JPS6358656B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for tempering metal materials.

[Prior Art] One of the main purposes of hot tempering is to close and press the roughness defects that occur when metal solidifies. In recent years, demand for high-quality forged products has increased, and for example, the content of special metal elements has increased in forged steel materials.Also, as larger products are required, steel ingots have become smaller. It is getting larger. Therefore, grain defects exist not only in the center of the steel ingot but also in a wider area in the cross section of the steel ingot, and the properties of the steel ingot are deteriorating.

For the purpose of closing and crimping such rough defects by forging, a method of forging using flat anvils with different widths of the upper and lower anvils is shown in Japanese Patent Publication No. 58-19373.
The feature of this method is that when the anvil width is smaller than the thickness of the material, tensile stress due to the so-called Mannesmann effect is generated in the center of the material where there is a cracking defect, which occurs when the anvil width is smaller than the thickness of the material. Since this is disadvantageous in crimping defects, an attempt is made to use a vertically asymmetrical anvil to shift the position where the Mannesmann effect appears from the center of the material where the roughness defect exists.

[Problems to be Solved by the Invention] However, in the above conventional method, since the axial length of one of the anvils (for example, the upper anvil) is short, the number of reductions required to complete the reduction of the entire shaft length increases,
Since the axial length of the other anvil (for example, the lower anvil) is long, there is a disadvantage that the material is always in contact with the anvil and the temperature of the material decreases significantly due to heat transfer to the anvil.

In addition, in the conventional method described above, the deformation of the material due to forging is essentially asymmetrical, so the material bends during forging, and to prevent this, it is unavoidable to turn the material over during the forging process. It is time-consuming to straighten a bent material, and if it is not completely straightened, it may cause buckling, especially when upsetting.
In the case of shaft materials, this tends to cause eccentric rotation of the product. As described above, in the conventional method, it takes a long time to expand and the temperature of the material decreases significantly, so there is a drawback that in some cases, reheating is required during the process. In addition, the roughness defects are not only present in the center of the material.
If the area is spread over a wide area within the material cross section, even if you repeat rolling only in an arbitrary reference direction and a direction rotated 90 degrees from the reference direction, the rolling direction will always be 45 degrees.
Only the same region of the X-shape in the degree direction undergoes large plastic deformation, and the other regions do not undergo effective plastic deformation, so the smelting effect is small.

The object of the present invention is to efficiently apply large plastic deformation under compressive stress over a wide range of material cross sections, and to improve material quality through the smelting effect as well as crimping rough defects.

[Means for Solving the Problems] The method for hot-melting a metal material according to the present invention is such that when hot-melting a metal material, the metal material is covered with a vertically symmetrical V-anvil having an apex angle of 120 degrees to 150 degrees. After rolling down the material to be rolled at a reduction rate of 6% or more in an arbitrary reference direction set on the cross section of the material to be worked, the material to be worked is rolled within the rolled section by 90± from the reference direction.
A rolling process in which the rolled material is rotated by 10 degrees and rolled down at a rolling reduction rate of 6% or more, and the material to be rolled is formed into a substantially regular octagonal cross section through the rolling process from the reference direction.
135±10 degrees and 225±10 degrees (± relative to reference direction)
45±10 degrees) and a rolling process in which the rolling stock is reduced by 6% or more in each case, is included at least once during the rolling process.

[Function] According to the present invention, by rolling the material with a reduction rate of 6% or more using vertically symmetrical V anvils of 120 to 150 degrees, in the X-shaped region connecting the contact edges of the upper and lower anvils and the center Plastic deformation becomes large under compressive stress.
However, with any reference direction set for the material cross section,
Even if rolling is repeated only in a direction rotated by 90±10 degrees from this reference direction, only the X-shaped region will always undergo large plastic deformation, and the other parts will not undergo large plastic deformation. Therefore, in the present invention, the reference direction of the above-mentioned material and the
In addition to rolling from the 135° and 225° directions at a reduction rate of 6% or more, plastic deformation under compressive stress occurs in a wider area of the material, and To enable effective crimping of rough defects. In addition, since we only use a V anvil at 120 to 150 degrees during the series of forging processes,
There is no need to change the anvil in the middle of the process, the deformation is always symmetrical, no bending occurs, and production efficiency is improved.

