JPH11264016A - Method for heat treating stainless steel and heat resistance stainless steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat treating method for stainless steel in which stainless steel with poor heat resistance is subjected to heat treatment and capable maintaining sufficient surface hardness even if being exposed to a high temp. after that and to provide a heat resistant stainless steel obtained by this heat treating method. SOLUTION: This heat treating method for a stainless steel is the one is which a stainless steel contg. at least, by weight 0.10 to 0.60% carbon, 6.00 to 18.00% chromium and <=4.00% molybdenum is subjected to plasma carburizing and quenching to harden the surface part, and next, high temp. tempering is executed to secondarily harden the surface part. At this time, the hardness of the surface part after the secondary hardening is preferably regulated to >=58 by C scale of Rockwell hardness, by which an inexpensive and economical stainless steel excellent in heat resistance, corrosion resistance, workability and wear resistance can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for heat-treating stainless steel capable of maintaining a sufficient surface hardness even when exposed to high temperatures, and a heat-resistant stainless steel obtained by such a heat treatment method. Specifically, for example, the track shaft and the slide member are relatively movable via rolling elements such as balls or rollers, such as the linear guide device shown in FIG. 1, the ball screw shown in FIG. 2, or a ball spline (not shown). The present invention relates to a material that is preferably applied to the material of the linear motion device assembled in the above.

[0002]

2. Description of the Related Art A linear guide device and a ball screw will be briefly described. In addition, regarding the ball spline,
The description is omitted because the function is almost the same as that of the linear guide device.

[0003] First, the linear guide device shown in FIG. 1 includes a track rail (track axis) 1 on which a ball rolling surface 1a is formed in a longitudinal direction and a plurality of balls 2 as rolling elements. A slide table (slide member) 3 fitted to the rail 1 and having an infinite circulation path for the ball inside. The slide table 3 moves on the track rail 1 as the ball 2 circulates. Reciprocate. However, there is also a case where the track rail 1 is reciprocated with the slide table 3 as the fixed side.

[0004] The slide table 3 is a table or the like (not shown).
And a pair of end plates 6 fixed to the front and rear end faces of the block 5. The infinite circulation path is formed on the block 5 with a load ball rolling surface 5b and a ball return hole 5c formed corresponding to the ball rolling surface 1a of the track rail 1, and with the load balls formed on both end plates 6. A turning path (not shown) communicating the rolling surface 5b and the ball return hole 5c.

Next, the ball screw shown in FIG. 2 is used together with the above-mentioned linear guide device, and gives a stroke of a linear motion to the slide table 3 in accordance with the rotation amount of a motor (not shown). is there.

As shown in the figure, the ball screw has a screw shaft 11 and a nut 12 in which helical ball rolling grooves 11a and 12a are formed by predetermined leads and are fitted into each other.
And a number of balls 13 as rolling elements arranged between the ball rolling grooves 11a and 12a.

The linear motion devices such as the linear guide device and the ball screw described above are required to have characteristics such as durability, wear resistance, and dimensional stability. In particular, these characteristics are important in a portion where the ball rolls while receiving a load. For this reason, high carbon low chromium steel, which is a bearing steel, is usually used as the material. However, in recent years, the manufacturing process or use environment of the linear motion device has been diversified, and heat resistance and corrosion resistance are often required.

[0008] When heat resistance is required for a linear motion device, alloy tool steel or high-speed tool steel for cold dies is usually used. When corrosion resistance is required, a relatively hard alloy is used. A high SUS440 type martensitic stainless steel is used.

An alloy tool steel or a high-speed tool steel contains tungsten (W), molybdenum (Mo), vanadium (V), chromium (Cr), etc., which have a high affinity for carbon (C), and is quenched. Since hard carbides are formed and hardened, the wear resistance is high. In addition, secondary precipitation carbides are formed by high-temperature tempering and secondary hardened,
Softening due to temperature rise in the manufacturing process or use environment is unlikely to occur. Therefore, it is preferably used for a linear motion device requiring heat resistance.

[0010] The martensitic stainless steel is transformed into martensite by quenching, and then tempered at an appropriate temperature to precipitate chromium carbide, thereby improving strength and toughness. In particular, the SUS440 type has a large carbon content and has the highest hardness among stainless steels, and is therefore preferably used as a linear motion device requiring corrosion resistance.

[0011]

However, alloy tool steel or high-speed tool steel has disadvantages in that the material itself is expensive, it is difficult to process, and the production cost is high. In addition, SUS440 type stainless steel is softened when exposed to high temperatures in a manufacturing process or a use environment, and its hardness is somewhat insufficient for a linear motion device. Furthermore, there is a problem that it is more expensive than ordinary bearing steel.

