Abstract
Among the available high-strength steels, there is growing demand for dual phase (DP) steels for wide application in the automotive industry owing to their good combination of high strength, ductility and formability. Also, the use of innovative welding technologies like laser beam welding (LBW) has growing importance in the field of high-strength steel because of its excellence in providing high-quality welds, high welding speed, high power density, low heat input, a narrow heat-affected zone and low heat distortions as compared to the conventional gas metal arc welding process. However, the hardening and softening in the heat-affected zone is a major issue when welding high-strength steel, i.e. DP steel grades, greatly affecting the strength, formability and plasticity of the whole-welded joint and thus affecting service performance and reliability. Based on preliminary experiments, the optimal welding condition was a nominal laser power of 1.0 kW and a welding speed of 8 mm/s. The aim of this work is to analyse and compare the weld and heat-affected zone characteristics, microstructure and mechanical properties of DP steels with 1-mm thick butt joints of DP800 and DP1200 high-strength steel (HSS) by diode laser beam welding. The effects of post-weld heat treatment (PWHT) on the strengthening of the laser-welded joints were evaluated by microstructural examinations under optical microscope and scanning electron microscope, and mechanical properties were examined by microhardness test, three-point bending tests and tensile tests.
Highlights
Advanced high-strength steels are extensively used in automotive sectors due to their extraordinary combined propertiesRecommended for publication by Commission IV - Power Beam ProcessesWeld World (2020) 64:671–681 SteelLaser beam welding (LBW) and post-weld heat treatment parameters (PWHT) ProcessLaser beam spot Laser power (W)Welding speedGas flow rate (l/min) DP800/DP1200
The specimen was milled from the welded sheets, and all transverse tensile tests were executed according to ISO 4136:2012 standard with MTS 810.23-250 kN electric hydraulic universal testing equipment
The diode laser can be ideal in terms of post-weld heat treatment (PWHT, power = 275 W, speed = 4 mm/s, gas flow rate = 7 l/min) since both the welding and the heat treating of the weld and heat-affected zone (HAZ) can be performed with one heat source by adjusting the focus area
Summary
Laser beam welding (LBW) is a high power density welding process with more than 106 W/cm, which is about 1000 times higher than in conventional arc welding [14]. If the welding heat input is low (as in LBW), hardening can occur, indicating that the cold cracking sensitivity [18] and its influence on the HAZ is significantly lower and the microstructure degradation is less than in conventional arc welding technologies [14, 19]. The diode laser is a unique technology that provides the opportunity to perform welding and post-weld heat treatment (PWHT) with a rectangular beam source, which is in many cases the best shape to cover a wider area for surface hardening or tempering. The major aim was to analyse microstructural changes and the mechanical properties of two automotive high-strength DP steels (DP800 and DP1200) and the effects of PWHT on the improvement of joint characteristics using diode laser technology. The microstructure, microhardness, strength properties and bending performance were examined to evaluate joint behaviour, including the weld zone and HAZ
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
