ERW pipe flattening cracking analysis

ERW pipe flattening test weld cracking is mostly due to micro-cracks, brittle phase inclusions, coarse grains, caused by the band structure. Rational design of chemical composition, reducing inclusions in steel and ribbon organization, forming, welding and heat treatment process parameters were optimized control, can effectively reduce the weld cracking index inclusions and improve high-frequency ERW pipe weld cracking performance anti-crush. Ferrite / pearlite banded structure is hot-rolled steel in common a phenomenon banded structure has a great influence on the performance of steel, will decrease the ductility and toughness.

Low magnification analysis does not appear in the weld fracture. The microstructure can be judged by the organization does not have near the fracture due to welding temperature changes, which can determine the cause of the pipe welding process is not squashed fracture. Mechanical properties and the results of the analysis show that the spectral composition of the high-strength steel; plasticity respect, 31.25% of the coils of plastic does not meet the standards, 62.5% of the coils of plastic slightly larger than the standard one percentage point or exactly equal to the standard value , only 6.25% of the coil is greater than 30% of the plastic. Overall, high strength steel to, and low plasticity. According to the inclusion of ratings and scanning electron microscopy analysis can be seen, a lot of steel inclusions, and the level of more than 3.0. Serious is the reason for the non-metallic inclusions in a significant cracking. By microstructure analysis and scanning electron microscope analysis shows that strip banded serious, the highest level reached B4.0 level. Produce these banded structure, there are two reasons, one is not properly controlled during hot rolling process resulting in serious banded, the other is the inclusion became banded nucleation mother. On the microstructure, the hot rolling process control process is aggravated by improper banded structure of the main reasons, so the focus is how to eliminate banded controlled rolling process. From the above analysis shows, quantity and high levels of non-metallic inclusions (sulfides) and severe plastic strip banded structure is leading to the main reason for the low and cracking. So steelmaking process should reduce the content of non-metallic inclusions, especially sulfide. Hot rolling finishing temperature should be adjusted to reduce the banded structure.