JP7640237B2 - Martensitic stainless steel material, its manufacturing method, and slide member - Google Patents

Description

The present invention relates to a martensitic stainless steel material, a manufacturing method thereof, and a sliding member.

Sliding components such as bearings are components that support the shafts of components that rotate or reciprocate, and are widely used in a variety of fields. For example, in automobiles and industrial machinery, rolling bearings are commonly used to support the rotating shafts of components. Also, in high-pressure pumps and injectors, retaining members are commonly used to support reciprocating shafts.

Depending on the application, sliding members may be used in environments prone to corrosion, so they need to be made from materials suitable for the environment in which they will be used. For example, Patent Document 1 proposes that, as a material for bearings used in environments prone to contamination by foreign matter or muddy water, steel containing 0.60-0.95 wt% C, 10.0-13.0 wt% Cr, 0.2-1.5 wt% Si, and 0.2-1.0 wt% Mn is used, with at least one of 0.5-2.0 wt% Mo and 0.5-2.0 wt% V added to disperse and precipitate fine Mo- or V-based carbides of 50-300 nm, with the remainder being Fe and unavoidable impurities.

Patent No. 4441947

However, conventional materials used for sliding parts are susceptible to corrosion and wear when used in salty environments, resulting in a shortened service life for the sliding parts. For this reason, there has been a demand for the development of materials for sliding parts that can be used suitably in various environments, including salty environments.

The present invention has been made to solve the above problems, and aims to provide a martensitic stainless steel material with excellent corrosion and wear resistance, a manufacturing method thereof, and a sliding member.

As a result of intensive research focusing on martensitic stainless steel materials, the inventors discovered that the above problems could be solved by controlling the composition, as well as the components and average particle size of the carbonitrides contained in the metal structure, and thus completed the present invention.

That is, the present invention has a composition including C: 0.28 to 0.70 mass%, Si: 2.0 mass% or less, Mn: 2.0 mass% or less, Cr: 10 to 17 mass%, Mo: 3.0 mass% or less, N: 0.008 to 0.40 mass%, Ti: 0.1 mass% or less, Nb: 0.5 mass% or less, V: 1.0 mass% or less, and W: 1.0 mass% or less, the total amount of Nb, V, and W is 0.1 to 2.0 mass%, and the balance is Fe and impurities;
The martensitic stainless steel material has a metal structure containing at least carbonitrides having a Cr content of 25 mass% or less and a total amount of Nb, V and W of 10 mass% or more as carbonitrides, and the average grain size of all of the carbonitrides is 5.0 μm or less .

The present invention also provides a method for producing the martensitic stainless steel material,
a hot working step of heating a stainless steel having a composition containing 0.28 to 0.70 mass% C, 2.0 mass% or less Si, 2.0 mass% or less Mn, 10 to 17 mass% Cr, 3.0 mass% or less Mo, 0.008 to 0.40 mass% N, 0.1 mass% or less Ti, 0.5 mass% or less Nb, 1.0 mass% or less V, and 1.0 mass% or less W, the total amount of Nb, V, and W being 0.1 to 2.0 mass%, with the balance being Fe and impurities, to 1200°C or higher, and then hot working the stainless steel at a reduction in area of 90% or more to obtain a worked material;
An annealing step of annealing the workpiece;
a quenching step of quenching the annealed workpiece at 1050 to 1200 ° C;
A sub-zero treatment step of subjecting the quenched processed material to a sub-zero treatment;
and a tempering step of tempering the sub-zero treated worked material under conditions such that the LMP, expressed by the following formula (1), is 7000 to 17000.
LMP=(t+273)×(C+log tr) (1)
In the formula, t is the heating temperature (° C.), C is a material constant 20, and tr is the holding time (h) at the heating temperature.

Furthermore, the present invention is a sliding member containing the martensitic stainless steel material.

The present invention provides a martensitic stainless steel material with excellent corrosion and wear resistance, a manufacturing method thereof, and a sliding member.

The following is a detailed description of the embodiments of the present invention. The present invention is not limited to the following embodiments, and it should be understood that modifications and improvements to the following embodiments, as appropriate, based on the ordinary knowledge of those skilled in the art, fall within the scope of the present invention, provided they do not deviate from the spirit of the present invention.

