Machinability of Sprayed Coatings of 13 Cr Stainless Steel, Eutectoid Steel and Aluminum Bronze

Machinability of overlay coatings which are cut with engine lathe is investigated. Five kinds of thermal spray materials are used; 13% chromium stainless steels made in U. S. A and in Japan, eutectoid steel made in U. S. A. and aluminum bronzes made in U. S. A. and in Japan. The materials made in U. S. A. are thermal sprayed with wire flame spraying equipment and those made in Japan sprayed with arc spraying one on the 29mm in diameter mild steel bar for about 2.5mm in thickness. The cutting conditions are as follows: WC type carbide cutting tool, negative back rake angle, 10, 25 and 40m/min for cutting speed, 0.1 mm/rev for feed, 0.1, 0.25 and 0.5mm for depth of cut. Results obtained are as follows; 1) The radial cutting forces are greater than the tangential forces because of the negative back rake angle. 2) Flame splayed coatings of the 13 Cr stainless steel made in U. S. A. had poor machinability region when the cutting speed was faster than 25m/min and the depth of cut was thicker than 0.25mm, however arc sprayed coatings of similar material made in Japan could be cut without any problem inspite of being harder than the ones made in U. S. A.. 3) Flame sprayed eutectoid steel coatings could be cut in the almost cutting conditions though they had the similar hardness value as that of the flame sprayed 13 Cr stainless steel made in U. S. A.. 4) Sprayed aluminum bronze coatings showed good machinability in the all cutting conditions. 5) Because of the layered structure containing pores, the surface roughness of the sprayed coatings after cutting is greater than that of the theoretical value of cutting surface, especially in the cases of 13 Cr stainless steel and eutectoid steel