CN114480790A - Method and apparatus for manufacturing steel product - Google Patents
Method and apparatus for manufacturing steel product Download PDFInfo
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- CN114480790A CN114480790A CN202110834451.5A CN202110834451A CN114480790A CN 114480790 A CN114480790 A CN 114480790A CN 202110834451 A CN202110834451 A CN 202110834451A CN 114480790 A CN114480790 A CN 114480790A
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 142
- 239000010959 steel Substances 0.000 title claims abstract description 142
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 62
- 238000000034 method Methods 0.000 title claims description 19
- 238000011282 treatment Methods 0.000 claims abstract description 138
- 238000005496 tempering Methods 0.000 claims abstract description 134
- 238000010438 heat treatment Methods 0.000 claims abstract description 75
- 238000001816 cooling Methods 0.000 claims abstract description 62
- 238000010791 quenching Methods 0.000 claims abstract description 31
- 230000000171 quenching effect Effects 0.000 claims abstract description 24
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 21
- 229910052799 carbon Inorganic materials 0.000 description 21
- 238000005255 carburizing Methods 0.000 description 21
- 239000007789 gas Substances 0.000 description 8
- 230000006698 induction Effects 0.000 description 8
- 238000002791 soaking Methods 0.000 description 8
- 238000012546 transfer Methods 0.000 description 7
- 238000010586 diagram Methods 0.000 description 6
- 238000001556 precipitation Methods 0.000 description 6
- 230000002265 prevention Effects 0.000 description 6
- 239000000498 cooling water Substances 0.000 description 4
- 238000012545 processing Methods 0.000 description 4
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 4
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 239000010949 copper Substances 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 239000003112 inhibitor Substances 0.000 description 2
- VNWKTOKETHGBQD-UHFFFAOYSA-N methane Chemical compound C VNWKTOKETHGBQD-UHFFFAOYSA-N 0.000 description 2
- 229910001566 austenite Inorganic materials 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 230000000052 comparative effect Effects 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000001257 hydrogen Substances 0.000 description 1
- 125000004435 hydrogen atom Chemical class [H]* 0.000 description 1
- 229910000734 martensite Inorganic materials 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 230000035515 penetration Effects 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- 238000012360 testing method Methods 0.000 description 1
- 239000002023 wood Substances 0.000 description 1
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
- C21D1/18—Hardening; Quenching with or without subsequent tempering
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/25—Process efficiency
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
Technical Field
The present invention relates to a method and an apparatus for manufacturing a steel product.
Background
In order to improve the strength of steel products, quenching and tempering methods for carburized steel members have been widely used. Here, in a steel product including a hard portion having high hardness and a tough portion having high toughness, it is necessary to perform different treatments for each portion in order to impart these properties.
Jp 2011-140697 a discloses a method of quenching a steel product having a portion requiring hardness and a portion requiring toughness.
Disclosure of Invention
As disclosed in jp 2011-140697 a, the following procedure is generally adopted in quenching and tempering in the production of a steel product having a hard portion and a tough portion. That is, first, the entire carburized steel member is subjected to quenching treatment to harden the entire surface of the steel member, thereby obtaining a carburized and quenched component. Thereafter, only a portion (for example, a threaded portion) to be a ductile portion is subjected to, for example, high-frequency heating (induction heating) by a coil, and then a partial tempering treatment is performed.
However, in the steel product 1 having a threaded portion as the ductile portion 2 shown in fig. 1A and 1B, for example, the hard portion 3 requiring high hardness and the ductile portion 2 requiring high toughness are arranged at positions very close to each other, for example, at a position where the distance D between the two is several millimeters (more specifically, 7 mm). Therefore, during the tempering treatment, the heat supplied to the portion to be the tough portion 2 is transferred to the portion to be the hard portion 3 by conduction, and the portion to be the hard portion 3 is indirectly tempered, so that the hardness of the hard portion 3 may be reduced. Furthermore, in order to suppress a 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 treatment, the portion to be the tough portion 2 may not be sufficiently softened to a predetermined hardness (cannot be tempered), and thus high toughness may not be imparted to the tough portion 2. On the other hand, if too much heat is input to the portion that becomes the flexible portion 2, the structure may become hardened by re-quenching (the sintered compact き).
