新型烧结高铬铸铁的冲击磨粒磨损性能

本文对比研究了烧结、铸造亚共晶高铬铸铁和TM52钢结硬质合金在不同冲击功条件下的抗冲击磨粒磨损性能,利用扫描电子显微镜(SEM)观察分析磨损表面磨损形式及亚表层的微裂纹发展,开展磨损机制的分析探讨。结果表明,采用液相烧结技术制备的高铬铸铁具有优异的抗冲击磨粒磨损性能。烧结高铬铸铁在中、低冲击功条件下耐磨性能均明显优于TM52(4~10倍),在中、高冲击功工况下的耐磨性能相比铸造高铬铸铁提高10倍以上。烧结高铬铸铁的磨损机制主要是显微切削,当冲击功高时还会发生疲劳剥落磨损和脆性碎裂。烧结高铬铸铁中的短杆状M_7C_3型碳化物对金属基体的割裂和应力集中较小,而马氏体为主的基体具有高强韧性,能够有力地支撑和保持其中的碳化物均匀分散,阻滞微裂纹的萌生和扩展。     

脉冲电流参数对过共晶高铬铸铁近液相线熔化后凝固组织的影响

对过共晶高铬铸铁近液相线溶化后的凝固过程进行脉冲电流处理,研究了脉冲电流参数（脉冲电压和频率）对凝固组织的影响.发现脉冲频率和电压的增大都有助于过共晶高铬铸铁凝固组织中碳化物的细化和粒化.脉冲频率的增大促进大量细小颗粒状初生碳化物的析出,离异共晶现象变得更加明显,层片状共晶碳化物减少.脉冲电压的增加促进初生碳化物细化和粒化,片状共晶碳化物变短.过高的电压也促进离异共晶,导致更多的初生碳化物的形成.      

变温超固相线液相烧结工艺对15Cr系高铬铸铁显微组织及性能的影响

为解决常规定温超固相线液相烧结出现的烧结温度窗口狭窄和产品力学性能对烧结温度波动敏感的问题,采用变温超固相线液相烧结工艺制备了粉末冶金高铬铸铁,研究了变温超固相线液相烧结的高温阶段工艺参数对15Cr系高铬铸铁显微组织和力学性能的影响,并与定温超固相线液相烧结制备的合金进行了对比.研究发现,变温超固相线液相烧结制备的合金...     

多元合金化高铬铸铁在雷蒙机上的应用研究

设计出一种多元合金化高铬铸铁,其组织为马氏体和碳化物以及少量的残余奥氏体,硬度为HRC61～65,冲击韧性8～12J cm2,耐磨性为高锰钢的12倍,普通高铬铸铁的3倍。     

铸铁合金的遗传效应及其利用

研究了亚共晶，过共晶铸铁合金液在不同热状态下凝固组织，以及组织对力学性能的影响等，发现，炉料对铸件产生明显的组织遗传效应，随合金液过热温度的升高，铸件吉石墨相的数量减少且变细，碳化物增多，组织趋于均匀，合金的硬度提高，冲击韧性下降；随合金液保温时间延长，组织遗传性衰退，石墨相球化，碳化物变细，设计的热处理新工艺能提高合金的力学性能，根据遗传观点，分析了试验结果及其意义，探讨了热速处理的作用机理。     

淬火温度对添加B_4C的ASP30粉末冶金高速钢组织及力学性能的影响

采用粉末冶金方法制备添加B_4C的全致密ASP30高速钢,样品在1 040℃到1 200℃范围内淬火,并且经过560℃三次回火,研究淬火温度对其力学性能及显微组织的影响。采用扫描电子显微镜、洛氏硬度计和材料力学性能测试机研究高速钢的组织和力学性能。结果表明:添加质量分数为0.025%B_4C的ASP30粉末冶金高速钢在1 160℃下烧结2 h后会形成月牙形液相碳化物,从而获得全致密的烧结组织。随淬火温度升高,显微组织中碳化物的数量明显减少,基体中合金元素固溶含量提高,基体晶粒长大,断口形貌呈准解理断裂但断口平整度下降。随淬火温度升高,钢的硬度提高,最高值达到69 HRC。抗弯强度、断裂韧性均下降,抗弯强度最高值达4 357MPa,断裂韧性最高值为48.6 MPa/m1/2。冲击韧性先升高后下降,在1 080℃最高为18.85 J/cm2。     

