In order to investigate the strain hardening behavior and the correlation of characterization parameters of high deformability pipeline steel,nine kinds of ferrite/bainite(F/B)multi-phase steels with different volume fractions of bainite were obtained by thermo-mechanical controlled processing(TMCP).The relationships among the characterization parameters of strain hardening capability for high deformation pipeline steel,such as strain hardening exponent,stress ratio,yield strength/tensile strength ratio(yield ratio)and elongation,the correlation mechanisms as well as the connotations and the scopes of application of the parameters were investigated by analyzing the mechanical properties and strain hardening behavior.The results show that the stress ratio of Rt2.0/Rt1.0 and uniform elongation have positive linear correlation with the strain hardening exponent,while yield ratio has a negative nonlinear correlation with the strain hardening exponent.There is a linear relationship between stress ratio of Rt5.0/Rt1.0 and strain hardening exponent under certain conditions,the relationships among stress ratio of Rt1.5/Rt0.5,total elongation and strain hardening exponent are not obvious.The correlation mechanisms of these parameters had been reasonably elucidated by strain hardening analysis;moreover,the connotations and scopes of application for the parameters were also discussed.It is indicated that strain hardening exponent,uniform elongation,and stress ratio of Rt2.0/Rt1.0 should be used as the major parameters for characterizing the strain hardening capability of plastic deformation stage for the F/B multi-phase steel,while yield ratio and stress ratio of Rt5.0/Rt1.0 should be used as minor parameters.Data of industrial production were employed to verify the above conclusions,and a good agreement had been obtained.
Journal of Iron and Steel Research
ferrite/bainite multi-phase steel
high deformability pipeline steel
strain hardening exponent
yield strength/tensile strength ratio