控制冷却对含Nb钢组织性能的影响研究

为了进一步提高含Nb钢的强度，降低含Nb钢的开发成本，通过实验室热轧试验研究超快冷、超快冷+层流冷却和层流冷却3种冷却模式对含Nb钢的组织演变和力学性能影响。结果表明，与层流冷却相比，试验钢采用超快冷后组织中出现针状铁素体和贝氏体，晶粒尺寸细化，位错显著增加，析出物粒子更为细小，试验钢力学性能显著提高。超快冷的主要强化机制为相变强化、细晶强化、位错强化和析出强化。超快冷+层流冷却模式下，随着终冷温度的降低，软相组织减少、硬相组织增多，试验钢的强度升高。随着出超快冷温度的降低，多边形铁素体体积分数逐渐减少且晶粒更为细小，针状铁素体体积分数增多，试验钢强度得到提高，断后伸长率略有降低。以上结果为超快冷工艺条件下开发低成本含Nb钢奠定了理论基础。

Research of the Effect of Controlling Cooling on Microstructure and Mechanical Properties for Nb Bearing Steel

To further improve the strength and reduce development cost of Nb bearing steel, the effects of three cooling methods, including ultra fast cooling, ultra fast cooling added laminar cooling and laminar cooling, on microstructure evolution and mechanical properties of Nb bearing steel have been investigated by hot rolling experiment at laboratory. The results indicate that：Compared with the experimental steel adopting laminar cooling technology, the experimental steel adopting ultra fast cooling technology obtains acicular ferrite and bainite, the grain size is refined, the dislocation density increases significantly, the size of precipitations is refined and mechanical properties improve remarkably. The main strengthening mechanisms under ultra fast cooling condition include phase transformation strengthening, refine grain strengthening, dislocation strengthening and precipitation strengthening. Under the ultra fast cooling added laminar cooling, with the decrease of final cooling temperature, the strength of experimental steel increases resulting from the decrease of soften phase fraction and increase of harden phase fraction. With the decrease of ultra fast cooling ending temperature, the strength of experimental steel increases and the elongation decreases slightly due to the decrease of polygonal ferrite fraction, grain refining and the increase of acicular ferrite fraction. The above results lay the theoretical foundation for developing low cost Nb bearing steel under ultra fast cooling condition.