含氮Inconel690合金的凝固偏析和相析出行为研究

IMR OpenIR

	含氮Inconel690合金的凝固偏析和相析出行为研究
	江荣
学位类型	硕士
导师	刘奎
	2011
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料加工工程
关键词	690合金微观偏析析出相过热温度熔化速度 Alloy 690 Microsegregation Precipitates Superheating Temperature Melting Rate
摘要	"Incone1690合金（以下简称690合金）是一种含Cr约30wt.%的奥氏体型镍基耐蚀合金，由于其具有优异的耐应力腐蚀开裂(SCC)性能而被广泛用做核电站蒸汽发生器传热管用材料。690合金中含有微量的S、N，以及少量的Ti、C等合金元素，凝固过程中这些元素易于产生微观偏析，导致有害相析出，影响合金的热加工性能和耐蚀性能。因此，为进一步优化690合金成分，提高其综合性能，本文采用光学显微镜(OM)、电子探针显微分析仪(EPMA)、扫描电镜(SEM)和透射电镜(TEM)，系统研究了含氮690合金凝固过程的元素偏析和相析出行为，并研究和讨论了熔体过热温度和熔化速度对690合金中氮化物演化行为的影响。采用“等温凝固淬火法”研究了N 含量为0.001-0.110wt%的690合金的凝固行为。结果表明，N元素不影响690合金的液相线温度，但降低固相线温度。当N含量从10ppm增加到1100ppm时，固相线温度由1362oC降低到1354oC。Ti、Cr、Ni、Fe在凝固过程中产生微观偏析，其中Ti、Cr是正偏析元素，而Ni、Fe是负偏析元素。随着N含量增加，残余液相中Cr浓度升高，Ti和Ni浓度降低，而N含量对Fe浓度的影响不明显。C和S在终凝区内具有明显的偏聚倾向。 N元素影响690合金凝固过程中形成的析出相类型。低N含量(10~200ppm) 690合金中的析出相为TiN、Ti(C, N)、Ti4C2S2和(Ti, Cr)S，而高N含量(300~1100ppm) 690合金中的析出相为TiN、(Ti, Cr)N、CrS、Cr2C和Cr7C3。 TiN或Ti(C, N)类型氮化物是690合金主要的凝固析出相。随着过热温度的升高和熔化速度的降低，凝固析出的微米尺度TiN的体积分数显著降低。随着过热温度的升高，TiN平均尺寸减小，形态由规则的块状转变为细小的颗粒状。熔化速度对TiN平均尺寸及形态的影响不明显。690合金凝固样品经均匀化退火和冷压缩变形后，在再结晶退火过程中弥散析出大量亚微米尺度的Ti(C, N)，其析出量随过热温度的升高而增加，随熔化速度的升高而降低。弥散分布的亚微米尺度的Ti(C, N)不能有效阻止晶粒长大，但可以提高690合金基体强度。"
其他摘要	"Inconel Alloy 690 (hereinafter called Alloy 690) is an austenitic nickel-based corrosion resistant alloy with about 30wt.% chromium content. It is the most applicated steam generator tubing material of Pressured Water Reactor (PWR) in nuclear power plants because of its superior resistance to stress corrosion cracking (SCC). However, the trace elements such as S, N and the minor alloying elements such as Ti, C contained in Alloy 690 much easily tend to segregate in the front of liquid connected already solidified metal during the alloy solidification process. And sometimes their severe segregation corresponds to certain detrimental phase precipitation, which is harmful to the hot workability and corrosion resistance of Alloy 690. In this thesis, the optical microscope (OM), electron probe microanalysis (EPMA), scanning electron microscope (SEM) and transmission electron microscope (TEM) have been used to investigate segregation and phase precipitation behavior during isothermal solidification process in nitrogen-containing Alloy 690. The results are expected to be pretty helpful for further optimizing the composition of Alloy 690 and improving its corrosion resistance. Additionally, the effects of superheating temperature and melting rate on the evolution behavior of TiN in Alloy 690 have also been studied. The “isothermal solidification and quenching” method has been employed to study N effect on the solidification characteristic of Alloy 690. The results indicate that N has no influence on the liquidus temperature, but lowers the solidus temperature of Alloy 690 by 8 oC when its N content increases from 10ppm to 1100ppm. Ti and Cr are strong positive segregated elements, while Ni and Fe are negative segregated elements. With the increasing N content, the concentration of Cr in the residual liquid becomes significantly enriched, whereas the Ti and Ni concentration decreases markedly. It seems that N does not obviously affect the concentration of Fe both in the solidfided solid and in the residual liquid. In addition, C and S show severe positive segregation tendency in the final solidification zone, even though their contents are quite low. Nitrogen has a significant effect on types of precipitates formed during isothermal solidification process. In the Alloy 690 with low N content (10~200ppm), the precipitates are Ti(C, N), TiN, Ti4C2S2 and (Ti, Cr)S; while in the Alloy 690 with high N content (300~1100ppm), the precipitates are TiN, (Ti, Cr)N, CrS, Cr2C and Cr7C3. Precipitation of TiN or Ti(C, N) during solidification is one of distinct characteristics of Alloy 690. As the superheating temperature rises and melting rate decreases, the volume fraction of micron-scale primary TiN decreases dramatically. The average size of TiN reduces with the superheating temperature, and its morphology transforms from regular blocky to granular accordingly. However, the melting rate has little influence on the average size and morphology of TiN. After homogenization annealing and cold compression deformation, there is a great deal of sub-micron scale Ti(C, N) precipitating dispersedly in the Alloy 690 during recrystallization annealing, and the amount increases with the rising superheating temperature and decreases with the increasing melting rate. Although those dispersed sub-micron scale Ti(C, N) particles fail to hinder grain growth, they can act as a strengthener and improve the mechanical property of Alloy 690."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64384
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	江荣. 含氮Inconel690合金的凝固偏析和相析出行为研究[D]. 北京. 中国科学院金属研究所,2011.