The martensitic stainless steel material according to an embodiment of the present invention has a composition containing C: 0.28 to 0.70 mass%, Si: 2.0 mass% or less, Mn: 2.0 mass% or less, Cr: 10 to 17 mass%, Mo: 3.0 mass% or less, N: 0.008 to 0.40 mass%, Ti: 0.1 mass% or less, Nb: 0.5 mass% or less, V: 1.0 mass% or less, and W: 1.0 mass% or less, with the total amount of Nb, V and W being 0.1 to 2.0 mass%, and the balance being Fe and impurities.
In this specification, the term "impurities" refers to components that are mixed in due to various factors in raw materials such as ores and scraps and manufacturing processes during industrial production of martensitic stainless steel materials, and are acceptable within a range that does not adversely affect the present invention. For example, the impurities include unavoidable impurities. Specific examples of impurities include O: 0.01 mass% or less, P: 0.04 mass% or less, S: 0.40 mass% or less, Sn: 0.3 mass% or less, Ta: 0.1 mass% or less, REM: 0.01 mass% or less, Bi: 0.1 mass% or less, and Pb: 0.1 mass% or less.

In addition, the martensitic stainless steel material according to the embodiment of the present invention may further contain one or more selected from Ni: 0.05 to 2.0 mass%, Cu: 0.01 to 2.0 mass%, and Al: 0.1 mass% or less.
Moreover, the martensitic stainless steel material according to the embodiment of the present invention may further contain B: 0.1 mass % or less.
Furthermore, the martensitic stainless steel material according to the embodiment of the present invention may further contain one or more selected from Ca: 0.02 mass% or less, Mg: 0.02 mass% or less, Zr: 0.02 mass% or less, Hf: 0.02 mass% or less, and Co: 0.10 mass% or less.

<C: 0.28-0.70% by mass>
C is an element necessary for obtaining a martensite structure (a metal structure containing a martensite phase) and forming carbonitrides by quenching. In order to obtain this effect sufficiently, the C content is controlled to 0.28 mass% or more, preferably 0.35 mass% or more. On the other hand, if the C content is too high, the carbonitrides become excessively coarse, and the desired corrosion wear resistance cannot be obtained. Therefore, the C content is controlled to 0.70 mass% or less, preferably 0.55 mass% or less, more preferably 0.45 mass% or less.
Here, in this specification, the term "carbonitride" refers to a compound in which carbon and/or nitrogen are bonded to a metal element (e.g., Cr, Nb, V, W, Ti, etc.). Note that carbides containing almost no nitrogen and nitrides containing almost no carbon also fall under the category of "carbonitride" in this specification.

<Si: 2.0% by mass or less>
Although Si is an effective element for deoxidization, excessive addition of Si increases the manufacturing cost. Therefore, the Si content is controlled to 2.0 mass% or less, preferably 0.8 mass% or less, and more preferably 0.5 mass% or less. On the other hand, the lower limit of the Si content is not particularly limited, but is preferably 0.01 mass% or more, more preferably 0.05 mass% or more, and more preferably 0.1 mass% or more.

<Mn: 2.0% by mass or less>
Mn is an effective element for deoxidization like Si, but excessive addition of Mn increases the manufacturing cost. Therefore, the Mn content is controlled to 2.0 mass% or less, preferably 0.8 mass% or less, and more preferably 0.5 mass% or less. On the other hand, the lower limit of the Mn content is not particularly limited, but is preferably 0.01 mass% or more, more preferably 0.05 mass% or more, and more preferably 0.1 mass% or more.

<Cr: 10-17% by mass>
Cr is an essential element for imparting corrosion resistance. Cr is also an element that generates carbonitrides to reduce corrosion wear resistance. Considering various environments, including environments containing salt, the Cr content is controlled to 10 mass% or more, preferably 10.5 mass% or more. On the other hand, if the Cr content is too high, it will cause an increase in manufacturing costs. Therefore, the Cr content is controlled to 17 mass% or less, preferably 16 mass% or less, and more preferably 15 mass% or less.

