Composition Design And Heat Treatment Test Of EA4T Axle Steel

With the rapid development of high-speed and heavy-duty railway in our country,the requirement of axle,the most critical component of railway locomotive and vehicle,which is related to the safety of railway operation,is becoming higher and higher.The original JZ(LZ)40 steel and JZ(LZ)50 steel are not suitable for the axle of high-speed and heavy-duty locomotive.Therefore,it is urgent to introduce and develop EA4 T steel with better mechanical properties as the axle steel of heavy-duty electric locomotive for domestic railway freight transportation.In this paper,EA4 T axle steel design and heat treatment test research are carried out to meet the needs of developing high-performance locomotive axles in the production process of FXD3 type eight axle AC drive fast passenger electric locomotive newly developed by CRRC Dalian Locomotive Co.,Ltd.According to the requirements of European standard EN 13261:2009 and iron standard TJ/JW 037-2014 on the structure and properties of EA4 T axle steel,this paper studies the design of chemical composition,the heat treatment characteristics of EA4 T axle steel,the influence of tempering temperature on the structure,hardness and impact properties,the tensile,impact and fatigue properties and the analysis of fracture morphology of equal efficiency axle samples.The results are as follows:With the increase of heating temperature,the austenite grain size and the maximum grain size of EA4 T axle steel show a trend of slowly increasing first and then rapidly increasing,while the no uniformity factor shows a trend of basically unchanged first and then increasing,and the corresponding temperature of all folding points is 1000?.In the end quenching test with different heating temperature,when the distance from the end is less than or equal to 7 mm,the heating temperature has no effect on the hardness;but when the distance is more than 7 mm,the hardness of the steel will increase with the increase of the heating temperature.The CCT curves of EA4 T axle steel heated at 880 ? and 920 ? show completely the transformation regions of ferrite,pearlite,bainite and martensite,and the heating temperature has little effect on the starting transformation point(MS)and the ending transformation point(MF)of martensite,but it has great effect on the precipitation time of ferrite and the starting transformation point(BS)with bainite transformation Influence.However,when tempering after quenching,the hardness of EA4 T axle steel decreases and the impact energy increases with the increase of tempering temperature.When the tempering temperature is 600??650?,the hardness meets the requirements of European standard and iron standard,and the maximum impact energy can reach 199J;however,EA4 T axle steel has slight high temperature tempering brittleness.After 900 ? 5h water quenching and 640 ? × 7h water-cooling,the microstructure of the equivalent axle is basically tempered M / B structure,the grain size is grade 8,The fatigue limit is 368 Mpa and 303 Mpa respectively,and the ratio of the two is 1.21,which meet the requirements of European standard and iron standard.Finally,the heat treatment process of EA4 T axle steel is determined by considering the test results obtained and the maximum heating temperature limit of the heat treatment furnace of the company.The parameters of quenching and tempering process are 900?×5h water quenching(water temperature?40?)and 650?×6h water cooling,respectively.The structure and mechanical properties obtained by the optimized heat treatment process meet the requirements of European standard EN13261:2009 and iron standard TJ/JW 037-2014,and achieve the expected goal of meeting the high standard technical requirements of locomotive axle.