Ultra-high Chromium grinding Ball Quality Index: Chromium contents ≥12.0%-28.0 %, carbon contents between 1.80%-3.30% are all called high chromium grinding ball, the national standard requires high chromium grinding ball hardness (HRC) must ≥58, impact value AK ≥3.0 j / 2. If the hardness of the ultra-high Chromium grinding Ball must