<Mo: 3.0% by mass or less>
Mo is an element effective for improving the corrosion resistance of martensitic stainless steel materials. However, since Mo is expensive, if the Mo content is too high, it will cause an increase in manufacturing costs. Therefore, the Mo content is controlled to 3.0 mass% or less, preferably 2.8 mass% or less, and more preferably 2.5 mass% or less. On the other hand, the lower limit of the Mo content is not particularly limited, but is preferably 0.01 mass% or more, more preferably 0.03 mass% or more, and even more preferably 0.05 mass% or more.

<N: 0.008 to 0.40% by mass>
N is an element necessary for forming carbonitrides to improve corrosion wear resistance. If the N content is too high, the carbonitrides become excessively coarse, and the desired corrosion wear resistance cannot be obtained. Therefore, the N content is controlled to 0.40 mass% or less, preferably 0.18 mass% or less. In addition, since excessive reduction of the N content leads to an increase in refining costs, it is controlled to 0.008 mass% or more, preferably 0.01 mass% or more.

<Ti: 0.1% by mass or less>
Ti is an element that improves corrosion wear resistance by bonding with C and N to form carbonitrides. If the Ti content is too high, the carbonitrides become excessively coarse, and the desired corrosion wear resistance cannot be obtained. Therefore, the Ti content is controlled to 0.1 mass% or less, preferably 0.09 mass% or less. On the other hand, the lower limit of the Ti content is not particularly limited, but is preferably 0.001 mass% or more, more preferably 0.005 mass% or more.

<Nb: 0.5% by mass or less>
Nb is an element that improves corrosion wear resistance by bonding with C and N to form carbonitrides. If the Nb content is too high, the carbonitrides become excessively coarse, and the desired corrosion wear resistance cannot be obtained. Therefore, the Nb content is controlled to 0.5 mass% or less, preferably 0.45 mass% or less. On the other hand, the lower limit of the Nb content is not particularly limited, but is preferably 0.01 mass% or more, more preferably 0.05 mass% or more, and even more preferably 0.1 mass% or more.

<V: 1.0% by mass or less>
V is an element that improves corrosion wear resistance by bonding with C and N to form carbonitrides. If the V content is too high, the carbonitrides become excessively coarse, and the desired corrosion wear resistance cannot be obtained. Therefore, the V content is controlled to 1.0 mass% or less, preferably 0.8 mass% or less, and more preferably 0.5 mass% or less. On the other hand, the lower limit of the V content is not particularly limited, but is preferably 0.01 mass% or more, more preferably 0.03 mass% or more, and even more preferably 0.05 mass% or more.

<W: 1.0% by mass or less>
W is an element that improves corrosion wear resistance by bonding with C and N to form carbonitrides. If the W content is too high, the carbonitrides become excessively coarse, and the desired corrosion wear resistance cannot be obtained. Therefore, the W content is controlled to 1.0 mass% or less, preferably 0.8 mass% or less, and more preferably 0.5 mass% or less. On the other hand, the lower limit of the W content is not particularly limited, but is preferably 0.01 mass% or more, more preferably 0.03 mass% or more, and even more preferably 0.05 mass% or more.

<Total Amount of Nb, V and W: 0.1 to 2.0% by mass>
As described above, Nb, V and W combine with C and N to form carbonitrides. Carbonitrides contribute to improving corrosion wear resistance, but depending on the contents of elements (particularly Cr, Nb, V and W) contained in the carbonitrides, sufficient corrosion wear resistance may not be obtained. From the viewpoint of forming carbonitrides with excellent corrosion wear resistance, the total amount of Nb, V and W is controlled to 0.1 to 2.0 mass%, preferably 0.2 to 2.0 mass%, more preferably 0.3 to 1.5 mass%.

<Ni: 0.05-2.0% by mass>
Ni is an element that contributes to improving strength. From the viewpoint of obtaining the effect of Ni, the Ni content is preferably controlled to 0.05 mass% or more, more preferably 0.06 mass% or more. However, if Ni is excessively contained, the manufacturing cost increases, and there is a risk that a residual austenite phase is generated during quenching, resulting in a decrease in toughness. Therefore, the Ni content is preferably controlled to 2.0 mass% or less, more preferably 0.50 mass% or less, and even more preferably 0.30 mass% or less.

