Impact of Phosphorus Element

Phosphorus element is generally expressed as [P].

Phosphorus’s influences to steel properties

1. To deteriorate the welding properties of steel.
2. To reduce the plasticity and toughness of steel, thus steel is cold brittleness, that is, the impact toughness of steel at low temperatures is significantly reduced.
3. To make steel easily processed
4. The fluidity of the steel liquid is improved and benefits steel casting.
5. To strengthen the corrosion resistance of alloy steel
6. To improve the magnetic conductivity of electrical silicon steel.
7. For the vast majority of steel grades, [P] is a harmful element.

Basic conditions and methods of dephosphorization

Phosphorus removal is an important task at steelmaking production. There are the following methods of dephosphorization.

1. The alkalinity of the slag should be appropriately high and there shall be good liquidity.  The slag alkalinity is controlled at 2.5 to when dephosphorization.
2. It shall improve the oxidation of the slag properly.
3. Proper temperature. Although the low temperature is conducive to the exothermic reaction, the low temperature is not conducive to the melting of lime, is not conducive to the diffusion reaction, and thus will also eventually affect the rate of dephosphorization reaction. Therefore, in order to obtain the best dephosphorization effect, the melt pool temperature can＊t be too high nor too low.
4. Large slag volume may improve the effect of dephosphorization.

Rephosphorization

Rephosphorization refers to the phenomenon that phosphorus content in melting later period turns higher than in the middle period, as well as the finished steel phosphorus content is higher than the phosphorus content in steel liquid.

Reason for Rephosphorization

1. Excessive furnace temperature will keep dephosphorus reaction reversal.
2. At tapping, it may add iron alloy to reduce FeO of the slag greatly. At the same time, deoxidation products such as SiO2 will also make the slag alkalinity greatly reduced, so that the phosphorus reaction in the reverse direction.
3. The iron alloy itself brings into a certain amount of phosphorus.
4. In the above-mentioned causes, the alkalinity and temperature gen have less effect of rephosphorization.