Tailor Welded Partition Blanks: New Methods Improve the Ductility of Ultra-high-strength Welded Joint

Abstract

A novel quenching and partitioning (Q&P) processing was applied to the ultra-high-strength tailor welded blanks (TWBs) with an equiaxed martensite, retained austensit and carbides in the weld. The Q&P processing consisted of a cooling step and a partition step at 450°C for 10 s to 30 s. The fraction of martensite after the processing was nearly 64%. During partitioning, carbides precipitates with an average size of 30 nm formed inside the martensite. Currently, the interstitial content of austenite was increased to an average of almost 1.2 wt.%. After Q&P processing, the TWB of partition joints exhibited outstanding mechanical properties including a yield strength of 450 MPa, a tensile elongation of 15% at room temperature, and a formability ratio of 108.72% and 81.66%, with respect to the BMs DP1180 and DP590. Furthermore, the tempered martensite formation and austenite ductile-effect were attributed to the formability improvement of ultra-strength-steel TWBs.