<Cu: 0.01 to 2.0% by mass>
Cu is an element that contributes to improving strength and corrosion resistance. From the viewpoint of obtaining the effect of Cu, the content of Cu is preferably controlled to 0.01 mass% or more, more preferably 0.02 mass% or more. On the other hand, if Cu is excessively contained, there is a risk of the toughness decreasing. Therefore, the content of Cu is preferably controlled to 2.0 mass% or less, more preferably 0.50 mass% or less, and further preferably 0.20 mass% or less.

<Al: 0.1% by mass or less>
Al is an element that is effective in deoxidization and improves oxidation resistance and corrosion resistance. In addition, Al also has the effect of increasing the cleanliness of inclusions and improving wear resistance. However, if Al is contained in excess, the improvement in oxidation resistance and corrosion resistance will saturate, and AlN and Al-based oxides will coagulate and become coarse, causing squealing during wear. Therefore, the content of Al is preferably controlled to 0.1 mass% or less, more preferably 0.080 mass% or less, and even more preferably 0.05 mass% or less. On the other hand, the lower limit of the content of Al is not particularly limited, but is preferably 0.001 mass% or more, more preferably 0.005 mass% or more, and even more preferably 0.01 mass% or more.

<B: 0.1% by mass or less>
B is an element that forms BN to improve wear resistance. However, if an excessive amount of B is contained, the hardenability is excessively improved and the toughness is deteriorated. Therefore, the content of B is preferably controlled to 0.1 mass% or less, more preferably 0.0040 mass% or less. On the other hand, the lower limit of the content of B is not particularly limited, but is preferably 0.0002 mass% or more, more preferably 0.001 mass% or more.

<Ca: 0.02% by mass or less>
Ca is an element that improves the hot workability of martensitic stainless steel materials. However, if Ca is contained in excess, the corrosion resistance deteriorates. Therefore, the Ca content is preferably controlled to 0.02 mass% or less, more preferably 0.0050 mass% or less. On the other hand, the lower limit of the Ca content is not particularly limited, but is preferably 0.0002 mass% or more, more preferably 0.0005 mass% or more.

<Mg: 0.02% by mass or less>
Mg is an element that inevitably enters stainless steel produced by a general-purpose refining method. In addition, excessive Mg content generates large and hard MgO, which adversely affects the polishability of martensitic stainless steel materials. Therefore, the Mg content is preferably controlled to 0.02 mass% or less, more preferably 0.0050 mass% or less. On the other hand, the lower limit of the Mg content is not particularly limited, but is preferably 0.0002 mass% or more, more preferably 0.0005 mass% or more.

<Zr: 0.02% by mass or less>
Zr is an element that improves corrosion resistance and heat resistance. However, excessive Zr content increases the manufacturing cost. Therefore, the Zr content is preferably controlled to 0.02 mass% or less, more preferably 0.0050 mass% or less. On the other hand, the lower limit of the Mg content is not particularly limited, but is preferably 0.0002 mass% or more, more preferably 0.0005 mass% or more.

<Hf: 0.02% by mass or less>
Hf is an element that improves corrosion resistance and oxidation resistance at high temperatures. However, excessive Hf content increases the manufacturing cost. Therefore, the Hf content is preferably controlled to 0.02 mass% or less, more preferably 0.0050 mass% or less. On the other hand, the lower limit of the Hf content is not particularly limited, but is preferably 0.0002 mass% or more, more preferably 0.0005 mass% or more.

<Co: 0.10% by mass or less>
Co is an element that improves toughness and high-temperature corrosion resistance. However, excessive Co content increases the manufacturing cost. Therefore, the Co content is preferably controlled to 0.10 mass% or less, more preferably 0.050 mass% or less. On the other hand, the lower limit of the Co content is not particularly limited, but is preferably 0.001 mass% or more, more preferably 0.003 mass% or more.

