氮在非调质钢中的作用

ROLE OF NITROGEN IN NON-QUENCHED AND TEMPERED STEEL

介绍了氮在非调质钢中所起的有益作用。在Nb ,V ,Ti三种微合金化元素中 ,钒有较高的溶解度 ,是非调质钢最常用也是最有效的强化元素。钒在钢中通过形成细小析出相起细化晶粒和沉淀强化作用。与碳相比 ,氮与钒有更强的亲和力 ,且氮化物更稳定 ,因此 ,氮对控制钒的析出起更重要的作用。大量研究结果表明 ,非调质钢中增氮改变了钒在相间的分布 ,促进V(C ,N)析出 ,使析出相的颗粒尺寸明显减小。因而氮增强了非调质钢中钒的沉淀强化作用 ,大幅度提高钢的强度。氮通过促进V(C ,N)析出 ,有效地钉扎奥氏体 -铁素体晶界 ,细化了铁素体晶粒。细小的V(C ,N)析出相促进晶内铁素体的形成 ,进一步细化了铁素体组织。对微钛处理非调质钢 ,增氮还提高TiN颗粒的稳定性 ,更有效地阻止奥氏体晶粒长大。充分利用廉价而丰富的氮 ,在保证一定的强度水平下 ,可节约贵重钒合金 ,进一步降低非调质钢的成本。因此 ,氮是非调质钢中经济有效的微合金化元素。

The beneficial roles of nitrogen in non-quenched and tempered steel were described.Among Nb,V,Ti,the solubility of vanadium is high in medium carbon steel.Therefore,vanadium is the most effective and common use strengthening element for non-quenched and tempered steel.Vanadium added into the steel plays two essential roles-grain refinement and precipitation strengthening by the fine carbo-nitrides precipitates. Compared with carbon,the affinity of vanadium to nitrogen is higher and the nitrides are more stable than carbides.Hence,nitrogen play an important role in controlling precipitation of vanadium carbonitrides in microalloyed steel.The experimental results show the increase in the nitrogen content in non-quenched and tempered steel changes vanadium interphase distribution,promotes precipitation of V(C,N),decreases the particle size of V(C,N) precipitates,hence,enhances precipitation strengthening effect of vanadium in the steel and improves strength of the steel by a big margin.Because nitrogen promotes precipitation of V(C,N),pins austenite-ferrite boundary effectively and refines the ferrite grain.The fine V(C,N) precipitates promote intragranular ferrite nucleation,furthe ,refine ferrite.In non-quenched and tempered steel treated by microalloying element Ti,the increase in nitrogen content makes TiN particles more stable,retards the growth of austenite grain effectively.The full use of cheap and plentiful nitrogen can save expensive vanadium alloy,further decrease the production cost of non-quenched and tempered steel,provided a given strength level of the steel is ensured.Therefore,the nitrogen is a very cost-effective microalloying element in the steel.