Fig. 5 — Weldability diagram for 42 mm/s (100 in./min) with impurity content as a function of Creq/Nieq. Note Nieq was calculated assuming 10% N loss. A is primary austenite solidification, F primary ferrite solidification, and D dualmode solidification. Other indicates non2169 type. mercial 21-6-9 alloy, 10, showed cracking at 42 mm/s travel speed as the solidification mode had shifted to primary austenite. However, other 21-6-9 alloys (both experimental and commercial) with similar impurity levels that also had primary austenite solidification showed no cracking. Alloys with impurity contents less than 0.02 wt-% or primary ferrite solidification were crack free. Figure 6 shows the weldability diagram developed for 85 mm/s. The Creq/Nieq of 1.75 separating primary austenite from primary ferrite solidification has not shifted as the travel speed was increased from 42 to 85 mm/s. At 85 mm/s, all but one of the alloys in the range of 1.55 to 1.75 Creq/Nieq exhibit primary austenite solidification compared to the variation of solidification modes in that Creq/Nieq range at 42 mm/s travel speed. The cracking behaviors observed are similar to those found at 42 mm/s, with no cracking in alloys with primary ferrite solidification, and the majority of the alloys with Creq/Nieq less than 1.75 and impurity contents of 0.02 wt-% and greater displaying cracking. One alloy, 30, of 18Cr-2Ni- 12Mn type, at Creq/Nieq of 1.92, showed primary austenite solidification and minor cracking, and again, because the focus of this work was Type 21-6-9, the cracking demarcation was drawn discounting the Alloy 30 point at 85 mm/s. Again, of the commercial 21-6-9 alloys, only Alloy 10 showed cracking. The other eight 21- 6-9 alloys with primary austenite solidification mode showed no cracking even at similar impurity levels. Also similar to the observations at 42 mm/s, at the highest travel speed, there was still variation in solidification mode at constant Creq/Nieq where the vertical crack demarcation line is located. Alloy 59 showed dual solidification modes with high impurity content and Creq/Nieq of 1.79 while primary ferrite solidification was observed in several alloys at lower impurity content. Uncertainty values are not presented on the weldability diagrams shown in Figs. 4–6 because the plots become difficult to interpret with the large number of error bars. Uncertainty of the chemical analysis was calculated using one standard deviation of the analysis for each element based on the three measurements of each alloy for chemical composition. With the average standard deviation for each element from all the alloys, the uncertainty of the Cr and Ni equivalents were calculated. The maximum and minimum equivalents calculated gave an uncertainty of ±0.019 Creq/Nieq. The uncertainty calculated for the impurity content is ±0.0015 wt-% P + 0.2S. Graphically on the plots, these uncertainty values would be approximately twice the size of the symbols plotted. Given the uncertainty values calculated, the results presented for the three weldability diagrams are considered reasonable. To summarize the weldability diagram results, cracking is expected when both impurity contents (P + 0.2S) are greater than 0.02 wt-% and primary austenite solidification occurs for all travel speeds. At 21 mm/s travel speed, a minimum Creq/Nieq of 1.55 for primary ferrite solidification is required. As travel speed increases to 42 and 85 mm/s, the minimum Creq/Nieq for primary ferrite solidification increases to approximately 1.75. Similar to previous weldability diagrams (Refs. 3, 5), the horizontal line separating cracking and crack-free regions in the diagram is drawn flat with no slope, indicating there is no change in minimum impurity content for any alloy with primary austenite solidification. The variability in cracking in the impurity content range of 0.02–0.03 wt-% discussed previously may indicate that a broader line or uncertainty bands may be appropriate on the horizontal portion of the cracking boundary. No ‘knee’ or curvature was included in the cracking line, with both the vertical and horizontal pieces connecting at a common point. Given the lack of data points in the region that would contain the curvature and the uncertainty associated with the data points of the diagrams, no curvature was included in the cracking boundary. Unlike some previously developed diagrams, the vertical cracking boundary was drawn at a slight inclination to indicate that solidification mode may WELDING RESEARCH 414-s WELDING JOURNAL / NOVEMBER 2016, VOL. 95 Fig. 6 — Weldability diagram for 85 mm/s with impurity content as a function of Creq/Nieq. Note Nieq was calculated assuming 10% N loss. A is primary austenite solidification, F primary ferrite solidification, and D dualmode solidification. Other indicates non2169 type.
Welding Journal | November 2016
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