Brief analysis of heat treatment process of chromium alloy casting ball (1)

Abstract: The heat treatment process of chrome alloy full casting ball was analyzed, the heat treatment process curve was determined, and the specific measures to improve the wear resistance of high chromium cast ball were put forward.

Keywords: high chromium grinding media balls, heat treatment, abrasive resistance

Cheng Huajing , Zhangwei

(Ma Anshan Dongyou steel balls company, 2020 Year)

In our country’s grinding industry, grinding balls’ consumption is very large; improving the wear resistance of grinding bodies (ball) has wide economic benefits. The wear resistance of the casting grinding ball is closely related to its heat-treatment process. Through the experimental study on the heat treatment process of the casting ball of the chromium alloy, the changes of the casting ball’s metallographic structure and properties are analyzed, the heat treatment process for improving the wear resistance of chromium alloy casting grinding ball was put forward.

Cr is the main alloy element, suitable amount of CR can not only produce Cr carbide with high hardness, but also improve hardenability. The chemical compositions of SR grinding balls used in the experiment were: C 2.6% ー30% , Cr 15% ー20% , Si < 1.0% , Mn < 1.0% , P < 0.10% , S < 0.10% .

1.Heat treatment and determination of process curve

(1) To bring the experiment closer to reality. The investigation was carried out on an industrial quenching furnace. The furnace is a continuous pusher type with an effective size of L2.76 × 1.4 × 1.1 m, the fuel is diesel oil, and the maximum operating temperature is 1100 °C. The furnace’s temperature can be precisely controlled, and the ball casting furnace is heated slowly and evenly, which effectively reduces the generation of thermal stress. To avoid large stress caused by rapid heating up, the quenching heating rate is limited to 100 °C/h.

(2) To get the best temperature of quenching fire, in practice, the different size of the cast ball, in the different temperature of quenching fire under the cold speed and hardness of quenching fire into the measurement, and draw the curve line see Figure 1, Figure 2

The 1, 2, 3, and 4 cast balls in the figure are 17mm, 30mm, 60mm, and 90mm. The peak value of each curve in the figure corresponds to each type of cast ball’s optimal quenching temperature, which can be solved as the quenching temperature and the amount of carbonated substance extracted are the most suitable. As can be seen from FIG. 2 and 3, the smaller the ball, the faster the cooling rate. The best the quench fire temperature is lower, the bigger the ball, the slower the cold quench fire temperature, the best the quench fire temperature is higher, thus can determine the best quench fire temperature is cold quench fire temperature function. The quenching fire engineering curve is shown in Fig. 3.

quenching temperature of the casting balls
quenching hardness of the casting grinding balls

SR casting ball after quenching and tempering is required to improve the toughness of the casting ball and eliminate the tempering force. For the quasi know tempering temperature on the hardness of ring, the experiment will ~ 30 mm ballpoints don’t fall under 940 ℃, 980 ℃, 1040 ℃ temperature for 5 h, air cooling in the small diameter of the cold plate, then each of the quenching temperature degrees each set of test bar points don’t in line with the tempering temperature, back to the furnace air cooling after the fire, and measure its hard degree, tempering treatment is in consecutive industrial furnace fuel in the furnace of fire back into the line, the tempering of the furnace shall be strictly controlled. The correlation between the hardness and tempering temperature of the cast ball after tempering is shown in Figure 4.

quenching process of the high chrome grinding balls
tempering temperature of the casting grinding media balls

The hardness of the SR casting ball changed little at 200 ~ 400 °C after tempering at different temperatures and decreased sharply after tempering at more than 420 °C. Accordingly, the tempering process and curve are determined, as shown in Fig. 5.

tempering process of the grinding balls