JPH0924436A - Method for forging forged parts with large deformation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent generation of defects such as cracks in a large deformation by achieving the forging after a layer with reduced carbon content is formed on a stock to be worked. SOLUTION: Carbon steel or structural alloy steel containing 0.3-1.6% carbon is forged with large deformation. The carbon content of the layer of 0.3-4mm in thickness on the surface of a stock to be worked is <=0.3%. The surface inside of the stock is decarburized to reduce the carbon content of the surface layer. Steel of <=0.3% carbon content is cladded by welding through the thermal spraying on the outside of the surface of the stock. The large deformation forging is achieved on a part which is largely deformed so that the deformation ratio is >=50% in the forging, and carburization is achieved after forging, or the layer with reduced carbon content is removed by machining. When the layer with reduced carbon content is formed by decarburization, the carbon powder or carburizing agent in paste condition is applied to prevent decarburization to a part of the stock whose deformation ratio is <=50% in the forging.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a method for forging a forged part in which a steel material is highly deformed by cold forging.

[0002]

2. Description of the Related Art Conventional high-deformation cold forged parts are manufactured by softening annealing for softening a material to be processed, spheroidizing cementite in steel, and softening annealing for the purpose of improving mold life and high-precision forming. Is subjected to spheroidizing annealing to reduce deformation resistance and increase ductility. After that, forging is performed to form a predetermined component shape. However, when there is a portion that needs to be highly deformed, the forging is performed in several steps because the forming cannot be completed in one step.

[0003]

The above-mentioned conventional high deformation forged parts have the following problems. When softening annealing or spheroidizing annealing is performed on a material to be processed, when the material is heated, oxygen in the air causes oxide scale to be generated, and decarburization occurs near the surface of the material. Here, decarburization reduces the post-quenching effect and reduces the fatigue strength, which is an important strength problem depending on the type of material steel. However, when cold forging high carbon steel,
In parts with high deformation, defects such as cracks and cracks are likely to occur on the surface, and there is a problem in that a predetermined molded product cannot be obtained.

Further, a component which is highly deformed at the time of forging is usually forged in several steps. This is because when the forging in one step is performed, stress is concentrated due to work hardening of the highly deformed portion, and the die Or damage to the molded product or galling between the mold and the molded product may occur. Therefore, it is necessary to divide the process into several steps and insert annealing in the middle to soften the molded product to mold it into a predetermined shape. An object of the present invention is to provide a forging method that prevents defects when the material to be processed is highly deformed.

[0005]

The above object can be achieved by forming a layer having a reduced carbon content on a material to be processed and then forging. The material to be processed is carbon steel or structural alloy steel, and the carbon content is 0.3% to 1.6.
% Steel is desirable. The thickness of the layer having a reduced carbon content on the surface of the material to be processed may be 0.3 mm to 4 mm, and the carbon content of this layer may be 0.3% or less. For the layer with reduced carbon content, decarburize the surface of the material to be processed in an atmosphere such as oxidizing, or spray low carbon steel wire with a carbon content of 0.3% or less on the surface of the material to be processed. It is preferably formed by applying a padding, and in this case, a heat diffusion treatment may be applied in order to enhance the adhesion between the padded part and the material.

Further, the material to be processed has a deformation rate of 50 during forging.
It is applied to a material having a high deformation ratio of not less than%, and is not applied to a work material having a deformation ratio of not more than 50%. When a layer with a reduced carbon content is formed by decarburization, decarburization is performed by applying charcoal powder or carburizing agent in a paste form to the work material part whose deformation rate during forging is 50% or less. It is necessary to prevent After forging, a carburizing treatment may be performed, or a layer having a reduced carbon content may be removed by machining to perform a tempering treatment.

[0007]

As described above, by forming a layer having a reduced carbon content on the surface of the material to be processed and then forging, the deformation resistance and ductility are lower than those in the inside, and the deformation in the highly deformed portion is The surface layer relaxes the strain,
It is possible to prevent cracks or cracks generated on the surface. If the carbon content of the material to be processed is 0.3% or less,
No defects are generated even when highly deformed, and therefore the carbon content of the layer formed on the material to be processed is usually 0.3% or less. For example, α-Fe (carbon content of 0.025
Higher deformation forging can be supported by using a lower carbon content of about (% or less).

The upper limit carbon content of the material to be processed is 1.
Although it is 6%, when it exceeds this value, it becomes cast iron, and since graphite that is free carbon is crystallized in a lump form, this graphite becomes a starting point during forging and is accompanied by internal fracture. The thickness of the layer in which the carbon content has been reduced is that the surface layer of a black leather material that is usually purchased from a steel manufacturer is a material in which the carbon content has already been reduced by decarburization of about 0.3 mm. By controlling the upper limit to 4 mm or less, it is possible to easily restore the original carbon content of the material by post-carburizing.

