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Effect of fine scale microstructure and inclusions on the toughness of ultra high strength low alloy medium carbon steels.

机译：微观组织和夹杂物对超高强度低合金中碳钢韧性的影响。

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摘要

When fracture is due to micro-void coalescence the toughness of ultra high strength steels is determined by the nature of the inclusions in the steel and by the fine-scale microstructure of the steel. It has been previously shown for the steels HY180 (0.1 wt.% carbon) and AF1410 (0.16 wt.% carbon) that one can improve toughness by increasing inclusion spacing through the use of rare-earths and similarly increase toughness by having inclusion types that are resistant to void nucleation though the use of titanium additions.;Extensive mechanical testing was performed by tensile testing, plane strain fracture toughness tests and Charpy impact toughness tests. True stress-true strain curves were obtained by applying the method of Bridgman. The inclusion analysis of the micrographs obtained using SEM was used to obtain the average inclusion radius, inclusion volume fraction and inclusion spacing. Void nucleation curves were obtained to characterize the strain at which inclusions first nucleate voids. Subsequently the critical interfacial stress at which these inclusions nucleate voids was also obtained. The retained austenite content was measured using X-Ray diffraction while analysis of thin foils and extraction replicas was performed using Transmission Electron Microscopy (TEM).;The results of this investigation shows that both rare earth additions and small titanium additions can be used to improve the toughness of low alloy ultra high strength steels both with or without silicon additions by altering different aspects of the inclusions and fine scale microstructure.;The purpose of this work has been to determine the extent to which rare-earth additions and titanium additions can be used to control inclusion characteristics and improve the toughness of ultra high strength low alloy steels such as 4340 (0.4 wt.% carbon) and 300M. Because silicon additions on the order of 2 wt.% can be used to increase the strength of 0.4 wt.% carbon low-alloy steels without resorting to increased carbon levels, this work also examined the degree to which silicon content influences the inclusion distributions when rare-earth additions or titanium additions are used to modify inclusion type. Two separate low-alloy systems, 4340 and Base+Ni+Si series alloys were investigated.
机译：当断裂是由于微孔聚结而引起时，超高强度钢的韧性取决于钢中夹杂物的性质和钢的细尺度微观结构。以前已经证明，对于HY180钢（碳含量为0.1 wt。％）和AF1410钢（碳含量为0.16 wt％），可以通过使用稀土元素增加夹杂物间距来提高韧性，并且通过具有以下几种类型的夹杂物来提高韧性：通过使用钛添加材料，可以抵抗空洞形核。通过拉伸测试，平面应变断裂韧性测试和夏比冲击韧性测试进行了广泛的机械测试。采用Bridgman方法获得了真实的应力-真实应变曲线。使用SEM获得的显微照片的夹杂物分析用于获得平均夹杂物半径，夹杂物体积分数和夹杂物间距。获得空隙形核曲线以表征夹杂物首先形核空隙的应变。随后，还获得了这些夹杂物成核的空隙的临界界面应力。残留奥氏体含量是通过X射线衍射测量的，而薄箔和提取复制品的分析是使用透射电子显微镜（TEM）进行的；研究结果表明，稀土添加和少量钛添加均可用于改进通过改变夹杂物和细观微观组织的不同方面来研究含或不含硅的低合金超高强度钢的韧性。这项工作的目的是确定稀土和钛的添加程度用于控制夹杂物特性并提高超高强度低合金钢（例如4340（含碳0.4 wt。％）和300M）的韧性。因为可以使用大约2 wt。％的硅添加量来增加0.4 wt。％的碳低合金钢的强度而无需增加碳含量，所以这项工作还研究了硅含量在多大程度上影响夹杂物分布的程度。稀土添加物或钛添加物用于改变夹杂物类型。研究了两种独立的低合金系统4340和贱+ Ni + Si系列合金。

著录项

  • 作者

    Choudhary, Pranay.;

  • 作者单位

    Carnegie Mellon University.;

  • 授予单位 Carnegie Mellon University.;
  • 学科 Engineering Metallurgy.;Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2010
  • 页码 302 p.
  • 总页数 302
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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