服役態(tài)Cr35Ni45Nb合金高溫真空滲碳行為及相演化機(jī)理研究
發(fā)布時(shí)間：2018-12-26 10:00
【摘要】：采用乙炔真空滲碳方式對(duì)服役6 a的乙烯裂解爐管合金Cr35Ni45Nb進(jìn)行了加速滲碳處理,并利用SEM,XRD及定量電子探針等手段對(duì)滲碳前后爐管內(nèi)壁的滲碳行為及相演化機(jī)理進(jìn)行系統(tǒng)研究.結(jié)果表明,爐管內(nèi)表面形成了較厚的Cr2O3/Si O2復(fù)合氧化層.復(fù)合氧化層表現(xiàn)出良好的抗腐蝕能力,是阻止C滲入爐管內(nèi)部的有效障礙.材料的抗?jié)B碳能力主要取決于表層Cr2O3的連續(xù)性、致密性和亞表層Si O2的穩(wěn)定性.在低氧分壓且具有還原性的氣氛中,表層的Cr2O3層逐漸碳化為Cr3C2,并且Cr3C2逐漸剝離和脫落,使得保護(hù)性Cr2O3膜的抗?jié)B碳能力逐漸減弱甚至消失.亞表層的Si O2雖具有優(yōu)良的熱力學(xué)穩(wěn)定性,但Si較低的活度使得Si O2層不夠連續(xù),仍有部分C從氧化層空隙間滲入.當(dāng)移除該復(fù)合氧化層或者滲碳時(shí)間足夠長(zhǎng)使得復(fù)合氧化層抗?jié)B碳能力急劇減弱時(shí),爐管材料內(nèi)部由于發(fā)生嚴(yán)重的內(nèi)部滲碳使得組織結(jié)構(gòu)發(fā)生了顯著變化:枝晶間碳化物嚴(yán)重合并和粗化,并原位發(fā)生由M23C6到M7C3的轉(zhuǎn)變,同時(shí)在碳化物內(nèi)部析出類似于離異共析狀的蠕蟲狀g相.距表面越近,C活度越高,導(dǎo)致在約0.5 mm深的范圍內(nèi)發(fā)生以大量石墨析出為特征的金屬塵化現(xiàn)象.碳化物的嚴(yán)重合并粗化以及金屬塵化現(xiàn)象會(huì)造成爐管組織的嚴(yán)重弱化、宏觀裂紋的產(chǎn)生以及爐管服役壽命的降低.
[Abstract]:The accelerated Carburizing of ethylene cracking furnace tube alloy Cr35Ni45Nb with 6 years service was carried out by means of acetylene vacuum carburization, and SEM, was used. The Carburizing behavior and phase evolution mechanism of furnace tube before and after Carburizing were systematically studied by XRD and quantitative electron probe. The results show that a thick Cr2O3/Si O 2 composite oxide layer is formed on the inner surface of the furnace tube. The composite oxidation layer exhibits good corrosion resistance and is an effective barrier to prevent C from infiltrating into the furnace tube. The carburization resistance of the material mainly depends on the continuity, compactness and stability of Si O 2 in the surface layer. In the atmosphere of low oxygen partial pressure and reductive atmosphere, the surface layer of Cr2O3 was gradually carbonized into Cr3C2, and Cr3C2 was gradually stripped and shedded off, which made the Carburizing resistance of protective Cr2O3 film weakened or even disappeared. Although the Si O 2 in the subsurface layer has excellent thermodynamic stability, the low activity of Si makes the Si O 2 layer not continuous enough, and some C is still infiltrating between the oxidation layer voids. When the composite oxidation layer is removed or the carburizing time is long enough, the Carburizing resistance of the composite oxide layer decreases sharply. Due to the serious carburization inside the furnace tube, the microstructure of the furnace tube is changed significantly: the dendrite carbides are merged and coarsened, and the transformation from M23C6 to M7C3 occurs in situ. At the same time, a vermicular g phase similar to a divorced eutectoid is precipitated in the carbides. The closer it is to the surface, the higher the activity of C is, which leads to the dedusting of large amount of graphite in the depth range of 0. 5 mm. The serious coalescence and coarsening of carbides and metal dust will lead to the serious weakening of furnace tube structure, the occurrence of macroscopic cracks and the decrease of service life of furnace tubes.
【作者單位】： 北京科技大學(xué)材料科學(xué)與工程學(xué)院;中國(guó)特種設(shè)備檢測(cè)研究院;
【基金】：國(guó)家高技術(shù)研究發(fā)展計(jì)劃資助項(xiàng)目2012AA03A513~~
【分類號(hào)】：TG156.81
，
本文編號(hào)：2391934
[Abstract]:The accelerated Carburizing of ethylene cracking furnace tube alloy Cr35Ni45Nb with 6 years service was carried out by means of acetylene vacuum carburization, and SEM, was used. The Carburizing behavior and phase evolution mechanism of furnace tube before and after Carburizing were systematically studied by XRD and quantitative electron probe. The results show that a thick Cr2O3/Si O 2 composite oxide layer is formed on the inner surface of the furnace tube. The composite oxidation layer exhibits good corrosion resistance and is an effective barrier to prevent C from infiltrating into the furnace tube. The carburization resistance of the material mainly depends on the continuity, compactness and stability of Si O 2 in the surface layer. In the atmosphere of low oxygen partial pressure and reductive atmosphere, the surface layer of Cr2O3 was gradually carbonized into Cr3C2, and Cr3C2 was gradually stripped and shedded off, which made the Carburizing resistance of protective Cr2O3 film weakened or even disappeared. Although the Si O 2 in the subsurface layer has excellent thermodynamic stability, the low activity of Si makes the Si O 2 layer not continuous enough, and some C is still infiltrating between the oxidation layer voids. When the composite oxidation layer is removed or the carburizing time is long enough, the Carburizing resistance of the composite oxide layer decreases sharply. Due to the serious carburization inside the furnace tube, the microstructure of the furnace tube is changed significantly: the dendrite carbides are merged and coarsened, and the transformation from M23C6 to M7C3 occurs in situ. At the same time, a vermicular g phase similar to a divorced eutectoid is precipitated in the carbides. The closer it is to the surface, the higher the activity of C is, which leads to the dedusting of large amount of graphite in the depth range of 0. 5 mm. The serious coalescence and coarsening of carbides and metal dust will lead to the serious weakening of furnace tube structure, the occurrence of macroscopic cracks and the decrease of service life of furnace tubes.
【作者單位】： 北京科技大學(xué)材料科學(xué)與工程學(xué)院;中國(guó)特種設(shè)備檢測(cè)研究院;
【基金】：國(guó)家高技術(shù)研究發(fā)展計(jì)劃資助項(xiàng)目2012AA03A513~~
【分類號(hào)】：TG156.81
，
本文編號(hào)：2391934
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