Seamless surface cracks, opening wide outside off who called the opening is narrow, are known as fine as hair hairline. This deficiency is mainly caused by genetic tube surface cracks, but also affect the rate of qualified products mainly seamless. Seamless billet surface cracks causes, with the process (even casting, molding) varies.
Internal causes refers to its own internal quality of the ingot. In order to prevent or avoid the slab surface cracks, domestic metallurgical worker has been engaged in exploring, trying to find out the causes of the billet surface cracks have achieved consensus on the following points:
A l compared with steel rimmed steel and silicon killed steel crack high sensitivity, low alloy steel containing N b cracking susceptibility further increases. This is because the A lN, N b (C, N), N bC other along the original C-phase grain boundaries, the grain boundary embrittlement and easy to crack. Sulfides along the grain boundary segregation, formation of the liquid film or a low melting intergranular precipitation, resulting in grain boundary embrittlement, making it easy to crack. Eutectoid ferrite thin film is formed on the C phase boundary, also contributed to the generation and propagation of cracks.
The impact bubbles
Subcutaneous bubbles will also be rolled tube surface exposed cracks. Therefore, more than ever to become a rolling bubble crack crack sentence. In fact, the rolling bubbles crack crack is significantly different. Tube rolling on the main crack crack crack even if there are air bubbles, is minimal.
External means until finished steel ingot after stripping on all aspects of seamless quality.
Ingot quality is internal, rolling process is external, such as ingot poor quality, but the rolling process is good, even if the cracks will be lighter, to make up deficiencies acquired the purpose of the clean-up work for pipe billet is very important. In other countries, use more flame tube or mechanical Flayer Flayer treatment. Truly seamless tube surface cracks pose a hazard only 5% of the total number of cracks to 6%, the rest can crack during rolling Flattening and disappear. Although we can not completely avoid the cracks, but it can improve the process and operation of some of the shallow depth of the crack, the crack through the clean-up will eliminate hazards.