CN114480790A - Method and apparatus for manufacturing steel product - Google Patents

Abstract

A method for producing a steel product having a hard portion and a tough portion, wherein a portion of a steel member after quenching to be the tough portion is subjected to tempering treatment in which the portion is heated to a tempering temperature and then cooled immediately. A steel product manufacturing device provided with a hard portion and a tough portion, comprising: the tempering treatment of the steel member is performed by heating the portion that becomes the ductile portion of the steel member to a tempering temperature in the heating treatment section and then immediately moving the steel member to the cooling treatment section by the moving mechanism.

Description

Manufacturing method of steel product and manufacturing apparatus of steel product

technical field

The present invention relates to a manufacturing method of a steel product and a manufacturing device of the steel product.

Background technique

In order to improve the strength of steel products, the methods of quenching and tempering the carburized steel components are widely used. Here, in a steel product having a hard portion having high hardness and a tough portion having high toughness, in order to impart these properties, it is necessary to treat each portion differently.

Japanese Patent Laid-Open No. 2011-140697 discloses a method for quenching a steel product having a portion requiring hardness and a portion requiring toughness.

SUMMARY OF THE INVENTION

As in Japanese Patent Application Laid-Open No. 2011-140697, the following procedures are generally employed in quenching and tempering when manufacturing a steel product having a hard portion and a tough portion. That is, first, a quenching treatment is performed on the entire steel member after carburization, and the entire surface of the steel member is hardened, thereby obtaining a carburized and quenched part. After that, only the portion (for example, the threaded portion) that becomes the tough portion is subjected to high-frequency heating (induction heating) using, for example, a coil, and a partial tempering treatment is performed.

However, for example, in the steel product 1 having the threaded portion as the tough portion 2 shown in FIGS. 1A and 1B , the hard portion 3 requiring high hardness and the tough portion 2 requiring high toughness are arranged at very close positions, such as two The distance D between them is a position of several millimeters (more specifically, 7 mm). Therefore, during the tempering treatment, the heat supplied to the portion that becomes the tough portion 2 is transferred to the portion that becomes the hard portion 3 by conduction, and the portion that becomes the hard portion 3 is indirectly tempered, and the hard portion 3 exists. the possibility of hardness reduction. Furthermore, in order to suppress the decrease in the hardness of the hard portion 3, if the heat input to the portion to be the tough portion 2 is reduced during the tempering process, the portion to be the tough portion 2 cannot be sufficiently softened to a predetermined hardness (can not be tempered). , there is a possibility that high toughness cannot be imparted to the tough portion 2 . On the other hand, when the heat input to the part which becomes the tough part 2 is too much, there exists a possibility that it will become a requenched structure and harden.

Therefore, in the tempering treatment when manufacturing a steel product having a hard portion and a tough portion, it is required to develop a method that can suppress the transfer of heat to the portion serving as the hard portion while applying an appropriate amount of heat to the portion serving as the tough portion. hot method.

The present invention has been made in view of such a situation, and an object thereof is to provide a method for producing a steel product and an apparatus for producing a steel product that can prevent a reduction in the hardness of the hard part while ensuring the toughness of the ductile part.

The method for producing a steel product according to the present invention is a method for producing a steel product including a hard portion and a tough portion, wherein the portion of the quenched steel member that becomes the tough portion is heated to a tempering temperature. Temper treatment immediately after cooling.

In the method for producing a steel product of the present invention, in the tempering treatment, the portion of the quenched steel member that becomes the ductile portion is heated to the tempering temperature, and then immediately cooled, so that the soaking temperature is not maintained, so that the tendency to become Heat input other than the ductile portion. Therefore, the tempering hardness (for example, 440HV or less) required for the tough part can be easily obtained, and the risk of requenching can be reduced. In this way, in the present invention, in the tempering treatment, an appropriate amount of heat can be easily applied to the portion that becomes the tough portion, the robustness of the tough portion can be improved, and the portion that becomes the hard portion can be suppressed compared with the prior art. The heat transfer of the part can ensure high hardness in the hard part.

