4Cr14Ni14W2Mo钢离子渗氮层剥落的研究

研究了经不同加热温度锻造、固溶和７５０℃时效后钢的晶粒度、孪晶、碳化物的分布及纯氨和氨加氩做介质离子渗氮后渗层组织、相组成、应力状态、氮碳浓度分布、剥落坑形貌。分析表明：纯氨离子渗氮后表面层的碳向里扩散，并出现一峰值：氨加氩渗氮降低了渗层中氮浓度，从而降低了渗层中的应力，这是消除该钢渗氮层剥落的有效途径。     

经过渗氮的钢在硼砂浴中浸渍形成的碳氮化合物覆层

将经过渗氮的钢在含V、Nb、Cr的硼砂浴中浸渍保持,依靠这些元素和钢中的C和N结合形成V、Nb、Cr的碳氮化合物层。随着处理时间延长,若氮全部被消耗,则在碳氮化合物上面形成碳化物层。渗氮对于增加层厚相防止造成紧接渗层下的母材软化层是有效的。碳氮化合物覆层的钢的耐磨性和碳化物覆层钢的耐磨性大致是相同的,只要渗氮时间不过份的长,其冲击值和淬火回火的情况大致相同。     

碘对氮碳共渗钢件组织和硬度的影响

在６００￣７００℃地不同材料进行了催渗氮碳共渗，对试样进行了金相分析，硬度测定，对渗层进行电子探针成分析。结果表明，在共析温度以下进行催渗氮碳共渗，具有渗速快、渗层硬度高的特点；化合物随催渗温度升高而增厚，致密碳共渗后快冷，在渗层获得含氮碳的马氏体组织，用该工艺处理轮模具等零件，变形小，耐磨性高，零件的寿命高。     

超级马氏体不锈钢的等离子渗氮和氮碳共渗

超级马氏体不锈钢(SMSSs)是典型的新一代13%Cr马氏体钢,含碳量较低,并含镍和钼,故具有更好的可焊性和低温韧性。研究表明,不锈钢低温等离子渗氮或氮碳共渗可形成硬的表层从而提高耐磨性。本文对SMSS试样分别在400℃、450℃和500℃进行了等离子渗氮和氮碳共渗,并对处理后的SMSS试样分别采用光学显微镜、显微硬度、XRD和干磨损试验进行了表征。X射线衍射分析证明,氮化铬含量随着渗氮和氮碳共渗温度的升高而增加,也显示出铁和铬的碳化物含量随着处理温度的升高而增加。不同温度下处理后的试样均随着处理温度的升高,磨损体积减小、耐磨性提高。对经等离子处理和未处理的试样所观察到的主要磨损机制都是凿削磨损。     

氨水浓度对38CrMoAl钢液相等离子体电解渗氮层显微组织及性能的影响

在不同氨水浓度的电解液中，采用液相等离子体渗透技术在38CrMoAl钢表面制备了渗氮层。采用光学显微镜(OM)、扫描电镜(SEM)和X射线衍射仪(XRD)等对渗氮层的显微组织、相组成进行了观察和分析，并采用Parstat2273电化学工作站测试了渗氮层的耐蚀性能，并对其显微硬度和耐磨性进行了测试，研究了氨水浓度对38CrMoAl钢液相等离子体渗氮显微组织与性能的影响。结果表明：随着氨水浓度的增大，渗氮层中的白亮层厚度呈增加趋势，分布着针状的氮化物和细小碳化物的扩散层厚度和渗氮层最大显微硬度值呈先增加后降低的趋势；当氨水浓度为60%时，渗氮层厚度达160μm,其中扩散层为112μm,渗氮层硬度最高为1023 HV0.1,约是基体硬度的3.5倍；渗氮层主要以Fe₂N、Fe₃N相等为主；渗氮层的耐磨性能和耐腐蚀优于基体。     

铝型材挤压模具失效分析

H13钢模具在生产铝型材的过程中出现早期软化、变形、开裂和磨损等问题,采用化学成分分析、硬度测试和显微组织观察等检测方法,对模具失效原因进行分析.结果表明:该模具在渗氮前进行的淬火和回火工艺不合理,存在少量夹杂和未溶解的碳化物,使其整体韧性不高;其渗氮层厚度较薄,且渗氮层硬度偏低,组织不稳定,渗氮层与基体的结合力较差,...     

