Microstructure And Mechanical Properties Of Nano TiC Reinforced Martenstic Stainless Steel

Stainless steel has excellent comprehensive properties.In recent years,civil demand for stainless steel is still increasing.However,modern industrial production has put forward higher requirements for the performance of stainless steel.civil demand for stainless steel has slowly changed from quantity demand to quality demand.It takes a lot of time and energy to develop new and higher-performance steel grades,which is costly and difficult.However,it is relatively easy to strengthen existing steel grades.Traditional strengthening methods include precipitation strengthening,fine grain strengthening,heat treatment strengthening and work hardening,among which fine grain strengthening can improve the strength and plasticity of stainless steel at the same time.The methods commonly used for grain refinement of stainless steel include rapid heating method,cyclic heat treatment method,thermomechanical treatment method,etc.These common grain refinement methods have certain disadvantages.The method of adding nano-ceramic particles can effectively refine the grain,and has the characteristics of low addition content,good reinforcement effect and simple operation,which can well meet the requirements of industrial production.In this paper,from the perspective of heterogeneous nucleation and microstructure refinement,different contents of nano TiC are added into martensitic stainless steel.Firstly,TiC particles with particle size less than 100 nm are prepared by DC arc plasma method,and then different contents of nano TiC are introduced into matrix stainless steel by vacuum arc melting.TiC nano-particle reinforced steel with different addition contents(0wt.%,0.1wt.%,0.25wt.%,0.5wt.%)was subjected to solid solution treatment at1130 ? for three hours,then cooled to-55 ? for two hours in a constant temperature and humidity box after water quenching,and then heated to room temperature with equipment.Finally,TiC nanoparticle reinforced steel with particle content of 0.25wt.% was heat treated by air cooling after heat preservation at 360 ?,420 ?,480 ? and 540 ? for two hours.The microstructure and mechanical properties in different States were characterized,and the best addition content of nano TiC and the best heat treatment process were explored.the final conclusions are as follows:(1)Nanoparticles are uniformly distributed in the matrix without agglomeration,which has a good refining effect on the as-cast austenite grains of the matrix steel,and the refining effect increases with the increase of particle content.Adding 0.25wt.% TiC nanoparticles has the best refining effect.The original austenite grain size ranges from 50-350 ?m to 20-100 ?m,and the average grain size decreases from 234.4 ?m to 62.9 ?m m.The continuous increase will affect the phase transformation of the matrix steel,which is not conducive to obtaining excellent properties.(2)Considering the microstructure and mechanical properties in solid solution state,0.25wt.% is the best addition content of nano-TiC.The microstructure is composed of refined lowcarbon lath martensite and sub-micron cellular retained austenite dispersed among laths,which has excellent mechanical properties.Compared with the base steel,the tensile strength is increased by 23.31%,the microhardness is increased by 7.12%,and the elongation is increased by 99%(3)The hardness improvement of solid solution nano-particle reinforced steel is due to the high hardness and thermal mismatch effect of TiC,the strength improvement is due to the joint action of Hall-petch strengthening,Orowan strengthening and thermal mismatch strengthening,and the plasticity improvement is due to the refinement of microstructure and the increase of large-angle grain boundary.The increase of dimples on tensile fracture after adding nano-TiC is also consistent with the plastic improvement of nano-particle reinforced steel.(4)The steel reinforced with 0.25wt.% nanoparticles was aged at different temperatures.By comparing microstructure and the mechanical properties,it was found that 420 ? was the best aging temperature,the hardness increased to 458.45 HV compared with 346.01 HV in solid solution,with an increase of 32.5%,and the tensile strength increased from 1094.92 MPa to1318.37 MPa,with an increase of 20.4%,While maintaining a good elongation of 11.47%.