Here, in the tempering treatment, preferably, the portion that becomes the tough portion is heated to the tempering temperature and then cooled immediately a plurality of times in succession.

Moreover, it is preferable that the said tempering temperature is 690 degreeC or more and 725 degrees C or less.

Furthermore, it is preferable that the temperature at which the part to become the tough part is heated to the tempering temperature and then cooled immediately is 100° C. or lower.

In addition, it is preferable to perform one operation of cooling immediately after heating to the tempering temperature for 30 seconds for the portion to be the tough portion.

The apparatus for manufacturing a steel product according to the present invention is a manufacturing apparatus for a steel product including a hard part and a tough part, and is characterized by comprising: a heat treatment part that heats the steel member; and a cooling treatment part that cools the steel a member; and a moving mechanism capable of moving the steel member to each treatment portion, wherein, in the tempering treatment of the steel member, a portion that becomes a tough portion of the steel member is heated to the tempering in the heat treatment portion Immediately after the temperature is reached, the moving mechanism moves the steel member to the cooling treatment section.

In the manufacturing apparatus of the steel product according to the present invention, in the tempering treatment, after the portion to be the tough part is heated to the tempering temperature in the heat treatment part, the steel member can be moved to the cooling treatment part by the moving mechanism. Therefore, the portion of the quenched steel member that becomes the ductile portion is heated to the tempering temperature, and then immediately cooled, so that soaking is not maintained, heat input to other than the portion that becomes the ductile portion can be suppressed. Therefore, the tempering hardness required for the tough part can be easily obtained, and the risk of requenching can be reduced, and high hardness can be ensured in the hard part.

Here, in the tempering process of each steel member, it is preferable that the said moving mechanism performs the movement from the said heating process part to the said cooling process part a plurality of times.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of a steel product and the manufacturing apparatus of a steel product which can prevent the reduction of the hardness of a hard part in the state which ensured the toughness of a tough part can be provided.

Description of drawings

The features, advantages, and technical and industrial implications of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like reference numerals designate like elements.

1A is a schematic perspective view for explaining an example of a steel product provided with a hard portion and a tough portion obtained by one embodiment of the manufacturing method according to the present invention.

1B is a schematic partial cross-sectional view for explaining an example of a steel product including a hard portion and a tough portion obtained by one embodiment of the manufacturing method according to the present invention.

FIG. 2 is a graph showing an example of a temperature change (thermal curve) of a portion that becomes a tough part in a conventional tempering treatment.

FIG. 3 is a graph showing an example of a temperature change (thermal curve) of a portion that becomes a tough part in a tempering process according to an embodiment of the manufacturing method according to the present invention.

4A is a schematic diagram for explaining the precipitation of ε-carbide in a steel member during heating in a conventional tempering treatment.

FIG. 4B is a schematic diagram for explaining the growth of ε-carbides generated during soaking in a conventional tempering treatment.

5A is a diagram for explaining ε-carbide in the steel member when tempering operations (operations for cooling immediately after heating) are performed 1 to 3 times in the tempering treatment in the embodiment of the manufacturing method according to the present invention Schematic diagram of the precipitation.

5B is a diagram for explaining ε-carbides in the steel member when tempering operations (operations for cooling immediately after heating) are performed 1 to 3 times in the tempering treatment in the embodiment of the manufacturing method according to the present invention Schematic diagram of the precipitation.

5C is a diagram for explaining the ε-carbide in the steel member when tempering operation (operation for cooling immediately after heating) is performed 1 to 3 times in the tempering treatment in the embodiment of the manufacturing method according to the present invention Schematic diagram of the precipitation.

FIG. 6 is a graph showing the relationship between the tempering temperature and the hardness of the tough part in the tempering treatment of a conventional example.

7 is a graph showing the hardness distribution of the ductile portion in the tempering treatment (number of tempering operations: 1 to 3 times) in the tempering treatment in one embodiment of the conventional example and the manufacturing method according to the present invention.

FIG. 8 is a schematic diagram for explaining an embodiment of the manufacturing apparatus according to the present invention.

