轧钢过程中导卫用WC-Co基合金的磨损机理与组织变化

运用扫描电镜、能谱分析、洛氏硬度计、光学分析天平以及XRD等手段,研究一种轧钢导卫用WC-Co基合金在轧钢过程中的物理性能变化及表层的组织变化、磨损情况和磨损机理。合金在1000℃左右的温度下轧制2000t45钢之后,发现使用前后的密度并没有发生明显变化,但硬度却由使用前的56HRC下降到了使用后的49HRC。分析发现,硬度下降的原因是因为合金中部分大晶粒在使用过程中发生了动态再结晶,形成了许多尺寸为200nm左右的纳米晶。另外,对合金的磨损情况研究表明,其主要的磨损机制是塑性剪切变形和犁沟效应,其次粘着磨损和疲劳磨损也是合金表面磨损机制之一。最后还建立了犁沟效应和疲劳磨损模型。     

35CrMo钢表面铁基激光熔覆层的组织和耐磨性能

采用CO2激光熔覆装置将LC3530铁基粉熔覆在35CrMo钢基体表面,研究了熔覆层的显微组织、硬度和耐磨性能,并与基体的进行对比。结果表明:基体组织为回火索氏体,晶粒尺寸在20μm左右,而熔覆层的组织为均匀细小的等轴晶,晶粒尺寸大多在8μm;基体的平均硬度为254.1HV,而熔覆层的平均硬度为640.5HV,且硬度分布更加均匀;在相同试验条件下,熔覆层试样的磨损量仅为基体试样的1/7,磨损系数是基体试样的1/5,且磨损后熔覆层试样的表面粗糙度较磨损前的大幅下降,表明激光熔覆后35CrMo钢的耐磨性能得到显著提高;基体试样的磨损机制为犁削磨损,而熔覆层试样的磨损机制为微观切削,其优异的耐磨性能与含有铁、铬、钼和碳等元素的高硬度合金碳化物的形成有关。     

冷却方式与时效温度对60NiTi合金硬度和组织的影响

系统研究了冷却方式、时效温度对60NiTi合金硬度和组织的影响,结果表明：相比于退火处理试样,正火或淬火处理能显著提高合金的硬度;正火试样300℃时效处理能进一步提高合金硬度,而400,500,600℃时效处理使合金硬度降低,其中600℃时效处理合金硬度下降最显著;通过正火+300℃时效处理后合金的硬度由铸态试样的31 HRC提高到60 HRC。金相与X射线衍射（XRD）结果表明,正火和淬火处理后的60NiTi合金晶粒中没有粗大针状析出相形成。获得均匀细小的组织并避免Ni₄Ti₃相在冷却及时效过程中粗化并转变成Ni₃Ti相是得到高硬度60NiTi合金的关键。     

NiTi合金表面改性及其微动磨损性能研究

采用多弧离子镀技术在NiTi形状记忆合金表面制备TiN涂层。利用SRVⅢ摩擦磨损试验机研究NiTi合金表面改性后在37℃Hank’s模拟体液中微动磨损性能,分析法向载荷对TiN合金磨损机制的影响规律。利用SEM扫描电镜及能谱考察磨损表面形貌,结果表明：制备的TiN涂层表面致密均匀,无明显缺陷。说明TiN涂层可有效提高基体的耐磨性能,其磨损机制主要表现为剥落损伤与磨粒磨损并存。TiN涂层显微硬度为784 HV,远高于基体,TiN/NiTi膜基硬度比缓慢下降,涂层与基体结合强度高。     

晶粒尺寸对WC硬质合金刀具材料摩擦磨损性能的影响

研究了三种不同晶粒尺寸的硬质合金材料的摩擦磨损性能,测量了摩擦系数,采用扫描电子显微镜观察分析了硬质合金磨损表面的形貌变化。结果表明,随着滑动速度和载荷的提高,硬质合金的摩擦系数呈下降的趋势;相同条件下,随着晶粒的减小,硬质合金的摩擦系数略有升高。粗晶粒的硬质合金主要磨损机制为WC晶粒脱落造成的磨粒磨损,细晶粒硬质合金磨损机制主要表现为塑性变形。     