Therefore, in the tempering treatment in the production of a steel product including a hard portion and a tough portion, there is a demand for development of a method capable of suppressing heat transfer to the portion to be the hard portion while applying an appropriate amount of heat to the portion to be the tough portion.
The present invention has been made in view of such circumstances, and an object thereof is to provide a method and an apparatus for manufacturing a steel product, which can prevent a decrease in hardness of a hard portion while ensuring toughness of a tough portion.
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, and is characterized in that a portion of a steel member after quenching, which is to be the tough portion, is subjected to tempering treatment in which the portion is heated to a tempering temperature and then cooled immediately.
In the method for producing a steel product according to the present invention, in the tempering treatment, the portion of the steel member after the quenching treatment to be the ductile portion is heated to the tempering temperature and then immediately cooled without being kept uniformly heated, and therefore, heat input to portions other than the portion to be the ductile portion can be suppressed. Therefore, the temper hardness (for example, 440HV or less) required for the ductile portion can be easily obtained, and the risk of re-quenching can be reduced. As described above, in the present invention, in the tempering treatment, an appropriate amount of heat can be easily applied to the portion to be the tough portion, thereby improving the robustness of the tough portion, and heat transfer to the portion to be the hard portion can be suppressed, and high hardness can be ensured in the hard portion, as compared with the conventional art.
Here, in the tempering treatment, it is preferable that the portion to be the ductile portion is continuously heated to the tempering temperature and then cooled immediately.
The tempering temperature is preferably 690 ℃ or higher and 725 ℃ or lower.
Further, it is preferable that the portion to be the ductile portion is heated to a tempering temperature and then immediately cooled to 100 ℃.
Further, it is preferable that the portion to be the ductile portion is heated to the tempering temperature and then cooled immediately 1 time in 30 seconds.
The steel product manufacturing apparatus according to the present invention is a steel product manufacturing apparatus including a hard portion and a tough portion, and is characterized by including: a heat treatment unit that heats the steel member; a cooling treatment unit that cools the steel member; and a moving mechanism capable of moving the steel member to each of the treatment portions, wherein in the tempering treatment of the steel member, the moving mechanism moves the steel member to the cooling treatment portion immediately after the portion that becomes the ductile portion of the steel member is heated to the tempering temperature in the heating treatment portion.
In the manufacturing apparatus for steel products according to the present invention, in the tempering treatment, the portion that becomes the ductile portion is heated to the tempering temperature in the heat treatment portion, and then the steel member can be moved to the cooling treatment portion by the moving mechanism. Therefore, the portion of the steel member after the quenching treatment to be the ductile portion is heated to the tempering temperature and then immediately cooled, and the soaking is not maintained, so that the heat input to the portion other than the portion to be the ductile portion can be suppressed. Therefore, the tempered hardness required for the tough portion is easily obtained, the risk of re-quenching is reduced, and high hardness can be ensured in the hard portion.
Here, it is preferable that the moving mechanism moves from the heating treatment section to the cooling treatment section a plurality of times in the tempering treatment of each steel member.
According to the present invention, it is possible to provide a method and an apparatus for manufacturing a steel product, which can prevent a decrease in hardness of a hard portion while ensuring toughness of a tough portion.
Drawings
Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like reference numerals show like elements.
Fig. 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 an embodiment of the production method according to the present invention.
Fig. 1B is a schematic partial sectional view for explaining an example of a steel product including a hard portion and a tough portion obtained by an embodiment of the manufacturing method according to the present invention.
Fig. 2 is a graph showing an example of a temperature change (thermal profile) of a portion serving as a ductile portion in the tempering treatment of the conventional example.
Fig. 3 is a graph showing an example of a temperature change (thermal profile) of a portion serving as a ductile portion in the tempering treatment according to the embodiment of the manufacturing method of the present invention.
