Dephosphorization of steels has become a very important metallurgical technique in steelmaking process to produce high quality steels. The content of P in liquid steel during tapping, deoxidation, inert gas blowing, and casting can increase gradually due to its introduction with deoxidizers and reduction from a slag.
What is Dephosphorization process?
The dephosphorization processes (reduction in the phosphorus content) of pig iron consist in oxidizing the phosphorus and combining it with calcium and other components, which are injected into the hot metal deeply, resulting in compounds which are transferred to the slag and, thus, removed from the metal.
Is phosphorus used to make steel?
Phosphorus in steel can have beneficial as well as harmful effects. Phosphorus is also used as an additive in steels to improve machining characteristics and atmospheric corrosion resistance. Detrimental effects of phosphorus in steel include various forms of embrittlement which reduce the toughness and ductility.
How is phosphorus removed from steel?
The method entails melting a prepared slag in a separate furnace and tapping into the ladle before steel tapping. The induction furnace steel is then tapped onto this slag. The rapid mixing of the slag with the steel during tapping completes the removal of phosphorus even while tapping is going on.
What are the conditions that Favours Dephosphorization?
Conditions for dephosphorization: High basicity of slag is required. aFeO in slag should be high; slag should be oxidizing. However for efficient dephosphorization the FeO content of slag should be in between 15 to 16%. Low temperature favours high K9.
What is TBM in steel making?
In order to improve the quality of steel, Thyssen Bottom Metallurgy (TBM) technology is used. The TBM process was developed at ThyssenKrupp Stahl AG oxygen steelmaking shops. Products range from plain low carbon steels to sophisticated alloyed grades.
Why is phosphorus used in steel?
Phosphorus prevents the sticking of light-gage sheets when it is used as an alloy in steel. It strengthens low carbon steel to a degree, increases resistance to corrosion and improves machinability in free-cutting steels.
What if phosphorus is high in steel?
P increases strength and hardness and decreases ductility and notch impact toughness of steels. The adverse effects on ductility and toughness are greater in quenched and tempered higher C steels.
What are the three thermodynamic Favourable conditions for Dephosphorization?
Conditions for dephosphorization: aCaO in slag should be high. This means slag should have free dissolved lime. High basicity of slag is required. aFeO in slag should be high; slag should be oxidizing.
Why is vanadium added to steel?
Vanadium increases the tempering stability of quenched steel and produces a secondary hardening effect. Vanadium can refine the grains, increase the strength and yield ratio and low-temperature toughness after normalizing, and improve the welding performance of ordinary low-alloy steel.
What is the role of phosphorus in steel?
What role does Sulphur and phosphorus plays in steel?
Phosphorus (P): Phosphorus is usually added with sulphur, to improve machinability. The Phosphorus present in Austenitic stainless steels increases strength. However, it has a detrimental effect on corrosion resistance and increases the tendency of the material to crack during welding.
Why do some steels require dephosphorization?
Some steels require particularly low P levels to avoid too high ductile/brittle transition temperature or tempering brittleness. From the equilibrium point of view, lower temperatures, high slag basicity, and high oxidation of the bath favor dephosphorization.
Are Feo and Cao necessary slag constituents for dephosphorization?
These studies observed that FeO and CaO are necessary slag constituents for the dephosphorization of steel. These studies also showed that the dephosphorization reaction is exothermic and that the slag capacity for dephosphorization decreases with temperature.
How does temperature affect the dephosphorization of slag?
The studies have also observed that dephosphorization is enhanced by a decrease in temperature and increase in FeO content and basicity of the slag. Many correlations have been developed to predict the P partition ratio as a function of metal and slag composition as well as temperature.
Is the hot metal dephosphorization pretreatment in the converter working in Japan?
Since 1987, many steelmaking plants in Japan had been concerned about the hot metal dephosphorization pretreatment in the converter and had made rapid progress on this technology.
