700MPa冷轧低合金超高强钢的典型连续退火工艺

Typical continuous annealing technology of cold-rolled 700 MPa ultra-high strength low-alloy steel

为了开发新一代冷轧低合金超高强钢，利用连续退火实验机对Ti-0．12％、Nb-0．076％的冷轧低合金超高强钢进行连续退火实验，设计了760～830℃四种不同退火温度，研究了退火温度对实验钢的相组成、晶粒尺寸和力学性能的影响．在800℃退火、400oC过时效的条件下，可得到铁素体和少量贝氏体的组织，铁素体晶粒尺寸约为1．4μm，屈服强度可达700MPa．同时利用扫描电镜和透射电镜观察到钢中存在大量纳米尺寸的亚晶结构、少量位错以及纳米级的Ti、Nb的析出物．这些微结构单元对强度有较大的提升作用．

In order to develop a new generation cold-rolled ultra-high strength low-alloy steel, continuous annealing experiments of a Ti-0. 12% , Nb-0. 076% cold-rolled ultra-high strength low-alloy steel were done on a continuous annealing test machine. The influence of annealing temperature on the phase composition, grain size, and mechanical properties of the steel was investigated at four dif- ferent annealing temperature ranges from 760 ℃ to 830 ℃. The final composition is ferrite and a small amount of bainite under 800 ℃ annealing and 400 ℃ over-aging conditions, the ferrite grain size is about 1.4 μn, and the yield strength reaches up to 700 MPa. A large number of nanometer size sub-crystal structures, a small number of dislocations, and nano-Ti and Nb precipitates are observed by scanning electron microscopy and transmission electron microscopy. Those microstructures improve the strength a lot.