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Influence of dissolved hydrogen on the fatigue crack growth behaviour of AISI 4140 steel.

机译：溶解氢对AISI 4140钢疲劳裂纹扩展行为的影响。

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摘要

Many metallic structural components come into contact with hydrogen during manufacturing processes or forming operations such as hot stamping of auto body frames and while in service. This interaction of metallic parts with hydrogen can occur due to various reasons such as water molecule dissociation during plating operations, interaction with atmospheric hydrogen due to the moisture present in air during stamping operations or due to prevailing conditions in service (e.g.: acidic or marine environments). Hydrogen, being much smaller in size compared to other metallic elements such as Iron in steels, can enter the material and become dissolved in the matrix. It can lodge itself in interstitials locations of the metal atoms, at vacancies or dislocations in the metallic matrix or at grain boundaries or inclusions (impurities) in the alloy. This dissolved hydrogen can affect the functional life of these structural components leading to catastrophic failures in mission critical applications resulting in loss of lives and structural component. Therefore, it is very important to understand the influence of the dissolved hydrogen on the failure of these structural materials due to cyclic loading (fatigue). For the next generation of hydrogen based fuel cell vehicles and energy systems, it is very crucial to develop structural materials for hydrogen storage and containment which are highly resistant to hydrogen embrittlement. These materials should also be able to provide good long term life in cyclic loading, without undergoing degradation, even when exposed to hydrogen rich environments for extended periods of time.;The primary focus of this investigation was to examine the influence of dissolved hydrogen on the fatigue crack growth behaviour of a commercially available high strength medium carbon low alloy (AISI 4140) steel. The secondary objective was to examine the influence of microstructure on the fatigue crack growth behaviour of this material and to determine the hydrogen induced failure mechanism in this material during cyclic loading. The secondary objective of this investigation was to determine the role of inclusions and their influence in affecting the fatigue crack growth rate of this material. Compact tension and tensile specimens were prepared as per ASTM E-647, E-399 and E-8 standards. The specimens were tested in three different heat treated conditions i.e. annealed (as received) as well as two austempered conditions. These specimens were precharged with hydrogen (ex situ) using cathodic charging method at a constant current density at three different time periods ranging from 150 to 250 hours before conducting fatigue crack growth tests. Mode 1 type fatigue tests were then performed in ambient atmosphere at constant amplitude using load ratio R of 0.1. The near threshold fatigue crack growth rate, fatigue threshold and the fatigue crack growth rate in the linear region were determined. Fatigue crack growth behaviour of specimens without any dissolve hydrogen were then compared with the specimens with different concentration of dissolved hydrogen.;The test results show that the dissolved hydrogen concentration increases with the increase in charging time in all three heat treated conditions and the hydrogen uptake shows a strong dependence on the microstructure of the alloy. It was also observed that the microstructure has a significant influence of on the fatigue crack growth and SCC behaviour of the alloy with dissolved hydrogen. As the dissolved hydrogen concentration increases, the fatigue threshold was found to decrease and the near threshold crack growth rate increases in all three heat treated conditions showing the deleterious effect of hydrogen, but to a different extent in each condition. Current test results also indicate that the fatigue crack growth rates in the linear region increases as the dissolved hydrogen content increases in all three heat treated conditions. It is also observed that increasing the austempering temperature decreases the resistance to hydrogen embrittlement. An interesting phenomenon was also observed in annealed specimen charged with hydrogen for 250 h which had an unusually high fatigue threshold (DeltaKth).
机译：许多金属结构部件在制造过程或成型操作（例如车身框架的热冲压）和使用过程中会与氢接触。金属零件与氢的这种相互作用可能是由于多种原因而发生的，例如电镀过程中水分子解离，由于冲压过程中空气中的水分或由于使用中的主要条件（例如：酸性或海洋环境）而与大气氢相互作用。 ）。与其他金属元素（例如钢中的铁）相比，氢的尺寸要小得多，它可以进入材料并溶解在基体中。它可以将自身置于金属原子的间隙位置，金属基体中的空位或位错，或合金中的晶界或夹杂物（杂质）处。这种溶解的氢会影响这些结构部件的功能寿命，从而在关键任务应用中导致灾难性故障，从而导致生命和结构部件的损失。因此，了解溶解氢对循环载荷（疲劳）对这些结构材料的破坏的影响非常重要。对于下一代氢基燃料电池汽车和能源系统，开发用于氢存储和容纳的结构材料具有非常高的抗氢脆性非常关键。这些材料还应能够在循环负载下提供良好的长期使用寿命，即使长时间暴露在富氢环境中也不会降解。该研究的主要重点是研究溶解氢对氢的影响。市售高强度中碳低合金（AISI 4140）钢的疲劳裂纹扩展行为。第二个目的是研究微观结构对该材料疲劳裂纹扩展行为的影响，并确定在循环加载过程中该材料中氢诱导的失效机理。这项研究的第二个目的是确定夹杂物的作用及其对这种材料疲劳裂纹扩展速率的影响。根据ASTM E-647，E-399和E-8标准制备致密的拉伸试样和拉伸试样。在三个不同的热处理条件下（即退火（原样））和两个奥氏体温度条件下对样品进行了测试。在进行疲劳裂纹扩展测试之前，在150至250小时的三个不同时间段内，使用恒定电流密度的阴极充电方法对这些样品进行氢（非原位）充电。然后在环境大气中以0.1的负载比R以恒定振幅执行模式1型疲劳测试。确定了线性区域的近阈值疲劳裂纹扩展速率，疲劳阈值和疲劳裂纹扩展速率。然后比较了没有任何溶解氢的试样与具有不同溶解氢浓度的试样的疲劳裂纹扩展行为。;测试结果表明，在所有三种热处理条件下，溶解氢的浓度随着充电时间的增加而增加，并且氢的吸收显示出对合金微观结构的强烈依赖性。还观察到，显微组织对溶解氢的合金的疲劳裂纹扩展和SCC行为具有重要影响。随着溶解氢浓度的增加，在显示氢有害作用的所有三个热处理条件下，疲劳阈值均降低且接近阈值的裂纹扩展速率增加，但在每种条件下程度不同。当前的测试结果还表明，在所有三种热处理条件下，线性区的疲劳裂纹扩展速率均随着溶解氢含量的增加而增加。还观察到提高奥氏体化温度会降低对氢脆的抵抗力。在充有氢气250小时的退火样品中还观察到一个有趣的现象，该样品具有异常高的疲劳阈值（DeltaKth）。

著录项

  • 作者

    Ramasagara Nagarajan, Varun.;

  • 作者单位

    Wayne State University.;

  • 授予单位 Wayne State University.;
  • 学科 Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2014
  • 页码 195 p.
  • 总页数 195
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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