Detailed ways

As a steel product having a portion requiring high hardness (hard portion) and a portion requiring high toughness (toughness portion), for example, as shown in FIGS. carburized parts of the threaded part). 1A and 1B are schematic diagrams for explaining an example of a steel product having a hard part and a tough part obtained by the present invention, and FIG. 1A is a schematic perspective view thereof, and FIG. 1B is an enlarged view of the broken line part of FIG. 1A . Schematic partial cross-sectional view.

Here, the steel product 1 provided with the tough portion 2 may be damaged due to delayed failure or the like if it is used as it is (for example, by tightening the screw portion) after quenching the carburized steel member. In order to prevent this, the part that becomes the tough part (hereinafter sometimes referred to as the pre-tough part) is usually subjected to partial tempering treatment by induction heating to soften it to a desired hardness (for example, 440HV or less), and adjust the hardness , thereby ensuring high toughness.

In addition, in the conventional tempering treatment, as shown in FIG. 2 , first, the pre-toughened portion (threaded portion) of the steel member is heated for a heating time H (for example, several seconds) by a high-frequency coil or the like (induction heating). to tempering temperature. Next, the pre-toughened portion is held at a high temperature (for example, about 700° C.) during the soaking time U (for example, about 10 seconds) (soaking: continuous heating). The pre-ductile portion is then cooled (eg, water cooled) during a cooling time C (eg, several seconds).

At this time, in the conventional tempering treatment, as shown in FIG. 4A , in the first stage, that is, during the heating time H, ε-carbide 8 is precipitated in the steel member. Next, as shown in FIG. 4B , in the second stage, that is, during the soaking time U, the ε-carbide 8 generated in the steel member grows. As a result, the pre-toughened portion subjected to the tempering treatment softens to a desired hardness.

In addition, FIG. 2 is a graph showing an example of a temperature change (thermal curve, temperature profile) of a portion serving as a tough part in a conventional tempering treatment. 4A is a schematic diagram for explaining the precipitation of ε-carbides in a steel member during heating in a conventional tempering treatment, and FIG. 4B is a diagram for explaining the growth of ε-carbides generated during soaking Sketch map.

As described above, in the conventional tempering treatment, since heat is input to the pre-toughened portion during the heating time H and the soaking time U, the heat is directed to a portion (hereinafter sometimes referred to as a hardened portion) located near the pre-toughened portion. Pre-hardened part) transfer, the pre-hardened part may be softened by tempering. Therefore, in the conventional tempering treatment, in order to suppress the heat transfer to the pre-hardened portion, the heat input to the pre-toughened portion is limited, and the tempering treatment of the pre-toughened portion may not be satisfactorily performed to a desired hardness (for example, 440HV or less). Therefore, in the conventional tempering treatment, it may be difficult to obtain the tempering hardness required for the tough part.

Here, the following Table 1 shows the tempering temperature (maximum reaching temperature) (° C.) and the hardness (HV) of the obtained tough part in the tempering treatment of a conventional example. relationship chart.

[Table 1]

As shown in these figures, in the conventional tempering treatment, the tempering range for preventing requenching and imparting desired hardness is a narrow range (705 to 725° C. in FIG. 6 ). For example, if the tempering temperature is 700° C. and the heat input to the pre-toughened portion is reduced, the pre-toughened portion may not be sufficiently softened. In addition, for example, when the tempering temperature is 740° C., there is a possibility that the heat input to the pre-toughened portion becomes a requenched structure and hardens.

On the other hand, in the manufacturing method of the steel product according to the present invention (hereinafter sometimes referred to as the present manufacturing method), in the tempering treatment, the pre-toughness portion of the quenched steel member is heated to the tempering temperature. Immediately carry out the cooling tempering operation. Specifically, as shown in FIG. 3 , a tempering operation is performed once (one cycle) in which the pre-toughened portion is heated (induction heating) for a heating time H (for example, several seconds) with a high-frequency coil or the like. Immediately after reaching the tempering temperature, during the cooling time C, cooling is performed with cooling water or the like. Next, if necessary, this tempering operation is continuously performed, for example, twice or three times in total, to intermittently heat the pre-toughened portion. 3 is a graph showing an example of the temperature change (thermal curve, temperature profile) of the pre-toughened portion when the tempering operation is repeated three times in one embodiment of the present manufacturing method.

