JPS6012410B2 - Spheroidizing annealing method for high carbon steel hot forgings - Google Patents

Description

[Detailed Description of the Invention] This invention utilizes the forging heat after hot forging high carbon steel to complete spheroidizing and annealing in a short time (approximately 1/4 of the conventional time) and shortens the annealing time. This relates to the spheroidized sintered anchor method, which aims to omit the shot process for scale removal.

In general, in order to facilitate cutting and plastic working, and to obtain excellent rolling fatigue resistance and sliding wear resistance after quenching and tempering,
Spheroidizing annealing is considered to be one of the extremely important operations for high carbon steel, and when performing spheroidizing annealing in large quantities, the conventional process is as shown in Figure 1.

In other words, after forging, a forged product that has been cooled to room temperature is A,
After holding for 7.5 to 8 hours at about 78,000 above the transformation point, A,
It is slowly cooled to about 720 oo just below the transformation point, held again for 7.5 to 8 hours, and then subcooled to about 500 qo at a rate of 1000 oo/h to 10,000 oo/day and then air cooled to room temperature. However, this conventional method not only requires a long heat treatment (approximately 2 field hours to 2 observation hours), but also requires a large amount of heat for reheating, and requires a shot process after annealing to remove scale. be. This invention was researched and developed for the purpose of solving the above-mentioned problems, and the structure of this invention will be explained below according to the embodiments shown in FIGS. 2 to 4.

In the drawings, the present invention is shown at approximately 800°C to 10°C after hot forging.
0,000 to 60,000 to 72 with conventional air cooling, that is, generally at a cooling rate of about 1,200 qo/day.
Cool to 0°C, and from the above temperature to 740°C to 780°C.
After heating for about 20 minutes to 4 hours, boil 100q again.
It relates to a spheroidizing annealing method in which the material is slowly cooled to 700 qo at a cooling rate of 0/day or less, and then air-cooled to room temperature.

To explain the temperature range and processing time limitations of the above hot holding using an example in which SUJ-2 material was hot forged at 1200 oo and made into a bearing race. , A. If soaking is maintained at a temperature above the transformation point, precipitation of silk-like cementite is observed, and machinability deteriorates. When annealing a large quantity, install a soaking furnace and set the temperature to 6 to cool all forged products below the transformation point.
00qo to 720qo is suitable. A. During heating, the layered cementite melts at its tips and strongly curved parts due to transformation, and the fragmented residual cementite aggregates and becomes nearly spherical, so it must be maintained at a soaking temperature of 74,000 to 78,000. is required, and at a holding temperature of 740 qo or less, layered pearlite will precipitate even if the treatment time is prolonged. At 780 qo or more, the state becomes almost completely homogeneous austenite and carbides are reduced.

If the treatment time is less than 2 minutes, the spheroidization will not proceed sufficiently, and the spheroidization will be almost completely completed in about 2 to 3 hours. When dulling large quantities, it is difficult to uniformly heat all forged products, so a soaking time of 2 minutes to 4 hours is appropriate. Similarly, air cooling is used, i.e. about 120,000 kg/day.This is because during hot forging, the carbon melted at the forging temperature becomes supersaturated in the next cooling process and must be precipitated, but at that time, the cooling rate is is slow (600oo/
If the cooling rate is less than a day, there is a risk of reticular cementite precipitation.) Because the carbon diffusion rate is high, precipitation occurs preferentially at austenite grain boundaries, resulting in silky cementite. In this case, the silk-like cementite does not disappear even after the next 740-780 pm reheating and keeping it at a scorching temperature for 20 minutes to 4 hours. On the other hand, when cooling at a high rate of 600 to 700 oo (there is no risk of silk cementite precipitation at 120,000 oo/day (equivalent to air cooling)), the degree of supercooling is large and the carbon diffusion rate is Because of their small size, carbide precipitation occurs finely and uniformly within austenite grains, even if it becomes layered due to pearlite transformation, resulting in the following (7)
40 to 78,000) x (20 minutes to 4 hours) to form a spheroid.

Regarding the cooling rate of cooling to 700 qo after the above-mentioned soaking, various tests were conducted at a cooling rate of 100 oo/H or less, and it was found that the heat pattern of the present invention could perform a spheroidization treatment comparable to conventional products.

Note that even with the same heat pattern, layered pearlite precipitates at a cooling rate of 200 q○/day. Conventionally, as shown in FIG. 1, the slow cooling process from 78,000 has been a problem. In other words, it has been said that when the degree of slow cooling is high, the size of cementite grains becomes larger, small cementite grains disappear, the hardness after sintering becomes lower, and machinability increases. 7
700o at a cooling rate of about 8000 to 10000/day
By slowly cooling the product to a temperature of 100°C and then air cooling it to room temperature, the grain size of the carbide (Fig. 3) is finer than that of the conventional product (Fig. 4), but HRB
Hardness below 9 peaks can be obtained.

The machinability is considered to be sufficient. When directly air-cooled from 78000, the hardness becomes HRBIOO and machinability deteriorates.

In addition, the treatment time in the above example was 7 hours or less, and almost no scale was observed after the dawn anchoring. The hardness of the above-mentioned phosphorescent material, the indentation value after dawn, and the amount of heat treatment strain are shown in the table below. Table note: Comparison of bran anchor hardness after heat treatment, crushing value after heat treatment, and heat treatment deformation between subordinate products and products of the present invention. 600 qo to 720 qo at cooling rate (equivalent to air cooling)
After cooling to 740°C to 780qo from the above temperature and keeping it at a scorching temperature for about 20 minutes to 4 hours, it was heated again to 100°C.
This invention relates to a spheroidizing phosphorous dulling method for high carbon steel hot forged products, which involves slow cooling to 700°C at a cooling rate of H or less, and then air cooling to room temperature. Almost the same results were obtained for the heat treatment value and heat treatment strain, and the amount of decarburization was approximately 0.
It is the 1st side. In addition, compared to the conventional method in which the residual heat of the forged product is effectively utilized and the forged product is cooled to room temperature and then annealed to spheroidize it again, the amount of heat used is significantly reduced, and the anchoring time is shortened and the shot process is reduced. It has excellent economic effects, such as the omission of .

[Brief explanation of drawings]

FIG. 1 is a schematic process diagram of a spheroidized flattened steel. FIG. 2 is a schematic process diagram of the spheroidized inscription according to the present invention. FIGS. 3 and 4 are enlarged views showing the structures of the present invention and the conventional structure after dawn anchoring, respectively. 1st
Figure 2 Figure 3 Figure 4

Claims (1)

[Claims] 1 In spheroidizing annealing of high carbon steel, when the hot forged product is air cooled to 600°C to 720°C,
High carbon steel hot forging characterized by heating again to 780°C, holding soak for 20 minutes to 4 hours, slowly cooling again to 700°C at a cooling rate of 100°C/H or less, and then air cooling to room temperature. Spheroidizing annealing method for products.