JP7300140B2 - Manufacturing method for hydrogen embrittlement-preventive steel workpiece - Google Patents

Description

TECHNICAL FIELD The present invention relates to a manufacturing method (refining method) for heat-treating a steel workpiece so that hydrogen embrittlement does not occur.

Heat treatment of steel workpieces is performed for various purposes such as increasing hardness, improving toughness, refining, and increasing brightness. In any case, a heating device is required, and the heating device may be a gas furnace (atmosphere furnace) using hydrocarbon gas such as natural gas or propane gas as a fuel (or carbon source), or an electric heater as a heat source. There are multiple types such as the vacuum furnace and muffle furnace that are used.

Whether the hardness is increased or tempered, quenching and tempering are performed after the heating process. For quenching, water or oil (that is, liquid) is used as a cooling means, and nitrogen gas or carbon dioxide gas is used. There are cases where such gas is used.

Delayed fracture due to hydrogen embrittlement is a major problem when heat-treating workpieces for hardening or thermal refining. That is, although hydrocarbon gas is often used as a heating means and a carbon source for carburizing, delayed fracture occurs when hydrogen penetrates into the workpiece during the heating process.

Hydrogen embrittlement is caused by hydrogen, but the main mechanism of hydrogen embrittlement has been that hydrogen itself causes embrittlement. However, the reality is that even if the residual hydrogen is zero, the delayed fracture has not been eliminated.

In this regard, the inventors of the present application speculate that the cause of hydrogen embrittlement is not the hydrogen itself, but the pores formed by the intrusion of hydrogen. While using as, by preventing or significantly suppressing the penetration of hydrogen into the work, we developed a hardness increasing technology that prevents or significantly suppresses the generation of voids in the work, and disclosed this in Patent Document 1. According to the technique of Patent Document 1, a very high delayed fracture prevention effect is exhibited compared to conventional products, and it has been highly evaluated in the market.

On the other hand, refining is one of the fields of heat treatment of steel workpieces. The concept of thermal refining is not necessarily clear, and there are documents that use the term thermal refining for heat treatment involving carburizing or nitriding followed by quenching and tempering. In any case, the heating step is essential, and as a heating means, a gas atmosphere furnace is generally used in which a hydrocarbon gas is thermally decomposed using electricity or gas as a heating source. There was a problem that the hydrogen contained in the steel penetrates into the workpiece and causes hydrogen embrittlement.

Regarding this point, it is thought that the heating should be performed in a carbon-free and hydrogen-free state without using gas as a heating means. For example, Patent Document 2 discloses a heat treatment method in which a workpiece is heated using a graphite-lined furnace (muffle furnace) and then quenched. If this heating means is used for refining, hydrogen embrittlement occurs. It is presumed that it can be refined to a state where it does not.

JP 2017-172035 A Republished WO2014/007046

The types of steel materials vary depending on their compositions and applications, but the mechanical properties and heat treatment properties are greatly affected by the amount of carbon and the blending elements. Addition of carbon increases hardness and improves hardenability. It affects various properties such as toughness and corrosion resistance. That is, various elements are added as modifiers in order to obtain performance that cannot be ensured by the addition of carbon alone.

In addition, JIS specifies various steel grades according to the amount of carbon and blending elements, etc. Users specify and purchase steel grades according to their use, but many steel workpieces do not have stable quality. stability (that is, stability of mechanical properties). For example, in the case of steel machine parts, the harder the better, the better. In order to ensure the smooth movement and durability of the entire device, the mechanical properties such as hardness, elasticity, and wear resistance should be uniformed. to ensure harmony with other parts.

Therefore, when we review the refining by heat treatment, we find that the hardenability of workpieces made of medium- and high-carbon alloy steel is particularly excellent, so even if special hardening treatments such as carburizing and nitriding are not performed, quenching and quenching will not be necessary. In many cases, the necessary hardness can be secured only by returning, and it can be said that there is a strong demand for stabilization of quality in each process for such a work.

Therefore, if we proceed further, in order to stabilize the quality in the heating process, in addition to creating a carbon-free and hydrogen-free atmosphere, we must prevent the carbon originally contained in the workpiece from diffusing. It is necessary to manage such as holding (so as not to decarburize), but in a graphite furnace such as Patent Document 2, it is a component of graphite, also related to the fact that the furnace is at atmospheric pressure. There is a risk that carbon will diffuse into the furnace and enter the work (carburize), but the amount of carburization varies depending on the work and is not constant, so there is a problem that it is difficult to stabilize the quality.