The martensitic stainless steel material according to the embodiment of the present invention has a metal structure containing carbonitrides.
The carbonitride contains 25 mass % or less of Cr and 10 mass % or more in total of Nb, V and W. By controlling the contents to such values, it is possible to form carbonitrides having excellent corrosion and wear resistance.
From the viewpoint of stably obtaining corrosion wear resistance by the carbonitride, the Cr content in the carbonitride is preferably 23 mass% or less, more preferably 20 mass% or less. On the other hand, the lower limit of the Cr content is not particularly limited, but is preferably 1 mass% or more, more preferably 3 mass% or more, and even more preferably 5 mass% or more. In addition, the total amount of Nb, V and W in the carbonitride is preferably 15 mass% or more, more preferably 20 mass% or more. On the other hand, the upper limit of the total amount of Nb, V and W is not particularly limited, but is preferably 60 mass% or less, more preferably 50 mass% or less.

In this specification, the Cr content and the total amount of Nb, V and W in the carbonitrides are calculated by extracting the carbonitrides from the martensitic stainless steel material and analyzing them using a SEM (scanning electron microscope) and EDS (energy dispersive X-ray analyzer). The carbonitrides can be extracted using the method described below.

The carbonitride has an average particle size of 5.0 μm or less. By controlling the average particle size in this range, corrosion wear resistance can be improved. The lower limit of the average particle size of the carbonitride is not particularly limited, but is preferably 0.1 μm or more, more preferably 0.3 μm or more, and even more preferably 0.5 μm or more.
In this specification, the average grain size of carbonitrides means the average circle equivalent diameter measured by observing a mirror-finished cross section of a martensitic stainless steel material with a Schottky scanning electron microscope. The circle equivalent diameter means the diameter of a circle having an area equal to the area of the carbonitrides appearing on the observed surface.

The martensitic stainless steel material according to the embodiment of the present invention preferably has a Vickers hardness of 600 HV or more, more preferably 650 HV or more, and even more preferably 700 HV or more. A Vickers hardness in this range can improve corrosion wear resistance. The upper limit of the Vickers hardness is not particularly limited, but is preferably 1000 HV, more preferably 900 HV, and even more preferably 800 HV.

The martensitic stainless steel material according to the embodiment of the present invention may be in the form of a plate material or a wire material, but is preferably in the form of a wire material.

The martensitic stainless steel material according to the embodiment of the present invention can be manufactured according to methods known in the art, except for melting stainless steel having the above composition. A typical manufacturing method for the martensitic stainless steel material according to the embodiment of the present invention includes a hot working process in which stainless steel having the above composition is heated and then hot worked to obtain a worked material, an annealing process in which the worked material is annealed, a quenching process in which the annealed worked material is quenched, a subzero treatment process in which the quenched worked material is subjected to a subzero treatment, and a tempering process in which the subzero treated worked material is tempered.

<Hot working process>
The hot working process is a process in which stainless steel having the above composition is melted, forged or cast, heated to 1200° C. or higher, and hot worked with an area reduction rate of 90% or more to obtain a worked material.
By setting the heating temperature at 1200° C. or higher, carbonitrides can be sufficiently dissolved and the heating (soaking) time can be shortened. The upper limit of the heating temperature is not particularly limited, but is preferably 1250° C. or lower. The heating time may be appropriately set depending on the heating temperature, and is not particularly limited.
By setting the reduction rate at 90% or more, the deformation of the carbonitride is promoted and the segregation region can be reduced. From the viewpoint of obtaining finer carbonitride and uniform dispersion, the reduction rate is preferably 95% or more. The upper limit of the reduction rate is not particularly limited, but is preferably 99.9% or less, more preferably 99.8% or less.

<Annealing process>
The annealing step is a step of annealing the worked material obtained in the hot working step.
By performing annealing, carbonitrides can be precipitated.
The annealing method is not particularly limited, but may be performed by heating to a predetermined annealing temperature and then slowly cooling.
The annealing temperature is not particularly limited, but is preferably 800 to 950° C., and more preferably 820 to 900° C. The annealing time may be appropriately set depending on the annealing temperature, and is not particularly limited, but is generally 1 to 10 hours.
The cooling rate of the slow cooling is not particularly limited, but is preferably 30° C./h or less.

