1. High chromium ball quality index
The chromium content of high chromium balls is greater than or equal to 10.0%. The carbon content is between 1.80% and 3.20%. According to the national standard, the hardness of the high chromium ball must not be less than 58HRC, and the impact value should be greater than or equal to 3.0J/cm2. If this hardness is high, the chromium balls must be quenched and tempered at high temperatures. At present, there are two methods of domestic high chromium ball quenching, including oil quenching and wind quenching. If the high chromium ball test hardness is less than 54HRC, it means that it has not been quenched.
2. Quality index of chromium ball
The chromium ball specifies a chromium content ranging from 3.0% to 7.0% and a carbon content between 1.80% and 3.20%. Its impact value should not be less than 2.0J/cm2. The national standard requires that the hardness of the chromium ball should be greater than or equal to 47HRC. To ensure quality, chromium balls should be tempered at high temperature to eliminate casting stress.
If the surface of the steel ball is black and red, it proves that the steel ball has been tempered at high temperature. If the surface of the steel ball still has a metallic color, we can judge that the steel ball has not been tempered at high temperature.
3. Low chromium ball quality index
In general, low chromium balls have a chromium content of 0.5% to 2.5% and a carbon content of 1.80% to 3.20%. Therefore, according to the national standard, the hardness of the low chromium ball should not be less than 45HRC, and the impact value should not be less than 1.5J/cm2. Low chromium balls also require high temperature tempering to ensure quality. This treatment eliminates casting stress. If the surface of the ball is dark red, it indicates high-temperature tempering. If the surface is still metallic, it indicates that the steel ball has not been tempered at high temperature.