研究了变形量对一种低碳Mn-B-Ti系贝氏体型冷作强化非调质钢力学性能的影响。结果表明,随着变形量的增加,实验材料的强度逐渐增加而塑性逐渐降低,其中屈服强度较抗拉强度增加的幅度大。应变硬化指数n随γ增大为先增加后降低,即约在γ=30%时,n出现一峰值。冷拔变形后1/3冷镦变形时的压缩应力随γ增加基本不变,临界压缩变形量则随γ增大而不断降低。随着γ的增加,实验钢未充氢样的慢拉伸缺口抗拉强度逐渐增加,而充氢后试样的缺口抗拉强度σBN和延迟断裂强度比R则显著降低。实验钢拉拔后再经400℃时效处理能够使其延迟断裂性能得到显著恢复。因此,在满足强度要求的前提下,应选择合适的变形量,以保证材料的冷镦和延迟断裂等性能。
Effect of deformation on mechanical properties of a low carbon Mn-B-Ti cold hardening microalloyed bainitic steel was studied.Experimental results show that with the increase of cold drawing reduction γ,strength increases and ductility decreases,and the increase of yield strength is more significant than that of tensile strength.The work hardening exponent n increases with increasing γ to the maximum value at γ=30% and then decreases.The compression stress of 1/3 cold heading after cold drawing keeps almost constant with the increase of γ,while the critical compression ratio after cold-drawing decreases with the increase of γ.The notch tensile strength increases with the increase of γ for the specimen without hydrogen charging,while both notch tensile strength and delayed fracture strength ratio significantly decrease with the increase of γ after hydrogen charging.It is found that the delayed fracture resistance could be significantly improved after annealing at 400 ℃.Therefore,with the precondition of required strength,γ should be chosen carefully to maintain a relatively high performance such as cold heading capability and delayed fracture resistance.
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