GH3230合金M23C6型碳化物的析出行为

研究了固溶态GH3230合金在800~1100 ℃时效不同时间下的碳化物析出行为。结果表明:GH3230合金固溶态组织主要为γ相+初生粒状碳化物M₆C+少量晶界粒状碳化物M₂₃C₆。试验合金在800~1100 ℃短时时效后,晶界和晶内析出的碳化物主要为M₂₃C₆型。其中晶界粒状M₂₃C₆型碳化物有沿着晶内长大的倾向,并逐渐变成胞状碳化物。在同一时效温度下,晶内碳化物析出数量会随着时效时间的增加而增加,此后会逐渐回溶,回溶开始的时间会随着时效温度的提高而逐渐提前。     

Precipitation path of secondary phases during solidification of the Co–25.5%Cr–5.5%Mo–0.26%C alloy

The solidification of the alloy ASTM F-75 ends with sigma phase formation instead of M₇C₃ carbide as presumed from literature. The M₂₃C₆ carbide observed in cast specimens precipitates from the sigma phase (σ) according to the global reaction σ+C→M₂₃C₆ over the range 1403–1303 K. Additionally, lamellar carbides appear below 1262 K for cooling rates lower than 35 K/min.     

固溶时效对SLM成形316L不锈钢块体件显微组织及硬度的影响

采用选区激光熔化技术(Selective laser melting, SLM)成功制备了316L不锈钢块体件,借助光镜(OM)和扫描电镜(SEM)及维氏硬度计研究了不同时效工艺(时效温度分别为650 ℃和850 ℃)对SLM成形316L不锈钢块体件显微组织以及显微硬度的影响。结果表明,SLM成形316L不锈钢块体件显微组织主要由细小柱状晶和蜂窝状晶粒组成。“层-层”和“道-道”熔池边界清晰可见,经固溶时效后边界基本消失,但晶界清晰可见,再结晶晶粒呈合并生长方式长大。650 ℃时效时,试样中少量M₂₃C₆分布于晶界,显微硬度相对较高;随着时效温度的升高,850 ℃时效后试样的晶粒进一步长大,沿晶界形成了大量不连续M₂₃C₆。     

服役态Super304H过热器钢管显微组织及力学性能

采用光学显微镜、扫描电镜和透射电镜等对某超超临界机组服役40 000 h后Super304H过热器钢管不同区域的显微组织和力学性能进行了分析。结果表明,服役40 000 h后Super304H钢管外壁出现异常长大的奥氏体晶粒,TEM测试表明外壁M₂₃C₆颗粒的粗化明显,且大量M₂₃C₆颗粒沿晶界连续分布,而MX相和富Cu相长大不明显;异常长大的晶粒导致服役态Super304H钢管外壁粗晶区的室温抗拉强度和冲击性能较供货态下降了21.9%和50%,粗晶区冲击试样断口沿晶断裂特征明显,其脆性显著增加,对Super304H钢管的服役安全性构成威胁,应加强监督消除因外壁奥氏体晶粒异常长大而带来的爆管等安全隐患。     

固溶处理对53Cr21Mn9Ni4N耐热钢组织及碳化物的影响

利用FactSage软件中的FSstel数据库对53Cr21Mn9Ni4N耐热钢的相图进行计算,分析了氮元素对凝固及冷却过程中相变及析出相的影响,得到了53Cr21Mn9Ni4N耐热钢平衡凝固及冷却相变路径图,并用OM、SEM、XRD、EDS等对53Cr21Mn9Ni4N耐热钢在1200 ℃固溶3、10、20、40和60 min后的显微组织及碳化物演变规律进行了研究。结果表明,53Cr21Mn9Ni4N耐热钢由1600 ℃平衡冷却至300 ℃的过程中完整的平衡相变路径为:液相+气体→液相→液相+δ铁素体→液相+δ铁素体+奥氏体→液相+奥氏体→奥氏体→奥氏体+M₂₃C₆→奥氏体+M₂(C,N)+M₂₃C₆→奥氏体+M₂(C,N)+M₂₃C₆+α铁素体→奥氏体+M₂(C,N)+M₂₃C₆+α铁素体+σ相。M₂₃C₆的析出温度随着氮含量的增加而降低,M₂(C,N)的析出物温度随着氮含量的增加而升高,M₂₃C₆会因M₂(C,N)的析出受到抑制。53Cr21Mn9Ni4N耐热钢的铸态组织非常不均匀,奥氏体呈树枝晶状生长,枝晶间析出大量层片状碳化物。随着固溶时间的增加,分布在枝晶间的层片状碳化物逐渐变成块状及短棒状,碳化物的数量逐渐减少,粗壮的树枝晶也逐渐变得细小。53Cr21Mn9Ni4N耐热钢在1200 ℃固溶后的组织及碳化物均得到明显改善。     

