Seamless steel pipe in the casting process, pulled out from the mold of the slab, the solidification interface of the crystal strength is very small, when the slab subjected to external forces (thermal stress, drum force, roller pressure, straightening force) exceeds, At the critical value, a crack occurs in the solid-liquid surface and propagates along the columnar crystal until the solidified shell can resist the external force.
Surface cracks in several cases: the crack across the thickness of the slab direction, the center of the equiaxed zone crack is a curved fine grain along the grain boundaries, the arc-side cracks are generally crack straight line crack, the outer arc side of the crack is generally crack along the crystal. The crack along the grain boundary is a stress crack, and the rip crack is a crack that crosses the grain destructively and is the result of the external force.
Improvements are as follows:
1, Improve the precision of the arc casting machine to avoid solidification at the initial solid-liquid interface is too large stress to prevent cracks along grain boundaries.
2, Using appropriate speed up the casting speed and within a certain range to increase the amount of cooling water, increase the water flow rate, lower water temperature and other methods to achieve forced cooling.
3, Strictly control the composition of steel, especially carbon content control.
4, Increase the electromagnetic stirring continuous casting, molten steel superheat control at 40 ℃ below.
