W-Ni-Fe중합금에서 칼슘이나 란타늄 첨가에 따른 황과 인에 의한 취화의 제거

Abstract

The impact energy of 93W-4. 9Ni-2. 1Fe(wt %) alloy decreases sharply with the concentration of sulfur added up to 200 ppm even after heat-treatment at 1150℃ in N₂ atmosphere and waterquenching. The result shows definitively that the S present at the level of a few tens ppm causes an embrittlemext of this alloy. The structure and the composition of the fracture surface are consistent with the previous suggestion that the embrittlement arises from S segregation at the grain-matrix interface. With the addition of Ca or La to the S doped alloy the impact energy increases to that of the alloy without S. The fracture structure and the S concentration measured at the interfaces also show that Ca or La addition suppresses effectively the S segregation at the grain-matrix interface by forming S containing Ca or La compounds. When Ca is added to the alloy to which no S was deliberately added (with about 19 ppm P and 1 ppm S), the impact energy does not vary with the cooling rate after the heat-treatment at 1150℃, and is unaffected by additional heat-treatment at 600℃. It appears that P segregation and its embrittling effect are also reduced by forming P containing Ca compounds. The variation of the impact energy of this alloy with the amount of S or P in the raw material powder or with the heat-treatment condition can therefore be substantially reduced by adding Ca or La.