Laser transformation hardening

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, its industrial acceptance has been limited, in comparison with other laser based processes such as cutting, welding, and marking. The reasons lie in a lack of knowledge concerning the process, and the large number of more familiar surface hardening processes that are commercially available. Within the last five years important developments have taken place in the technology of laser sources, optics, and software, which now enable the process to be viewed more favourably against competing processes. More suitable laser sources, such as multikilowatt Nd:YAG and diode lasers, and beam delivery optics have been developed. Sophisticated system control software now enables mathematical process models to be integrated into production systems. Computer aided design (CAD) software enables products to be redesigned, and life cycle performance and process comparisons can be evaluated rapidly. Thus automated laser hardening systems are now becoming available, suitable for treating components of widely varying size and shape. The requirements of codes for hardening can be met in a wide range of steels and cast irons. This review summarises the state of the art in the process, industrial practice, properties of hardened materials, and the software now available, and describes the areas in which work is needed to extend the industrial application of the process.