SAF2906双相不锈钢σ相析出规律与变形规律研究

发布时间：2018-06-23 22:02

  本文选题：双相不锈钢 + σ析出相　； 参考：《北京科技大学》2016年博士论文

【摘要】：SAF2906双相不锈钢与其它同类型的双相不锈钢相比有更好的耐腐蚀性能,更适合于海洋作业环境。但是,目前国内外对该材料的析出与变形规律的研究还是十分有限的,由于该钢种Cr、Mo、Ni等合金元素含量与早期的不锈钢不同,导致其在热加工过程中析出相特别是σ相的析出规律发生变化,因此不能简单运用传统双相不锈钢的析出规律对其进行判断,所以有必要对该钢种在变形过程中的析出规律进行系统研究,为其在实际生产中提供理论依据。本文以固溶与时效的方法对材料进行热处理加工并结合扫面电镜(SEM)、透射电镜(TEM)等设备对其进行组织观察：建立适用于该种材料的热力学模型并计算热力学参数；利用Gleeble高温热模拟机进行热模拟实验,对材料进行热压缩、热膨胀处理,并观察试验不同阶段的试样内部组织；运用恒温拉伸实验机对材料进行热拉伸处理并观察拉伸后的试样组织形貌,分析析出相对超塑性的影响。系统研究了SAF2906双相不锈钢析出相的析出行为以及变形规律。对经过固溶与时效处理的SAF2906双相不锈钢析出行为进行了研究,研究结果表明：经过高温固溶(1200℃)之后的试样无明显析出相,经过不同温度下的时效处理之后会有大量σ析出相出现；SAF2906双相不锈钢析山的σ相主要分布在铁素体内部与奥氏体／铁素体两相之间,但会有部分σ相出现在奥氏体中；σ相中的Cr元素含量随着时效温度的于升高面上升；与SAF2205、2507双相不锈钢相比,SAF2906双相不锈钢中的σ相Cr元素含量较高,最高可达70%,超过Fe元素含量成为析出相的主体元素。以固溶体热力学为基础,利用吉布斯-亥姆霍兹方程等热力学定律,建立了用于SAF2906双相不锈钢的热力学模型,并以此计算出不同成分的高铬σ相在母相内析出的化学驱动力,结果表明：Cr含量越高,6相越不容易析出,同时在SAF2906双相不锈钢中,高铬σ相的吉普斯自由能变化(△G)为负值,说明该种。相可以析出；运用Thermo-Calc软件对SAF2906试样进行热力学模拟,结果表明：试样内部各相的含量比例随温度变化趋势与试验结果相近,而析出相中的化学元素含量变化与试验数据略有不同；与SAF2205、2507双相不锈钢相比,SAF2906的奥氏体区域缩小,而σ相的形核区域大幅度增加,而且析出的温度下降,形核难度降低。利用jmatpro软件模拟出SAF2906双相不锈钢的TIT曲线与CCT曲线中的6相的析出趋势,SAF2906中σ相的析出温度区间有所扩大,但模拟结果中存在其它金属间化合物的析出相是不稳定相：经过不同变形量热压缩之后的SAF2906试样,其。相的析出驱动能有所提高,特别是在变形量高于70%之后,试样热压缩的应力—应变曲线的斜率明显上升,试样的应力上升加快,而此时的SEM图也同样显示出明显的σ相残余。对材料热变形过程中的内部组织进行了分析,其结果表明：热压缩过程中,在变形量低于60%之前,铁素体与奥氏体两相比例出现明显波动,当变形量高于70%之后,各相的含量较为平稳：析出相比例一直保持在1%至5%范围内的较低水平：热压缩过程中的σ析出相并没有明显的沿压缩方向的变形,而是与周围的铁素体相出现部分的交织,当变形量在70%以下时,析出相与周围还有明显边界,其形状也较为规整,当变形量达到80%以上,析出相的形状发生不规则变化并且与周围相出现相互扩散现象。利用恒温拉伸机对热处理之后的SAF2906S双相不锈钢进行恒温拉伸实验,结果表明：在冷轧压下量为85%时,随着固溶温度的提高,SAF2906双相不锈钢超塑性延伸率降低,当应变速率为1×10-3/s,变形温度为960℃条件下,随着固溶温度由1100℃升高至1350℃时,SAF2906双相不锈钢延伸率由1 430%降至670%；冷轧变形量对SAF2906超塑性性能具有非常大的影响,应变速率为1×10-3/s,变形温度为960℃时,固溶温度为1100℃的条件下,冷轧变形量在80%以下,延伸率小于800%,当冷轧变形量为85%时,延伸率达到1430%；SAF2906双相不锈钢的两相比例随回溶温度而变化。由于材料的两相组织,在960℃恒温拉伸时,大量σ相在SAF2906双相不锈钢铁素体内部以及两相边界处析出,同时固溶之后残余的奥氏体晶粒以及新生成的一次奥氏体又受到析出相的挤压不会过分长大,使得试样获得了细晶组织,有利于超塑变形前期品界滑移与品间滑动,提高SAF2906双相不锈钢在恒温拉伸时的延伸率
[Abstract]:SAF2906 duplex stainless steel has better corrosion resistance than other types of duplex stainless steel, and it is more suitable for marine environment. However, the research on the precipitation and deformation of this material is very limited at home and abroad. Because the content of the alloy elements such as Cr, Mo, and Ni is different from that of the early stainless steel, which causes it to be hot. The Precipitation Law of the precipitates, especially the sigma phase, is changed in the process of processing, so it is not simple to use the precipitation rule of the traditional duplex stainless steel to judge it. Therefore, it is necessary to systematically study the Precipitation Law of the steel in the process of deformation, and provide the theoretical basis for its actual production. The materials were treated by heat treatment and organized with scanning electron microscopy (SEM), transmission electron microscope (TEM) and other equipment. The thermodynamic model was established and thermodynamic parameters were established. Thermal simulation experiments were carried out by Gleeble high temperature thermal simulator to heat the material and heat expansion treatment. The internal microstructure of the sample at the same stage, the material was heated by the constant temperature tensile test machine and the microstructure of the specimen after tensile was observed. The influence of precipitation on the relative superplasticity was analyzed. The precipitation behavior and the deformation law of the precipitated phase of SAF2906 duplex stainless steel were systematically studied. The SAF2906 dual phase stainless steel was treated by the solution and the aging treatment. The precipitation behavior of steel has been studied. The results show that there are no obvious precipitates after high temperature solid solution (1200 C), and a large number of sigma precipitates appear after aging treatment at different temperatures. The sigma phase of SAF2906 duplex stainless steel is mainly distributed between the ferrite and the austenite / ferrite. The partial sigma phase appears in the austenite; the content of Cr elements in the sigma phase rises with the aging temperature. Compared with the SAF22052507 duplex stainless steel, the Cr element in the SAF2906 duplex stainless steel is higher, up to 70%, and the content of the Fe element is the main element of the precipitated phase. The thermodynamic law of the Gibbs Helmholtz equation was established, and