Abstract：Tempering hardness method for two different V, N content of anti-seismic reinforcing steel bars were studied on microstructure of tempering isothermal process and variation regulars of microhardness. V (C, N) precipitation theoretical thermo-kinetic in ferrite was quantitatively determined according to the J-M-A(Johnson-Mehl-Avrami)theory, and compared with the experimental PTT curve. V (C, N) precipitation rule was observed by transmission electron microscopy. The results show that due to the effects of abundant and dispersed second phase particles, the tempering microstructure of V-N microalloyed rebar (0.04V-0.0135N) is more uniform and fine than V microalloyed rebar (0.076V-0.0055N). The PTT curve which is attained from variety microhardness of two materials are consistent with the calculation result. V microalloyed rebar presents a "C" shape and its precipitation kinetics is accelerated in the nosal temperature zone about 670℃, V-N microalloyed rebar is monotonous curve, which is mainly affected by N content. Also in this experiment fibrous carbides, interphase precipitation of V(C,N) in supersaturated ferrite, and precipitations on dislocation after phase transformation are observed, their formation mechanism is discussed.
 CHARLEUX M, POOLE W J, MILITZER M, et al. Precipitation behavior and its effect on strengthening of an HSLA NB/TI steel [J]. Metall Mater Trans A, 2001,32(7):1635-1647.
 ABE F, TANEIKE M, SAWADA K. Alloy design of creep resistant 9Cr steel using a dispersion of nano-sized carbonitrides[J]. Int J Press Vessels Pip, 2007,84(2):3-12.
 DUNLOP G L,CARLSSON C J, FRIMODIG G. Precipitation of VC in ferrite and pearlite during direct transformation of a medium carbon microalloyed steel[J]. Metallurgical Transactions A,1978,9A:261-266.
 HONG S G, KANG K B, PARK C G. Strain-induced precipitation of NbC in Nb and Nb-Ti microalloyed HSLA steels [J]. Scr Mater, 2002, 46(2):163-168.
 LEE W H, KWAK J H, PARK C J. Study on the adaptation method of control model for Tandem cold rolling mill [J]. Proceedings of the Japan/USA Symposium on Flexible Auto-mation,1996,2(3):1035-1041.
 SHENG Guang-min, GONG Si-hong. Investigation of low cycle fatigue behavior of building structural steels under earthquake loading[J]. Acta Metallur Sin (English Letters), 1997,10(1):51-55.
 ZHU J Z, WANG T, ZHOU S H, et al. Quantitative interface models for simulating microstructure evolution[J]. Acta Materialia, 2004, 52(4):833-840.
 LEE B W, HONG S G, PARK C G, et al. Influence of Mo on precipitation hardening in hot rolled HSLA steels containing Nb[J]. Scripta Materialia, 2000,43(4): 319-324.
 ROBSON J D, BHADESHIA H K, MODELLING D H. Precipitation Se-quences in power plant steels:part I,kinetic theory[J]. Materials Science and Technology, 1997,13(8):631-639.
 QUISPE A, MEDINA S F, OMEZ M G, et al. Influence of austenite grain size on recrystallisation-precipitation interaction in a V-microalloyed steel[J]. Materials Science and Engineering A,2007,447(1): 11-18.
 方芳. C、N含量对钢中V(C, N) 析出行为的影响[D]. 北京:钢铁研究总院, 2009.
 HILLERT M, STAFFANSSON L I. The regular solution model for stoichiometric phases and iron metals[J]. Acta Chem Scand, 1970, 24(10):3618-3626.
 方芳, 雍岐龙,杨才福. V(C,N)在V.N微合金钢铁素体中的析出动力学[J]. 金属学报,2009,45(5):625-629. FANG Fang,YONG Qi-long,YANG Cai-fu. Precipitating kinetics of V(C,N) in ferrite of V-N microalloying steel[J]. Acta Metallurgica Sinica, 2009,45(5):625-629.
 VERVYNCKTA S, VERBEKENA K, THIBAUXC P, et al. Recrystallization-precipitation interaction during austenite hot deformation of a Nb microalloyed steel[J]. Materials Science and Engineering: A, 2011, 528(16): 5519-5528.
 ZAJAC S.Precipitation of microalloy carbo-nitrides prior and after transformation[J].Materials Science Forum, 2005, 501:75-86.
 DUTTA B, PALMIERE E J, SELLARS C M.Modeling the kinetics of strain induced precipitation in Nb microalloyed steels[J].Acta Metallurgica, 2001, 49(5):785-794.
 ROBSON J D. Modelling the overlap of nucleation, growth and coarsening during precipitation [J]. Acta Materialia, 2004, 52(5): 4669-4676.
 DOREMUS R H. The shape of precipitate particles in α-iron[J]. Acta Metallurgica,1957,5(7):393-397.
 OKAMOTO R, BORGENSTAM A, AGREN J. Interphase precipitation in niobium-microalloyed steels [J]. Acta Mater, 2010, 58(14):4783-4790.