On the other hand, the present applicant uses a stainless steel equivalent to SUS440C (hereinafter referred to as "S steel") independently developed as one of the materials for the linear motion device. This S steel has carbon: 0.50 to 0.55% by weight, chromium: 1
0.00-11.00% by weight, molybdenum: 0.35-
0.65% by weight, silicon: 0.30% by weight or less, manganese: 0.30% by weight or less, phosphorus: 0.03% by weight or less, sulfur: 0.03% by weight or less, nickel: 0.60% by weight or less , Copper: 0.20% by weight or less, oxygen: 0.001
5% by weight or less and containing unavoidable impurities, excellent in corrosion resistance and workability, inexpensive,
By performing vacuum quenching and tempering, it is possible to obtain characteristics required as a material for a linear motion device, for example, a surface hardness of 58 or more on a Rockwell hardness C scale (hereinafter referred to as "HRC"). There is. Therefore, the above-mentioned alloy tool steel, high-speed tool steel, SUS4
Even if 40 type stainless steel or the like is not used, it can be preferably used as a material for a linear motion device.

However, as described above, there is a problem of diversifying the manufacturing process or use environment of recent linear motion devices.
For example, when the nut 12 of the ball screw shown in FIG. 2 uses an ordinary hardened and tempered S steel in the form of an insert, the nut 12 is a sleeve 12 made of S steel.
Since c is manufactured by casting aluminum by die casting, S steel may be exposed to a high temperature of about 660 ° C. for a short time (ten seconds or more). At this time, the S steel is annealed, and the hardness of the surface portion may not be able to maintain the required hardness of 58 HRC or more.

Therefore, gas carburizing and quenching was performed to increase the hardness of the surface. However, since S steel is stainless steel, it must be carburized and quenched at a high temperature of, for example, about 1050 ° C. There was a problem that an oxide film was formed and carburization was hindered. In addition, vacuum carburizing and quenching are preferable in that carburizing and quenching can be performed without forming an oxide film on the surface, but the carburizing and quenching temperature is maintained at a high temperature of about 1050 ° C., which is the optimum carburizing and quenching temperature for stainless steel. I have to do
The life of the furnace was shortened, and there was a practical problem.

[0015] The present invention provides an effective heat treatment method for a stainless steel capable of heat-treating a stainless steel having poor heat resistance and maintaining a sufficient surface hardness even after being exposed to a high temperature, and a heat treatment method for the stainless steel. It is an object of the present invention to provide a heat-resistant stainless steel excellent in economic efficiency.

[0016]

According to a first aspect of the present invention, there is provided a method for heat treating stainless steel, comprising:
Stainless steel containing 0.60% by weight, 6.00 to 18.00% by weight of chromium, and 4.00% by weight or less of molybdenum is plasma-carburized and quenched to harden its surface, and then tempered at a high temperature. It is characterized in that the surface portion is secondarily cured.

According to the present invention, the carbon content of the stainless steel surface is increased and hardened by plasma carburizing and quenching, and then the iron carbide and alloy carbide are precipitated on the surface of the stainless steel by high-temperature tempering and secondary hardened. Can be. The stainless steel used is carbon (C) of 0.1
Since it contains chromium (Cr) and molybdenum (Mo), which are secondary precipitated carbides at the time of high-temperature tempering, secondary hardening easily occurs at the time of high-temperature tempering, and is subsequently exposed to high temperatures. However, heat-resistant stainless steel that is hardly softened and maintains sufficient surface hardness can be obtained. In addition, since the hardness of the surface portion whose carbon content has increased due to carburization can be increased, it is necessary even for stainless steel which cannot obtain the high hardness required for linear motion devices by ordinary quenching and tempering. Heat resistant stainless steel having a high hardness.

In addition, since carburizing and quenching are performed by plasma carburizing, an oxide film is not formed and the film has a brilliant property, so that it is possible to easily carburize stainless steel which is a hard carburizing material. Therefore, effective carburizing and quenching can be performed, so that carburizing time can be shortened, and there is no need to consider the life of the furnace unlike vacuum carburizing and quenching, which is economical and excellent in practical use.

Further, since carburizing is performed only during glow discharge, the amount of carbon to be carburized can be easily adjusted. Therefore, the amount of secondary precipitated carbide generated by the subsequent high-temperature tempering can be adjusted, and the hardness of the stainless steel after the secondary hardening can be adjusted.

According to a second aspect of the present invention, in the method for heat treating stainless steel according to the first aspect, the component composition of the stainless steel further includes silicon: 1.00% by weight or less, and manganese: 1.00% by weight or less. , Phosphorus: 0.03% by weight or less, sulfur: 0.03% by weight or less, nickel: 0.60% by weight or less, copper: 0.20% by weight or less, oxygen: 0.002
It contains 0% by weight and unavoidable impurities.

According to the present invention, even if stainless steel is inexpensive and has excellent corrosion resistance and workability, but does not have sufficient heat resistance, it can be formed by plasma carburizing and high-temperature tempering.
It is possible to obtain a heat-resistant stainless steel that hardly softens even when exposed to a high temperature and maintains a necessary and sufficient hardness.

