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High‐carbon and high‐chromium alloy steels are prone to pitting and intergranular corrosion, which reduces corrosion resistance. The precipitation behavior of the carbides of high‐carbon and high‐chromium alloy steels is one of the main factors affecting pitting and intergranular corrosion of stainless steel. In this study, 5Cr15MoV stainless steel was heated to 1,200℃ and then cooled by cooling rates varying from 25 to 150°C/min. The precipitation behavior of grain boundary carbides of 5Cr15MoV steel at different cooling rates, and its effect on the corrosion resistance of materials was studied. The results show that the carbides of 5Cr15MoV steel mainly precipitate along the grain boundaries, which leads to the formation of chromium‐depleted zones near the grain boundaries and reduces resistance to intergranular corrosion. It has been found that a higher cooling rate shortens the width of the Cr‐depleted zone near the boundary from 0.871 to 0.569 μm, reduces the Cr‐concentration gradient near the grain boundary from 36.422% to 12.667%, and suppresses the nucleus growth rate of grain boundary carbides. As the cooling rate increases, the corrosion current density decreases from 13.29 to 2.42 μA/cm2. The corrosion rate is the lowest, while the cooling rate is 150°C/min. The corrosion rate decreases from 218.339 to 158.488 mm/a. The phenomenon of intergranular corrosion and pitting corrosion was found to be weakened; and thereby, it is shown that an intensive cooling rate can improve the corrosion resistance of 5Cr15MoV steel.

The microstructure of A357 alloy modified by yttrium (Y) and its modification mechanism was investigated. The results show that under a sand casting condition, there was small or even no solution strengthening effect of Y on the A357 alloy. Y did not change the morphology of eutectic silicon but made it shorter, and Y increased the nucleation cores during its nucleation processes rather than promoting the formation of twinning during the growth processes. The solidification mode of many eutectic silicon phases changed from nucleating on the dendrites to heterogeneous nucleation of eutectic grains in the interdendritic liquid. The number and area of eutectic silicon clusters increased with increasing Y. A bright Al2Si2Y phase appeared even though Y was very low.