JP2020056078A - Martensitic stainless steel material, manufacturing method therefor, and slide member - Google Patents

Abstract

To further enhance aggressive abrasion resistance in existing martensitic steel kinds.SOLUTION: There is provided a martensitic stainless steel sheet having a chemical composition containing, by mass%, C:0.10 to 0.50%, Si:0.02 to 1.0%, Mn:0.02 to 1.0%, Ni:0.1 to 5.0%, Cr:12.0 to 18.0%, Ti:0 to 0.5%, Nb:0 to 0.5%, Zr:0 to 0.5%, V:0 to 0.5%, W:0 to 0.5%, and the balance Fe with inevitable impurities, and one or more kind selected from a group of Ti, Nb, Zr, V, and W of total 0.25 to 2.0%, and having area percentage of carbide of 1.0% or more in an observation surface in parallel to a rolling surface, and number density of carbide with circle equivalent boundary length of 10.0 μm or more of 60 or less per 2200 μm.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a martensitic stainless steel material having improved durability against abrasive wear and a method for producing the same. Further, the present invention relates to a sliding member using the martensitic stainless steel material.

  Martensitic stainless steel generally has good wear resistance due to its hard metal base. However, in many cases, the material does not have satisfactory durability against so-called "abrasive wear" in which the material surface is scraped off by a sliding surface of a contact partner material or hard foreign particles. Examples of applications where abrasive wear is likely to be a problem include a blade member, a tool member, a loom member that comes into contact with a yarn, and a current-carrying member that comes into sliding contact with another member.

  As a method for imparting abrasive wear resistance, a method of dispersing carbides of elements such as Ti, Nb, Zr, V, and W in a matrix (metal base) of a steel material is known (Patent Document 1). These carbides have a high melting point and are extremely hard. The amount generated is substantially determined at the time of casting.

JP 2000-192197 A

  Recently, there has been a demand for a stainless steel material having more improved abrasion resistance than the steel material disclosed in Patent Document 1. However, there is a limit to the improvement of abrasive wear resistance by hard carbide of elements such as Ti, Nb, Zr, V, and W. In addition, a significant review of the alloy components and a significant change in the manufacturing process require a great deal of cost.

  An object of the present invention is to provide a stainless steel material that further improves the abrasive wear resistance of existing martensitic steels by utilizing the effect of improving the abrasive wear resistance of the hard carbide.

  In the manufacturing process of a martensitic stainless steel sheet, usually, "hot rolled sheet annealing" is performed for a long time after hot rolling using a bell-type annealing furnace or the like. By this hot-rolled sheet annealing, the martensite phase present in the hot-rolled steel sheet is decomposed into a Cr-based carbide and a soft ferrite phase. This is because if a hard martensite phase exists before cold rolling, it becomes difficult to accurately perform cold rolling to a predetermined thickness. In addition, in the `` quenching treatment '' performed to obtain a martensite structure, when importance is placed on productivity, the temperature is usually rapidly raised to a predetermined heating temperature, and when the temperature is reached, the product is taken out of the furnace and immediately. A cooling heat pattern (so-called "soaking 0 seconds") is employed. In this case, a steel material having a structure in which a large number of relatively large Cr carbides remain in the martensite phase is obtained. On the other hand, in applications where importance is placed on wear resistance, it is advantageous to obtain a martensite structure as hard as possible. For that purpose, it is necessary to sufficiently dissolve the carbide in the austenite phase in the high austenite temperature range in the quenching treatment. In this case, a martensite structure in which hard carbides of elements such as Ti, Nb, Zr, V, and W remain but Cr carbides hardly exist is obtained.

  According to the study of the inventors, it has been found that the Cr carbide itself contributes to imparting a resistance to abrasive wear by controlling its abundance and size within a specific range. That is, in the present invention, in addition to hard carbides of elements such as Ti, Nb, Zr, V, and W, Cr carbides are directly used for improving abrasive wear resistance. Such an idea has never been seen before. Specifically, the following invention is disclosed.