Further, the material to be processed has a deformation rate of 50 during forging.
When the deformation ratio is low, the defects such as cracks and cracks are not likely to occur on the surface.

[0010]

The present invention will be described below with reference to the accompanying drawings. First, structural Cr-Mo steel SC with a carbon content of 0.4%
A cylindrical material (φ40 × 40 mm) of M440 material was heated in the atmosphere according to the heat treatment pattern shown in FIG. This heat treatment pattern controls the depth of the layer that lowers the carbon content, and at the same time, performs spheroidizing annealing for the purpose of softening the inside of the material to be processed. FIG. 2 shows the iron-carbon system phase diagram of the alloy steel, and FIG. 3 shows the carbon content from the surface of the material obtained when the alloy steel is subjected to the heat treatment of FIG.

By performing the heat treatment shown in FIG. 1, the raw material is first heated and held at 870 ° C. and the entire raw material is brought into an austenite (γ-Fe) state. Next, in the range of (a) shown in FIG. 3, austenite is transformed into α-Fe by decarburization, and subsequently, a diffusion layer (b) having a carbon concentration is formed. The boundary between the layers of (a) and (b) corresponds to C of FIG. 2, and the carbon content of (b) gradually increases to reach the steel substrate. Then, by cooling to 720 ° C. just below the A1 transformation point, the austenite state of the diffusion layer and the steel internal base material is decomposed into α-Fe and cementite (Fe3C), and the cementite is spheroidized by holding at this temperature.

The layer having a reduced carbon content of 0.3% or less, which has the effect of preventing defects during high deformation, corresponds to the range of FIG. 3C, and the depth of the layer is about 3 mm. Met. Next, the columnar material having the layer in which the carbon content was reduced was compressed and deformed as shown in FIG. 4, and the presence or absence of defects generated on the surface and the deformation resistance were measured as shown in FIG.
For the measurement of the deformation resistance, a press with a maximum compression load of 400 tons was used, and stress (deformation resistance) was derived from the load and the deformation rate (strain) when the column was compressed at room temperature. As a lubricant for the mold, a cylinder material was subjected to bonder treatment.

A conventional SCM which is spheroidized and annealed in a vacuum and has no layer with a reduced carbon content in the surface layer of the material.
In the No. 440 material (2 in FIG. 5), the defect of the crack 1 as shown in FIG. 4 occurred at the deformation rate of about 68%, but the columnar material having the layer with the reduced carbon content of the present invention (FIG. 5). 3)
No defect of crack 1 occurred on the surface even when compressed and deformed to 80%. Further, the layer having the reduced carbon content showed a slight effect on the deformation resistance, and the deformation resistance was about 5% lower than that of the conventional SCM440 material (2 in FIG. 5). The following experiment was conducted to verify this effect. Since the average carbon content of the layer of the present invention in which the carbon content is reduced (range of FIG. 3 (c)) is about 0.1%, the low carbon steel S10C material having a carbon content of 0.1%. The deformation resistance was measured (4 in Fig. 5), and it was about 2 compared with the conventional product (2 in Fig. 5).
Deformation resistance is as low as 5%. Therefore, it is effective to reduce the deformation resistance by providing a surface layer portion having a reduced carbon content as in the present invention, and even if highly deformed, the surface cracks 1
No defects occur.

After compressing and deforming the conventional SCM440 material (2 in FIG. 5) to about 50%, an intermediate annealing is performed in vacuum according to the heat treatment pattern shown in FIG. 1 and further 80%.
Was compressed and deformed (5 in FIG. 5). In this case, defects such as crack 1 and cracks did not occur on the surface. Therefore, a conventional molded product can be obtained by increasing the number of steps including annealing in the middle, but in the present invention, the predetermined molded product can be obtained in one step. In the molded article having the layer with the reduced carbon content described above, the layer with the reduced carbon content in FIG. 3C is compressed to be 1/3 (1 mm) thin.
Therefore, using mixed gas of Co + Co2, etc., 850-900
By carburizing at 3 ° C. for 3 hours and diffusing for 3 hours, the carbon concentration in the material could be almost restored, and the material was quenched. Alternatively, the outer diameter of the cylindrical material before forging is 3 m
The layer 1 mm in which the compressed carbon content after forging was reduced by increasing m was removed by machining, and then the entire tempering was performed.

