JPS597325B2 - Method of manufacturing cast steel shot - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is applicable to a blasting method in which a shot is projected onto the surface of a metal workpiece and the impact is used to remove scale, sand, etc. adhering to the surface, or a blasting method in which a shot is projected onto the surface of a metal workpiece and the impact is used to remove scale, sand, etc. attached to the surface. This invention relates to the production of shot used in peening, which prevents metal fatigue by forging.

A shot is a solid spherical iron particle with a diameter of 0.2 to 2.5 mm, which is circularly projected onto the surface of a workpiece at a projection speed of 50 to 90 ml sec by a high-speed projection rotor or high-pressure air. Therefore, it is necessary to have sufficient hardness to maintain the spherical shape of the workpiece and tenacity that will not crush it, and generally the hardness is HRC4.
It is set as 0 to 48.

Currently, in order to make cast steel products of this hardness, the carbon content is generally 0.
．． After hardening and tempering high carbon steel of about 9%, it is necessary to precipitate carbides and impart toughness.
%, Si0.69%, Mn0.70%, P0.022%
Molten iron with a composition of 80.029% is spheroidized at approximately 1600°C with high-pressure water using the surface tension of iron, and by this underwater quenching, a HRC 60-65 martensite structure is created. This is heated and dried to remove surface moisture, then held at a temperature of around 800°C for about 30 minutes, then quenched in water again, and after drying, held at a temperature of 500 to 600°C for about 30 minutes. Tempering is performed to create a mixed structure of martensite + bainite, and the specified hardness is HRC4.
0 to 48 have been obtained.

As is well known, the quenched hardness of steel increases primarily in proportion to the amount of carbon contained, as shown in the table of the attached drawings.

Hardened steel is unstable because it brings the equilibrium state at high temperature to low temperature, and tempering is necessary to remove this internal stress and give it appropriate toughness. 200 to 60 depending on the type of item.
Reheating to 0°C is performed.

However, tempering increases tenacity but decreases hardness, so the hardness must be increased by that amount in advance, and as mentioned above, high carbon steel is used in the manufacture of shot. Therefore, it was necessary to make it to a certain level of hardness.

As mentioned above, in the past, high carbon steel was used to obtain shot with a certain hardness and tenacity through a quenching and tempering process, which required a large number of processes, poor production efficiency, and required a heat treatment furnace, which is the tempering equipment. However, there were drawbacks such as high production costs.

As a result of intensive research to solve the above-mentioned drawbacks, the present inventor found that the tempering process can be omitted by quenching using steel with a lower carbon content than before, and based on this knowledge, As a result of further research, the particle size was 0.2~
The present invention was completed based on the discovery that the target hardness (HRC 40 to 48) can be obtained with a shot having a diameter of 2.5 mm even if the carbon content is small.

That is, in the present invention, molten iron with a carbon content of 0.13 to 0.21% is quenched in water to form metal particles with a particle size of 0.2 to 2.5 mm, and then heated to 150 to 200°C. The gist of the present invention is a method for producing cast steel shot, which is characterized in that it is dried to obtain cast steel shot having a hardness of HRC 40 to 48.

In the present invention, molten iron having a carbon content of 0.13 to 0.21% is quenched in water.

If the carbon content is less than 0.13%, the desired hardness cannot be obtained, and if it exceeds 0.21%, the hardness becomes too large and the material becomes brittle, requiring tempering, which is not preferable.

The grain size is 0.2 to 2. 5mmφ
of metal particles are obtained.

By using metal particles with a particle size of 0.2 to 2.5 mm, the desired hardness (HRC40) can be achieved even with a low carbon content.
~48) is obtained.

That is, when particles having a particle size of 0.2 to 2.5 mm are quenched in water, the metal structure changes instantaneously and uniformly, and uniform hardness is obtained even within the particles.

On the other hand, those with a large particle size (particle size of 2.5 in.
Even if the hardness near the surface reaches the target hardness (HRC 40 to 48) during underwater quenching, the internal hardness remains smaller and does not reach the target hardness.

Therefore, even if molten iron with a carbon content of 0.13 to 0.21% is quenched in water, the particle size will be 2.5%. If the diameter exceeds 5 mm, uniform hardness cannot be obtained to the inside of the particle, and the hardness required as a shot cannot be achieved, so that it cannot be put to practical use.

By setting the particle size to 0.2 to 2.5 mm as in the present invention, it has become possible for the first time to achieve a uniform hardness of HRC 40 to 48 from the vicinity of the particle surface to the inside.

According to the present invention, since the carbon content of molten iron is initially low (0.13 to 0.21%) (in the conventional method, the carbon content is 0.89%), after being quenched in water, tempering is performed. There is no need to carry out tempering, and the necessary tenacity can be obtained even if tempering is carried out.

The metal particles obtained as described above are heated and dried at 150 to 200°C for 2 minutes to complete the production of the cast steel shot of the present invention.

According to the present invention, since the tempering process can be omitted, a heat treatment furnace, which is a conventional tempering equipment, is not required, and processing costs, fuel costs, etc. can be significantly reduced, and as a result, production costs can be significantly reduced.
This has the effect of reducing the

Next, examples of the present invention will be shown.

Example: Molten iron with the carbon content shown in Table 1 is quenched in water to reduce the particle size to 0.
, 2 to 2.5 to obtain metal particles, then 150 to 20
After drying by heating to 0° C., hardness (HRC) was measured.

The results are shown in the same table. The obtained shot was repeatedly projected using a crushing tester to measure the number of times a certain amount of remaining amount was reached (lifetime value) and compared with conventional shots. It was found that the material was sufficiently excellent in tenacity.

[Brief explanation of drawings]

The figure is a graph showing the relationship between the quenching hardness of copper and the carbon content.

Claims (1)

[Claims] 1 Molten iron with a carbon content of 0.13 to 0.21% is quenched in water to obtain a particle size of 0.2 to 2. A method for producing cast steel shot, characterized in that metal particles having a diameter of 5 amφ are prepared and then heated and dried at 150 to 200°C to obtain cast steel shot having a hardness of HRC 40 to 48.