Pore defects on the surface of stainless steel pipes

1. Appearance of surface pores
Discrete "inverted Ω" open holes are formed on the surface of the round tube. The hole opening is round and the diameter is smaller than the inside. The diameter is smaller than the slag hole. The inner wall is smooth and there is no residue like slag. Surface pore defects all occur on 304 stainless steel pipes that are not electroplated during rainy season or humid weather.
2. Causes of surface pores
After analysis, it is believed that when the hydrogen content in the 304 stainless steel product pipe exceeds its saturated solubility in the steel, during the solidification process of the crystallizer, the gas solubility decreases with the temperature drop and structural changes, and hydrogen will precipitate in the steel. , nitrogen and carbon monoxide gases, nucleate and grow into small bubbles. The floating process of small bubbles will further absorb gas and gradually grow up, further accelerating the floating speed. Those bubbles whose floating speed is greater than the solidification speed of molten steel and far away from the meniscus can be smoothly eliminated, while the bubbles whose floating speed is smaller than the solidification speed of molten steel and close to the meniscus are captured by the primary groove-shaped solidification shell. When the static pressure of molten steel continues to increase and Under the combined action of the vibration of the crystallizer and the continuous stretching and healing of the billet shell, the bubbles break through the solid shell and are released to form pore defects.
3. Surface pore control measures
1> Strengthen the management of 304 stainless steel pipe raw materials, keep all kinds of materials dry, and take measures to prevent rain and moisture when transporting materials in rainy seasons. The storage time of lime should not exceed 12 hours, and the alloy must be baked before use. Steel cannot be made when the converter flue or ladle furnace cover is leaking.
2> During the operation of the ladle furnace, adjust the dust removal air volume in a timely manner, maintain a slight positive pressure at the furnace mouth, and strengthen the control of the reducing atmosphere in the furnace; shorten the slag formation time to ≤8 minutes, improve the submerged arc effect, and reduce the suction volume of molten steel.
3> The cooling time of soft blown 304 stainless steel pipe raw materials should be extended.
4> Ensure the oxidation-free pouring protection effect throughout the entire process. Pay special attention to the argon sealing protection effect of the long nozzle of the ladle to prevent the liquid steel from absorbing air. The middle ladle adopts a double-layer coating structure.
The above is the quality problem of pores on the surface of 304 stainless steel pipes. Surface pore defects occur in pipes that have not been electroplated during the rainy season or humid weather. Therefore, 304 stainless steel pipe manufacturers must strengthen the management of raw materials, keep all kinds of materials dry, and take measures for transportation during the rainy season.