As another embodiment, the same material as described above is subjected to overlay thermal spraying on the surface of the material with a pure iron wire. Material size is φ3
It is a 4 x 40 mm cylinder and has a built-in thermal spray coating only on the outer periphery.
The layer was 3 mm. After that, by performing the heat treatment pattern shown in FIG. 1 in a vacuum, it was possible to simultaneously perform the diffusion treatment for perfecting the adhesion between the sprayed portion and the material and the internal spheroidizing annealing. The carbon concentration distribution obtained here is almost the same as that shown in FIG.
No crack 1 was generated on the surface until compression to 0%, and the deformation resistance was similar to that shown in 3 of FIG.

Further, carbon powder or carburizing agent (charcoal: 60 to 70%, BaC) is formed on the upper and lower end surfaces of the SCM440 cylindrical material.
o3: 20 to 30%, NaCo3: 10 to 20%, coke: 10 to 20%) is applied as a paste with methanol, isopropanol or water glass (sodium silicate solution). Then, when the columnar material is annealed in the atmosphere using the heat treatment pattern of FIG. 1, only the side surface of the material has a carbon distribution as shown in FIG. 3, but the carbon concentration on the upper and lower end surfaces does not change and the carbon distribution inside the material It was the same. When this material is forged as shown in FIG. 6, the side surface is a highly deformed portion of about 70% or more, but since it has a layer with a reduced carbon content, there is no defect of crack 1 and the upper and lower end surfaces are 50 Since it is a low deformation portion of less than or equal to%, of course, there is no defect of crack 1. This part is a part that has hardness only on the upper and lower end faces, and the upper and lower end faces were quenched by high frequency after forging.

[0017]

As described above, according to the present invention, cracking during high deformation is achieved by forming a layer having a reduced carbon content on the surface of a material to be processed such as high carbon steel and then forging. It has become possible to prevent defects such as cracks. Furthermore, compared to conventional materials that do not have a layer with a reduced carbon content,
Since it is possible to prevent defects such as cracks and cracks, conventional materials can be annealed in the middle to obtain a predetermined forged product, and forging of several steps can be molded in one step with the product of the present invention, shortening the process it can.

Further, since the deformation resistance is reduced, it is possible to reduce the degree of die wear during forging, and further contribute to the improvement of die life.

[Brief description of drawings]

FIG. 1 is a graph showing a spheroidizing annealing and a heat treatment pattern for controlling the depth of a layer for lowering the carbon content.

FIG. 2 is a graph showing an iron-carbon system state.

FIG. 3 is a graph showing the carbon concentration obtained by the heat treatment pattern of FIG.

FIG. 4 is an explanatory perspective view showing a cylindrical material before and after compression deformation.

FIG. 5 is a graph showing the measurement results of deformation resistance and the presence or absence of defects occurring on the surface.

FIG. 6 is a front view showing a cylindrical material before and after compression deformation.

[Explanation of symbols]

1 is a crack generated on the surface of the molded product, 2 is a conventional SCM44
Deformation resistance curve of 0 material, 3 is deformation resistance curve of the present invention, 4 is deformation resistance curve of S10C material, and 5 is a deformation resistance curve when conventional SCM440 material is subjected to intermediate annealing and forged from 50%.

Claims (8)

[Claims] 1. A method for forging a high deformation forged part, which comprises forming a layer having a reduced carbon content on a material to be processed and then forging. 2. The material to be processed is 0.3% to 1.6%
2. The method for forging a high deformation forged part according to claim 1, wherein the carbon steel containing the above carbon or a structural alloy steel is used. 3. The method for forging a high deformation forged part according to claim 1, wherein the thickness of the layer having a reduced carbon content on the surface of the material to be processed is 0.3 mm to 4 mm. 4. The method for forging a high deformation forged part according to claim 1, wherein the carbon content of the layer having a reduced carbon content on the surface of the material to be processed is 0.3% or less. 5. The carbon content-reduced layer is decarburized on the inside of the surface of the material to be processed or by spraying a steel material having a carbon content of 0.3% or less on the outside of the surface of the material to be processed. The method for forging a high deformation forged part according to claim 1, wherein the forging is performed by forming a padding having excellent adhesion. 6. The work material has a deformation ratio of 5 during forging.
The method for forging a high deformation forged part according to claim 1, wherein there is a portion that is highly deformed by 0% or more. 7. The highly deformed forged part according to claim 1, wherein after the forging, a carburizing process is performed or a layer having a reduced carbon content is removed by machining to perform a tempering process. Forging method. 8. When forming the layer having a reduced carbon content by decarburization, carbon powder or a carburizing agent is applied in a paste form to the work material portion having a deformation rate of 50% or less during forging. The method for forging highly deformed forged parts according to claim 1, wherein the forging is applied to prevent decarburization.