本文選題：奧氏體耐熱鋼 + 鈮��； 參考：《鄭州大學》2017年碩士論文

【摘要】：目前,全球80%以上的商品原鎂是我國通過外熱硅熱法生產(chǎn)。煉鎂還原反應(yīng)器是硅熱法煉鎂重要的部件,也是原鎂生產(chǎn)最為主要的成本構(gòu)成之一。目前煉鎂還原反應(yīng)器的主流材質(zhì)為奧氏體耐熱鋼,但傳統(tǒng)的反應(yīng)器用奧氏體耐熱鋼高溫性能較差,易產(chǎn)生蠕變失穩(wěn)及熱疲勞開裂破壞,使用壽命較短,大幅增加原鎂冶煉成本。因此,開發(fā)新型的反應(yīng)器用奧氏體耐熱鋼,對降低原鎂的冶煉成本,提高企業(yè)經(jīng)濟效益具有重要意義。本論文在ZG35Cr26Ni8NRE的基礎(chǔ)上添加合金元素鈮,重點探究了鈮含量對煉鎂還原反應(yīng)器用耐熱鋼微觀組織、常規(guī)力學性能、高溫抗氧化性能、抗熱疲勞性能和高溫抗蠕變性能的影響;利用光學顯微鏡、X射線衍射儀、掃描電子顯微鏡及其附帶的能譜儀探究了Nb元素含量對其組織和性能的影響機理,主要研究結(jié)果如下:未添加Nb元素的耐熱鋼基體組織為奧氏體+第二相,奧氏體晶粒比較粗大,晶界分布大量鏈狀碳化物,晶內(nèi)分布大量骨骼狀碳化物,碳化物類型主要為M23C6型和M7C3型,其中M主要為Cr、Fe和Mn;添加Nb元素后的耐熱鋼基體組織不變,但奧氏體晶粒明顯細化,晶粒細化程度隨Nb含量增加而提高,碳化物除M23C6型和M7C3型外,還出現(xiàn)片狀的Nb C、Nb N和Nb2CN,這類碳化物的數(shù)量隨Nb含量的增加逐漸增多,但當鈮含量達到1.5%時,組織中各類碳化物出現(xiàn)長大粘連的現(xiàn)象。在1000℃和1200℃條件下,Nb元素的添加對抗氧化性是不利的,隨著Nb含量的增加,耐熱鋼的抗氧化性逐漸下降,并且隨著溫度升高,抗氧化性能下降越顯著。1000℃×150 h高溫氧化試驗后,未添加Nb元素的耐熱鋼為完全抗氧化的,添加Nb元素的耐熱鋼為抗氧化的;1200℃×150 h高溫氧化試驗后,未添加Nb元素的耐熱鋼為弱抗氧化的,添加Nb元素的耐熱鋼為不抗氧化的。在熱疲勞上限溫度為1200℃條件下,循環(huán)150次后,耐熱鋼的抗熱疲勞性能隨Nb元素含量的增加呈先提升后降低的趨勢,未添加Nb元素的耐熱鋼熱疲勞裂紋最長,為7.321 mm;添加1.0%Nb的耐熱鋼熱疲勞裂紋最短,為5.221 mm。熱疲勞試驗后,耐熱鋼組織中M23C6型碳化物長大粗化,而MC型碳化物則彌散細小的分布在基體中。在外加載荷為20 MPa、溫度為1000℃的條件下,耐熱鋼的高溫抗蠕變性能隨Nb含量增加逐漸降低。加載80 h后,未添加Nb元素的耐熱鋼延伸率為0.4365%;添加0.5%Nb的耐熱鋼延伸率為0.4925%;添加1.0%Nb的耐熱鋼延伸率為4.726%,宏觀出現(xiàn)明顯伸長但無頸縮;添加1.5%Nb的耐熱鋼在試驗進行34 h后發(fā)生斷裂,斷口呈韌性斷裂特征,存在明顯頸縮。綜合鈮對煉鎂還原反應(yīng)器用奧氏體耐熱鋼組織及性能的影響規(guī)律和機理,本文建議在反應(yīng)器用奧氏體耐熱鋼中鈮元素的添加量不宜超過0.5%。
[Abstract]:At present, more than 80% of the world's primary magnesium is produced by the external thermal silicon thermal process in China. Magnesium reduction reactor is an important part of silicothermic magnesium smelting and one of the most important cost components in magnesium production. At present, the main material of magnesium reduction reactor is austenitic heat-resistant steel, but the high temperature property of austenitic heat-resistant steel used in traditional reactor is poor, and the creep instability and thermal fatigue cracking are easy to be destroyed. The service life is shorter, and the cost of original magnesium smelting is greatly increased. Therefore, the development of a new type of austenitic heat-resistant steel for reactor is of great significance in reducing the smelting cost of raw magnesium and increasing the economic benefit of enterprises. In this paper, the effect of niobium content on microstructure, conventional mechanical properties, high temperature oxidation resistance, thermal fatigue resistance and creep resistance of heat-resistant steel for magnesium reduction reactor was studied based on the addition of niobium on the basis of ZG35Cr26Ni8NRE. The influence mechanism of NB content on microstructure and properties was investigated by means of optical microscope X-ray diffractometer, scanning electron microscope and its accompanying energy spectrometer. The main results are as follows: the microstructure of the heat-resistant steel without NB element is the second phase of austenite, the austenite grain is coarse, a large number of chain-like carbides are distributed at the grain boundary, and a large number of skeletal carbides are distributed in the grain boundaries. The carbides are mainly M23C6 type and M7C3 type, in which M is mainly Cr-Fe and Mn.The matrix microstructure of heat-resistant steel after adding NB element does not change, but the austenite grain is refined obviously, and the grain refinement degree increases with the increase of NB content. In addition to the M23C6 type and M7C3 type, there are also sheets of NB Con NB N and NB 2CN. The amount of these carbides increases with the increase of NB content. However, when the niobium content reaches 1.5%, the adhesion of all kinds of carbides in the tissue is observed. The addition of NB element at 1000 鈩，

本文編號：1834334