SUPPLEMENT TO THE WELDING JOURNAL, NOVEMBER 2016 Sponsored by the American Welding Society and the Welding Research Council Laser Weldability of 21Cr6Ni9Mn Stainless Steel: Part 2 — Weldability Diagrams Fourteen commercial and 20 experimental 2169 alloys, as well as seven other highN and highMn austenitic stainless steels, were welded at different speeds to develop Introduction Solidification cracking is a well-known weldability issue with austenitic stainless steels, with solidification mode and impurity content being important factors. Part 1 of this study (Ref. 1) presented the effects of S and P on solidification cracking under primary austenite solidification, and the relationship between solidification mode chemical composition represented as Creq as a function of Nieq for Type 21Cr-6Ni-9Mn (21-6-9), an alloy also known as Nitronic® 40. Previous research on welding of austenitic stainless steels related solidification cracking to both solidification mode and impurity content by developing weldability diagrams (Refs. 2–6). The weldability diagrams mapped cracking behavior on a plot of impurity content of P plus S vs. Creq/Nieq. In the weldability diagram at low Creq/Nieq, primary austenite solidification occurs and cracking was present unless the combined impurity content was below approximately 0.02 wt-%. As Creq/Nieq increases above some critical value where primary ferrite solidification occurs, WELDING RESEARCH cracking is prevented regardless of impurity content. The weldability diagrams were originally developed for arc welding. Later it was discovered that the rapid solidification conditions of highenergy density welding at high travel speeds in austenitic stainless steels can cause a shift to primary austenite solidification when primary ferrite solidification mode would be expected (Refs. 7– 12). One theory to explain the shift holds that increasing solidification rates increase the undercooling at the solidification front, thereby increasing the stability of the austenite relative to the ferrite (Refs. 4, 13). The shift in solidification behavior also changes the composition ranges that are crack susceptible (Refs. 4, 14), which led to the development of weldability diagrams for pulsed laser welding of 300 series austenitic stainless steels (Refs. 4–6). The weldability diagrams discussed above relate solidification cracking to alloy composition and impurity levels for 300 series stainless steels for both laser and arc welding. It is unlikely that the diagrams developed for 300 series stainless steels are pertinent to solidification cracking of 21-6-9. Given the higher N and Mn content of 21-6-9, the relationship between solidification cracking and chemical composition for 21-6-9 is likely different than predicted by existing weldability diagrams. In the weldability diagrams developed thus far (Refs. 2–6), the effects of S and P have been equally weighted NOVEMBER 2016 / WELDING JOURNAL 409-s weldability diagrams BY S. B. TATE, D. A. JAVERNICK, T. J. LIENERT, AND S. LIU ABSTRACT In this second part of the study, weldability diagrams developed to relate solidification crack susceptibility and chemical composition for laserwelded Type 21Cr6Ni9Mn (2169) stainless steel are presented. Sigmajig testing on 14 commercial 2169 alloys, 20 experimental 2169 alloys, and seven other highN, highMn austenitic stainless steels was used to develop weldability diagrams for solidification crack susceptibility for laser welding of Type 2169. Three travel speeds were used to show the changes in minimum Creq/Nieq for primary ferrite solidification as solidification rate increased with travel speed. Primary austenite solidification was observed below 1.55 Creq/Nieq (Espy equivalents) at 21 mm/s travel speed. At 42 mm/s travel speed, a mix of solidification modes were displayed for alloys from 1.55 to 1.75 Creq/Nieq. Primary ferrite solidification was observed above 1.75 Creq/Nieq at both 42 and 85 mm/s travel speeds. No solidification cracking was observed for alloys with primary ferrite solidification. Variable cracking behavior was found in alloys with primary austenite solidification, but in general, cracking was observed in alloys with greater than 0.02 wt% combined impurity content according to (P + 0.2S). KEYWORDS • Solidification Cracking • Stainless Steel • Weldability Diagrams • Nitronic S. B. TATE (stephen.tate@aksteel.com), formerly a graduate student at the Colorado School of Mines, is with AK Steel Corp., Middletown, Ohio. D. A. JAVERNICK (daj@lanl.gov) and T. J. LIENERT (lienert@lanl.gov) are with the Los Alamos National Laboratory, Los Alamos, N.Mex. S. LIU (sliu@mines.edu) is with the Colorado School of Mines, Golden, Colo.
Welding Journal | November 2016
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