Influence of alloying with titanium and molybdenum on grain size high strength pipe steel

Abstract

In Kazakhstan, there is a growing demand for oil and gas pipes and general-purpose pipes made of steels with high performance properties, high-quality blanks for mechanical engineering and structural steel for construction. The work was carried out within the framework of the Targeted Financing Program, in which, as one of the most urgent, the task was set to expand and improve the range of steel products of steel-smelting enterprises, which are in demand, first of all, in the domestic market. Some questions on microalloying with molybdenum and titanium are considered. The article presents the main results of experimental heats to obtain high-strength structural steel with titanium and molybdenum. Metallographic studies of experimental laboratory samples were carried out using an Olympus 51ВХ (TRF) light microscope. The metallographic analysis of the studied samples showed that the base steel 09G2S of the current production has a ferrite-pearlite structure. The grains have an acicular structure (the formation of polygonal ferrite) and correspond to 5-6 points. At the same time, heterogeneity is observed. The results of the study of laboratory samples alloyed with molybdenum and titanium (sample No.1 and No.2) confirm the effectiveness of the impact of microalloying elements on grain refinement, which is due to the release of a significant amount of carbonitrides of the type (MoCN, TiCN) along the grain boundaries. The microstructure of both samples consists of two well-defined phases - ferrite and pearlite, and the grain size corresponds to 7-8 points.