What is grey cast iron how to improve hardness?

How to improve the hardness of gray iron castings?This is a difficult problem encountered by many gray cast iron enterprises.The following inoculant manufacturer Anyang Jinsheng Metallurgical mainly from the charge ratio, chemical composition, liquid iron overheating and composite inoculation and other aspects to share for you in detail how to improve the hardness of gray iron castings;

1. Burden ratio

Using the method of pig iron + scrap steel + return charge + recarburizer, the nitrogen in recarburizer is used to change the shape and length of graphite to improve the hardness of gray iron castings.

2, molten iron overheating

For gray iron castings, increasing the temperature of molten iron in a certain range can make the graphite refined, the matrix compact, and the tensile strength and Brinell hardness of cast iron increased.The overheating temperature of molten iron should be controlled within 1500-1530℃ and the overheating time should be controlled within 10min.

3, inoculant and inoculation method

The inoculation treatment of gray cast iron is usually in the molten iron after slowly adding inoculation agent (75 ferrosilicon commonly used in China), inoculation treatment of gray cast iron, hardness will tend to be uniform, improve the performance of mechanical processing, but also increase the strength of gray cast iron.

The standard hardness of gray iron castings is between HB170-240.

4. Control chemical composition

(1) Many smelting companies believe that sulfur is harmful, and the lower the content of sulfur in liquid iron, the better. In fact, this is not the case, and "silicon carbonization" and "manganese sulfur ratio" should be considered in gray iron castings.The Mn = 1.71 S + (0.2 ~ 0.5).

Chemical composition table of HT250: CpSimntis 3~3.3≤0.121.65~2.050.7~1.1≤0.05≤0.12

(2) low alloying, add one or two alloy elements, when adding, should consider the content of carbon element, do not blindly pursue hardness;