【摘要】：第二代核電站一回路系統(tǒng)主要由奧氏體-鐵素體雙相不銹鋼構(gòu)建而成,長(zhǎng)期在327℃的高溫環(huán)境下工作。該溫度會(huì)導(dǎo)致雙相不銹鋼中的鐵素體發(fā)生調(diào)幅分解,從而引起材料的力學(xué)性能發(fā)生改變。為此,本文對(duì)一回路主泵泵殼制造材料CF8與主管道制造材料Z3CN20.09M雙相不銹鋼進(jìn)行了一系列的加速老化試驗(yàn),并試驗(yàn)考察了熱老化對(duì)材料沖擊韌性、低周疲勞性能以及棘輪性能的影響。研究結(jié)果對(duì)于一回路系統(tǒng)材料的失效評(píng)定與壽命評(píng)估等工作具有重要的參考價(jià)值。本文采用沖擊試驗(yàn)機(jī)考察了熱老化對(duì)CF8雙相不銹鋼的沖擊韌性的影響。研究結(jié)果表明,在所有的沖擊溫度下,隨著老化時(shí)間的延長(zhǎng),材料的沖擊裂紋形成能與裂紋擴(kuò)展能均逐漸下降,韌脆轉(zhuǎn)變溫度逐漸升高。通過SEM對(duì)材料的斷口觀察發(fā)現(xiàn),原始態(tài)材料的斷口有大量韌窩,表現(xiàn)為韌性斷裂;老化1000 h時(shí),材料斷口表現(xiàn)為準(zhǔn)解理斷裂特征;老化時(shí)間超過3000 h后,材料的斷口表現(xiàn)為完全解理斷裂。這說明隨著老化時(shí)間的增加,材料逐漸脆化。Z3C N20.09M雙相不銹鋼的低周疲勞試驗(yàn)結(jié)果表明熱老化對(duì)材料的疲勞性能也有較大的影響。研究發(fā)現(xiàn),隨著熱老化時(shí)間的增加,材料的應(yīng)力響應(yīng)與疲勞壽命逐漸增加。采用SEM對(duì)試樣斷面觀察發(fā)現(xiàn),原始態(tài)與老化后的材料的疲勞微裂紋均在相界萌生,之后通過相近微裂紋的聯(lián)合與合并逐漸成長(zhǎng)為宏觀裂紋。宏觀裂紋以穿晶形式擴(kuò)展至試樣完全斷裂。材料疲勞壽命隨老化時(shí)間增加而延長(zhǎng)可歸因于熱老化使鐵素體韌性降低。低周疲勞試驗(yàn)時(shí)老化材料中的鐵素體中更易產(chǎn)生被相界牢牢束縛在鐵素體內(nèi)的滑移帶,有利于減輕相界處的應(yīng)力集中與變形不協(xié)調(diào),從而延緩了疲勞裂紋在相界處的萌生。Z3C N20.09M的單軸棘輪試驗(yàn)結(jié)果表明,棘輪應(yīng)變隨平均應(yīng)力與應(yīng)力幅值的增加而增大,卻隨應(yīng)力率與老化時(shí)間的增加而降低。此外,加載歷史對(duì)材料的棘輪應(yīng)變也有很大的影響。采用Ohno-Wang II模型與考慮老化時(shí)間影響的改進(jìn)模型分別對(duì)原始態(tài)與老化后的Z3CN20.09M雙相不銹鋼的棘輪應(yīng)變進(jìn)行了預(yù)測(cè),預(yù)測(cè)結(jié)果與試驗(yàn)結(jié)果吻合較好。
[Abstract]:The first loop system of the second generation nuclear power plant is mainly constructed of Austenite-Ferritic duplex stainless steel and works at high temperature of 327C for a long time. This temperature will lead to the amplitude modulation decomposition of ferrite in duplex stainless steel, which will lead to the change of mechanical properties of the material. In this paper, a series of accelerated aging tests were carried out on the main pump shell manufacturing material CF8 and the main pipeline manufacturing material Z3CN20.09M duplex stainless steel, and the impact toughness of the material was investigated. Effects of low cycle fatigue properties and ratcheting properties. The research results have important reference value for the failure assessment and life evaluation of primary loop system materials. The effect of thermal aging on the impact toughness of CF8 duplex stainless steel was investigated by impact testing machine. The results show that at all impact temperatures, with the prolongation of aging time, the impact crack formation energy and crack propagation energy of the material decrease gradually, and the ductile-brittle transition temperature increases gradually. Through the observation of the fracture surface of the material by SEM, it is found that the fracture surface of the original material has a large number of dimples, showing ductile fracture, and the fracture surface of the material shows quasi-cleavage fracture characteristics when aging for 1000 hours. When the aging time is more than 3000 h, the fracture surface of the material shows complete cleavage fracture. The results show that the material becomes brittle with the increase of aging time. The results of low cycle fatigue test of Z3C N20.09M duplex stainless steel show that thermal aging also has a great influence on the fatigue properties of the material. It is found that with the increase of thermal aging time, the stress response and fatigue life of the material increase gradually. SEM was used to observe the cross section of the sample. It was found that the fatigue microcracks of the original state and the aged materials originated at the phase boundary, and then gradually grew into macrocracks through the combination and combination of similar microcracks. The macroscopic crack propagates to the complete fracture of the specimen in transgranular form. The prolongation of fatigue life with the increase of aging time can be attributed to the decrease of ferrite toughness caused by thermal aging. In low cycle fatigue test, it is easier to produce slip band firmly bound by phase boundary in ferrite in aging material, which is beneficial to reduce the inconsistency between stress concentration and deformation at phase boundary. Thus, the initiation of fatigue crack at the phase boundary is delayed. The uniaxial ratcheting test results of Z3C N20.09M show that the ratcheting strain increases with the increase of average stress and stress amplitude, but decreases with the increase of stress rate and aging time. In addition, the loading history also has a great influence on the ratchet strain of the material. The ratcheting strain of the original state and the aged Z3CN20.09M duplex stainless steel was predicted by Ohno-Wang II model and the improved model considering the effect of aging time, and the predicted results are in good agreement with the experimental results.
【學(xué)位授予單位】：天津大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2016
【分類號(hào)】：TG142.71

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本文編號(hào)：2492534