喷射成形高速钢中碳化物的类型与形貌

采用OM、SEM、XRD、EPMA、AFM等方法,对利用喷射成形技术生产的高速钢组织中碳化物类型与形貌进行了分析.结果表明:该钢显微组织为细小、均匀的等轴晶,其中主要存在M6C和MC两种类型的碳化物,其中骨骼状M6C型碳化物分布于晶界处,较大的颗粒状MC型碳化物主要分布于晶界交界处,细小的笋状MC型碳化物均匀分布于晶粒内部.     

双辊薄带连铸高速钢铸带中碳化物的形成及演变

采用光学显微镜观察了在工业双辊薄带连铸机上制备的M2高速钢铸带中的碳化物,利用二次枝晶间距计算了铸带的凝固速率;并用扫描电镜和透射电镜研究了高温热处理后铸带中亚稳相M2C碳化物的演变情况。结果表明:双辊薄带连铸高速钢工业铸带的凝固速率为1.7×103K.s-1,比实验室铸带的5.4×102K.s-1高一个数量级,远远高于工业铸锭的2×10-1K.s-1;双辊薄带连铸工艺可以细化高速钢铸带中的共晶碳化物,并获得较多的亚稳相M2C碳化物,在高温热处理过程中M2C碳化物与部分奥氏体反应生成稳定相M6C和MC碳化物,使碳化物分布更加均匀弥散。     

Nb含量对制氢转化炉管HP合金组织转变规律影响的研究

离心铸造的HP40和HP40-Nb合金被广泛用作制氢转化炉炉管材料,通常管壁温度可高达1000℃。通过观察HP40和HP40-Nb合金在原始铸态和高温状态下的显微组织,研究了不同Nb含量对合金共晶组织稳定性的影响。采用扫描电镜和X射线衍射仪研究了炉管材料的显微组织和相结构。研究结果表明:在碳含量0.4%左右的HP合金中,Nb含量0.210%~0.357%时主要起到固溶强化作用,共晶碳化物主要是M7C3,仅有少量的富Nb共晶MC散布在晶界上;当Nb含量0.89%~1.55%时,HP40-Nb原始铸态组织中析出了富Cr的M7C3碳化物和富Nb共晶MC。对于高温状态下的HP40-Nb合金,在晶界和枝晶间形成的富Nb共晶的MC提高了原始共晶组织的稳定性,使得炉管材料的使用温度可向高温推移。     

双辊薄带连铸高速钢铸带中碳化物的形成及演变

采用光学显微镜观察了在工业双辊薄带连铸机上制备的M2高速钢铸带中的碳化物,利用二次枝晶间距计算了铸带的凝固速率;并用扫描电镜和透射电镜研究了高温热处理后铸带中亚稳相M2C碳化物的演变情况。结果表明：双辊薄带连铸高速钢工业铸带的凝固速率为1．7×10^3K·S^-1,比实验室铸带的5．4×10^2K·S^-1高一个数量级,远远高于工业铸锭的2×10^1K·S^-1;双辊薄带连铸工艺可以细化高速钢铸带中的共晶碳化物,并获得较多的亚稳相M2C碳化物,在高温热处理过程中M2C碳化物与部分奥氏体反应生成稳定相M6C和MC碳化物,使碳化物分布更加均匀弥散。     

喷射成形S390高速钢的组织和性能

研究了喷射成形S390高速钢组织和性能,结果表明:喷射成形S390高速钢沉积坯具有低的氧含量,仅为18ppm,组织无宏观偏析,主要有M6C和MC两种碳化物相,碳化物呈均匀弥散分布在晶界和晶内。经过热处理后,喷射成形S390合金的抗弯强度可达4044MPa,合金硬度随淬火温度呈上升趋势,在1250℃淬火后,硬度达到了HRC69.3。     

