稀土对低碳微合金高强钢冷却过程组织演变的影响

Effect of rare earth elements on micro-structure evolution of low carbon microalloyed high strength steel during cooling

低碳微合金高强钢因其具有高强度、较好的塑韧性被应用到交通运输、石油管道等行业。稀土在钢中有净化钢液、细化晶粒和微合金化的作用,进而能提升材料的诸多性能。因此,在600 MPa低碳微合金高强钢中加入稀土La,通过热膨胀仪对有、无稀土的微合金高强钢在不同冷速下相变点进行测定;利用SEM对不同冷速下的组织进行分析。结果表明,稀土的加入使低碳微合金高强钢的相变临界点A_(c1)、A_(c3)升高;使珠光体转变的临界冷速降低、孕育期增大。珠光体转变推迟,更容易获得贝氏体组织,且促进贝氏体的形貌由粒状向板条状转变。

Low-carbon microalloyed high-strength steel is used in transportation, oil pipeline and other industries because of its high strength and better plastic toughness. Rare earths can purify molten steel, refine grains and microalloying in steel, thus improve many properties of materials. Therefore, rare earth lanthanum was added into 600 MPa low-carbon microalloyed high strength steel. The phase transition point of the microalloyed high-strength steel with and without rare earths at different cooling speeds was measured by a thermal dilatometer and the microstructure under different cooling speeds was analyzed by SEM. The results show that the addition of rare earth increases the critical points of phase transformation A_(c1) and A_(c3) of low-carbon microalloyed high-strength steel. It reduces the critical cooling rate of pearlite transformation and increases the incubation period. The transformation of pearlite is delayed, the bainite structure is easier to obtain, and the morphology of bainite is promoted to transform from granular to lath.