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.

In this letter, the residual stress (RS) induced by the high vacuum (2 x 10(-4) mbar) electron beam welding (EBW) of two high strength steels (HSS) i.e. quenched and tempered (Q + T) steel and thermo mechanical controlled steel (TMCP) with plate thickness 15 mm for specific applications in construction engineering, vehicle industry (trucks, mobile cranes, railway vehicles) etc. was analysed. X-ray diffraction (XRD) method has been used for the comparative analysis through the surface RS distributions in EB welded HSS, 5960QL and 5960M butt joint. Combination of power beam process with cutting edge technology of residual measurement for HSS characterise the novelty of this study. The results showed that the maximum longitudinal tensile stress near the weld toe of the EB welded 5960QL joint is higher than the 5960M. The transverse residual stress in the 5960QL and 5960M welded samples shown the characteristic W-shape of residual stress distribution.

In recent years, ultra-high-strength structural (UHSS) steel in quenched and tempered (Q+T) conditions, for example, S960QL has been found in wider application areas such as structures, cranes, and trucks due to its extraordinary material properties and acceptable weldability. The motivation of the study is to investigate the unique capabilities of electron beam welding (EBW) compared to conventional gas metal arc welding (GMAW) for a deep, narrow weld with a small heat-affected zone (HAZ) and minimum thermal distortion of the welded joint without significantly affecting the mechanical properties. In this study, S960QL base material (BM) specimens with a thickness of 15 mm were butt-welded without filler material at a welding speed of 10 mm/s using the high-vacuum (2 × 10⁻⁴ mbar) EBW process. Microstructural characteristics were analyzed using an optical microscope (OM), a scanning electron microscope (SEM), fractography, and an electron backscatter diffraction (EBSD) analysis. The macro hardness, tensile strength, and instrumented Charpy-V impact test were performed to evaluate the mechanical properties. Further, the results of these tests of the EBW joints were compared with the GMAW joints of the same steel grade and thickness. Higher hardness is observed in the fusion zone (FZ) and the HAZ compared to the BM but under the limit of qualifying the hardness value (450 HV10) of Q+T steels according to the ISO 15614-11 specifications. The tensile strength of the EBW-welded joint (1044 MPa) reached the level of the BM as the specimens fractured in the BM. The FZ microstructure consists of fine dendritic martensite and the HAZ predominantly consists of martensite. Instrumented impact testing was performed on Charpy-V specimens at −40 °C, which showed the brittle behavior of both the FZ and HAZ but to a significantly lower extent compared to GMAW. The measured average impact toughness of the BM is 162 J and the average impact toughness value of the HAZ and FZ are 45 ± 11 J and 44 ± 20 J, respectively.

In this paper, the effect of autogenous diode laser beam welding (LBW) and the influence of post weld heat treatment (PWHT) on microstructural changes and mechanical properties of dual phase DP1400 high strength steel (HSS) butt welded joint are studied and presented. LBW and PWHT were performed on 1 mm sheet thickness using 3 and 5 kW diode laser systems, respectively. The technology ensures high quality welded joints in HSS and facilitate the welding and PWHT by same process and equipment. Microstructure evaluation was performed using optical and scanning electron microscopy. Related to the mechanical properties, tensile tests, fractography of fractured tensile specimens and three-point bending tests were carried out. The microstructural examination presented the constituents of martensite and ferrite in the heat affected zone (HAZ) and fusion zone (FZ) consists of predominantly lath martensite with ferrite and some bainite. Tempered martensite was observed after PWHT in HAZ and FZ. The hardening peaks observed in coarse-grained and fine-grained subzones were significantly reduced by the novelty technology, i.e. PWHT and thereby cold cracking sensitivity. The fractography of the fractured tensile specimens showed characteristic features of ductile failure.

In this paper, we presented the dataset values of full width at half maximum (FWHM) with errors at each point corresponding to the value of longitudinal and transverse residual stress along the three lines for 14 points measured in the EBW welded joints (S960QL and S960M) of the related article [1]. This dataset is used to plot figures and describes their correspondence points with the interrelation of the residual stress graphs (Fig. 4) of the article [1]. The shape of the diffracted peak can be characterised in a simple way by the FWHM, which is the width in degree at half the peak height after background extraction. The measured width consist of instrumental and metallurgical broadening. The variation or increase in FWHM is resulted from the crystalline lattice defect e.g. solute foreign atoms, dislocations and grain boundary. Conversely, if we can determine the physical broadening, we get more information about the structure of the investigated material. In addition, the optical microscopic image of the base materials and weld microstructure are the other parts of the data. Diffraction data were collected using centreless X-ray diffraction (XRD) during in situ residual stress measurement of high strength structural steels S960QL and S960M. A more detailed interpretation of the data presented in this article is provided in article [1]. The presented data are produced as part of the main work entitled “Comparative evaluation of residual stresses in vacuum electron beam welded high strength steel S960QL and S960M butt joints [1]”.