Achieving continuous cold rolling of martensitic stainless steel via online induction heat treatment

The continuous cold rolling of martensitic stainless steel (MSS) has not been achieved so far because of the poor weld toughness caused by the occurrence of the brittle martensite. How to improve the toughness of MSS weld is then one of the most concerned challenges in steel rolling industries. In this paper, the toughness of the MSS weld was increased to meet the rolling requirement by introducing the online induction heat treatment into laser-arc hybrid welding. The heat treatment parameters were optimized, which was the heating temperature of 650 degrees C and the holding time longer than 5 s. The weld toughness characterized by Erichsen cupping value was increased from 5.7 mm to 8.7 mm, while the bearable rolling reduction was increased from 25% to 75%. The microstructure-toughness-bearable rolling reduction relationship was established according the experimental results. The mechanism of the microstructure transformation was explained by the thermodynamic calculation of austenite stability, which is dominated by the diffusion behavior of alloying elements. The toughness improvement was discussed according to the microstructure transformation and the crack propagation behaviors, which is closely related to the austenite content and the martensite with high-angle misorientation.