Study Of Microstructure And Properties Of Stainless Steel/Carbon Steel Clad Rebar

The stainless steel/carbon steel clad rebar has been gradually studied by more and more materials scholars and engineering filed because of its excellent corrosion resistance and good appearance,as well as its higher mechanical properties and lower cost.It is considered as the most promising new type of composite material for building.However,the study of stainless steel/carbon steel clad rebar is still in the beginning stage at present,and the research on the mechanism of rolling forming still stays in the laboratory hot roll-cladding of high-cost and low-efficiency.The uneven distribution of coating thickness and the unstable of bonding properties are still the key factors,which restricting the wide application of stainless steel/carbon steel clad rebar:And the microstructure and the composite process of the interface should be further studied.Based on this,the thermal simulation experiments were utilized to simulate the rolling deformation process of stainless steel/carbon steel clad rebar.However,due to the small size of the clad rebar studied by the thermal simulation experitments and the complex deformation mechanism of the interface,there is no reference to the analysis of the microstructure and properties.While the application of stainless steel clad plate is relatively early,the research on the microstructure of interface,interface precipitates,element diffusion and so on are more maturer,which can provide reference for the research of stainless steel clad rebar.Therefore,the analysis of microstructure and properties of the clad plate made by the same material as the clad rebar was the guidance,the influence of process parameters such as deformation degree,deformation temperature and others on the microstructure and properties of stainless steel/carbon steel clad rebar was studied,the reasonable parameters of stainless steel/carbon steel clad rebar were preliminarily determined,and the main conclusions were as follows:(1)The stainless steel/carbon steel clad plate was prepared by vacuum hot roll-cladding in the laboratory.The effects of air cooling and rapid cooling+slow cooling on microstructure and properties of the interface of clad plate were.studied.A good metallurgical bonding with no unwelded zone was achieved by these two processes at the interface.In the process of rapid cooling+slow cooling,the bainite was formed in the carbon steel side and the grains were refined due to the rapid cooling rate.Meanwhile,shortened the cooling time in the high temperature stage,the diffusion of Cr and Ni slowed down,and the amount of precipitated chromium carbides near the interface was reduced,which contributes to the improvement of the corrosion resistance of stainless steel.The shear strength of the clad plate prepared by these two processes was far higher than the national standard and the bonding properties of the interface was excellent.Because of the finer grains and a certain amount of bainite were formed under the rapid cooling+slow cooling,which made the better mechanical properties than air cooling.(2)The effects of two deformation degrees at 50%and 70%on the microstructure and properties of stainless steel clad rebar were studied.It was found that the content of pearlite in the carbon steel side increased and the size of grain decreased with the increase of deformation degree.The finer and more dispersed inclusions near the interface were conducive to the formation of a strong metallurgical bonding at high temperature and great force.The tensile test results showed that the greater deformation degree,the greater the tensile strength and elongation of stainless steel clad rebar,indicating that the mechanical properties of the clad rebar were better when deformation degree was 70%.(3)The effects of two deformation temperatures at 950? and 1050? on the microstructure and properties of stainless steel clad rebar were studied.It was found that bainite was formed in the carbon steel side and the size of grain increased with the increase of deformation temperature.The interface was relatively clean,with only a small amount of inclusions dispersed,which could promote strong bonding of stainless steel and carbon steel at higher deformation temperatures.The tensile test results showed that the tensile strength increased and elongation decreased of stainless steel clad rebar with the deformation temperature increased,indicating that the bainite formed at 1050?,which was beneficial to the strength of the clad rebar.(4)The effects of the cooling rates at 1?/s?2?/s?5?/s and 10?/s on the microstructure and properties of stainless steel clad rebar were studied.It was found that the microstructure of carbon steel transformed into bainitic,acicular ferrite and the grain size decreased with the increase of cooling rate.The diffusion of Cr and Ni become slower on both sides which contributed to the decrease of chromium carbides precipitation near the interface and the improvement of the corrosion resistance of stainless steel.The tensile test results showed that the tensile strength increased with the increase of cooling rate,while the elongation was basically opposite.With lower cooling rate of 2?/s?5?/s,the microstructure of finer acicular ferrite,finer pearlite and an amount of bainite could ensure that the clad rebar had sufficient strength and good plasticity.