Nb对V、N微合金化压力容器钢珠光体形态及低温韧性影响

为了在保证强度同时提升压力容器钢低温韧性,以铌(Nb)取代部分钒(V),研究Nb的添加对V、N微合金化正火压力容器钢板显微组织和力学性能的影响。结果表明,Nb+V试验钢相比于V试验钢,在强度保持630 MPa的同时可显著提升低温冲击韧性,-20、-40、-60℃冲击吸收功分别提升59、44、29 J。原因主要为Nb的添加促进了细小铁素体转变,其含量的增加使钢的塑韧性增强。此外V和Nb+V钢中碳原子扩散系数在平均转变温度下分别为2.64×10^-13、2.14×10^-13 cm²/s, Nb的添加降低了珠光体生长速度、增加了珠光体转变过程中的过冷度,从而细化了珠光体团簇和片层间距。EBSD分析可知以Nb取代部分V后试验钢有效晶粒尺寸由7.7μm减小至5.8μm,大角度晶界比例由83.1%增加至85.5%。微合金元素Nb的细晶作用及对大角度晶界比例提升的贡献也可以大幅提高钢的低温冲击韧性。

Effect of Nb on pearlite morphology and low temperature toughness of V,N microalloyed pressure vessel steel

The effect of Nb on microstructure and mechanical properties for V, N microalloyed normalizing pressure vessel steel was studied by substituting niobium (Nb) for part of vanadium (V) to improve the low temperature toughness while ensuring the strength. The results show that the low temperature impact toughness of Nb+V test steel increases significantly compared with V steel when the strength maintains 630 MPa. The low temperature impact energy of -20, -40, -60 ℃ increases by 59, 44, 29 J respectively, because the addition of Nb promotes the transformation of fine ferrite and enhances plasticity and toughness of steel. In addition, the diffusion coefficients of carbon atoms in V and Nb+V test steel are 2.64×10-13, 2.14×10-13 cm2/s at the average transformation temperature. Nb refines the pearlite clusters and lamellar spacing by reducing the growth rate of pearlite and increasing the undercooling degree during the transformation process. EBSD results show that the effective grain size decreases from 7.7 μm to 5.8 μm and the percentage of high angle grain boundary increases from 83.1% to 85.5% after Nb replacing part of V. The fine grain effect of Nb and its contribution to the increase of large angle grain boundary ratio can greatly improve the low temperature impact toughness.