The effect of heat input on the microstructure and mechanical properties of dissimilar S700MC/S960QC high-strength steels (HSS) using undermatched filler material was evaluated. Experiments were performed using the gas metal arc welding process to weld three samples, which had three different heat input values (i.e., 15 kJ/cm, 7 kJ/cm, and 10 kJ/cm). The cooling continuous temperature (CCT) diagrams, macro-hardness values, microstructure formations, alloy element compositions, and tensile test analyses were performed with the aim of providing valuable information for improving the strength of the heat-affected zone (HAZ) of both materials. Micro-hardness measurement was conducted using the Vickers hardness test and microstructural evaluation by scanning electron microscopy and energy-dispersive X-ray spectroscopy. The mechanical properties were characterized by tensile testing. Dissimilar welded samples (S700MC/S960QC) with a cooling rate of 10 °C/s (15 kJ/cm) showed a lower than average hardness (210 HV5) in the HAZ of S700MC than S960QC. This hardness was 18% lower compared to the value of the base material (BM). The best microstructure formation was obtained using a heat input of 10 kJ/cm, which led to the formation of bainite (B, 60% volume fraction), ferrite (F, 25% volume fraction), and retained austenite (RA, 10%) in the final microstructure of S700MC, and B (55%), martensite (M, 45%), and RA (10%), which developed at the end of the transformation of S960QC. The results showed the presence of 1.3 Ni, 0.4 Mo, and 1.6 Mn in the fine-grain heat-affected zone of S700MC. The formation of a higher carbide content at a lower cooling rate reduced both the hardness and strength.

The study evaluates numerically and experimentally the effect of welding heat input parameters on the microstructure and hardness of the heat-affected zone (HAZ) of quenched and tempered (QT) and thermo-mechanically controlled process (TMCP) 690-MPa high-strength steel. Numerical analyses and experimental comparisons were applied using three heat input values (10, 14, and 17 kJ/cm) in order to predict the thermal fields during welding. Experimental analysis was carried out of the microstructure and microhardness behavior in different HAZ areas. The numerical values indicate that the maximum respective values of temperature measured in QT steel and TMCP steel were about 1300 and 1200 °C for a heat input of 10 kJ/cm, 1400 and 1300 °C for a heat input of 14 kJ/cm, and 1600 and 1450 °C for a heat input of 17 kJ/cm. The cooling times resulted, for a heat input of 10 kJ/cm, in numerical t_8/5 (14.5 s) and experimental (18.84 s) increases in hardness in the coarse-grain heat-affected zone (CGHAZ) of the QT steel (317 HV0.1), due to the formation of bainite and lath martensite structures with grain growth. Decreased hardness in the CGHAZ of TMCP steel (240 HV0.1) was caused by primary recrystallization of the microstructure and the formation of more equilibrium products of austenite decomposition. Increasing the heat input (14 to 17 kJ/cm) led to numerical t_8/5 (29 s) and experimental (36 s) decreases in hardness in the CGHAZ of QT steel (270 HV0.1) due to the full austenite (thermal weld cycle), and maintained the relative value of TMCP steel (235 HV0.1).

This study concerns the weldability of dissimilar Ultra high-strength steel (UHSS) and advanced high-strength steel (AHSS), which is used in the modern machine industry. The materials offered superior strength as well as relatively low weight, which reduces microstructure contamination during a live cycle. The choice of the welding process base of the base material (BM) and welding parameters is essential to improve the weld joint quality. S700MC/S960QC was welded using a gas metal arc welding (GMAW) process and overmatched filler wire, which was performed using three heat input (7, 10, and 15 kJ/cm). The weld samples were characterized by a Vickers-hardness test, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The test reveals a decrease of softening areas in the HAZ and the formation of the stable formation of Bainite-Ferrite for S700MC and Bainite-martensite for S960QC when the heat input of 10 kJ/cm is used. It is recommended to use the GMAW process and Laser welding (Laser beam-MIG), with an optimal welding parameter, which will be achieved a high quality of manufacturing products.

Dissimilar welding offers exiting benefits for a wide range of engineering applications, such as automotive bodies, piping systems of nuclear power plants, health equipment. The main advantages of dissimilarwelding applications areweight reductions, lower costs, unique properties combinations, and improved energy-efficiency. The properties of dissimilar weld depend on the type of welding process used, the accuracy of the process parameters control, the characteristics of the base metal and the heat treatment procedures. The current study reviews the scientific literature on the topic of thermal analysis of dissimilar high-strength steels (HSS) welding. The review of experimental data was carried out to analyze the variable heat input effect on dissimilar welds. The results indicate the welds mechanical properties irregularity and reduction in toughness and tensile strength due to uneven changes in the microstructure. Furthermore, postweld heat treatment (PWHT) often resulted in the formation of intermetallic compounds whose properties are dependent on the duration of treatment. The research results can be used to optimize the heat input of the HSS welding process.

Ultra-high-strength steel (UHSS) is a complex and sophisticated material that allows the development of products with reduced weight but increased strength and can assist, for example, in the automotive industry, saving fuel in vehicles and decreasing greenhouse gas emissions. Welding UHSS has a certain complexity, mainly due to the higher alloys and heat treatments involved, which can result in a microstructure with higher sensitivity to welding. The primary purpose of the current work was to select the best parameters of the gas metal arc welding (GMAW) for welding the S960 material based on prediction methods. To achieve the expected results, a finite element analysis (FEA) was used to simulate and evaluate the results. It was found that the welding parameters and, consequently, the heat input derived from the process greatly affected the UHSS microstructure. Using FEA and estimating the extension of the heat-affected zone (HAZ), the peak temperature, and even the effect of distortion and shrinkage was possible. With an increase in the heat input of 8.4 kJ/cm, the estimated cooling rate was around 70 °C/s. The presence of a softening area in the coarse grain heat-affected zone (CGHAZ) of welded joints was identified. These results led to an increase in the carbon content (3.4%) compared to the base metal. These results could help predict behaviors or microstructures based on a few changes in the welding parameters.

This study aims to investigate the optimum heat input required to overcome the negative consequence of the thermal properties of austenitic stainless steel to produce welded joints free of distortion. An experimental investigation using robotic-MAG and fiber-laser welding processes has been used in other to investigate angular, longitudinal distortion (bending), and microstructural constituents in the heat-affected zone (HAZ) of different welded joints. Ten 316L steel, butt-joints were made by different travel 25 speeds at the range of (7–11 mm/s). A highly sensitive 2D-laser device has been used to measure the distortion then, a microstructural investigation was done using an optical micrograph, Scanning Electron Microscopy (SEM) coupled with the Electron Dispersive Spectrometer (EDS). The laser-fiber welding process results indicated optimum parameters to prevent distortion when applying welding speed of 2.2 m/min, the power source of 2.5 kW, and the focal position of 3 mm. In MAG welding, test results revealed an increase of longitudinal distortion (bending) from 1.2 mm to 3.6 mm when raising the heat input from 0.3 to 0.472 kJ/mm. When increases welding speed (11 mm/s), angular distortion was approximately 2.1° on the left side and 1.7° on the right side. Microstructural investigations revealed the proportionality between heat input and carbides formations on the grain boundaries of HAZ. They were also the formation of etching pores and some ferrite content (10%) on the weld center.