45Mn2 steel is a kind of high strength steel, general yield strength in the more than 700 mpa, main use for high strength structural steel pipe. Delamination defects from the mechanism, it is generally believed the non-metallic inclusion in billet can destroy the continuity of steel pipe and compactness, even serious inclusions in steel pipe internal stratification. Another think is hydrogen induced cracks that caused by hydrogen gathered in steel metal intecolor steel sheetrnal gas pressure is too high, form white spots inside the pipe billet, crack extension occurred in the process of rolling in, eventually forming delamination defects.
In addition, the two-high skew rolling perforation of non-uniform deformation of stress more than plastic strength can also cause delamination. In smelting under the condition of strict control, more than a third case, the control measures are as follows: 1, improve the toughness of plastic tube billet Improve the cleanliness of molten steel, reduce harmful inclusions; Increase the continuous casting slab equiaxed crystal ratio, reduce center segregation and loose; A reasonable cooling system is adopted to avoid crack in slab internal appear; To logoff slab or rolling billet adopts the slow cooling galvanized steel coil process, reduce internal stress, so as to ensure the tube billet and the pipes of the organization and mechanical performance meet the requirements of technical standard.
2, the reasonable control of heating temperature By measuring thermoplastic curve, selecting the best heating temperature. Tube billet heating also note there is enough heat preservation time, in order to reduce the deformation resistance and improve plastic toughness. 3, to reduce the roll speed Roll speed is the key parameter of perforation technology, in the process of roll speed changes from low to high, there is a start to appear a layered critical roll speed. Roll speed is low, the pipe to form pore space; Roll speed is high, and capillary tube billet formed easily delamination defects. In order to eliminate the tube billet and capillary delamination defects, should reduce the roll speed began to layered below critical roll speed. Hunan Great steel Pipe co.,ltd