胀断连杆用中碳非调质钢的析出强化行为

 利用金相显微镜、透射电镜及X射线衍射仪等分析了2种不同钒质量分数(0.15 %、 0.28 %)的胀断连杆用中碳非调质钢在热锻及空冷后的微合金碳氮化物析出相的成分及粒度分布等特征，并探讨了其析出强化行为。结果表明，随着钢中钒质量分数的增加，组织细化，铁素体增加，珠光体片层间距减小，同时含钒、铬的M(C，N)型析出相的数量增多。2种试验钢中分别约有质量分数48 %、64 %的钒处于M(C，N)相中，M(C，N)相中又分别有约质量分数42.6 %、56.7 %的颗粒尺寸小于10 nm，这些细小粒子主要弥散分布在铁素体内，其沉淀强化增量分别为140.0和232.6 MPa。当试验钢中钒质量分数较高时，不仅可获得与传统胀断连杆用C70S6钢相当的抗拉强度和冲击功，而且还可获得远高于C70S6钢的屈服强度和屈强比，因而适合用来制造高性能胀断连杆。

Precipitation behavior of medium-carbon steel for fracture splitting connecting rod

The microstructure characteristics especially the distribution， morphology and particle size of vanadium carbonitride precipitates in hot-forged medium-carbon micro-alloyed steel for fracture splitting connecting rod with two different vanadium contents (0.15 %， 0.28 %) were examined by OP， TEM and XRD， and their precipitation behavior were analyzed. The results reveal that both the volume fraction of ferrite and the amount of V-rich M(C，N) particles increase， the pearlite interlamellar spacing decreases with increased V content. Further the physical-chemical phase analysis shows that about 48 % and 64 % V of the total in the steel are tied up in the M(C，N) precipitates of the two tested steels， respectively. Meanwhile， the mass percent of fine particles (less than 10 nm) in the two steels is about 42.6 % and 56.7 %， respectively， and the corresponding yield strength increments are 140.0 and 232.6 MPa. It’s concluded that medium-carbon steel with higher V content possesses not only has comparable tensile strength and impact energy absorbed with that of conventional steel C70S6 for fracture splitting connecting rod， but also has much higher yield strength and yield strength ratio， and therefore， is more suitable to fabricate high performance fracture splitting connecting rod.