Influence of unevened grains of metal on the mechanical properties of seamless hot – rolled pipes

Seamless hot – rolled pipes are a popular metal product on the world market. During operation, pipelines are subjected to cyclic loads associated with temperature fluctuations, vibrations near compressor stations, and pressure drops in the transformed medium. One of the ways to ensure high performance properties is to manage the quality of pipe metal, including that laid in the process of metallurgical production. All the basic physical and mechanical properties of metal materials are structurally sensitive and significantly depend on both the grain size and the degree of uniformity of the grain structure, that is, on the different grain sizes. For metallographic research, samples of pipes with the size of 70,0×12,5 mm of S460NH steel were selected with satisfactory (#1) and unsatisfactory (#2) results of the impact. It was found that the inhomogeneous (multi – grained) microstructure in sample #2 was the reason for obtaining unsatisfactory results of the impact. As a result, it was found that one of the most important characteristics that can guarantee stable and satisfactory results of mechanical characteristics, in particular the impact performance, is a homogeneous grain structure.