Abstract
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.
Highlights
IntroductionEmerging technologies in various manufacturing applications (e.g., construction of facilities, piping systems of nuclear power plants, and automotive power plants) require and could significantly benefit from joining different steel grades
Emerging technologies in various manufacturing applications require and could significantly benefit from joining different steel grades
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 retained austenite austenite (RA) (10%), which developed at the end of the transformation of S960QC
Summary
Emerging technologies in various manufacturing applications (e.g., construction of facilities, piping systems of nuclear power plants, and automotive power plants) require and could significantly benefit from joining different steel grades. Welding dissimilar materials is not without its difficulties, and this challenge has caused researchers to explore new materials. The potential advantages of these new materials are that they could be environmentally beneficial, have lower manufacturing and maintenance costs, and their thermal properties may make them easier to use in hot or cold climates [1,2,3]. In the construction of many structures such as vehicles (i.e, automobiles), reducing the weight has a significant impact on durability, effectiveness, and operating costs. Improved characteristics in the weld joint can lead to the beneficial outcomes of lower weight and increased rigidity. In dissimilar welding of high-strength steels (HSS), knowledge of the correlation between heat input data and alloy elements formed in the heat-affected zone (HAZ) may enable
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