the thermodynamic model of the SAF2906 duplex stainless steel was established, and the chemical driving force precipitated in the parent phase of the high chromium sigma phase of different components was calculated. The results showed that the higher the Cr content, the less the 6 phase could be precipitated, and the high chromium sigma phase of the GIP in the SAF2906 duplex stainless steel. The variation (delta G) is negative, which shows that the phase can be precipitated. The thermodynamic simulation of SAF2906 samples is carried out by Thermo-Calc software. The results show that the content ratio of each phase in the sample varies with the test result with the temperature, and the chemical element content in the precipitated phase is slightly different from the experimental data; and SAF22052507 Compared with the duplex stainless steel, the austenite region of SAF2906 is reduced, and the nucleation area of the sigma phase increases greatly, and the precipitation temperature drops and the difficulty of nucleation is reduced. The precipitation trend of the TIT curve of the SAF2906 duplex stainless steel and the 6 phase in the CCT curve is simulated by JMatPro software, and the precipitation temperature range of the sigma phase in the SAF2906 is expanded, but the simulation of the precipitation temperature is expanded. The precipitated phase of other intermetallic compounds is an unstable phase: the precipitating drive of SAF2906 after heat compression after different deformation is improved, especially after the deformation is higher than 70%, the slope of the stress-strain curve of the specimen is obviously increased, and the stress of the sample increases faster, and the S at this time. The EM diagram also shows a significant residual of sigma phase. The internal structure of the material during the thermal deformation process is analyzed. The results show that the proportion of ferrite and austenite fluctuates obviously in the process of thermal compression before the deformation is below 60%, and the content of each phase is more stable when the deformation is higher than 70%: the proportion of precipitation phase has been all the time. It is maintained at a lower level in the range of 1% to 5%: the sigma precipitates in the thermal compression process have no obvious deformation along the compression direction, but are partially interwoven with the surrounding ferrite phase. When the deformation amount is below 70%, the precipitated phase has a distinct boundary, and its shape is more regular, when the deformation amount is above 80%, the precipitated phase is more than 80%. The shape of the SAF2906S double phase stainless steel after heat treatment is subjected to constant temperature stretching experiment. The results show that the superplastic elongation of SAF2906 duplex stainless steel decreases with the increase of the temperature of the cold rolling, when the temperature is 85%, and the strain rate is the same as the strain rate. 1 x 10-3/s, with the deformation temperature of 960 C, with the solid solution temperature rising from 1100 to 1350 C, the elongation of SAF2906 duplex stainless steel is reduced from 1430% to 670%, and the cold rolling deformation has a great influence on the superplastic properties of SAF2906, the strain rate is 1 x 10-3/s, the deformation temperature is 960 C, and the solid solution temperature is 1100 C under the condition of 1100. The deformation amount is below 80% and the elongation is less than 800%. When the cold rolling deformation is 85%, the elongation reaches 1430%. The two phase ratio of SAF2906 duplex stainless steel varies with the resolution temperature. Due to the two phase structure of the material, a large amount of sigma phase precipitates in the internal and two phase boundary of SAF2906 double phase stainless steel ferrite at the constant temperature of 960 C, and the solution is solid solution at the same time. After the residual austenite grain and the newly formed austenite, the extrusion of the precipitated phase will not be overgrown, which makes the specimen obtain the fine grain structure, which is beneficial to the slip of the product boundary in the early stage of the superplastic deformation, and the elongation of SAF2906 duplex stainless steel at constant temperature stretching.
【学位授予单位】：北京科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TG142.71

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