富Nb復合碳氮化物對22Cr15Ni3.5CuNbN奧氏體鋼焊接模擬熱影響區組織和性能的影響

黃一君; 張麥倉; 謝錫善

doi:10.13374/j.issn2095-9389.2019.07.007

富Nb復合碳氮化物對22Cr15Ni3.5CuNbN奧氏體鋼焊接模擬熱影響區組織和性能的影響

doi: 10.13374/j.issn2095-9389.2019.07.007

北京科技大學材料科學與工程學院, 北京 100083

詳細信息

通訊作者:
張麥倉, E-mail: mczhang@ustb.edu.cn

中圖分類號: TG401
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出版歷程
- 收稿日期: 2018-11-09
- 刊出日期: 2019-07-01

A simulation of the effect of Nb-rich carbonitride on the structure and properties of weld HAZ of 22Cr15Ni3.5CuNbN austenitic steel

School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China

More Information

Corresponding author: ZHANG Mai-cang, E-mail: mczhang@ustb.edu.cn

摘要

摘要: 采用Gleeble熱模擬的方法, 通過模擬焊接過程中快速加熱和冷卻的熱循環過程, 得到1150~1300 ℃不同峰值溫度下22Cr15Ni3.5CuNbN奧氏體鋼擴大的熱影響區組織, 并對其進行沖擊性能分析. 對熱影響區組織的研究表明, 實驗鋼的母材中存在一定量富Nb復合碳氮化物, 有效釘扎晶界, 且與大量位錯纏結. 在焊接過程中, 該富Nb復合碳氮化物經歷溶解與重新析出的復雜過程: 當峰值溫度為1150 ℃時, 僅小顆粒的富Nb碳氮化物發生了溶解, 而峰值溫度為1300 ℃時, 富Nb復合碳氮化物經歷溶解與重新析出, 呈現網狀的組織形貌, 且其整體尺寸增加. 富Nb復合碳氮化物的演化導致了沖擊功的變化, 經歷焊接熱循環條件的實驗鋼較母材具有更高的沖擊韌性, 隨著峰值溫度的升高, 沖擊韌性呈現先升后降的趨勢, 其中在峰值溫度為1150 ℃時實驗鋼的沖擊韌性最高.
- 奧氏體不銹鋼 /
- 碳氮化鈮 /
- 焊接熱影響區 /
- 熱模擬 /
- 沖擊韌性
Abstract: Niobium is a strong carbonitride-forming element. The evolution of Nb-rich carbonitride in austenitic steels during welding has an important effect on the ductility of the heat-affected zone (HAZ). The new austenitic heat-resistant steel of 22Cr15Ni3.5CuNbN, a candidate material for ultra-super critical boiler superheater and reheater serviced at 620-650 ℃, contains 0.5% Nb, which will significantly affect the steel's weldability; therefore, it is necessary to study the microstructure and properties of the weld HAZ of the steel and provide a reference for the further applications of this new material. Because of the narrow weld HAZ of this material, the extended HAZ structure of 22Cr15Ni3.5CuNbN austenitic steel at different peak temperatures from 1150 ℃ to 1300 ℃ was obtained by Gleeble thermal physical simulation method in this study, aiming to simulate the thermal cycling process of the welding process, and impact performance tests were carried out. The results show that a certain amount of Nb-rich composite carbonitrides is present in the base metal of the experimental steel, which effectively pins the grain boundaries and entangl with a large number of dislocations. The Nb-rich composite carbonitride underwent a complex process of dissolution and re-precipitation during the simulated welding process. When the peak temperature was at 1150 ℃, only small particles of Nb-rich carbonitrides were dissolved, while when the peak temperature reached 1300 ℃, the Nb-rich composite carbonitride underwent dissolution and re-precipitation, showing a "mesh" structure, and its overall size increased. The evolution of Nb-rich composite carbonitrides led to changes in the impact energy of this steel. The impact toughness of the experimental steel subjected to welding thermal cycling condition was higher than that of the base metal. With the increase in the peak temperature, the impact toughness first increased and then decreased. The impact toughness of the steel reached the highest when the peak temperature was at 1150 ℃.
- austenitic stainless steel /
- niobium carbonitriding /
- heat-affected zone /
- thermal simulating /
- impact toughness

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圖 1 鎢極氬弧焊熱影響區各區域峰值溫度分布^[12]

Figure 1. Peak temperature distribution in HAZ during TIG welding^[12]

