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首页> 外文学位 >Effect of boron on microstructure and mechanical properties of low carbon microalloyed steels.
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Effect of boron on microstructure and mechanical properties of low carbon microalloyed steels.

机译：硼对低碳微合金钢的组织和力学性能的影响。

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摘要

Low carbon bainitic steels microalloyed with Nb, Ti and V are widely used for the pipeline, construction and automobile industries because of their excellent combination of strength, toughness and weldability. Boron as another major alloying element has been also frequently used in this type of steels since the 1970s. The purpose of adding boron is to improve the hardenability of the steel by promoting bainite formation.;It has been realized that Boron can only be effective as a strengthening element when it is prevented from forming BN and/or Fe23(C, B) 6 precipitates. Therefore, Boron is always added together with other alloying elements which are stronger Nitride or Carbide formers, such as Ti and Nb. However, the formation of complex bainitic structures and the interaction with precipitates at industrial coiling temperature are not adequately understood.;In this study, the effect of boron on the microstructure and mechanical properties of a low carbon Nb-B steel was studied by a hot compression test (50% reduction at 850 °C) followed by quenching samples into a salt bath. The microstructures of the tested samples were examined through optical microscopy and SEM; and the mechanical properties of these samples were investigated by micro-hardness and shear punch tests.;The results indicate that during thermo-mechanical controlled rolling (TCR), the final properties of the products not only depend on the applied deformation but also depend on the coiling temperature where phase transformation takes place. According to the investigation, two strengthening mechanisms are responsible for the strength of the steel at the coiling temperature: phase transformation and precipitation. Under optical microscopy, the microstructures of all specimens appear to be bainite in a temperature range from 350 °C to 600 °C without distinct differences. However, the SEM micrographs revealed that the microstructures at 550 °C are very different from the microstructures transformed at the other holding temperatures.;Two strength peaks were observed at 350 °C and 550 °C in the temperature range studied. It is believed that the NbC precipitates are the main contributor to the peak strength observed at 550 °C because the kinetics of NbC is quite rapid at this temperature. The strength peak at 350 °C is mainly due to the harder bainitic phase, which formed at relatively lower temperature.
机译：与Nb，Ti和V微合金化的低碳贝氏体钢由于具有强度，韧性和可焊接性的优异组合，因此广泛用于管道，建筑和汽车行业。自1970年代以来，硼作为另一种主要的合金元素也经常用于这种类型的钢中。添加硼的目的是通过促进贝氏体的形成来提高钢的淬透性。现已认识到，硼仅在防止形成BN和/或Fe23（C，B）6时才能有效地用作增强元素。沉淀。因此，总是将硼与其他较强的氮化物或碳化物形成元素（例如Ti和Nb）一起添加。然而，对于复杂的贝氏体组织的形成以及在工业卷取温度下与析出物的相互作用尚不充分了解。；在本研究中，通过热轧研究了硼对低碳Nb-B钢的显微组织和力学性能的影响。压缩测试（在850°C下降低50％），然后将样品淬灭到盐浴中。通过光学显微镜和SEM检查测试样品的微观结构。结果表明，在热机械控制轧制（TCR）过程中，产品的最终性能不仅取决于所施加的变形，还取决于发生相变的卷取温度。根据调查，钢在卷取温度下的强度有两种强化机制：相变和析出。在光学显微镜下，所有样品的微观结构在350°C至600°C的温度范围内均为贝氏体，没有明显差异。然而，SEM显微照片显示550°C的显微组织与在其他保温温度下转变的显微组织有很大差异。;在研究的温度范围内，在350°C和550°C观察到两个强度峰。据信，NbC沉淀是在550°C观察到的峰值强度的主要因素，因为NbC在此温度下的动力学相当快。 350°C时的强度峰值主要归因于在相对较低的温度下形成的较硬的贝氏体相。

著录项

  • 作者

    Lu, Yu.;

  • 作者单位

    McGill University (Canada).;

  • 授予单位 McGill University (Canada).;
  • 学科 Engineering Materials Science.
  • 学位 M.Eng.
  • 年度 2008
  • 页码 99 p.
  • 总页数 99
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 工程材料学;
  • 关键词

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