多边形铁素体/针状铁素体双相管线钢的应变硬化行为

对X70管线钢进行临界区热处理,制备出四种铁素体/针状铁素体(PF/AF)体积分数不同的双相管线钢。用电子背散射衍射(EBSD)分析了PF含量对这种双相管线钢的晶粒尺寸、大角度与小角度晶界的比例以及几何必要位错密度(GND)的影响；通过Hollomon和修正C-J方程分析了这种钢的应力比与应变硬化指数(n值)的关系,以及不同PF体积分数双相管线钢的塑性变形和应变硬化的机理。结果表明,PF/AF双相管线钢的应变硬化能力几乎与应力比无关,而应变硬化指数与均匀延伸率表现出特定的线性关系。随着PF体积分数的提高,这种钢的颈缩点后移且应变硬化行为由两阶段向三阶段转变。PF体积分数的改变,对其第I和第II阶段的应变硬化能力有显著的影响。

Strain Hardening Behavior of Polygonal Ferrite and Acicular Ferrite Dual-phase Pipeline Steel

Four polygonal ferrite/acicular ferrite (PF/AF) dual-phase steels with different volume fractions of polygonal ferrite were processed by heat treatment process. The effect of soft phase (polygonal ferrite) ratio on the effective grain size and geometrically necessary dislocation density (GND) was analyzed by electron backscattered diffraction (EBSD). While the relationship between stress ratio and strain hardening exponent (n), as well as the tensile deformation behavior and the relevant strain hardening mechanism of dual-phase pipeline steels of PF/AF dual-phase steels with different PF volume fractions were assessed by means of empirical formulas of the so called Hollomon analysis and modified C-J analysis. The results show that the strain hardening ability of PF/AF dual-phase steel is almost independent of stress ratio, while the strain hardening index has a specific linear relationship with the uniform elongation. With the increase of volume fraction of polygonal ferrite, the necking point moves backward and the strain hardening behavior changes from two-stage to three-stage process. The change of volume fraction of polygonal ferrite has a significant effect on the strain hardening ability of the first and second stages.