In addition, in atmospheric furnaces such as gas furnaces and muffle furnaces, there is a possibility that a large amount of oxygen remains in the furnace, so there is also the problem that the work is easily oxidized (not only the problem of oxidation of iron, but also the work There is also a problem that the contained carbon combines with the oxygen contained in the air to form carbon dioxide gas, which is diffused from the workpiece and decarburized, resulting in a decrease in hardness.).

On the other hand, if a vacuum furnace is used as a heating means, there is no problem of carburization, oxidation, or decarburization, but conventionally, vacuum furnaces are used in combination with gas quenching, so quenching increases hardness. may be inadequate.

The present invention has been made in view of such circumstances, and aims to provide a method for obtaining a steel work excellent in quality stability while preventing hydrogen embrittlement.

TECHNICAL FIELD The present invention relates to a method of manufacturing a steel workpiece made of any one of SUJ, SCM, SKS, and CNCM defined by JIS by heat-treating it in a state in which hydrogen embrittlement does not occur.

And the invention of the present application is
"A heating process performed using a vacuum furnace that heats under reduced pressure, a quenching process using oil or water in a quenching chamber attached to the vacuum furnace via a relay passage with a shield door, and the a tempering step performed using a tempering furnace attached to the quenching chamber or separate from the quenching chamber,
The heating step includes a temperature raising step in which the temperature is raised to a predetermined temperature while the vacuum furnace is filled with nitrogen gas without reducing the pressure, and a temperature raising step in which the temperature is raised to a predetermined temperature in a state in which the vacuum furnace is filled with nitrogen gas. The predetermined temperature is set to 790 to 850 ° C., which is a temperature range in which nitriding and decarburization do not occur in the steel work,
After the heating step , the quenching step is performed by opening the shield door and transferring the steel workpiece from the vacuum furnace to the quenching chamber and immersing it in an oil bath or a water bath,
The tempering step is then performed at 150-650°C.”
It is configured.

In addition to the above-mentioned chromium, manganese, boron, nickel, and titanium, the metal elements added to improve hardenability include cobalt, boron, copper, and tungsten. defined in accordance with the provisions of

The present invention includes SUJ containing chromium , SCM containing chromium and molybdenum, SKS (tool steel) containing chromium, tungsten, molybdenum and vanadium, nickel and chromium as particularly suitable materials among the steel types specified by JIS. Any of the SNCMs are targeted.

Claim 2 specifies the relationship between the heating process and the quenching process. That is, in claim 1,
"After the heating process by the vacuum furnace is completed, the shield door is opened and the work is transferred to the hardening chamber while the hardening chamber is maintained at approximately the same degree of vacuum as the vacuum furnace, and then the shield door is opened. After closing, oil quenching takes place in the quenching chamber, which is maintained under reduced pressure.”
It is configured.

Although claim 2 specifies oil quenching as a quenching method, the present invention does not exclude water quenching. It is possible to employ water quenching in consideration of various factors such as the steel type and shape of the workpiece.

In the present invention, since a vacuum furnace is used as the heating furnace, the interior of the furnace can be maintained in a carbon-free state to reliably prevent carburization. Therefore, deterioration due to carburization/nitriding can be prevented, and deterioration due to decarburization does not occur. Therefore, the desired hardness can be obtained by utilizing the characteristics of the steel grade with excellent hardenability. In addition, since quenching uses oil or water as a cooling means, it is possible to obtain high hardness without variation by rapid cooling, and it is also excellent in workability.

Therefore, according to the present invention, it is possible to efficiently manufacture steel workpieces having uniform hardness and various mechanical properties and excellent quality stability. Therefore, it is suitable as a manufacturing method (hardening refining method) for machine parts and the like. It is possible that soot generated in the carburizing process of other workpieces adheres to the inner surface of the vacuum furnace, but it is virtually impossible for carbon molecules to diffuse from the soot and enter the workpiece. Therefore, even if the vacuum furnace is used for carburizing, the effect of the present invention is not affected.

Although there are various types of steel materials, it can be said that any one of SUJ, SCM, SKS, and SNCM specified in the present invention is suitable as the steel type of the work in consideration of the quenching specification and application .