Fig. 4A is a schematic diagram for explaining the precipitation of epsilon-carbides in a steel member during heating in a conventional tempering treatment.
Fig. 4B is a schematic diagram for explaining the growth of ∈ -carbides that are generated during soaking in the tempering treatment of the conventional example.
Fig. 5A is a schematic view for explaining the precipitation of epsilon-carbides in the steel member when 1 to 3 times of tempering operations (operations of cooling immediately after heating) are performed in the tempering treatment in the embodiment of the manufacturing method according to the present invention.
Fig. 5B is a schematic view for explaining the precipitation of epsilon-carbides in the steel member when the tempering treatment in the embodiment of the production method according to the present invention is performed 1 to 3 times (the operation of cooling immediately after heating).
Fig. 5C is a schematic view for explaining the precipitation of epsilon-carbides in the steel member when the tempering treatment in the embodiment of the production method according to the present invention is performed 1 to 3 times (the operation of cooling immediately after heating).
Fig. 6 is a graph showing the relationship between the tempering temperature and the hardness of the ductile portion in the tempering treatment of the conventional example.
FIG. 7 is a graph showing the hardness distribution of the ductile portion in the tempering treatment (the number of tempering operations: 1 to 3 times) in the conventional example and the manufacturing method according to the embodiment of the present invention.
Fig. 8 is a schematic diagram for explaining an embodiment of the manufacturing apparatus according to the present invention.
Detailed Description
Examples of steel products having a portion (hard portion) requiring high hardness and a portion (tough portion) requiring high toughness include steel products having a threaded portion as the tough portion 2 (a carburized component with a threaded portion) shown in fig. 1A and 1B. Fig. 1A and 1B are schematic views for explaining an example of a steel product provided with a hard portion and a tough portion obtained by the present invention, fig. 1A is a schematic perspective view thereof, and fig. 1B is a schematic partial sectional view in which a dotted line portion of fig. 1A is enlarged.
Here, the steel product 1 including the ductile portion 2 may be damaged by delayed fracture or the like when used as it is (for example, a fastening screw portion) after quenching the carburized steel member. In order to prevent this, a part to be a tough portion (hereinafter, sometimes referred to as a pre-tough portion) is usually subjected to partial tempering treatment by induction heating to soften the part to a desired hardness (for example, 440HV or less) and the hardness is adjusted, thereby ensuring high toughness.
In the conventional tempering treatment, as shown in fig. 2, first, the pre-tough portion (threaded portion) of the steel member is heated (induction heated) to a tempering temperature by a high-frequency coil or the like for a heating time H (for example, several seconds). Subsequently, the pre-tough section is held (soaking: continuous heating) at a high temperature (for example, about 700 ℃) for a soaking time U (for example, about 10 seconds). The pre-tough section is then cooled (e.g., water cooled) during a cooling time C (e.g., a few seconds).
In this case, in the conventional tempering treatment, as shown in fig. 4A, epsilon-carbides 8 are precipitated in the steel member in the first stage, i.e., during the heating time H. Next, as shown in fig. 4B, in the second stage, i.e. during the soaking time U, epsilon-carbides 8 produced in the steel component grow. As a result, the tempered pre-tough portion is softened to a desired hardness.
Fig. 2 is a graph showing an example of a temperature change (thermal profile, temperature profile) of a portion to be a ductile portion in the conventional tempering treatment. Fig. 4A is a schematic diagram for explaining the precipitation of epsilon-carbides in a steel member during heating in the tempering treatment of a conventional example, and fig. 4B is a schematic diagram for explaining the growth of epsilon-carbides generated during soaking.
In this way, in the conventional tempering treatment, heat is input to the pre-hardened portion during the heating time H and the soaking time U, and therefore the heat is transmitted to a portion to be a hardened portion (hereinafter, sometimes referred to as a pre-hardened portion) located in the vicinity of the pre-hardened portion, and the pre-hardened portion may be tempered and softened. Therefore, in the conventional tempering treatment, heat input to the pre-hardened portion is limited in order to suppress heat transfer to the pre-hardened portion, and the tempering treatment of the pre-hardened portion may not be performed satisfactorily to a desired hardness (for example, 440HV or less). Therefore, in the conventional tempering treatment, it is sometimes difficult to obtain the tempering hardness required for the toughness portion.
