本文選題：雙相不銹鋼 + σ析出相��； 參考：《北京科技大學(xué)》2016年博士論文

【摘要】：SAF2906雙相不銹鋼與其它同類型的雙相不銹鋼相比有更好的耐腐蝕性能,更適合于海洋作業(yè)環(huán)境。但是,目前國內(nèi)外對該材料的析出與變形規(guī)律的研究還是十分有限的,由于該鋼種Cr、Mo、Ni等合金元素含量與早期的不銹鋼不同,導(dǎo)致其在熱加工過程中析出相特別是σ相的析出規(guī)律發(fā)生變化,因此不能簡單運(yùn)用傳統(tǒng)雙相不銹鋼的析出規(guī)律對其進(jìn)行判斷,所以有必要對該鋼種在變形過程中的析出規(guī)律進(jìn)行系統(tǒng)研究,為其在實(shí)際生產(chǎn)中提供理論依據(jù)。本文以固溶與時(shí)效的方法對材料進(jìn)行熱處理加工并結(jié)合掃面電鏡(SEM)、透射電鏡(TEM)等設(shè)備對其進(jìn)行組織觀察：建立適用于該種材料的熱力學(xué)模型并計(jì)算熱力學(xué)參數(shù)；利用Gleeble高溫?zé)崮M機(jī)進(jìn)行熱模擬實(shí)驗(yàn),對材料進(jìn)行熱壓縮、熱膨脹處理,并觀察試驗(yàn)不同階段的試樣內(nèi)部組織；運(yùn)用恒溫拉伸實(shí)驗(yàn)機(jī)對材料進(jìn)行熱拉伸處理并觀察拉伸后的試樣組織形貌,分析析出相對超塑性的影響。系統(tǒng)研究了SAF2906雙相不銹鋼析出相的析出行為以及變形規(guī)律。對經(jīng)過固溶與時(shí)效處理的SAF2906雙相不銹鋼析出行為進(jìn)行了研究,研究結(jié)果表明：經(jīng)過高溫固溶(1200℃)之后的試樣無明顯析出相,經(jīng)過不同溫度下的時(shí)效處理之后會(huì)有大量σ析出相出現(xiàn)；SAF2906雙相不銹鋼析山的σ相主要分布在鐵素體內(nèi)部與奧氏體／鐵素體兩相之間,但會(huì)有部分σ相出現(xiàn)在奧氏體中；σ相中的Cr元素含量隨著時(shí)效溫度的于升高面上升；與SAF2205、2507雙相不銹鋼相比,SAF2906雙相不銹鋼中的σ相Cr元素含量較高,最高可達(dá)70%,超過Fe元素含量成為析出相的主體元素。以固溶體熱力學(xué)為基礎(chǔ),利用吉布斯-亥姆霍茲方程等熱力學(xué)定律,建立了用于SAF2906雙相不銹鋼的熱力學(xué)模型,并以此計(jì)算出不同成分的高鉻σ相在母相內(nèi)析出的化學(xué)驅(qū)動(dòng)力,結(jié)果表明：Cr含量越高,6相越不容易析出,同時(shí)在SAF2906雙相不銹鋼中,高鉻σ相的吉普斯自由能變化(△G)為負(fù)值,說明該種。相可以析出；運(yùn)用Thermo-Calc軟件對SAF2906試樣進(jìn)行熱力學(xué)模擬,結(jié)果表明：試樣內(nèi)部各相的含量比例隨溫度變化趨勢與試驗(yàn)結(jié)果相近,而析出相中的化學(xué)元素含量變化與試驗(yàn)數(shù)據(jù)略有不同；與SAF2205、2507雙相不銹鋼相比,SAF2906的奧氏體區(qū)域縮小,而σ相的形核區(qū)域大幅度增加,而且析出的溫度下降,形核難度降低。利用jmatpro軟件模擬出SAF2906雙相不銹鋼的TIT曲線與CCT曲線中的6相的析出趨勢,SAF2906中σ相的析出溫度區(qū)間有所擴(kuò)大,但模擬結(jié)果中存在其它金屬間化合物的析出相是不穩(wěn)定相：經(jīng)過不同變形量熱壓縮之后的SAF2906試樣,其。相的析出驅(qū)動(dòng)能有所提高,特別是在變形量高于70%之后,試樣熱壓縮的應(yīng)力—應(yīng)變曲線的斜率明顯上升,試樣的應(yīng)力上升加快,而此時(shí)的SEM圖也同樣顯示出明顯的σ相殘余。對材料熱變形過程中的內(nèi)部組織進(jìn)行了分析,其結(jié)果表明：熱壓縮過程中,在變形量低于60%之前,鐵素體與奧氏體兩相比例出現(xiàn)明顯波動(dòng),當(dāng)變形量高于70%之后,各相的含量較為平穩(wěn)：析出相比例一直保持在1%至5%范圍內(nèi)的較低水平：熱壓縮過程中的σ析出相并沒有明顯的沿壓縮方向的變形,而是與周圍的鐵素體相出現(xiàn)部分的交織,當(dāng)變形量在70%以下時(shí),析出相與周圍還有明顯邊界,其形狀也較為規(guī)整,當(dāng)變形量達(dá)到80%以上,析出相的形狀發(fā)生不規(guī)則變化并且與周圍相出現(xiàn)相互擴(kuò)散現(xiàn)象。利用恒溫拉伸機(jī)對熱處理之后的SAF2906S雙相不銹鋼進(jìn)行恒溫拉伸實(shí)驗(yàn),結(jié)果表明：在冷軋壓下量為85%時(shí),隨著固溶溫度的提高,SAF2906雙相不銹鋼超塑性延伸率降低,當(dāng)應(yīng)變速率為1×10-3/s,變形溫度為960℃條件下,隨著固溶溫度由1100℃升高至1350℃時(shí),SAF2906雙相不銹鋼延伸率由1 430%降至670%；冷軋變形量對SAF2906超塑性性能具有非常大的影響,應(yīng)變速率為1×10-3/s,變形溫度為960℃時(shí),固溶溫度為1100℃的條件下,冷軋變形量在80%以下,延伸率小于800%,當(dāng)冷軋變形量為85%時(shí),延伸率達(dá)到1430%；SAF2906雙相不銹鋼的兩相比例隨回溶溫度而變化。由于材料的兩相組織,在960℃恒溫拉伸時(shí),大量σ相在SAF2906雙相不銹鋼鐵素體內(nèi)部以及兩相邊界處析出,同時(shí)固溶之后殘余的奧氏體晶粒以及新生成的一次奧氏體又受到析出相的擠壓不會(huì)過分長大,使得試樣獲得了細(xì)晶組織,有利于超塑變形前期品界滑移與品間滑動(dòng),提高SAF2906雙相不銹鋼在恒溫拉伸時(shí)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.
【學(xué)位授予單位】：北京科技大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TG142.71

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