Some aspects in studying corrosion of 25Kh1MF (25Cr1MoW) steel fasteners after aluminizing

The resistance to atmospheric corrosion of 25Kh1MF (25Cr1MoW) steel after aluminizing and thermal improvement has been studied. It is established that the reduced resistance of the aluminized layer to atmospheric corrosion is caused by surface defects such as cracks or pores or by absence of a layer containing the intermetallide Fe3Al. In the aluminized layer containing aluminum-doped ferrite, aluminum nitrides have been found that prevent cold diffusion welding of fasteners’ thread surfaces.

Effects of Hot Band Annealing on the Precipitation of Copper Sulfide in Fe-3%Si Steel

Hot bands of Fe-3%Si steel containing 0.24%Cu were characterized to examine the precipitation of copper sulfides following different heat treatment schedules. It was found that copper sulfides were dominantly in a sphere shape. From 950°C to 1050°C, the precipitates were the complex of copper sulfides and aluminum nitrides. The size of the precipitates decreased and the distribution increased as the temperature increased. However, from 1050°C to 1150°C, the precipitates size increased and the distribution decreased with the rise of temperature. The precipitates were mainly complex copper-manganese sulfides. When the sample was annealed at 1050°C, air cooled to 900°C and boiling water quenched, the most fine and disperse precipitates were obtained. The average size and distribution of the precipitates was 37nm and 2.72μm-2, respectively.