The process of GB T 6653 HP325 welding steel cylinder is: blanking, stamping, necking, welding, X-ray UT, annealing, X-ray examination, shot blast, spray paint, tightness test.
Cracks occur when the head is stamped or retracted, and most of the waste HP325 steel cylinder products are caused by such defects.
There are two categories of cracks condition: one is a large number of non metallic inclusions exist in the crack; the other is the content of inclusions at the crack is not high, but the microstructure is unnormal tissue (acicular ferrite and granular bainite). This kind of case mainly occure within 40 meters of the GB T 6653 HP325 steel coil tail. Now we mainly analyze this kind of situation.
The high yield strength of GB T 6653 HP325 stamping steel plate should be responsible for the cracking. The high yield strength results in the excessive residual stress in the stamping parts, resulting in the redistribution of stress concentration and the local residual stress exceeding the fracture strength during the machining process. Such defects mainly occure within 40 meters of the GB T 6653 HP325 steel coil tail due to that when the HP325 steel coil is finished, the forming roll of bending machine clasp immediately. At the same time, the water is opened to spray a lot of cooling water to the outer ring of HP325 steel coil, resulting in the water quenching of the outer ring of GB T 6653 HP325 steel coil. The yield strength of the coil is higher than that of the other parts, which is increased by 30 MPa to 40MPa.
In order to reduce the influence of rolling machine shaped water on HP325 steel coil tail strength, we can set off machine water at the tail distance of 40 meters, to reduce the temperature drop of outer HP325 steel coil, weaken the water quenching effect, make the HP325 steel coil tail structure and performance improved.
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