[Example] As a result of rolling a material with a circular cross section with a 135-degree vertically symmetrical V anvil according to the present invention as shown in Fig. 1A at a rolling reduction rate of 10%, the strain distribution in the rolling direction was as follows. Figure 1B
As shown in , make an X connecting the upper and lower anvil edges and the center.
It was observed that the plastic strain was large in the character-shaped region, and was greatest at the center. Furthermore, the strain distribution in the direction orthogonal to the rolling direction was similar, and it was observed that the shear strain increased in the X-shaped region, except at the center (the shear component was zero at the center due to symmetry).

By the way, a necessary condition for improving the cast structure and crimping the roughness defects by forging is that the area undergoes large plastic deformation under compressive stress, and from this point of view, areas other than the X-shaped area are unfavorable. It is necessary to incorporate a wider area into the X-shaped area. Furthermore, regarding compressive stress, according to the conventionally known slip line field theory for plane strain, as shown in FIG. 2, if the contact width B with the anvil is equal to or larger than the thickness H, that is, B≧H In the case of , the maximum principal stress is always compressive stress in regions R and P, and in the case of a 135-degree vertically symmetrical V anvil, as shown in Figure 3, if the circular cross-section material is reduced by 6% or more,
It was confirmed through experiments that the above condition of B≧H could be obtained. That is, in the present invention, the apex angle is approximately
The reason why the material to be worked is reduced by more than 6% with a 135 degree vertically symmetrical V anvil is as explained above.As a result, the above-mentioned The defect will be effectively crimped.

When the result of FIG. 1B is converted to the original cross section, FIG. 4A is obtained. The X-shaped region shown in FIG. 4A is an effective region for crimping of rough defects. Here, in order to form and heat the material into an octagonal cross section, first roll down in the reference direction (0 degree direction reduction) shown in Figure 4A, then rotate the material 90 degrees in the 90 degree direction. It is sufficient to repeat the rolling process alternately, and since any surface is directly rolled down by the anvil, there will be no problems such as surface cracks, but basically only the X-shaped area is effectively deformed, so As shown in Figure B, a small part of the center of the material (material diameter D as a semi-quantitative value equivalent to the diameter)
The effect of crimp defect crimping can only be obtained for approximately 20% of cases.

Therefore, in the present invention, after the cross section of the material is formed into a substantially regular octagon by the above-mentioned 0 degree - 90 degree direction reduction, it is rotated 135 degrees from the reference direction and rolled down by 135 degrees (Fig. 4C), Furthermore, we will perform a 225 degree directional reduction (Fig. 4D) in which the material is rotated 90 degrees and reduced, and based on the fact that the X-shaped area receives effective reduction in these reductions, as a result, a wider area in the center of the material will be (approximately 45% of the material diameter D as a semi-quantitative value equivalent to the diameter) and the area D in Figure 4
It is possible to compress the rough defects in the white areas and improve the textured structure.

It should be noted that during rolling, as shown in Figure 4 A to D, it is not necessary to continuously perform 0°-90° and 135°-225° direction reduction, and in the rolling process, the reference direction ( 0 degree direction) and 0 degree -90
If the reduction in the direction of 135 degrees to 225 degrees is included at least once before the forging is completed, the above effect can be obtained.

Furthermore, if you want to achieve a perfect tempering effect, angles of 22.5 degrees, 112.5 degrees, 157.5 degrees from the standard direction of the material, etc.
If the reduction is carried out in the direction of 247.5 degrees so that the area with little plastic deformation, indicated by the dots in Figure 4D, becomes an X-shaped area, it is possible to apply effective reduction to the entire cross section of the material. These reductions are not necessary unless the product diameter is significantly larger than the diameter of the cast material. In addition, even if you use a V-anvil with an apex angle of approximately 135 degrees, that is, 120 degrees to 150 degrees, the angle will be 0 degrees to 150 degrees.
A similar effect can be expected by applying pressure in the directions of 90 degrees and 135 degrees to 225 degrees. In addition, the rotation angle of the material to be tempered from the reference direction is also ± for each value.
Almost the same effect can be expected even if there is an error of about 10 degrees, but when moving from 90 degrees to 135 degrees,
It is necessary to form the cross section into a substantially regular octagon. If such a substantially regular octagonal shape is not formed, there is a disadvantage that the material is likely to be twisted or bent.