Here, FIGS. 5A to 5C are schematic diagrams for explaining the precipitation of ε-carbide when the tempering operation is continuously repeated three times in the tempering treatment in one embodiment of the present production method. As shown in this figure, compared with FIG. 5A which shows the state of the ε-carbide 8 in which the number of times of the above-mentioned tempering operation is the first time, the second time ( FIG. 5B ) and the third time ( FIG. 5C ) each When this tempering operation is repeated each time, more specifically, each time heating is started again, new ε-carbides 8 are generated in the steel member. Therefore, the total amount of the ε-carbides 8 precipitated in the steel member increases each time the tempering operation is repeated, that is, each time the intermittent heating is performed, and further softens. In the present invention, as described above, by intermittently performing the tempering treatment by heating for a short time, the temperature rise of the prehardened part other than the prehardened part that requires high hardness can be suppressed, and it can be reliably made without softening. Only the desired portion, ie, the pre-toughened portion, is easily softened to the desired hardness. Furthermore, by performing such a tempering treatment, the risk of re-quenching can be reduced, and the tough part of the steel product manufactured using the tempering treatment of the present invention can have excellent robustness. In addition, in the present invention, by reducing the number of tempering operations (for example, to one or two), the tempering treatment time can be further shortened, and more steel products can be produced in a short time.

Hereinafter, specific embodiments to which the present invention is applied will be described in more detail with reference to the accompanying drawings. In addition, this invention is not limited to the following embodiment, In the range which does not deviate from the summary, it can change suitably. In addition, in order to clarify description, these description and drawing are abbreviate|omitted and simplified as appropriate.

<Manufacturing method of steel products>

This manufacturing method is a manufacturing method of the steel product provided with a hard part and a tough part. Here, the hard portion refers to a portion required to have high surface hardness, and corresponds to the portion indicated by reference numeral 3 in the steel product 1 shown in FIGS. 1A and 1B . In addition, a tough part is a part which is required to have high toughness, and corresponds to the part (thread part) shown by the code|symbol 2 in the steel product 1 shown to FIG. 1A, FIG. 1B. In addition, the hard part and the tough part may be mixed, but from the viewpoint of easily imparting properties of both, they are preferably arranged at different positions. In addition, in the steel product 1 shown in FIGS. 1A and 1B , as described above, the distance D between the ductile portion 2 and the hard portion 3 is very close, and is arranged at intervals of several mm. Therefore, the heat input of the tempering treatment performed on the portion serving as the tough portion tends to transfer heat to the portion serving as the hard portion disposed in the vicinity, and the tempering treatment tends to be applied to an undesired portion.

Here, from the viewpoint of preventing requenching, the hardness of the tough part (Vickers hardness: HV) is preferably 260 HV or more, more preferably 300 HV or more, and still more preferably 350 HV or more. In addition, from the viewpoint of imparting high toughness, the hardness of the tough portion is preferably 440HV or less, more preferably 430HV or less, still more preferably 420HV or less, and particularly preferably 410HV or less.

From the viewpoint of having high hardness, the hardness of the hard portion is preferably 500 HV or more, and more preferably 520 HV or more. The upper limit of the hardness of the hard portion can be appropriately set according to the properties required of the steel product to be produced, and is not particularly limited.

The hardness of each part of the steel product can be measured based on the Vickers hardness (HV) test method (test force: 5 kgf) prescribed in JISZ2244:2009.

Here, in the present manufacturing method, as described above, the portion (pre-toughness portion) of the quenched steel member to be the tough portion is subjected to a tempering treatment in which it is heated to the tempering temperature and then cooled immediately. In this way, unlike the conventional tempering treatment, since soaking is not performed, the growth of ε-carbide is suppressed, and the control of toughness becomes easy. In addition, since cooling is performed immediately after heating for a short period of time, heat transfer to a portion (pre-hardened portion) serving as a hard portion can be suppressed.