碳钢渗氮过程中碳原子的迁移

对４５，Ｔ８，Ｔ１３钢试样进行气体渗氮。应用Ｘ－ｒａｙ，ＳＥＭ，ＴＥＭ研究了渗氮过程中碳原子的迁移，结果表明：由渗氮试样的碳浓度分布曲线可精确确定渗氮层深。并对碳迁移机制进行了初探。     

Q235钢低温渗铬及渗氮复合工艺的研究

采用双层辉光离子渗铬与随后的离子渗氮工艺相结合,在Q235钢表面分别进行渗铬＋渗氮、渗氮＋渗铬＋渗氮以及渗氮＋渗铬复合工艺处理;考察不同工艺条件下渗层的组织及性能。结果表明：前两种工艺表面均出现离子氮化白亮层（ε相）;三种工艺渗层主要相组成为：铁一铬固溶体（Fe-Cr）、铁的碳化物（Fe3C）和氮化物（Fe3N）、铬氮化合物（Cr2N）及少量的铬碳化合物（Cr23C6）。在本实验条件下,渗铬＋渗氮的渗层表面显微硬度最高,达到760HV,耐磨性最好,强化效果最明显。     

应用N.M.处理消除表层过共析碳化物疵病

过共析钢过高的含碳量常带来碳化物粗大和网状带状偏析.传统的高温正火工艺不但能耗高,有时效果也不理想.而结合淬火加热进行固溶渗氮,利用氮强烈扩大奥氏体区、降低A1和Acm点的原理,促使表层碳化物溶入奥氏体内,淬火后得到高硬度的含氮马氏体和适量残留奥氏体.随着碳化物的溶解,各种碳化物疵病基本或完全消除.与传统工艺相比本工艺有极大节能效果.文中对含氮马氏体化(N.M.)处理给出明确定义,并介绍了N.M.处理消除剪毛机刀片碳化物疵病和改善某宇航零件与军工齿轮碳氮共渗层组织的应用效果.     

等离子表面复合渗合金层碳化物相的研究

利用等离子表面合金化技术，在碳钢表面进行W、Mo、C共渗，共渗合金层中W当量质量分数超过10％，含碳量超过平衡碳计算值，碳饱和度达1．6以上，约是一般冶金高速钢碳饱和度的两倍。用X射线衍射分析了共渗合金层中碳化物的结构类型；用电子探针进行微区成分分析，测定碳化物的成分，并计算了碳化物中碳原子与合金元素之间的原子比。结果表明，共渗合金层中的碳化物主要是由合金元素W、Mo和C形成的M6C型碳化物及少量的M2C型碳化物。M6C型碳化物中碳原子与合金元素之间的原子比为1．6～3．2：1平均为2．4。与一般冶金低合金高速钢中的合金元素与碳原子比相比较，范围窄，且偏低。     

Characterisation of creep-weak zones (white bands) in grade 91 weld metal

Abstract

A microstructural study of creep failure in grade 91 weld metal has revealed two primary modes of creep failure. In addition to creep fractures along columnar grain boundaries (typical of weld metal creep failure), creep fractures were also found along creep-weak 'white bands' which had formed at the inter-bead boundaries. The white-band regions consisted of material where the M₂₃C₆ carbides had dissolved during creep testing; the loss of carbides had allowed recrystallisation of the martensitic structure to ferrite and consequently this material was much softer than the bulk weld metal. The element mapping over the weld metal by laser-induced breakdown spectroscopy demonstrated that there was significant inhomogeneity in the distribution of certain elements, most significantly, chromium. This inhomogeneity resulted in strong activity gradients in carbon (even though the carbon concentration was homogeneous following welding) resulting in carbon loss from the alloy-depleted regions, the associated dissolution of carbides and the recrystallisation that accompanied this, and thus the poor mechanical properties which resulted in creep failure.     

碳含量对热等静压态FGH96合金碳化物的影响

对不同碳含量的FGH96成型合金中碳化物进行了研究,并对合金原始粉末表面成分偏析进行了测定,以深入探讨碳含量对合金中碳化物的影响。结果表明:FGH96合金中碳含量的增加,提高了原始粉末表面碳含量和富Ti层厚度;HIP(热等静压)态FGH96中碳化物主要为富Ti和Nb的MC,随着碳含量升高,合金中分布在原始粉末颗粒边界(previous particle boundary,PPB)上和PPB以外区域的碳化物含量均逐渐升高,而非PPB碳化物含量上升的幅度相对较大;合金中碳含量越高,PPB碳化物中强碳化物形成元素的含量越低,非PPB碳化物的成分不受合金碳含量的影响;碳的加入促进了PPB碳化物的粗化,并扩展了其尺寸分布的范围;合金中碳含量越高,PPB碳化物的平均自由程越小,合金在室温下的断面收缩率越低。     

