Surface melting technique of small diameter stainless steel pipe by means of yttrium aluminium garnet laser

Abstract A new method of surface melting by using a high power yttrium aluminium garnet laser was developed. This method is applicable to a long distance and narrow space, because of the good accessibility of the laser beam through optical fibre. A desensitization of sensitized type 304 stainless steel pipe was demonstrated by using this technique. A melted layer of thickness approximately 200 μm had a very finite solidification structure, which contained approximately 1.5% δ-ferrite. The average chemical composition of this layer was almost the same as that of type 304 stainless steel, and a band of 300 μm thickness under the melted layer underwent solution heat treatment (SHT). As a result of such surface melting, the melted layer exhibited superior resistance to intergranular stress corrosion cracking (IGSCC). Since the SHT layer is highly resistant to IGSCC generally, it may be possible to improve the IGSCC resistance of base metal to a comparatively deep extent (500 μm from the surface) by this technique.