it exceeds 5mm, it is judged as "no" and recorded as "×". Furthermore, the Vickers hardness (aging hardness) of the aging treated material was also measured.

[0035] As shown in the figure, for the steels of Examples 1 to 11, the flatness of the solution-treated steel after shape correction was all rated "Acceptable" or higher, and the hardness of the aged steel was 450 HV or higher. Furthermore, the MA values ​​were within the range of 1.0 to 4.5, the H values ​​were within the range of 5.0 or higher, and the retained γ content of the solution-treated steel was within the range of 0.2 to 8.0% by volume. With the exception of Example 1, the hardness of the solution-treated steel was 380 HV or lower. In Example 1, the hardness was higher at 386 HV, but the flatness was "Acceptable."

[0036] On the other hand, in Comparative Example 1, the Mn content is lower than in the examples, resulting in a low MA value. Furthermore, in Comparative Example 2, the Ni content is low, resulting in a low MA value. Furthermore, the amount of retained γ is low in all cases, and the flatness rating is "No." This low amount of retained γ is believed to increase the hardness of the solutionized material, and even shape correction does not improve flatness.

[0037] In Comparative Example 3, while the amounts of each element in the composition are comparable to those in the Examples, the MA value is large and the H value is small. As a result, the hardness of the aged material is low. It is believed that increasing the MA value increases the amount of retained γ, which excessively reduces the hardness of the solutionized material, preventing the aged material from achieving sufficient hardness. Furthermore, decreasing the H value is believed to reduce the precipitation hardening ability during the aging treatment, potentially contributing to the inability to achieve sufficient hardness in the aged material.

[0038] In Comparative Example 4, although the amounts of the various elements in the composition are comparable to those in the Examples, the H value is small. Consequently, the hardness of the aged material is low. This is presumably because, while the solution-treated material has the same hardness as in the Examples, the H value is small, resulting in low precipitation hardening ability during the aging treatment.

[0039] In Comparative Example 5, the Si content is low. As a result, the hardness of the aged material is low. This is believed to be because, although the hardness is comparable to that of the examples at the time of solutionization, the low Si content prevents sufficient hardness from being achieved through aging.

[0040] Comparative Example 6 contains almost no Co, and the other components and MA values ​​are approximately the same as those of Example 7. In Comparative Example 6, while the solution hardness is also approximately the same as that of Example 7, the aging hardness is lower. In other words, it is clear that the Co content in Example 7, while barely affecting the solution hardness, significantly contributes to the aging hardness. This is also true for the relationship between Comparative Example 7 and Example 11, and for the relationship between Comparative Example 8 and Example 2.

[0041] Thus, in the case of the steels of Examples 1 to 11, it is possible to impart relatively low hardness to the solutionized material, enabling excellent flatness to be achieved through shape correction, while also imparting high hardness to the aged material. In other words, precipitation-hardening martensitic stainless steel, and its solutionized and aged materials, are obtained, which can provide a press plate having both high hardness and excellent flatness.

[0042] In addition, the ranges of the chemical compositions of the steels of the present invention including Examples 1 to 11 are specified as follows.

[0043] C contributes to mechanical strength after solid solution formation, while also stabilizing the austenite phase. It suppresses the formation of delta ferrite at high temperatures and increases the amount of retained austenite after solution treatment. Therefore, excessive C content reduces precipitation hardening ability during aging treatment. Taking this into account, the C content, in mass%, is within the range of 0.01 to 0.07%, preferably 0.02 to 0.06%, and more preferably 0.03 to 0.05%.

[0044] Si is added for deoxidation and is an important element for generating G phase through aging treatment to achieve mechanical strength. On the other hand, Si is a ferrite-forming element, and excessive Si content increases the delta ferrite phase, deteriorating hot workability. Taking this into account, the Si content is set within a range of 0.05 to 2.25% by mass, preferably 1.05 to 2.05%, and more preferably 1.35 to 1.85%.

[0045] Mn is an element that stabilizes the austenite phase, suppresses the formation of delta ferrite, and contributes to the formation of retained austenite. On the other hand, excessive amounts of Mn can cause a large amount of retained austenite, reducing the mechanical strength after aging. Taking this into account, the Mn content, in mass%, is within the range of 0.5 to 5.0%, preferably 0.6 to 4.0%, and more preferably 0.8 to 3.0%.

[0046] Ni is an element that stabilizes the austenite phase, suppresses the formation of the delta ferrite phase, and contributes to the formation of retained austenite. Furthermore, it is an important element that contributes to improving mechanical strength by forming the G phase during aging. On the other hand, if contained in excessive amounts, a large amount of the austenite phase remains, which reduces the mechanical strength after aging. Taking these factors into consideration, the Ni content is within the range of 4.5 to 10.0% by mass, preferably 5.5 to 9.0%, and more preferably 6.5 to 8.0%.

