AISI 410钢膏剂渗硼工艺渗层的组织与性能

通过膏剂渗硼工艺对AISI 410钢进行表面强化,分析了渗硼层的组织形貌,并测试了其硬度、耐磨损性能以及耐腐蚀性能。结果表明,渗硼层主要由FeB、Fe₂B相组成,渗硼层/母材的结合界面较平坦;渗硼层外渗区硬度达1400 HV0.5以上,内渗区硬度达1100 HV0.5以上;渗硼处理后试样表面摩擦因数和截面磨痕面积显著减小,耐磨损性能得到改善;在电化学腐蚀试验中,渗硼试样自腐蚀电位大于母材试样、自腐蚀电流密度小于母材试样,说明渗硼处理降低了AISI 410钢表面的腐蚀倾向,其表面耐蚀性得到提高。     

渗扩时间比对AISI 316不锈钢渗氮层组织与性能的影响

采用真空两段渗氮工艺,在不同的强渗、扩散时间下对AISI 316不锈钢进行渗氮处理,通过X射线衍射(XRD)、扫描电镜(SEM)、光学显微镜(OM)、显微硬度测试和摩擦磨损试验等分析了渗氮层的组织和性能。结果表明,经过12 h的真空渗氮后,AISI 316不锈钢表面形成了一层由γ′-Fe₄N、ε-Fe_2-3N和CrN等相组成的渗氮层,其表面硬度和耐磨性能相较于基体均有明显的提高。其中,渗扩时间比为1∶1(强渗6 h、扩散6 h)时的渗层厚度约为96 μm,表面硬度约为1069 HV0.5,是基体表面硬度的4.5倍,在20 N载荷下的磨损量约为基体的1/3;渗扩时间比为1∶2(强渗4 h、扩散8 h)时的渗层厚度约为120 μm,ε-Fe_2-3N相衍射峰增强,在20 N载荷下的磨损量约为基体的1/30。延长扩散时间能增加渗氮层厚度,改善表面形貌,进一步提高不锈钢的耐磨性。     

3D FE MODELLING OF SUPERFICIAL RESIDUAL STRESSES IN TURNING OPERATIONS

In this paper, the residual stresses on workpiece surface after cutting operations are studied by means of 3D finite element method (FEM) simulations and the results are compared with the experiments. In particular, the effects of feed rate and tool nose radius on the final workpiece residual stresses when turning AISI 1045 steel bars were analyzed; two different approaches were utilized for the simulative models. In the first approach incremental Lagrangian and Eulerian solvers were coupled to reach both mechanical and thermal steady state conditions performing a single cutting pass, while the second approach consisted of an incremental Lagrangian simulation in which consecutive turning passes were considered in order to reach mechanical and thermal steady state. The simulation results were finally compared with the experimental ones: the agreement between them is satisfactory even if the numerical errors are, in some cases, remarkable.     

Refinement of tempered martensite structure and its effect on wear mechanism in SAE 8620

All mechanical components that undergo sliding or rolling contact are subjected to some degree of wear. Carburising treatment is important in improving wear characteristics of AISI 8620 gear steel. An experimental investigation was conducted on carburised AISI 8620 steel. Gas carburising of the specimens was carried out in sealed quenched furnace at 1198 K for 6 h followed by hardening at 1133 K, oil quenching at 393 K and followed by tempering at 453 K. Carburised cryotreated samples were cooled in a controlled manner soaked at 88 K for 16 h in a cryoprocessor subsequently followed by soft tempering at 373 K. Specimens were characterised by microhardness test, wear test and retained austenite content by XRD. 3D wear surface response and 2D contour map showed that wear rate decreased by 32% in the case of carburised cryotreated specimens as compared to only carburised specimens. It was concluded that there was an improvement in hardness and wear resistance of carburised cryotreated steel as compared to only carburised steel. Refinement and densification in martensitic structure resulted in shift in wear transition from severe wear regime to mild wear regime.     

