Delamination Defects of Structural Steel Pipe

Delamination defects of structural steel pipe

From the mechanism, it is generally believed the non-metallic inclusion in billet can destroy the continuity of 45 # steel tube structure and density, serious mixed even within 45 # steel structure stratification. Another think is hydrogen induced cracks that caused by hydrogen gathered in steel metal internal 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 structure of 45 # steel plastic toughness

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 process, reduce internal stress, so as to ensure the tube billet and finished product structure of 45 # steel structure and mechanical properties 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 time of heat preservation, in order to reduce the deformation force and improve the structure of 45 # steel 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; Pipe and roll speed high, 45 # steel tube structure is easy to form a hierarchical defects. 45 # structural steel pipe structure in order to eliminate the tube billet and delamination defects, should reduce the roll speed began to layered below critical roll speed.

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