Further, in the present production method, in the tempering treatment, it is preferable that the pre-toughened portion is heated to the tempering temperature and then cooled immediately a plurality of times in succession. By repeating the tempering operation consisting of heating and cooling a plurality of times, ε-carbide is formed every time the intermittent heating is performed, so that it is easier to soften than the conventional method.

In addition, the above-mentioned tempering temperature means the highest temperature reached when the pre-toughness portion is heated in the tempering treatment, and can be appropriately set according to the steel product to be produced. From the viewpoint of imparting high toughness to the tough portion, the tempering temperature is preferably 690°C or higher, more preferably 695°C or higher, and further preferably 700°C or higher. In addition, from the viewpoint of preventing requenching of the pre-toughened portion, the tempering temperature is preferably 725°C or lower, and more preferably 720°C or lower.

In addition, the cooling temperature at the time of cooling immediately after heating the pre-toughened part to the tempering temperature can be appropriately set, but from the viewpoint of preventing heat transfer to the hard part, it is preferably 100°C or lower, more preferably 50°C or lower, More preferably, it is room temperature (for example, 25°C).

In the present production method, from the viewpoint of production efficiency, the tempering treatment time per one steel product is preferably 60 to 100 seconds. Therefore, for the pre-toughened portion, the primary tempering operation of heating to the tempering temperature and then cooling is preferably performed within 30 seconds, more preferably within 20 seconds, and even more preferably within 15 seconds.

The heating rate and cooling rate of the pre-toughened portion in the above tempering treatment can be appropriately changed according to the required tempering treatment time, and are not particularly limited.

The present production method may include, for example, the following steps.

- A step (preparation step) of preparing a steel member (pre-steel product) having a portion serving as a tough portion and a portion serving as a hard portion.

- A step of applying carburizing treatment to the aforementioned steel member (carburizing treatment step).

A step of subjecting the steel member after the carburizing treatment to a quenching treatment (quenching treatment step).

- A step of heating the portion of the quenched steel member to be the tough part to the tempering temperature, then immediately cooling it, and performing the tempering treatment (tempering treatment step).

In addition, the present production method may further include the following steps.

- The step of cooling the portion to be the hard part during the above-mentioned tempering treatment (pre-hard part cooling step).

- A step of reducing the amount of carbon intrusion into the portion to be the tough part by using a carburizing means before or during the carburizing treatment (carburizing step).

These respective steps may be performed sequentially, or a plurality of steps (eg, a carburizing treatment step and a carburizing step, a tempering treatment step, and a pre-hardened part cooling step) may be performed in parallel.

The steel member should just have a pre-toughened part and a pre-hardened part, and the shape and the like are not particularly limited. However, as described above, from the viewpoint of performing appropriate tempering treatment and imparting appropriate properties to each part, it is desirable to use it at a position where the pre-toughened part and the pre-hardened part are separated (at least at a position where the two parts do not come into contact with each other). ) of the steel members.

The carburizing treatment of the steel member can be suitably used conventionally known carburizing treatment, and is not particularly limited as long as it can add carbon to the surface of the steel member (particularly, the hard portion). As the carburizing treatment, for example, solid carburizing using charcoal as a carbon source, gas carburizing using gases containing carbon dioxide, hydrogen, methane, etc. as main components, vacuum gas carburizing in which gas carburizing is performed after vacuuming, And plasma carburizing by plasma-forming gas, etc. Among them, gas carburizing, vacuum gas carburizing, and plasma carburizing are preferably used from the viewpoints of safety and workability.

For the quenching treatment of the carburized steel member (including the pre-hardened portion and the pre-toughened portion), a conventionally known quenching treatment can be appropriately used, and is not particularly limited. In the quenching treatment, the steel member is heated to an austenite structure by, for example, induction heating by a high-frequency coil, and then rapidly cooled to transform into a martensite structure.

