Shrinkage porosity kills the tiny pores inside the steel ingot. The tiny pores that are concentrated in the axial zone are called loose in the center, and the tiny pores scattered in other parts are generally loose. Porosity is generally inspected by the transverse acid corrosion sample of the steel billet or steel. The degree of porosity is assessed according to the standard rating chart, and is divided into grades 1 to 5. Porosity destroys the compactness of the steel structure and reduces the plasticity and toughness of the steel. For alloy steels and high-quality carbon structural steels with strict internal densification requirements, the technical standards stipulate that the porosity should be less than Class 2 or Class 3. The looseness of the steel ingot is caused by the condensation and shrinkage of the molten steel in some small enclosed areas during the solidification process of the steel ingot. Steel grades with large shrinkage tend to have a large degree of porosity. Porosity is usually associated with segregation. When the steel contains high levels of gas, non-metallic inclusions and impurity elements such as sulfur and phosphorus, the degree of porosity increases. Choose a reasonable ingot shape, improve the purity of molten steel, control appropriate injection temperature and injection speed, and help reduce the degree of porosity. Increasing the compression ratio of ingot rolling can significantly reduce the porosity rating and weaken its adverse effects.
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