SURFACE HARDENING METHOD

PURPOSE:To relax fusing treating conditions and to form a hardened layer free from defects, by forming a hard-faced layer of Co-base self-fluxing alloy, a hard-faced layer of Ni-base self-fluxing alloy, and a thermally sprayed layer of Ni-base self-fluxing alloy on a base material in order adjacently to each other and then applying fusing treatment to the thermally sprayed zone. CONSTITUTION:Hard facing by welding is applied by using a Co-base self-fluxing alloy to a deposition surface 3 formed by machining the end of a steel tube 1, to which machining is applied to form a hard-faced layer 5. Subsequently, an Ni-base self-fluxing alloy is welded adjacently to the hard-faced layer 5 to form a hard-faced zone 9, to which machining is applied to form a hard-faced layer 11, a boundary surface 15, and a worked surface 13. Then, an Ni-base self-fluxing alloy is thermally sprayed on the worked surface 13 adjacent to the hard-faced layer 11 to form a thermally sprayed zone 17, and this thermally sprayed zone 17 is subjected to fusing treatment and machining so as to be formed into a thermally sprayed layer 19. By this method, a surface-hardened layer 21 consisting of the hard-faced layers 5, 11, and the thermally sprayed layer 19 can be formed.