Study On Microstructure,Mechanical Properties And Heat Treatment Of Fe-15.8Mn-7.8Al-0.77C-5.1Ni Low Density Cast Steel

The brake discs,the important components of the high-speed train braking system in China,are currently monopolized by foreign countries.With the rapid development of China's railway network and the prominent energy and environmental issues,it has become an urgent problem to be solved by independently developing a brake disc material with superior performance and realizing its localization and weight reduction.This project develops a low-density cast steel Fe-15.8Mn-7.8Al-0.77C-5.1Ni on the basis of low-alloy high-strength cast steel that has been industrialized.The density was reduced by adding lightweight elements such as Al and Mn.Ni element was added to induce the second phase of nano-scale B2.toughening.Its tensile strength can reach more than 920 MPa,the elongation is higher than 15%,and the weight loss effect can reach 9.6%.The effects of annealing,solid solution and aging on microstructure and mechanical properties were studied by means of OM,XRD,SEM and high temperature friction and wear tests.The friction and wear properties under service conditions were studied.The results are as follows:The low-density steel composition is designed in combination with the phase diagram,and it is the austenitic ferrite duplex steel at room temperature.Because there is no solid phase transition point,the solution test is carried out with a wide temperature.The tensile strength after solid solution at 850 ° C and 900 ° C is higher than 920 MPa,and the yield strength is higher than 690 MPa.The elongation is only 11%.With solution temperature Continue to increase grain growth,strength decreases and shows good plasticity.The solid solution aging process was optimized by orthogonal test,and a large number of diffused nano-scale B2-Fe Al phases were obtained to achieve strengthening and toughening.The yield strength was higher than 800 MPa and the elongation was higher than 15%.The B2 phase is superior to the ?-carbide as a strengthening phase,and Fe-15.8Mn-7.8Al-0.77C-5.1Ni has a higher yield strength than other rolled low-density steels,and the tensile strength has no disadvantage.By quantitatively analyzing the size and quantity of B2 nanophase,the strengthening and toughening mechanism is studied.The contribution of the second phase strengthening to the Fe-15.8Mn-7.8Al-0.77C-5.1Ni low-density steel yield strength is higher than 22%,and the fine grain strengthening is less than 3%.The second phase by solid solution aging treatment strengthening is an important means of strengthening and toughening low-density cast steel.The service performance of low-density cast steel for high-speed brake disc materials was studied by high-temperature friction and wear test.The friction coefficient of test steel was higher than 0.25,which was in line with the international railway alliance's friction coefficient for brake discs.The experimental results show that the main wear mechanism in the high temperature friction and wear process is abrasive wear,oxidative wear and adhesive wear.The higher strength and impact energy make the friction coefficient of the material decrease,and the wear amount decreases correspondingly.which improves the strength of the material and Impact work is an effective way to reduce wear.