Nb对灰铸铁高温抗拉强度和抗氧化性的影响

研究了高温条件下,w（Nb）量为0.037%和0.11%对灰铸铁抗拉性能和抗氧化性能的影响,试验结果表明：w（Nb）量为0.037%时,试样为脆性断裂;w（Nb）量为0.11%时,产生了韧性断裂,试样断口出现了韧窝。铸铁加Nb后,石墨和珠光体得到细化,与此同时,富Nb相镶嵌于基体上,有利于提高灰铸铁的抗拉强度;Nb使石墨细化的作用也使氧原子难以进入基体内部,阻止氧化反应,有利于提高灰铸铁的抗氧化性。     

Nb对灰铸铁相变温度的影响

用热膨胀测量和热分析方法测定了Nb对灰铸铁共析温度、共晶凝固温度的影响。试验结果表明：（1）在灰铸铁升温过程中,由于富Nb相对C原子的拖曳作用,以及富Nb相降低了渗碳体的溶解速度,从而降低了珠光体向奥氏体转变的温度,提高了铸铁的高温稳定性;（2）在灰铸铁降温过程中,由于晶界处的Nb析出,降低了奥氏体的不稳定性,以及富Nb相中Nb对C原子的拖曳作用,推迟了奥氏体向珠光体转变;（3）Nb降低了灰铸铁的共晶凝固温度。     

灰铸铁表面高铬铸铁铸渗层的组织与性能研究

采用铸渗工艺在灰铸铁表面制备高铬铸铁铸渗层,并研究了不同涂敷层厚度对灰铸铁表面铸渗层的铸渗质量、显微硬度及耐磨性能的影响。结果表明:涂敷层厚度为4 mm的试样,铸渗层深度最大,渗层组织分布均匀,铸渗层显微硬度在1200 HV以上,耐磨性是基体试样的2倍。     

Nb在灰铸铁中的存在形态

用附带能谱的扫描电镜研究了Nb在灰铸铁中的存在形态,结果显示：少量Nb以原子形式固溶于基体,绝大多数Nb形成富Nb相镶嵌在基体上面;富Nb相形态丰富,有块状（包括方块状和三角形）、不规则形状（包括X型、Y型）以及条棒状;在富Nb相形成过程中,TiN可能作为异质核心,因而对富Nb相的形成起了促进作用。     

铸铁与钛丝原位反应的研究

采用1138℃下保温2h方法,让提前置于铸铁中的钛丝与周围碳原子原位反应生成TiC增强铸铁复合材料,对复合区进行显微组织观察分析、显微硬度测量、耐磨性能测试。结果表明,复合区硬度最高达3182HV0.05,平均硬度是基体的12～15倍。复合材料的耐磨性相对于铸铁标准试样提高了3.22倍。     

铌在铸铁中的应用及其作用情况介绍

介绍了铌合金在灰铸铁、球墨铸铁、不完全激冷（indefinite chill）铸铁和镍抗可焊接（weldable Ni-Resist）铸铁中的应用情况;分析了铌合金在铸铁中的作用机理,认为NbC能为共晶团提供核心是加Nb细化共晶团的原因,而且NbC的弥散分布可以提高铸铁耐磨性、硬度和强度;综述了铌合金化技术原理,指出铸铁加铌合金化主要有与固体废铁料一起加入大块料和出铁时加入细颗粒两种较为经济的方法。     

铸铁与铬丝原位反应的研究

采用1135℃×20min的工艺,让提前置于铸铁中的铬丝与周围碳原子原位反应生成M7C3[(Fe,Cr)7C3]型铸铁复合材料,对复合区进行显微组织观察分析、显微硬度测量、耐磨性能测试.结果表明,复合区硬度最高达到1750 HV0.05.平均硬度是基体的9～11倍.复合材料的耐磨性相对于铸铁标准试样提高了2.89倍.     

铸铁与铌丝原位生成NbC_P/Fe复合材料

利用铸铁浇注将Nb丝均匀复合固定于铁基体内.然后在1165℃保温2h,让提前置于铸铁中的铌丝与周围碳原子原位反应生成NbC颗粒增强铸铁复合材料,对复合区进行显微组织观察分析、显微硬度测量.结果表明,复合区域显微硬度最高值达到1930HV0.05,复合区域的平均显微硬度为1827HV0.05,是基材的8～9倍.复合试样的室温两体磨料相对耐磨性是铸铁的2.71倍,耐磨性能良好.     

Nb元素对高熵合金涂层组织与力学性能的影响

利用激光熔覆技术在Q235基体表面制备CoCrFeNiTi_0.8Nb_y(y=0.25,0.5,0.75,1.0)涂层.采用光学显微镜、X射线衍射仪、扫描电子显微镜、能谱分析仪等方法分析涂层的相结构和微观组织等;用显微维氏硬度计、摩擦磨损试验机测试涂层的硬度与耐磨性能.结果表明,组织中呈现典型的树枝晶结构,加入Nb元素,涂层微观组织的尺寸减小,增加Nb元素含量时,高熵合金涂层的晶体结构由体心立方相(body-centered cubi,BCC)、少量的面心立方相(face-centered cubic,FCC)和Fe₂(Ti,Nb)型的Laves相组成;在细晶强化、固溶强化和第二相强化的共同作用下提高了涂层的显微硬度;中间相的存在一定程度上可以阻碍犁削切削过程的进行,进而提高了涂层的耐磨性能;CoCrFeNiTi_0.8Nb_0.75涂层的硬度和耐磨性最好,硬度为710 HV,约为基体的4倍,涂层的磨损量最小,磨痕较为平整.     

