Centre De Recherches Metallurgiques-centrum Voor Research in De

Centre De Recherches Metallurgiques

Yves Jean Respen

Mario Economopoulos

Marios Economopoulos

Paul Andre Cosse

Stephane H Wilmotte

The elastic limit and breaking load of steel sections are improved by a process of surface quenching and self-tempering comprising a cooling stage followed by rapid cooling which is interrupted to allow the quenched surface layer of the section to be tempered by heat from non-quenched inner portions of the section. The rapid cooling is succeeded by a slow cooling.

Process for improving the quality of steel sections

At the outlet of the finishing stand of a rolling mill, a cooling apparatus is arranged to surface quench only the outer layer of the flat face of a steel section by a cooling fluid. The cooling conditions are adjusted so that, at the outlet of the cooling zone, the unquenched parts of the section are at a temperature still sufficiently high to temper the quenched face, and so that the austenite is transformed into ferrite and carbides in the unquenched parts of the section.

Apparatus for improving the quality of steel sections

In the rolling mill the temperature of the product is reduced to between Ac.sub.3 and Ac.sub.3 + 150.degree. C before it enters the finishing stands. The product emerging from the finishing stands is quenched to provide a surface layer of martensite and/or bainite. Subsequently the heat of the core of the product is allowed to raise the temperature of the surface layer to between 450.degree. and 750.degree. C, so that the quenched layer is tempered.

Producing rolled steel products

Steel rod or bar at the exit of the finishing stand of a hot rolling mill is superficially quenched, so that the surface layer of the rod or bar is given a bainitic or martensitic structure. Immediately after quenching, the core of the rod or bar is at about 850.degree. C and, therefore, still austenitic. Subsequent air cooling allows the austenite to transform to ferrite and carbides, while the surface layer is tempered by the heat transferred to it from the core.

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Herstal, Belgium

Yves Jean Respen