Effect Of Cooling Rate On Microstructure And Mechanical Properties Of Fe-Mn-Al-C High Strength Low Density Steel

With the promotion of energy saving and emission reduction,automobile lightweight has become an urgent demand of automobile industry.Fe-Mn-Al-C series low-density and high-strength steel has attracted extensive attention due to its excellent mechanical properties,low density and good corrosion resistance.Heat treatment conditions have great influence on the microstructure and mechanical properties of Fe-Mn-Al-C low-density steel.At present,there are many researches on the effect of solution and aging on the microstructure and mechanical properties of Fe-Mn-Al-C low-density steel,but the research on the effect of cooling rate on the microstructure,precipitates and deformation mechanism is still relatively scarce.Therefore,three different cooling rates(water cooling,air cooling and furnace cooling)will be adopted for austenite low-density Fe-30Mn-11Al-1.2C steel,and then comparative study will be carried out,the effect of cooling rate on microstructure,precipitates and mechanical properties of austenitic low density steel was investigated.The main conclusions are as follows:(1)The cooling rate of solution treatment significantly affects the microstructure of Fe-30Mn-11Al-1.2C austenitic low-density steel.The microstructure of water cooling,air cooling and furnace cooling are austenite +??carbides,austenite + ??carbides and austenite + ??carbides + ?*carbides,respectively.The size,volume fraction and morphology of ??carbides are completely different under different cooling rates.With the decrease of cooling rate,the size and volume fraction of ??carbides increase.The results show that the distribution of ??carbides is spherical after water cooling,rectangular after air cooling,and non-uniform,multi-scale and multi-level morphology after furnace cooling.(2)The mechanical properties of Fe-30Mn-11Al-1.2C austenitic low-density steel were significantly affected by the size,volume fraction and morphology of ??carbides.With the increase of the size and volume fraction of ??carbides,the yield strength of the material increases.At the same time,the work hardening ability of the material is reduced due to the inhibition of the refinement of slip band during deformation.However,heterogeneous,multi-scale and multi-level ?? carbides can improve the work hardening ability of the material as well as the strength.(3)The interaction between dislocations and spherical,heterogeneous,multi-scale and multi-level ??carbides is a shear through mechanism.A large number of slip bands are formed during tensile deformation of water cooled and furnace cooled steel,and the deformation mechanism is plane slip mechanism.