In the heating process using a vacuum furnace, it is possible to put the workpiece into the vacuum furnace, seal it, and then depressurize it at the same time as heating it. There is a problem that the speed is slow and the work heating efficiency is not good. On the other hand, filling the furnace with air to raise the temperature improves the high thermal efficiency, but other problems such as oxidation and decarburization appear.

On the other hand, if the furnace is filled with nitrogen gas as in the present invention and the temperature is raised, the nitrogen gas that convects in the furnace quickly raises the temperature to a predetermined heating temperature without oxidizing or decarburizing the workpiece. can be made Therefore, it is possible to improve the processing efficiency while ensuring the quality of the heat treatment.

Quenching using a liquid has advantages over gas quenching, such as shortening the processing time and increasing hardness. In particular, oil quenching has the advantage of preventing cracks and stabilizing quality. And, in order to secure the advantage, it is necessary to put the workpiece taken out from the vacuum furnace into the oil bath as soon as possible.

In this case, it is conceivable to set the quenching chamber to atmospheric pressure, reduce the pressure in the vacuum furnace to atmospheric pressure, and then move the workpiece to the quenching chamber. There is a risk of On the other hand, it is conceivable to fill the vacuum furnace and the hardening chamber with an inert gas such as nitrogen gas before moving the work, but this takes a long processing time, so there is a risk that hardenability will deteriorate due to the temperature drop of the work. be.

On the other hand, as in claim 2 , when the quenching chamber is depressurized and the work is moved from the vacuum furnace to the quenching chamber, the work can be quickly immersed in the oil bath without temperature drop, oxidation, or decarburization. , it is possible to provide a work held at a desired hardness. That is, high-quality heat treatment can be provided.

1 is a schematic diagram of an apparatus used to implement the present invention; FIG. It is a graph which shows the relationship with the hydrogen diffusion amount of temperature rising temperature, (B) is the partial enlarged view which took the vertical axis|shaft of (A) large. 4 is a graph showing the relationship between the hardness after tempering and the amount of retained austenite. (A) is a graph showing the relationship between tempering temperature and indentation depth, (B) and (C) are diagrams showing an indentation depth inspection method.

(1). Implementation Apparatus Next, an embodiment of the present invention will be described with reference to the drawings. First, heat treatment equipment for carrying out the present invention will be described with reference to FIG.

The heat treatment equipment is the same as the conventional equipment, and includes a vacuum furnace 1, a quenching chamber 2 and a tempering furnace 3 as main elements. The tempering furnace 3 may be attached to the quenching chamber 2 or may be separated therefrom. In addition, it is also possible to perform the tempering process in the vacuum furnace 1 .

The vacuum furnace 1 is provided with a work inlet 4 open to the outside and a relay passage 5 communicating with the hardening chamber 2 , both of which are covered with doors 6 and 7 . The quenching chamber 2 is provided with an exit 8 with a door 9 . An oil tank 10 is provided in the quenching chamber 2, and the work quenched in the oil tank 10 is drained of oil by equipment provided inside or outside the quenching chamber 2, and then put into the tempering furnace 3. The tempering furnace 3 may be conventional, such as a gas-heated atmospheric furnace.

The vacuum furnace 1 is also used for carburizing, and has a hydrocarbon gas inlet 15 and a nitrogen gas inlet 16 open. A hydrogen gas cylinder 18 is connected, and a nitrogen gas cylinder 20 is connected to the nitrogen gas inlet 16 via a second pipeline 19 . Acetylene is commonly used as the hydrocarbon gas.

Needless to say, hydrocarbon gas is used for carburizing treatment and is not used in this embodiment. In the case of the exclusive vacuum furnace of the present invention, neither the hydrocarbon gas cylinder 18 nor the hydrocarbon gas inlet 15 is required.

A gas discharge port 21 is opened in the vacuum furnace 1 , and a vacuum pipe 23 that is evacuated by a vacuum pump 22 is connected to the gas discharge port 21 . Vacuum line 23 is also connected to hardening chamber 2 . A large number of electric heaters 24 are arranged inside the vacuum furnace 1 , and each heater 24 is connected to a power source 25 .

A bypass line 26 is provided in a portion of the vacuum line 23 near the vacuum furnace 1 , and a hydrogen concentration sensor 27 is provided in the bypass line 26 . The hydrogen concentration sensor 27 is an essential sensor in the carburizing and quenching process, and is not required in this embodiment, but can be used to confirm that the interior of the vacuum furnace 1 is in a hydrogen-free state. The vacuum furnace 1 is provided with a temperature sensor 28 and an oxygen concentration sensor 29 . The temperature sensor 28 is required for the control of this embodiment, but the oxygen concentration sensor 29 is not necessarily required.