Next, a tempering operation of heating the pre-toughened portion of the quenched steel member to the tempering temperature and immediately cooling is performed one or more times (preferably multiple times) by the tempering treatment of the present manufacturing method described above. Thereby, the steel product provided with the hard part which has high hardness and the tough part which has high toughness can be obtained.

In addition, in the present manufacturing method, in the tempering treatment, when the pre-toughened portion is heated to the tempering temperature, the pre-hardened portion may be simultaneously cooled. As a result, it is possible to more easily prevent softening due to heat transfer to the pre-hardened portion due to heat input to the pre-toughened portion during the tempering treatment.

In addition, in the present manufacturing method, when the steel member is carburized, carbon prevention means (for example, by putting a carbon prevention cap made of copper on the pre-toughened portion) can reduce the amount of carbon intrusion into the pre-toughened portion. , to prevent the increase in the hardness of the pre-toughened part during quenching.

Further, before the carburizing treatment of the steel member, a carburizing agent as a carbon preventing means may be applied to the pre-toughened portion. Thereby, the amount of intrusion of carbon into the pre-toughened portion during the carburizing treatment can be reduced, and the increase in hardness during the quenching treatment of the pre-toughened portion can be further suppressed.

<Manufacturing equipment for steel products>

The manufacturing apparatus for a steel product according to the present invention (hereinafter sometimes referred to as the present manufacturing apparatus) is a manufacturing apparatus for a steel product including a hard part and a tough part. This manufacturing apparatus is provided with the heat processing part for heating a steel member, the cooling processing part for cooling the said steel member, and the moving mechanism which can move the said steel member to each processing part. In FIG. 8 , as an embodiment of the present manufacturing apparatus, a heating processing unit 4 a including a heating coil as the heating processing means 4 , a cooling processing unit 5 a including a cooling jacket as the cooling processing means 5 , and a moving mechanism 6 are described. A (high frequency) tempering device that can move in the vertical direction of the paper surface.

Here, in the tempering treatment of the steel member 7 (the treatment part), the moving mechanism 6 causes the steel member 7 to be heated to the tempering temperature immediately after the pre-toughness portion 7a (threaded portion) of the steel member 7 is heated to the tempering temperature at the heat treatment portion 4a. The member 7 (particularly, the pre-toughened portion 7a) moves toward the cooling treatment portion 5a. Here, the cooling process part 5a may be equipped with the air jacket (not shown) for water removal after water cooling, for example. In addition, the present manufacturing apparatus may be provided with fixing means not shown, and can perform heat treatment, cooling treatment, or movement by a moving mechanism in a state in which the steel product is fixed by the fixing means.

In addition, in the tempering treatment of each steel member, in order to perform the tempering operation consisting of the above-mentioned heating and cooling a plurality of times, it is preferable that the moving mechanism performs the movement from the heat treatment part to the cooling treatment part a plurality of times. In addition, when performing the above-mentioned tempering operation a plurality of times, in order to heat-process the pre-toughened part again, the movement from the cooling-processing part to the heating-processing part is performed one or more times by the moving mechanism.

The heat treatment means 4 included in the present manufacturing apparatus is not particularly limited as long as it can heat the steel member (particularly the pretoughened portion) to the tempering temperature, and a known means can be appropriately used. In FIG. 8, as the heat treatment means 4, a high-frequency (heating) coil for induction heating is used.

In addition, the heat-processing part 4a means the area|region where the heat-processing of the steel member 7 is performed by the heat-processing means 4 in this manufacturing apparatus. The heat treatment conditions such as the preferable tempering temperature (maximum attained temperature) are as described above, so the description is omitted.

The cooling treatment means 5 included in the manufacturing apparatus is not particularly limited as long as it can heat the steel member (particularly the pre-toughened portion 7a ) to the tempering temperature and then immediately cool it, and any known means can be appropriately used. In FIG. 8 , a cooling jacket (more specifically, cooling water) is used as the cooling treatment means 5, and an air jacket is also provided in order to remove water.