According to a third aspect of the present invention, in the method for heat treating stainless steel according to the first or second aspect, the plasma carburizing and quenching is performed at 1000 to 1100 ° C, and the high temperature tempering is performed at 400 to 600 ° C. It is characterized by being

According to the present invention, since plasma carburizing and quenching are performed at 1000 to 1100 ° C., sufficient carburizing and quenching of stainless steel can be performed, and necessary carburizing can be performed in a short time. Furthermore, since high temperature tempering is performed at 400 to 600 ° C.,
It does not anneal even when exposed to a temperature lower than the high-temperature tempering temperature, and even when exposed to a temperature higher than the high-temperature tempering temperature, the hardness does not easily decrease for a short time, which is necessary. Sufficient hardness can be maintained.

The invention according to claim 4 is the invention according to claims 1 to 3.
The method for heat treating stainless steel according to any of
It is characterized in that the hardness of the surface portion after the secondary curing is 58 or more on a C scale of Rockwell hardness.

According to the present invention, Rockwell hardness C
Since stainless steel having a hardness of 58 or more on a scale can be obtained, the stainless steel obtained by this method has excellent heat resistance, corrosion resistance, workability, and wear resistance, and is inexpensive and economical. It can be preferably used as a material for an apparatus.

The heat-resistant stainless steel according to the fifth aspect of the present invention comprises at least 0.10 to 0.60% by weight of carbon and chromium:
A stainless steel containing 6.0 to 18.00% by weight and molybdenum: 4.00% by weight or less, wherein the surface portion of the stainless steel is hardened by plasma carburizing and quenching at 1000 to 1100 ° C. Secondary hardening is performed by high-temperature tempering at 600 ° C., and the hardness of the surface after the secondary hardening is 58% on a Rockwell hardness C scale.
It is characterized by the above.

According to the present invention, at least carbon: 0.1.
10 to 0.60% by weight, chromium: 6.00 to 18.00
% By weight, molybdenum: a stainless steel containing 4.00% by weight or less is subjected to plasma carburizing and quenching at 1000 to 1100 ° C. and high-temperature tempering at 400 to 600 ° C., so that the surface of the stainless steel is secondarily hardened. A stainless steel that is hard to soften even when heated to a high temperature and has heat resistance can be obtained. Further, since its hardness is 58 or more on the C scale of Rockwell hardness, it can be preferably used as a heat-resistant material for a linear motion device.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION The heat treatment method for stainless steel of the present invention and the heat-resistant stainless steel obtained by the heat treatment method will be specifically described.

The heat treatment method of the present invention comprises at least carbon:
0.10 to 0.60% by weight, chromium: 6.00 to 18.
A stainless steel containing 00% by weight and molybdenum: 4.00% by weight or less is subjected to plasma carburizing and quenching to harden its surface, and then is subjected to high-temperature tempering to secondarily harden the surface.

In order to secondary harden the surface of stainless steel during high-temperature tempering, it is necessary that the surface of stainless steel contains a component composition that generates secondary precipitated carbides. Carbon, which is an element essential for carbide formation, can easily adjust the amount of carburization by plasma carburization. Therefore, the amount of secondary precipitated carbides precipitated during high-temperature tempering changes, so that the hardness of the surface after the secondary hardening can be easily adjusted.

The stainless steel used in the method for heat treating stainless steel according to the present invention, and the heat treatment conditions of plasma carburizing and quenching and high-temperature tempering are described below, and the heat-resistant stainless steel obtained by the heat treatment method is described. I do.

(1) Stainless steel As the stainless steel used in this method, chromium (C) is used to increase the hardness (so-called secondary hardening) by forming fine secondary precipitated carbides by high-temperature tempering.
r), molybdenum (Mo), tungsten (W), vanadium (V), and other elements containing a large amount of an element having a strong carbide-forming ability are preferable. Among these, it is preferable to contain chromium and molybdenum when corrosion resistance and workability are particularly taken into consideration.

When stainless steel having excellent corrosion resistance and workability is used as a material for a linear motion device, a stainless steel having a hardness that could not be obtained before the heat treatment is subjected to heat treatment by plasma carburizing and high-temperature tempering. Stainless steel having any composition can be used as long as the hardness can be made higher than the hardness before the heat treatment.
Among such stainless steels, at least carbon:
0.10 to 0.60% by weight, chromium: 6.00 to 18.
It is preferable that the composition contains at most 00% by weight and molybdenum: 4.00% by weight. Further, silicon: 1.00% by weight or less, manganese: 1.00% by weight or less, and phosphorus: 0.1% by weight.
03% by weight or less, sulfur: 0.03% by weight or less, nickel: 0.60% by weight or less, copper: 0.20% by weight, oxygen:
Those containing 0.0020% by weight or less and unavoidable impurities are more preferable.

