A novel V–N microalloying method is adopted to produce pipeline steels using a two‐stage thermomechanical controlled processing involving relaxation process and accelerated cooling. The main objective of the current work is to study the novel practice in terms of microstructure, mechanical properties, and strain‐hardening behavior. The microstructure of the experimental steels consists of polygonal ferrite (PF), quasi‐polygonal ferrite (QF), acicular ferrite (AF), and granular bainite (GB). Mechanical properties including strength, ductility, and low‐temperature toughness of V–N microalloyed steels meet the requirements of X80 pipeline steels. Yield strength, tensile strength, total elongation, and −20 °C impact energy are 639 MPa, 761 MPa, 21.0%, and 283 J when the volume fraction of PF is 9.1%, and 603 MPa, 724 MPa, 24.1%, and 214 J when the volume fraction of PF increases to 30.4%. The V–N microalloyed steels exhibit high strain‐hardening ability, and the values of strain‐hardening exponent are 0.12 and 0.11 based on Hollomon analysis.

中文翻译：

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多边形铁素体和针状铁素体组成的钒氮微合金管线钢的组织，力学性能和应变强化行为

采用一种新颖的V–N微合金化方法，该方法采用两步热机械控制工艺（包括松弛过程和加速冷却）来生产管线钢。当前工作的主要目的是研究微观结构，力学性能和应变硬化行为方面的新颖实践。实验钢的显微组织由多边形铁素体（PF），准多边形铁素体（QF），针状铁素体（AF）和颗粒贝氏体（GB）组成。V–N微合金钢的机械性能（包括强度，延展性和低温韧性）满足X80管线钢的要求。当PF的体积分数为9.1％和603 MPa，724 MPa，24.1％时，屈服强度，拉伸强度，总伸长率和-20°C冲击能分别为639 MPa，761 MPa，21.0％和283 J，当PF的体积分数增加到30.4％时为214J。V–N微合金钢具有很高的应变硬化能力，根据Hollomon分析，应变硬化指数的值分别为0.12和0.11。