Effect of Chemical Composition on Susceptibility to Weld Solidification Cracking in Austenitic Weld Metal
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AUSTENITIC metals such as stainless steels and Ni-based alloys are highly susceptible to weld hot cracking, such as solidification cracking.[1,2] These metals have been often welded with other metals such as low alloy steels, carbon steel, and so on. When the dissimilar welding is applied, the Schaeffler diagram,[3] which consists of the chromium equivalent Creq (= pct Cr + pct Mo + 1.5 9 pct Si + 0.5 9 pct Nb) and nickel equivalent Nieq (= pct Ni + 30 9 pct C + 0.5 9 pct Mn), is often used to estimate the microstructure and the brittleness based on the weld metal compositions. The austenite single-phase region in the diagram has high hot cracking susceptibility, especially solidification cracking, and thus welding in this region is often avoided.[4] Solidification cracking occurs within the mushy zone, and the susceptibility depends on the chemical composition, cooling rate, constraint conditions, and so forth. The influence of the chemical elements on the susceptibility of austenitic metals has been investigated.[5–10] Elements
KOTA KADOI is with the Joining and Welding Research Institute, Osaka University, Osaka, 567-0047, Japan. Contact e-mail: [email protected] KENJI SHINOZAKI is with the Graduate School of Engineering, Hiroshima University, Hiroshima, 739-8527, Japan. Manuscript submitted April 3, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
with low partition coefficients, such as sulfur and phosphorous, are known to enhance the susceptibility owing to a low liquidus temperature corresponding to segregation at the end of solidification. Thus, control of the chemical composition is usually applied, for example, a total content of sulfur and phosphorous of less than 100 ppm, to prevent cracking.[5,6] A Creq/Nieq ratio of > 1.48 has also been proposed for formation of around 5 pct of the ferrite phase for higher solubility of the elements.[7,8] Niobium, silicon, boron, and titanium are also known to increase the susceptibility because of their low partition coefficients.[9,10] In the future, it will become difficult to avoid welding in the austenite single-phase region with increasing application of dissimilar welds. Therefore, prevention of cracking is required based on the knowledge of the relationship between the chemical composition in the region and the solidification cracking susceptibility. However, past studies investigating the influence of elements such as sulfur, phosphorous, and niobium on the susceptibility have been carried out with fixed or specific contents of iron, chromium, and nickel. Thus, the effect of these elements on the susceptibility with changing constituent composition of the austenite phase in the austenite single-phase region, such as the distribution of the susceptibility in Schaeffler diagram, is still not clear. The aim of this work was to systematically and quantitatively investigate the influence of the chemical composition, especially the niobium content, Creq, and
molten pool.[11,12] In this study, the solidification cracking susceptibility was examined within the weld metal. Thus
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