Next, the reason why the preferable composition of stainless steel is limited to the above range will be described.

Carbon (C) is an essential element for carbide formation. When carbon (C) is present in a large amount on the surface of stainless steel, carbon (C) combines with an element having a strong carbide-forming ability to produce more secondary precipitated carbides. Can be. Since a large amount of carbon can be contained in the surface portion of stainless steel by plasma carburization, stainless steel having a small carbon content can be used. However, the carbon content is 0.10% by weight
If it is smaller, the oxygen (O ₂ ) concentration in the stainless steel is reduced to 0.
Since it cannot be kept below 0020% by weight, the fatigue life is shortened when the heat-treated stainless steel is used for a linear motion device or the like. Therefore, the lower limit of the carbon content is 0.1.
It is preferably at least 10% by weight, particularly preferably at least 0.20% by weight. On the other hand, if the carbon content exceeds 0.60% by weight, not only the obtained hardness is saturated and a sufficient carburizing effect cannot be obtained, but also the machinability and cold workability are inferior, and further, it occurs during high temperature tempering. The secondary precipitated carbides on the surface become coarse crystals and easily become the starting point of fatigue fracture. Therefore, the upper limit of the carbon content is 0.60% by weight or less, particularly 0.1% by weight.
It is preferable that the content be 5% by weight or less.

Chromium (Cr) is more easily oxidized than iron (Fe), and its oxide is dense and hardly corroded by oxidizing acids such as nitric acid as well as in the air. It is also an indispensable element for stainless steel because it has improved oxidation resistance, and because it is an element forming secondary precipitated carbides, its content is the hardness after secondary hardening, corrosion resistance, workability, heat resistance. Has a great effect on Increasing the chromium content improves corrosion resistance. Further, by bonding with a large amount of carbon contained in the surface portion by plasma carburization, many fine chromium carbides are precipitated, so that the hardness of the surface portion can be further improved. If the chromium content exceeds 18.00% by weight, the secondary precipitated carbides generated at the time of high-temperature tempering become huge crystals, and the required hardness required cannot be obtained. Therefore, the upper limit of the chromium content is preferably 18.00% by weight or less, particularly preferably 11.00% by weight or less. Further, when the chromium content is less than 6.00% by weight, the corrosion resistance is reduced and a sufficient amount of chromium carbide cannot be precipitated, so that the surface portion has a desired hardness (for example, 58HRC). Can not. for that reason,
The lower limit of the chromium content is 6.00% by weight or more, especially 1% by weight.
The content is preferably 0.00% by weight or more.

Molybdenum (Mo) is an element forming secondary precipitated carbides, and further promotes the refinement of carbides to reduce temper embrittlement. Therefore, secondary hardening provides high hardness stainless steel. It is an important element in that it can provide heat resistance at high temperatures. However, if the content exceeds 4.00% by weight, molybdenum tends to segregate at the grain boundaries, so that a surface layer in which carbides are uniformly deposited cannot be obtained, and furthermore, the secondary layer of the surface generated at the time of high-temperature tempering is not obtained. The desired hardness (for example, 58HRC) cannot be obtained by promoting the coarsening of the precipitated carbide. Therefore, the upper limit of the molybdenum content is preferably 4.00% by weight or less, particularly preferably 1.00% by weight or less. Also, if sufficient secondary hardening can be shown by chromium, molybdenum does not have to be intentionally contained,
Preferably, the content is 0.50% by weight or more.

The following elements are not directly involved in stainless steel in terms of improving heat resistance by high-temperature tempering.
In practical use, they are preferably added to impart various properties.

[0039] Silicon (Si) is added as a deoxidizing agent. Since it has a low affinity for carbon, it does not form carbides, but forms a solid solution with ferrite to increase hardness and strength.
If it is contained in excess of wt%, machinability and cold workability will be reduced. Therefore, the silicon content was limited to 1.00% by weight or less.

Manganese (Mn) is added as a deoxidizing agent. It also combines with sulfur to prevent red-hot embrittlement,
It has the effect of improving the hardenability by lowering the transformation point by forming a solid solution and increasing the strength and toughness. However, if added in excess of 1.00% by weight, machinability and cold workability deteriorate. Therefore, the manganese content is limited to 1.00% by weight or less.

Phosphorus (P) has the effect of improving corrosion resistance. However, when added in excess of 0.03% by weight, segregation occurs at the grain boundaries and the secondary workability and fatigue life are reduced. Therefore, the phosphorus content is limited to 0.03% by weight or less.

Sulfur (S) combines with manganese to form MnS
To prevent red hot embrittlement. However, MnS is soft and brittle, and causes a decrease in mechanical properties.
It is preferably at most 5% by weight. However, it is particularly preferable to limit the sulfur content to 0.03% by weight or less in consideration of a material for a linear motion device exposed to a manufacturing process or a use environment at a high temperature.

