大直径锻造耐磨钢球的热处理工艺

采用二次加热淬火和低温回火工艺改善?120 mm锻造耐磨钢球的使用性能,研究了二次加热淬火工艺中不同升温速率和淬火冷却时间对钢球硬度分布、冲击性能和显微组织的影响.得出钢球的最佳热处理工艺为:以2.8℃/min的速率升温至840℃并保温1 h,出炉空冷至800℃后淬入35℃水中冷却350～400 s,然后出水空冷至80...     

Low-Cost,High-Speed Domain Refinement without Damage to Insulative Coatings

Rolling large- diameter hardened steel balls over the surface of high- permeability grain- oriented electri-cal steel allows lines of plastic deformation to be laid down. Choice of proper Young’s modulus and ball diameter enables artificial grain boundaries to be created, producing appropriate domain refinement and loss reduction.     

微粒子喷丸中碳钢疲劳性能分析

使用旋转弯曲疲劳试验机进行了中碳钢10~9cyc的疲劳实验,分析了直径100μm的钢球和陶瓷球喷丸处理后材料的疲劳性能及实验过程中残余应力的稳定性.与未喷丸试样相比,2种微粒子喷丸试样的疲劳极限分别提高了35%和23%.根据实验过程中对残余应力的跟踪测试,详细分析了残余应力松弛的过程及机理,阐述了疲劳极限提高机理及其控制因素.     

电磁球式平衡系统平衡方法及结构设计研究

针对电磁球式主动平衡系统，分析其工作原理，归纳钢球对应补偿能力的计算方法，讨论由已知不平衡量计算两个钢球相位的过程，并将多球情况按一定规则简化为两球情况，得到不平衡量和钢球数量、相位的关系。在特定转子直径下，建立平衡系统结构的三维模型，基于Ansoft Maxwell有限元分析平台，采用控制变量法依次研究了永磁体排布方式、直径、厚度和电磁结构对平衡转速和补偿量等的影响规律，最终完成了结构设计。结果表明：采用相邻永磁体极性相反交替排布，永磁体直径为6 mm、厚度为4 mm,电磁结构外壳长度略小于铁心长度时，平衡系统能取得较为合理的转速和最大补偿量。     

Effects of relative humidity on tribological properties of boron carbide coating against steel

Boron carbide coatings of 100 nm thick were synthesized on silicon substrate by DC magnetron sputtering using B₄C target with a mixture of Ar and methane (CH₄ at 1.2 vol.%) as processing gases. Tribological properties of the coating were studied in relation to the effects of relative humidity (RH). Reciprocating wear tests using 3 mm diameter steel balls as a counterpart were carried out at three relative humidity conditions. Confocal microscopy was used to observe worn surfaces and the wear scars on the steel balls. Elemental composition of the coating and worn surfaces were characterized using X-ray photoelectron spectroscopy and Auger electron spectroscopy. The tribological properties of boron carbide coating slid against steel ball were strongly affected by relative humidity. Lower and steady friction coefficient and higher wear resistance for both the coating and the steel ball were achieved at higher relative humidity. At high RH, tribochemical reaction occurred in the sliding surfaces, forming boric acid and carbon in a graphitic form on the worn surface of coating and a soft layer on the ball surface. The formation of boric acid on boron carbide coating combined with graphite structure led to the low and stable friction of boron carbide coating in medium and high relative humidity conditions. Smooth layer was formed on the worn surface of the steel ball at high relative humidity due to the tribochemical reaction. Low and steady value of friction coefficient and reduction of wear loss of both steel ball and boron carbide coating were attributed to the formation of the soft layer.     

Enhanced tribological properties of PECVD DLC coated thermally sprayed coatings

This research investigates the enhancement of the tribological properties of various thermally-sprayed coatings (APS Ni-50Cr, APS Al₂O₃-13%TiO₂ and HVOF WC-17Co) on steel substrate, achieved through the deposition of a thin DLC-based film. Higher adhesive strength between thin films and thermally-sprayed coatings compared to the simple thin film/carbon steel system was found by scratch testing. Dry sliding ball-on-disk tests performed under lower contact pressure conditions (5 N normal load, 6 mm diameter alumina ball) indicated a significant decrease in wear rates and friction coefficients of thermally-sprayed coatings when the thin DLC-based film is employed; little differences exist between the tribological behaviour of the various thin film/thermal spray coating systems and that of DLC-based film on carbon steel. Under higher contact pressure conditions (10 N normal load, 3 mm diameter alumina ball), the thin film/WC-Co system exhibited the best wear performance. These results indicate the superior tribological performance of DLC/thermal spray coating systems, especially under severe contact conditions.     