碳化物对冷轧条件下轧辊中裂纹行为的影响

利用扫描电镜、透射电镜研究碳化物对冷轧过程中高铬铸铁及高钒高速钢轧辊中裂纹行为的影响。结果表明,裂纹萌生及扩展与碳化物的精细结构、碳化物与基体界面结构及碳化物形态有关。高铬铸铁中的M7C3具有层错结构,轧制过程中M7C3内部易于造成位错塞积而萌生裂纹,经短距离扩展后形成贯穿的主裂纹,导致轧辊迅速失效。高钒高速钢中的VC内部弥散分布着大量富钼的纳米级MC型碳化物,起到钉扎VC内部位错的作用,促使形成位错环而吸收轧制能量,裂纹不易在VC内部萌生,而主要萌生于VC与基体界面,并沿球形VC的表面扩展,扩展到VC侧面时出现裂纹钝化现象。VC与基体界面的部分共格关系能够延缓界面裂纹萌生,VC良好的形态有助于裂纹钝化,提高轧辊的抗疲劳性能及寿命。     

喷射成形工艺对高速钢组织和性能的影响

研究了喷射成形工艺对高合金化高速钢组织和性能的影响,结果表明:喷射成形工艺制备T15高速钢沉积坯件,坯件经过热加工后,致密度都达到99%以上,无宏观偏析,碳化物呈现均匀弥散分布在晶界和晶内,主要有M6C和MC两种碳化物相,经过热处理后,合金的抗弯强度平均达到4673MPa。在1250℃淬火后,最高硬度可达67.6HRC。     

喷射成形高速钢的组织和性能

研究了喷射成形工艺对高合金化高速钢组织和性能,结果表明:喷射成形工艺制备了直径300mm高合金化高速钢沉积坯,表面质量良好,可以满足直接锻造要求。喷射成形高速钢组织无宏观偏析,碳化物呈现均匀弥散分布在晶界和晶内,主要有M6C和MC两种碳化物相,氧含量只有约20ppm左右。经过热处理后,喷射成形T15合金的抗弯强度平均达到4800MPa。硬度随着淬火温度的提高逐渐升高,喷射成形T15M合金在1250℃淬火后,硬度达到了69.3HRC。     

高速鋼淬火加热时晶粒度的控制

高速钢属于莱氏体钢。它最大的特点是具有较高的红硬性,工作温度达600℃时仍能保持高的硬度和良好的切削性能。这种性能主要是由于高速钢成分中有较高的合金含量。例如W18Cr4V钢中合金含量为23％,W6Mo5-Cr4V2钢中合金含量17％。这些元素组成复杂的碳化物M6C、M23C6和MC。高速钢中含有较多的碳化物并且在高温加热时不能完全溶解。例如     

高速工具钢中碳化物的形态

<正> 在高速工具钢中存在着M6C、M2C、MC三种类型的初生碳化物。这些碳化物都是在凝固过程中从钢液中结晶出来,成为最终产品中的未溶碳化物残存在钢中,起着增加耐磨性、防止奥氏体晶粒粗化的作用。但是,这些碳化物的硬度均大于HV1500,几乎没有塑性,因而存在形态、粒度及其分布、相对量等对材料的机械性能都有极大的影响。其中具有Fe3(W,Mo)3C～Fe4(W,Mo)2C 成分的M6C 型碳化物在高速钢工具钢的初生碳化物中构成比例最大,必须在浇铸时尽量地进行细化。照片1(a)是SKH2(18W—4Cr—1V)     

Solidification and abrasion wear of white cast irons alloyed with 20% carbide forming elements

Three different white cast irons with compositions of Fe–3%C–10%Cr–5%Mo–5%W (alloy no. 1), Fe–3%C–10%V–5%Mo–5%W (alloy no. 2) and Fe–3.5%C–17%Cr–3%V (alloy no. 3) were prepared in order to study their solidification and abrasion wear behaviors. Melts were super-heated to 1873 K in a high frequency induction furnace, and poured at 1823 K into Y-block pepset molds. The solidification sequence of these alloys was investigated. The solidification structures of the specimens were found to consist of austenite dendrite (γ); (γ+M₇C₃) eutectic and (γ+M₆C) eutectic in the alloy no. 1; proeutectic MC; austenite dendrite (γ); (γ+MC) eutectic and (γ+M₂C) eutectic in the alloy no. 2, and proeutectic M₇C₃ and (γ+M₇C₃) eutectic in the alloy no. 3, respectively.

