To achieve the hardness of cast chrome grinding balls, which contains more than 10.0% chrome and 1.80%-3.20% carbon, the hardness (HRC) of the cast grinding ball must be more than 58 degrees and the impact value is AK 3.0 j / cm2. High Chrome Ball must be treated by high-temperature quenching and tempering.
Casting chrome grinding ball is usually used for large-scale mining of various cement plants, chemical plants, power plants, quartz sand plants, Silica sand plants, and so on.
Cast Grinding Ball can be divided into three categories, including high chrome ball, medium chrome ball, and low chrome ball.

1. High Chrome Grinding Balls Quality Indicators:
The chromium content of a high chrome ball is 10.0% or more. The carbon content is between 1.80% and 3.20 %. According to the National Standard, the hardness of the high chrome ball must not be less than 58HRC; the impact value should be greater than or equal to 3.0 j / cm2. High chrome balls of this hardness must be quenched and tempered at high temperatures. At present, there are two kinds of quenching methods for high chrome balls in China, including oil quenching and air quenching. If the hardness of the High Chromium Ball is below 54HRC, it means that it has not been hardened.

2. Medium Chrome Grinding Balls Quality Indicators:
Medium chrome grinding balls are defined to contain chrome between 3.0% and 7.0%. And carbon contents between 1.80% and 3.20%. It should have an impact value of no less than 2.0 J/cm2. National Standard requirements in chrome ball hardness should be greater than or equal to 47 HRC. In order to ensure quality, the medium chromium ball should be tempered at a high temperature to eliminate casting stress.
If the surface of the grinding ball is black and red, it shows that the grinding ball has been tempered at a high temperature. If the grinding ball still has a metallic surface, we can judge that the grinding ball has not been tempered at a high temperature.

3. Low chrome grinding balls quality indicators:
In general, low chrome balls contain 0.5% to 2.5% chrome and 1.80% to 3.20% carbon. Therefore, according to the national standard, the low chromium ball hardness should not be less than 45HRC, impact value should not be less than 1.5 j / cm2. Low chromium balls also require high-temperature tempering to ensure quality. This treatment can eliminate casting stress. If the surface of the grinding ball is dark red, it shows that it has been tempered at a high temperature. If the surface is still metallic, indicating that the ball has not been tempered by high temperature.

4. The production process of casting grinding balls:
Inspection of raw materials — Proportioning materials — Medium frequency furnace melting — Mould casting — Quenching — Tempering — Testing — Packaging.

5. Standard Test Method for quality of casting grinding balls:
The chemical composition of the cast high chrome ball is following the bellow tables. Non-compliance with the following table can be produced according to customer requirements

Grade No.	Chemical Composition, %
	C	Si	Mn	Cr	Mo	Cu	V	Ti	P	S
ZQCrG1	2.0-3.5	≤1.0	0.5-2.5	10-16	≤1.0	≤1.0	≤0.3	≤0.15	≤0.1	≤0.1
ZQCrG2				16-22
ZQCrG3				22-28
2..The nominal diameter, allowable deviation, maximum diameter, and minimum diameter of cast high chromium ball shall be in accordance with the following table
Nominal diameter	20	25	30	40	50	60	70	80	90	100
Allowable deviation of diameter	+2.0  -1.0			+2.0  -1.0				+3.5    -1.0
Difference between maximum diameter and minimum diameter	≤1.8		≤2.4	≤3.0	≤3.6		≤4.2		≤4.6