Abstract
The annealed and welded mechanical properties of titanium-stabilized 18 percent chromium (18Cr) ferritic steels were studied as functions of molybdenum content (0, 1, and 2 percent) and residual levels. The residual elements carbon, nitrogen, manganese, silicon, nickel, copper, and molybdenum were evaluated at low levels typical of virgin-charge, vacuum melt practice and at moderate levels typical of electric-arc furnace melt practice. It was found that the residual elements manganese, silicon, nickel, and copper and excess titanium [defined as total titanium minus that necessary for stabilization of carbon plus nitrogen (C + N)] influenced annealed and welded tensile properties to the greater degree, whereas titanium, (C + N), and molybdenum additions of 1 and 2 percent were more influential on as-welded toughness. Impact transition temperatures of welds were lowered by as much as 100 deg F (55 deg C) in 18Cr alloys by decreasing residual, titanium, and (C + N) levels from typical to very low levels. Titanium was found to be the most potent solid solution strengthening element. Titanium was approximately twice as effective as molybdenum and slightly more effective than the combined effects of other substitutional residual elements. For light-gage applications such as sheet, strip, or welded tubing, a good combination of strength, ductility, and toughness was found with a low (C + N), low-titanium, low-residual analysis at all molybdenum levels studied. For heavier-gage applications such as plate or piping, where ductility and toughness are probably more sensitive to grain size and annealing and welding variables, it is also implied that a low-residual, low-titanium, low (C + N) analysis would be beneficial for a good combination of toughness and ductility.
Published Version
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