In addition, the cooling process part 5a means the area|region where the cooling process of the steel member 7 is performed by the cooling process means 5 in this manufacturing apparatus. The cooling treatment conditions such as the preferable cooling temperature are as described above, and therefore the description is omitted.

The moving mechanism 6 included in the present manufacturing apparatus is not particularly limited as long as it can move the steel member 7 to both the heat-treated portion 4a and the cooling-treated portion 5a during the tempering treatment, and known ones can be appropriately used. mechanism. In FIG. 8 , as the moving mechanism 6, a moving device that can move in the vertical direction of the paper is used.

Furthermore, in the present manufacturing apparatus, when the pre-tough portion 7 a is heated by the heat treatment means, the cooling treatment of the pre-hardened portion 7 b may be performed in parallel by the cooling treatment means 5 . This makes it easier to prevent the heat transferred to the pre-hardened portion 7a from being softened due to heat transfer to the pre-hardened portion 7b. At this time, it is preferable that the arrangement of the heat treatment means 4 and the cooling treatment means 5 takes into consideration the arrangement of the pre-tough parts 7 a and the pre-hardened parts 7 b of the steel member 7 and the arrangement based on the moving distance of the moving mechanism 6 . In this way, by adjusting the arrangement of the two means, adjustment of the induction heating direction and the discharge direction of the cooling water can be easily performed, and the heating of the pre-tough portion 7a and the cooling of the pre-hardened portion 7b can be performed more reliably.

In addition, the present manufacturing apparatus may be provided with a carbon preventing means (not shown), by which, before or during the carburizing treatment, the intrusion of carbon into the pre-toughened portion 7a can be suppressed, and the quenching can be appropriately suppressed The hardness of the pre-toughened portion at the time of processing increases. As the carbon preventing means, for example, a carbon preventing cap or a carbon preventing agent can be used. Specifically, before the carburizing treatment, the pre-toughened portion can be prevented from entering the pre-toughened portion by putting a carbon cap made of copper or the like on the pre-toughened portion to perform the carburizing treatment. In addition, by applying a carbon inhibitor to the pre-toughened portion before the carburizing treatment, it is possible to suppress the intrusion of carbon into the pre-toughened portion, and to further suppress the increase in hardness during quenching.

Hereinafter, the present invention will be described in more detail using examples, but the present invention is not limited to these examples.

[Example 1]

As shown in FIG. 8 , a high-frequency feedback loop including a heating coil as the heating treatment means 4, a cooling jacket as the cooling treatment means 5, an air jacket for water removal, and a moving mechanism 6 that can move in the vertical direction of the paper is used. A fire apparatus is used to temper the steel member 7 subjected to the carburizing and quenching treatment. As shown in FIG. 8 , the steel member 7 has a threaded portion as a pre-ductile portion 7 a and a shaft portion as a pre-hardened portion 7 b.

Then, the steel member 7 is set in the heat-treated part 4a by fixing means not shown. Next, the threaded portion of the steel member 7 is heat-treated at a tempering temperature (maximum temperature) of 700° C. with a heating coil. Then, when the heating to the tempering temperature of the screw portion is completed (heating time: 3 seconds), the screw portion is moved to the cooling treatment portion 5 a by the moving mechanism 6 . Then, the threaded portion was cooled to room temperature (25° C.) by a cooling jacket (cooling water). After this cooling process, the water removal of the steel member 7 is performed by the air jacket (not shown) provided together with the cooling jacket. In Example 1, each of the above-mentioned heating treatment and the above-mentioned cooling treatment in the tempering treatment was performed once.

Thus, a steel product having a tough portion and a hard portion was produced. In this order, three steel products were produced, respectively. The Vickers hardness of the tough part of the obtained steel product was measured by the above-mentioned method, and the results were 436HV, 434HV, and 432HV, indicating that the desired hardness (440HV or less) was obtained. Moreover, the Vickers hardness of the hard part of the obtained steel product was all 500HV or more.

