合金钢中钛铌钒碳氮化物的析出及稀土的影响

Precipitation of Carbonitride containing Ti,Ni,V and Effect of Rare Earths in Alloy Steel

随着工业生产发展的需要,对合金钢的性能有了更高的要求。钢中添加一定量的Nb、V、Ti等微合金元素可以改善钢的性能。Nb、V、Ti合金钢中较低含量的N、C较容易析出弥散细小的第二相碳氮化物粒子可以有效的细化晶粒、产生沉淀强化;高氮情况下,钢中析出的不规则大尺寸氮化物恶化钢的性能。适量氮析出的VN促进了晶内针状铁素体形核,可以提高低温韧性。晶界析出的VC、Nb C可以阻碍晶粒长大,但是钢中过高的Nb、C含量会导致沿晶界析出几十微米的长条状碳化物,降低晶界相关的性能。固溶的稀土原子偏聚在晶界,减少了合金元素在晶界偏聚析出;稀土元素将原本可以作为碳化物形核核心的镁铝尖晶石改质为不可作为形核核心的稀土化合物,有效降低了大尺寸碳化物的数量;稀土抑制了铌碳化物在高温下析出,低温下有助于析出小尺寸碳化物;稀土球化了不规则碳化物的形状,减少了尖角部位的应力集中,有效提升了合金钢中第二相碳化物对钢性能的有利影响。

With the development of industrial production,the properties of alloy steels have higher requirements. The properties of steel can be improved by adding a certain amount of Nb,V,Ti and other microalloying elements. The lower contents of N and C in Nb,V and Ti alloy steels are easy to precipitate fine second-phase carbonitrides,which can effectively refine the grain size and produce precipitation strengthening. Under the condition of high nitrogen,irregular large size nitride precipitates from steel deteriorate the properties of steel. VN precipitated by proper amount of nitrogen can promote the nucleation of intracrystalline acicular ferrite and improve the toughness at low temperature. The VC and Nb C precipitated from grain boundary can inhibit the grain growth,but the high content of Nb and C in steel will lead to the precipitation of tens of microns of long strip carbides along grain boundary and reduce the grain boundary-related properties. Rare earth atoms in solid solution are segregated at grain boundaries,which reduces the segregated precipitation of alloying elements at grain boundaries. The rare earth elements transform the magnesia-alumina spinel,which can be used as the core of carbide nucleation,into the rare earth compound,which can not be used as the core of carbide nucleation,effectively reducing the number of large size carbides. Rare earth inhibits the precipitation of niobium carbide at high temperature,but helps the precipitation of small size carbide at low temperature. The rare earth spheroidizes the irregular shape of carbide,reduces the stress concentration at the sharp corners,and effectively enhances the beneficial effect of the second phase carbide in the alloy steel on the steel properties.