Table 1 below shows the tempering temperature (maximum reaching temperature) (c) and the Hardness (HV) of the obtained tough portion in the tempering treatment of the conventional example, and fig. 6 shows a graph showing the relationship between the two in table 1.
[ Table 1]
As shown in these figures, in the conventional tempering treatment, the tempering range for preventing re-quenching and imparting a desired hardness is narrow (705 to 725 ℃ in fig. 6). For example, if the tempering temperature is 700 ℃ and the heat input to the pre-tough portion is reduced, the pre-tough portion may not be sufficiently softened. Further, for example, if the tempering temperature is 740 ℃, heat input to the pre-toughness portion is large, the pre-hardened portion may become a re-quenched structure and be hardened.
On the other hand, in the method for producing a steel product according to the present invention (hereinafter, may be referred to as the present production method), in the tempering treatment, a tempering operation is performed in which the pre-tough portion of the steel member after the quenching treatment is heated to a tempering temperature and then immediately cooled. Specifically, as shown in fig. 3, 1 (1 cycle) tempering operation is performed in which the pre-tough portion is heated (induction heated) to the tempering temperature by a high-frequency coil or the like for a heating time H (for example, several seconds), and then immediately cooled by cooling water or the like for a cooling time C. Subsequently, this tempering operation is continuously performed, for example, repeated 2 or 3 times in total, as necessary, and the pre-tough portion is intermittently heated. Fig. 3 is a graph showing an example of the temperature change (thermal profile, temperature profile) of the pre-tough portion when the tempering operation is repeated 3 times in the embodiment of the present manufacturing method.
Here, fig. 5A to 5C are schematic diagrams for explaining the precipitation of ∈ -carbides when the tempering operation is continuously repeated three times in the tempering treatment in the embodiment of the present production method. As shown in the figure, compared with fig. 5A showing the state of the epsilon-carbides 8 in which the number of the above tempering operations is the first time, new epsilon-carbides 8 are generated in the steel member every time the tempering operation is repeated the second time (fig. 5B) and the third time (fig. 5C), more specifically, every time heating is restarted. Therefore, the total amount of the epsilon-carbides 8 precipitated in the steel member increases every time the tempering operation is repeated, that is, every 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, it is possible to suppress the temperature rise of the pre-hard portion requiring high hardness other than the pre-tough portion, and to reliably and easily soften only the desired portion, that is, the pre-tough portion to a desired hardness without softening it. Furthermore, by performing such tempering treatment, the risk of re-quenching can be reduced, and the ductile portion 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 1 or 2), 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 drawings. The present invention is not limited to the following embodiments, and can be modified as appropriate without departing from the spirit and scope of the invention. In addition, for the sake of clarity of the description, the description and the drawings are appropriately omitted or simplified.
< method for producing Steel product >
The method for manufacturing a steel product having a hard portion and a tough portion. Here, the hard portion is a portion required to have high surface hardness, and corresponds to a portion indicated by reference numeral 3 in the steel product 1 shown in fig. 1A and 1B. The ductile portion is a portion required to have high toughness, and corresponds to a portion (threaded portion) indicated by reference numeral 2 in the steel product 1 shown in fig. 1A and 1B. The hard portion and the tough portion may be present in a mixture, but are preferably disposed at different positions from the viewpoint of easy application of the properties to both. In the steel product 1 shown in fig. 1A and 1B, the distance D between the ductile portion 2 and the hard portion 3 is very close to each other and is arranged at intervals of several mm as described above. Therefore, the heat input of the tempering treatment performed on the portion to be the tough portion easily transfers heat to the portion to be the hard portion disposed nearby, and the tempering treatment is easily performed on an undesired portion.