<Quenching process>
The quenching process is a process in which the annealed workpiece is quenched at 1050 to 1200°C.
By performing quenching, a martensite structure can be obtained.
The quenching method is not particularly limited, but may be such that the annealed workpiece is held at 1050 to 1200° C., preferably 1090 to 1150° C., and then rapidly cooled.
If the quenching temperature is less than 1050° C., the amount of dissolved C is insufficient, resulting in reduced hardness, whereas if the quenching temperature exceeds 1200° C., the crystal grains become coarse, resulting in reduced toughness and the formation of excessive retained austenite.
The holding time at the quenching temperature may be appropriately set depending on the quenching temperature, and is not particularly limited, but is generally from 10 minutes to 2 hours.
The quenching method is not particularly limited, but may be air cooling, water cooling, oil cooling, or the like.

<Sub-zero treatment process>
Sub-zero treatment is a process in which hardened workpieces are subjected to sub-zero treatment.
By performing sub-zero treatment, the amount of austenite remaining after quenching (hereinafter referred to as "residual austenite") can be reduced. In other words, a part of the retained austenite is transformed into martensite, and the reduction in the amount of retained austenite can increase the hardness.
The method of the sub-zero treatment is not particularly limited, but may be such that the quenched workpiece is held at a temperature of 0° C. or lower, preferably at a temperature of −77 to −196° C. For example, the quenched workpiece may be immersed in liquid nitrogen (−196° C.) for a predetermined period of time.
The retention time may be appropriately set depending on the temperature, and is not particularly limited, but is typically 30 minutes to 1 hour.

<Tempering process>
The tempering process is a process for tempering the sub-zero treated processed material.
Tempering can impart toughness to the martensite structure formed by the quenching and sub-zero treatment steps.
The tempering step is carried out under conditions such that the LMP is 7,000 to 17,000, preferably 8,000 to 15,000.
Here, LMP is the Larson-Miller parameter and is expressed by the following equation (1).
LMP=(t+273)×(C+log tr) (1)
In the formula, t is the heating (tempering) temperature (° C.), C is a material constant, and tr is the holding time (h) at the heating temperature. Note that the material constant C is about 20 for most heat-resistant steels.
If the LMP is less than 7000, the recovery of toughness is insufficient, whereas if the LMP exceeds 17000, the hardness and the amount of retained austenite decrease.
A typical tempering process is carried out at a heating temperature of 120 to 300° C. and a holding time of 30 minutes to 2 hours.

The martensitic stainless steel material according to the embodiment of the present invention has excellent corrosion wear resistance. In addition, the martensitic stainless steel material according to the embodiment of the present invention also has excellent corrosion resistance. Therefore, the martensitic stainless steel material according to the embodiment of the present invention can be used in various applications that require corrosion wear resistance and corrosion resistance. In particular, the martensitic stainless steel material according to the embodiment of the present invention is suitable for use in sliding members such as bearings.

The present invention will be described in detail below with reference to examples, but the present invention should not be construed as being limited to these.
<Experiment 1>
100 kg of stainless steel having the composition shown in Table 1 was melted in a vacuum melting furnace and cast into a slab of Φ180 mm. Next, the slab was heated to 1230°C, hot worked to Φ10 mm (reduction of area 99.7%), and cooled to room temperature to obtain a wire (worked material). Next, the wire was annealed in a batch furnace at 850°C for 2 hours and slowly cooled. Next, the annealed wire was cut into a length of 100 mm, held at the quenching temperature shown in Table 2 for 10 minutes, and air-cooled to a temperature of 50°C or less. Next, the quenched wire was immersed in liquid nitrogen for 30 minutes to perform sub-zero treatment. Next, the tempering temperature was controlled to obtain the LMP shown in Table 2, and the tempering treatment was performed, followed by air cooling to obtain a test material (martensitic stainless steel material). In the tempering treatment, the holding time was set to 60 minutes, and the material constant C for calculating the LMP was set to 20.

The following evaluations were carried out on the test materials obtained above.

(Composition of carbonitride)
A test piece of 5 mm in length was cut out from the test material, the entire surface was polished with #400, and then electrolysis (100 mV constant voltage) was performed in a non-aqueous solution (10% by mass maleic anhydride + 2% by mass tetramethylammonium chloride + remaining methanol) to dissolve 1 g of the matrix. Next, the sample was filtered through a filter with a hole diameter of 0.2 μm to extract the residue. The obtained residue was dried on the filter and then identified with an X-ray diffraction device. As a result of the identification, it was confirmed that inclusions and oxides were not detected, and the residue was carbides and nitrides.
The composition of the carbonitrides was determined by using a scanning electron microscope (SEM) and an energy dispersive X-ray analyzer (EDS) to randomly select five locations on the residue, determining the contents of Cr, Nb, V and W by area analysis, and taking the average value as the result.