高碳马氏体钢球淬火开裂失效分析

T7-T8钢的热轧方坯模锻制的120mm耐磨钢球经锻后余热淬火，多数钢球开裂。对断口和材料组织形貌分析后，发现热处理工艺不合理造成的淬火应力大及组织粗大是导致钢球开裂的主要原因，     

Effect of colloidal silica addition on compressive strength of frozen mould

Abstract

The frozen mould which is produced by refrigerating the mixture of sand and water has the possibility to improve both the casting cost and the poor working environments such as noise, vibration and dust. The transition of mechanical properties of the frozen mould when it was transforming into thawed and dried states was examined. The compressive strength of the standard frozen mould consisting of only sand and water dramatically decreased when it was thawed and the strength was not recovered by drying. In contrast, the frozen mould produced by substituting colloidal silica solution for water showed some compressive strength even in thawed state and the strength was elevated by subsequent drying. The reusability of the sand mixture with colloidal silica solution was also evaluated. The compressive strengths did not deteriorate with any reclamation. The above results prove that the frozen mould with colloidal silica solution has an excellent industrial potential.     

8Cr4Mo4V材料钢球滚动接触疲劳试验研究

为了评价当前工艺水平航空主轴承用8Cr4Mo4V材料钢球滚动接触疲劳性能,以9.525 mm直径的8Cr4Mo4V材料钢球为研究载体,采用五球疲劳试验机开展不同应力水平下接触疲劳试验,对试验失效钢球通过失效模式与失效断口演变形式分析,确定试验数据有效性,同时提出简单程序数据处理方法对试验数据进行分析,获得不同失效概率下的钢球疲劳寿命并形成P-N疲劳曲线。结果表明:当前工艺水平航空主轴承用8Cr4Mo4V材料钢球滚动接触疲劳寿命是国外1992年试验国外材料钢球疲劳寿命的3倍以上;通过对9.525 mm直径8Cr4Mo4V材料钢球疲劳试验数据分析,求解出应力寿命函数的待定系数,可预测出不同应力水平下的接触疲劳寿命。     

Al-SiC powder preparation for electronic packaging aluminum composites by plasma spray processing

Powders of pure aluminum (Al) with 55 and 75 vol.% SiC particles were ball milled in a conventional rotating ball mill with stainless steel and ZrO₂ balls for 1–10 h. The morphology and microstructure of the milled powders have been observed and analyzed by scanning electron microscopy (SEM) and energy dispersive x-ray (EDX). The milled powders were plasma sprayed onto a graphite substrate to obtain Al matrix composites with high SiC volume fraction. SiC particles in the milled powders existed in two forms; i.e., the combination of Al into composite powder and individual. Plastic Al particles were broken during ball milling, and fine Al particles can be coated onto the surface of SiC particles. Iron contamination in the milled powders occurred when stainless steel balls were used. The iron level can be effectively controlled by using ZrO₂ ball media. The milling efficiency by ZrO₂ balls is inferior to that by stainless steel balls. Longer milling time was required with ZrO₂ balls to achieve the same effect as obtained with stainless steel balls. SiC particles in the sprayed composites from the milled powders exhibited a reasonably uniform distribution and high volume fraction.     

