Study On Mechanical And Wear Resistance Of 25Cr3Mo3NiNbZr Steel

With the increasing demand for weight loss and life extension of pressure vessel steel,the traditional pressure vessel steel represented by PCrNi3MoV steel cannot meet the requirements of complex service conditions and life extension.Therefore,25Cr3Mo3NiNbZr steel with good strength and toughness matching has been developed.25Cr3Mo3NiNbZr steel has excellent high temperature strength and good low temperature toughness.It is a potential long-life pressure vessel steel,which can meet the material performance requirements of increasingly stringent service conditions for body-worn weapons.The microstructure,mechanical properties and wear resistance of 25Cr3Mo3NiNbZr steel determine its service life and service stability.Its high strength,toughness and wear performance are inseparable from the carbide precipitation behavior.In order to better play the performance characteristics of25Cr3Mo3NiNbZr steel,it is necessary to systematically study its microstructure,carbide precipitation behavior and wear performance,reveal its internal mechanism,and optimize the corresponding heat treatment parameters.Therefore,the influence of heat treatment process on the microstructure and mechanical properties of25Cr3Mo3NiNbZr steel was studied,and the precipitation behavior of carbide was qualitatively and quantitatively studied.The wear performance of the service life was compared with that of PCrNi3MoV steel.The wear resistance mechanism of25Cr3Mo3NiNbZr steel was discussed and revealed by several factors including the accelerated test of different wear modes and the combination of microstructure,mechanical properties and carbide precipitation behavior.The major studies are as follows:?1?The effects of quenching temperature and tempering temperature on the microstructure and mechanical properties of 25Cr3Mo3NiNbZr steel were studied by changing the parameters of heat treatment process,at the same time,PCrNi3MoV steel used in traditional pressure vessel was compared.The results show that the heat treatment process with the best strength and toughness matching is obtained by changing the quenching temperature and tempering temperature of 25Cr3Mo3NiNbZr steel and making full use of the secondary hardening effect of carbide forming elements.Its room temperature strength and high temperature strength are increased by about 200MPa compared with PCrNi3MoV steel.After the quenched and tempered treatment of PCrNi3MoV steel,the structure is tempered sorbite,the precipitation phase is only M₃C carbide,no secondary hardening phenomenon obviously.The MC carbide contained Nb element precipitated in 25Cr3Mo3NiNbZr steel ensures that the austenite grains do not grow at high temperatures.25Cr3Mo3NiNbZr steel is tempered sorbite after tempering,during the tempering process,M₃C,M₂C and M₆C carbides are precipitated gradually.The precipitation of M₂C carbide causes secondary hardening of the material.550?is the precipitation temperature of M₂C carbide.At this temperature,the strength and hardness of the 25Cr3Mo3NiNbZr steel peaked.?2?For the two hardness grades of 25Cr3Mo3NiNbZr and PCrNi3MoV steel,the wear resistance of abrasive wear and impact wear under different wear time and impact work conditions were studied.The results show that the hardness is higher and the wear resistance is better when the wear conditions are the same;The wear loss increases with the increase of wear time;the greater the impact energy,the more the wear loss;Under the conditions of abrasive wear and impact wear,when the hardness grade is the same,the 25Cr3Mo3NiNbZr steel has small loss of weight,small furrow width,low roughness and better wear resistance than PCrNi3MoV steel.Research on high hardness grade wear resistant samples found that the type and size of the precipitated phase affect the wear resistance.The 25Cr3Mo3NiNbZr steel contains the MC type carbide NbC and the M₂C type carbide with the largest wear resistance,while the PCr3Ni3MoV steel has poor wear resistance of the M₃C type carbide;The percentage of precipitated phase with size between 1 and 36 nm in 25Cr3Mo3NiNbZr steel is 53.1%higher than that of PCrNi3MoV steel,and the carbide size is finer,and it has greater hindrance to crack propagation during wear and it is the main reason for the improvement of wear resistance.