冷轧双相钢连续退火组织的转变

Experimental Study on Microstructure Evolution in Continuous Annealing of Cold-Rolled Dual Phase Steels

采用光学显微镜与扫描电镜观察分析了实验钢冷轧组织在连续退火过程中的再结晶与相变规律,研究了过时效回火对双相钢显微组织的影响。实验表明,在连续退火初期的加热过程中,在600-720℃大量进行再结晶。加热速度对再结晶行为有较大影响,以10℃/s加热,再结晶将持续到双相区。珠光体在低于720℃的加热过程中变化不明显,而铁素体晶界与晶内出现球状碳化物颗粒。双相区退火过程中,奥氏体首先在珠光体处形成,原铁素体晶界与晶内的碳化物颗粒也形成奥氏体岛。800℃保温后缓慢冷却至630-680℃可以得到合理比例的双相钢组织。当过时效温度大于300℃,马氏体分解,碳化物颗粒析出,将对双相钢性能产生不良影响。

The recrystallization, austenization and overaging of cold rolled strip during continuous annealing were investigated by optical microscopy and scanning electron microscopy. The experimental results show that recrystallization of deformed ferrite is strongly influenced by heating rate and occurs mainly between 600 ℃ and 720 ℃. When heated with 10 ℃/s, recrystallization will continue in intercritical area. Pearlite changes inconspicuously during the heating process below 720 ℃, while there is lots of spherical cementite distributed at the ferrite grain boundaries as well as in the grains. During intercritical annealing, austenite forms in pearlite area firstly and cementite particles in ferrite grains and at boundaries are also transformed into austenite island. Slow cooling down to 630-680 ℃ after soaking at 800 ℃ is advantageous to get reasonable proportion of two phases. When overaging temperature is over 300 ℃, martensite is decomposed into carbide, which is harmful to mechanical properties of dual phase steels.