Welded 22 Cr 5 Ni duplex stainless steel is often used for chloride-containing environments and sour service applications. Chloride stress corrosion cracking (CSCC) during service poses a threat to the service life of the weldment. Yield strength and resistance to CSCC are considered to depend on the weld metal ferrite content, which is variously required to be 30 to 60%, 30 to 70 ferrite number, 35 to 75%

From a metallurgical point of view, DSS generally requires solidification as essentially 100% ferrite, followed by the formation of austenite only in the solid-state. This solidification mode, as depicted in Fig. 1a is considered to be responsible for both high yield strength and resistance to CSCC. The WRC-1992 diagram (Fig. 1b) indicates 100% ferrite solidification at as low as 20 ferrite number (about 14% ferrite).

Fig. 1 an Elevated temperature region of a pseudo-binary phase diagram for DSS. The shaded region represents the range for commercial alloys. Source: (Ref: 1). b WRC-1992 diagram, including solidification mode boundaries. Source:( Ref: 2)

In a recent work carried out by Nanavati, Kotecki & Soman (Ref: 3)  in collaboration with a filler metal manufacturer to investigate the minimum ferrite content to obtain the required minimum weld metal yield strength and resistance to CSCC. In this study, 22 Cr 5 Ni weldments with weld metal ferrite content in the range of 14% to 30%, or 20 to 40 ferrite number, obtained by increasing the filler metal nickel content above the normal 9%, have been prepared and investigated. It was found that yield strength and tensile strength requirements of base metal and filler metal classifications were exceeded at all ferrite levels investigated and that no CSCC was observed after 1000-h exposure in the ASTMG 123 boiling 25% sodium chloride test.

Ref: 1 Lippold JC, Kotecki DJ (2005) Welding metallurgy and weldability of stainless steels. Wiley, Hoboken, pp 234–262.

Ref: 2 Kotecki DJ, Siewert TA (1992) WRC-1992 constitution diagram for stainless steel weld metals: a modification of the WRC-1988 diagram. Weld J 71(5):171-s–178-s American Welding Society, Miami

Ref: 3 P. K. Nanavati & D. J. Kotecki & Sanjay N. Soman (2019), Effect of weld metal ferrite content on mechanical properties and stress corrosion cracking resistance in 22 Cr 5 Ni duplex stainless steel,  Welding in the World, https://doi.org/10.1007/s40194-019-00708-1. Published online 13 February 2019

Print:- Welding in the World 63 (3), 793-805