Here, from the viewpoint of preventing re-quenching, the hardness (vickers hardness: HV) of the ductile portion is preferably 260HV or more, more preferably 300HV or more, and further preferably 350HV or more. From the viewpoint of imparting high toughness, the hardness of the toughness 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 500HV or more, and more preferably 520HV or more. The upper limit of the hardness of the hard portion may be set as appropriate depending on the properties required for the steel product to be produced, and is not particularly limited.
The hardness of the parts of the steel product may be based on JISZ 2244: the Vickers Hardness (HV) test method (test force: 5kgf) specified in 2009.
In the present manufacturing method, as described above, the portion of the steel member after the quenching treatment that becomes the ductile portion (pre-ductile portion) is subjected to the tempering treatment in which the portion is heated to the tempering temperature and then cooled immediately. Thus, unlike the conventional tempering treatment, since soaking is not performed, the growth of epsilon-carbides is suppressed and the toughness can be easily controlled. Further, since the heating is performed for a short time and then the cooling is performed immediately, heat transfer to a portion (pre-hard portion) to be a hard portion can be suppressed.
In the present manufacturing method, it is preferable that the tempering treatment is performed by heating the pre-tough portion to the tempering temperature and then cooling the pre-tough portion immediately. Since the tempering operation consisting of heating and cooling is repeated a plurality of times, epsilon-carbides are generated at each intermittent heating, and therefore, softening is easier than in the conventional method.
The tempering temperature is a maximum reaching temperature at the time of heating the pre-tough portion in the tempering treatment, and may 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 ℃ or higher, more preferably 695 ℃ or higher, and further preferably 700 ℃ or higher. From the viewpoint of preventing the re-quenching of the pre-tough portion, the tempering temperature is preferably 725 ℃ or less, and more preferably 720 ℃ or less.
The cooling temperature at the time of immediately cooling after heating the pre-tough portion to the tempering temperature may be appropriately set, but from the viewpoint of preventing heat transfer to the hard portion, is preferably 100 ℃ or lower, more preferably 50 ℃ or lower, and even more preferably room temperature (e.g., 25 ℃).
In the present manufacturing method, the tempering treatment time per 1 steel product is preferably 60 to 100 seconds from the viewpoint of production efficiency. Therefore, the primary tempering operation of heating to the tempering temperature and then cooling immediately is preferably performed for 30 seconds or less, more preferably for 20 seconds or less, and still more preferably for 15 seconds or less, in the pre-ductile portion.
The heating rate and the cooling rate of the pre-annealed portion in the tempering treatment may be appropriately changed according to the required tempering treatment time, and are not particularly limited.
The present manufacturing method may include the following steps, for example.
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 carburizing the steel member (carburizing step).
A step of performing a quenching treatment on the steel member after the carburizing treatment (quenching treatment step).
A step of heating a portion of the steel member after the quenching treatment, which portion becomes a ductile portion, to a tempering temperature, immediately cooling the portion, and performing a tempering treatment (tempering treatment step).
The manufacturing method may further include the following steps.
A step of cooling a portion to be hardened during the tempering treatment (pre-hardening portion cooling step).
A step of reducing the amount of carbon entering a portion to be a tough portion by using a carbon prevention means before or during the carburizing treatment (a carbon prevention step).
These steps may be performed sequentially, or a plurality of steps (for example, a carburizing step, a carbon prevention step, a tempering step, and a pre-hard portion cooling step) may be performed in parallel.
The steel member may have a pre-tough portion and a pre-hard portion, and the shape and the like thereof are not particularly limited. However, as described above, from the viewpoint of performing an appropriate tempering treatment and imparting appropriate properties to each portion, it is preferable to use a steel member disposed at a position where the pre-tough portion and the pre-hard portion are separated (a position where at least both portions do not contact).
The carburizing treatment of the steel member may be any known carburizing treatment as long as it can add carbon to the surface of the steel member (particularly, hard portion), and is not particularly limited. Examples of the carburizing treatment include solid carburizing using wood carbon as a carbon source, gas carburizing using a gas containing carbon dioxide, hydrogen, methane, or the like as a main component, vacuum gas carburizing in which the gas is carburized after evacuation, and plasma carburizing in which the gas is plasmatized. Among them, gas carburizing, vacuum gas carburizing, and plasma carburizing are preferably used from the viewpoint of safety and operability.