[1] In mass%, C: 0.10 to 0.50%, Si: 0.02 to 1.0%, Mn: 0.02 to 1.0%, Ni: 0.1 to 5.0% , Cr: 12.0 to 18.0%, Ti: 0 to 0.5%, Nb: 0 to 0.5%, Zr: 0 to 0.5%, V: 0 to 0.5%, W: 0 to 0.5%, with the balance being Fe and inevitable impurities, having a chemical composition containing 0.25 to 2.0% in total of at least one selected from the group consisting of Ti, Nb, Zr, V and W. Then, on an observation surface whose surface is polished and finished by electrolytic etching, the area density of carbides is 1.0% or more, and the number density of carbides having a circumference equivalent to a circle of 10.0 μm or more is 60 or less per 2200 μm ^2. , Martensitic stainless steel.
[2] On a steel material whose surface has been adjusted to a structure in which the number density of carbides having a circumference equivalent to 10.0 μm or more is 90 or more per 2200 μm ^{2 on} the observation surface finished by electrolytic etching after polishing the surface. Quenching to form a martensitic structure after heating under the condition that the maximum attained temperature T _M is 1000 to 1100 ° C. and the residence time in the temperature range of 1000 ° C. to T _M (° C.) is 3 to 10 seconds. The process for producing a martensitic stainless steel material according to the above [1], wherein the process is performed.
[3] The method for producing a martensitic stainless steel material according to the above [2], wherein the steel material is a steel plate having a thickness of 0.1 to 3.5 mm.
[4] The method for producing a martensitic stainless steel material according to the above [2] or [3], wherein after the quenching, a tempering treatment is performed at 150 to 700 ° C for 1 to 120 minutes.
[5] A sliding member using the martensitic stainless steel material according to [1].

  The “circumferential perimeter” of a given carbide particle means the circumference of a circle having the same area as the particle.

  ADVANTAGE OF THE INVENTION According to this invention, the further improvement of the abrasive wear resistance was able to be aimed at using the conventionally well-known martensitic stainless steel type.

An optical microscope photograph of a martensitic stainless steel material of Comparative Example No. A2-14 in which many coarse carbide particles are present. Binary image obtained by image processing of the photograph of FIG. The optical microscope photograph of the martensitic stainless steel material of the present invention example No. A2-16 which has a small amount of coarse carbide particles. Binary image obtained by image processing of the photograph of FIG.

(Target steel type)
In the present invention, a specific content of at least one of Ti, Nb, Zr, V, and W among martensitic stainless steels which form a martensitic structure at room temperature when cooled from a high-temperature austenite single-phase temperature region is specified. For steel types contained in the range. The specific chemical composition range is as follows.
In mass%, C: 0.10 to 0.50%, Si: 0.02 to 1.0%, Mn: 0.02 to 1.0%, Ni: 0.1 to 5.0%, Cr: 12.0 to 18.0%, Ti: 0 to 0.5%, Nb: 0 to 0.5%, Zr: 0 to 0.5%, V: 0 to 0.5%, W: 0 to 0% Chemical composition containing 0.2% to 2.0% of at least one selected from the group consisting of Ti, Nb, Zr, V, and W, with the balance being Fe and inevitable impurities.

  Hereinafter, “%” regarding the chemical composition of steel means mass% unless otherwise specified. The content of each element can be determined within the above range. However, considering a sufficient level of hardness of the martensite phase and cost, the C content is 0.20 to 0.50%, Content is 0.2 to 0.8%, Mn content is 0.2 to 8%, Ni content is 0.1 to 0.5%, and Cr content is 12.0 to 15.0%. Is more preferable.

