TWI Industrial Member Report Summary 682/1999
B J Ginn and T G Gooch
Nitrogen is a major alloying element in ferritic-austenitic stainless steels as it makes significant contributions to strength, corrosion resistance, phase balance and microstructural stability. Control of nitrogen during welding is therefore essential to achieve optimum weldment properties. However, nitrogen can be lost from weld metal, especially in tungsten inert gas (TIG) welds made using argon shielding gas, and the addition of nitrogen to the shielding gas to counter this effect has been variously propounded. At the same time, weld metal porosity can occur in welds made by a range of arc processes and this is generally considered to be largely a result of nitrogen evolution from the solidifying weld metal. Work was therefore carried out to examine the dependence of weld metal porosity on deposit nitrogen level using the TIG process with a range of shielding gases and welding conditions to produce joints in a representative superduplex steel.
- To evaluate the use of high nitrogen shielding gas relative to the incidence of porosity in duplex stainless steel TIG weld metals.