Nickel (Ni) makes ferrite fine and enhances hardenability, so that its addition can easily increase strength and toughness. However, the nickel content was limited to 0.60% by weight or less in view of the disadvantage of being expensive and increasing the temper brittleness.

Copper (Cu) is effective for improving precipitation hardening and sulfuric acid resistance in stainless steel. However, since it causes red hot embrittlement, the content is usually preferably 0.35% by weight or less. However, the copper content was limited to 0.20% by weight or less in consideration of the manufacturing process and the use environment at a high temperature.

Oxygen (O) produces oxides with other metal elements, segregates at grain boundaries, and causes red hot embrittlement. In particular, 0.
If the content exceeds 0020% by weight, the fatigue life may be reduced. Therefore, it is preferable to limit the oxygen content to 0.0020% by weight or less, particularly 0.0015% by weight or less.

The stainless steel described above is made of chromium (C
r) and molybdenum (Mo), the plasma carburizing quenching and high-temperature tempering produce secondary precipitated carbides on the surface and secondary hardening, so that they are not easily softened even when subsequently exposed to high temperatures. Sufficient surface hardness (eg, 58
It can be a heat-resistant stainless steel maintaining HRC). In addition, since the amount of carbon on the surface can be increased by carburization, even if the stainless steel cannot obtain a high hardness (for example, 58HRC) required for a linear motion device by ordinary quenching and tempering, the surface of the surface can be hardened. Since the hardness can be increased, the required hardness (for example, 58 HR)
Heat-resistant stainless steel having C).

(2) Plasma carburizing and quenching Plasma carburizing is usually performed in an atmosphere of a hydrocarbon gas system such as propane gas (C ₃ H ₈ ) in an atmosphere of 1 to 10 Torr (133 to 10 Torr).
The pressure is reduced to 1333 Pa), and a glow discharge is generated while the stainless steel to be treated is used as a cathode and the electrode is used as an anode while heating. Accelerate the carbon ions generated at this time,
This is done by striking a stainless steel surface.

Since carburization is performed only during glow discharge, the carbon concentration on the surface of stainless steel can be easily adjusted by a simple method of adjusting the discharge time, which is superior to vacuum carburization. ing. Since the difference in carbon concentration on the surface greatly affects the amount of secondary precipitated carbide generated during high-temperature tempering, the hardness of the surface portion of the stainless steel obtained after the heat treatment can be easily adjusted. In the heat-resistant stainless steel of the present invention, a preferable surface carbon concentration is 1.3 to 2.3% by weight.

Further, since hydrogen ions are present in the plasma atmosphere, carburization can be performed while preventing the chromium in the stainless steel from forming chromium oxide on its surface by its reducing action. The carburized stainless steel has a brilliant effect, and can be carburized more effectively than vacuum carburized stainless steel, which is a hard carburizing material. It is economical because there is no need to consider the life of the device, and it is practically excellent.

FIG. 3 shows an example of plasma carburizing and quenching conditions. The plasma carburizing and quenching treatment is usually 8
This is performed while the temperature is maintained at 00 to 1100 ° C for 1 to 24 hours. During this time, first, a first soaking treatment is performed in an inert atmosphere such as nitrogen, and then a reduction treatment (clean-up treatment) of the stainless steel surface is performed in a reducing gas atmosphere with hydrogen. Plasma carburizing is performed in the atmosphere so as to have a predetermined carbon content,
Finally, diffusion treatment is again performed in an atmosphere of an inert gas such as nitrogen. Thereafter, quenching treatment may be performed. However, in the case of stainless steel, in order to perform sufficient quenching, the material is once placed in an inert atmosphere such as nitrogen at 1000 to 1100 ° C. for 0.5 to 3 hours.
It is preferable to quench the steel after the second soaking heat treatment for a period of time. It is preferable that the cooling rate at the time of quenching is performed at a cooling rate of about normal oil cooling. A martensite structure is formed by quenching.

(3) High-temperature tempering High-temperature tempering is for recovering the toughness of the quenched stainless steel and for secondary hardening the surface.
Performed on plasma carburized and quenched stainless steel.

By high-temperature tempering, carbides and the like are precipitated from the supersaturated martensite structure to make the structure close to a stable structure, and the toughness can be recovered.

The desired hardness required for stainless steel (eg, 58 HRC) is provided by secondary hardening during high temperature tempering. After the heat treatment, the stainless steel is not annealed even if it is exposed to a temperature lower than the high temperature tempering temperature, and even if it is exposed to a temperature higher than the high temperature tempering temperature, for a short time. Hardness hardly decreases, and desired surface hardness (for example, 58HRC)
Heat-resistant stainless steel maintaining the above.

The temperature for the high temperature tempering is preferably from 400 to 600 ° C., particularly preferably from 450 to 530 ° C. The high temperature tempering time is usually 1 to 3 hours.