Effect of Intergranular Precipitation on the Internal Oxidation Behavior of Cr–Mn–N Austenitic Stainless Steels

The effect of intergranular precipitation on the internal oxidation behavior of Cr–Mn–N austenitic steels at 1000 °C in dry air atmosphere was investigated using scanning electron microscope, transmission electron microscope, and X-ray diffraction analysis. The results show that intergranular M23C6 carbide morphologies play an important role on the internal oxidation behavior of Cr–Mn–N steels. During the period of the oxidation, both discontinuous chain-shaped and continuous film-shaped intergranular M23C6 carbides precipitated along the grain boundaries. Internal oxides of silica preferentially intruded into the matrix along grain boundaries with discontinuous M23C6 carbide particles, while silica was obviously restricted at the interfaces between the external scale and matrix on the occasion of continuous film-shaped M23C6 carbides. It is seemed that reasonable microstructure could improve the oxidation resistance of Cr–Mn–N steels.     

Precipitation Behavior and Mechanical Properties of a 16Cr-25Ni Superaustenitic Stainless Steel Weld Metal During Post-weld Heat Treatment

A 16Cr-25Ni superaustenitic stainless steel weld metal for austenitic stainless steel/ferrite heat-resistance steel dissimilar metal weld was designed and prepared through tungsten inert-gas welding. The precipitate evolution and its correlation with mechanical properties were investigated during post-weld heat treatment (PWHT) at 690 °C for up to 12 h. The primary precipitates in the as-welded weld metal were identified as Mo-rich M₆C carbides in the interdendritic region and semicontinuous fine-sized M₂₃C₆ carbides along grain boundary. After PWHT, three types of precipitates coexisted in the interdendritic region: primary M₆C carbides, newly precipitated Mo-rich M₂X carbonitrides and some of the secondary M₂₃C₆ carbides. Additionally, mass secondary M₂₃C₆ carbides formed and coarsened along grain boundary. No undesirable intermetallic phases formed during the whole period. The M₂X and interdendritic M₂₃C₆ improved the strength of the weld metal after PWHT, but the elongation and impact toughness degraded, which were mainly owing to the intergranular M₂₃C₆ carbides that changed the fracture mode from ductile transgranular mode to mixed mode of transgranular and intergranular fracture. Meanwhile, the coarsening of M₂X carbonitrides may lead to the elongation loss during 8 h to 12 h. Evolution of impact toughness was also related to the M₂X carbonitrides, which made the crack easier to propagate compared with austenitic matrix and contributed to the decline of impact toughness. However, due to the sluggish precipitation of M₂X carbonitrides with longer holding time, the decreasing trend became slow from 4 to 12 h. The results showed that PWHT should be controlled within 8 h to obtain better combination of strength and ductility.     

