Properties of Ultra-fine Grained V-microalloyed Dual Phase Steels
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摘要: 研究了钒微合金化对高强双相钢微观组织及性能的影响。与Fe-0.186C-1.5Mn-0.3Si-0.008N参照钢相比, 加入0.14%V带来如下效果: ①在冷轧及退火状态铁素体晶粒高度细化;②严重推迟在连续退火过程中铁素体向奥氏体转变的初始动力学;③慢冷条件下铁素体开始转变温度稍微提高, 但珠光体和贝氏体转变被抑制, 导致淬透性提高;④在临界退火温度≤740℃时观察到未溶渗碳体;⑤750℃/180 s退火后铁素体相中发现大量V (C, N) 析出 (平均直径7.4 nm), 而马氏体 (奥氏体) 中析出物稀少, 尺寸更大 (平均直径13.4 nm);⑥不含钒参照钢抗拉强度随马氏体体积分数增量为~16 MPa/%, 而含钒钢由于晶粒细化和铁素体选择强化, 强度随马氏体含量变化增量相当低 (~4 MPa/%), 在马氏体体积分数>45%变软。Abstract: The effect of vanadium microalloying on the microstructure and properties of a high strength dual phase steel was studied.Compared to the Fe-0.186C-1.5Mn-0.3Si-0.008 N reference alloy it was found that the addition of 0.14 %wt.V resulted in:①A very significant ferrite grain size refinement in the cold rolled and annealed state.②During continuous annealing the initial ferrite to austenite transformation kinetics was strongly retarded.③On slow cooling the ferrite start transformation temperature was slightly increased but the pearlite and bainite transformations were suppressed,resulting in a net overall increase in hardenability.④Undissolved cementite was observed at intercritical annealing temperatures ≤740 ℃.⑤After annealing at 750 ℃/180 s intense V(C,N) precipitation(mean diameter 7.4 nm) was observed in the ferrite phase whereas precipitates were scarce in martensite (austenite) and much larger (mean diameter 13.4 nm).⑥The increase in tensile strength with martensite fraction of the reference alloy was ~16 MPa/%. However,the vanadium alloy showed a much lower sensitivity to martensite content(~4MPa/%) due to grain refinement and selective strengthening of the ferrite phase,and actually became softer than the reference steel at martensite fractions > 45%.At iso-tensile strength the fracture strain and hole expansion coefficient of the V alloy showed some improvement over the reference steel,however the gains were much smaller than those obtained by tempering.
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Key words:
- DP steels /
- AHSS /
- ultra-fine grains /
- vanadium microalloying
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