Study On Microstructure And Properties Of A New Low Alloy Wear Resistant Cast Steel Reinforced By V-N

Due to the severe service conditions,the wear-resistant cast steels used for the lining plate of a self-grinding machine and semi-self-grinding machine must have higher hardness and excellent impact toughness,so as to play the role of wear resistance and wear reduction,and achieve the purpose of enhancing the service life of the whole equipment.Cr-Mo alloy wear resistant cast steels have excellent wear resistance and is widely used as the lining plate of a self-grinding machine and semi-self-grinding machine,but it has some problems such as high alloy content,low plastic toughness and high manufacturing cost.Aiming at the above problems,based on ZG31Mn2Si low-alloy wear-resistant cast steel with good wear resistance and relatively simple alloy composition,a new type of wear-resistant cast steel reinfored by vanadium and nitrogen was developed by combining microcontrol of alloying elements with vanadium nitrogen microalloy strengthening technology.The effect of carbon content on the microstructure and properties of wear-resistant cast steel was analyzed by simulation calculation and experimental research.The effect of vanadium content on microstructure transformation and carbonitride precipitation behavior was analyzed.The effect of heat treatment process on microstructure and properties of wear resistant cast steel was studied.The relationship between vanadium nitrogen reinforcement and microstructure,mechanical properties and wear resistance was established.On the basis of theoretical research,small-scale trial production and trial use are carried out.Compared with the original product,the service life has been improved and the production cost has been controlled effectively,which has accumulated the theoretical foundation for the research and development of vanadium-nitrogen micro-alloy strengthening technology in the field of wear-resistant cast steel and provided the operation experience for the industrialization.The results show that with the increase of C content,the lamellar martensite decreases,the acicular martensite increases,the hardness of the material increases,and the impact toughness decreases.The wear resistance increases first and then decreases,mainly because when the content of C is low,the material hardness is low,the plastic toughness is high,and the wear mechanism is mainly plastic deformation wear;when the content of C is too high,the material hardness is high,but the plastic toughness is poor,and the wear mechanism is mainly brittle fracture wear.When C content is about 0.4wt%,the impact toughness and hardness of the sample have a good match,the wear mechanism is micro-fatigue wear,wear resistance is the best.In order to further improve wear resistance,the properties of low alloy wear resistant cast steel with C content of 0.4 wt%were optimized by vanadium nitrogen microalloy strengthening technology.The simulation results show that V content has a great influence on M（C,N）precipitation behavior during the cooling process.With the increase of V content,the initial precipitation temperature and the maximum precipitation amount of M（C,N）increase obviously.The addition of V can effectively control the growth of austenite grain.When heating temperature≥1100℃,the austenite grains grow abnormally because the heating temperature is close to or above the dissolution temperature of M（C,N）in austenite.It can be found that V content affects the critical cooling rate of martensitic transformation during the static continuous cooling process.When V content was 0.069wt%,the critical cooling rate was 10℃/s,and when V content increased to 0.186 wt%,the critical cooling rate decreased to 5℃/s.After heat treatment,compared with the samples without vanadium nitrogen reinforcement,the hardness and v-notch impact toughness increased by about 1.5 HRC and 10 J/cm²,respectively.The relative wear resistance increased by 9.5%～15%.The strengthening mechanism of vanadium and nitrogen was revealed.The increase of V content promotes the precipitation of carbonitride and reduces the solid solubility of C and N elements in martensite,resulting in the decrease of hardness and improvement of impact toughness.When tempering at 300℃,the first kind of brittleness appeared,but the increase of V content promoted the transition from short rod to granular,and tempered the brittleness.The impact wear experiments of low temperature tempering steel show that the precipitated nano carbonitride can strengthen the matrix and hinder the growth of microcrack,and improve the wear resistance.When tempering temperature is higher,Fe₃C particles with a larger size are precipitated at the boundary of the original martensite,and M（C,N）particles with a smaller size are precipitated inside.The synergistic effect of the two precipitates helps the material resist the longitudinal embedding and tangential movement of the abrasive,thus improving the wear resistance.It is found that the wear resistance of the new wear resistant cast steel is improved by about 15.7%in comparison with the original chrome molybdenum steel liner,and the manufacturing cost is effectively reduced.