W對(duì)新型Nb穩(wěn)定化奧氏體耐熱鑄鋼1000 ℃蠕變性能的影響

W對(duì)新型Nb穩(wěn)定化奧氏體耐熱鑄鋼1000 ℃蠕變性能的影響EFFECTS OF W ON CREEP BEHAVIORS OF NOVEL Nb-BEARING AUSTENITIC HEAT-RESISTANT CAST STEELS AT 1000 ℃

以新設(shè)計(jì)的4種不同W含量（0~4.87%，質(zhì)量分?jǐn)?shù)）的Nb穩(wěn)定化奧氏體耐熱鑄鋼為研究對(duì)象，通過(guò)在1000 ℃、50 MPa條件下的蠕變性能測(cè)試和蠕變前后的組織分析，研究了W對(duì)奧氏體耐熱鑄鋼1000 ℃蠕變行為的影響機(jī)理。結(jié)果表明：合金的最小蠕變速率隨W含量的增加先降低后增高。合金的主要析出相為Nb(C, N)和富Cr相。W含量的增加對(duì)Nb(C, N)的影響很小，但明顯促進(jìn)富Cr碳化物析出，并促使(Cr, Fe, W)7C3轉(zhuǎn)變?yōu)?Cr, Fe, W)23C6。而且，過(guò)量的W添加會(huì)促進(jìn)金屬間化合物?相析出。在蠕變過(guò)程中，合金的基體還會(huì)二次析出納米級(jí)的Nb(C, N)，阻礙位錯(cuò)運(yùn)動(dòng)，從而進(jìn)一步提高合金的蠕變強(qiáng)度。但是，富Cr相胞團(tuán)，尤其是胞團(tuán)內(nèi)的?相，會(huì)促進(jìn)蠕變裂紋形核長(zhǎng)大，從而提高合金的蠕變速率，降低蠕變壽命。

In order to comply with more stringent emissions and fuel economy regulations worldwide, the operation temperature of exhaust components for automotive gasoline engines is now reaching to as high as 1000 ℃, about 200 ℃ higher than the conventional standard. As a result, the incumbent materials for exhaust manifolds and turbine housings are being pushed beyond their high-temperature strength and oxidation limitations. Therefore, there is an urgent demand from automotive industries to develop novel and cost-effective alloys that are durable against these increased temperatures. In this work, the effect of W additions on the creep behavior of a series of Nb-bearing austenitic heat-resistant cast steels is investigated at 1000 ℃ and 50 MPa. Microstructures before and after creep rupture tests are carefully characterized to investigate the microstructural evolution during creep deformation. The minimum creep rate of these alloys shows a trend from decline to rise as the W addition is increased. Microstructural analyses reveal that the W addition does not affect the formation of primary Nb(C, N), whereas significantly improves the precipitation of Cr-rich carbides, as well as accelerating the phase transformation from (Cr, Fe, W)7C3 to (Cr, Fe, W)23C6. Moreover, the excessive addition of W leads to the formation of the intermetallic ?-phase. During creep deformation, the secondary precipitation of nano-scale Nb(C, N) also aids in the strengthening of the creep resistance through pinning the dislocations. However, the cellular Cr-rich phase that contains ?-phase significantly accelerates the nucleation and propagation of creep cracks, thereby increasing the creep rate and decreasing the creep life.

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