Fundamental Research On High Chromium Cast Steel/Carbon Steel Bimetallic Composite Produced By Liquid-Solid Bonding

As the composite roll can combine the advantages of different materials together,its application in the field of metallurgical rolling is becoming more and more widely.The quality of the composite roll interface affects the performance of the whole roller directly.Based on this background,high chromium cast steel/carbon steel bimetallic composite produced by liquid-solid bonding has been researched in this paper.Firstly,the influence of elements on the precipitation phase of high chromium cast steel during the equilibrium solidification process was studied by using Thermo-Calc software.Secondly,high chromium cast steel/carbon steel bimetallic composite were produced by liquid-solid bonding,and the the bonding mechanism of interface was investigated.Finally,the effects of the bonding position,liquid-solid volume ratio and heat treatment parameters on the interfacial region microstructure and properties of the composite material were analyzed.The main research findings are shown as follows:(1)Carbide precipitation of high chromium cast steel are mainly including the two kinds of M7C3 and M23C6,With the increase of C content,the initial precipitation temperature and the maximum precipitation of M7C3 are all increasing,while M23C6 shows a decreasing status,when the content of C is 1.0%,the solidification interval is the largest.With the increase of Cr content,the initial precipitation temperature and the maximum precipitation amount of M23C6 are all increasing too,but the solidification interval shows a decreasing tendency.(2)In this paper,the bonding interface from the bottom to the top(150 mm,120 mm,80 mm,40 mm)of the composite has been studied.The higher the interface position,the larger the grain size at the interface.The carbide network structure of the high chromium cast steel is weakened,the bending degree of the bonding line is deepened,the transition layer of the interface is widened and the diffusion degree of elements is enhanced simultaneously.The bonding mechanism of the composite interface is the result of the combined action of the two binding mechanisms:fusion bonding and diffusion bonding.(3)Liquid-solid volume ratios in the resarch were 4.73,9.72 and 22.91.With the increase of the ratio of liquid to solid,the interface of the composite is more likely to be intertwined,the grain size at the interface becomes larger,the diffusion degree of the elements increases too,and the microhardness at the interface changes more gently.When liquid-solid volume ratio is greater than 9.72,the thickness of the interfacial transition layer is essentially the same,and the widmanstaten is appeared on the carbon steel side.(4)After the granulation treatment,the interface of the high chromium cast steel showed a droplet-like diffusion to the carbon steel side,the elements diffusion increase,the interface transition layer is widened;The carbide network structure of M7C3 dissolved,broken network,changed into small strips and granular.(5)The tests were carried out at a quenching temperature of 900℃,950℃,1000℃,1050℃ and 1100℃ respectively.With the increase of the quenching temperature,the change of hardness at the interface becomes very gentle and the interface transition layer becomes wider gradually,later basically unchanged;When the quenching temperature is 1050 ℃,the microhardness of the interface is the most gentle.(6)The tests were carried out at a tempering temperature of 400℃,450℃,500℃ and 1100℃ respectively.When the tempering temperature is 450℃,the interface transition layer of the composite is the widest,and the change of the microhardness at the interface is the most gentle.More suitable heat treatment process for bimetallic composite is granulation treatment +1050℃ quenching 1.5 h + 450℃ tempering 2 h.