Atomic-scale APFIM and TEM investigation of grain boundary microchemistry in Astroloy nickel base superalloys

Electron microscopy and atom-probes techniques, including 3D (three-dimensional) atom-probe, were applied to the investigation of grain-boundary (GB) microchemistry and interfacial segregation phenomena in nickel base superalloys, Astroloy. Diffraction patterns and EDX microanalyses exhibit the presence of intergranular M₂₃C₆ chromium enriched carbides as well as intragranular TiC precipitates. Complex phases containing Zr, C and S were also observed. Three-dimensional images as provided by the tomographic atom-probe revealed the presence of a strong segregation of both boron and molybdenum at grain boundaries. Considerable chromium enrichment at γ′-γ′ grain boundaries and slight carbon segregation to GBs, whatever their chemical nature, were also detected. All these segregants are distributed in a continuous manner along the boundary over a width close to 0.5 nm. Experiments show that segregation occurs during cooling and more probably between 1200 and 800°C. Boron, chromium and molybdenum GB enrichments are thought to be mainly controlled by an equilibrium segregation process. No segregation of zirconium was detected.     

Morphology of M23C6 precipitation in L12-ordered Ni3(Al, Cr)

A transmission electron microscope investigation has been performed on the morphology of M₂₃C₆ precipitation in L1₂-ordered Ni₃(Al, Cr) containing 0.1–0.5 mol% of carbon. By aging at temperatures around 1073 K after solution annealing at 1423 K, fine octahedral-shaped precipitates of M₂₃C₆ bounded by {111} facets appear first on the dislocations and then in the matrix. The shapes of the precipitates are not always equilateral but tetragonal or elongated octahedral ones appear during aging. Planar growth faults were observed in some of the octahedral precipitates. After prolonged aging or by aging at higher temperatures, these shapes of precipitates become unstable. The M₂₃C₆ precipitates then adopt a rod-like morphology elongated parallel to the 100 directions and characterized by steps bounded by {111} facets.     

深冷处理后回火温度对15Cr超级马氏体不锈钢组织及耐点蚀性能的影响

利用场发射扫描电镜、透射电镜以及电化学综合测试系统对15Cr超级马氏体不锈钢(SMSS)经不同热处理工艺处理后的显微组织变化和第二相碳化物及其对该钢腐蚀行为的影响进行了研究。结果表明,试验钢经不同热处理工艺处理后组织均由板条马氏体、奥氏体以及M₂₃C₆型碳化物颗粒组成,随着回火温度的增加,试验钢中逆变奥氏体含量增加,且在650 ℃回火时达到体积分数最大值41.41%。当回火温度高于600 ℃时第二相碳化物开始析出,且650 ℃回火后碳化物数量及尺寸较600 ℃增多。点蚀电位随着回火温度的增加而降低,第二相碳化物的析出降低了试验钢的点蚀电位,促进了亚稳点蚀位置的形成,从而降低了试验钢的耐腐蚀性能。     

高碳马氏体不锈钢M390与奥氏体不锈钢304闪光对焊的微观组织及力学性能

通过闪光对焊方法连接M390高碳马氏体不锈钢与304奥氏体不锈钢.通过室温拉伸试验、显微硬度测试表征了焊接接头的力学性能.采用扫描电镜(SEM)、能谱分析(EDS)和X射线衍射(XRD)分析了焊接接头的微观组织形貌、元素扩散及各区域相组成.结果表明,利用合适的焊接工艺参数,M390与304之间可以形成焊缝形貌美观、抗拉...     

Y12Cr18Ni9Cu易切削钢的平衡凝固相变与MnS析出行为

采用Thermo-Calc热力学软件对Y12Cr18Ni9Cu易切削钢在500～1800℃的析出相进行了热力学计算并得到了平衡凝固相变路径图。结果表明,Y12Cr18Ni9Cu易切削钢的平衡相主要有MnS、液相、δ-铁素体、奥氏体、M₂₃C₆、M₂(C,N)、σ相。平衡凝固和冷却相变路径：液相→液相+MnS→液相+δ-铁素体+MnS→液相+δ-铁素体+MnS+奥氏体→δ-铁素体+MnS+奥氏体→MnS+奥氏体→MnS+M₂₃C₆+奥氏体→MnS+M₂₃C₆+奥氏体+M₂(C, N)→MnS+M₂₃C₆+σ相+奥氏体+M₂(C, N)。随着S含量增加,MnS的析出量逐渐增加,析出温度也逐渐升高,Mn含量变化对MnS相的析出量几乎没有影响,但Mn含量增加会使MnS析出温度升高。Y12Cr18Ni9Cu易切削钢中的硫化物呈球形、椭球形、纺锤形或短棒状并以...     

