1991 Volume 9 Issue 1 Pages 111-116
A series of Fe-Cr-Ni ternary alloys were surface-treated by laser beam at four traveling velocities and an investigation was carried out to determine the effect of rapid solidification on the microstructures and ferrite content of laser surface-treated alloys. The cooling rates in laser surface-treated alloys were estimated to be 1.9×103K/s-2×105K/s by cell size. It was found that the variation of ferrite content with increasing cooling rate could be categorized into five types. The first one was that ferrite content was always 0% and did not change with cooling rate. The second one was that ferrite content decreases with increasing cooling rate, and this was corresponding to the change in solidification mode from primary austenite to full austenite or from primary ferrite to massive solidification. The third one was that ferrite content increases with increasing cooling rate, as for this type it was found that solidification mode was always fully ferritic while solid state transformation after solidification was suppressed. The fourth one was that ferrite content first increased and then decreased with increasing cooling rate. TIG weld metal of this type solidifyed in form of primary ferrite and solid state transformation from ferrite to austenite occured during cooling, but in the laser surface treated specimen alloy solidifyed in form of the rod-like eutectic and no solid state transformation occured, so ferrite content increased a little. When cooling rate became larger than the critical cooling rate, solidification mode changed to the massive solidification and ferrite content decreased. The last one was that ferrite content was always 100% and did not vary with cooling rate. From these results it can be said that it is necessary to modify the Schaeffler diagram for rapid solidification process. So in present study the ferrite content in all specimens surface-treated by laser beam were measured and modified Schaeffler diagarams for four different cooling rates were given. By analysis of these data, the experimental formula to estimate ferrite line in the modified Schaef ler diagram for any cooling rate was presentated.