  Ti, Nb, Zr, V and W are elements constituting extremely hard carbide. In order to sufficiently exhibit abrasive wear resistance, one or more of these elements must be contained in a total content of 0.25% or more. On the other hand, if the total content of Ti, Nb, Zr, V, and W is too high, the productivity may be reduced. For example, Ti deteriorates the flow of molten metal at the time of smelting casting, and Nb precipitates as an intermetallic compound and becomes a factor of reducing toughness. As a result of various studies, the total content of Ti, Nb, Zr, V, and W is limited to a range of 2.0% or less, and more preferably 0.6% or less. In addition, it is preferable that each content of each element of Ti, Nb, Zr, V, and W is made into the range of 0.5% or less. Aiming for a higher content may lead to an increase in steelmaking costs.

〔carbide〕
In the present invention, in order to improve abrasive wear resistance, a structure state in which carbides of one or more elements of Ti, Nb, Zr, V, and W are dispersed. The carbides of these elements have a high melting point and form in molten steel before casting. Even if a heat history is added in the subsequent manufacturing process, it remains in the steel material with almost no change. This type of carbide is very hard. The provision of abrasive wear resistance by such a hard carbide is disclosed in Patent Document 1 and the like, and the effect of the present invention is also utilized in the present invention. When the chemical composition of the steel is controlled within the above range, the effect of improving abrasive wear resistance by hard carbide of at least one element selected from Ti, Nb, Zr, V and W can be enjoyed.

In the present invention, a Cr carbide whose size is controlled to a relatively small size is used in order to obtain a further effect of improving abrasive wear resistance. Cr carbide is mainly a Cr ₂₃ C ₆ type precipitation phase, and is usually generated in a large amount in a steel material when a martensite phase is decomposed into a Cr carbide and a ferrite phase by hot-rolled sheet annealing. Then, at the time of high-temperature heating in the "quenching treatment" performed to obtain a martensite structure, the Cr carbide solid-dissolves in the austenite phase.

  Generally, in the quenching treatment when producing a martensitic stainless steel material, a short-time heating with a soaking temperature of 0 seconds is often performed in the austenite single-phase temperature range. In this case, the cooling is started before the complete dissolution and disappearance of the Cr carbide, so that a steel material having a microstructure in which the Cr carbide remains in a matrix (metal base) composed of a martensite phase is obtained. Since the heat treatment can be performed in a short time, the productivity is high. Further, the hardness of the martensite phase is relatively low, which is advantageous in terms of workability. On the other hand, when it is desired to obtain a martensite structure as hard as possible, it is advantageous to carefully carry out heating in the quenching treatment to cause C constituting the Cr carbide to form a solid solution in the austenite matrix as much as possible. In this case, a martensite structure having almost no Cr carbide is obtained, and a hard martensite phase is obtained because the amount of C dissolved in the martensite phase is large. Since the wear resistance is improved by hardening the matrix, it is advantageous for applications such as cutting tools. However, there is room for improvement in abrasive wear resistance.

  In the present invention, by controlling the conditions of the quenching treatment strictly as described later, a metal structure in which a sufficient amount of Cr carbides capable of exhibiting the effect of improving the abrasive wear resistance is obtained. Specifically, it is necessary that the area ratio of carbide is 1.0% or more on the observation surface whose surface is polished and finished by electrolytic etching. The carbides for which the area ratio is measured include both Ti, Nb, Zr, V, and W carbides and Cr carbides. Since the amounts of carbides of Ti, Nb, Zr, V, and W hardly change by the quenching treatment, unless the Cr carbide is sufficiently present, the regulation of “area ratio of carbides of 1.0% or more” cannot be satisfied. It is more preferable that the area ratio of the carbide is adjusted in the range of 8.0% or less.

