大型重载零件高浓度深层渗碳渗层硬度分布的计算机模拟

在对高浓度深层渗碳的特点进行分析的基础上,考虑到碳化物的析出与溶解、温度及碳浓度对扩散行为的影响,气氛环境对相界面碳传递过程的影响,淬火烈度对渗碳层冷却效果的影响,提出了一种新的模拟高浓度深层渗碳渗层硬度分布的方法。     

Corrosion by carbonaceous gases,carburization and metal dusting,and methods of prevention†

Abstract

Exposure of metallic materials to carbonaceous gases can lead to (i) carburization, i.e. internal carbide formation causing embrittlement and failure especially at high temperatures of cracking tubes for olefine production, (ii) metal dusting, a disintegration of metals to a dust of carbon and fine metal particles, occurring at intermediate temperatures, e.g. in synthesis gas for ammonia or methanol production or in direct reduction of iron ores, and (iii) coking, the carbon deposition which is an annoying phenomenon in many processes. The mechanisms of these phenomena are well understood now and they can be suppressed or effectively retarded either by the presence of some sulphur in the process gases and/or by a protective dense oxide scale. This review describes the mechanisms and kinetics of corrosion by carbonaceous gases and the fundamentals of prevention.     

低温气体渗碳对304L奥氏体不锈钢抗氢性能的影响

对304L奥氏体不锈钢进行低温(470℃)气体渗碳,采用光学显微镜(OM),电子探针显微分析仪(EPMA)以及X射线应力分析仪(IXRD)研究了304L奥氏体不锈钢低温气体渗碳强化层的厚度、碳含量及残余应力分布。通过电化学充氢实验,结合X射线相结构分析(XRD),慢应变单轴拉伸试验,扫描电镜(SEM)观察以及氢含量检测等方法分析低温气体表面渗碳对304L不锈钢抗氢脆性能的影响。研究表明:304L不锈钢经30 h低温气体表面渗碳处理后,形成了约22μm的渗碳层,渗碳层中碳含量和残余应力在表面最高,分别为2%(质量分数)及-1.47 GPa,并沿深度方向梯度减小;低温气体表面渗碳大幅度提高304L不锈钢表面的稳定性,在充氢过程中不产生马氏体相变,从而提高其抗氢性能。此外,渗碳层中的压缩残余应力对抑制H扩散,也起到了积极的作用。     

BH催渗工艺对12CrNi3渗碳钢组织和性能的影响

针对12CrNi3钢薄壁齿轮气体渗碳工艺存在温度高、周期长、畸变大的弊端,导致薄壁重载齿轮组织状态不佳,畸变不受控等问题,在原超级渗碳工艺的基础上添加BH-5催渗剂,开展BH催渗试验。结果表明,当渗碳层深为(1.5±0.1) mm时,BH渗碳可提升效率20%以上;使用BH催渗使12CrNi3钢渗碳后晶粒度达到7级,渗层硬度梯度下降更平缓,摩擦性能提高,畸变减小。     

低碳钢激光膏剂渗碳组织及性能研究

采用在０８＃钢试样表面上涂覆渗碳膏剂，用ＣＯ２激光束进行辐照，结果表明该工艺渗层硬度高、渗碳速度快，说明激光膏剂渗碳是一种很有应用前景的新工艺。     

胶状碳包覆前驱体工艺制备超细、纳米碳化钨粉的研究

介绍了一种以高团聚态纳米W为原料,采用胶状碳包覆前驱体工艺,低成本、高效率制备高稳定性、低氧、均质、粒状超细和纳米WC粉末的新方法,并对碳化工艺条件进行了探讨。结果表明,氢气氛可以加速C-W反应过程;WC粉对原料W粉的粒度分布特征具有继承性;采用比表面积平均粒度为46.1nm的W粉为原料,当碳化温度由1 000°C增加至1 300°C时,WC的BET比表面积平均粒度由68.6 nm增加至339.4nm,氧含量由0.44%降低至0.10%。     

Metal dusting

Metal dusting is a catastrophic carburization of steels which leads to disintegration of the material to a mixture of powdery carbon and metal particles leaving pits and grooves. The phenomenon was simulated by carburization of low-and high-alloy steels in CO-H₂-H₂O mixtures at carbon activities > 1 in the temperature range 600–700°C. The occurance of an unstable carbide M₃C (M=Fe, Ni), as an intermediate in metal dusting, was proven—the reaction sequence involves over saturation of the metal matrix with carbon, M₃C formation at the surface, subsequent decomposition of the M₃C layer M₃C3 M+ C, leading to carbon with interspersed metal particles which act as catalysts for additional carbon deposition from the gas atmosphere. With increasing Ni content in Fe-Ni alloys, typical metal dusting is suppressed, but another mode of deterioration was observed, involving graphite growth on the grain boundaries. The high-alloy, chromia-forming alloys showed metal dusting only when chromia formation was suppressed by electropolishing the materials.     

金属材料在高温含碳气氛中的腐蚀

本文综述了材料在高温含碳气氛中的腐蚀,包括金属粉化和碳化,讨论了材料在含碳气氛中的腐蚀机理和腐蚀动力学。     

功能梯度硬质合金球齿的研制

作者对含 η相的烧结体的碳含量、其高温渗碳时间、温度以及烧结体本身尺寸大小对无 η相区的厚度和钴梯度形成的影响进行研究。结果表明 :烧结体的碳含量必须足够低 ,才能使烧结体中间形成富钴层 ;提高渗碳温度有利于液相钴向烧结体内部迁移 ;对尺寸大小不同的烧结体 ,应选择不同的渗碳时间     

热轧双层复合铁基合金的CD渗碳

研究了 50钢与Fe V合金复合轧制双层材料CD渗碳层的组织与性能。结果表明 ,热轧态复合界面 50钢一侧由于碳的扩散出现厚度约 50 μm的铁素体区。在随后的CD渗碳过程中 ,铁素体区消失。复合界面两侧组织差异不大。在Fe V合金复合层渗透的情况下 ,自Fe V合金表面经界面至 50钢内部 ,硬度梯度平缓。Fe V合金层在 950℃、1 40 %C碳势下渗碳 5h ,表面无Fe3 C析出 ,淬火后可获得高硬度渗层组织。渗层表面为马氏体基体和弥散的碳化物 ,尺寸为 1 0 0nm左右。Fe 1 69%V合金渗层表面硬度高达 82 5HV ,超过淬火、回火后的Cr1 2MoV钢