JPH0759724B2 - Method of processing and quenching steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial field of application) The present invention is directed to strengthening the surfaces of steel materials and steel parts (products) to stabilize the quality of steel. The present invention relates to a processing and quenching method.

(Prior Art) Conventionally, surface hardening treatments such as carburizing and quenching, nitriding, and nitrocarburizing are well known as methods for strengthening the surface of steel materials and steel parts (products). There is also a way to add.

For example, as a method of applying processing together with the latter surface treatment, as illustrated in FIG. 4, the article 1 to be treated is first charged into the article reservoir 2 and then the heating furnace equipped with the low frequency heating coil 3a. 3, heated to 1000 ° C. in about 30 seconds, for example, and then the object to be treated 1 is sent to the high temperature carburizing furnace 4 in which the object to be treated 1 is carburized for 25 minutes at 1050 ° C. and 50 minutes. After being subjected to a diffusion process for a minute (depth of about 1.2 mm) or immediately after cooling to a warm zone (600 to 850 ° C), it is sent to a forging machine (or rolling machine, etc.) 5 and this forging machine (or rolling machine) Etc.) After processing in 5, quenching agent for water, oil, etc. 6a
Immediately insert into the quenching tank 6 containing
Then, for example, 150 to 180 with respect to the hardened workpiece 1.
After tempering at ° C, the oxide film on the surface was removed by sandblasting or the like for finishing (according to the invention described in Japanese Patent Application No. 60-165966).

(Problems to be Solved by the Invention) However, in such a carburizing and quenching method in which processing is performed together with the conventional surface treatment, after the carburization in the high temperature carburizing furnace 4 is completed, the forging machine (or the rolling machine, etc.) 5 is used. Since the processed product 1 was processed in the atmosphere, and after completion of the processing, it was quickly put into the quenching tank 6 containing the quenching agent 6a such as water or oil for quenching, so that the forging machine (or rolling machine, etc.) 5) The surface temperature of the article to be processed 1 is lowered by contact with the mold, and the quenching hardness may be lowered or varied due to this temperature decrease, because the processing is performed in the atmosphere. Oxidation and decarburization on the surface of the object to be processed 1 may cause problems such as formation of an oxide film and reduction of surface hardness, and it is difficult to finish the temperature of the object to be processed 1 at the end of processing. Because, due to the variation of the quenching temperature,
In particular, when the product 1 to be processed is a mass-produced product, the hardness and dimensional accuracy may vary among products, which remains a problem.

(Object of the Invention) The present invention has been made in view of the above-mentioned problems of the prior art, in which the hardness and dimensional accuracy of the workpiece to be processed and hardened after the quenching treatment are remarkably small, and a stable quality steel material and steel portion are provided. It is an object of the present invention to provide a method for processing and quenching steel that can be used to obtain (products) and the like.

[Structure of the Invention] (Means for Solving Problems) The present invention is directed to surface hardening treatment such as high temperature carburizing, ordinary carburizing, and carbonitriding in whole or in part at an austenite temperature above the A ₁ transformation point of steel. After strengthening, the surface strengthening of steel with a hardened structure such as martensite or bainite by cooling the surface-hardened material containing at least a portion of the austenite by processing such as forging or rolling.
In a processing and quenching method such as forging direct quenching, after the processing is finished, at least the surface is heated to a temperature higher than the temperature after the processing is finished and / or carburized to reduce the surface oxide film and form a decarburized layer. It is characterized in that recovery and / or quenching temperature is made uniform, and then quenching is performed.In one embodiment, at least the surface after completion of the processing is simply treated at a temperature higher than that after completion of the processing. In order to make the quenching temperature uniform by reheating it to a higher temperature, quenching can be performed by dipping in a neutral salt bath or a liquid carburizing salt bath in a neutral salt bath of 500 to 900 ℃. It is characterized by reducing the surface oxide film, recovering the decarburized layer or making the quenching temperature uniform, and then quenching.

The steel material to which the present invention is applied is, for example, a material suitable for case hardening such as SC material, S-CK material, SNC material, SNCM.
Material, SCr material, SCM material, SMn material, SMnC material, etc. are used.
D Carburizing steel and two-phase carburizing steel.

When carrying out work-hardening for surface strengthening on a product to be processed made of such a steel material, for example, as shown in FIG. 1, the product 1 to be processed is first charged into the product reservoir 2. After that, it is sent to a heating furnace 3 equipped with a low-frequency heating coil 3a and heated to, for example, an austenitizing temperature or higher, and then the article to be treated 1 is sent to a high-temperature carburizing furnace 4 and this high-temperature carburizing furnace 4
Immediately or after warming (eg 600 to 850 ° C) after carburizing and diffusing the treated product 1
After cooling to a forging machine (or rolling machine, etc.) 5, processing is performed, and then, for example, a liquid carburizing bath (bath temperature is, for example, 850 to 900).
C.) 7a is put in the bath 7 and the processed product 1 is charged and held by immersion to reduce the surface oxide film, recover the decarburized layer, and make the quenching temperature uniform. The hardness and dimensional accuracy of the quenched product are remarkably stable by rapidly charging and quenching in the quenching tank 6 containing the quenching agent 6a such as oil, and then appropriately tempering after quenching and then sandblasting. The surface should be finished by, for example,

(Example 1) A round bar (diameter 50 mm) made of JIS SNCM420H steel was used as a material, and the temperature of the round bar in the high temperature carburizing furnace 4 was 1050 ° C for 25
Minute high temperature carburizing and 50 minutes diffusion process (target depth 1.2mm)
Then, it was forged into a gear shape by a forging machine (die temperature 200 ° C) 5 by the tooth profile overhanging method at a warm forging temperature of 850 ° C, and then a neutral salt bath (BaCl ₂ : 70, 850 ° C) was used. KCl: 1
0, NaCl: 20) After soaking in bath 7 containing 7a for 1 minute,
A spur gear having a module 3 and 17 teeth was manufactured by charging in a quenching tank 6 containing quenching oil 6a at 0 ° C. and quenching.

