Development Of Ti Microalloyed Martensitic Wear-Resistant Steel With High Strength And Toughness And Study Of Its Application Performance

With the continuous development of science and technology and in-depth exploration of unknown fields,service conditions for wear-resistant steel are becoming more and more complex and harsh,and higher comprehensive properties（such as wear-resistant,welding,fatigue,corrosion,processing）are required.In present paper,Ti micro-alloyed martensitic wear-resistant steel was developed to meet the comprehensive performance for wear-resistant steel applied under complex working conditions such as coal mining and transportation.Manufacturing process was studied to control Ti precipitation and martensite structure using thermal simulation and lab experiment,industrialized manufacture technology,mechanical properties test（tensile,impact,cold bending,fatigue,residual stress）,microstructure characterization（high temperature confocal microscope,optical microscope,scanning electron microscopy and electron back scattering diffraction analysis,transmission electron microscope）,phase analysis,application performance study（immersion corrosion test,electrochemical test,stir wear experiment,welding experiment,HIC experiment）.Typical problems were analyzed and resolved during industrial production.Finally,a"fine martensite+nano precipitated phase"HB500wear-resistant steel was developed,which can be produced industrially and stably.Moreover,the integrated application properties of the steel was studied.Main research contents and results are as follows:Firstly,the growth tendency of austenitic grain during heating,hot deformation behavior of the phase during rolling,and phase change behavior during the process of cooling and heat treatment were investigated,the austenitic grain size,precipitation of Ti,microstructure and performance could be controlled well through the whole process.The function relationship of austenite grain size with heating temperature and holding time were presented as lnD=7.26-4982/T and D=4.32t^0.21 respectively.The C and N precipitated phases of Ti had good stability at high temperature stage and could effectively hinder austenite grain boundary movement.The finer the austenite grains are,the more favorable they are for the phase deformation nucleus and internal quadratic nucleation,and the finer the martensite structure is.The thermal deformation increased the temperature of martensite transformation and decreased the critical cooling rate of martensite transformation.The rolling temperature in the austenite recrystallization zone should be controlled at1000～1100℃,so that the austenite grains could be fully refined and kept uniform.When the deformation temperature of the unrecrystallized zone was relatively low,a large number of distorted austenite could be obtained to refine martensite structure.The final rolling temperature should be controlled at 820℃～860℃.The DQ+RQ+T process was the best way to control the precipitation of Ti and refine the martensite structure,so as to obtain the best combination strength and toughness.Secondly,based on the theory of lab research,the composition control range and core processes of the Ti microalloyed wear-resistance steel were determined,some typical problems existing in industrial production were gradually solved,such as slab crack,larger inclusions granules of TiN,temper brittleness,residual stress,delayed crack,etc.,and the critical control points in industrial production technology were finally formed.The results of industrial production showed that the Ti microalloyed wear-resistant steel had good strength and toughness,which were higher than that in national standard.The structure and performance were uniform due to the fine effective grain size of 1.96μm and 2.28μm for 8mm and 30mm steel plate respectively.By refining grains,the low-temperature toughness was improved and the fatigue performance was better than that of the Cr-Ni-Mo-Nb wear-resistance steel.The second phase precipitation of Ti reached the nanometer level and would not damage the impact toughness and fatigue performance.Finally,the corrosion wear resistance and welding crack resistance of Ti microalloyed wear-resistant steel were studied by comparing to the Cr-Ni-Mo-Nb martensite wear-resistant steel.The interaction components of corrosion and wear accounted for 25.09%and40.18%of the corrosion wear rate,respectively.Strain hardening changed the surface of materials,grain boundaries and internal state of grains,which was the main reason for the interaction between corrosion and wear.Grain refinement can weaken strain hardening and improve toughness,which was the fundamental reason for improving corrosion and wear resistance.The mechanical composition of the Ti microalloyed wear-resistant steel could avoid the embrittlement caused by abnormal structure in the local area of CGHAZ.The undissolved second phase of Ti at high temperature effectively prevented the growth of austenite grains during the thermal cycle of welding,so as to refine the CGHAZ structure and reduce the embrittlement effect of coarse grains.HIC experiment showed that Ti microalloyed wear-resistant steel had stronger hydrogen induced cracking resistance,which further proved that grain refinement could improve the welding cracking resistance of wear-resistant steel.The Ti microalloyed HB500 wear-resistant steel developed with low cost and high performance,could be produced industrially and stably,which could meet the requirements for wear-resistant steel under complex working conditions,and had a good application prospect.