Tempering of steel during laser treatment

Abstract

This study concentrates on the annealing effects of a laser-treated area by a successive laser pass in a plain carbon, a chromium, and a tungsten steel. Transmission electron microscopy (TEM), optical microscopy (OM), and wear and hardness measurements revealed substantial effects on the properties and microstructure of the plain carbon and tungsten steel which have a partly martensitic cellular structure after the first laser treatment. Close to the melt zone, martensite was again formed, whereas further away, nucleation of carbides was observed. The hardness increased in the former area and decreased in the latter. An analytical model sustained that the softening is due to carbon diffusion and martensite tempering. The softer zone in the tungsten steel exhibited a decrease of wear rate relative to the not-annealed zone in contrast to the plain carbon steel. Besides some diffusion, no annealing effects were found in the chromium steel which possessed an austenitic cellular structure after the first laser treatment.

Surface microrelief and hardness of laser hardened and ultrasonically peened AISI D2 tool steel

“…Microhardness (7.8 GPa) obtained after combined LSH + UIT process is higher than that observed after LSH of AISI H13 steel (5.3 GPa) [49] or comparable with that of AISI D6 steel (~6-8 GPa) [50]. A couple of works were dwelt with the laser melting treatment of chromium carbon steel [51] and tool steel [9]. The former steel was reported to have unchanged hardness after LMT, but the latter one was conversely hardened.…”

Study on the softening in overlapping zone by laser-overlapping scanning surface hardening for carbon and alloyed steel

“…For the practical application of large areas laser quenching, softening in overlapping zone is a problem that has to be solved. Recently, Tani et al [9,10] presents an original tempering model for the prediction of the hardness reduction in multiple laser paths. The reaustenitization of the martensite and the non-constant tempering temperature are considered during the modeling of tempering.…”

Functionally graded materials produced by laser cladding

“…Examples of laser surface processing techniques include laser transformation [2], surface melting (LSM) [3], laser surface alloying (LSA) [4± 6] and laser surface cladding (LSC) [7]. In the case of LSM, the surface performance of the Al-alloy substrate is modi®ed mainly by the homogenization and re®nement of the microstructure.…”