Development of autocompleting friction welding method

Abstract

This paper describes an autocompleting friction welding method that was carried out to weld with an insert piece set between fixed base metals. The base metal was low carbon steel, and the faying surface of the fixed specimen had a 10 mm diameter. The effect of the thickness of the insert piece (insert thickness) on the joining phenomena was investigated. When the insert thickness was 3˙2 mm and the friction welding conditions were a friction speed of 27˙5 s^–1 and friction pressure of 36 MPa, the insert piece had a shear fracture toward the circumferential direction in the peripheral portion of the weld interfaces by the initial peak produced during the friction process. The joint also had cracks at the adjacent region of the weld interfaces, although it had the same tensile strength as the base metal. On the other hand, the joint made using the insert piece with a groove on its peripheral portion had the same tensile strength as the base metal, where it fractured. This joint also had 90° bend ductility without cracks. In this case, the optimum insert thickness was 4˙0 mm, and the thickness at the bottom of the grooves (groove bottom thickness) was 1˙2 mm with an 11 mm inner groove diameter, and the friction welding conditions were a friction speed of 27˙5 s^–1 and friction pressure of 36 MPa. In conclusion, a sound friction welded joint was made by an autocompleting friction welding method.     

白马选厂一期二段磨矿加小直径钢球试验研究

在钒钛磁铁矿选矿的磨矿过程中,使用直径40 mm的小钢球作为二段磨矿介质,替代现有在攀枝花-西昌地区的钒钛磁铁矿的选矿过程,二段磨机常用的直径60 mm的钢球,对提高白马选矿厂二段磨机的生产效率有积极作用,可降低选矿工序成本,提高选矿效果。     

Simulation on stress of large diameter CADI grinding ball based on ANSYS

The falling ball tests were carried out on the Φ125 mm diameter Carbidic Austempered Ductile Iron(CADI) grinding balls with Mn content of 2.0wt.%, 2.3wt.%, 2.6wt.% and 3.0wt.%, respectively, and the kind of grinding ball with the most serious spalling was selected for stress simulation. The stress distribution between four grinding balls in the elbow of the falling ball test device when they collided with each other was simulated based on ANSYS. Results of the falling ball tests show that the spalling and mass loss of a CADI grinding ball increases with the increase of Mn content, and the CADI grinding ball with 3.0wt.% Mn shows the most obvious spalling and mass loss. The simulation results of stress distribution of a CADI grinding ball show that the maximum impact stress does not appear in the center of the contact area, but in the annular area(inner diameter of ～20 mm and outer diameter of ～50 mm) in the section with a depth of 5-15 mm below the grinding ball surface. The actual spalling of the ball is consistent with the simulation results, and the oxide-based impurities in CADI grinding ball accelerate the spalling of the grinding ball in service.     

Change in shape of a cold formed and annealed stainless steel sheet and joining with use of this change

An austenitic stainless steel sheet with thickness 1.0 mm is V-bent, U-O press formed and roll-formed. Metastable austenitic stainless steel is partly transformed into martensite when cold formed and is reversed in annealing, followed by a volume change. Taking this into consideration, V-bend angle and outer diameter are measured before and after annealing of the V-channel and the pipe obtained. By evaluating the change, effects of the punch radius, reduction in outer diameter, stability of austenite, rolling direction and annealing temperature on the opening of the channel and the swelling of the pipe are made clear. For comparison a uniaxial tensile test is also performed and the volume fraction of martensite is measured. Maximum change in V-bend angle for 301 stainless steel is 5° when the punch radius is 10 mm and the V-channel is annealed at 1023K. For 301 stainless steel, 50% of the material is transformed into martensite and 80% of the transformed martensite is reversed at 1023K. Also for the roll-formed or U-O formed pipe, outer diameter of the pipe is changed by some 0.2%. Taking advantage of this change, the pipe can be joined with the carbon steel pipe and the obtained joining strength is about 25 MPa.     

一种高铬铸铁磨球的生产

采用高含碳量，中、偏高的含铬量；铸型的大部分为金属型、冒口局部为砂型，低温去应力热处理工艺生产的高铬铸铁磨球在实际使用中达到了高耐磨、抗冲击、低成本的良好效果。     

The Impact of Corrosion on the Mechanical Behavior of Welded Splices of Reinforcing Steel S400 and B500<Subscript>c</Subscript>

The reinforcing steel, used in concrete structures, when corroded causes reduction of the strength properties and especially drastic reduction of ductility. Steel corrosion constitutes an important factor of progressive devaluation of its mechanical properties and serious reduction of the integrity of structures. The problem becomes more evident specifically for structures near coastal areas where salt corrosion is predominant. Reinforced concrete columns and beams are quite often extended by welding new steel reinforcement to the already corroded existing steel. In the present article the impact of corrosion on the mechanical properties of welded splices of reinforcing Steel S400 and B500_c is examined. An experimental investigation was conducted and tensile and compressive results are presented for welded precorroded S400 and noncorroded B500_c steel splices. The mechanical behavior of welded splices in tension are different in compression and depend strongly on the level of corrosion of the S400 bars.     

