【摘要】：310S奧氏體耐熱不銹鋼用于高放廢物儲置罐材料,在焊接高放廢物儲置罐時焊接熱影響區(qū)粗晶區(qū)(CGHAZ)的晶粒粗化嚴(yán)重,導(dǎo)致其力學(xué)性能的降低。為了滿足高放廢物儲置罐焊接熱影響區(qū)粗晶區(qū)的強(qiáng)度和韌性的要求,通過微合金化的方法抑制晶粒的長大。本論文利用金相顯微鏡、掃描觀察、透射電子顯微鏡,sysweld軟件等對儲置罐用310S鋼的CGHAZ區(qū)的組織和力學(xué)性能進(jìn)行了系統(tǒng)的研究。論文主要內(nèi)容如下:1.310S鋼自熔焊數(shù)值模擬基于sysweld軟件建立了焊接熱源模型,模擬了實(shí)際的單道自熔焊實(shí)驗,提取得到了CGHAZ區(qū)的焊接熱循環(huán)曲線,模擬的焊接溫度場與實(shí)驗測得的溫度場吻合、焊接熱源參數(shù)選取的合理,建立的焊接熱源模型可靠,為下一步的測定CGHAZ的力學(xué)性能奠定基礎(chǔ)。2.310S鋼相組成及其析出相研究基于Thermo-Calc熱力學(xué)計算軟件計算了310S鋼的相組成、合金元素對相組成的影響,為制定310S鋼合理的含鋁范圍以及為后續(xù)的固溶工藝奠定了基礎(chǔ),同時也為該材料的焊接熱影響區(qū)的溫度選擇提供了參考。計算結(jié)果表明,隨著Al含量的變化,310S鋼的組織保持不變,但AlN析出相的數(shù)量發(fā)生變化,并且AlN析出相由二次析出轉(zhuǎn)變?yōu)橐淮挝龀觥ｋS著Nb含量的增加,310S鋼的固相線開始下降。MX相和Z相的含量逐漸增加。3.不同Al、Nb含量的310S鋼BM和CGHAZ區(qū)的微觀組織及析出相研究通過對含Al和含Nb鋼的組織觀察。發(fā)現(xiàn)粗晶區(qū)的奧氏體晶粒尺寸和母材的大致相當(dāng)。說明Al和Nb元素都對粗晶區(qū)奧氏體晶粒有抑制長大的作用。隨Al含量的增加,AlN析出相逐漸增多。且Al含量越多的310S鋼,在經(jīng)過鑄造、鍛造、熱軋后,殘存了一次AlN相并且其顆粒尺寸比較粗大,對材料的力學(xué)性能產(chǎn)生損害。當(dāng)Al含量為1.38%時,310S鋼中析出了δ-鐵素體。在鑄造過程中,Al會優(yōu)先進(jìn)入δ-鐵素體中,減少了AlN相的含量。隨著Nb含量的增加,MX相有所增加,抑制粗晶區(qū)奧氏體晶粒長大的能力有所增加。4.Al、Nb含量對310S鋼力學(xué)性能的影響研究發(fā)現(xiàn)AlN在拉伸變形過程中,會阻止晶粒的變形,當(dāng)Al含量較高時(1.38%),δ-鐵素體沿拉伸方向延展,會起到“硬相”的作用,從而增加了材料的塑性。由于AlN和δ-鐵素體的顯微硬度都高于奧氏體基體,會降低310S鋼的韌性。MX相在310S鋼中對拉伸影響不明顯,三種含Nb鋼的母材和粗晶區(qū)的抗拉強(qiáng)度大致相當(dāng)。對沖擊功造成的影響比較大,隨Nb含量的增加,沖擊功不斷降低。焊接熱循環(huán)前后,0Nb鋼沖擊功明顯下降,而對同種成分的含Nb鋼來說,母材和粗晶區(qū)沖擊強(qiáng)度大致相當(dāng)。
[Abstract]:310s austenitic heat-resistant stainless steel is used for high level radioactive waste storage tank material. The coarse grain coarsening of (CGHAZ) in heat affected zone (HAZ) is serious, which results in the decrease of mechanical properties. In order to meet the requirement of strength and toughness of coarse grain zone in heat affected zone (HAZ) of high level radioactive waste storage tank, grain growth was restrained by microalloying. In this paper, the microstructure and mechanical properties of 310S steel for storage tank in CGHAZ region were systematically studied by metallographic microscope, scanning observation, transmission electron microscope and sysweld software. The main contents of this paper are as follows: 1.The welding heat source model based on sysweld software is established by numerical simulation of self-fusion welding of steel, and the welding heat cycle curve of CGHAZ region is obtained by simulating the actual experiment of single-pass self-fusion welding. The simulated welding temperature field coincides with the measured temperature field, the welding heat source parameters are selected reasonably, and the welding heat source model is reliable. The phase composition and precipitates of 2.310S steel were studied. The phase composition and the effect of alloying elements on the phase composition of 310S steel were calculated based on Thermo-Calc thermodynamics calculation software. It lays a foundation for the formulation of reasonable range of aluminum in 310S steel and for the subsequent solid solution process, and also provides a reference for the selection of the temperature of the welding heat affected zone of the material. The results show that with the change of Al content, the microstructure of 310S steel remains unchanged, but the number of AlN precipitates changes, and the precipitation phase of AlN changes from secondary precipitation to primary precipitation. With the increase of Nb content, the solid line of 310S steel began to decrease, and the contents of MX phase and Z phase increased gradually. The microstructure and precipitate phase of 310s steel BM and CGHAZ with different Al,Nb content were studied by observing the microstructure of the steel containing Al and Nb. It is found that the grain size of austenite in the coarse grain region is approximately the same as that of the base metal. The results show that both Al and Nb can inhibit the growth of austenite grains in coarse grain region. With the increase of Al content, the precipitate phase of AlN increases gradually. After casting, forging and hot rolling, the 310S steel with more Al content has a residual AlN phase and its particle size is relatively large, which causes damage to the mechanical properties of the material. When Al content is 1.38, 未 -ferrite is precipitated in 310S steel. In the process of casting, Al will preferentially enter 未-ferrite, reducing the content of AlN phase. With the increase of Nb content, the MX phase increases, and the ability of inhibiting austenite grain growth in coarse grain region increases. 4. The effect of AlN content on mechanical properties of 310S steel is studied. It is found that AlN can prevent the grain from deforming during tensile deformation. When the content of Al is high (1.38%), 未 -ferrite extends along the tensile direction, which will play the role of "hard phase", thus increasing the plasticity of the material. Because the microhardness of AlN and 未 -ferrite is higher than that of austenitic matrix, the toughness of 310S steel will be reduced. The tensile strength of the three kinds of Nb containing steels is similar to that of the base metal and coarse grain zone, and the effect of MX phase on tensile strength is not obvious in 310S steel. The impact on the impact work is great. With the increase of Nb content, the impact work decreases. Before and after welding thermal cycling, the impact energy of 0Nb steel decreases obviously, but for the same composition of Nb steel, the impact strength of base metal and coarse grain region is about the same.
【學(xué)位授予單位】：沈陽理工大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TG457.11

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本文編號：2276311