淬火和低温处理对X30CrMoN151组织性能影响

 为了探索X30 CrMoN 15 1高氮马氏体钢的最佳淬火+低温处理工艺,利用OM、XRD、SEM、EDS和EBSD等方法研究了不同淬火温度和低温处理对高氮钢显微组织和性能的影响规律。结果表明,当奥氏体化温度低于1 050 ℃,原奥氏体晶粒长大缓慢,当奥氏体化温度高于1 050 ℃后晶粒长大加剧。随着奥氏体化温度的升高,碳化物溶解加剧,油淬后的残余奥氏体呈线性升高;低温处理后残余奥氏体大幅度减少,奥氏体化温度越高冷处理后残余奥氏体下降越多。钢的硬度随淬火温度先升高后降低,在1 000 ℃硬度最高;低温处理后,硬度随淬火温度先升高后降低,在1 030 ℃硬度最高。钢的冲击韧性随淬火温度先升高后降低,在1 030 ℃时冲击韧性最佳;低温处理后,钢的冲击韧性大幅度下降。     

钨合金白口铸铁共晶碳化物团球化的研究

针对钨合金白口铸铁脆性大,应用于承受冲击载荷的工况下安全性差,使用范围受到严格限制,探讨了碱金属元素钾、钠对钨合金白口铸铁组织和性能的影响。结果表明:钨合金白口铸铁经钾、钠处理后,共晶碳化物由网状分布变为团块状甚至团球状分布,碳化物明显细化,分布均匀性增大,分析了共晶碳化物团球化的机理。碳化物形态的改善,导致钨合金白口铸铁的冲击韧性和抗冲击磨损能力明显提高。     

喷射成形高合金工具钢的组织与力学性能

采用喷射成形工艺制备了高合金工模具钢,对沉积坯进行了热锻致密化处理和淬火+回火热处理.对比分析了喷射沉积态合金和电渣重熔态合金的组织形态和力学性能.结果表明:喷射成形材料晶粒组织为均匀细小的等轴晶,碳化物细小且弥散分布,有效解决熔铸态合金热锻后仍无法完全消除的成份偏析和粗大网状碳化物的问题.由于喷射沉积态材料具有良好的组织形态,使得喷射沉积态的强度和冲击韧性比电渣重熔态分别提高了40%和18%.由于喷射沉积态材料中非金属夹杂物的影响,使得材料的冲击韧性值偏低,有待进一步优化工艺,减少夹杂物的含量,提高材料的力学性能.     

基于神经网络算法钒钛改性高铬铸铁的热处理工艺研究

采用神经网络算法技术,以钒含量、钛含量、淬火温度、淬火冷却方式、回火温度和回火冷却方式作为输入层参数,以耐磨损性能和冲击韧性为输出层参数,可以构建出6×24×12×2四层拓扑结构的钒钛改性高铬铸铁热处理工艺优化模型。模型输出的耐磨损性能平均相对预测误差为2.8%、冲击韧性平均相对预测误差为2.5%。模型不仅具有较佳的预测能力和较高的预测精度,而且在热处理生产线上具有很好的应用效果,使产线上的钒钛改性(0.8%钒+0.5%钛)高铬铸铁的平均晶粒尺寸减小32%、磨损体积减小50%、冲击韧性提高62%。     

Smoking: high hazards in high school

BACKGROUND: Young people in school are at an impressionable age, peer pressures are intense, and the probability that they will pick up a high-risk behavior, such as smoking, is high. The key to reduction of smoking among adults is to target our prevention efforts at young adults and teens. OBJECTIVE: To study the prevalence and trend of smoking among young adults and teens and to formulate guidelines on smoking reduction to guide those who counsel young people. STUDY DESIGN: The study design is cross sectional. METHODS: This study is based on the data from the Oklahoma Behavioral Risk Factor Surveillance System and the National Youth Risk Behavioral Surveillance System - the two systems that monitor the prevalence of behaviors that most influence health. RESULTS: The prevalence of smoking among young adults (age 18-24) in Oklahoma is high at more than 21%. The disturbing feature is that it is higher among young females than among young males. The prevalence of smoking among young adults is the highest among high school dropouts and is more than 38%. It is lower among high school graduates (about 28%) and lowest among college graduates (about 18%). The percentage of smoking among students who classify themselves as current smokers rises from 23% to 30% as the students progress from grade 9 to 12 and the percentage of frequent smokers increases from 8% to 16%. CONCLUSIONS: Guidelines suggested for counselors are: 1. Along with smoking, look for comorbid behaviors such as alcohol use, drug abuse, and high-risk sexual behavior. 2. Ask whether the student has easy access to free cigarette samples. 3. Check whether the teen is trying to lose weight; suggest appropriate methods for losing weight if smoking is being used for losing weight. 4. Target health education efforts early in a student's school career starting in elementary school, but concentrate especially at the 8th or 9th grade level to have maximum preventive impact.     