Furthermore, the heat treatment facility has a control device (control means) 30 . A control device 30 controls the opening and closing of valves 31 provided in the respective pipelines 17 , 19 , 23 . A heater power source 25 and sensors 27 , 28 , 29 and the like are electrically connected to the control device 30 .

(2).Heat Treatment Process The workpiece W undergoes a heating process using the vacuum furnace 1, a quenching process using the quenching chamber 2, and a tempering process using the tempering furnace 3, and undergoes hardening and refining processes. be. In the heating step, for example, the temperature is raised to the set temperature (850° C.) and then the heating is continued for a predetermined time. The heating temperature is determined by the type of steel, and the heating time varies greatly depending on the thickness and shape of the workpiece, the throughput of one batch, and the like.

It is necessary to raise the temperature inside the vacuum furnace 1 in the heating step. In the heating step, nitrogen is introduced into the inside of the vacuum furnace 1 from the nitrogen gas inlet 16 to fill the inside of the vacuum furnace 1 with nitrogen gas. in the state of Therefore, the vacuum furnace 1 is not decompressed in the temperature rising process. Due to the thermal expansion of the nitrogen gas, the inside of the vacuum furnace 1 becomes a positive pressure higher than the atmospheric pressure. , it is also possible to keep the inside of the vacuum furnace 1 at a predetermined pressure.

The heat treatment using the vacuum furnace 1 is a batch process, but when the heat treatment including carburizing and nitriding is performed intermittently, the inside of the vacuum furnace 1 is heated by residual heat during the second and subsequent heat treatments. Therefore, it can be said that the heating time is often different for each batch process.

Since the inside of the vacuum furnace 1 is filled with nitrogen gas in the temperature raising step, convection of the nitrogen gas heated to a high temperature occurs inside the vacuum furnace 1, and the temperature inside the furnace can be quickly raised. Since the interior of the vacuum furnace 1 is filled with nitrogen, which is an inert gas, and oxygen does not exist, oxidation and decarburization do not occur during the temperature rising process. When the inside of the furnace reaches a set temperature (for example, 850° C.), the vacuum pump 22 is driven to discharge the nitrogen gas and reduce the pressure inside the vacuum furnace 1 to shift to steady heating (steady heating process) . Therefore, the steady heating process under reduced pressure becomes heating by radiant heat.

As disclosed in Patent Document 1, carburization can be performed at, for example, 4 to 10 torr, but in this embodiment, there is no hydrocarbon gas or nitrogen gas, so the gas partial pressure in the furnace is zero (strictly speaking, A very small amount of gas remains, but it is negligible.). Therefore, the degree of vacuum is higher than in carburizing.

Prior to finishing the heating process in the vacuum furnace 1, the hardening chamber 2 is decompressed and set to the same degree of vacuum as the vacuum furnace 1. When the heating process is finished, the door 7 of the relay passage 5 is opened, and the work W is transferred to the hardening chamber 2 by a transfer device (not shown). It is immersed and quenched. Therefore, the work W does not come into contact with air in the hardening chamber 2 and is not oxidized or decarburized.

After that, the work W is pulled up from the oil tank 13 to drain the oil (washed and dried), and then tempered using the tempering furnace 3. - 特許庁The temperature of the quenching oil is, for example, 80° C., and the tempering temperature and time are determined in consideration of various factors such as the steel type, thickness, and size.

If the oil in the oil bath 10 contains moisture, the moisture is easily evaporated due to the depressurization of the quenching chamber 2 . Therefore, when the workpiece W is immersed, the moisture may evaporate and expand. However, since the oil is a polymer compound of carbon and hydrogen, the oil itself does not evaporate and expand, so the moisture evaporates and expands. Even if there is, it is very small, and there is no trouble such as oil splashing around. In addition, since the quenching process is also performed as a batch process, even if the oil contains water, it will scatter and disappear in the first process, and the phenomenon of vaporization and expansion will not appear in the subsequent processes. In addition, the oil tank 13 is provided with a cooling device such as a water-cooled type.

