The vacuum treatment of molten steel shall be carried out at a vacuum degree of 67pa (holding time) for 15min, and weak hydrogen blowing shall be used for stirring at the same time. Add A1 line as required after air breaking; The interval of adding A1 line is more than 3min, then feeding x13mm CASI wire 250-350m, soft hydrogen blowing time, 15min; When A1 line is not added, the x13mm CASI wire (200-300m, soft hydrogen blowing time) is directly fed after air breaking for 10min; The interval from the end of soft hydrogen blowing to the start of continuous casting) is 8min, which is conducive to the full floating of inclusions in steel.

板坯连铸

Slab continuous casting

P20钢板坯断面规格为250mmx2100mmo由于钢中含有Cr等微合金化元素，且易在晶界析出，造成晶界脆化，使得钢的高温延展性变差，因此连铸拉速不能太快，结合工艺装备条件，将拉速设定为0.85一0.90m/min;钢水浇铸过程中过热度控制在15℃以内;P20属于中碳合金钢，中碳连铸板坯存在冷却、二次切割、存放倒运过程中低温状态开裂的现象，同时钢中还含有较高的微合金化元素，在结晶过程中易使钢的晶界脆化，导致该钢种在冷却过程中产生较大的热应力和组织应力，因此该钢种在连铸时适合采用中等强度的冷却方式;板坯进行堆垛冷却，以利于钢中气体及应力释放，要求堆垛冷却时间)48ho

The Section specification of P20 steel slab is 250mmx2100mmo. Because the steel contains microalloying elements such as Cr, which is easy to precipitate at the grain boundary, resulting in grain boundary embrittlement and poor high-temperature ductility of the steel, the continuous casting casting speed can not be too fast. Combined with the process equipment conditions, the drawing speed is set as 0.85-0.90m/min; In the process of molten steel casting, the superheat shall be controlled within 15 ℃; P20 is a medium carbon alloy steel. The medium carbon continuous casting slab cracks at low temperature during cooling, secondary cutting, storage and transportation. At the same time, the steel also contains high microalloying elements, which is easy to embrittle the grain boundary of the steel during crystallization, resulting in large thermal stress and structural stress during cooling, Therefore, the steel is suitable for medium strength cooling during continuous casting; The slab shall be cooled by stacking to facilitate the release of gas and stress in the steel, and the stacking cooling time is required) 48ho

加热制度

Heating system

P20钢中Cr等合金元素的含量较高，冷坯加热时由于内外温差较大而产生很大内应力，易产生裂纹，严重时导致板坯在加热炉中断裂。因此需要对入炉板坯进行预热处理，同时在加热初期保持缓慢加热，避免因加热速度过快而产生裂纹或板坯断裂。钢坯的出炉温度应该控制在1150一1200℃，并保证钢坯加热均匀。

The content of Cr and other alloy elements in P20 steel is high. During cold slab heating, due to the large internal and external temperature difference, it is easy to produce cracks, which will lead to slab fracture in the heating furnace. Therefore, it is necessary to preheat the incoming slab and keep heating slowly at the initial stage of heating to avoid cracks or slab fracture due to too fast heating speed. The discharge temperature of the billet should be controlled at 1150-1200 ℃, and the billet should be heated evenly.