新型25Cr-20Ni奧氏體耐熱鋼蠕變過程中析出相演變

新型25Cr-20Ni奧氏體耐熱鋼蠕變過程中析出相演變Precipitation Evolution in a Modified 25Cr-20Ni Austenitic Stainless Steel during Creep at 750℃

本文研究了一種新型25Cr-20Ni奧氏體耐熱鋼在750℃蠕變過程中析出相演變及其對性能的影響。研究結果表明，當蠕變時間較短時，析出相為M23C6和(Nb, V)(C, N)相。M23C6主要分布在晶界位置，(Nb, V)(C, N)相在晶內彌散析出。隨著蠕變時間增加，晶界位置M23C6發生長大和Ostwald熟化，但(Nb, V)(C, N)相具有較好的尺寸穩定性。同時，隨蠕變時間增加，組織中出現σ相。σ相首先在晶界位置析出，隨蠕變時間延長，σ相在晶內也會析出。研究還發現，大量σ相依附于(Nb, V)(C, N)相析出，這是由于(Nb, V)(C, N)相的析出導致附近奧氏體基體中局部位置C、N元素含量減少，從而促進了σ相的形核。實驗發現，不同應力條件下蠕變試樣均為沿晶斷裂，當蠕變時間較短時，裂紋在晶界位置M23C6處產生，引起沿晶開裂。隨著蠕變時間增加，σ相在晶界析出后，裂紋更容易在晶界σ相處產生，導致蠕變延伸率隨蠕變時間增加而減小。

25Cr-20Ni austenitic stainless steels are widely used as structural materials in nuclear industries and power plants for their excellent corrosion resistance and creep properties at elevated temperature. It is generally accepted that precipitation during creep is a key factor influencing the creep properties However, the evolution of precipitation is complicated due to the interaction of the alloy elements. To investigate the precipitation behaviors in the researched steel, a modified 25Cr-20Ni austenitic stainless steel has been crept at 750℃ under stress of 100-180 MPa. The microstructure observation indicates that M23C6 and (Nb, V)(C, N) precipitates are formed in short creep time. M23C6 precipitates are mainly generated at grain boundaries and (Nb, V)(C, N) particles are dispersively distributed in austenitic matrix. The grain boundary M23C6 carbides are significantly coarsened with the increasing creep time, while (Nb, V)(C, N) carbonitrides show high dimensional stability. As the creep time further prolongs, σ-phases are generated, first at grain boundaries and then at inner grains. Meanwhile, large amounts of σ-phases are formed around (Nb, V)(C, N) particles, indicating the σ-phase precipitation is accelerated by (Nb, V)(C, N) carbonitrides. Composition analysis and thermodynamic calculation are subsequently performed attempting to elucidate the precipitation mechanism of σ-phase. Carbon and nitrogen depleted zone is detected at the interface between (Nb, V)(C, N) precipitates and austenitic matrix. A correlation between σ-phase and C、N contents has been calculated by Thermo-Calc, which shows that the mass fraction of σ-phase increases with the decreasing C、N contents. On account of the thermodynamic calculations and experimental studies, it seems reasonable that the σ-phase formation can be induced by the carbon and nitrogen depletion in austenitic matrix. Additionally, owing to the poor cohesion between grain boundary M23C6 precipitates and austenitic matrix, cracks are inclined to propagate along grain boundaries, resulting in intergranular creep fracture. With the precipitation of σ-phase at grain boundaries after long time creeping, the cracks are primarily generated at σ-phase, further deteriorating the creep plasticity.

全文下載：https://pan.baidu.com/s/1P4B8po-5O-kq7_YA9BMpdg?

作為值得信賴的合作伙伴和高品質金屬合金的半成品供應商，通項公司擁有完善的服務體系和專業的團隊。在同客戶交易的過程中，我們力求根據不同的應用需求將我們的產品做到精益求精。針對當前和未來的市場需求，通項公司致力于為客戶提供優質的金屬材料解決方案。

TXCO has been a reliable partner and supplier of sophisticated and high-quality semi-finished products maed of alloys. In dialogue with our customers, we optimise our products to meet the specific application requirements. TXCO develops the superior alloy material solutions for current and future challenges.

獲取更多我們供應的產品和服務信息，請致電086-021-3113 6111或發電子郵件service@txco.ltd聯系我們，您也可以通過微信，微博，領英，臉書，推特和谷歌+與我們互動。

For more information on the products and services that we supply, call us at 086-021-3113 6111 or email us at service@txco.ltd. You can also get in touch on social media, we are constantly active on Weixin, Weibo, LinkedIn, Facebook, Twitter and Google+.