JPS58167045A - Hot forging of steel material - Google Patents

Abstract

PURPOSE:To enable extend forging of a large steel material using a press of relatively small capacity in a process that performs extend forging of axially symmetrical steel material between upper and lower anvils, by making sectional form perpendicular to the direction of extend forging rectangular during the stage of extend forging. CONSTITUTION:When extend forging a steel material 3 between upper and lower anvils 1, 2, extend forging is started in a state that the sectional form perpendicular to the direction of extend forging is, for instance, nearly circular. Then, in an optional stage during the stage of extend forging, the sectional form perpendicular to the direction of extend forging is made rectangular or nearly rectangular, and the ratio of longer side to shorter side is made 1.4 or more. The material is then extend forged to desired final form such as square, octagon etc. of axial symmetry. By this way, the height H of the steel material when it is rectangular can be made small, and W/H can be made large without enlarging the width W of anvils 1, 2. Accordingly, internal cavities of a large-sized steel material can be pressure welded, and a formed product free from deffects can be obtained.

Description

[Detailed description of the invention] The present invention relates to a method for hot forging steel materials.

In conventional hot forging methods for steel materials, for example, when it is desired to obtain an axially symmetrical forged product such as a rotor shaft for a generator, the following steel materials are forged and drawn. That is, as shown in FIGS. 1 and 2, pressing force was applied to the steel material 3 between the upper anvil 1 and the lower anvil 2, and the steel material was forged and stretched in the left-right direction in FIG. The cross-sectional shape perpendicular to the forging direction of the steel material 3 during forging (that is, the shape of the steel material 3 shown in Fig. 1) is an axially symmetrical shape such as a circle, a rectangular shape, or a square, or a shape close to it. It was kept. Even in this method of hot forging steel, when the shape of the steel 3 is small, the plastic flow extends to the center as shown in Figure 3, and the voids inside the steel 3 (in the solidification process of the steel ingot) voids formed inside)
It was possible to forge and stretch it so that it was crimped.

However, when the width W of the upper anvil 1 and the lower anvil number 2 is smaller than the height H of the steel material 3, that is, when W/H is small, as shown in FIG. A portion (i.e., a portion where plastic deformation does not occur) that is not affected by plastic flow due to the force applied by the lower metal number 2 is created in the center of the steel material 3. Therefore, the void in the center of the steel material 3 is not crimped. The above-mentioned problem is very serious because one of the purposes of hot forging is to eliminate defects by compressing the voids that would otherwise remain and result in a molded product with internal defects.

In order to solve the above problem, it is possible to increase the width W of the upper anvil l and the lower anvil number 2, but if the width W is increased, the contact area between the upper anvil l and the lower anvil number 2 and the steel material 3 will increase. As it gets bigger, it becomes necessary to apply a lot of force, which exceeds the ability of the press.

Therefore, the width W of the upper anvil 1 and the lower anvil 2 could not be made larger than a predetermined value. For this reason, it has been impossible to forge and elongate the large steel material 3 without using a powerful press.

The present invention was made by focusing on the above-mentioned problems in the conventional hot forging method for steel materials. The purpose is to obtain an intermediate forging method.

Hereinafter, the present invention will be described in figures 5 to 11 of the attached drawings showing embodiments thereof.
This will be explained based on the diagram.

First, the configuration will be explained.

The steel material 3 is forged between the upper anvil 1 and the lower anvil 2,
At this time, first, as shown in Fig. 5, forging is started with the cross-sectional shape perpendicular to the forging and stretching direction being, for example, approximately circular. Then, at any stage during the forging and stretching, the cross-sectional shape perpendicular to the forging and stretching direction is made rectangular or approximately rectangular, as shown in FIG. The ratio of the length of the long side to the short side of the rectangle should be at least 1.4 as described later. It is forged and drawn into a desired final cross-sectional shape such as a rectangular shape. In short, at any stage of the forging and stretching process, the cross-sectional shape perpendicular to the forging and stretching direction is made to be rectangular or approximately rectangular. By doing this, the height H of the steel material 3 when it is rectangular can be reduced, and the value of W/H can be increased without increasing the width W of the upper anvil 1 and the lower anvil number 2. Therefore, it is possible to press the internal voids of a large steel material and obtain a defect-free molded product without increasing the press capacity.

