Screw and manufacturing method thereof

摘要

A first powder and a second powder are mixed to obtain a spray powder. The first powder contains 5 wt% to 9 wt% of boron (B), 9 wt% to 11 wt% of chrome (Cr), 4 wt% to 5 wt% of silicon (Si), and nickel (Ni). The second powder contains a metal element M, the second powder being tungsten (W) and/or molybdenum (Mo). The spray powder has a molar ratio of M and B ranging from 0.75:1 to 1:1. A sprayed film is formed on at least a portion of one of a screw tip, a check ring and a seal ring by spraying the spray powder. A heat-treatment is applied to the sprayed film to form a boride Ni(MxBy).