Fiber laser welding of hot stamping steel: effect of in situ annealing on the microstructure and mechanical properties
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RESEARCH PAPER
Fiber laser welding of hot stamping steel: effect of in situ annealing on the microstructure and mechanical properties Raquel Alvim de Figueiredo Mansur 1 & Vagner Braga 1 & Vinicius Machado Mansur 1 & Daolun Chen 2 & Milton Sergio Fernandes de Lima 1 Received: 5 February 2020 / Accepted: 15 September 2020 # International Institute of Welding 2020
Abstract Advanced high-strength steel (AHSS) is a class of promising materials for safe and lightweight structural applications in the transportation industry due to its high energy absorption capacity during severe plastic deformation. However, some types of AHSS tend to become brittle after welding and fail during forming operations. This paper proposes a novel method of laser welding AHSS class of 22MnB5 steel by induction-heating the samples in the bainitic range, which was identified via a theoretical analysis using finite element and physical metallurgy modeling. The calculated annealing temperature was 485 °C, and the subsequent laser parameters were set at a power of 800 W and a welding speed of 2 m/min. The welds performed on such pre-heated samples showed a bainitic microstructure consisting of bainitic ferrite along with uniformly distributed ultrafine carbide precipitates, in contrast to an almost fully martensitic microstructure conducted at room temperature. The average value of microhardness in the heat-affected zone thus decreased from ~ 670 HV without pre-heating to ~ 280 HV with pre-heating. The laser welds with pre-heating exhibited not only a slightly higher yield strength and elongation, despite a slightly lower ultimate tensile strength, but also a superior drawability with an Erichsen index increase by 28% compared with the welds without preheating. Keywords Advanced high-strength steel . Laser beam welding . Tensile properties . Formability
1 Introduction Advanced high-strength steel (AHSS) is a special class of materials, mainly applied to automotive components, where the application allows weight savings due to reduced thickness, improved crash resistance, and resistance to peak loads [1]. These types of steel are usually furnished as tailored blanks, then cut, welded, pressed, and heat-treated to obtain desired properties. One notable advance in the use of AHSS is the possibility to combine strains forming with heat treating operations in the same equipment. Hot stamping is an Recommended for publication by Commission IV - Power Beam Processes * Milton Sergio Fernandes de Lima [email protected] 1
Photonics Division, Instituto de Estudos Avancados, Sao Jose dos Campos, Brazil
2
Departament of Mechanical and Industrial Engineering, Ryerson University, Toronto, Canada
innovative process by which AHSS is more efficiently formed into complex shapes than with traditional cold stamping [2]. The process involves the heating of the steel blanks until they are malleable, followed by deformation and rapid cooling in a specially designed die, creating a transformed and hardened material. The ability to effectively combine strength and
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