The effect of laser hardening on the operation resistance of rolls of multi-roll mills and the quality of the rolling strip

Abstract

The results of experimental studies of the process of laser hardening of rolls of multi-roll mills during linear and spiral hardening of samples from Kh9VMFSh steel are presented. It was found that during linear laser treatment, the depth of the hardened layer significantly depends on the power of laser radiation and the speed of translational motion of samples; at the same time, it weakly depends on the diameter of the laser beam. Corresponding graphs, which are more convenient for practical use for selection of technological modes of laser processing, have been built. With spiral laser hardening, the surface of axisymmetric parts is subjected to cyclic heating, the number of cycles of which depends on the speed of translational motion and rotation speed. It is established that decrease of the temperature of the surface layers of the part heated by laser radiation practically does not occur due to thermal conductivity at a sufficiently high value of the rotation speed. It is shown that increase of the rotation speed of samples from 1,000 to 10,000 min-1 leads to increase of the depth of the hardened layer from 0.72 to 1.60 mm with a slight enlargement of hardness of the surface layers, while the depth of the hardened layer significantly depends on the speed of translational motion of the samples and their diameter; it should be taken into account when developing technological modes of laser hardening. Pilot-industrial tests of working rolls during rolling of the strip with 0.012×200 mm cross-section, made from L63 brass, showed that the surface purity of the rolled strip increased from the 7 th to the 8 th class of roughness, and the number of breaks decreased by 1.5-1.8 times. When rolling a strip of nickel NP-2 at a 20-roll mill 300, it was found that consumption of rolls that have been subjected to laser processing is 2 times less than consumption of volume-hardened rolls, while transverse thickness has decreased to ± 3 % (compared with ± 5 % during rolling in volume-hardened rolls).