低合金高强钢针状铁素体组织特征和形成机理

针状铁素体是一种具有大角度晶界、高位错密度的板条状中温转变组织,该组织能有效细化晶粒并具有良好的强韧性匹配.因此,通常在低合金高强度钢焊缝和粗晶区中,利用细小的夹杂物来诱导针状铁素体形成,形成有效晶粒尺寸细小的针状铁素体联锁组织或者针状铁素体和贝氏体的复合组织,使其具有良好的韧性.然而,相关研究对针状铁素体组织的形成机理和控制原理的解释并不十分清楚,对于针状铁素体的定义和理解也存在差异.总结了针状铁素体的本质、相变、形核、形态、晶体学取向关系、长大行为、细化机理和力学性能等方面的特征,归纳了奥氏体晶粒尺寸、转变温度、冷却速度、夹杂物类型和尺寸等对针状铁素体形成的影响,提出了针状铁素体组织形态和转变机理方面几个仍需深入研究的问题和方向.

Microstructure characteristics and formation mechanism of acicular ferrite in high-strength low-alloy steels

Acicular ferrite is one kind of lath- like microstructure forming under intermediate temperature with high angle grain boundary and high dislocation density. It has a strong effect on grain refinement and good combination of high strength and toughness. Fine inclusions in high- strength low- alloy steels are widely used to induce nucleation of acicular ferrite to form fine- grained interlocked microstructure of acicular ferrite in weld metal and/or fine- grained mixed microstructure of acicular ferrite and bainite in coarse- grained HAZ which can improve the impact toughness in weld joint. However, the formation mechanism and control principle of acicular ferrite are not fully understood. There are still some disputes on the definition and explanation of acicular ferrite. The nature, transformation, nucleation, morphology, crystallographic orientation, growth behavior, mechanism of grain refinement and mechanical properties of acicular ferrite as well as the effects of prior austenite grain size, transformation temperature, cooling rate and type and size of inclusion on formation of acicular ferrite were summarized. Finally, some issues on the microstructure characteristics and formation mechanism of acicular ferrite were pointed out for further research.