Non-conventional laser beam geometries for laser transformation hardening of mild steels

In transformation hardening of steels it is desirable to have a slow heating rate and a rapid cooling rate to achieve full transformation. To date laser transformation hardening has been carried out using circular or rectangular beams which result in rapid heating and cooling. Although the use of different beam intensity distributions within the circular or rectangular laser beams has been studied to improve the process, no other beam geometries have been investigated so far for transformation hardening. This paper presents an investigation into the effects of non conventional laser beam geometries in transformation hardening. Finite element modelling technique has been used to simulate the steady state and transient effects of moving beams in transformation hardening of EN43A steel. The results are compared with experimental data. The work shows that neither of the two commonly used beams; circular and rectangular are optimum beam shapes for transformation hardening. The homogenisation temperatures exceed the melting points for these beam shapes. Triangular forward (Tri F) beam geometry has been shown to produce the best thermal history to achieve better transformation and highest hardness due to slower heating without sacrificing the processing rate and hardening depths, under the same laser power input as that for circular and rectangular beams.