(4) Hardness Secondary precipitated carbides are formed on the surface of stainless steel obtained by plasma carburizing and quenching and high-temperature tempering, and the hardness of the surface is determined by ordinary quenching / tempering or carburizing / quenching / tempering. The hardness is higher than that obtained by performing the above. Furthermore, its hardness does not easily decrease even when exposed to high temperatures, and a stainless steel having heat resistance can be obtained. The hardness of the stainless steel obtained by such heat treatment can be obtained only by plasma carburizing and quenching and high temperature tempering, but cannot be obtained by other carburizing and quenching and room temperature tempering.

As the hardness of stainless steel, a hardness of 58 or more on the C scale of Rockwell hardness is required.
It is preferable as a material for a linear motion device as shown in FIG. 1 or FIG. Also, when used for other purposes,
Other hardness (for example, 56HRC, 57HCR, etc.) may be used.

Although the present invention is a method of heat treating stainless steel, its surface is secondarily hardened by plasma carburizing and quenching, and as a result, it hardly softens even when exposed to high temperatures (hardness). Is not limited to stainless steel, and other steels may be used as long as they can impart a property that does not cause much reduction of the steel.

For example, tool steels for hot dies such as SKD61 and SKD62 cannot obtain a hardness of 58HRC or more even after high-temperature tempering after normal quenching. If plasma carburizing and high temperature tempering are performed, the hardness can be easily increased to 58HRC.
It can be adjusted as described above, and can be imparted with a property of not easily softening even after being exposed to a high-temperature atmosphere.

Further, like SKD4 and SKD5,
Even if high temperature tempering is performed after normal quenching, even if the hardness is less than 50 HRC, even for tool steel for hot dies,
By the heat treatment method of the present invention, the hardness can be adjusted to 58 HRC or more, and it is possible to impart a property that is not easily softened even when exposed to a high-temperature atmosphere thereafter.

The same applies to hot die tool steels such as 3Cr-3Mo steel and 3Ni-Mo steel.

Accordingly, even steels other than the above-mentioned stainless steels contain components capable of forming secondary precipitated carbides by high-temperature tempering, that is, chromium, molybdenum, tungsten, vanadium and the like. If such a material is used, carburized carbon and carbides are generated on the surface by plasma carburization and are secondarily cured, and as a result, a property (heat resistance) that is hard to soften even when exposed to high temperatures can be imparted. Therefore, although it is inexpensive, it is extremely economical as a material for the linear motion device can be used for the linear motion device even if the material does not withstand the conventional use and has poor heat resistance. However, the heat treatment method and heat-resistant stainless steel for stainless steel according to the present invention can be applied not only to linear motion devices but also to other uses.

[0062]

Next, the present invention will be described more specifically with reference to examples and comparative examples of the present invention.

Example 1 Test pieces (outer diameter φ33 mm × inner diameter φ27 m) were prepared using stainless steel having the composition shown in Table 1.
m × 30 mm in length), and plasma carburizing and high-temperature tempering were performed under the following conditions to obtain a stainless steel piece of the present invention.

[0064]

[Table 1]

Plasma carburizing and quenching conditions; Plasma carburizing conditions: 960 ° C., 60 minutes, C ₃ H ₈ gas atmosphere Discharge current: 7 A, discharge voltage: 490 V Second soaking conditions: 1050 ° C., 30 minutes, nitrogen gas atmosphere Quenching 1050 ° C. 60 ° C, cooling medium: oil High temperature tempering conditions; tempering temperature, time 500 ° C, 2 hours Atmosphere In air

On the other hand, a test piece (outer diameter φ33 mm × inner diameter φ27 m) was prepared using stainless steel having the same component composition as shown in Table 1.
m × 30 mm in length), and subjected to vacuum quenching and normal temperature tempering under the following conditions to obtain a stainless steel piece for comparison.

Vacuum quenching conditions; Heating temperature (at the time of quenching) 1030 ° C. Heating time (at the time of quenching) 1.5 hours Atmosphere Vacuum quenching 1030 ° C. → normal temperature, cooling medium: nitrogen gas Tempering conditions at normal temperature; tempering temperature, time 170 ° C., 2 Time Atmosphere In the air

The obtained stainless steel pieces of the present invention and comparative stainless steel pieces were cast by aluminum die casting. The casting temperature was 639 ° C., the casting time was 6 seconds, and the respective surface hardnesses after cooling to room temperature were measured. The surface hardness was measured using a Vickers hardness meter under a load of 300 gf.
The obtained values were converted to Rockwell C scale (HRC) values.

The hardness of the stainless steel piece of the present invention is 700 ±
It was 20 Hv (equivalent to 60 HRC) and sufficient hardness could be obtained as a material for a linear guide device, but the comparative stainless steel piece was 600 ± 20 Hv (equivalent to 55 HRC).
Met.