(3).Evaluation of Examples Next, the test results of the examples shown in FIG. 2 and subsequent figures will be described. In the examples, SUJ2, which is widely used for bearings, was used. FIG. 2 is a graph showing the relationship between the heating temperature and the amount of hydrogen released. In the example, the vacuum furnace 1 was used for heating at 850° C. for 40 minutes, and in the comparative example, a gas furnace using propane was used. After heating at 850° C. for 40 minutes using an atmosphere furnace, oil quenching was performed. After the temperature was lowered to normal temperature by natural cooling, the temperature was raised to 600° C. at a temperature elevation rate of 100° C./h, and the amount of hydrogen released was measured.

In (A) of FIG. 2, the example and the raw material are overlapped with each other as almost zero, so the range of 0.005 ppm/min is enlarged and displayed in FIG. 2 (B). In both FIGS. 2(A) and (B), the lines for the example and the raw material are positioned slightly above 0, but this is a measure to clarify the lines, and in fact the horizontal axis The portion close to and parallel to the is substantially zero.

From FIG. 2, it can be said that the Comparative Example absorbs a large amount of hydrogen, while the Examples of the present application substantially do not absorb hydrogen, like the green material. Therefore, the phenomenon of hydrogen penetrating into the steel and forming voids does not occur.

In FIG. 2(B), in the example, the amount of hydrogen released is substantially 0, whereas the green material releases very little hydrogen from a temperature range slightly lower than 500 ° C. phenomena can be seen. The reason for this is not clear, but in the examples, the hydrogen contained during steelmaking was diffused during the heating process, whereas the hydrogen contained during steelmaking was around 500°C in the green material. It is presumed that it is released due to the steel structure change from the

FIG. 3 shows the relationship between the hardness (HRC) after tempering and the amount of retained austenite (γ). ing.). Hardening of steel by quenching is roughly a phenomenon in which the structure of steel changes to an austenite structure and then changes to a martensite structure, so there is a positive correlation between hardness and the amount of retained austenite. In addition, since the phenomenon of reversion of the structure increases when the tempering temperature is high, the hardness and the amount of retained austenite decrease when the tempering temperature increases.

In both Examples and Comparative Examples, the hardness and the amount of retained austenite basically decreased as the temperature increased in accordance with the principle of quenching and tempering. Always lower points than examples. In addition, as a second feature, the amount of retained austenite in the comparative example is consistently reduced although there is a change in the slope, whereas in the example, the range is lower than that in the comparative example up to about 260 ° C. It decreases, turns to increase with one lower peak at about 260 ° C., turns to decrease with an upper peak at about 280 ° C., and from about 270 ° C., the retained austenite amount of the example exceeds that of the comparative example. mentioned.

That is, in the comparative example, the hardness and the amount of retained austenite have a simple positive correlation, and both simply decrease as the temperature increases, whereas in the example, the hardness is a positive function of the temperature. While the amount of retained austenite simply decreases, there is a range in which the amount of retained austenite once turns to an increase, indicating a mismatch between the hardness and the amount of retained austenite.

The reason why the hardness of the examples is always lower than that of the comparative examples is considered to be that the comparative examples are carburized by heating, whereas the examples are not carburized. It is understood that the fact that the amount of retained austenite in the examples tends to be smaller than that in the comparative examples is also due to the presence or absence of carburization. However, it is not clear why there are regions in the examples where the amount of retained austenite increases even when the tempering temperature is increased. We would like to clarify this point as a future work.

In FIG. 4, a steel ball 34 was pressed against a sample 33 to form an indentation, and the maximum height H of the recess after plastic deformation was measured while changing the tempering temperature. It is therefore similar to the Rockwell hardness test .

The sample 33 has an outer diameter of 20 mm and a thickness of 10 mm, and the steel ball 34 is SUJ2, which is the same material as the sample 33, and has an outer diameter of 19.05 mm. The pressing load (maximum contact surface pressure) was 3.8 GPa, and the pressing holding time at the maximum load was 10 seconds. The test was performed at three equidistant locations, and the average value of the three locations was used as the test value.

From FIG. 4A, it can be seen that the indentation depth peaks at about 250 to 260° C. in both the comparative example and the working example. This tendency is understood to be consistent with the fact that the amount of retained austenite in the examples turned upward from about 260° C. in FIG. , and it is conceivable that factors other than hardness and the amount of retained austenite are acting.

