JPH0368105B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a steel for wheels and a heat treatment method for the same, with the aim of improving the hardenability of the rim portion of an integral wheel and making the hardening hardness distribution uniform. As is well known, a one-piece wheel is a wheel in which the tire and wheel center are made integrally by rolling or casting.
Naturally, the material is required to have wear resistance and heat cracking resistance, so it is necessary to heat treat it to increase its quenched hardness. Its quenched hardness is
It is said that H _B of about 300 to 340 is desirable. On the other hand, wheels are used by reshaping the tread surface of the rim, which wears out during use, to about 30mm on each side.
Therefore, the wheel has a depth of 30mm.
Quenching hardness of H _B 300-340 is required. The conventional method for heat treatment of wheels is to heat the wheels at a temperature of 850°C for 2 hours, then continuously cool only the rim portion with water, and then air-cool and temper the wheels at a temperature of 500 to 600°C. However, conventional wheels have C: 0.57~
0.75%, Si: 0.15-0.35%, Mn: 0.60-0.90%,
P: 0.035% or less, S: 0.035% or less, remainder substantial
Since steel made of Fe is used as wheel steel, it has poor hardenability, and since it is continuously water cooled during hardening, if the surface hardness of the tread is satisfied, the internal hardness is low; if the internal hardness is satisfied, the internal hardness is low. Surface hardness is too high, H _B 300 over the entire tread depth 30mm
It was not possible to achieve a uniform hardness of ~340. Figure 1 shows an example of the conventional quenching hardness distribution of the rim. Figure a shows the case where the C content is 0.63%.
Figure b shows the quenching hardness distribution when the C content was increased to 0.72%. Note that l ₁ , l ₂ , and l ₃ are all 30 mm. That is, in the case of Figure a, the surface hardness of the rim part is satisfactory but the internal hardness is low, and in the case of Figure b, the internal hardness is satisfactory but the surface hardness is too high. This invention eliminates the above-mentioned conventional non-uniformity of quenching hardness and improves H _B over the entire depth of 30 mm.
This paper proposes a steel for wheels that has a quenching hardness of 300 to 340 and a heat treatment method for the same. This invention will be explained in detail below. This invention can be used as wheel steel without changing the conventional composition.
Improved hardenability by using steel containing Cr and Mo, and improved quench hardness distribution by dividing cooling after heating into three stages: water cooling, air cooling, and water cooling. The main feature is that That is, the gist of this invention is that Ci: 0.15 to 0.25
%, Mo: 0.15-0.30%, S: 0.035% or less, P:
0.035% or less, Mn: 0.60-0.90%, Si: 0.15-0.35
%, C: 0.57 to 0.75%, the balance being substantially Fe, and the wheel made of the steel is heated at a temperature of 830°C or higher and 860°C or lower.
Hold and heat for ~3 hours, then heat for 30 seconds to 1 minute.
500 to 1000 water is injected onto the tread and flange of the wheel to cool it, and after air cooling for 30 seconds to 1 minute and 30 seconds,
Spray 1,000 to 1,500 ml of water onto the tread and flange for 5 to 7 minutes again to cool it, and then
The heat treatment method is characterized by tempering by holding at a temperature of 600°C for 4 to 6 hours. In this invention, the components of the wheel steel are limited for the following reasons. As mentioned above, Cr is necessary to improve the hardenability of the wheel tread and flange, and if it is less than 0.15%, this effect will not be obtained, and if it is less than 0.25%.
If it exceeds this, it will have an adverse effect on thermal cracking of the wheels, so it was limited to a range of 0.15 to 0.25%. Mo is necessary to prevent temper brittleness, and in order to obtain this effect, 0.15% or more is required, but since Mo addition is accompanied by an increase in cost, the upper limit was limited to 0.30%. If the content of S and P exceeds 0.035%, it will adversely affect the impact properties, so it is desirable that the content is 0.035% or less. If Mn is less than 0.60%, strength and hardenability will decrease.
If it exceeds 0.90%, it will adversely affect impact properties, so 0.60 to 0.90% is preferable. If Si is less than 0.15%, deoxidation will be insufficient and impact properties will be adversely affected, and if it exceeds 0.35%, sand flaws will occur. C is necessary to obtain wear resistance and is 0.57%
If it is less than 0.75%, the effect will not be obtained, and if it exceeds 0.75%, thermal cracks will occur, so it is necessary to keep it in the range of 0.57 to 0.75%. In addition, in this invention, the heat treatment conditions for the wheel made of the above-mentioned wheel steel, that is, the cooling conditions for quenching the tread and flange portion, are set to a temperature of 830°C or higher for 1 to 30 minutes.
After heating and holding for 3 hours, 500 ~ 30 seconds to 1 minute
Spray 1,000 ml of water onto the tread and flange of the wheel to cool it, cool it in the air for 30 seconds to 1 minute and 30 seconds, and then spray it again with 5 ml of water.
This is done by spraying 1,000 to 1,500 ml of water onto the tread surface and flange for ~7 minutes to cool it down.The reason why quenching is time-quenched is to improve the internal hardness without increasing the surface hardness too much. This is to make it happen. FIGS. 2 and 3 are temperature curves and hardenability curves during quenching, which were obtained through experiments by the inventors. In other words, as shown in Figure 2, during the first water cooling, the surface temperature decreases from the quenching temperature of 850°C to 720°C, which is the quenching transformation point, but the temperature at a distance of 30 mm from the water cooling end is still close to the quenching temperature. be. Then, air cool for 30 seconds to 1 minute and 30 seconds.
The surface temperature decreased to 720℃, but due to internal heat, it decreased to 750℃.
Increase temperature to ℃. Therefore, in the second water cooling, the difference between the quenching temperature and the transformation point is smaller the closer to the tread surface, and the distance from the water cooling end is 30 mm.
However, the temperature is only slightly lower than when quenching was done at the initial quenching temperature of 850℃. As a result, although the temperature of the tread surface is relatively low, a predetermined hardness can be obtained by rapid cooling in the second water cooling, and the temperature increases as you go further inside from the tread surface, but in the second water cooling, The cooling rate decreases as it goes inward from the tread surface, and the specified hardness is also obtained. Therefore, the hardness in the area 30 mm deep from the water cooling end is shown in Figure 3. As shown, it falls within the range of 340 to 300H _B , and the variation is small. but,
In the conventional quenching method, which uses continuous water cooling, the temperature at the tread surface is high, and rapid cooling overlaps with that temperature, and although the temperature inside the tread surface is high, rapid cooling does not proceed, resulting in There is a difference between the hardness of the tread surface and its internal hardness, and even if the internal hardness is satisfactory, the surface hardness is too high. In this way, when quenching is done as a time quench, the entire area from the tread depth to 30mm is
Appropriate hardness of H _B 300 to 400 can be obtained. In addition, the first time and water cooling are 500 ~ 30 seconds to 1 minute.
The reason for setting the temperature to 1000 is to obtain an appropriate temperature distribution from the tread surface to the inside thereof due to the above cooling from a temperature of 830° C. or higher, as shown in FIG.
In addition, the air cooling holding time was set to 30 seconds to 1 minute and 30 seconds because the temperature distribution from the tread surface to the inside of the tread during the first water cooling is suitable for the second water cooling, as shown in Figure 2. The holding time is determined to be sufficient for the temperature distribution to shift to a certain temperature distribution. Furthermore, the second water cooling is performed for 5 to 7 minutes at 1000~
The value 1500 was determined by determining the time and amount of cooling water that would provide the best cooling performance from the temperature distribution from the tread surface to the inside of the tread suitable for quenching as shown in Figure 2 to obtain the quenching effect. . Furthermore, during quenching, holding at a temperature of 830°C or higher for 1 to 3 hours is necessary to achieve at least 1 to 3 hours of quenching with the components of the wheel steel of the present invention.
It is necessary to heat it to a temperature of 830℃ or higher, and
Because it is necessary to uniformly heat the wheels to 830°C or higher, the heating time should be at least 1 hour.Heating at 860°C or higher or for more than 3 hours will result in wheel scale loss and thermal energy loss, so the heating temperature should be set at 830°C.
℃ or more and 860°C or less, and the heating time is set as a suitable holding time of 1 to 3 hours. Next, embodiments of the invention will be described. [Example] A wheel made of steel having the chemical composition shown in Table 1 (diameter: 1092 mm, width: 136 mm, flange height:
28.5mm) was heated at a temperature of 850℃ for 2 hours, cooled by spraying 800℃ of water from the wheel tread for 40 seconds after heating, kept air-cooled for 1 minute, and heated to 1300℃ for 6 minutes.
Water was injected from the same tread surface to cool it, and then the temperature was maintained at 550°C for 5 hours to temper it. Fig. 4 shows the quenching hardness distribution of the rim portion at that time. From Figure 4, in this invention method, the depth is 30 mm from the water cooling end.
It was possible to harden an area of mm to an appropriate hardness range of 340 to 300H _B. 【table】