(Average particle size of carbonitride)
A test piece having a length of 10 mm was cut out from the test material, cut in half parallel to the rolling direction, and the cut surface was mirror-polished. Then, using a Schottky scanning electron microscope (SU5000 manufactured by Hitachi High-Tech Corporation), the size (circle equivalent diameter) of the carbonitrides present in an observation area of 50 × 50 μm was measured in 10 visual fields. The method used was to capture an image using automatic particle analysis, recognize the particles, and measure the size of the carbonitrides. The average particle size of the carbonitrides was calculated as the average value of the sizes of the carbonitrides measured in 10 visual fields.

(Vickers hardness)
The Vickers hardness was measured using a Vickers hardness tester, by cutting out a test piece from the test material, and measuring the Vickers hardness in accordance with JIS Z2244: 2009. The test force was 294.2 N. The Vickers hardness was measured at any five points, and the average value was used as the result.

(Corrosion and wear resistance test)
A test piece (pin) was cut out from the test material, and the corrosion wear resistance was evaluated by a pin-on-disk friction wear tester. SUS440C (steel type M) was used for the disk. The pin-on-disk friction wear test was performed at a sliding speed of 2.0 m/s, a load of 5.0 kgf, and a time of 30 minutes while dropping a 3 mass% NaCl solution. In addition, the height of the pin before and after the test was measured to determine the volume of the pin before and after the test, and the wear volume was calculated by subtracting the volume of the pin after the test from the volume of the pin before the test. The volume of the pin was calculated by the following formula (2).
V = πr ² h (2)
In the formula, V is the volume of the test piece (pin) (mm ³ ), r is the radius of the test piece (mm), and h is the height of the test piece (mm).
In this evaluation, pin wear volumes of 20 ^mm3 or less were judged as ⊚, those between 20 ^mm3 and 30 ^mm3 or less were judged as ◯, and those exceeding 30 ^mm3 were judged as x.

The results of each of the above evaluations are shown in Table 2.

As shown in Table 2, Test Nos. 1 to 16 (invention examples) which satisfied the specified composition and had a metal structure containing the specified carbonitrides showed good results in the corrosion wear resistance test and the Vickers hardness evaluation.
In contrast, Test Nos. 17 to 26 (Comparative Examples), which did not have the prescribed composition and metal structure, did not have sufficient evaluation results in the corrosion wear resistance test. Also, Test Nos. 24 and 26 did not have sufficient Vickers hardness.

<Experiment 2>
In experiment 2, the heating temperature and area reduction rate in the hot working process, the quenching temperature and the tempering temperature were changed to carry out an experiment. Specifically, 100 kg of stainless steel of steel type A3 was melted in a vacuum melting furnace and cast into a slab of Φ180 mm. Next, the slab was heated to the heating temperature shown in Table 3, and then hot worked to have the area reduction rate shown in Table 3, and cooled to room temperature to obtain a wire (processed material). Next, the wire was annealed at 850°C for 2 hours in a batch furnace and slowly cooled. Next, the annealed wire was cut into a length of 100 mm, held at the quenching temperature shown in Table 3 for 10 minutes, and air-cooled to a temperature of 50°C or less. Next, the quenched wire was immersed in liquid nitrogen for 30 minutes to carry out a sub-zero treatment. Next, the tempering temperature was controlled to obtain the LMP shown in Table 3, and the tempering treatment was carried out, followed by air cooling to obtain a test material (martensitic stainless steel material). In the tempering treatment, the holding time was set to 60 minutes, and the material constant C for calculating the LMP was set to 20.

The test materials obtained above were evaluated in the same manner as in Experiment 1. The results are shown in Table 3.

As shown in Table 3, in Test Nos. 27 and 28 (invention examples) which were hot worked with a reduction in area of 90% or more, the average grain size of the carbonitrides was small, and the evaluation results of the corrosion wear resistance test were good.
In contrast, in Test Nos. 29 and 30 (Comparative Examples) which were hot worked with a reduction in area of less than 90%, the average grain size of the carbonitrides was large, and the evaluation results of the corrosion wear resistance test were insufficient.

