API oil casing folding defects solutions

The production of API oil casing is prone to outer folding defects, which significantly affect product quality and require stringent control measures.

Outer folding defects are primarily caused by oxide particles on the edge, leading to element segregation and the formation of brittle inclusions such as SiO2 and silicates, particularly at the grain boundaries. These inclusions can cause intergranular fractures, with excess amounts of elements like Al, Mg, Ca, S, P, Mn, and Si further exacerbating the issue. Effective control of these factors is essential to mitigate the formation of outer folds.

Smelting Process

Carbon Control: Ensure a consistent carbon level, avoiding post-blow carbon control endpoints greater than 0.10%.

Converter Slag: Enhance the effect of converter slag and maintain strict slag control. Use slag removal processes with a steel ladle slag thickness of less than 50mm.

Double Slag Operation: Perform double slag operations to control the phosphorus content in the molten steel.

Refining Process

LF Refining: Ensure the LF refining process lasts for at least 20 minutes.

Deoxidation: Strengthen deoxidation to achieve optimal impurity removal. Maintain refining slag basicity of ≥2.5 and slag content ≤1%, with a white residue retention time of ≥15 minutes.

Argon Blowing: After refining, conduct bottom blowing with argon for at least 10 minutes to aid in the removal of inclusions from the molten steel.

Casting Process

Protective Measures: Use ladles, tundishes, and argon seals for protective casting to prevent oxidation.

Casting Temperature: Maintain a tundish superheat of less than 20°C.

Mold Control: Implement mold level brake control and electromagnetic stirring.

Special Flux: Utilize special fluxes to ensure the quality of the slab surface.

Finishing Processes

To reduce the occurrence of white spots caused by hydrogen-induced cracking, employ a slow cooling process for billets and bars.

By adhering to these processes, the production of API oil casing can be optimized to reduce outer folding defects and enhance overall product quality.