INVESTIGATION OF THE INFLUENCE OF TENSION ROLLING TECHNOLOGY ON THE GEOMETRY AND MICROHARDNESS OF PIPE BLANKS MADE OF St1kp STEEL GRADE

Abstract

The article presents the results of a comprehensive study on the effect of cold pipe bending technology using rolling with high tension on the microstructure and microhardness of the weld seam of pipe blanks made of St1kp steel. The study investigated three variants of weld seam location relative to the bending zone were investigated: on the outer side, in the median plane, and on the inner side of the bend. Experimental studies were conducted using a specially developed hardware complex for the cold deformation of metal pipes by the rolling method. The research found that the rolling technology with tension leads to a significant increase in microhardness in the weld seam area due to the formation of quenched structures caused by local heating of the material and subsequent water cooling during deformation. The maximum increase in microhardness (by 29.5%) was achieved when the weld seam was located on the inner side of the bend. It is shown that all obtained bends meet the requirements of OST 36-42–81 for ovality (not more than 6%), with the minimum ovality (3.29%) observed when the weld seam is located on the outer side of the bend. Metallographic studies confirmed the change in microstructure of the material in the weld joint area after rolling bending. The results of the study confirm the effectiveness of rolling technology for producing high-quality bent pipe bends from welded straight-seam pipes with enhanced strength characteristics in the weld seam zone, which has important practical significance for pipeline construction.