(Example 2) A test piece (outside diameter φ33 mm × inside diameter φ27 m) was prepared using stainless steel having the component composition shown in Table 1.
m × 30 mm in length), plasma carburized and quenched under the same conditions as in Example 1, and then tempered at various temperatures for 1 hour.

On the other hand, a test piece (about 15 mm × 10 mm) was prepared using stainless steel having the component composition shown in Table 1, and subjected to vacuum quenching under the same conditions as in Example 1; Tempering at a temperature of 1 hour.

The hardness of the obtained test piece was measured and is shown in FIG. The surface hardness was measured on a C scale (HRC) using a Rockwell hardness tester.

The test piece subjected to plasma carburizing and quenching was 500
At a tempering temperature of ° C., the hardness increased to 60.5 HRC by secondary hardening, which was sufficient for a linear guide device. On the other hand, the hardness of the test piece subjected to vacuum quenching was increased by the secondary curing at a tempering temperature of 500 ° C.
6HRC.

(Example 3) A test piece (about 15 mm × 10 mm) obtained by using a stainless steel having the composition shown in Table 1 and subjecting it to plasma carburizing and high-temperature tempering under the same conditions as in Example 1.
mm) and a test piece obtained by vacuum quenching at 1050 ° C. and high temperature tempering at 500 ° C. for 2 hours (about 15 mm × 10
mm).

FIG. 5 shows that each of these test pieces was 100-70.
It is a graph of the measurement result of the high temperature hardness measured while keeping it in a high temperature atmosphere of 0 degreeC for 5 minutes. At this time, each temperature was maintained for 5 minutes, and a Vickers hardness (Hv) was measured by applying a load of 300 gf for 10 seconds. The Rockwell hardness (HRC) is the Vickers hardness (Hv) obtained.
And converted.

From these results, it can be seen that even if a stainless steel which has been subjected to plasma carburizing and high-temperature tempering and has a hardness of 660 Hv (equivalent to 58 HRC) or more when cooled to room temperature after high-temperature tempering, , The deformation resistance is reduced, indicating a low hardness. However, the test pieces subjected to plasma carburizing and high-temperature tempering had significantly higher high-temperature hardness than the test pieces subjected to vacuum quenching and high-temperature tempering. This indicates an excellent effect that the heat-resistant stainless steel of the present invention can be used continuously even in a relatively high-temperature atmosphere.

Example 4 Test pieces (outer diameter φ60 × inner diameter φ25 × length 10 mm) were prepared from stainless steel having the composition shown in Table 2, and were subjected to plasma carburizing and quenching under the following conditions. Thus, a stainless steel piece of the present invention was obtained.

[0078]

[Table 2]

Plasma carburizing and quenching conditions; first soaking heat treatment 960 ° C., 0.5 hours Plasma carburizing 960 ° C., 1.5 hours, C ₃ H ₈ gas atmosphere Discharge current: 7 A, discharge voltage: 490 V Diffusion treatment 960 ° C., 1 .5 hours Second soaking heat treatment 1050 ° C, 0.5 hour, nitrogen gas atmosphere Quenching 1050 ° C → 60 ° C, cooling medium: oil High temperature tempering condition; tempering temperature, time 550 ° C, 2 hours atmosphere in air

On the other hand, a test piece (outer diameter φ60 mm × inner diameter φ25 m) was prepared using stainless steel having the same component composition as shown in Table 2.
mx 10 mm in length) and subjected to vacuum quenching and normal temperature tempering under the following conditions to obtain a stainless steel piece for comparison.

Vacuum quenching conditions; Heating temperature (at the time of quenching) 1030 ° C Heating time (at the time of quenching) 3.0 hours Atmosphere Vacuum quenching 1030 ° C → room temperature, cooling medium: oil Room temperature tempering condition; tempering temperature, time 150 ° C, 2 hours Atmosphere In the air

A thrust rolling life test was performed on the obtained stainless steel pieces of the present invention and comparative stainless steel pieces. The thrust rolling life test was performed using a thrust life tester under the following conditions.

Thrust rolling life test conditions; Load ball diameter: 9.525 mm Number of load balls: 6 Load ball pitch diameter: φ45 mm Load ball material: SUJ2 Lubricating oil amount: 80 cm ³ / min Lubricating oil: Spar Multi 68 oil (Idemitsu Kosan) Number of rotations: 800 rpm Load load: 627.2 N / ball

As the rolling life, the test was stopped when flaking occurred on the rolling surface of the test piece, and the number of rotations at that time was taken as a Weibull distribution to calculate the L ₁₀ and L ₅₀ life. FIG. 6 shows a Weibull distribution of the relationship between the number of rotations and the damage life.