The quenching treatment of the carburized steel member (including the pre-hardened portion and the pre-tough portion) may be any conventionally known quenching treatment, and is not particularly limited. In the quenching treatment, the steel member is heated to an austenite structure by induction heating using, for example, a high-frequency coil, and then rapidly cooled to be transformed into a martensite structure.
Next, by the above-described tempering treatment in the present manufacturing method, a tempering operation is performed in which the pre-tough portion of the steel member after the quenching treatment is heated to a tempering temperature and then immediately cooled, at least once (preferably, a plurality of times). Thus, a steel product having a hard portion having high hardness and a tough portion having high toughness can be obtained.
In the present manufacturing method, the pre-hardened portion may be simultaneously cooled when the pre-tough portion is heated to the tempering temperature in the tempering treatment. This makes it possible to more easily prevent the heat input to the pre-hardened portion during the tempering treatment from being transferred to the pre-hardened portion and causing softening.
In addition, in the present manufacturing method, when the steel member is carburized, the amount of carbon entering the pre-toughness portion can be reduced by using a carbon prevention means (for example, by putting a carbon prevention cap made of copper on the pre-toughness portion), and the hardness of the pre-toughness portion can be prevented from increasing during the quenching treatment.
Further, before the steel member is carburized, a carbon inhibitor may be applied to the pre-toughness portion as a carbon preventing means. This reduces the amount of carbon entering the pre-toughness portion during the carburizing process, and can further suppress an increase in hardness during the quenching process of the pre-toughness portion.
< apparatus for producing Steel product >
The steel product manufacturing apparatus according to the present invention (hereinafter, may be referred to as the present manufacturing apparatus) is a steel product manufacturing apparatus including a hard portion and a tough portion. The manufacturing apparatus includes a heating processing unit for heating a steel member, a cooling processing unit for cooling the steel member, and a moving mechanism capable of moving the steel member to each processing unit. Fig. 8 shows a (high frequency) tempering apparatus including a heating section 4a having a heating coil as the heating means 4, a cooling section 5a having a cooling jacket as the cooling means 5, and a moving means movable in the vertical direction of the paper as the moving mechanism 6, as an embodiment of the manufacturing apparatus.
Here, in the tempering treatment of the steel member 7 (treatment member), the moving mechanism 6 moves the steel member 7 (particularly, the pre-ductile portion 7a) to the cooling treatment portion 5a immediately after the pre-ductile portion 7a (threaded portion) of the steel member 7 is heated to the tempering temperature in the heating treatment portion 4 a. Here, the cooling processing section 5a may be provided with a water-cooled air jacket (not shown) for water removal, for example. The manufacturing apparatus may further include a fixing means, not shown, and may perform a heating process or a cooling process, or a movement by a moving mechanism, in a state where the steel product is fixed by the fixing means.
In the tempering treatment of each steel member, it is preferable that the moving mechanism moves from the heating treatment section to the cooling treatment section a plurality of times in order to perform the tempering operation composed of the heating and cooling a plurality of times. When the tempering operation is performed a plurality of times, the movement mechanism moves the pre-toughness portion from the cooling treatment portion to the heating treatment portion at least once to heat the pre-toughness portion again.
The heat treatment means 4 of the present manufacturing apparatus is not particularly limited as long as it can heat the steel member (particularly, the pre-ductile portion) to the tempering temperature, and known means can be appropriately used. In fig. 8, a high-frequency (heating) coil for induction heating is used as the heat treatment means 4.
The heat treatment portion 4a refers to a region where the heat treatment means 4 performs the heat treatment of the steel member 7 in the manufacturing apparatus. The preferable heat treatment conditions such as the tempering temperature (maximum reaching temperature) are as described above, and therefore, the description thereof is omitted.