On the other hand, if there are many coarse carbides, the effect of improving abrasive wear resistance cannot be obtained. The reason is that Cr carbide, which is not as hard as Ti, Nb, Zr, V and W carbides, is considered to exhibit the effect of improving abrasive wear resistance only by dispersing as relatively small particles. Can be In addition, when the amount of coarse Cr carbides is large, the amount of solute C in the matrix is also small. Therefore, the wear resistance of the matrix composed of the martensite phase is reduced, and the abrasive wear resistance is reduced. It is presumed that this will have an adverse effect on the improvement of the quality of the water. If there are many coarse Cr carbides, the corrosion resistance also decreases. As a result of various studies, it is important to control the metal structure to have a number density of carbides having a circumference equivalent to a circle of 10.0 μm or more and 60 or less per 2200 μm ² . The measurement target of the number density includes both carbides of Ti, Nb, Zr, V, and W and Cr carbides. As described above, the amounts of carbides of Ti, Nb, Zr, V, and W hardly change by the quenching treatment. Further, in the above-described chemical composition range, the number density of carbides having a circumference equivalent to a circle of 10.0 μm or more does not increase more than 60 per 2200 μm ² only by the carbides of Ti, Nb, Zr, V, and W. . Therefore, when the amount of coarse Cr carbides can be sufficiently reduced by heating during the quenching treatment, the number density of carbides having a circumference equivalent to a circle of 10.0 μm or more is 60 or less per 2200 μm ^2. A metallographic structure is obtained.

(How to determine the area ratio of carbide)
An observation surface obtained by polishing the surface of the steel material and finishing by oxalic acid electrolytic etching is observed with an optical microscope, and an observation image is collected at a resolution of 2,000,000 dots / inch or more. The total observation area is 40,000 μm ² or more in total for one or a plurality of non-overlapping fields selected at random. The total area Sp (μm ² ) of the carbide particles present in the visual field is calculated by an image processing device, and the Sp is divided by the total observation area (μm ² ) to determine the area ratio (%) of the carbide.

(How to find the number density of carbide with a circumference equivalent to 10.0 μm or more)
For an observation image having an observation total area of 40,000 μm ² or more collected by the method described in the above `` How to Determine the Area Ratio of Carbide '', the area of each carbide particle was measured by an image processing apparatus, and the circumference equivalent to a circle was 10. The number of carbides of 0 μm or more is counted. Particles whose particles are partially cut off by the boundary of the visual field are counted when the circumference equivalent to the circle calculated by the area of the portion existing in the visual field is 10.0 μm or more. From counted the total number of carbide Np (number) and the total area of the observation field ([mu] m ^2), defines the number density of the equivalent circle perimeter 10.0μm or more carbides per 2200μm ² (pieces / 2200μm ^2).

[Manufacturing process]
The martensitic stainless steel having excellent abrasive wear resistance can be manufactured by, for example, the following steel sheet manufacturing process.
Casting → hot rolling → hot strip annealing → (cold rolling → intermediate annealing) → finishing cold rolling → (finishing annealing) → processing → quenching → (tempering)
The steps in parentheses can be performed as needed. After each annealing, quenching or tempering, pickling is usually performed. In the present invention, as described above, Cr carbide is used for improving abrasive wear resistance. The form (amount and size) of the Cr carbide can be controlled by heat treatment. In the above-mentioned manufacturing process, it is particularly important to set conditions for hot-rolled sheet annealing and quenching.

(Hot rolling)
The slab is heated and held at 1150-1250 ° C. for 1 hour or more, extracted, and hot-rolled to obtain a hot-rolled steel sheet. The thickness of the hot-rolled steel sheet may be set, for example, in the range of 3.0 to 5.0 mm.

(Hot rolled sheet annealing)
After hot rolling, the so-called “as hot” hot-rolled steel sheet is subjected to hot-rolled sheet annealing at 750 to 850 ° C. for 5 hours or more. By maintaining the heating in this temperature range, the martensite phase, which is often present in the hot-rolled steel sheet, is decomposed into carbide and a soft ferrite phase. If the holding temperature is too high, it enters the austenite single-phase temperature range, which causes the generation of new martensite during cooling. If the holding temperature is too low or the holding time is too short, the martensitic phase cannot be sufficiently decomposed, and the structure state in which the coarse carbides are sufficiently present as a steel material for quenching ( More specifically, it becomes difficult to prepare a carbide having a circle equivalent circumference of 10.0 μm or more in a number density of 90 or more per 2200 μm ² . Further, when the martensite phase remains, the productivity in the cold rolling step deteriorates.