The high temperature transformation of high speed steel

Low tempered hardnesses on high speed steels which had been hardened in vacuum or atmosphere furnaces and gas quenched led to a search for a reaction occurring above 1400°F and probably initiated as a result of the slower cooling rate of the gas quench. A standard TTT evaluation was carried out on Ml, M2 high carbon, M3, and M7 high speed steels, quenching from conventional hardening temperatures, into salt baths maintained at 2000° to 1500°F. Examination of these specimens indicated the presence of a reaction occurring at all temperatures investigated but having its maximum rate at 1700° to 1800°F. The reaction involved precipitation of an MoC/Mo₂C carbide at grain boundaries and within the grains, with the amount of precipitate increasing with time. The precipitation of MoC/Mo₂C is directly related to the loss in tempered hardness and apparently causes this effect by 1) reducing precipitation hardening on tempering, 2) drastically lowering retained austenite contents, and 3) reducing as-quenched hardnesses.     

MgO对高碱度高铝烧结矿的影响

 随着钢铁企业高铝铁矿粉使用比例的提高,带来了高炉炉渣黏度增大、渣铁分离困难等一系列问题。采用烧结杯试验,研究了MgO含量增加对高碱度高铝烧结矿经济技术指标、冷强度和冶金性能的影响,采用Nova400 NanoSEM型场发射扫描电子显微镜分析了烧结矿微观结构。试验结果表明,高碱度高铝烧结矿中MgO质量分数从1.72%提高到2.49%时,垂直烧结速度降低4.38 mm/min,利用系数降低0.51 t/(m2·h),低温还原粉化指数增加6.7%;当烧结矿中MgO质量分数为2.11%时,转鼓指数和还原度最高,分别达到61.93%和86.39%;Mg2+主要固溶在磁铁矿晶格中并替代Fe2+,替代的质量分数最高达3.64%,生成的含镁磁铁矿抑制烧结矿降温过程中由Fe₃O₄→Fe₂O₃氧化过程的相变,减少了二次赤铁矿的生成,有利于改善烧结矿的低温还原粉化性能。研究结果可以为改善高碱度高铝烧结矿性能和提高炉渣流动性提供理论指导和参考依据。     

宝钢3号高炉高煤比条件下的高利用系数生产研究

宝钢3号高炉通过技术创新和开发,不断完善操作技术水平,改善原燃料条件,1999年在维持煤比200kg/t以上的同时,实现年均利用系数2．303,2000年高炉利用系数再创新高,月均最高达到2．145,宝钢高煤比高利用系数冶炼技术达到世界领水平。     

高碳钢高温力学性能研究

在Gleeble-2000动态热模拟试验机上采用凝固法研究了高碳钢的高温力学性能.测定了tZD(零塑性温度)、tZS(零强度温度).在4×10-4/s应变速率条件下,所测钢种在熔点到750 ℃范围存在两个脆性温度区域,即熔点到1 300 ℃的第Ⅰ脆性温度区域和750～925 ℃的第Ⅲ脆性温度区域.在第Ⅲ脆性温度区域,γ单相AIN、NbN等氮化物在γ晶界的析出和在γ α两相区先共析α相呈网膜状,在γ晶界的析出是造成钢脆化的主要原因.通过控制钢中氮、铝含量,以及采用合理的冷却方式可以提高钢种的内在质量.     