脉冲电沉积制备纳米晶钴-镍合金薄膜的摩擦学性能

采用直流电、单脉冲和双脉冲制备纳米晶钴-镍(Co-Ni)合金薄膜。用原子力显微镜(AFM)和表面轮廓仪分析薄膜表面形貌与表面粗糙度,用MV-2T显微硬度计测试薄膜的硬度,用球盘式摩擦磨损试验机的评价Co-Ni合金薄膜的摩擦磨损性能,用扫描电子显微镜分析Co-Ni合金薄膜的摩擦磨损机制。研究发现,电沉积技术显著影响纳米Co-Ni薄膜的表面形貌、硬度和摩擦磨损性能与机制。直流电制备的Co-Ni合金薄膜柱状晶较粗,硬度较小,但其表面粗糙度较小;双脉冲制备的纳米Co-Ni合金薄膜柱状晶较细,硬度最高,且表面粗糙度最小。双脉冲制备的纳米晶CoNi合金薄膜的磨损率比直流电制备的降低了近一个数量级,直流电制备的Co-Ni合金的磨损机制为严重黏着磨损和磨粒磨损,而双脉冲制备的Co-Ni合金薄膜表现为轻微的疲劳磨损和磨粒磨损。     

脉冲电沉积制备的纳米晶钴-镍合金薄膜的摩擦学性能

采用直流电、单脉冲和双脉冲制备纳米晶钴-镍(Co-Ni)合金薄膜。用原子力显微镜(AFM)和表面轮廓仪分析薄膜表面形貌与表面粗糙度,用MV-2T显微硬度计测试薄膜的硬度,用球盘式摩擦磨损试验机的评价Co-Ni合金薄膜的摩擦磨损性能,用扫描电子显微镜分析Co-Ni合金薄膜的摩擦磨损机制。研究发现,电沉积技术显著影响纳米Co-Ni薄膜的表面形貌、硬度和摩擦磨损性能与机制。直流电制备的Co-Ni合金薄膜柱状晶较粗,硬度较小,但其表面粗糙度较小;双脉冲制备的纳米Co-Ni合金薄膜柱状晶较细,硬度最高,且表面粗糙度最小。双脉冲制备的纳米晶CoNi合金薄膜的磨损率比直流电制备的降低了近一个数量级,直流电制备的Co-Ni合金的磨损机制为严重黏着磨损和磨粒磨损,而双脉冲制备的Co-Ni合金薄膜表现为轻微的疲劳磨损和磨粒磨损。     

搅拌摩擦加工对AM60B镁合金高温摩擦磨损性能的影响

在不同的旋转速度和进给速度下对AM60B镁合金进行搅拌摩擦加工(FSP),研究FSP对AM60B镁合金微观组织和硬度的影响;研究搅拌摩擦加工之后的AM60B镁合金在不同温度下的摩擦磨损性能,并分析其磨损机制。结构表征结果表明:FSP使AM60B镁合金搅拌区的晶粒细化,热机影响区的晶粒再结晶,热影响区的晶粒变长;随着旋转速度的升高晶粒尺寸增大。摩擦磨损试验结果表明:随着试验温度的升高,FSP处理试样的磨损率增大,摩擦因数增大;1 600 r/min、200 mm/min下的FSP处理试样,在25℃时的磨损率是母材的70%,200℃时的磨损率为母材的95%;25℃下,AM60B镁合金的磨损机制为磨粒磨损和轻微的剥层磨损,FSP处理试样的磨损机制主要是磨粒磨损,而100和200℃下,AM60B镁合金和FSP处理试样磨损机制均为严重的剥层磨损;200℃下,进给速度为200 mm/min,旋转速度为2 400 r/min时,试样表面磨损最严重,进给速度为300 mm/min,旋转速度为2 000 r/min时,试样表面磨损最轻,这可能是由于FSP引起了镁合金的硬度变化,从而影响了耐磨性的变化。     

工业纯钛板多道次搅拌摩擦加工区的组织及摩擦磨损性能

在不同旋转速度下对工业纯钛板进行3道次搅拌摩擦加工(FSP),研究了FSP区的显微组织、硬度及摩擦磨损性能,并分析了纯钛板FSP前后的磨损形貌及磨损机制。结果表明:搅拌区组织发生了剧烈的塑性变形,形成了细小均匀的再结晶组织,且随着旋转速度提高,晶粒明显细化;FSP区的最高显微硬度可达到430HV,较基体的(230HV)提升了87%;FSP区的平均摩擦因数和磨损率分别可达0.24和5.36×10~(-4) mm~3·N~(-1)·m~(-1);基体的磨损机制为粘着磨损,FSP区的磨损机制主要为磨粒磨损。     

