Table 1. Chemical composition (in weight-%) of the studied duplex stainless steel EN 1.4462.

No abstract

The influence of Cr and N additions on the mechanical properties of a Fe-Mn-C steel was investigated. The chemical composition was found to have a pronounced effect on the strain-hardening behavior, due to the strain-induced sequence of the ␥ : : ␣Ј martensitic transformations. It was found that Cr and N suppress this transformation sequence. At Cr levels higher than 7.5 mass pct, no ␣Ј martensite was formed, which led to a pronounced improvement of the ductility. The differences in transformation behavior can be attributed to the change in the intrinsic stacking-fault energy (ISFE): in the compositional range studied, Cr and N additions cause an increase of the ISFE.

Hot torsion tests were performed on a duplex stainless steel (DSS)-type EN1.4462 steel. The temperature was varied in the range from 950 ЊC to 1200 ЊC, while the strain rate was varied from 0.01/s to 2/s. The mean flow stress (MFS) was fitted to the hyperbolic sine function proposed by Sellars and Tegart. An activation energy for plastic deformation of Q HW ϭ 425 kJ/mol was obtained. The high value was explained by the fact that, in addition to the softening of ferrite (␣ ) and austenite (␥ ), there was a decrease in the volume fraction of the high-strength austenite with increasing temperature. For higher values of the Zener-Holomon parameter (Z ), the MFS showed a linear dependence on ln (Z ), which was related to the gradual disappearance of a yield-point-elongation-like effect. This yield-point-elongation-like effect was characterized by a nonstrengthening plateau during the initial stages of plastic deformation. The strain to rupture and the dynamic softening were both found to decrease for higher values of ln (Z ). Therefore, the ductility was directly related to the amount of dynamic softening, i.e., dynamic recrystallization (DRX) of the austenitic phase. At higher strain rates, significant dynamic softening was only observed for temperatures above 1100 ЊC. The strainrate sensitivity (m) was found to vary from 0.13 at 950 ЊC to 0.22 at 1200 ЊC.

The corrosion resistance of spot-welded and induction-heated austenitic stainless steels EN 1.4301 and EN 1.4318 was investigated in 3.5% sodium chloride solution at ambient temperature. In potentiostatic measurements pitting corrosion of spot-welded and induction-heated samples occurs at lower potentials than in the base materials. The corrosion pits initiate on the heat-tinted areas. In immersion tests the surface of the spot welds was not attacked but crevice corrosion was found between the sheets around the spot welds. The compositions and structures of the heat-tinted oxides were investigated by surface spectroscopy. The results indicate the yellow, red and blue oxides to have a double-layered structure with an iron-rich and chromium-depleted outer layer and a less iron and more chromium containing inner layer. A chromium-depleted layer was found in the base material under the yellow heattinted oxide on an induction-heated sample. Significant amounts of copper contamination were found on the spot-weld surface near the weld edge.