[Cold rolling, annealing]
The steel sheet after the hot-rolled sheet annealing is made a steel sheet having a target thickness by cold rolling. The target plate thickness can be set in a range of 0.1 to 3.5 mm. It may be managed in a range of 1.0 to 2.0 mm. Intermediate annealing is performed if necessary. The final cold rolling performed before being subjected to the processing described below is referred to as “finishing cold rolling”. After finish cold rolling, final annealing is performed as necessary. The annealing is called "finishing annealing". Annealing conditions may be 750 to 850 ° C. and soaking for 0 to 60 seconds for both intermediate annealing and finish annealing. When the finish annealing is omitted, the rolling reduction in the finish cold rolling is preferably 5 to 50%. If a cold-rolled steel sheet having a reduction ratio of more than 50% is subjected to the processing described below as it is, the workability may be insufficient depending on the application.

〔processing〕
In this specification, a steel material subjected to a quenching process is referred to as a “steel material”. This steel material usually has a shape equal to or close to the shape of the final product. The cold rolled steel sheet after the finish cold rolling or the cold rolled annealed steel sheet after the finish annealing is subjected to a process such as press forming to obtain a steel material to be subjected to a quenching process.

[Hardening treatment]
The steel material to be subjected to the quenching treatment was a very hard carbide in which at least one element of Ti, Nb, Zr, V, and W and carbon were bonded in the matrix of the ferrite phase, and grew mainly by hot-rolled sheet annealing. It has a metal structure in which Cr carbide is dispersed. In many cases, the Cr carbide has a large size with a circumference equivalent to a circle of 10.0 μm or more. Hereinafter, carbide having a circle-equivalent circumference of 10.0 μm or more is referred to as “coarse carbide”. According to the study by the inventors, among the coarse carbides, the Cr carbide is a factor that reduces the abrasive wear resistance. It also becomes a factor that lowers corrosion resistance. On the other hand, it was found that the small-sized Cr carbide contributed to the improvement of the abrasive wear resistance.

  In order to enjoy the effect of improving the abrasion resistance of the Cr carbide, the solid solution of the coarse Cr carbide dispersed in the matrix is advanced during heating in the quenching treatment, and the small-sized Cr carbide remains. Thereby, the effect of improving the abrasive wear resistance by the contribution of both the very hard carbides of Ti, Nb, Zr, V, and W and the small-sized Cr carbide is obtained, and the abrasive wear resistance is improved as compared with the conventional case. Martensitic stainless steel material can be realized. Therefore, it is important to perform the quenching treatment under the condition that the Cr carbide can sufficiently remain in a small size state.

As a result of detailed research, the inventors have adjusted the above-mentioned chemical composition and, for a steel material in which carbides having a circle equivalent circumference of 10.0 μm or more exist at a number density of 90 or more per 2200 μm ² , After heating under the condition that the maximum attainment temperature T _M is 1000 to 1100 ° C. and the residence time in the temperature range of 1000 ° C. or more and T _M (° C.) or less is 3 to 10 seconds, a “quenching treatment” for cooling is performed. In this way, to obtain a martensitic stainless steel material having a metallographic structure in which “the area ratio of carbides is 1.0% or more and the number density of carbides having a circle-equivalent circumference of 10.0 μm or more is 60 or less per 2200 μm ² ” Was found, and an effect of improving abrasive wear resistance was obtained. The carbides of Ti, Nb, Zr, V and W hardly change by this quenching treatment.

