Duplex & Super Duplex Stainless Steel TIG Welding Rods
A relatively modern group of stainless engineering steels is the Duplex series of alloys. These material consist of approximately 50:50 austenite and ferrite phases in the matrix, hence their descriptive dual-phase name.
The dual phase microstructure is achieved by using lower nickel content in the range 1.5 to around 6 wt % but maintaining chromium content in the 21-25 wt % range .Nitrogen is typically 0.2wt % (0.1-0.3 wt % ) and there are minor additions of other useful elements including molybdenum. Carbon content is typically <0.03wt % in order to minimise loss of chromium through the formation of chromium carbide precipitates, especially along grain boundaries under various temperature cycles.
The filler metal nickel content is held at a higher level than the equivalent base alloy in order to control the ferrite level balance within the weld deposit.
Consequently these materials have high tensile strength and corrosion resistance which offsets stress corrosion cracking and pitting corrosion. The alloys in the category have high value PREN numbers (pitting resistance).
The common solid welding wire filler metals are ER2209 , ER2307 & ER2553 & ER2594 and their coated electrode and tubular wire equivalents.
Duplex stainless alloys have good weldability but carefully selected procedures are necessary in order to produce sound welded joints and for maximum corrosion resistant properties, so the stress corrosion cracking and pitting corrosion susceptibility is nullified.