The cooling treatment means 5 included in the manufacturing apparatus is not particularly limited as long as it is a means capable of heating the steel member (particularly, the pre-ductile portion 7a) to the tempering temperature and then immediately cooling the steel member, and a known means can be appropriately used. In fig. 8, as the cooling treatment means 5, a cooling jacket (more specifically, cooling water) is used, and an air jacket is provided for water removal.
The cooling unit 5a is a region in which the cooling treatment of the steel member 7 is performed by the cooling treatment means 5 in the manufacturing apparatus. Since the cooling process conditions such as the preferred cooling temperature are as described above, the description thereof will be omitted.
The moving mechanism 6 included in the manufacturing apparatus is not particularly limited as long as it can move the steel member 7 to the two portions of the heat treatment portion 4a and the cooling treatment portion 5a in the tempering treatment, and a known mechanism can be appropriately used. In fig. 8, a moving device capable of moving in the vertical direction of the paper is used as the moving mechanism 6.
Further, in the present manufacturing apparatus, when the pre-hardened portion 7a is subjected to the heat treatment by the heat treatment means, the pre-hardened portion 7b may be subjected to the cooling treatment by the cooling treatment means 5 in parallel. This makes it easier to prevent the heat transferred to the pre-hardened portion 7b from being transferred to the pre-hardened portion 7a and softening the same. In this case, the heat treatment means 4 and the cooling treatment means 5 are preferably arranged in consideration of the arrangement of the pre-ductile portion 7a and the pre-hard portion 7b of the steel member 7 and the arrangement based on the moving distance of the moving mechanism 6. By adjusting the arrangement of the two means in this way, the adjustment of the induction heating direction, the cooling water discharge direction, and the like can be easily performed, and the heating of the pre-hardened portion 7b and the cooling of the pre-hardened portion 7a can be more reliably performed.
The manufacturing apparatus may further include a carbon prevention means (not shown) by which carbon can be prevented from entering the pre-toughness portion 7a before or during the carburizing treatment, and the increase in hardness of the pre-toughness portion during the quenching treatment can be appropriately suppressed. As the carbon preventing means, for example, a carbon preventing cap or a carbon preventing agent can be used. Specifically, the carbon can be prevented from entering the pre-toughness portion by performing the carburizing treatment by putting a carbon-proof cap made of copper or the like on the pre-toughness portion before the carburizing treatment. Further, by applying the carbon inhibitor to the pre-toughness portion before the carburizing treatment, the penetration of carbon into the pre-toughness portion can be suppressed, and the increase in hardness during quenching can be further suppressed.
The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.
[ example 1]
As shown in fig. 8, a steel member 7 subjected to carburizing and quenching treatment is tempered using an induction tempering apparatus including a heating coil as a heating treatment means 4, a cooling jacket as a cooling treatment means 5, a gas jacket for water removal, and a moving mechanism 6 movable in the vertical direction of the paper surface. As shown in fig. 8, the steel member 7 has a threaded portion as the pre-hardened portion 7a and a shaft portion as the pre-hardened portion 7 b.
Then, the steel member 7 is set in the heat treatment portion 4a by a fixing means not shown. Next, the screw portion of the steel member 7 was subjected to a heat treatment with a tempering temperature (maximum reaching temperature) of 700 ℃. Then, the screw portion is moved to the cooling treatment portion 5a by the moving mechanism 6 while heating of the screw portion to the tempering temperature is completed (heating time: 3 seconds). Then, the threaded portion was cooled to room temperature (25 ℃) by a cooling jacket (cooling water). After the cooling treatment, the steel member 7 is dewatered by an unillustrated air jacket provided together with the cooling jacket. In example 1, the heating treatment and the cooling treatment in the tempering treatment were performed once for each.
Thus, a steel product having a tough portion and a hard portion was produced. In this order, 3 steel products were produced. The vickers hardness of the toughness portion of the obtained steel product was measured by the above method, and as a result, 436HV, 434HV and 432HV were obtained, and it was found that a desired hardness (440HV or less) was obtained. The vickers hardness of the hard portion of the obtained steel product is 500HV or more.