TIG焊Fe基非晶合金堆焊层的组织和性能

以一种含Fe、Cr、B、Mn、Si等元素的新型Fe基合金药芯焊丝作为堆焊材料,利用TIG焊在13Mn钢的基体上制备堆焊层.借助SEM、XRD、DSC等手段观察和分析了堆焊层的组织形貌、物相构成及非晶相的起始晶化温度,同时测定了堆焊层的显微硬度和常温耐磨性能.结果表明:新型Fe基合金堆焊层结构均匀致密,与基体结合性好;堆焊层中非晶含量约为31.06 vol％,起始晶化温度Tx=582.3℃;堆焊层具有较高的显微硬度与耐磨性能,近表面的显微硬度达1000～1200 HV0.1,耐磨性能优于高铬铸铁,尤其是水冷处理的堆焊层耐磨性为高铬铸铁的2倍.     

Nb在铸铁中的物理冶金学作用原理

介绍了Nb在铁基合金中的存在形式,根据NbC和NbN在不同铁基合金中的溶度积公式,分析了Nb在铸铁中的存在形式。在此基础上,分析了Nb在铸铁中的作用机理。固溶Nb具有非常重要的调节共析相变及强化铁素体基体的作用,凝固过程析出的Nb（C,N）可显著提高耐磨性,在奥氏体温度区间晶界析出的Nb（C,N）能有效阻止晶粒长大,合适的成分设计和工艺措施可充分发挥Nb的作用效果。     

Nb对灰铸铁热疲劳性能的影响

采用Uddeholm热疲劳方法测定了Nb对灰铸铁热疲劳性能的影响,试验结果表明：（1）Nb的加入能够提高灰铸铁的抗热疲劳性能,随着w（Nb）的增加,试样最大裂纹深度和宽度都逐渐减小;（2）由于Nb细化石墨使裂纹源减少和裂纹扩展途径变细,Nb元素能够改善材料表面经热疲劳处理后恶化的性能。     

Enhancement of wear resistance and impact toughness of as cast hypoeutectic high chromium cast iron using niobium

The effect of niobium additions on the as-cast microstructure of a hypoeutectic high-Cr cast iron containing 2.2 wt.% C and 16.5 wt.% Cr was investigated. With increasing niobium content, the eutectic M₇C₃ carbides were refined and became less elongated as well as its volume fraction was decreased gradually. The first precipitated NbC particles could be act as heterogeneous substrate of proeutectic austenite and a barrier to M₇C₃ grain growth. The morphology of NbC carbides changed with increasing niobium content. Such NbC particles were increased with increasing Nb content and subsequently contributed to increased hardness. Optimum toughness was obtained for the irons alloyed with 2.14% Nb. The effects of applied load and Nb-additions on wear resistance of high chromium cast iron have been studied. The results showed that wear resistance increases with increasing Nb addition. Furthermore, the effectiveness of the NbC particles on the weight loss was more evident at higher loads.     

Investigation of improving wear performance of hypereutectic 15%Cr-2%Mo white irons

This study aimed at optimizing impact toughness and abrasion wear resistance of 15%Cr-2%Mo hypereutectic abrasion-resistant white irons. The effects of dynamic solidification, niobium addition, combined action of them and heat treatment have been investigated. Investigations were performed by means of the image analyzer, scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS) and X-ray diffraction. Impact toughness and abrasion wear resistance tests were conducted. Fracture and worn surfaces were studied. Results indicated that microstructural control during solidifciation is the most valuable tool to attain the optimum combination between impact toughness and wear resistance in hypereutectic iron. Combined action of Nb addition and dynamic solidifciation improves impact toughness and wear resistance even more than the action of each individual factor. In the as-cast condition, impact toughness and abrasion resistance were increased after dynamic solidification compared to statically solidified one by 71.4% and 10%, respectively. This enhancement was increased to 114.3 % and 28.8 % by adding 2% Nb. Lower tempering temperature of 260°C exhibits better impact and abrasion resistance than the sub-critical tempering temperature of 500°C.     

制动盘用高碳当量灰铸铁的铌合金化

研究了微合金元素铌对剁车盘用亚共晶和过共晶两种高碳当量灰铸铁组织和性能的影响.结果表明,添加0.10%左右的Nb,可以细化高碳当量灰铸铁中片状石墨;材料的硬度、楔压强度随之提高,且抗热裂性明显提高.     

Microstructure and wear properties of low-alloy phosphoric gray cast irons

The effects of various alloying elements on the microstructure and wear properties of phosphoric gray cast irons were examined. The wear properties of gray cast irons were examined with wear tests in the lubricated condition at various final loads and sliding speeds. It is found that the microstructure and the morphology and size of flaky graphite do not change much with a small addition of alloying elements such as V, Nb, Mo and Cr. However, the wear resistance of phosphoric gray cast iron is found to increase significantly with an increasing amount of alloying element. For a given amount of alloying element, it is found that V and Nb are very effective, whereas Mo and Cr are less effective in increasing the wear resistance of phosphoric gray cast iron. The increase in the hardness of steadite caused by the segregation of carbide-forming elements is found to be responsible for the excellent wear resistance of low-alloy phosphoric gray cast irons.     

高强度D型石墨铸铁的研究进展

综述了灰铸铁中产生D型石墨的原因，D型石墨对灰铸铁性能的影响以及D型石墨灰铸铁的应用。国内外的研究表明：深过冷，在灰铸铁中加入提高过冷度的合金元素（钛，铝，锑，碲，稀土元素等）或者二者的结合都会促进生成D型石墨；D型石墨灰铸铁具有较高的强度，较好的抗氧化性，抗生长性，抗热疲劳性和耐磨性；D型石墨灰铸铁已经广泛用于生产玻璃模具，压缩机缸体，压缩机曲轴等铸件。笔者还介绍了采用钒钛生铁生产的D型石墨合金铸铁凸轮轴的性能特点及其应用情况。