Fiber Laser Welding of SAF 2507 Duplex Stainless Steel
Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
Duplex stainless steels are very special kind of material which contains equal amount of ferrite and austenite phases. This brings to it high mechanical strength and corrosion resistance as a combined structure of austenitic and ferritic steels. However, without providing suitable conditions, their mechanical and anti corrosive properties is affected during the welding processes. Differ from the austenitic steels which can be laser welded autogenously, duplex grades gives better results in austenite promotion by welding with nitrogen and nickel contained filler wire. Moreover, addition of noble element-nitrogen mixture gas is also improving the austenite phase ratio. In this work, third generation SAF 2507 duplex stainless was welded under autogenous laser and cold wire assisted laser processes. The investigations can be divided into 3 main parts. First of all, the contribution of wire assisted laser process to the weld quality is examined and found from the results that the addition of filling wire promotes 41% of austenite phase over the total volume. This number is maximum 31% in autogenously laser welded samples. Secondly, the effect of laser scanner utilization was tested on wire assisted laser welding. By comparing to the literature works, the austenite phase growth increase 11% with respect to the autogenously laser welded ones which is a quite promising result. Finally and most importantly the cooling rate tendency is examined. To perform this, numerical calculations of heat flow had been done and cooling times from 2187⁰C to 940⁰C were calculated for each sample. With respect to cooling times, it was concluded that the thicker plate cools faster than the thinner one. Moreover, addition of a filler wire to the system contributes for tuning the microstructure of the weld in the name of austenite promotion and refine fusion zone structures by comparing to the autogenously welded samples.
Place, publisher, year, edition, pages
2012. , 47 p.
Technology, Duplex steel, laser welding, cold wire, heat transfer, cooling rate
IdentifiersURN: urn:nbn:se:ltu:diva-58354Local ID: ef0e64b5-5d62-430c-8cf9-c8deaa8f716aOAI: oai:DiVA.org:ltu-58354DiVA: diva2:1031742
Subject / course
Student thesis, at least 30 credits
Materials Engineering, master's level
Validerat; 20120621 (anonymous)2016-10-042016-10-04Bibliographically approved