JPS60149715A - Heat treatment of low-carbon martensitic stainless steel - Google Patents

Abstract

PURPOSE:To improve the strength and toughness of low-carbon martensitic stainless steel by heating the steel to a prescribed temp. and cooling it slowly. CONSTITUTION:Low-carbon martensitic stainless steel is heated, held at 900- 1,000 deg.C, and cooled slowly. The slowly cooled steel may be heated again, held at <=350 deg.C, and cooled slowly. Thus, high strength and toughness are provided to the steel.

Description

[Detailed description of the invention] It relates to a heat treatment method.

Conventionally, so-called 13cr-Ni cast steel has been widely used as steel for runners, pumps, propellers, etc. where cavitation or earth and sand abrasion occurs. However, in the case of large wings, this 13Cr-Nth steel
In order to prevent carbide precipitation in the austenite region and ensure toughness, it was necessary to soften the steel by rapid cooling from the quenching temperature and tempering. Therefore, the high strength was 14%, and the cavitation resistance and abrasion resistance against earth and sand could not be sufficiently satisfied.

The steel that is the object of the present invention is basically what is generally called so-called 13cr-4Vi cast steel containing Ni. As mentioned above, this 13Cr-Ni cast steel is acceleratedly cooled from a high temperature (austenite region) in order to prevent carbide precipitation in the austenite region, and then in the case of large-sized cast steel, it is cooled to 600% in order to remove residual stress and ensure toughness.
Generally, it was tempered at a temperature around ℃. However, when the above treatment is carried out, the strength of this cast steel decreases to 7.
0 to 80 K9/■+2 The properties were not fully satisfactory.

The purpose of the present invention is to solve the above-mentioned problems, and to gradually cool low carbon martenzite stainless steel from a high temperature (austenite region) and either do not perform tempering or perform low-temperature tempering, thereby achieving low residual stress and high Strength, high corrosion resistance,
The object of the present invention is to provide a heat treatment method capable of obtaining cast steel with high wear resistance.

The purpose of this method is to heat and hold low carbon martensitic stainless steel in a temperature range of 900°C to 1,000°C and then slowly cool it, and to
This is achieved by heating and maintaining the temperature in a temperature range of 50° C. or lower and slowly cooling it.

Next, the present invention will be explained in more detail. The low carbon martensitic stainless steel that is the subject of the present invention basically consists of 0.04% or less CO, 13 to 6% N, and Cr on a weight basis.
1.5~], 9.5%, Mo 1% or less.

Steel with this composition is hereinafter referred to as low carbon martensitic stainless steel.

The present invention is a heat treatment according to the heat pattern shown in FIG. 1, which is carried out on the above-mentioned low carbon martenzite stainless steel. In other words, low carbon martensitic stainless steel is
It is heated to an austenitizing temperature of 00°C to 1,000°C, and by this heating, the carbide precipitated by the pretreatment is dissolved into a solid solution to form a single phase of austenite. In this case, if the austenitizing temperature is lower than 900°C, the carbides will not be sufficiently dissolved in the austenite phase, and if it exceeds 1000°C, the austenite crystal grains will become coarser, so the austenitizing temperature should be lowered to 900°C. -1000°C. Then, by uniform post-cooling, a product free of residual stress can be obtained. Figure 2 shows 1t'''T-T d of 13Cr-JJi steel, which is the subject of the heat treatment method of the present invention.
l+ wire, and as mentioned above, the steel that is the target of the heat treatment method of the present invention basically has carbon of 0.044 or less, so if it is cooled at a cooling rate that avoids the carbide precipitation nose N, carbide will be formed. was not precipitated, and it can be seen from FIG. 2 that an extremely slow cooling rate is sufficient. Since this steel has high self-hardening properties and can be austempered, it has high strength and high toughness and ductility even when slowly cooled. Furthermore, by performing low temperature tempering at 350° C. or lower after slow cooling, secondary hardening occurs and even higher strength can be obtained without impairing toughness.

Next, embodiments of the present invention will be described.

Sample materials having the chemical components shown in Table 1 were subjected to conventional heat treatment and heat treatment according to the present invention. Table 2 shows the mechanical properties of the above-mentioned sample AA which were tempered by the conventional heat treatment and the heat treatment of the present invention. In this Table 2, while the tensile strength is B 1,5 K7/ay2 in the conventional heat treatment,
According to the heat treatment of the present invention, the tensile strength is 10 G, G~10
It is considerably large at 8.1 Kg/vun2, while the ductility and impact properties are not significantly impaired.

Figure 3 shows a sample of steel with the mechanical properties shown in Table 2.
This is a diagram comparing the heat resistance of conventional heat treatment at 8 hours, for example. mf/, whereas those subjected to the heat treatment of the present invention have a diameter of about 43.5 m
g and about 2.5 mg, it can be seen that the one subjected to the heat treatment of the present invention is extremely superior in abrasion resistance.

As explained above, if low-carbon martenzite stainless steel that has been heat-treated to prevent explosions is used in launches, pumps, propellers, etc. where cavitation and dirt wear occurs, it will exhibit extremely excellent wear resistance (Di). .

[Brief explanation of the drawing]

Figure 1 is a graph showing the heat treatment pattern of the present invention, Figure 2 is a graph of the T-T-1 curve of stainless steel, which is the subject of the present invention, and Figure 3 is a comparison of the wear resistance of the present invention and the conventional one. It is a graph. Figure 1 <350'C

Claims (1)

[Claims] J low carbon martensitic stainless steel heated at 900°C to 1.
A method for heat treating low carbon martensitic stainless steel, the method comprising heating and maintaining it in a temperature range of 1,000°C and then slowly cooling it to impart high strength and toughness. 2 Low carbon martenzite stainless steel at 900℃~+,
After heating and maintaining in the temperature range of 000℃, it was slowly cooled, and then 3
A method for heat treating low carbon martensitic stainless steel, which comprises heating and maintaining the temperature in a temperature range of 50° C. or lower, slowly cooling it, and applying high strength and high equipment to 4"J'J.