The stainless steel slab of the present invention has a value of L ₁₀ = 1.7 ×
10 ⁶ times, L ₅₀ = 3.9 × 10 ⁶ times, and the comparative stainless steel piece L ₁₀ = 0.6 × 10 ⁶ times, L ₅₀ = 2.1 × 1
It showed excellent rolling life compared to 0 ⁶ times.

The carbon concentration of the surface layer of the stainless steel slab of the present invention was measured by EPMA analysis and found to be about 1.5% by weight due to the influence of carburizing and quenching. That is, the stainless steel slab of the present invention can contain a large amount of carbon on its surface by carburizing and quenching, and subsequently generates a large amount of secondary precipitated carbides by high-temperature tempering and is secondarily hardened. However, it has favorable characteristics that it can maintain a sufficient surface hardness and also has an excellent rolling life.

[0087]

As described above, according to the method for heat-treating stainless steel of the present invention, the surface of stainless steel containing a predetermined composition can be secondarily hardened by plasma carburizing and high-temperature tempering. Therefore, even for stainless steel, which cannot obtain sufficient hardness by ordinary quenching and tempering, a desired hardness (for example, 58 HRC)
The above can be considered. In addition, it is easy to carburize stainless steel, which is difficult to carburize, so carburizing time can be reduced,
Furthermore, since the amount of carburization can be changed, the hardness after secondary curing can be adjusted. By the heat treatment method of the present invention, a sufficient hardness (for example, 58H
A heat-resistant stainless steel maintaining RC) can be easily obtained.

In addition, although stainless steel is inexpensive and has excellent corrosion resistance and workability, heat resistance can be imparted even to stainless steel having insufficient heat resistance, and heat resistance, corrosion resistance, workability, and wear resistance can be improved. An excellent, inexpensive, and economical heat-resistant stainless steel can be easily obtained.

Further, according to the heat-resistant stainless steel of the present invention, the heat-resistant stainless steel has the heat resistance (the property that it is hard to be softened even when exposed to a high temperature), which cannot be obtained by ordinary carburizing and tempering of stainless steel. , Desired hardness (for example, 58H
(RC) or higher, so that it can be suitably used as a material requiring wear resistance and toughness. Further, since it has excellent corrosion resistance and heat resistance, it can be used in a variety of manufacturing processes and use environments. It can withstand the bad environment caused by the change.

[Brief description of the drawings]

FIG. 1 is a perspective view including a partial cross section showing a main part of a linear guide device.

FIG. 2 is a side view including a partial cross section showing a main part of the ball screw.

FIG. 3 is a graph showing an example of plasma carburizing and quenching conditions.

FIG. 4 is a graph showing the relationship between tempering temperature and hardness in a test piece subjected to plasma carburizing and quenching and a test piece subjected to vacuum quenching.

FIG. 5 is a graph showing a measurement result of hardness (high-temperature hardness) measured in a high-temperature atmosphere.

FIG. 6 is a graph showing a Weibull distribution of the relationship between life and failure probability.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 track rail 1a ball rolling surface 2 ball 3 slide 5 block 5a mounting surface 5b load ball rolling surface 5c ball return hole 6 end plate 11 screw shaft 11a ball transfer groove 12 nut 12a ball transfer groove 12c sleeve 13 ball

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁶ Identification code FI // C22C 38/44 C22C 38/44

Claims (5)

[Claims] 1. A stainless steel containing at least 0.10 to 0.60% by weight of carbon, 6.01 to 18.00% by weight of chromium, and 4.00% by weight of molybdenum is subjected to plasma carburizing and quenching. A method for heat-treating stainless steel, comprising: hardening the surface and then tempering at a high temperature to secondary harden the surface. 2. The composition of stainless steel according to claim 1, further comprising silicon: 1.00% by weight or less, manganese: 1.0% or less.
0% by weight or less, phosphorus: 0.03% by weight or less, sulfur: 0.
03% by weight or less, nickel: 0.60% by weight or less, copper:
2. The composition according to claim 1, further comprising 0.20% by weight or less, oxygen: 0.0020% by weight or less, and unavoidable impurities.
The method for heat treating stainless steel according to item 1. 3. The plasma carburizing and quenching is carried out at 1000 to 1
Performed at 100 ° C., and the high-temperature tempering is performed at 400 to 600 ° C.
The heat treatment method for stainless steel according to claim 1 or 2, wherein the heat treatment is performed. 4. The hardness of the surface portion after the secondary curing,
The method for heat treating stainless steel according to any one of claims 1 to 3, wherein the C scale of Rockwell hardness is 58 or more. 5. A stainless steel containing at least 0.10 to 0.60% by weight of carbon, 6.01 to 18.00% by weight of chromium, and 4.00% by weight or less of molybdenum. Is hardened by plasma carburizing and quenching at 1000 to 1100 ° C.
A heat-resistant stainless steel which is secondarily hardened by high-temperature tempering at 600 ° C., and has a hardness of 58 or more on the C scale of Rockwell hardness after the second hardening.