Microstructural characterization and abrasive wear performance of HVOF sprayed Cr3C2–NiCr coating

Cr₃C₂–NiCr coatings were deposited by high velocity oxy-fuel (HVOF) process with different spray parameters to examine dominant microstructural factors in abrasive wear of the coatings. The microstructure of the HVOF sprayed Cr₃C₂–NiCr coatings was characterized by scanning electron microscopy and transmission electron microscopy (TEM). The apparent average size and volume fraction of carbide particles in the coatings were estimated through a quantitative imaging analysis. The formation of carbide phases in the coating was discussed based on the TEM observation results. The abrasive wear behavior of the coating was evaluated by the dry rubber wheel abrasive wear test and the wear mechanisms were elucidated. Influences of apparent size and volume fraction of carbide particles on the abrasive wear weight loss were examined through correlating the proposed relation with the experimental results. Results showed that Cr₃C₂ particle size was significantly reduced after the spraying and Cr₇C₃ carbide was present around Cr₃C₂ particles, and Cr₂₃C₆ carbide was dispersed in NiCr alloy matrix with a nano-crystalline structure. The three carbides were formed in the coating through different mechanisms. The removal of carbide particles in the coating was mainly responsible for the abrasive wear of the coating. The content and particle size of the Cr₃C₂ carbides were the two key factors controlling the abrasive wear of the HVOF sprayed Cr₃C₂–NiCr coatings.     

G115马氏体耐热钢平衡析出相的热力学计算和分析

为了制备超10 t级G115马氏体耐热钢的大型铸件,需科学评估合金元素对析出行为的影响。采用Thermo-Calc软件的TCFe9数据库对G115马氏体耐热钢的平衡析出相进行热力学模拟计算,研究了主元素对G115钢平衡态析出相类型、析出量和析出温度的影响。计算结果表明:G115马氏体耐热钢在650 ℃下的析出相主要有MX相(FCC-A1#2:NbC)、M₂₃C₆、Laves相和富Cu相。其中NbC的析出温度为1148 ℃,M₂₃C₆的析出温度为871 ℃,Laves相的析出温度为811 ℃,富Cu相的析出温度为734 ℃。其中C和Cr对M₂₃C₆的析出有影响,C和Nb对NbC的析出有影响,W对Laves相的析出有影响,B对各相的析出均无明显影响。     

Mo对4Cr5Mo2V型热作模具钢热稳定性能的影响

研究了Mo对4Cr5Mo2V型热作模具钢热稳定性能的影响,并利用扫描电镜(SEM)和透射电镜(TEM)等方法分析材料的微观组织。结果表明,含1.9%Mo和含2.4%Mo试验钢在600 ℃时的热稳定性能差异较小;在650 ℃时,相比于含2.4%Mo试验钢,含1.9%Mo试验钢经过48 h保温后硬度值低了2.3 HRC,马氏体基体的回复程度更大,出现较多的富Cr的大颗粒球状M₂₃C₆型碳化物,尺寸在150~200 nm之间,而2.4%Mo钢中弥散析出了数量更多的细小M₂C型二次碳化物,阻碍了富Cr型碳化物的长大,因此其碳化物的平均粒径更小,具有更好的热稳定性。     

Effect of Aging Heat Treatment on the Microstructure and Creep Properties of the Cast Ni-Based Superalloy at Low Temperature

Effect of aging heat treatment on the grain boundary microstructure and creep properties of a cast Ni-based superalloy was investigated. With increasing aging temperature from 750 to 1000 ℃, M_(23)C_6 carbides along the grain boundaries evolve from fine distributed block, continuous film into the coarse discrete block. Moreover, the M_(23)C_6 carbides are mainly enveloped within γ’ layers along grain boundaries during 1000 ℃ aging. Creep rupture lifetime and elongation at 760 ℃ and 645 MPa are improved with increasing the aging temperature. In particular, the creep rupture lifetime of the specimens aging at 1000 ℃ is one order of magnitude higher than that of the specimens aging at 750 ℃. The enhancement of ductility induced by the γ’ envelopes plays a significant role in the improvement of creep rupture lifetime.     