超高碳钢球化组织与性能研究

对一种含碳量为1.41%的超高碳钢分别采用离异共析（DET）和淬火＋高温回火工艺球化后进行组织和力学性能研究。结果表明：球化处理后锻造组织中的碳化物得到充分球化,获得了铁素体基体上弥散分布超细球状碳化物的组织;其屈服强度和抗拉强度都有明显提高,伸长率达到17.5%,是一种优良的结构钢材料;超高碳钢拉伸过程中裂纹容易在大颗粒碳化物处萌生并扩展。     

碳量变化对高铬铸铁初生奥氏体稳定性的影响

通过改变高铬铸铁(Cr15)的含碳量,研究了高铬铸铁凝固过程中初生奥氏体中C、Cr量变化对初生奥氏体稳定性的影响。结果表明,较快的冷速条件下自液体中析出的初生奥氏体固溶的C、Cr量远高于平衡条件;在本试验冷却条件下,随着碳含量的增加,初生奥氏体中固溶的C量增加、Cr量减少,这使C原子的扩散增强,并且奥氏体过饱和程度增大,二次碳化物析出趋势增强;当二次碳化物未析出时,碳量的增加使奥氏体稳定性增加,而一旦二次碳化物析出,碳量的增加使奥氏体的稳定性变差;碳量2.63%为奥氏体能否析出二次碳化物的临界值。     

工模具钢的两相渗碳研究

虽然出现了多种多样的表面硬化技术,但渗碳仍然是生产上常用的表面化学热处理方法,它能有效地提高材料表面的耐磨性。而且生产工艺简单,成本低廉,在生产中一直广泛应用。该方法用于低碳钢或低碳合金钢的表面强化。已有相当成熟的工艺［１］。目前已逐渐用于共析钢和过共析钢［２］。由于这些材料本身含碳量很高,在渗碳温度下处于奥氏体和碳化物两相共存状态,所以把这种渗碳方法称之为两相渗碳。１　试验方法试验材料选用三种常见的工模具钢：热作模具钢３Ｃｒ２Ｗ８Ｖ、高速钢Ｗ１８Ｃｒ４Ｖ和Ｔ８钢。在自制的小型滴注式渗碳炉中渗碳…     

Internal oxidation and carburisation of heat-resistant alloys

The commercial alloys Nicrofer-HT, Alloy 800 and Type 304 stainless steel have been exposed under thermal cycling conditions to CO-CO₂ gas mixtures at temperatures of 650-750 °C. Thermal cycling led to repeated scale spallation which accelerated chromium depletion from the alloy subsurface regions. Subsequent dissolution of carbon and oxygen into the alloys led to extensive internal precipitation of carbides and oxides. The large volume fractions of carbide and oxide left small quantities of iron-nickel-rich metal. The in situ oxidation of internal carbides in the stainless steel led to large volume expansions and the development of mechanical stress. This was increased during thermal cycling, leading to disintegration of the surface regions. Temperature and surface treatment were both found to be significant factors in the resistance of alloys to the CO-CO₂ atmosphere.     

Effect of strong carbide forming elements in hardfacing weld metal

To achieve high carbon hard-facing weld metals with both high hardness and crack resistance, strong carbide forming elements Ti, Nb and V were alloyed into the weld metals, and their effect on the formation of carbides and the matrix microstructure were studied. Electron Probe Microanalysis (EPMA), Energy Dispersive Spectroscopy(EDS) and Transmission Electron Microscopy (TEM) were adopted to investigate the microstructure, then thermodynamics of the formation of carbides was calculated and their effect on the matrix was further discussed. It is revealed that Nb, Ti and V influence strongly the distribution and existing state of carbon, inducing precipitation of carbides accompanying with the depletion of carbon in matrix. But when only V are alloyed as carbide forming element, the carbides are scarce and distributed along grain boundaries, and the hard-facing alloy is too hard, while the using of only Nb or Ti could not reinforce the weld metals effectively. The hard-facing alloy reinforced with Nb, V a     

Nucleation and thermal stability of carbide precipitates in high Nb containing TiAl alloys

This work monitors the nucleation, growth and coarsening of carbides in powder metallurgically processed, high Nb containing TiAl alloys. The effects of carbon content, annealing conditions and internal defects on the precipitation and stability of carbides were systematically investigated by high energy X-ray diffraction and transmission electron microscopy. In general, at 800 °C the carbide microstructure can still change significantly up to 1000 h of annealing. It is found that a higher carbon concentration promotes the carbide precipitation process and increases the thermal stability of carbides. Internal interfaces and other crystallographic defects act not only as heterogeneous nucleation sites for perovskite Ti₃AlC carbides but also as carbon sinks. This retards the carbide nucleation in the interior of γ-TiAl grains. By homogenising the carbon distribution through solution heat treatment the nucleation of carbides in the γ-TiAl matrix is significantly accelerated as an effect of higher matrix carbon content.