热处理对USS122超高强度不锈钢强韧性及氢脆敏感性影响研究

发布时间：2018-02-13 11:05

  本文关键词： 超高强度不锈钢 固溶 时效 析出相 氢脆敏感性　出处：《兰州理工大学》2016年硕士论文　论文类型：学位论文

【摘要】：作为超高强度不锈钢的重要组成部分,马氏体沉淀硬化不锈钢因其优良的强韧性匹配、良好的耐蚀性,作为重要的工程结构用钢,在航空航天、海洋工程及能源等重大领域得到了广泛的应用。鉴于该钢种合金元素体系较为复杂,经过热处理后钢中的析出相种类较多,且随着强度的进一步提升,导致钢对氢脆的敏感性进一步提高,这些因素极大的制约了材料的进一步发展和应用。故此,针对热处理对1900MPa级别USS122超高强度不锈钢的强韧化机理和氢脆敏感性影响的研究,具有十分重要的理论意义和指导实际应用的价值。本文应用光学显微镜(Optical Microscopy)、扫描电子显微镜(Scanning Electron Microscopy)、透射电子显微镜(Transmission Electron Microscopy)、电子背散射衍射(EBSD Electron Back-scattered Diffraction)、Thermal-calc热力学计算等实验方法,分析和观察了不同热处理工艺下USS122钢的微观组织。实验结果表明,1080℃固溶处理后,钢中原始晶粒上分布的大量粗大M6C碳化物、χ相基本全溶,此时钢的综合力学性能最佳;固溶温度较低时(如1000℃),则第二相未全溶,影响了钢的韧性;固溶温度过高(如1100℃),则钢的组织显著粗大化,导致屈服强度下降。经1080℃固溶处理保温1h后油淬、-73℃深冷处理8h、540℃时效保温4h空冷(峰时效)后钢的综合力学性能最优,抗拉强度Rm≥1900MPa,冲击吸收功值达45J。此时,钢中析出了大量细小弥散的Laves相,尺寸在5~11nm左右,产生了强烈的沉淀硬化效应,极大地提高了钢的强度。时效温度较低或保温时间较短(欠时效)时,钢中析出量相较少;而过时效阶段时,钢中析出相变得粗大,降低了钢的强度。此外,钢中基体间隙处薄膜状逆转变奥氏体的形成对于钢韧性的提高具有重要意义。通过慢速应变拉伸实验和TDS氢热分析实验对钢充氢前后的缺口抗拉强度及全氢含量进行了测定。结果表明,充氢后钢中发生了氢脆现象,断口根部呈典型的沿晶断裂形貌,缺口抗拉强度有较大幅度下降,且钢的氢脆敏感性随时效温度的上升呈先上升后下降的趋势,与时效温度对钢的强度的影响规律相近;时效温度在520~560℃时氢脆敏感性最高。
[Abstract]:As an important part of ultra-high strength stainless steel, martensite precipitated hardened stainless steel, due to its excellent strength and toughness matching, good corrosion resistance, as an important engineering structure steel, in aerospace, In view of the complexity of the alloying element system, there are many kinds of precipitated phases in the steel after heat treatment, and with the further increase of the strength, the steel is widely used in many fields, such as ocean engineering and energy. As a result, the sensitivity of steel to hydrogen embrittlement is further improved, which greatly restricts the further development and application of materials. Therefore, the effect of heat treatment on the strengthening and toughening mechanism and hydrogen embrittlement sensitivity of 1900 MPA USS122 ultra high strength stainless steel is studied. In this paper, optical microscope, scanning electron microscope (SEM), transmission electron microscope (TEM), transmission electron microscope (TEM), transmission Electron microscopy( TEM) and EBSD Electron Back-scattered diffusion (EBSD) are used to calculate Thermal-calc thermodynamics. The microstructure of USS122 steel under different heat treatment conditions was analyzed and observed. The experimental results showed that after solution treatment at 1080 鈩，

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