As can be seen from the above results, the present invention can provide a martensitic stainless steel material with excellent corrosion and wear resistance, a manufacturing method thereof, and a sliding member.

Claims (13)

The composition includes C: 0.28 to 0.70 mass%, Si: 2.0 mass% or less, Mn: 2.0 mass% or less, Cr: 10 to 17 mass%, Mo: 3.0 mass% or less, N: 0.008 to 0.40 mass%, Ti: 0.1 mass% or less, Nb: 0.5 mass% or less, V: 1.0 mass% or less, and W: 1.0 mass% or less, the total amount of Nb, V, and W being 0.1 to 2.0 mass%, with the balance being Fe and impurities;
A martensitic stainless steel material having a metal structure including, as carbonitrides, at least carbonitrides having a Cr content of 25 mass% or less and a total amount of Nb, V and W of 10 mass% or more , and all of the carbonitrides having an average grain size of 5.0 μm or less . The martensitic stainless steel material according to claim 1, further comprising one or more selected from the group consisting of Ni: 0.05-2.0 mass%, Cu: 0.01-2.0 mass%, and Al: 0.1 mass% or less. The martensitic stainless steel material according to claim 1 or 2, further comprising 0.1 mass% or less of B. The martensitic stainless steel material according to any one of claims 1 to 3, further comprising one or more selected from Ca: 0.02 mass% or less, Mg: 0.02 mass% or less, Zr: 0.02 mass% or less, Hf: 0.02 mass% or less, and Co: 0.10 mass% or less. The martensitic stainless steel material according to any one of claims 1 to 4, having a Vickers hardness of 600 HV or more. The martensitic stainless steel material according to any one of claims 1 to 5, wherein the martensitic stainless steel material is a wire rod. The martensitic stainless steel material according to any one of claims 1 to 6, wherein the martensitic stainless steel material is used for a sliding member. A method for producing a martensitic stainless steel material according to claim 1,
a hot working step of heating a stainless steel having a composition containing 0.28 to 0.70 mass% C, 2.0 mass% or less Si, 2.0 mass% or less Mn, 10 to 17 mass% Cr, 3.0 mass% or less Mo, 0.008 to 0.40 mass% N, 0.1 mass% or less Ti, 0.5 mass% or less Nb, 1.0 mass% or less V, and 1.0 mass% or less W, the total amount of Nb, V, and W being 0.1 to 2.0 mass%, with the balance being Fe and impurities, to 1200°C or higher, and then hot working the stainless steel at a reduction in area of 90% or more to obtain a worked material;
An annealing step of annealing the workpiece;
a quenching step of quenching the annealed workpiece at 1050 to 1200 ° C;
A sub-zero treatment step of subjecting the quenched processed material to a sub-zero treatment;
and a tempering step of tempering the sub-zero treated processed material under conditions such that the LMP, represented by the following formula (1), is 7,000 to 17,000.
LMP=(t+273)×(C+log tr) (1)
In the formula, t is the heating temperature (° C.), C is a material constant 20, and tr is the holding time (h) at the heating temperature. A method for producing a martensitic stainless steel material according to claim 2,
The method for producing a martensitic stainless steel material according to claim 8, wherein the stainless steel further contains one or more selected from Ni: 0.05 to 2.0 mass%, Cu: 0.01 to 2.0 mass%, and Al: 0.1 mass% or less. A method for producing a martensitic stainless steel material according to claim 3,
The method for producing a martensitic stainless steel material according to claim 8 or 9, wherein the stainless steel further contains B: 0.1 mass% or less. A method for producing a martensitic stainless steel material according to claim 4,
The stainless steel further contains one or more selected from Ca: 0.02 mass% or less, Mg: 0.02 mass% or less, Zr: 0.02 mass% or less, Hf: 0.02 mass% or less, and Co: 0.10 mass% or less. The method for producing a martensitic stainless steel material according to any one of claims 8 to 10. A sliding member comprising the martensitic stainless steel material according to any one of claims 1 to 7. The sliding member according to claim 12, wherein the sliding member is a bearing.