wTi/wN和wAl对含B钢淬透性及力学性能的影响

针对具有不同 ω Ti/ω N 的低 Al-Ti-B 系列和高 Al-B 试验钢进行末端淬火试验和调质热处理试验,通过淬透性曲线、热力学计算、组织和力学性能的对比分析,研究了 ω Ti/ω N 和 Al 含量对含 B 调质钢淬透性及力学性能的影响.结果表明,低 Al-Ti-B 系列钢的 ω Ti/ω N 大于 3.42 时,Ti 能有效地固 N 保 B 提高淬透性,但过高的 ω Ti/ω N 又容易形成粗大的 TiN 颗粒降低韧性;ω Ti/ω N 小于 3.42 时,Ti 固 N 的能力有限,多余的 N 易与 B 结合形成BN 降低淬透性;试验钢中较合适的 ω Ti/ω N 为 3.93,保证了较高的淬透性和综合力学性能.高 Al-B 钢中较高的Al 含量(0.083%,质量分数)起到了固 N 保 B 的效果,其淬透性最好,能获得全厚度马氏体组织,具有高的强韧性.此外,钢中过高的 N 含量易与 Ti、B 结合形成对淬透性和韧性不利的粗大 TiN 和 BN 颗粒,为确保含 B 调质钢的淬透性和强韧性,应严格控制钢中的 N 含量.

Effects of w Ti/w N andw Al on hardenability and mechanical properties of B-containing steels

Jominy test and quenching and tempering heat treatment were carried out on B-containing low-Al-Ti-B and high-Al-B steels.Effects of ω Ti/ω N and Al content on the hardenability and mechanical properties were stud-ied by means of the hardenability curves,thermodynamic calculation,microstructure analyses and mechanical tes-ting.The results show that when ω Ti/ω N in low-Al-Ti-B steels is greater than 3.42,N is fixed effectively by Ti and B is free to improve hardenability,but too high ω Ti/ω N may lead to formation of coarse TiN particles,which is harmful to toughness.When ω Ti/ω N is less than 3.42,the ability of Ti to fix N is limited and the excess N easi-ly combines with B to form BN particles,which is also harmful to toughness.An optimum ω Ti/ω N of 3.93 is found to be favorable for a high hardenability and good mechanical properties.On the other hand,with an Al con-tent (mass fraction)of 0.083%,the high-Al-B steel exhibits the best combination of hardenability and mechanical properties due to the sufficient fixing N effect on Al.In addition,a high level of excess N promotes the formation of coarse particles of TiN and BN which are harmful to hardenability and toughness,and hence N content should be strictly controlled in B-containing steels.