Research Duplex Steel Flow Stress Model And Hardening Characteristics Based On Micromechanics

The research for the flow stress model of ferrite-martensite dual-phase steel which is preferred material for expandable tubular steel with low-cost and large expansion rate, not only conductive to explain the relationship between the dual-phase steel microstructure, the performance of each component phase and the mechanical characteristics of deformation (such as yield, tensile strength, work hardening, uniform elongation, etc.), but also can guide the dual-phase steel alloy design and production process, resulting in the dual-phase steel with excellent performance.Based on the analysis on the performance requirements of expandable tubular steel with low-cost and large expansion rate and the advantage of ferrite-martensite dual-phase steel such as no yield elongation, low yield strength, high tensile strength and well strength plastic matching and according to the typical composition of the expandable tubular dual-phase, low cost ferrite-martensite dual-phase steel(07MnSi) which was low carbon and making Mn, Si as the main alloying element was designed, and the phase transition point (Ac1and Ac3) was calculated that were about730℃and875℃.Though different subthermal quenching process, the different martensite content of the ferrite-martensite phase organization was obtained.Taking the special internal structure of the dual-phase steel as the starting point and using composite materials micromechanics, the quenched flow stress model of the dual-phase steel, the hardening law of the dual-phase steel, hardening rate and strain hardening exponent calculation model were established, which were based on non-uniform deformation of martensitic and ferrite phase.Based on these models, the relationship between the different subthermal quenching dual-phase steel microstructure, the performance of each component phase and the mechanical characteristics of deformation (such as yield, tensile strength, work hardening, uniform elongation, etc.) was discussed in detail in order to establish a link between the internal organizational structure and performance of the dual-phase steel.Using electronic tensile testing machine, the mechanical properties of07MnSi which were though different subthermal quenching were tested and the agreement of the calculated values of the model and the experimental data was obtained. Therefore it was feasible that these micromechanics models were used to predict and analyze the flow stress of the dual-steel during deformation. Based on combination of these models and the chemical composition performance, organization and structure requirements of expandable tubular steel with low-cost and large expansion rate, the relationship was established between the chemical composition performance requirements of expandable tubular steel with low-cost and large expansion rate and the organizational structure of the steel. It was concluded that expandable tubular dual-phase steel (07MnSi) could obtain the best mechanical properties at the water quench temperature of820℃as same as meet the requirements of expandable tubular steel with low-cost and large expansion rate. So the referenced theoretical basis was established to guide the dual-phase steel alloy design and production process.At last the inadequacy of the model and future prospects were pointed out.