AZ系镁合金的轻微-严重磨损转变研究

为研究AZ系镁合金的轻微-严重磨损转变机制,在0.1~4.0 m/s的滑动速度范围内对AZ31和AZ51镁合金进行干摩擦试验。研究不同滑动速度下载荷对磨损率、磨损机制的影响,绘制磨损转变图,分析磨损亚表层组织与性能变化。结果表明:轻微磨损区的磨损机制主要包括氧化、磨粒和剥层磨损,严重磨损区的磨损机制则为严重塑性变形和表面熔化;在轻微-严重磨损转变前后,亚表层经历塑性变形-再结晶的组织转变和应变强化-再结晶软化的性能变化,磨损表层发生再结晶软化是导致轻微-严重磨损转变的主要机制,据此建立判定轻微-严重磨损转变的表面临界再结晶温度准则,利用再结晶动力学计算不同滑动速度下的表面临界再结晶温度和转变载荷。     

Dry sliding wear in injection molded 17-4 PH stainless steel powder with nickel boride additions

Dry sliding wear behavior of injection molded 17-4 PH stainless steel powder with nickel boride additions has been studied on a pin-on-disc wear tester using an alloy steel pin and disc of hardness 63 HRC. The PIM alloys in the as sintered as well as in the precipitate-hardened conditions were investigated for their wear behavior. Wear rate was found to be initially decreased with the increasing nickel boride amount. Optical microscopy and XRD analysis were preformed to characterize the basic microstructures for all samples. SEM observations of the worn surfaces revealed plastics deformations with delamination of surface layers by subsurface cracks as the mechanism in the as sintered and precipitate-hardened conditions.     

弹簧钢洛氏硬度的测量不确定度评定

根据JJF1059—1999《测量不确定度评定与表示》的要求,采用某弹簧钢系统地对洛氏硬度的测量不确定度进行了评定。结果表明,本试验条件下的洛氏硬度的测量不确定度为0．9HRC。     

常用典型齿轮钢渗碳层的组织与性能

通过对3种齿轮钢20CrNi2Mo、17CrNiMo6、20CrMnMo进行渗碳及热处理,研究了不同渗碳时间后3种钢的表面碳含量及热处理前后的渗层硬度和组织。结果表明:3种钢的合金系数从高到低依次为20CrMnMo钢、17CrNiMo6钢、20CrNi2Mo钢,合金系数越大,相同渗碳条件下表面碳含量越高;高温回火前3种渗碳层的表面硬度均在45HRC以上,回火后均有所降低;高温回火前渗碳层的组织为马氏体、残余奥氏体等非平衡态混合组织。     

The wear resistance and worn metallography of pearlite,bainite and tempered martensite rail steel microstructures of high hardness

In order to find out whether it is worthwhile to produce premium rail steels harder than 36–39 HRC and to discover the best microstructure for wear-resistant rail an experimental Cr-Mo alloy rail steel was heat treated to pearlite, bainite and tempered martensite. Each microstructure was prepared at hardness levels of 38, 42 and 45 HRC. These were tested in a dual disk-on-disk machine that closely simulates wheel-rail contact in curves at 1/10 scale. Wear rates were established for dry, grease-sand and pure grease environments. Dry wear rates decreased significantly with increasing hardness in high rails with tempered martensite or bainite microstructures but were almost independent of hardness for pearlite in the range tested. Lubrication reduced the wear rates by up to two orders of magnitude for all microstructures. It is concluded that pearlite gives the best dry wear performance, and there is no advantage in increasing the hardness beyond 38–40 HRC. The superior performance of pearlite in dry wear appears to be due to a very pronounced work hardening near the wearing surface. Electron microscopy reveals a marked refinement in the pearlite microstructure near the wearing surface, and this may explain the high work hardening observed.     

