Study On The Effect Of High Chrome Waste Iron On Microstructure And Hardness Of High Chrome Cast Iron Roller

High chromium cast iron roll has been widely used in hot strip mill of modern iron and steel enterprises since 1980 s because of its low cost and good working performance.In order to reduce the production cost of roll,high chromium waste iron is used as the main raw material to produce high chromium cast iron roll in a roll factory.However,in the actual roll production process,it is found that there is a risk of heat treatment cracking after adding waste iron.Therefore,It is very significant to explore the causes of roll cracking after adding waste iron in production process in order to guide the utilization of waste iron and reduce the production cost of roll.In this paper,metallographic analysis and SEM,XRD,hardness tests were used to compare and study two kinds of high chromium cast iron rolls,with waste iron added and without waste iron added,produced under the same specification and casting process.The differences of microstructure and hardness between the as-cast microstructure and heat treatment process of the two materials were analyzed,which provides reference data for the rational utilization of waste iron.Compared with the as-cast matrix microstructure of the two kinds of cast iron rolls,the microstructure of the two kinds of cast iron is composed with eutectic lainite,martensite,retained austenite and a small amount of pearlite,but the morphology of secondary carbides in the matrix is different.The secondary carbides in high chromium cast iron without waste iron are rod-shaped and cubic particles,while the secondary carbides in high chromium cast iron with waste iron are only cubic particles.The results of different quenching temperature and cooling rate on phase transformation shown that both cast iron had good hardenability,and only a small amount of pearlite appeared in the matrix when cooling at 0.2 ℃/min.When the cooling rate was greater than or equal to 1 ℃/min,only martensite transformation occurred,but the addition of waste iron had a certain effect on the transformation of martensite.The Ms point of high chromium cast iron with waste iron increased slightly by about 30 ℃.The hardness of both materials increased after quenching.In the subsequent tempering process,the secondary hardening occurred due to the complete elimination of retained austenite in the matrix,and the secondary tempering could further eliminate the retained austenite.However,the tempering stability of retained austenite in high chromium cast iron with waste iron was slightly higher than that without waste iron.When the tempering temperature continued to rise,the matrix transformed to tempered sorbite.The secondary hardening phenomenon also occurred in the two materials during direct tempering,but the secondary hardening temperature was higher than that after quenching because of the as-cast segregation,and the tempering stability of retained austenite in high chromium cast iron with waste iron was slightly lower than that without waste iron.When the tempering temperature continued to rise,the matrix transformed to tempered sorbite.With the increase of tempering temperature,the rod carbide particles in the matrix of high chromium cast iron without waste iron gradually disappeared,the cubic particles partially dissolved and the rest grown up,while the secondary carbide particles in the matrix of cast iron with waste iron partly dissolved,and the rest of them grown up and had a tendency to connect.