Surface defect exists in heat resisting stainless steel
It is a very important symbol of product quality that whether there is visible defects or grinding trace on the surface of stainless steel plates or belts or not. Thanks to the modern equipmetn and the scientific and effective management in Stainless steel production technology, the condition of producing stainless steel with high quality surface is created. However, as production technology, the technology of metallurgical quality and hot rolled quality control as well as finished surface protection should be incessantly improvement, according to specific production conditions.
The chemical composition of stainless steel has a direct impact on the surface quality of finished products. With the combined action of high alloy content and developed columnar crystal as well as the second phase organization which exists in high temperature conditions, the thermoplastic of stainless steel is weakened. When surface crack occurs in hotwork process, residual defects will remain in the finished surface even if it is grinding eliminated. The thermoplastic property of the stainless steel which has single austenite structure at a high temperature, such as SUS310, will be apparently effected due to the enrichment of sulfur drawing to grain boundary at high temperatures, regardless of the ingot casting or casting blank. As a result, surface cracks occur on the bloom and casting. So, to reduce the sulfur content of steel can reduce steel hot shortness. Besides, with calcium killed and desulfurization, the residual amount of calcium can be controled in a level below 0.004%, which can prevent or reduce the precipitation of MnS. This also can improve the thermoplasticity effectively. Different from Austenitic stainless steel, the recrystallization speed of cable bulk phase in the hot deformation process of Duplex stainless steel is much faster. Under the joint action of innerstress and deformation extension force, hot cracks occur more easily along the phase boundary. In order to avoid this, it is an important measure that to reduce the sulfur content in steel and to weaken the hot shortness of the steel. In addition, a small amount of iron chain body exists in general OCr19N19 Austenitic stainless steel at a high temperature, leading to thermoplastic problem in actual production. This is also should be considered.
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