As the material temperature during heating in the quenching process, the value of the surface temperature of the steel material can be adopted. “The stay time in the temperature range of 1000 ° C. or more and T _M (° C.) or less” means the time during which the material temperature is in the range of 1000 ° C. or more and the maximum temperature T _M (° C.) or less. Control of the material temperature in a short time such that the residence time in the temperature range of 1000 ° C. or more and T _M (° C.) or less is 3 to 10 seconds is performed by loading the material in a furnace set at a temperature higher than T _M. When the temperature reaches a predetermined T _M (° C.), it can be removed from the furnace and cooled, or moved to a lower temperature zone. The heat pattern including the process of raising the temperature from room temperature can be obtained in advance by a preliminary experiment or computer simulation. After the heating, for example, it is desirable to cool so that the average cooling rate from 1000 ° C to 100 ° C is 1 to 150 ° C / s, more preferably 20 to 150 ° C / s. In this cooling process, the austenite matrix transforms into a martensite phase. As a result, a matrix (metal base) is a martensite phase, and a structure state in which carbides are dispersed in the matrix in the above-described predetermined amount and size is obtained.

FIG. 1 illustrates an optical micrograph of an observation surface parallel to a rolled surface of a steel material obtained in Example No. A2-14 (Comparative Example) of Table 2A described below. The heating conditions for the quenching treatment were such that the maximum temperature T _M was 1050 ° C., and the residence time in the temperature range of 1000 ° C. or more and T _M (° C.) was less than 1 second (soaking at 1050 ° C. and 0 seconds). Particles that appear relatively black are Nb carbides, and particles that appear relatively gray are Cr carbides. It has a metal structure with a large amount of carbides.

FIG. 2 illustrates a binarized image obtained by performing image processing on the photograph of FIG. As a result of analyzing the binarized image, the number of coarse carbides having a circumference equivalent to a circle of 10.0 μm or more was as large as 69/2200 μm ² . In the case of this steel sheet, the effect of improving the abrasive wear resistance was insufficient, and the corrosion resistance was poor.

FIG. 3 illustrates an optical micrograph of an observation surface parallel to the rolled surface of the steel material obtained in Example No. A2-16 (Example of the present invention) in Table 2A described below. The heating conditions for the quenching treatment were such that the maximum ultimate temperature T _M was 1050 ° C., and the residence time in the temperature range of 1000 ° C. or more and T _M (° C.) or less was 5 seconds. The difference in the heating conditions from the example of FIG. 1 is that the residence time in the temperature range of 1000 ° C. or more and T _M (° C.) or less was increased from less than 1 second to 5 seconds, but the amount of carbides was significantly reduced. You can see that This decrease in carbides is due to the progress of solid solution of Cr carbides. However, the small-sized Cr carbide remains sufficiently.

FIG. 4 illustrates a binarized image obtained by performing image processing on the photograph of FIG. As a result of analyzing this binarized image, the number of coarse carbides having a circumference equivalent to a circle of 10.0 μm or more was as small as 5/2200 μm ² . In this case, the abrasive wear resistance was significantly improved as compared with the example of FIG. 2, and the corrosion resistance was also improved. That is, by controlling the existence form of the Cr carbide by heating in the quenching treatment, the abrasive wear resistance can be significantly improved, and the corrosion resistance can be sufficiently secured.

[Tempering treatment]
The steel material after the above quenching has a hard martensite structure. When importance is placed on toughness and workability, the steel material after the quenching treatment can be further subjected to a tempering treatment if necessary. The tempering treatment is preferably performed under the condition of holding at 150 to 700 ° C. for 1 to 120 minutes.

  Using the martensitic stainless steel material obtained as described above as a material, a "sliding member" having excellent abrasive wear resistance can be manufactured. The blade is also included in the sliding member.

