离心机转鼓用奥氏体不锈钢应力腐蚀断裂研究

发布时间：2018-04-19 03:28

本文选题：奥氏体不锈钢 + 应力腐蚀　；参考：《青岛理工大学》2017年硕士论文

【摘要】：奥氏体不锈钢具有抗腐蚀性强、焊接性好、韧性大等优良的特点。奥氏体不锈钢因其价格低、抗蚀性好、在很宽的温度范围内具有较好的机械性能、能用在淡水环境、海水环境及酸性环境,本文以离心机转鼓用奥氏体不锈钢发生生产事故进行分析、研究。本论文从力学性能的测试、金相组织结构的观察、分析奥氏体不锈钢表面残余应力产生的原因、通过热处理消除残余应力及对循环物中控制氯离子对不锈钢腐蚀机理的探讨,从这几方面着手,分析并确定转鼓筒体碎裂、鼓底产生周向裂纹的原因,并提出合理化的建议,避免类似的事故再次发生。本论文主要的研究内容和结果如下:1.通过对试样的机械力学性能试验,和分析试验成果,可以得出:筒体材料的化学成分中Cr、Ni含量均未达到标准值,但是很接近,从对其进行机械性能测试结果分析,材料的综合机械性能是良好的,是典型的塑性材料。此种材料仍属于奥氏体不锈钢,确切的说接近于301不锈钢,而不是要求使用的304不锈钢。2.金相分析确定了:从碎片化验结果来看,Ni含量表面有明显降低,Ni含量对抗应力腐蚀作用甚大,同样应力腐蚀也会首先降低Ni的浓度,这完全符合应力腐蚀的特征。进一步观察,局部还可以看到二次裂纹和表面腐蚀坑。由某公司提供的“301”不锈钢材在某些腐蚀介质中,它的耐腐蚀能力是不够的。建议在考虑经济成本的前提下,选用含钼奥氏体钢(例0Cr18Ni12Mo2)或更加优良的双相不锈钢如00Cr22Ni5Mo3N。3.304不锈钢残余应力的研究。采取X射线衍射的方法测量不锈钢轮廓的残存应力。在冷加工成型过程,不锈钢转鼓的外轮廓面出现较大的残存拉应力,这是导致转鼓在现实应用中发生应力腐蚀裂纹的主要原因。4.去应力热处理的研究。先对304不锈钢有差别温度的去应力热处理,在把处理前后的外轮廓残存应力做比较,说明了热处理之后,不锈钢表面残余拉应力转变成压应力,且应力的数值有所降低。这对提高不锈钢的抗应力腐蚀性能是非常有用的。5.通过探讨循环物中Cl~-控制和对不锈钢腐蚀的机理,分析出离心机的物料中含有氧元素和硫酸根离子。引起设备应力腐蚀的介质是此物料引起的,应尽量避免。
[Abstract]:Austenitic stainless steel is characterized by strong corrosion resistance, good weldability and high toughness.Austenitic stainless steel has good mechanical properties in a wide range of temperature because of its low price and good corrosion resistance. It can be used in fresh water, seawater and acid environment.In this paper, the production accident of austenitic stainless steel used in centrifuge drum is analyzed and studied.In this paper, the causes of residual stress on austenitic stainless steel surface are analyzed by testing mechanical properties and observing metallographic structure. The residual stress is eliminated by heat treatment and the corrosion mechanism of stainless steel caused by controlling chlorine ion in circulating material is discussed.From these aspects, this paper analyzes and determines the causes of the breakage of the drum body and the circumferential crack in the bottom of the drum, and puts forward some reasonable suggestions to avoid the recurrence of similar accidents.The main contents and results of this thesis are as follows: 1.Through the mechanical and mechanical property test of the sample and the analysis of the test results, it can be concluded that the content of Cr-Ni in the chemical composition of the cylinder material is not up to the standard value, but it is very close.The comprehensive mechanical properties of the materials are good and typical plastic materials.The material is still austenitic stainless steel, close to 301 stainless steel, rather than 304 stainless steel. 2.Metallographic analysis shows that the surface of Ni content can obviously reduce the content of Ni to resist the stress corrosion, and the same stress corrosion will decrease the concentration of Ni at first, which fully accords with the characteristic of stress corrosion.Further observation shows that secondary cracks and surface corrosion pits can also be seen locally.The "301" stainless steel supplied by a company in some corrosive media has insufficient corrosion resistance.It is suggested that the residual stress of molybdenum bearing austenitic steel (0Cr18Ni12Mo2) or better duplex stainless steel such as 00Cr22Ni5Mo3N.3.304 stainless steel should be studied on the premise of economic cost.The residual stress of stainless steel profile was measured by X-ray diffraction.In the process of cold working, there is a large residual tensile stress on the outer contour of the stainless steel drum, which is the main reason for the stress corrosion cracking in the practical application of the drum.Study on stress free heat treatment.The residual stress of the surface of 304 stainless steel before and after treatment is compared. The residual tensile stress on the surface of 304 stainless steel is transformed into compressive stress and the value of stress is reduced.This is very useful for improving the stress corrosion resistance of stainless steel.By discussing the mechanism of Cl-control and corrosion of stainless steel in the circulating material, the oxygen element and sulfate ion in the material of centrifuge were analyzed.The medium that causes the equipment stress corrosion is caused by this material and should be avoided as far as possible.
【学位授予单位】：青岛理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG142.71;TG161

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