[0047] Cr is an element necessary for ensuring the corrosion resistance of stainless steel and also contributes to the formation of retained austenite. On the other hand, excessive Cr content can form a delta ferrite phase, reducing hot workability. Taking this into account, the Cr content, in mass%, is within the range of 10.0 to 17.0%, preferably 12.0 to 16.0%, and more preferably 13.0 to 15.0%.

[0048] Mo is an element necessary for ensuring the corrosion resistance of stainless steel and also contributes to the formation of retained austenite. On the other hand, excessive Mo content can lead to the formation of delta ferrite, which can reduce hot workability. Taking this into account, the Mo content, in mass%, is within the range of 0.1 to 1.50%, preferably 0.6 to 1.20%, and more preferably 0.7 to 1.00%.

[0049] Cu is an element that stabilizes the austenite phase, suppresses the formation of the delta ferrite phase, and contributes to the formation of retained austenite. Furthermore, it is an important element that contributes to improving mechanical strength by forming the ε-Cu phase through aging treatment. On the other hand, if it is contained in excessive amounts, a large amount of the austenite phase remains, thereby reducing the mechanical strength after aging treatment. Taking these into account, the Cu content is within the range of 0.30 to 5.0% by mass, preferably within the range of 0.40 to 3.0%, and more preferably within the range of 0.50 to 1.5%.

[0050] Al is added for deoxidation and is effective for stably containing Nb and Ti, which are easily oxidized and have poor addition utilization in the melt. On the other hand, since it increases the martensitic transformation start temperature (Ms point), excessive inclusion inhibits the formation of retained austenite. Furthermore, it increases the delta ferrite phase, deteriorating hot workability. Taking these factors into consideration, the Al content is within the range of 0.001 to 0.100% by mass, preferably 0.002 to 0.060%, and more preferably 0.002 to 0.020%.

[0051] Nitrogen stabilizes the austenite phase, suppresses the formation of delta ferrite, and contributes to the formation of retained austenite. On the other hand, excessive amounts of nitrogen cause a large amount of retained austenite, reducing the mechanical strength after aging. Furthermore, it primarily forms nitrides with Ti, creating a starting point for the plate's failure. Furthermore, this can cause the Ms point to shift, potentially leading to cracks in the slab. Taking these factors into consideration, the nitrogen content, in mass%, is set within the range of 0.001 to 0.020%, preferably 0.002 to 0.015%, and more preferably 0.003 to 0.010%.

[0052] Ti is an important element that contributes to mechanical strength by forming a G phase through aging treatment. However, excessive Ti content can form a delta ferrite phase, reducing hot workability. It can also shift the Ms point, potentially causing cracks in the slab. Taking these factors into consideration, the Ti content is set within a range of 0.15-0.55% by mass, preferably 0.20-0.50%, and more preferably 0.25-0.45%.

[0053] Nb is an important element that contributes to mechanical strength by forming a G phase through aging. However, excessive Nb content can form a delta ferrite phase, reducing hot workability. It can also shift the Ms point, potentially causing cracks in the slab. Taking these factors into consideration, the Nb content, as a percentage by mass, is within the range of 0.15-0.45%, preferably 0.20-0.40%, and more preferably 0.25-0.35%.

[0054] Co stabilizes the passive film, improving the corrosion resistance of stainless steel, and acts as a stabilizing element for the austenite phase, lowering the Ms point and affecting the formation of retained austenite. Furthermore, by improving hardenability, it increases the mechanical strength of the base material (matrix), ensuring the mechanical strength of the aged material. On the other hand, if excessively contained, excessive retained austenite is generated during solution treatment, and even with aging treatment, sufficient hardness cannot be achieved, and toughness is reduced. Furthermore, in the aged plates made from the steels of Examples 1 to 11, it was observed that Co contained more Co in the ε-Cu phase and less Co in the G phase. This indicates that Co affects the precipitation morphology of the ε-Cu phase and the G phase. Taking these into account, the Co content is set within the range of 0.03 to 0.80% by mass, preferably within the range of 0.05 to 0.50%, and more preferably within the range of 0.06 to 0.30%.

[0055] Phosphorus (P) is an element that inevitably enters steel. It segregates at grain boundaries and also concentrates in the final solidified portion during casting, promoting solidification cracking. It also reduces hot workability. Therefore, it is desirable to minimize its content, but excessive refining can increase manufacturing costs. Taking these factors into consideration, the P content is controlled to be 0.04% or less, preferably 0.030% or less, and more preferably 0.025% or less, in terms of mass%.

