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.

Background: Structure and properties of welded joints of low-alloy thermomechanically processed (09G2FB) and quenched and tempered shipbuilding steels (10XN2MD, 08XN3MD, and 12XN3MF), welded with manual metal arc welding (MMA) and submerged arc welding (SAW), were studied. Methods: Effects of specific energy input on the microstructure, mechanical properties, and impact energy of the heat-affected zone (HAZ) have been investigated, and probable reasons for crack formation in welded joints have been found.

Experiments were carried out to determine the properties of the welded joints in 8 mm thick high-strength steels produced by quenching and tempering and thermomechanical rolling with accelerated cooling (tensile strength 821-835 MPa). The dependence of the strength, elongation, hardness, impact energy and crack opening displacement on the heat input in the range 1.0 -0.7 kJ mm 21 was determined. The results show that the dependence of the strength of the welded joints decreases and that of the elongation increases. The heat input has only a slight effect on the impact energy and crack opening displacement in the heat-affected zone.

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.

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 t8/5 (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 t8/5 (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).