P92无缝钢管内表面裂纹分析及工艺优化

采用斜轧穿孔工艺生产大口径P92铁素体耐热无缝钢管过程中，钢管内表面易产生细小裂纹。通过金相分析、高温相变计算和高温加热试验等研究表明，内表面裂纹产生的主要原因是：中心有通孔的P92管坯在坯料加热过程中，由于加热温度过高和在炉时间过长(即表面氧化脱碳加重),导致管坯通孔近内壁产生大量的高温δ-铁素体相，管坯在随后的斜轧穿孔中，裂纹在塑性较差的高温δ-铁素体处产生和扩展。根据内表面裂纹的产生机制，通过对P92钢管化学成分的铬当量、镍当量按Cr_eq<13%、Ni_eq>4%进行控制，坯料保温温度由原工艺的1220～1250℃降为1190～1220℃,对穿孔机轧辊转速、辊距和顶伸量参数优化等工艺改进措施，有效地解决了大口径P92无缝钢管内表面易产生裂纹的问题，提高了P92无缝钢管的成材率和生产效率。

Inner-surface Cracks Analysis and Process Optimization of P92 Seamless Steel Pipe

During the production of large-sized P92 ferrite heat-resistant seamless steel pipe by rotary piercing process,the inner surface of the steel pipe is prone to produce small cracks. Through metallographic analysis,high-temperature phase transformation calculation and high-temperature heating test, the studies show that because of the higher heating temperature and the longer heating time,which increases the surface oxidation and decarburization,during the heating process of the P92 billet with a through hole in the center make a large number of high temperature δ ferrite phases near the inner wall and then the cracks generate and propagate around the δ Ferrite phases at the subsequent process of rotary piercing. According to the mechanism of internal surface cracks,through the control of the Cr＜13%,Ni_eq＜4% for P92 pipe chemical composition, the lowering of the billet heating temperature from 1220-1250 ℃ to 1190-1220℃,and the improvement parameters of roll speed,roll distance and the piercing point,the problem of cracks on the internal surface of large-diameter P92 seamless steel pipe is effectively solved,and the yield and production efficiency of P92 seamless steel pipe are improved.