The Effect Of Cold-rolled Deformation Reduction On The Thermo-mechanical Processes Of Mn12Ni2MoTi(Al) Steel

By thermomechanical processes,high manganese TRIP steel achieves both high tensile strength,excellent ductility and exceptional strain hardening potential simultaneously.In this paper,Mn12Ni2MoTi(Al)steel was used as the main research object to study the effects of different heat treatment processes on the microstructure and mechanical properties of 15% cold-rolled samples by means of scanning electron microscopy(SEM),X-ray diffraction(XRD),electron backscatter diffraction(EBSD),Vickers hardness tests and tensile tests.And the effects of cold rolling deformation on the microstructure and mechanical properties of Mn12Ni2MoTi(Al)steel were investigated by adding 35% and 65% cold-rolled samples.The main conclusions are as follows:(1)The 15% cold-rolled samples will obtain reverse transformation austenite during annealing in the two-phase region,and the highest austenite content will be obtained at an annealing temperature of 650°C.When annealed at 650°C,except for a small amount of rapidly formed massive austenite,most of the austenite nucleates between the martensite laths and thickens by consuming the adjacent martensite to form a stripshaped austenite.When annealed at 745°C,austenite will rapidly nucleate and form equiaxed crystals,but will transform into martensite during quenching;(2)After first-stage annealing in the two-phase region and secongary annealing at 480°C for 12 h,the austenite content and mechanical properties of the 15% cold-rolled samples were improved,but the microstructure became differet.The microstructure of the sample annealed at 650°C or 700°C is still uniform,while the microstructure of the sample annealed at 745°C become a dual-phase structure of austenite/martensite and the distribution is uneven,and the dark region is austenite,and the bright region is martensite.In adition,segregation of Mn elements exists in austenite;(3)After annealing at 650°C(1h)+480°C(12h),the 15% cold-roll samples were uniform microstructure,and combined with the strip-shaped austenite,the samples obtained a higher yield strength,and could continue to produce a TRIP effect in subsequent tensile deformation.The samples annealed at 745°C(1h)+480°C(12h)showed a large amount of martensite transformation at the initial stage of strain,but as the strain increased,the strength of the samples began to rise rapidly,so the yield strength was lower,but the work hardening effect is better.(4)Under the same heat treatment conditions,the larger the cold rolling deformation is,the more austenite content and stronger texture the samples has,and the easier it is to form austenite/martensitic laminate structure on the cross section,the smaller the laminate spacing is.Secondary annealing is favorable for the formation of the laminate structure,and the 35% cold-rolled samples does not form a clear laminate structure in the first annealing,but an approximate laminate structure is obtained after the secondary annealing;(5)When the austenite/martensitic two-phase structure is alternately arranged in laminate,the rate of martensite transformation of austenite can be effectively decreased during tensile deformation,and the TRIP effect can be provided for the subsequent stretching process,relieving strain concentration and improving tensile properties;...