摘要：Experiments were performed to perfect a process for the CO 2 laser welding of an ASTMA335 grade P22 steel for pipes operating at high temperatures. The corresponding conventional welding techniques require a rather complicated schedule that includes both pre- and post- heating to prevent cracks and martensite formations in melted and heat affected areas, and has a mean duration of several hours. Qualification of the laser-welded joints was performed according to section IX of the ASME standards. The following results were obtained:- defect-free joints without any form of preheating;- a post-weld subcriticai annealing process able to reduce the hardness of the melted area to 280 HVin a few minutes (the hardness of the as- welded melted zone is around 400 HV); a similar process was applied at the end of the weld pass by modulating the power density delivered to the welded joint.Correct temperature distribution during annealing was ensured by means of a control system using a two-colour optical pyrometer focussed on the joint surface, and computerised checking of the incident laser power.