[0056] S is an element that inevitably contaminates steel. It forms compounds with Mn and forms inclusions, reducing corrosion resistance. Furthermore, it segregates at grain boundaries, reducing hot workability. Therefore, it is desirable to minimize its content, but excessive refining increases manufacturing costs. Taking this into account, the S content, in mass%, is set to 0.0020% or less, preferably 0.0015% or less, and more preferably 0.0010% or less.

[0057] The representative embodiments of the present invention and variations based thereon have been described above, but the present invention is not necessarily limited thereto. Those skilled in the art can find various alternative embodiments and variations without departing from the spirit of the present invention or the appended claims.

Claims

1. A precipitation hardening martensitic stainless steel for a press plate, characterized in that: The invention has a composition comprising, in mass%, 0.01 to 0.07% C, 0.05 to 2.25% Si, 0.5 to 5.0% Mn, 4.5 to 10.0% Ni, 10.0 to 17.0% Cr, 0.1 to 1.50% Mo, 0.30 to 5.0% Cu, 0.001 to 0.100% Al, 0.001 to 0.020% N, 0.15 to 0.55% Ti, 0.15 to 0.45% Nb, 0.03 to 0.80% Co, 0.04% or less P, and 0.0020% or less S, with the remainder being Fe and unavoidable impurities. In the above-mentioned component composition, when the mass % of element M is set to [M], MA defined by MA=[Ni]+0.65×[Mn]+0.23×[Si]+0.62×[Cr]+0.25×[Mo]+0.35×[Cu]+30.6×([C]+[N])-16.5 is in the range of 1.0 to 4.5, and H defined by H=[Cu]+0.6×[Ni]+1.8×[Si]+3.8×[Ti]+1.8×[Nb]-0.9×[Mn]-13.8×([C]+[N]) is in the range of 5.0 or more.

2. A solid solution material of precipitation hardening martensitic stainless steel for a press plate, characterized in that: The invention has a composition comprising, in mass%, 0.01 to 0.07% C, 0.05 to 2.25% Si, 0.5 to 5.0% Mn, 4.5 to 10.0% Ni, 10.0 to 17.0% Cr, 0.1 to 1.50% Mo, 0.30 to 5.0% Cu, 0.001 to 0.100% Al, 0.001 to 0.020% N, 0.15 to 0.55% Ti, 0.15 to 0.45% Nb, 0.03 to 0.80% Co, 0.04% or less P, and 0.0020% or less S, with the remainder being Fe and unavoidable impurities. In the above composition, when the mass % of the element M is defined as [M], H defined by H=[Cu]+0.6×[Ni]+1.8×[Si]+3.8×[Ti]+1.8×[Nb]-0.9×[Mn]-13.8×([C]+[N]) is in the range of 5.0 or more, The invention has a dual-phase structure of a martensite phase and a retained austenite phase, wherein the amount of the retained austenite phase is 0.2 to 8% by volume, and has a hardness lower than 380 HV.

3. The solution-treated material of precipitation-hardening martensitic stainless steel for a press plate according to claim 2, wherein: In the above composition, when the mass % of element M is represented by [M], MA defined by MA=[Ni]+0.65×[Mn]+0.23×[Si]+0.62×[Cr]+0.25×[Mo]+0.35×[Cu]+30.6×([C]+[N])-16.5 is in the range of 1.0 to 4.

5.

4. An aging treated material of precipitation hardening martensitic stainless steel for a press plate, characterized in that: The invention has a composition containing, in mass%, C: 0.01-0.07%, Si: 0.05-2.25%, Mn: 0.5-5.0%, Ni: 4.5-10.0%, Cr: 10.0-17.0%, Mo: 0.1-1.50%, Cu: 0.30-5.0%, Al: 0.001-0.100%, N: 0.001-0.020%, Ti: 0.15-0.55%, Nb: 0.15-0.45%, Co: 0.03-0.80%, P: 0.04% or less, S: 0.0020% or less, with the remainder being Fe and unavoidable impurities. In the above composition, when the mass % of the element M is represented by [M], MA defined by MA=[Ni]+0.65×[Mn]+0.23×[Si]+0.62×[Cr]+0.25×[Mo]+0.35×[Cu]+30.6×([C]+[N])-16.5 is in the range of 1.0 to 4.5, It has a hardness of over 450HV.

5. The aging treated material of precipitation hardening martensitic stainless steel for press plate according to claim 4, characterized in that: In the above composition, H, which is defined by H=[Cu]+0.6×[Ni]+1.8×[Si]+3.8×[Ti]+1.8×[Nb]-0.9×[Mn]-13.8×([C]+[N]), is in a range of 5.0 or more.

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