Abstract

The peculiarities of process of the pulsed laser re-crystallization of T1 high-speed steel surfase in the ultrasonic field were studyed in this work. The changes of structural-and-strained condition of the surfase layers within the laser-ultrasonic influence and the following bulk tempering of crystallized melt were analysed. The YAG:Nd - solid-state laser with the pulse duration of ~ 1 ms and the energy per pulse up to. 300 J was used as the laser source. The ultrasonic vibrations with the frequency of 22 kHz and the amplitude up-to 10 μm were coupled into the laser melt continuously along or across the direction of laser influence. The one-hour bulk tempering of crystallized melt was realized in the temperature interval of 450-650 °C. In addition to the results [1], which show the influence of ultrasound coupling-in scheme on the change of proceeding speed of the heat-and-mass-transfer processes in the bath of laser melt, it was shown the distinctive peculiarity of longitudinal scheme of the ultrasound coupling-in during the rapid crystallization of laser melt in the formation of texture with the isolated [100] crystallographic direction. The following bulk tempering leads to the some more greater development of given texture with the maximum within 600 °C. It was noted the increase of tension residual stresses within the rapid crystallization of laser melt in the ultrasonic field, that apparently is the oonsequenoe of ultrasound influence on the process development of peritectic transformation of the δ-ferrite in the austenite. The decay of oversaturated solid solution by the following bulk tempering leads to the formation in the surfase layers of pressing residual stresses, which reach the greatest value in case, when the pulsed laser re-crystallization proceeds within the simultaneous coupling-in of ultrasonic vibrations into the melt in the longitudinal scheme. Side by side with the earlier obtained results [2] within the bulk tempering of oversaturated solid solutions the obviously expressed effect of increase of the lattice parameter of isolated basic M6C carbide phase up to 1.122 nm was fixed, that indicates on the considerable increase of tungsten portion in the composition of this carbide. For this the influence of ultrasonic vibrations is not affected on the observed conformity with a law.

© 1996 IEEE