Next, the necessity of setting the length ratio of the long side to the short side of the rectangular cross section to be at least 1.4 will be explained.

In FIG. 8, the region 5 where plastic deformation occurs in the case of a square cross section is shown as a shaded area, and in FIG. The larger the ratio of the height to width of the cross-sectional shape, the larger the area that undergoes plastic deformation. If the symbols L1, L2, Ll, and α are defined in FIG. 1O as shown in FIG.

L s / 2 = L 3 / 2 + (L z
/ 2 ) / t a na where α is generally about 4
5°, so LI=L3+L2 Therefore, L 3 / L 1 = 1-1 / (L t / L
z).

This relationship is illustrated in FIG. 11.

On the other hand, in a steel ingot, which is a raw material for steel, internal voids are distributed in a substantially circular area centered on the axis, and the diameter of the circle is approximately 30% of the outer diameter of the steel ingot. Therefore, if the plastic deformation extends from the axis of the steel material to a length of 30% of the total width of the steel material, a sufficient gap crimping effect can be obtained.

That is, it is sufficient if the value of L3/L1 is 0.3 or more.

For L3/Ll to be 063 or more, see Figure 11.

It can be seen that /Lz should be 1.4 or more.

Next, a large roller shaft material for a generator turbine was formed from approximately 400 mm of steel ingots, which shows the results of actual tests confirming the effectiveness of the method of the present invention, but 11 were formed using the conventional method (L I / L z < 1.4, the conventional method was used), and 11 pieces were hot forged by the method of the present invention using the same press. The shaft material thus forged and formed was inspected by ultrasonic testing, and was found to be excellent.
The results of classification into good and poor are shown in the table below.

(J’s “F4BJ”) Note that the numbers in parentheses indicate percentages based on the total number of 100.

This result shows that the method of the present invention can reliably compress the internal voids of the steel material.

Note that if the method of the present invention is used in combination with the method of forging and elongating a steel material by giving a temperature gradient, as disclosed in Japanese Patent No. 436035, the effect of gap compression bonding can be further enhanced.

As explained above, according to the present invention, between the start of forging and the end of forging, the cross-sectional shape perpendicular to the direction of forging of an axially symmetrical steel material is determined by the length of the long side and the short side. Since we have provided a process to make the steel into a rectangle or approximately rectangular with a side length ratio of at least 1.4, the effect is that it is possible to forge and stretch a large steel material using a press with a relatively small capacity and press-bond the internal voids. is obtained.

[Brief explanation of drawings]

Figure 1 is a front view showing a steel material forged by the conventional method;
Figure 2 is a side view of Figure 1, Figure 3 is a diagram showing plastic flow in the case of a low-height steel material, Figure 4 is a diagram showing plastic flow in the case of a high-height steel material, and Figures 5- Figure 7 is a diagram showing each process of forging according to the method of the present invention, Figure 8 is a diagram showing a plastic deformation area of a steel material with a square cross section, Figure 9 is a diagram showing a plastic deformation area of a steel material with a rectangular cross section, and Figure 10. is an enlarged view of the upper right corner of Figure 9, 1st
FIG. 1 is a diagram showing the relationship between L 1 /L z and L 3 /L +. l... Upper anvil, 2... Lower anvil number, 3... Steel material. Patent Applicant Japan Steel Works Co., Ltd. Agent Patent Attorney Toshiyuki Miyauchi 5 Figure 116 wI 7M Port g Wave f/90e4

Claims (1)

[Claims] In a hot forging method for steel materials in which steel materials with an axially symmetrical shape are forged and drawn in the upper and lower anvils, a cross section perpendicular to the direction of forging of the steel material is created between the start of forging and the end of forging. The shape has a ratio of the length of the long side to the length of the short side of at least 1.
4. A hot forging method for steel material, characterized by comprising a step of forming it into a rectangle or approximately rectangle.