热变形对超纯净管线钢组织的影响

Effect of hot deformation and followed cooling on microstructure of low-carbon microalloyed pipe-line steel

研究了成分和热变形对三种低碳微合金管线钢的连续冷却转变(CCT曲线)和组织的影响。结果表明:在含碳量为0.25％的低碳微合金钢中加入0.3％的MO能推迟铁素体、珠光体转变,扩大针状铁累体(Acicular ferrite)形成的冷却速度范围;高碳含量使针状铁素体向板条铁素体(Lath ferrite)转化。热变形使针状铁素体的形成温度区间从400～500℃扩大到450～700℃,显著加速相变过程,使CCT曲线明显向左上方移动,获得针状铁素体的临界冷却速度增加,抑制板条铁素体的形成,有利于获得细的针状铁素体组织,并细化岛状组织,但对残余奥氏体量影响不大。

The effect of composition and hot deformation on continuous cooling transformation and microstructure of low-carbon microallyed pipeline steel was investigated. The results show that the addition of 0.3% molybdenum to 0.025% low carbon micro-alloy steel depresses the formation of pearlite and widens the critical cooling rate region of AF structure formation. The hot deformation stimulated the formation of acicular ferrite/bainite and enlarged its transformation temperature zone during continuous cooling from 400-550 ℃ (without hot deformation) to 450-700 ℃ (with hot deformation), increased the critical cooling rate for AF transformation, inhibited the formation of lath ferrite/bainite, and refined the island constituents in the matrix. The island microstructure in lath and acicular ferrite would be as austenite, martensite, bainite or pearlite, and the concrete form of island structure was determined by cooling rates and the carbon content in austenite during process of phase transformation.