[Example 2]

A steel product having a tough portion and a hard portion was produced in the same manner as in Example 1, except that the number of tempering operations (heating and cooling) in the tempering treatment was changed to two. Specifically, after the cooling treatment section cools the heat-treated threaded section, the threaded section is moved to the heating treatment section by the moving mechanism again, and the heating treatment is carried out with the heating coil. When the tempering temperature is reached, the threaded section is It moved to the cooling process part, and cooled to room temperature. In this order, three steel products were produced, respectively. The Vickers hardness of the tough part of the obtained steel product was measured by the above-mentioned method, and the results were 414HV, 409HV, and 406HV, and it was found that the desired hardness was obtained. In addition, the Vickers hardness of the hard part of the obtained steel product was all 500HV or more.

[Example 3]

A steel product having a tough portion and a hard portion was produced in the same manner as in Example 1, except that the number of tempering operations (heating and cooling) in the tempering treatment was changed to three. In this order, three steel products were produced, respectively. The Vickers hardness of the tough part of the obtained steel product was measured by the above-mentioned method, and the results were 400HV, 404HV, and 408HV, indicating that the desired hardness was obtained. In addition, the Vickers hardness of the hard part of the obtained steel product was all 500HV or more.

[Comparative Example 1]

In the tempering treatment, after heating the thread portion, holding (soaking) at about 700° C. for 10 seconds, and then cooling to room temperature, the same procedure as in Example 1 was carried out to produce a tough portion and a hard portion. Qualitative steel products. In this order, three steel products were produced, respectively. The Vickers hardness of the tough part of the obtained steel product was measured by the above-mentioned method, and the results were 438HV, 433HV, and 434HV, indicating that the desired hardness was obtained. However, the Vickers hardness of the hard portions of the obtained steel products was less than 500HV, and it was found that the hard portions were softened in the above tempering treatment.

The hardness distribution of the tough part of the steel product obtained in each of these examples is shown in FIG. 7 .

As can be seen from the above, according to the present invention, in the tempering treatment when manufacturing a steel product having a hard portion and a tough portion, an appropriate amount of heat can be imparted to the portion serving as the tough portion, and the amount of heat to the portion serving as the hard portion can be suppressed. heat transfer. As a result, in a steel product having a tough portion and a hard portion, it is possible to prevent the hardness of the hard portion from decreasing while maintaining the toughness of the tough portion.

In addition, the present manufacturing method and the present manufacturing apparatus can be applied to steel products used in various applications such as vehicles such as automobiles and buildings. In addition, the constituent elements in the present embodiment can be appropriately replaced with other well-known constituent elements within the scope of not departing from the gist of the present invention.

Claims (7)

1. A method for producing a steel product comprising a hard portion and a tough portion, wherein the portion of a quenched steel member that becomes the tough portion is heated to a tempering temperature immediately after being heated to a tempering temperature. Cool tempering. 2 . The method for producing a steel product according to claim 1 , wherein, in the tempering treatment, an operation of heating to a tempering temperature and immediately cooling the portion to be the ductile portion is performed a plurality of times in succession. 3 . The said tempering temperature is 690 degreeC or more and 725 degrees C or less, The manufacturing method of the steel product of Claim 1 or 2 characterized by the above-mentioned. 4 . The method for producing a steel product according to claim 1 , wherein the temperature at which the portion to be the tough portion is heated to a tempering temperature and then immediately cooled is 100° C. or lower. 5 . 5. The method for producing a steel product according to any one of claims 1 to 4, wherein the portion to be the tough portion is heated to a tempering temperature within 30 seconds and then immediately cooled. 1 operation. 6. An apparatus for manufacturing a steel product, the steel product having a hard portion and a tough portion, characterized in that it includes: a heat treatment section, which heats the steel member; a cooling treatment section that cools the steel member; and a moving mechanism capable of moving the steel member toward each treatment part, However, in the tempering treatment of the steel member, the moving mechanism immediately causes the steel member to move toward the The cooling treatment section moves. 7 . The apparatus for manufacturing a steel product according to claim 6 , wherein, in the tempering process performed on each steel member, the moving mechanism performs multiple times from the heat treatment unit to the cooling treatment unit. 8 . movement.

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