耐高温磨损的合金钢导辊及高温耐磨性能研究

研究了一种具有奥氏体基体及碳化物硬质点的合金钢 ,并用于制造高速线材轧制生产线上的导辊 ,使用温度在 5 6 0℃下 ,合金钢导辊具有良好的耐磨性。分析了时效温度对奥氏体基体硬度及合金钢耐磨性的影响 ,研究表明提高奥氏体基体的硬度对改善合金钢高温耐磨性具有明显的作用。     

Simulation of roller guide wear in a high temperature test rig

Simulation of roller guide wear in rod or wire rolling mills has been performed in a high temperature test rig where the specimen rollers are in intermittent contact with the periphery of a heated rotating steel disc.By varying the time in contact during each cycle and deliberately superimposing a sliding component on the rolling contact, three components of guide roller wear were separated and quantified. The dominant component is wear due to sliding at the contact surface during rolling, followed by the isolated contribution from absolute rolling, while wear during roller acceleration is of less importance.Surface studies and the observed linear increase in wear vs. number of test cycles together with the linear increase in wear rate with normal force clearly show that abrasion by disc oxides is the dominant wear mechanism at elevated temperatures. The influence of disc temperature on the operating wear mechanisms as well as the resulting wear are also evaluated.A quantitative classification of four guide roller materials, a high chromium tool steel, two grades of high chromium cast iron and a cermet, has also been made. The hard cermet, containing about 50 vol.% titanium carbides, proved to be the outstanding material in roller guide applications.     

Effects of hardness on the solid particle erosion mechanisms in AISI 1060 steel

The mechanisms of mass loss were studied using impacts of single particles (WC spheres $\text{3}\text{16}$ in in diameter) for a 0.6% C steel (AISI 1060 steel) heat treated to give hardnesses of 12, 45 or 60 HRC. Both oblique and near-normal angles of impact were used. A new foil laminate was developed to measure rebound velocity and angle. Velocities of 100–200 m s^?1 were studied. A measurable mass loss was found only at 200 m s^?1. At a hardness of 12 HRC the mode of metal loss involved the loss of shear lips. At 60 HRC the dominant loss mode involves the intersection of adiabatic shear bands (ASBs) and shows a maximum mass loss at near-normal impact. The material with a hardness of 45 HRC shows both modes of mass loss and a maximum mass loss rate at oblique (30°) impact. ASBs on the surface and welding of target material to the impacting ball indicate a high temperature at the surface. However, the material welded to the particle is not a significant fraction of the material lost.     

Establishing a worldwide unified Rockwell hardness scale using standard diamond indenters

Recently developed microform measurement techniques have reduced the measurement uncertainties in the geometry of Rockwell diamond indenters. It is now possible to establish standard grade Rockwell diamond indenters characterized by high geometry uniformity, high hardness performance uniformity, interchangeability and reproducibility. By using the standard indenters under different national standard machines and a standardized testing cycle, a worldwide unified Rockwell hardness scale could be established with metrological traceability, stability and reproducibility. Geometrical measurements and hardness tests in five laboratories have shown that tightly controlled indenter geometry can significantly improve the consistency of Rockwell C hardness (HRC) measurements. These results support the feasibility of establishing a worldwide unified HRC scale with an expanded uncertainty (k=2) of approximately ±0.2 HRC and without significant bias with respect to an ideal scale.     

Selection of tool materials and surface treatments for improved galling performance in sheet metal forming

Galling is a known failure mechanism in automotive stamping. It results in increased cost of die maintenance and scrap rate of products. In this study, rectangular pan and U-channel stamping experiments are used to (1) investigate the effect of stress states on galling performance in sheet metal forming, (2) select proper tool materials and surface treatments for improved galling properties, and (3) differentiate galling performances of bare and coated steel sheets. The results indicate that problems with galling are of major interest at the regions where sheet materials deform under the action of compressive stress. For the four investigated tool materials, Mo–Cr alloy cast iron shows the best galling performance. A combination of hardening, surface polishing, and Cr coating is suggested as the optimum tool treatment in the forming of bare high-strength steel. Hot-dip galvanized steel shows better galling behaviors than galvannealed and bare steel sheets. Galling performances of hot-dip galvanized and bare steels are improved with increased hardness of the forming tool. However, galvannealed steel results in severe galling when the hardness of the forming tool is very high.