Formation Mechanism Study of Black and White Diagonal Stripes on Surface of Seamless 304 Stainless Steel Pipes

The composition, microstructure, phase structure and roughness in the area of the black and white stripes are observed and inspected on the surface of seamless 304 stainless steel pipes and the formation mechanism of the black and white stripes is analyzed.The analysis result shows that the composition, microstructure and phase structure are nearly identical and all within the standard range in the area of either the black or white stripe but the roughness of the white stripe area is obviously larger than that of the black stripe.The different degree of wear on the guide plate during the later period of hot piercing process causes the different roughness on the shells, which leads to occurrence of the black and white stripes on the surface of finished products.Therefore the occurrence of the black and white stripes on the surface of finished products can be avoided through shortening the working period of the guide plate properly and changing the guide plate with a new one on time.