Abstract: Microstructure and properties of Nb-Ti microalloyed ultra-high-strength steel (/% ： 0. 36C, 0. 45Si, 0. 63Mn,0.005P,0.002S,0. 83Ni, 1.2Cr,0. 23Mo,0.04Nb,0.01 Ti,0.004 0N,0.002 00) are studied by tensile tester, impact tester, metallographic microscope, transmission electron microscopy and other equipments. Of 200 kg VIM furnace melting with initial rolling at 1 050 °C and finishing rolled at 850 °C , the test steel organization mainly structure is bainite and pearlite. After quenching at 890 °C and tempering at 210 °C , the mechanical properties of steel are R_m 1 906 MPa, R_p0.2 1574 MPa,A 10. 0% and -40 °C 18 J,the organization has a small amount of lath martensite with both ends of a square , in addition to a mass of acicular martensite with both ends of sharp-angled y mostly with grain boundary angle in 60° , and its substructure appears a large number of twin, accompanied by microalloyed precipitates ； the microalloyed precipitates are mainly round or oval small size NbC. And a small amount of square and circular larger size (Ti, Nb) (C, N) precipitates, the greater size, the more obvious square characteristics, and the niobium content of precipitate phase reduces ,the titanium content increases.

摘要： 利用拉伸试验机、冲击试验机、光学显微镜、透射电镜等研究了Ni-Ti微合金化超高强度钢（/%:0.36C,0.45Si,0.63Mn,0.005P,0.002S,0.83 Ni,1.2Cr,0.23Mo,0.04 Nb,0.01Ti,0.004 0N,0.002 0O）的组织与性能。200 kg真空感应炉冶炼的试验钢开轧温度1 050_℃、终轧温度850℃,轧态组织以贝氏体和珠光体为主。经890℃淬火+210℃低温回火后,钢的R_m 1 906 MPa,R_p0.2 1 574 MPa,A 10.0%和-40℃KV218 J;组织中除含有少量两端呈方形的板条马氏体外,多为两端呈尖角的针状马氏体,大部分与晶界夹角呈60°,其亚结构出现较多孪晶,组织中微合金化析出物主要为尺寸较小的圆形或椭圆形NbC,以及少量尺寸较大的呈方形与圆形复合形态的析出物（Ti,Nb）(C,N),可以看出复合析出物尺寸越大、方形特征越明显,析出相中Nb含量降低,Ti含量升高。