Surface hardening by inducing phase transformations through the heating effect of a laser beam was one of the first laser based fabrication methods to be commercialised, in the early 1970s. However...

Laser Transformation Hardening

A study on the surface treatment of “Calmax” tool steel by a plasma transferred arc (PTA) process

Relationship between processing parameters, alloy atom diffusion distance and surface hardness in laser hardening of tool steel

A PC-based system for procedure developement in laser transformation hardening

Processing parameters in Laser Transformation Hardening have a great effect on microstructures produced via phase transformations. In order to establish the effects for a wide range of processing parameters a large amount of specimens has to be processed and examined by microstructural analysis from polished and etched samples. The process is time consuming and therefore the number of processed samples is often minimized. In the presented study polished surfaces of low alloy steel and plain carbon steel samples have been hardened in an inert gas atmosphere using a HPDL (High Power Diode Laser) beam. Surface relief formed during phase transformations has been photographed using DIC (Differential Interference Contrast) imaging. The effect of processing parameters on austenitization, microstructure and extent of martensitic transformation has been investigated. The hardness of each sample is measured. Experiments show that DIC imaging is a rapid and illustrative tool for microstructural analysis of iron-based material processing.Processing parameters in Laser Transformation Hardening have a great effect on microstructures produced via phase transformations. In order to establish the effects for a wide range of processing parameters a large amount of specimens has to be processed and examined by microstructural analysis from polished and etched samples. The process is time consuming and therefore the number of processed samples is often minimized. In the presented study polished surfaces of low alloy steel and plain carbon steel samples have been hardened in an inert gas atmosphere using a HPDL (High Power Diode Laser) beam. Surface relief formed during phase transformations has been photographed using DIC (Differential Interference Contrast) imaging. The effect of processing parameters on austenitization, microstructure and extent of martensitic transformation has been investigated. The hardness of each sample is measured. Experiments show that DIC imaging is a rapid and illustrative tool for microstructural analysis of iron-base...

Use of DIC imaging in examining phase transformations in diode laser surface hardening

The principles of laser transformation hardening were investigated using a low alloy special steel having a microstructure of pearlite and proeutectoid ferrite. Temperature fields and phase transformations were modelled. Particular attention was paid to increases of the Ac1 and Ac3 transformation temperatures owing to the rapid thermal cycles produced by laser heating. Dissolution of proeutectoid ferrite is shown to control the formation of a homogeneous hardened case. Experimental data are in good agreement with the predictions of the model. A diagram was constructed which describes the case geometry and microstructure in terms of the process variables and is an aid to optimising practical processing parameters. The models are flexible and may be used for laser transformation hardening of other ferrous alloys having inhomogeneous microstructures.MST/1606

M. Paju

Papers

Laser transformation hardening of low alloy hypoeutectoid steel