(Example 2) After forging into a gear shape by the forging machine 5 through the same steps as in Example 1, a carburizing salt bath (Na ₂ CO _{2) at} 880 ° C was used instead of the neutral salt bath.
Bathtub 7 containing 7a ( ₃ mains, manufactured by Parker Heat Treatment Co., Ltd.)
After immersing in the quenching tank 6 containing 80 ° C quenching oil 6a and quenching,
3, Spur gears with 17 teeth were manufactured.

(Comparative Example 1) Using a round bar (diameter 50 mm) made of JIS SNCM420H steel as a material, in a high temperature carburizing furnace 4 at 1050 ° C for 25
Minute high temperature carburizing and 50 minutes diffusion process (target depth 1.2mm)
Then, it is forged into a gear shape by the forging machine 5 by the tooth profile overhanging method at a warm forging temperature of 850 ° C, and then immediately put into the quenching tank 6 containing the quenching oil 6a at 80 ° C for quenching. As a result, a spur gear having module 3 and 17 teeth was manufactured.

(Evaluation Example) When the distribution of the cross-sectional hardness (Hv) of each spur gear manufactured in Examples 1 and 2 and Comparative Example 1 was measured, the results shown in FIG. 2 were obtained. Further, when the variation in pitch circle diameter of the gears (20 gears each) manufactured in Example 2 and Comparative Example 1 was measured by the over-ball diagram measurement method, the results shown in FIG. 3 were obtained.

As shown in FIG. 2, the gears manufactured in Examples 1 and 2 have a hardness higher than that of the gear manufactured in Comparative Example 1, and in particular, the gear manufactured in Comparative Example 1 has an outermost surface. The hardness is quite low. It is considered that such a large decrease in hardness on the outermost surface is due to a decrease in surface temperature due to contact with the mold during forging (rolling), oxidation on the surface, decarburization, and the like. Further, the hardness of the outermost surface of the gear manufactured in Example 1 is slightly reduced, which is presumably due to decarburization. On the other hand, in the gear manufactured in Example 2, the decarburized portion on the surface is Is clearly carburized, and it is clear that the hardness is increasing.

On the other hand, according to the measurement result of the variation of the pitch circle diameter shown in FIG. 3, in the case of Example 2 in which the steel is soaked by being immersed in a carburizing salt bath after working and before quenching, such soaking treatment is performed. It is clear that the variation in pitch circle diameter is significantly smaller than in the case of Comparative Example 1 which was not performed.

In the above example, the case where a salt bath is used as the heat treatment after working and before quenching is shown as an example, but in addition, heating (reheating) in N ₂ gas, RX carburizing gas, fluidized bed furnace, etc. ) And / or carburizing, it was confirmed that a steel component (product) such as a gear having a large surface hardness and a significantly small dimensional variation can be obtained.

[Effects of the Invention] As described above, according to the present invention, the A ₁
After performing the surface hardening treatment at the austenite region temperature of the transformation point or higher, in the method of quenching and hardening the steel by adding and cooling the surface hardening treatment material containing at least a portion of the austenite, at least on the surface after the end of the processing. By heating and / or carburizing to a temperature higher than the temperature after the end of the processing, the surface oxide film is reduced, the decarburized layer is recovered, the quenching temperature is made uniform, and then quenching is performed. It is possible to make the hardness of processed products such as steel materials, steel parts (products), etc. after processing and quenching large, and the variation of hardness is small, and the variation of dimensional accuracy is also extremely small. It is possible to improve the properties and fatigue resistance and to stabilize the quality, which is a very excellent effect.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an outline of work-hardening equipment in one embodiment of a work-hardening method for steel according to the present invention;
FIG. 3 and FIG. 3 are graphs illustrating the results of measuring the sectional hardness distribution and pitch circle diameter error distribution of each gear manufactured in Examples and Comparative Examples of the present invention, and FIG. 4 is the conventional work hardening of steel. It is explanatory drawing which shows the outline of the processing hardening equipment in a method. 1 ... Processed item, 4 ... High temperature carburizing furnace, 5 ... Forging machine, 6 ... Quenching tank, 7 ... Bathtub.

Claims (1)

[Claims] 1. A method for quenching and hardening a steel, which comprises performing a surface hardening treatment at an austenite temperature of at least the A ₁ transformation point of steel and then cooling the surface hardened material containing at least part of the austenite by working. After completion of the processing, at least the surface is heated to a temperature higher than the temperature after the completion of the processing and / or is subjected to carburization to reduce the surface oxide film, recover the decarburized layer, and make the quenching temperature uniform, A method for processing and quenching steel, characterized by performing quenching after that.