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圖 2 Gleeble熱模擬實驗中溫度-時間關系曲線

Figure 2. Curve of temperature against time during Gleeble thermal simulation

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圖 3 供貨態母材的顯微組織. (a)金相組織; (b)掃描電鏡圖像; (c)能譜分析結果

Figure 3. Microstructure of the supplied base metal: (a) OM; (b) SEM; (c) EDS

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圖 4 母材的透射電鏡分析結果. (a)晶界及晶內析出物; (b)晶內析出物與位錯的關系; (c)晶內析出物成分分布; (d)晶界析出物成分分布

Figure 4. TEM analysis results of the base metal: (a) precipitates distributed in grain boundaries and crystals; (b) relationship between dislocations and precipitates distributed in crystals; (c) composition of precipitates distributed in the crystal; (d) composition of precipitates distributed at grain boundaries

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圖 5 峰值溫度與沖擊性能的關系

Figure 5. Relationship between peak temperature and impact property

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圖 6 沖擊實驗斷口微觀形貌. (a₁)母材，缺口近端纖維區; (a₂)母材，缺口遠處放射區; (b₁)T_m=1150 ℃，缺口近端纖維區; (b₂)T_m=1150 ℃，缺口遠處放射區; (c₁)T_m=1200 ℃，缺口近端纖維區; (c₂) T_m=1200 ℃，缺口遠處放射區; (d₁) T_m=1250 ℃, 缺口近端纖維區; (d₂)T_m=1250 ℃，缺口遠處放射區; (e₁) T_m=1300 ℃，缺口近端纖維區; (e₂)T_m=1300 ℃，缺口遠處放射區; (e₃) T_m=1300 ℃，斷口處析出物

Figure 6. Fracture morphology of impact test: (a₁) base metal, proximal fiber zone close to the notch; (a₂) base metal, radiation zone far from the notch; (b₁) proximal fiber zone close to the notch at peak temperature of 1150 ℃; (b₂) radiation zone far from the notch at peak temperature of 1150 ℃; (c₁) proximal fiber zone close to the notch at peak temperature of 1200 ℃; (c₂) radiation zone far from the notch at peak temperature of 1200 ℃; (d₁) proximal fiber zone close to the notch at peak temperature of 1250 ℃; (d₂) radiation zone far from the notch at peak temperature of 1250 ℃; (e₁) proximal fiber zone close to the notch at peak temperature of 1300 ℃; (e₂) radiation zone far from the notch at peak temperature of 1300 ℃; (e₃) precipitate from fracture at peak temperature of 1300 ℃

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圖 7 不同峰值溫度下的組織情況. (a₁~a₃)峰值溫度T_m為1150 ℃; (b₁~b₃) 峰值溫度T_m為1300 ℃

Figure 7. Microstructures at different peak temperatures: (a₁-a₃)peak temperature is 1150 ℃; (b₁-b₃) peak temperature is 1300 ℃

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圖 8 峰值溫度達到1300 ℃時的晶界析出物成分分布. (a)晶界處的碳氮化物部分回溶; (b)三叉晶界處大塊碳氮化物的部分回溶

Figure 8. Composition of grain boundary precipitates at peak temperature of 1300 ℃: (a) partial dissolution of carbonitride at the grain boundary; (b) partial dissolution of lager carbonitride at triple junctions

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圖 9 峰值溫度為1300 ℃時富Nb復合碳氮化物形貌觀察. (a)復合生長的碳氮化物; (b)位錯平直化

Figure 9. Morphology of Nb-rich carbonitrides at a peak temperature of 1300 ℃: (a) carbonitrides with different morphologies; (b) dislocations that tend to be straight

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表 1 實驗用奧氏體耐熱鋼22Cr15Ni3.5CuNbN的化學成分(質量分數)

Table 1. Chemical composition of austenitic heat-resistant steel 22Cr15Ni3.5CuNbN?%

C	Si	Mn	P	S	Cr	Cu	Co	Ni	Nb	N	B	Fe
0.07	0.38	0.64	0.016	0.002	22.6	3.5	0.06	15.7	0.53	0.34	0.003	余量

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表 2 析出相在奧氏體中的形成自由能ΔG

Table 2. Free energy of precipitates formation in austenite

析出相	在γ-Fe中的ΔG/(J·mol^-1)
VC	-81208+92.97T
VN	-155439+97.95T
NbC	-14400+60.28T
NbN	-196323+75.56T
TiC	-202602+83.76T
TiN	-298600+80.37T

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