Thomas process

Thomas process was designated after the British Metallurgen Sidney Thomas (1850-1885) and designates a procedure for steelmaking. In such a way provided steel is called Thomas steel.


With the Thomas process (also “basic Windfrischverfahren “mentioned) it concerned a blowing or a Windfrischverfahren in such a way specified, with which by soil nozzles of the converter (“Thomas pear “) air was blown into the liquid pig iron.

The oxidation process, which lowers the carbon portion (“the carbon elimination “), supplied in this procedure enough warmth, in order to keep the steel liquid, an external heat supply was in the converters therefore not necessarily.

“The Thomas pear “was brick-lined with a basic working dolomite rock or dolomite tar mixture and was suitable particularly for melting phosphorus-rich iron ores.

The phosphorus oxidized to phosphorus pentaoxide with the limestone attached as an addition one clinker (“basic slag “) and came finely husbands under the designation “Thomas flour “as into the trade.

Thomas steel served for the manufacturing of rails, profile iron, and sheet metals. Nearly all structural steelworks of the 1950er and 1960er are built from this steel.

Disadvantages of the procedure

It had the wind freshness the large metallurgical disadvantage that inevitably large quantities of nitrogen (air consists of approximately 78% of nitrogen) and hydrogen were solved in the steel. In addition, often, phosphorus-rich iron ores in the basic Bessemer steel converter were blown. Phosphorus is one of the most dangerous steel companions. It lowers the tenacity, in particular at low temperatures, strongly. Nitrogen forms hard, brittle nitrides, which make likewise the steel less tough in the steel with iron and other alloying elements. In addition, it comes in the course of the years to additional nitrogen embrittlement in the steel. Thomas steels are very badly weldable. By the relative to high hydrogen content, it comes very easily the feared cold crack with weldings at old structural steelworks is therefore required highest caution. If at all they should be welded only with welding-rod materials of high tenacity. If necessary an expert is to be consulted.

The center of the sixties was stopped in the Federal Republic of Germany, since the beginning of the eighties in most countries, production by Thomas steel.

The Thomas process was replaced by the Linz-Donawitz-process.

Into the criticism Thomas steel came in November 2005, as in the cathedral country 82 Hochspannungsmasten in unusually strong snow and storm under the several times increased ice loading (~18.9 kg/m) bent. The operators, above all the RWE, considered the masts however not increased brittle failure-endangered. The RWE argued that with this natural catastrophe not only old masts from Thomas steel bent but also more modern masts from more modern materials. After a current appraisal of the Federal Institution for material research and – examination, which was given by the federal net agency in order, were the embrittlements with Thomas steel high voltage masts however a “substantial cause” for the wide power failures in the cathedral country. Thomas steel is not used already since the end of the 1960er years no more for Hochspannungsmasten, however today also still masts from years of construction are 1940 ago in the use.

See also: Bessemer converter