Method for reuse of steel sheet scrap

Abstract

A recycling method of scrap steel plate that can recycle scrap steel plates including scrap of high-tensile steel plate to produce good quality of cast iron efficiently, while avoiding unnecessary cost increase. In the recycling method, scrap of high-tensile steel plate and scrap of ordinary steel plate are collected together in a batch collecting process and, then, in a preparing process, the scrap steel plates collected are melted and if not less than 0.7 weight % manganese is contained in the hot metal, then the hot metal is prepared so that a sulfur content in the range of 0.02 to 0.2 weight % in the hot metal and rare earth element or misch metal which is two times as much as the sulfur content is added to the hot metal. To obtain spheroidal graphite cast iron, spheroidizing agent (which preferably comprises no rare-earth element but comprises bismuth) is added further to the hot metal after that.

Description

TECHNICAL FIELD [0001] The present invention relates to a recycling method of a scrap steel plate and, more particularly, to a recycling method of a scrap steel plate including scrap of high-tensile steel plate. BACKGROUND ART [0002] In recent years, a high-tensile steel plate (high-tensile plate) has been increasingly employed for a shell body or a shell plate of an automotive vehicle, for the purpose of improvement in collision safety and weight saving of the vehicle. [0003] On the other hand, scrap steel plates made when the steel plate of the automotive vehicle is pressed are generally used as main raw material of cast iron. In the collecting of the scrap steel plates, as a proportion of the scrap of high-tensile steel plate to an existing ordinary steel plate (mild steel plate) increases, the cast iron's properties reduce disadvantageously. [0004] The high-tensile steel plate contains more manganese, phosphorous and chromium than the ordinary steel plate contains. On the other ...

AI Technical Summary

Benefits of technology

[0015] When spheroidizing agent comprises bismuth, the spheroidal graphite can be granulated finely, and as such can provide further enhanced mechanical strengths such as fatigue strength, tensile strength and elongation. The spheroidizing agent usually comprises rare-earth elements. As compared with the spheroidal graphite cast iron produced by mixing bis...

Problems solved by technology

On the other hand, the cast iron has an iron base and a graphite structure, so that when the content of manganese, phosphorous and chromium increases in the cast iron, the cast iron has a hard, brittle structure with cementite (Fe3C), which is called chill, being mixed, around a thin-walled area thereof, thus causing the problem that the cast iron reduces in easiness for casting and in machinability and mechanical nature, so that the cast iron cannot be used for structural parts.

However, the former measure of adding the high-purity pig iron to the scrap steel...

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