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing an example of the quenching hardness distribution of the rim portion of a conventional wheel; Fig. 2 is a chart showing the temperature curve during quenching in the present invention; Fig. 3 is a chart showing the hardenability curve of the same; FIG. 4 is a chart showing the quenching hardness distribution of the rim portion in an example of the present invention.

Claims (1)

[Claims] 1 Cr: 0.15-0.25%, Mo: 0.15-0.30%, S:
0.035% or less, P: 0.035% or less, Mn: 0.60 to 0.90
%, Si: 0.15 to 0.35%, C: 0.57 to 0.75%, and the balance is substantially Fe. 2 Cr: 0.15-0.25%, Mo: 0.15-0.30%, S:
0.035% or less, P: 0.035% or less, Mn: 0.60 to 0.90
%, Si: 0.15 to 0.35%, C: 0.57 to 0.75%, and the balance is substantially Fe at 830°C.
Heat it by keeping it at a temperature of 860℃ or less for 1 to 3 hours, and after heating, spray 500 to 1000 ml of water on the tread and flange of the wheel for 30 seconds to 1 minute to cool it.
After air cooling for 30 seconds to 1 minute and 30 seconds, reheat to 1000 for 5 to 7 minutes.
1. A method for heat treatment of steel for wheels, characterized by injecting water at a temperature of ~1,500 °C onto the tread surface and flange to cool it, and then tempering by holding at a temperature of 500 to 600°C for 4 to 6 hours.