A steel having a chemical composition shown in Table 1 was melted, and the obtained slab was heated at 1150 to 1250 ° C. for 2 hours, extracted, hot-rolled, and heated to a thickness of 3.0 to 4.0 mm. It was a rolled steel sheet. The hot-rolled steel sheet was subjected to hot-rolled sheet annealing under the condition of holding at a temperature set between 750 and 850 ° C. for 6 hours. Next, after pickling, cold rolling, intermediate annealing, pickling, finish cold rolling, and finish annealing were performed. The heating temperature of the intermediate annealing and the finish annealing was 750 to 850 ° C., and the rolling reduction of the finish cold rolling was 30 to 50%. Here, a test piece cut out from a steel sheet having a thickness of 1.0 to 2.0 mm after the above-described finish annealing was used as a “steel material”, which was subjected to a quenching treatment under heating conditions shown in Tables 2A and 2B. . The cooling of the quenching treatment was performed by sandwiching the test piece between two water-cooled copper plates and rapidly cooling. In this case, the range of about average cooling rate is 25 to 150 ° C. / s from 1000 ° C. to 100 ° C. (in the example below the maximum temperature T _M is 1000 ° C. to 100 ° C. from T _M). Each of the steel materials after the quenching treatment had a metal structure in which the matrix was a martensite phase. In some examples (Nos. A2-22, 23, 24, and 25), after the quenching, a tempering treatment was performed at 300 ° C. for 30 minutes. The steel material obtained by subjecting the plate material after quenching treatment or the plate material after tempering treatment thus obtained to pickling was used as a test material and subjected to the following investigations. The thickness of the test material is in the range of 1.0 to 2.0 mm.

(Hardness measurement)
The Vickers hardness HV30 (test force 294.2N) was measured on the plate surface of the test material (plate surface perpendicular to the plate thickness direction) in accordance with JIS Z2244: 2009.

(Carbide area ratio)
According to the above-mentioned "How to determine the area ratio of carbide", the observation surface obtained by finishing the plate surface of the test material (the plate surface perpendicular to the plate thickness direction) by oxalic acid electrolytic etching is observed by an optical microscope. The area ratio (%) of the carbide was determined. Observation images were collected at a resolution of 2 million dots / inch. An area of a total of 409394.4 μm ² was observed for 10 randomly selected visual fields. In the image processing, the brightness was binarized so that the carbide particles were displayed in black.

(Number density of coarse carbide)
According to the above-mentioned "How to determine the number density of carbides having a circumference equivalent to a circle of 10.0 μm or more", the observation surface obtained by finishing the plate surface of the test material by oxalic acid electrolytic etching is observed with an optical microscope, and the circumference equivalent to the circle is determined. The number density of “coarse carbide” having a length of 10.0 μm or more (pieces / 2200 μm ² ) was determined. Here, the same observation image as that of the above-described measurement of the carbide area ratio (a binarized image of a total of 409394.4 μm ² ) was used.

(Specific wear)
The abrasive wear resistance was evaluated by a pin-on-disk wear test. The disk to which the SiC abrasive paper with a count of 800 (abrasive paper coated with SiC abrasive grains having a particle size of P800 specified in JIS R6010: 2000) is rotated, and cut out from the test material on the surface of the abrasive paper The surface of a circular test piece having a diameter of 8 mm was pressed with an additional load of 20N. A wear test was performed under a dry condition under the conditions of a rotational speed of 140 rpm, a friction speed of 0.66 m / s at the center of the test piece, a friction distance of 200 m at the center of the test piece, and a specific wear amount C (mm ³ / m) according to the following equation (1). / N) was calculated.
Specific wear amount C = W / (L × F) (1)
Here, W is the amount of wear (mm ³ ) of the test piece, L is the friction distance = 200 m, and F is the additional load = 20 N.
In this test, if the specific wear amount is 40 × 10 ⁻⁵ mm ³ / m / N or less, it can be evaluated as having extremely excellent abrasive wear resistance. Therefore, those having a specific wear amount of 40 × 10 ⁻⁵ mm ³ / m / N or less were determined to be acceptable.

