Formability of in-situ Austempered Transformation-induced Plasticity Steels After Laser Beam Welding

Abstract

Laser welded Transformation-induced plasticity (TRIP) steels are known to generate martensite in the fusion (FZ) and the heat-affected (HAZ) zones. To solve this issue, the present study proposes a high temperature (HT) welding to avoid decay below the martensite start temperature after laser welding. Therefore, an inductive heating has been used to reach 500 °C before laser weld of superposed 1.6mm thick TRIP steel class 750. After welding the temperature was kept constant at 500 °C for more 10 minutes in order to austemper. The microstructures of the welds at high temperature are composed of bainite and residual austenite with an FZ hardness up to 300 HV, compared to 450 HV of the ambient temperature (AT) weld. The HT values of hardness are slightly higher than a traditional post-weld heat treatment (TW), 300 HV compared to 250 HV, because of the tempering kinetics in each case. Erichsen cup indentation tests shown the HT coupons presents better formability compared to the AT or TW conditions. The present contribution highlights a possible solution to the intrinsic brittleness during cold forming of laser welded TRIP 750 steel by applying an inductive in-situ austempering.

Hardening Effects of In-Situ Aging for a Laser Welded Maraging Steel

“…One thermocouple welded to the bottom surface of the plate recorded the temperature profile. The furnace and laser setup were reported elsewhere (Braga et al, 2018).…”

A Comparative Study of Abbreviated Heat Treatments for SAE 4130 Steel After Laser Welding

“…In the RT case, the specimen is welded in the usual way, but the HT case requires an external heating source. This was accomplished by an induction furnace specially conceived for the current experiment and reported elsewhere 11 . The temperature evolution of the specimen was recorded by a thermocouple (TC) soldered to the lower surface of the workpiece.…”

“…In previous studies, the present authors proved the usefulness of an in-situ inductive heating of the base material during and after the laser beam interaction for controlling the volume fraction of martensite in FZ and HAZ. Braga et al 11 produced a bainitic fusion zone instead of a martensitic one when transformation-induced plasticity (TRIP) steels were laser welded at 500 °C and keeping isothermal for 10 minutes. These in-situ austempered welded sheets presented an outstanding behavior in cup-drawing tests.…”