Effect Of Nickel Pig Iron On Microstructure And Properties Of Gray Cast Iron

Gray cast iron with its excellent casting properties,wear resistance,thermal conductivity and damping properties,has been widely applied to actual production,such as the automobile brake disc and brake drum,s production.However,the mechanical properties of gray cast iron are relatively poor.At present,in order to improving the mechanical properties of gray cast iron,it,s commonly used to add some alloying elements.However,in recent years the price of alloy elements is going up gradually.The addition of alloying elements will inevitably increase the cost.Nickel pig iron refers to a small amount of nickel(1.6%-1.8%)and chromium(2%-3%),which is similar to ordinary pig iron smelting method.And the price of the nickel pig iron is slightly higher than the ordinary pig iron on the market.In this paper,the gray cast iron was producted by the addition of the nickel pig iron,ordinary pig iron and scrap steel.And the mechanical properties,microstructure and the stress of gray cast iron samples were analyzed.In mechanical performance: with the increasing of the proportion of nickel pig iron(nickel and chromium content),the tensile strength were showed a trend of first increasing and then decreasing,and hardness were showed a rising trend.When the carbon content was 3.4%,the chromium content was 0.4%(nickel pig iron ratio of 12%),the mechanical properties was the best,the strength for 212 MPa and the hardness for 205HB;when carbon content was 3.6%,the chromium content was 0.5%(nickel pig iron ratio of 14.9%),the mechanical properties was the best,the strength for 204 MPa,the hardness for 198HB;when the carbon content was 3.8%,the chromium content was 0.7%(nickel pig iron ratio of 20.8%),the mechanical properties was the best,the strength for195 MPa and the hardness for204 HB.In metallographic organization: as the proportion of nickel pig iron(nickel,chromium content)increasing,the A type graphite becomes fine gradually and the pearlite increases gradually.But with the nickel pig iron ratio(Ni,Cr)exceeding a certain range,the D type graphite appeared and began to increase gradually,the free cementite appeared and increased gradually.When the content of carbon was 3.4%,the content of chromium was 0.4%(the proportion of nickel pig iron was about 12%),the graphite morphology and the matrix structure were the best.When the carbon content was 3.6%,the chromium content was 0.5%(the ratio of nickel pig iron was about 14.9%),the graphite morphology and the matrix structure were the best.When the content of carbon was 3.8%,and the content of chromium was about 0.6%(the ratio of nickel pig iron up to 17.9%),the graphite morphology and matrix structure were the best.In the aspect of internal stress: the internal stress of the 3 groups specimens was tested,and with the increasing of the proportion of nickel pig iron(nickel and chromium),the internal stress in the structure showed an increasing trend.In practical application: nickel pig iron was used in the production of SG20 and HCCM brake disc material.The mechanical properties,graphite morphology and matrix structure could meet the material requirements and the cost was saving.The experimental results were showed that,on the one hand,the nickel pig iron application can improve the properties of gray cast iron;on the other hand,it can reduce the cost of production,therefore,it has great economic benefit in the application of gray cast iron.