Phosphorus is an important alloying element in steel and is normally present in steels in low concentrations, ranging from 0.003 to 0.084 percent. Although small additions of phosphorus are beneficial for improving certain properties in steel, like strength and machinability, too much phosphorus in the steel microstructure can cause several quality issues.
Phosphorus can form different types of phases such as martensite and phosphorus-rich particles, which can degrade the properties of steel and cause intermittent brittleness and cracking. Additionally, it hinders surface corrosion resistance, and reduces weldability, impacting the steel’s performance and thus its usability.
Therefore, it’s necessary to control the phosphorus content of steel, especially when steels are used in applications where strength, weldability, and corrosion resistance is critical.
Though phosphorus can be removed by various processes like acid pickling, alkaline leaching and electrorefining, the most widely used and cost-effective method is to dephosphorize steel by vacuum-oxygen degassing. In the process, the molten steel is cleansed in vacuum by oxygen, which combines with phosphorus, sulfur and other impurity elements present in the steel and forms oxide particles.
The process of vacuum-oxygen decarburization reduces the surface carbon content by combining it with oxygen as well, making the steel more machinable. The decarburized steel is also known as low-carbon steel.
The effective control of phosphorus in steel is important to guarantee the desired properties required for the performance of the steel in end use applications. This is especially the case for steel parts that are used in automotive, shipbuilding, oil and gas pipelines and other types of high-end products.
The removal of phosphorus from steel serves multiple objectives that are necessary for the quality of the steel and its usability purposes.
An important factor to consider while removing phosphorus from steel is that it should be done while also controlling the temperature and viscosity of the steel as this can provide added benefit by preserving the steels properties.
In conclusion, phosphorus must be eliminated from steel in order to obtain the desired properties and increase its usability. Vacuum-oxygen degassing is the most effective and cost-efficient process to dephosphorize steel. Thus, to ensure effective control of the phosphorus content in steel, vacuum-oxygen degassing should be used.
