It was verified that SAE 4130 steel plates crack when laser beam welded at room temperature (RT). To overcome this problem, this work proposes a high temperature (HT) laser welding in order to reduce the residual stresses and create a bainitic structure instead of a martensitic one. A conventional post-welding heat treatment (PWHT) had been used as a comparison for HT. The centerline crack disappeared after a heat treatment of both in-situ (HT) or after inserting in a furnace (PWHT) at 500 °C for 10 minutes. The finite element analyses indicated a residual stress reduction from 163.70 to 3.72 MPa in the fusion zone (FZ) of the welds from RT to HT. The hardness obtained in FZ depends on the thermal cycle induced microstructure of the welds as 400 HV, 340 HV and 250 HV, for martensite (RT), tempered martensite (PWHT) and bainite (HT) micro-constituents. The proposed in-situ high-temperature laser beam welding method proved its usefulness to solve the center crack issue in SAE 4130 joints.
The aim of this work was to evaluate the porosity, microstructure, hardness, and electrochemical behavior of AISI 316 steel layers deposited on an AISI 347 steel substrate using the LMD process. Depositions of two, four, and six layers with a 0.5 mm height for each layer were performed at a speed of 375 mm/min, a power of 250 W, a focal distance of 5 mm, and without overlapping laser tracks. The results showed epitaxial growth of the deposited layers in relation to the substrate and a predominantly austenitic microstructure with ferrite as the substrate. The deposited layers presented a dendritic microstructure with a mean porosity of 4.5%. The porosity decreased as the number of deposited layers increased, affecting the pitting corrosion resistance. The sample with six deposited layers showed greater pitting corrosion resistance, whereas the corrosion current speeds were similar for the studied samples. Vickers hardness tests showed that the hardness decreased as the distance from the substrate increased, and the hardness decreased close to the remelted regions.
Dual Phase steels are one of the most used advanced high-strength materials in the industry, due to its combination of a ductile ferritic matrix and disperse hard martensite islands, which provide outstanding mechanical properties for components to be cold stamped. This work investigated fiber laser welding applicability in Dual Phase 600 1.6 mm thick steel sheets, evaluating potential welding impacts on properties of the material for industrial applications. A first set of bead-on-plate welds was generated to define best parameters for subsequent tests. A second set was prepared, consisting of butt joints welded in the optimized condition. Weld microstructure was characterized as 100% martensitic at fusion zone (FZ), with growing fractions of ferrite at Heat Affected Zone (HAZ) as one moves away from fusion line. Hardness is around 60% higher at FZ than at BM, being maximum at supercritical HAZ due to its highly refined microstructure and HAZ softening was not observed. Tensile and Erichsen cupping tests presented similar strength results between welded and non-welded specimens, with slight ductility reduction. Finally, numeric simulations based on Finite Element Analysis were carried out to estimate temperature evolution, phase proportions, residual stresses and distortion levels, achieving excellent agreement with experimental results.
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