鋼中に生成する硫化物系非金属介在物の挙動について

Abstract

The effects of varied elements on the behaviors of sulfides and relative nonmetallic inclusions in a resulfurized steel were morphologically investigated using small scale ingots, whose compositions were based on 0.1%C killed steels with and without Cr and/or Mo.At the same time the effects of deoxidizing conditions before solidification were studied, e. g. of various grades of Al killed conditions and vacuum melting process.The morphological observation of sulfides etc.was mainly carried out with the microscope; in addition the results were certified by the qualification with the electron probe X-ray micro-analyser and the identification of electrolyzed residues of inclusions by the X-ray diffraction method.The obtained results were as follows:1. In the case of low carbon steels, the increased S content makes FeS coalesce and float up without forming a network, while the increased C content easily forms an FeS network on the primary grain boundaries.2. The increased Mo content up to 2% has a tendency to change the FeS phase to MnS when precipitated in primary crystals, although there exists no increased concentration of Mo in the sulfides.3. In the case of Cr-containing steels, the studied morphological aspects of sulfides and selenides were notably affected by the deoxidizing conditions before solidified. Those phenomena can presumably be interpreted from the relations between the natures of deoxidation products and the nucleation of sulfides.4. Many kinds of sulfide and selenide inclusions occurring in various conditions were analyzed qualitatively with respect to the effect of Mo and also to the hot plasticity. A relation was observed between the compositions and crystal structures of sulfides and their plasticities also in accord with the Mo contents.