Results and discussion Microstructural evolutions The complicated thermal

As illustrated in Fig. 2c, the as-received HSLA steel substrate had elongated grains comprised predominantly of fine pearlite colonies in a ferritic matrix. When this structure was submitted to the cladding process, the maximum temperature reached values above the upper RS 127445 temperature (Ac3) for a brief time and thus, a limited austenitization was possible. Generally, based on the cooling rate experienced upon cooling, the austenite can undergo either an austenite to ferrite transformation or a displacive transformation regime. Then, based on the phases formed during the first thermal cycle, reheating by deposition of the subsequent layer may lead to the formation of polygonal ferrite, tempered martensite, or granular bainite [15]. In the present study, due to the significant difference in the thermal conductivity of the SDSS (at 20 °C, about 14 W·m− 1·K− 1) and HSLA steel (at 20 °C, about 90 W·m− 1·K− 1), large austenite grains were formed during heating in the heat-affected zone (HAZ). Upon cooling, a large quantity of rheumatoid arthritis coarse austenite grains transited to coarse ferrite and the remainder transformed to fine pearlite. However, as is evident in Fig. 2d, because of limited austenitization, even after the second thermal cycle, some untransformed allotriomorphic proeutectoid ferrites remained at the grain boundaries. Evolution of such a microstructure was due to the uncontrolled tempering during the deposition of the second layer [16] and [17].