Fabrication of nanostructured Mo coatings on Al and Ti substrates by ball impact cladding

Nanostructured multicomponent Mo coatings were fabricated on Ti and Al substrates by ball impact cladding at room temperature in an ambient atmosphere. The process involved subjecting the substrate and Mo foil fixed at the top of a vibration chamber to high-energy collisions with balls. The coating formation was the result of a simultaneous process of mechanically induced plastic flow, nanocrystallization, and interdiffusion caused by the ball collisions. Plastic deformation refined the grains at the Mo foil/substrate interface to the nanometre scale. The size of nanocrystalline grains in the Mo coatings ranged between 2 nm and 10 nm. The ball collisions caused atomic level intermixing of different elements, introduced into the surface from the steel balls used for milling, and solid solubility improved remarkably. The hardness of the Mo coatings on the Al and Ti substrates was 552 and 1010 HV, respectively. The initial hardness of the Mo foil was 287 HV. The high hardness of the Mo claddings was attributed to the fine grain structure, formation of supersaturated solid solutions, and high residual compressive stresses.     

Non-destructive measurement of residual stresses in carbon steel weld joints

Abstract

Residual stress measurements have been carried out on 8 and 12 mm thickness carbon steel single V weld joints by X -ray diffraction and ultrasonic techniques. The maximum tensile and maximum compressive stresses on the surface of the 12 mm carbon steel weld joint are higher than those on the surface of the 8 mm carbon steel weld joint. The results also indicate that the variation in the surface residual stress across the weld is different from that for the through thickness residual stresses. The effect of constraint, which depends on the thickness of the weld joint, is found to influence the surface and through thickness residual stresses. The effect of stress relief annealing heat treatment on residual stresses was also studied.     

Development of semi-dieless metal bellows forming process

A novel semi-dieless metal bellows forming process with local induction heating and axial compression without using any conventional dies is proposed. Firstly, the thickening of a tube is induced by local heating and axial compressive force. Secondly, the buckling of the tube occurs, producing a convoluted shape. The seamless tubes used are stainless steel SUS304 with an outer diameter of 5 mm and a thickness of 0.5 mm and 0.3 mm. The effects of compression ratio on the profiles of the bellows such as convolution height, pitch and thickness are investigated experimentally. It is found that convolution height can be controlled by compression ratio. Additionally, the mechanism of this process for fabrication of the metal bellows can be clarified by loading curve during processing. Furthermore, the validity of a two-step compression technique for improving convolution height and pitch is verified. The fundamental of the proposed technique can be confirmed as a basic key processing to fabricating metal bellows with various dimensions and small quantities.     

Effect of gas flow rate on shapes of weld bead sections. Study on high‐speed surface treatment by arc with laser (2nd report)

Recently, lightening, speed-up and decreasing vibration of the transport vehicles have been discussed for improving of environmental problems. As one solution, the material hybrid concept using aluminum alloys and high strength steels has been proposed. Therefore, new welding processes by which these dissimilar materials can be joined in high reliability and productivity are demanded. Laser roll welding was developed for joining of dissimilar metals by M. Kutsuna, M. Rathod and A. Tsuboi in 2002. Up to now, a CO₂ laser has been used as a heat source. In the present work, laser roll welding of low carbon steel and aluminum alloy using a 2 kW fibre laser was investigated to improve the joint properties due to the effective heating characteristics. Effects of the process parameters were studied. Otherwise, the influences of process parameters on the weldability, the formation of intermetallic compound layer and the mechanical properties have been investigated. As a result, various types of intermetallic compound layer were confirmed at the laser roll welded joint interfaces. When intermetallic compound layer thickness was less than 10 μm, the specimen was a failure in the base metal of low carbon steel in the tensile shear test.