STEREOLOGICAL ALTERATIONS OF NONMETALLIC INCLUSIONS, FRACTURE MORPHOLOGY AND ALLOY IMPACT STRENGTH AFTER BLOWING ACTIVE POWDERS INTO LIQUID STEEL

Reported here is an analysis of effectiveness of the process of steel refining by the method of injecting active powders. Apart from a brief assessment of the technological aspect, attention is focused principally on changes in morphology and stereological characteristics of the nonmetallic inclusions (NMI). As a result, there are the only appreciable changes due to this refining process. Since, as a consequence, the impact strength of the material is considerably enhanced, the curve of alloy transition to:the brittle state is defined by means of parameters describing the set of inclusions. The model obtained in this way describes change in plastic properties against numerical characteristics of the nonmetallic phase for any arbitrary temperature. This enables a quantitative assessment-to be made of such refining effects as reduction in number and size of inclusions and differentiation in size of these particles. The consequences of these changes are, respectively: linear improvement in impact strength with temperature increase; exponential:rise in impact strength, particularly during work at low temperatures; slowed rate of impact strength decrease at positive temperatures, and increase at low temperatures. The analytical description presented can be an effective tool both for quantitative evaluation of steel refining results and for analysis of the role of NMI in the decohesion process.