In this paper

the resistance spot welding of Q

&

P980CR steel under conventional welding parameters is studied. Due to the high carbon equivalent of Q

&

P980 base metal

the joints contain much hardening structure and manifest poor plasticity

resulting in interface fracture in the tensile-shear tests. Thus

the optimization scheme with the additional postheat current pulse is put forward.Based on SORPAS numerical simulation

the influence of the postheat pulse welding current and welding time on the cooling rate of section-t

8/5

of the welding joints is studied

and the optimized welding parameters are determined. The experimental results show that the postheat current pulse increases the tensile-shear strength and cross-tension strength of the welding joints

and the failure mode of the joints changes from interface fracture to pullout fracture

indicating that the postheat current pulse effectively reduces the cooling rate and improves the toughness of the welding joints.