[ example 2]
A steel product including a ductile portion and a hard portion was produced in the same manner as in example 1, except that the number of tempering operations (heating treatment and cooling treatment) in the tempering treatment was changed to 2. Specifically, after the cooling treatment section has cooled the screw section after the heating treatment, the screw section is moved again to the heating treatment section by the moving mechanism, the heating treatment is performed by the heating coil, and the screw section is moved to the cooling treatment section while reaching the tempering temperature, and is cooled to room temperature. In this order, 3 steel products were produced. The vickers hardness of the toughness portion of the obtained steel product was measured by the above-described method, and as a result, 414HV, 409HV and 406HV were obtained, and it was found that a desired hardness was obtained. The hardness of the hard portion of the obtained steel product is 500HV or more.
[ example 3]
A steel product including a ductile portion and a hard portion was produced in the same manner as in example 1, except that the number of tempering operations (heating treatment and cooling treatment) in the tempering treatment was changed to 3. In this order, 3 steel products were produced. The vickers hardness of the toughness portion of the obtained steel product was measured by the above-described method, and as a result, it was found that the desired hardness was obtained at 400HV, 404HV and 408 HV. The hardness of the hard portion of the obtained steel product is 500HV or more.
Comparative example 1
A steel product having a tough portion and a hard portion was produced in the same manner as in example 1, except that the screw portion was heat-treated and then held (soaked) at about 700 ℃ for 10 seconds and then cooled to room temperature after the tempering treatment. In this order, 3 steel products were produced. The vickers hardness of the toughness portion of the obtained steel product was measured by the above-described method, and as a result, 438HV, 433HV and 434HV were obtained, it was found that a desired hardness was obtained. However, all of the obtained steel products had a vickers hardness of less than 500HV, and it was found that the hard portion was softened in the tempering treatment.
The hardness distribution of the ductile portion of the steel products obtained in these examples is shown in fig. 7.
As described above, according to the present invention, in the tempering treatment in the production of a steel product including a hard portion and a tough portion, an appropriate amount of heat can be applied to the portion to be the tough portion, and heat transfer to the portion to be the hard portion can be suppressed. As a result, in the steel product having the tough portion and the hard portion, the hardness of the hard portion can be prevented from decreasing while the toughness of the tough portion is ensured.
The production method and the production apparatus can be applied to steel products used in various applications such as vehicles such as automobiles and buildings. In addition, the components in the present embodiment may be replaced with other known components as appropriate without departing from the scope of the present invention.
Claims (7)
1. A method for manufacturing a steel product having a hard portion and a tough portion, characterized in that a portion of a steel member after quenching, which is to be the tough portion, is subjected to tempering treatment in which the portion is heated to a tempering temperature and then cooled immediately.
2. The method of manufacturing a steel product according to claim 1, wherein in the tempering treatment, an operation of heating a portion to be the ductile portion to a tempering temperature and then immediately cooling the portion is continuously performed a plurality of times.
3. A method of manufacturing a steel product according to claim 1 or 2, characterized in that the tempering temperature is 690 ℃ or more and 725 ℃ or less.
4. The method of manufacturing a steel product according to any one of claims 1 to 3, wherein a temperature at which a portion to be the ductile portion is immediately cooled after being heated to a tempering temperature is 100 ℃ or lower.
5. The method of manufacturing a steel product according to any one of claims 1 to 4, wherein 1 operation of heating to a tempering temperature and then cooling immediately is performed on the portion to be the ductile portion for a period of 30 seconds or less.
6. A steel product manufacturing apparatus that includes a hard portion and a tough portion, the steel product manufacturing apparatus comprising:
a heating treatment unit that heats the steel member;
a cooling treatment unit that cools the steel member; and
a moving mechanism capable of moving the steel member to each treatment section,
wherein the moving mechanism moves the steel member to the cooling treatment unit immediately after the portion that becomes the ductile portion of the steel member is heated to the tempering temperature in the heating treatment unit in the tempering treatment of the steel member.
7. The steel product manufacturing apparatus according to claim 6, wherein the moving mechanism performs a plurality of movements from the heat treatment unit to the cooling treatment unit in the tempering treatment of each steel member.
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