Hereinafter, specific implementation results of the present invention will be explained. A 5% Cr steel ingot with a diameter of 1000 mm was uniformly heated to 1200°C, and after being taken out of the furnace, one was forged by the method of the present invention and the other was forged by the conventional method to obtain a diameter of 600 mm.
mm shaft material was manufactured. In the present invention, the rolling direction is 0 degrees - 90 degrees - 0 degrees - 135 degrees - 225 degrees - 135 degrees - 0
The temperature was -90 degrees, and it took about 25 minutes to complete the process. On the other hand, in the conventional method, it is first formed into a roughly square shape of 900 mm x 900 mm, then rolled down in the 0 degree direction and turned over.
A cycle of rolling down in the 180 degree direction, then rotating 90 degrees, rolling down in the 90 degree direction, reversing again, and rolling down in the 270 degree direction was repeated. In this conventional method, the amount of reduction per round was set at 100 to 150 mm in order to reduce bending as much as possible during forging, but the number of reductions was limited due to the correction of the bend and the short axial length of the upper anvil. In addition to the large increase in heat and time required, there was also a temperature drop due to heat transfer to the lower anvil, and it was necessary to reheat it midway through. When the materials obtained by both of these methods were inspected by ultrasonic flaw detection, no defects were detected in the forged material according to the present invention, whereas those obtained by the conventional method At a position 0.3 to 0.4 times the radius from the axis of the direction, 1.0 mm in diameter
The following defects were detected.

[Effects of the Invention] As described above, the method for tempering a metal material according to the present invention has an apex angle of 120 when hot tempering a metal material.
After rolling down the material to be melted in an arbitrary reference direction set on the cross section of the material to be rolled at a reduction rate of 6% or more using a vertically symmetrical V anvil of 150° to 150 degrees, the material to be melted is rolled from the reference direction within the rolled cross section. A rolling process in which the rolled material is rotated by 90±10 degrees and rolled down at a rolling reduction rate of 6% or more, and the material to be rolled is formed into a substantially regular octagonal cross section by the rolling process, and the rolled material is rolled by 135±10 degrees from the reference direction. degree and rotated 225 ± 10 degrees (±45 ± 10 degrees with respect to the reference direction), both 6%
The above rolling step is included at least once during the rolling step. Therefore, it is possible to efficiently apply large plastic deformation under compressive stress over a wide range of material cross sections, and not only to compress roughness defects but also to enhance material quality improvement due to the smelting effect.

[Brief explanation of drawings]

Figure 1A is a schematic diagram showing the state in which a circular cross-section material is tempered with a 135° vertically symmetrical V anvil at a reduction rate of 10%.
Figure B is an iso-strain diagram in the rolling direction of a 10% rolled material, Figure 2 is a schematic diagram showing the slip line field of a material compressed with a vertically symmetrical anvil, and Figure 3 is a circular cross-section material with a 135 degree vertically symmetrical V anvil. A diagram showing the relationship between the rolling reduction rate and B/H when rolling down. FIG. 3 is a schematic diagram showing a region with large plastic deformation and a region with almost no plastic deformation in each. 1... V anvil, 2... tempered material.

Claims (1)

[Claims] 1 When hot-melting metal materials, the apex angle is 120
After rolling down the material to be melted in an arbitrary reference direction set on the cross section of the material to be rolled at a reduction rate of 6% or more using a vertically symmetrical V anvil of 150° to 150 degrees, the material to be melted is rolled from the reference direction within the rolled cross section. A rolling process in which the rolled material is rotated by 90±10 degrees and rolled down at a rolling reduction rate of 6% or more, and the material to be rolled is formed into a substantially regular octagonal cross section by the rolling process, and the rolled material is rolled by 135±10 degrees from the reference direction. degree and rotated 225 ± 10 degrees (±45 ± 10 degrees with respect to the reference direction), both 6%
A method for smelting a metal material, characterized in that the smelting step is performed at least once during the smelting step.