本文選題：雙相不銹鋼UNS　切入點(diǎn)：S32205　出處：《西南石油大學(xué)》2015年碩士論文

【摘要】：為降低天然氣集輸管線成本的同時(shí)保證其耐蝕性,本文選擇了物美價(jià)廉的雙相不銹鋼UNS S32205作為研究對(duì)象,研究了其在相關(guān)環(huán)境中的耐蝕性。通過(guò)大量基礎(chǔ)性實(shí)驗(yàn)完成了對(duì)其組織、力學(xué)性能和耐蝕性能的研究或評(píng)價(jià),在此基礎(chǔ)之上,一方面由差示掃描量熱法技術(shù)研究造成其組織和性能劣化的原因——相變,另一方面,通過(guò)模擬實(shí)際氣田工況環(huán)境的腐蝕全浸實(shí)驗(yàn)和掃描電化學(xué)顯微鏡技術(shù)研究其實(shí)際應(yīng)用的終點(diǎn)——宏觀耐蝕性和微觀腐蝕行為。主要研究結(jié)論如下： 原材料母材兩相呈帶狀組織；焊縫出現(xiàn)范性較差的魏氏體組織；焊縫Ni元素含量高于標(biāo)準(zhǔn)規(guī)定的2%以上,根焊位置出現(xiàn)夾雜和裂紋缺陷；HAZ鐵素體含量約為29%,低于標(biāo)準(zhǔn)規(guī)定的下限30%。 UNS S32205在濕H2S-Cl-環(huán)境中能抵抗多種形式的環(huán)境開(kāi)裂EC,但在含Cl-環(huán)境中不耐點(diǎn)蝕。三氯化鐵點(diǎn)蝕實(shí)驗(yàn)顯示母材腐蝕速率(288.36～618.26mg.dm-2,d-1),焊縫腐蝕速率(0.00～1.63mg-dm-2·d-1)。由GB/T17899對(duì)UNS S32205的應(yīng)用可知,該標(biāo)準(zhǔn)并不適用UNS S32205點(diǎn)蝕電位的評(píng)價(jià)。UNS S32205在3.5wt.%NaCl溶液中的極化曲線顯示其表面的析氫行為在某一電位區(qū)間(-0.5～-1.0V)受到抑制,這可以為其陰極保護(hù)提供指導(dǎo)。 DSC實(shí)驗(yàn)顯示經(jīng)固溶處理(1050～1080℃溫度區(qū)間水淬)的原材料中仍然存在a’、χ和M7C3相等二次相,而降溫過(guò)程中同時(shí)受保溫溫度和降溫速率影響的一個(gè)二次相的吸熱轉(zhuǎn)變,在1095伍1235℃時(shí)最劇烈(保溫溫度1150℃1250℃,降溫速率10-50K/min)。因此,所研究UNS S32205的原始熱處理工藝(1050～1080℃溫度區(qū)間水淬)是不當(dāng)?shù)?該溫度區(qū)間UNS S32205有極大的二次相析出的可能。 SECM顯示在實(shí)驗(yàn)條件下,UNS S32205奧氏體和鐵素體晶內(nèi)均發(fā)生點(diǎn)蝕,兩相中的某一相作為大陰極析氫,而另一相不析氫,析氫相晶內(nèi)點(diǎn)蝕電流峰值更強(qiáng)。析氫相與不析氫相上耐蝕合金元素富集區(qū)均可成為析氫位置。除單獨(dú)存在的耐蝕合金元素貧化區(qū)(或結(jié)垢)對(duì)應(yīng)的正向電流峰和富集區(qū)對(duì)應(yīng)的負(fù)向電流峰,兩相內(nèi)均有成對(duì)(或成組)出現(xiàn)的毗鄰正向電流峰和負(fù)向電流峰。推斷陽(yáng)極溶解位置可能對(duì)應(yīng)兩種結(jié)構(gòu)：一是其對(duì)應(yīng)耐蝕合金元素貧化區(qū),二是其對(duì)應(yīng)表面沉積的KC1型結(jié)垢,后者可能性更大一些。如果是前者,根據(jù)其幾微米的間距判斷,對(duì)應(yīng)耐蝕合金元素富集區(qū)和貧化區(qū)是由調(diào)幅分解形成。對(duì)全部SECM空間圖像所呈現(xiàn)電流峰的投影形貌做歸納總結(jié),發(fā)現(xiàn)無(wú)論是菱形、多邊形、錐形、“雙子”形抑或是梭形的峰投影,其較小較尖銳的頭均指向附近的另一個(gè)峰投影。
[Abstract]:In order to reduce the cost of natural gas gathering pipeline and ensure its corrosion resistance, UNS S32205, a duplex stainless steel with good quality and low price, was selected as the research object, and its corrosion resistance in the relevant environment was studied.The research and evaluation of its microstructure, mechanical properties and corrosion resistance have been carried out through a large number of basic experiments. On the one hand, on the one hand, the reason for the deterioration of the microstructure and properties is studied by differential scanning calorimetry (DSC).On the other hand, the macroscopical corrosion resistance and microscopic corrosion behavior of the gas field were studied by simulating the full-immersion corrosion test and scanning electrochemical microscope (SEM).The main findings are as follows:The two-phase microstructure of the raw material is zonal, the microstructure of the welds is poor, and the Ni content of the weld is more than 2% higher than the standard.The content of HAZ ferrite at the root welding position is about 29, which is 30 below the lower limit specified in the standard.UNS S32205 can resist many kinds of environmental cracking in wet H2S-Cl-environment, but it is not resistant to pitting corrosion in Cl-containing environment.The corrosion rate of base metal is 288.36 ~ 618.26 mg 路dm ~ (-2) / d ~ (-1) and the corrosion rate of weld is 0.003 mg ~ (-1) mg ~ (-2) ~ (-1) 路d ~ (-1) ~ (-1).According to the application of GB/T17899 to UNS S32205, this standard is not suitable for evaluating the pitting potential of UNS S32205. The polarization curve of UNS S32205 in 3.5wt.%NaCl solution shows that the hydrogen evolution behavior of UNS S32205 surface is inhibited in a potential range of -0.5 ~ 1.0V, which can provide guidance for cathodic protection.The DSC experiment shows that there is still a second phase, 蠂 and M7C3, in the raw materials quenched at 1050 ~ 1080 鈩，

本文編號(hào)：1718981