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Effect of Hot Torsion Parameters on Development of Ultrafine Ferrite Grains in Microalloyed Steel

B Eghbali , M Shaban

钢铁研究学报(英文版)

Hot torsion testing was performed on a low carbon Nb-Ti microalloyed steel to study the effects of hot torsion parameters, strain and strain rate, on ultrafine ferrite grains production through dynamic strain-induced transformation, at a deformation temperature just above Ar3. The initiation and evolution of ultrafine ferrite grains were studied. The results show that the amount of strain and strain rate has conversely effect on the volume fraction and grain size of ultrafine ferrite grains. With increasing strain, the interior of austenite grains become activated as nucleation sites for fine ferrite grains. As a result, ferrite grains continuously nucleate not only at the former austenite grain boundaries but also inside the austenite grains which leads to a rapid increase in volume fraction of ultrafine grains. Increasing of strain rate reduces the tendency of ferrite grains coarsening so that ultrafine ferrite grains are achieved, while the volume fraction of ultrafine grains decreases at the same strain level.

关键词: dynamic strain induced transformation , grain refinement , ferrite , hot torsion , steel

Microstructure Evolving Behaviors of Undercooled Ultrafine Austenite Grains During Deformation

YAO Shengjie , DU Linxiu , LI Guanglong , JIAO Xing , WANG Guodong

钢铁研究学报(英文版)

Samples with ultrafine grained austenite were prepared by repetitive rapid heating and quenching for three times and were used to investigate the dynamic microstructural evolving behaviors at different temperatures. A simultaneous development of dynamic straininduced transformation (DSIT) and austenite grain growth was detected at the deformation temperatures above Ar3, while only DSIT happened as the deformation proceeded at lower temperatures close to and below Ar3. In addition, a reverse ferritetoaustenite transformation was also observed. Most of the straininduced ferrite nucleated on the boundaries of ultrafine prior austenite grains, especially at the corners and no evidence about intragranular nucleus was obviously obtained.

关键词: ultrafine grained austenite , ferrite , dynamic straininduced transformation (DSIT) , grain growth

中间坯快冷技术对Q345A厚板表层组织和性能的影响

杨颖，侯华兴，张哲

钢铁

采用热模拟技术、力学性能测试技术和金相分析技术研究了中间坯快冷技术对Q345A厚板表层组织和性能的影响。结果表明：经过中间坯冷却+回温轧制后，在距钢板表层2mm内获得细化的铁素体组织，晶粒平均直径在1μm左右，弥散分布着少量珠光体。基体组织和常规TMCP轧制态相似，是块状铁素体与珠光体整合组织。中间坯快冷技术不会降低钢板基体的力学性能和低温韧性，钢板表层的硬度略高于心部。与常规的TMCP工艺相比，钢板具有良好的止裂能力。

关键词: Q345A , heavy steel plate , intermediate billet , ferrite , thermo mechanical control process (TMCP) , grain refining

CSP流程生产经济型热轧双相钢的工艺与组织性能

韩斌，谭文，汪水泽，张超，蔡晓辉

钢铁

为了在CSP产线上开发新一代经济型热轧双相钢，并确定生产的最佳成分和工艺，介绍了在武钢CSP生产线进行580MPa级热轧双相钢的工业化生产试制情况。分别采用C-Mn-Si系和C-Mn-Si-Cr系钢为原料，通过控制轧制和基于超强冷却设备的控制冷却工艺，成功开发出抗拉强度580MPa级热轧双相钢。通过比较分析2种成分钢的力学性能和微观组织，结果表明：经济型的C-Mn-Si系钢相对于C-Mn-Si-Cr系钢具有屈服强度低、屈强比小、伸长率大的特点，虽然马氏体量相对较少，但具有马氏体呈岛状更加均匀分布在铁素体晶界上等典型双相钢的特征，同时提出了生产过程中控制铁素体析出量和促进马氏体形成的具体措施。

关键词: CSP , hot rolling strip , economical dual phase steel , martensite , ferrite , control cooling

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