A scratching type abrasion test was carried out in the states of as-cast (AS), homogenized (AH), air-hardened (AHF) and tempered (AHFT) using the abrasive paper with 120 mesh SiC and 10 N application load. In all the specimens, the abrasion wear loss was found to decrease in the order of AH, AS, AHFT and AHF states. Abrasion wear loss was lowest in the specimen no. 2 and highest in the specimen no. 1 except for the as-cast and homogenized states in which the specimen no. 3 showed the highest abrasion wear loss. The lowest abrasion wear loss of the specimen no. 2 could be attributed to the fact that it contained proeutectic MC carbide, eutectic MC and M₂C carbides having extremely high hardness. The matrix of each specimen was fully pearlitic in the as-cast state but it was transformed by heat-treatments to martensite, tempered martensite and austenite. From these results, it becomes clear that MC carbide is a significant phase to improve the abrasion wear resistance of white cast iron.     

高温时效对25Cr35Ni-Nb合金碳化物的影响

25Cr35Ni-Nb合金被广泛用作乙烯裂解炉和制氢转化炉炉管材料,服役温度高达1050℃。将25Cr35Ni-Nb合金炉管在不同温度时效100 h,通过对不同温度显微组织的观察和维氏硬度测试,研究了不同温度时效后碳化物的变化规律。研究结果表明：随着时效温度的升高,晶界碳化物宽度不断增大,由原始铸态平均宽度1.5μm,增大到1200℃时效后的5.3μm;从900℃到1100℃,奥氏体晶内碳化物平均尺寸由1μm长大至2μm,然而,随着时效温度提高至1200℃,晶内碳化物平均尺寸下降至1.7μm。当时效温度从900℃增加为1100℃时,维氏硬度从173 HV10升高为192 HV10,1200℃时,维氏硬度为193 HV10。碳化物尺寸及维氏硬度与时效温度之间定量关系对炉管服役温度范围的确定提供了参考。     

某带钢连续热浸镀机组卧式连续退火炉水冷炉辊的开裂原因

采用宏观和微观形貌观察、化学成分分析、显微组织观察、硬度测试等方法,对某带钢连续热浸镀机组卧式连续退火炉水冷炉辊的开裂原因进行了分析。结果表明:水冷炉辊辊套成分中不含铌元素,镍元素含量偏低,导致组织中形成网状富铬碳化物析出相;辊套内腔结垢、水冷不畅使水冷炉辊产生局部过热,导致工作侧辊套基体中粒状合金碳化物的析出和网状富铬碳化物的长大,使工作侧辊套的脆性增加;随着结垢的沉积,水冷炉辊出现轴承转动不畅,甚至堵转现象;在热应力、扭力作用下,裂纹在网状富铬碳化物析出相中形成并沿网状碳化物逐渐向基体内扩展,最终导致水冷炉辊的开裂。     

Microstructure–Property Relationships in M50-NiL and P675 Case-Hardened Bearing Steels

Case-hardened steels, widely used in high-performance ball and roller bearings, have high surface hardness and a gradient in material properties (hardness, yield strength, etc.) as a function of depth; therefore, they behave as functionally graded materials. Understanding the mechanical properties due to gradients in the subsurface microstructure of case-hardened steels is important for modeling the effects of cyclic damage induced by rolling contact fatigue. In the current study, two different commercially available case-carburized steels (P675, M-50 NiL) and two through-hardened steels (M-50, case P675) were characterized to obtain relationships among the volume fraction of subsurface carbides, indentation hardness, elastic modulus, and yield strength as a function of depth. A variety of methods including microindentation, nanoindentation, ultrasonic measurements, compression testing, rule of mixtures, and upper and lower bound models were used to determine the above relationships and compare the experimental results with model predictions. In addition, the morphology, composition, and properties of the carbide particles are also discussed. It was found that the subsurface hardness and volume fraction of carbides are linearly related. Finally, it was found that the estimation of composite modulus from a well-established model compares with measurements from the ultrasonic method and compression tests. The results presented are of immediate engineering relevance to the bearing industry, with importance to modeling of microstructure and its effects on rolling contact fatigue life.     