Tribological behaviour of AISI 316L stainless steel for biomedical applications

Abstract

The aim of this research is to study the tribological behaviour of AISI 316L stainless steel for surgical implants (total hip prosthesis). The tribological behaviour is evaluated by wear tests, using tribometers ball on disc and sphere on plane. These tests consisted of measuring the weight loss and the friction coefficient of stainless steel (SS) AISI 316L. The oscillating friction and wear tests have been carried out in ambient air with an oscillating tribotester in accord with standards ISO 7148, ASTM G99-95a and ASTM G133-95 under different conditions of normal applied load (3, 6 and 10 N) and sliding speed (1, 15 and 25 mm s^?1). A ball of 100Cr 6, 10 mm in diameter, is used as counter pairs. These tribological results are compared with those carried out with a tribometer type pin on disc under different conditions of normal load applied P (19·43, 28 and 44 N) and sliding speed (600 and 1020 rev min^?1). The behaviour observed for both samples suggests that the wear and friction mechanism during the tests is the same, and to increase the resistance to wear and friction of biomedical SS AISI 316L alloy used in total hip prosthesis (femoral stems), surface coating and treatment are necessary.     

Using Mather-type plasma focus device for surface modification of AISI304 Steel

A 2.8 kJ plasma focus device with a nitrogen gas filling and a copper anode capsulated by aluminum was used to modify the surface of AISI304 steel substrate, in order to improve its properties. The treatment was carried out using a various number of nitrogen plasma focus shots at a pressure of 0.5 mbar and at two steel sample distances (20 and 40 mm) from the anode. The plasma diagnostics was made using the voltage and current curves recorded by a voltage divider, Rogowskii coil, accompanied with calculations using a five phase radiative Lee model (RADPF5.15a) to determine the temperature and plasma density.The surface hardness of AISI304 steel was increased by ∼175% after plasma treatment and the thickness of the treated layers was about 1-2 μm. Results show that the surface hardness is increased with increasing shot number and decreased with increasing distance from the anode. Changes in surface morphology and the elemental composition were investigated by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX).     

Effect of Different Surface Treatment Methods on the Friction and Wear Behavior of AISI 4140 Steel

In this study,the effects of various surface treatments on the friction and wear behavior of AISI 4140 steel have been evaluated.Sample surfaces of AISI 4140 steel were treated by quenching,carburizing,boronizing and plasma transferred arc (PTA) modification.The microstructural characteristics of surface treated steel samples were examined by optical microscopy and scanning electron microscopy (SEM).The mechanical properties of the samples including the surface roughness,microhardness,and abrasive and adhesive wear characteristics were also evaluated.Wear tests were applied by using a block-on-disc configuration under dry sliding conditions.The wear behavior and friction characteristics of the samples were determined as a function of sliding distance.Each sample group was compared with the other sample groups,and it was observed that the carburized samples demonstrated the lowest weight losses;however,PTA-treated samples demonstrated the lowest coefficient of friction in comparison to the other sample groups at the same sliding distance.     

激光冲击处理对AISI304钨极氩弧焊接接头残余应力的影响

利用激光冲击波对AISI304不锈钢氩弧焊接接头进行了表面强化处理,用X-350A型X射线应力仪测定了其激光冲击处理后残余应力,分析了残余应力的产生机理.结果表明,激光冲击处理后AISI304焊接接头残余应力为110MPa左右,其强化效果十分明显,显著地降低了焊接接头残余拉应力,并使残余应力分布趋向均匀.     

Behavior of AISI 316L Steel Subjected to Uniaxial State of Stress at Elevated Temperatures

This paper presents an experimental investigation on an AISI 316L stainless steel regarding mechanical properties and short uniaxial creep tests at elevated temperatures. The short time creep tests were carried out under different but constant stresses. The obtained data of ultimate tensile strength, yield strength, creep curves and effects of elevated temperatures on mechanical properties were presented. For a selected rheological model,material parameters were obtained. As a justification, such rheological model is implemented in the finite element procedure for an uniaxially stressed specimen in selected environmental conditions.     

MC complex carbide in AISI M2 high-speed steel

MC complex carbide was observed in spray formed AISI M2 high-speed steel. This carbide was extracted from samples after austenitizing and tempering. The carbide was characterized by X-ray diffraction, X-ray fluorescence and scanning electron microscopy. The extracted MC is a type of carbide not yet reported in the open literature. It is a face centered cubic carbide with lattice parameter a = 0.417028(4) nm, very close to the VC carbide but with a totally different chemical composition. The M represents the metallic elements (at.%): 36.70 V, 19.72 Cr, 2.67 Fe, 32.31 Mo and 8.60 W.