(Corrosion resistance)
A test piece cut from the test material (back and end face seals: provided) was subjected to a salt spray test with a 5% aqueous solution of sodium chloride at 35 ° C. for 72 hours to check for the occurrence of red rust. When no occurrence of red rust was observed, it was evaluated as ○ (corrosion resistance; good), and when it was observed, it was evaluated as x (corrosion resistance; insufficient).
The results are shown in Tables 2A and 2B.

  In the steel material of the present invention example, by controlling the existence form of Cr carbide, the total amount of carbides of at least one element of Ti, Nb, Zr, V and W and Cr carbide (carbon carbide area ratio) is sufficiently secured, A metal structure with a small amount of coarse carbides was obtained. As a result, the abrasive wear resistance was improved, and the corrosion resistance was also good.

On the other hand, in Comparative Examples A1-1, A1-2, A2-1 to A2-6, the maximum attained temperature T _M was too low in the quenching treatment, so that the solution of Cr carbide was insufficient and coarse carbides were formed. Many metal structures. As a result, the abrasion resistance was poor and the corrosion resistance was poor.

Comparative Examples A1-3, A1-4, A1-6, A1-7, A2-7, A2-8, A2-11, A2-12, A2-15, A2-15, A2-17, A2-18, In A2-21 and A2-24, the residence time at 1000 ° C. or more and T _M or less in the quenching treatment was too short, so that the solution of Cr carbide was insufficient and the metal structure was rich in coarse carbides. As a result, the abrasion resistance was poor and the corrosion resistance was poor.

In Comparative Examples A1-21 and A9-2, since the residence time at 1000 ° C. or more and T _M or less was too long in the quenching treatment, the solid solution of the Cr carbide excessively progressed, and the metal structure in which the Cr carbide hardly remained remained. As a result, the carbide area ratio was lower than the stipulation of the present invention. In this case, although the presence of Nb carbide in A1-21 and the presence of carbides of Ti, Nb and V in A9-2, respectively, the effect of improving the abrasive wear resistance is produced, but the degree of the improvement is the same as that of the present invention. It was smaller than the one.

  Comparative Examples B1-1 and B2-1 do not contain one or more elements selected from the group consisting of Ti, Nb, Zr, V, and W, or the total content thereof is too low. Does not exhibit the effect of improving abrasive wear resistance. The poor corrosion resistance in B1-1 is considered to be due to the high content of solid solution C in the steel.

Claims (5)

In mass%, C: 0.10 to 0.50%, Si: 0.02 to 1.0%, Mn: 0.02 to 1.0%, Ni: 0.1 to 5.0%, Cr: 12.0 to 18.0%, Ti: 0 to 0.5%, Nb: 0 to 0.5%, Zr: 0 to 0.5%, V: 0 to 0.5%, W: 0 to 0% 0.5%, the balance being Fe and inevitable impurities, having a chemical composition containing 0.25 to 2.0% in total of one or more selected from the group consisting of Ti, Nb, Zr, V, and W, The surface area of the carbide is 1.0% or more, and the number density of the carbide having a circumference of 10.0 μm or more corresponding to a circle is 60 or less per 2200 μm ^{2 on} the observation surface obtained by polishing and polishing the martensite. Stainless steel. On the observation surface finished by polishing and electroetching the surface, the highest reached for steel materials whose number density of carbide with a circumference equivalent to 10.0 μm or more is adjusted to 90 or more per 2200 μm ² , After heating under the condition that the temperature T _M is 1000 to 1100 ° C. and the residence time in the temperature range of 1000 ° C. or more and T _M (° C.) or less is 3 to 10 seconds, cooling is performed to perform a quenching treatment to obtain a martensitic structure. A method for producing a martensitic stainless steel material according to claim 1.   The method for producing a martensitic stainless steel material according to claim 2, wherein the steel material uses a steel plate having a thickness of 0.1 to 3.5 mm.   The method for producing a martensitic stainless steel material according to claim 2 or 3, wherein after the quenching, a tempering treatment is performed at 150 to 700 ° C for 1 to 120 minutes.   A sliding member using the martensitic stainless steel material according to claim 1.