Abstract
Laser heat treatments of metastable austenitic stainless steel AISI 301 are presented aiming to elucidate the relation between heat treatment, transformation and mechanical properties after heat treatment. It is assumed that the observed phase reversion of martensite to austenite is due to a diffusional transformation mechanism governed by nucleation and growth leading to submicron grains. Based on this assumption it is demonstrated that the reverse transformation can be successfully predicted by the proposed model. Subsequently the effect of the heat treatment on the hardness is reviewed. It is shown that the proposed hardness-model, in combination with the proposed isothermal transformation model, is in agreement with the observed behavior. Amongst others it is successfully predicted that the isothermal transformation precedes the recrystallization of the retained austenite and that the post-heat treatment grain size has a large effect on the behavior through the Hall-Petch effect.
Highlights
Laser heat treatment is becoming increasingly adopted in industry for its ability to locally adjust material properties where needed
Isothermal Transformation In 2009 Somani has investigated the relation between alloying content and the possibility of athermal transformation and showed that AISI 301 could revert athermally provided that the heating rate is sufficient [5]
In the current investigation a less stable AISI 301 is investigated and the chromium and nickel equivalents of this grade, in combination with the heating rate, are such that it is expected that athermal transformation is negligible and only isothermal transformation is considered in the model
Summary
Laser heat treatment is becoming increasingly adopted in industry for its ability to locally adjust material properties where needed It offers product designers using austenitic stainless steel the ability to design products with extreme combinations of strength ranging from 200 to 2200 MPa yield stress in a single product. To realize these material property combinations, the material is subjected to a high temperature (over 650 ◦C) for a short time (0 - 100 seconds) and allowed to cool back to room temperature before subsequent processing. During diffuse α to γ transformation, equiaxed finely grained austenite is formed with low dislocation density whereas diffusionless transformation produces lath-shaped austenite with a high dislocation density [2]
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