Effects of Isothermal Aging on Microstructure and Mechanical Property of Low-Carbon RAFM Steel

In order to investigate the microstructure and mechanical property evolution of low-carbon reduced activation ferritic/martensitic(RAFM) steel during isothermal aging, the normalized and tempered specimens were aged at 600 °C for 500,1000, and 3000 h, respectively. The microstructural evolution with aging time was analyzed, including the precipitation and growth of M_(23)C_6 and MX-type carbides as well as the formation of Laves phase. The results indicate that the coarsening of M_(23)C_6 is more obvious than that of MX with increase in aging time. During the long-term thermal exposure, the Fe_2 W Laves phase precipitates adjacent to M_(23)C_6 along the prior austenite grain boundaries and packet boundaries. Lower carbon content can delay the precipitation of Laves phase compared to the steel containing higher carbon. In addition, the Laves phase precipitated along boundaries can provide the precipitation strengthening, slightly increasing the tensile strength of low-carbon RAFM steel after aging for 3000 h.     

真空低压渗碳对304与316L奥氏体不锈钢组织和性能的影响

采用真空低压渗碳技术对304和316L奥氏体不锈钢进行表面强化,利用光学显微镜、扫描电镜、Thermo-Calc热力学软件、X射线衍射仪和显微硬度计等对渗碳层显微组织、相组成及硬度分布进行分析表征,计算了奥氏体不锈钢渗碳层中不同衍射峰的偏移量及渗碳前后晶格常数的变化量。结合钼对奥氏体不锈钢渗碳过程的影响,对比研究了304和316L奥氏体不锈钢渗碳后,在渗碳层深度、表面硬度及碳化物的析出规律等方面的差异。结果表明,经750 ℃真空渗碳2.6 h后,304和316L奥氏体不锈钢晶格常数分别增加了1.33%和1.14%,形成了由膨胀奥氏体和Cr₂₃C₆组成的渗碳层,Cr₂₃C₆在渗碳层中主要以条状沿膨胀奥氏体晶界析出,表面硬度较基体硬度均提升了两倍以上。     

热处理对稀土5Cr钢组织及析出相的影响

以稀土5Cr钢为对象,研究了热处理工艺(870、900、930 ℃保温50 min水淬,670、690、710 ℃保温90 min回火)对其组织及第二相析出行为的影响。结果表明,试验钢经870 ℃淬火后,组织未完全奥氏体化;随着淬火温度的升高,试验钢完全奥氏体化,原始奥氏体平均晶粒尺寸从900 ℃的13.49 μm增大到930 ℃的15.01 μm,且组织均匀性明显下降。合适的淬火温度为900 ℃。在670~710 ℃回火后,组织分布为回火屈氏体、回火屈氏体+回火索氏体、回火索氏体。回火后第二相为分布在基体上的Cr₇C₃碳化物及在界面聚集的Cr₂₃C₆碳化物。随着回火温度的升高,Cr₂₃C₆碳化物比例逐渐增加。为避免回火过程中M₂₃C₆型碳化物的聚集和粗化,合适的回火温度为690 ℃。     

GH141合金的凝固偏析特性及均匀化处理

利用光学显微镜、扫描电镜及能谱分析仪分析了经真空感应+真空自耗冶炼的GH141合金自耗锭的铸态组织及凝固偏析特性,并研究了均匀化处理温度和时间对GH141合金微观组织、析出相、元素偏析情况的影响规律。结果表明,GH141合金铸锭存在明显枝晶偏析,Ti、Mo偏聚于枝晶间,Al、Co、Cr偏聚于枝晶干;枝晶间主要析出相为MC和M₆C+M₂₃C₆碳化物。在均匀化过程中,随着均匀化温度的升高和时间的延长,枝晶组织消除、碳化物回溶、偏析元素逐渐扩散均匀;经1190 ℃×48 h均匀化处理后,合金成分基本均匀,大部分碳化物已回溶。