Influence of tool microstructure on galling resistance

In sheet metal forming, different types of tool steels are used depending on sheet quality. In the present work, influence of amount, and type, of primary carbides and carbo-nitrides was investigated regarding tool galling resistance against austenitic stainless steel. A significant impact of amount of carbides on galling resistance was observed and tool performance was improved as volume fraction increased. However, no influence of carbide type was distinguished. Alloying by nitrogen further improved the galling resistance and best tool performance was observed for a tool steel comprising only carbo-nitride M(C,N) particles. Besides transfer of sheet material, several other tool damage mechanisms were observed such as cracking, micro-chipping and abrasive scratching.     

Chromium�Cmanganese iron alloy system design cast in metal and sand moulds for erosion resistance: a positron lifetime study

Erosion characteristics of high chromium (Cr, 16?C19%) alloy cast iron with 5% and 10% manganese (Mn) prepared in metal and sand moulds through induction melting are investigated using jet erosion test setup in both as-cast and heat-treated conditions. The samples were characterised for hardness and microstructural properties. A new and novel non-destructive evaluation technique namely positron lifetime spectroscopy has also been used for the first time to characterise the microstructure of the material in terms of defects and their concentration. We found that the hardness decreases irrespective of the sample condition when the mould type is changed from metal to sand, On the other hand, the erosion volume loss shows an increasing trend. Since the macroscopic properties have a bearing on the microstructure, good credence is obtained from the microstructural features as seen from light and scanning electron micrographs. Faster cooling in the metal mould yielded fine carbide precipitation on the surface. The defect size and their concentration derived from positron method are higher for sand mould compared to metal mould. Lower erosion loss corresponds to smaller size defects in metal mould are the results of quicker heat transfer in the metal mould compared to the sand mould. Heat treatment effects are clearly seen as the reduced concentration of defects and spherodisation of carbides points to this. The erosion loss with respect to the defects size and concentration correlate very well.     

The influence of primary carbides and test parameters on abrasive and erosive wear of selected PM high speed steels

The aim of this investigation has been to further the understanding of the contribution given by the primary carbides to the abrasive and erosive wear resistance of six HSS's, and to evaluate different test methods. With abrasives significantly harder than the primary carbides of the HSS's, two- and three-body abrasion rates showed only small variations with primary carbide volume fraction, size and type. However, using abrasives/erodants softer than the carbides the qualitative results were similar for the two- and three-body abrasion tests and for the erosion test, with the wear resistance increasing with the volume fraction primary carbides.     

热处理对原位烧结(Ti,V)C钢结硬质合金组织及耐磨性的影响

利用粉末冶金技术,原位烧结合成了(Ti,V)C钢结硬质合金,并用扫描电镜、X射线衍射仪等研究了热处理对原位烧结(Ti,V)C钢结硬质合金组织和耐磨性的影响。结果表明:烧结态(Ti,V)C钢结硬质合金基体组织为细珠光体组织;1 000℃淬火后的组织转变为片状马氏体+(Ti,V)C硬质相颗粒+少量未溶碳化物;回火过程中合金具有较高的抗回火稳定性,在500℃左右回火时存在二次硬化现象;该合金在1 000℃淬火、经250,500℃回火后具有较好的耐磨性。     

Effect of carbide size on the abrasion of cobalt-base powder metallurgy alloys

A study of the effect of carbide size on the abrasion resistance of two cobalt-base powder metallurgy alloys, alloys 6 and 19, was conducted using low stress abrasion with a relatively hard abrasive, A1₂O₃. Specimens of each alloy were produced with different carbide sizes but with a constant carbide volume fraction. The wear test results show a monotonie decrease in wear rate with increasing carbide size.Scanning electron microscopy of the worn surfaces and of wear debris particles shows that the primary material removal mechanism is micromachining. Small carbides provide little resistance to micromachining because of the fact that many of them are contained entirely in the volume of micromachining chips. The large carbides must be directly cut by the abrasive particles. Other less frequently observed material removal mechanisms included direct carbide pull-out and the formation of large pits in fine carbide specimens. These processes are considered secondary in the present work, but they may have greater importance in wear by relatively soft abrasives which do not cut chips from the carbide phase of these alloys. Some indication of this is provided by limited studies using a relatively soft abrasive, rounded quartz.