In addition, in the example, the indentation depth is always higher than in comparative example 2, and compared to comparative example 1, the indentation depth is shallower in the tempering temperature range lower than about 220 ° C., but there is a tendency Therefore, it can be said that the indentation depth is deeper than that of the comparative example. This means that the example is softer than the comparative example, but it can be read from FIG. 4(A) that the relationship between the indentation depth and the temperature change is stable. It is understood that this is because there is no carburization/decarburization and the structure is stable.

In Comparative Example 1 , the rate of change of the indentation depth with respect to the temperature change is large, so to speak, the numerical values are wild.

In any case, it can be said that the problem of hydrogen embrittlement does not occur in the examples because hydrogen is not mixed in, as compared with the comparative examples using the gas atmosphere furnace. In addition, although the hardness of the examples is slightly lower than that of the comparative examples, there is no practical problem as long as the hardness required for the product is maintained, and low hardness means excellent toughness. It has excellent durability.

Rockwell hardness (HRC) in Fig. 3 and indentation depth in Fig. 4 are important evaluation factors for bearing components (balls, rollers, inner races, outer races) and gears where pressure is applied. However, in the embodiment of the present invention, delayed fracture due to hydrogen does not occur, so it can be said that extremely high durability can be ensured. Therefore, it can be said that high commercial value can be imparted to members made of hardenable general-purpose steel grades such as bearing steel.

In addition, there are many steel parts that rise in temperature during use, such as engine components and transmissions. For parts that reach 250 to 260°C during use, use the results shown in Fig. 4(A). Then, if the tempering temperature is set to about 250 to 260° C., deformation can be suppressed to a minimum and delayed fracture can be firmly prevented to ensure high durability.

In particular, delayed fracture is a serious problem for members to which repeated loads or alternating loads are applied, members with large load fluctuations, or members such as bolts that are constantly under load (load). It can be said that by using the applied member, the stability and durability of quality can be significantly improved, and the commercial value can be greatly improved.

Various external forces act on steel members, and strengths required for members include tensile strength, bending strength, shear strength, etc. in addition to compressive strength. Therefore, in terms of tensile strength, for example, the effect of shifting the yield point upward is expected.

The work of the present invention includes both finished products, such as gears and bearing members, and intermediate products that are post-processed. Moreover, the present invention does not deny performing other heat treatments as a post-process. For example, it is possible to increase the surface hardness while preventing hydrogen embrittlement by further carburizing, nitriding, or carbo-nitriding the workpiece heat-treated in the present invention by the method of Patent Document 1 and then quenching it.

The present invention can be embodied in practice. Therefore, it can be used industrially.

REFERENCE SIGNS LIST 1 vacuum furnace 2 quenching chamber 3 tempering furnace 4 work inlet of vacuum furnace 5 work outlet of vacuum furnace 8 relay passage 13 oil tank 16 nitrogen gas inlet 18 hydrogen concentration sensor 20 nitrogen gas cylinder 22 vacuum pump 30 control device

Claims (2)

A method of manufacturing a steel workpiece made of any one of SUJ, SCM, SKS, and SNCM defined by JIS by heat-treating it in a state where hydrogen embrittlement does not occur ,
A heating step performed using a vacuum furnace that heats under reduced pressure, a quenching step using oil or water in a quenching chamber attached to the vacuum furnace via a relay passage with a shield door, and the quenching a tempering step performed using a tempering furnace attached to the chamber or separate from the quenching chamber;
The heating step includes a temperature raising step in which the temperature is raised to a predetermined temperature while the vacuum furnace is filled with nitrogen gas without reducing the pressure, and a temperature raising step in which the temperature is raised to a predetermined temperature in a state in which the vacuum furnace is filled with nitrogen gas. The predetermined temperature is set to 790 to 850 ° C., which is a temperature range in which nitriding and decarburization do not occur in the steel work,
After the heating step , the quenching step is performed by opening the shield door and transferring the steel workpiece from the vacuum furnace to the quenching chamber and immersing it in an oil bath or a water bath,
The tempering step is then performed at 150-650° C.
A method for manufacturing a hydrogen embrittlement resistant steel workpiece. After the heating process by the vacuum furnace is completed , the shield door is opened to transfer the work to the hardening chamber while the hardening chamber is maintained at substantially the same degree of vacuum as the vacuum furnace, and then the shield door is closed. After that, quenching with oil is performed in the quenching chamber maintained in a reduced pressure state,
A method for manufacturing a hydrogen embrittlement resistant steel workpiece according to claim 1.

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