Demanganisation of high manganese pig iron to produce high manganese slag

Abstract

Pig iron with a high manganese content makes further processing to steel using converter technology difficult and unprofitable. In the present study, external demanganisation of high manganese pig iron before the oxygen converter process has been investigated. Pilot plant experimental heats were designed and carried out to optimise the demanganisation process, to produce hot metal adequate for the conventional LD converter, and high manganese slag suitable for the production of silicomanganese. Various high manganese pig irons with different [Si]/[Mn] contents were treated by injection of various oxidisers at varying temperatures, slag basicities and injection rates. The optimum conditions for the demanganisation process have been attained by injection of an oxygen gas–manganese ore mixture at the injection rate of 6.8 L min^-1kg^-1 into molten high manganese pig iron with a [Si]/[Mn] ratio of 0.3 at an initial temperature of 1350°C and slag basicity of 0.3–0.4.     

Microstructure characteristics of spray-formed high vanadium and cobalt high speed steel

The microstructure of high vanadium and cobalt high speed steel(high-V/Co HSS) and the morphology of its carbides were analyzed by optical microscope(OM),scanning electron microscope(SEM),electron probe microanalysis(EPMA),X-ray power diffraction(XRD),atomic force microscopy(AFM) and single phase erosion(SPE).The results suggest that the as-sprayed high-V/Co HSS has fine equiaxed grains(about 20 μm in size),which were homogeneously distributed.The carbides have two classical morphologies:one is fine particles(about 2 μm in size) distributed along the grain boundaries and the other is needle-like one,distributed on the grain boundaries.There are MC carbides,M2C carbides,M6C carbides and Cr2WC2 carbides in the as-sprayed high-V/Co HSS samples,however,in the as-cast high-V/Co HSS,there are MC carbides and Cr2WC2 carbides only.The SPE results show that there are two types of MC carbides in the as-sprayed HSS:the sphere one and the particle-like one.The former is about 2 μm in size and the latter is less than 1 μm,dispersed inside the grains,quite different from the MC carbides in the as-cast HSS.According to the AFM results,the skeleton-like M6C carbides of the as-sprayed high-V/Co HSS are embedded in the matrix along the grain boundaries.It is found that there are sharp membrane pieces on the carbides.Some small bamboo-shoot-like MC carbides grow from the matrix and are dispersed inside the grain.Those larger MC carbides are spherical particles embedded at the grain boundary junctions.     

Recent developments of the high strength and high ductility nanostructured materials

This talk will summarize the recent work related to a kind of new nanomaterials produced by the SMAT (surface mechanical attrition treatment).The concept of surface nanocrystallization of materials will be presented.In terms of the grain refinement mechanism induced by plastic deformation,a novel surface mechanical attrition(SMA) technique was developed for synthesizing a nanostructured surface layer on metallic materials in order to upgrade the overall properties and performance.The grain refinement mechanism of the surface layer during the SMA treatment will be analyzed in terms of the nanostructure observations in several typical materials.Very high yield stress(5 times of the base material) on the surface layer of the material obtained by the SMAT has been observed.The effect of surface nanostructures on the mechanical behavior and on the failure mechanism of metallic material shows the possibility to develop a new strength gradient composite using co-rolling and nitriding.The role of residual stress induced during the treatment will be investigated and discussed.The developed materials are also porosity free materials which can be used as reference material for the local mechanical behavior investigation technique such as the nanoindentation.A general concept for obtaining high strength and high ductility nanostructured materials will be presented.The exceptional high strength and high ductility steels have developed.The simulation of the mechanisms for improving ductility of high strength nanostructured materials will be presented.The potential applications for the land transportation vehicles(car,bus,train) and wind energy have been investigated.Some examples of concept design for the integration of the advanced nanostructured steels will be presented.     

高密度高强度高精度粉末冶金同步器齿毂生产工艺探讨

粉末冶金零件在汽车上的应用越来越广泛。粉末冶金同步器齿毂是汽车零部件中难度较大的一类。高密度高强度高精度粉末冶金同步器齿毂的生产工艺研究是中国现阶段的主要研究方向之一。长期的生产工艺研究表明,先进的生产工艺是粉末冶金同步器齿毂大批量国产化的关键。     

CNS tumours in south-western Finland: high location, high incidence

The Department of Paediatrics at the University Central Hospital of Turku, Finland has 130,000 children under 17 y of age within its catchment area. We collected all 103 cases of newly diagnosed CNS tumours from the 15-y period of 1981-95. The incidence was 5.3:100,000, a figure twofold those usually presented. During the period 1981-85 the incidence was lower (4) than during the subsequent 5-y periods (5.7 and 6.2). There were no statistical differences between the incidences of the supra- vs infratentorial brain tumours. Optic glioma was unusually common (17%, CI 13.9-20%).