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Processing and production of steel

Making holes in stainless steel products Production methods and applications of stainless steel Stainless steel new technologies Machining of stainless and heat-resistant steels Stainless steel production Rolling mills for stainless steel Strip forming process Methods of processing stainless steel Heat treatment of stainless steel Stainless steel turning Stainless steel milling Cold rolling of stainless steel sheet Grinding stainless steel. Methods of melting stainless steel Installations with a three-roller rolling mill

1. the Bessemer method

Acid lining of the converter, developed by an English engineer. Bessemer in the middle of XIX century allows to remelt cast iron enriched with silicon with minimum content of phosphorus and sulfur. Lining of the Bessemer converter is acidic — silica brick. Pig iron (0.7−1.2%Si) is poured into the converter at 1250−1300 °C and blown with air. This oxidizes silicon, carbon and manganese, and the oxides form an acid slag. After this the blowing is finished. The steel is poured into a ladle, simultaneously deoxidizing it. Since the slag is acidic, sulfur and phosphorus are not removed during smelting.

2. the thomas method

The Thomas Method was suggested by Thomas at the end of the 19th century, for refining cast iron enriched with phosphorus. The inner lining of the Thomas converter is the basic one (tar and molomite). An air box is attached to the converter shell from below. Blowing through lances (nozzles) enters the converter. Lime is loaded into the converter to form the basic slag. Pig iron (0.3 — 0.5%Si, 1.6 — 2.0%P; <0.08%S;) heated to 1250°C is then poured and blown with air. This oxidizes silicon, carbon and manganese and removes sulfur and phosphorus in the resulting slag. The blow-out is completed, when the phosphorus content of the metal is reduced by a factor of 30.

Disadvantages

These two methods have a common disadvantage — saturation of steel with nitrogen, which enters the melt from the air when blowing metal. Therefore, Thomas and Bessemer and steel are more brittle and prone to aging. Therefore, these methods have now been superseded by oxygen-converter smelting with upper and lower blast feeding.

3. Oxygen converter.

A basic lined converter with oxygen blowing through a water-cooled lance is used. Oxygen is used from above. The following charge materials are used:

  • liquid pig iron;
  • scrap metal;
  • slag-forming materials (lime, feldspar, iron ore, bauxites).

Before smelting, scrap is loaded into the ladle of the converter and pig iron heated to 1300−1400°C is poured into it. After this, a water-cooled ladle is introduced into the ladle and oxygen is supplied through it. Lime, bauxite and iron ore are poured into the ladle as blowing begins. The oxygen circulates and mixes the metal with the slag and oxidizes manganese, silicon and carbon. Intense oxidation heats up the mixture. Phosphorus is bound by FeO and CaO If the phosphorus is more than 0.15%, the slag is drained and new slag is loaded to remove it. Removal of sulfur in the slag takes place during the whole smelting process. Oxygen supply is terminated when the carbon content in the metal corresponds to the specified one. After that the deoxidants and alloying additives are injected into the ladle. Smelting time in a 50- to 350-tons capacity converter is less than an hour.

4. Smelting in the converter with bottom blowing.

Steel scrap is loaded into the converter and liquid iron is poured in. During pouring the converter lies almost horizontally, so that liquid iron does not flood lance, through which at this time nitrogen or air is blown, powdered lime is blown, sometimes with the addition of melting spar. Then oxygen is turned on and the converter is put in an upright position. Blowing oxidizes silicon, carbon, and manganese. A slag is formed, into which phosphorus and sulfur pass. Blowing is completed at the specified carbon content in the metal. Decarbonization occurs more intensively due to bath agitation and more complete oxygen assimilation.

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