Effect Of Surface Hardening Research Articles

Effects of CO2 Laser Surface Hardening in the Unlubricated Wear of Ductile Cast Iron Against Alumina

The microstructure of a ferrito-pearlitic ductile cast iron has been modified by CO2 laser surface hardening. Analysis of the laser-processed surfaces showed a dramatic increase in microhardness. Dry sliding wear of laser-treated specimens against an alumina counterbody has been investigated by “ball-on-disk” testing. The evolution of the wear coefficient, as well as metallographic observations, revealed an oxidational wear mechanism. The wear resistance of the laser-treated samples was significantly enhanced. The laser-treated cast iron has a better resistance to abrasion and plastic deformation. The improvement of the wear resistance was due to the fine and homogeneous microstructure produced after laser-treatment. Wear plots showing the evolution of wear coefficient with normal load, sliding velocity, and humidity have been established. The wear of the laser-treated cast iron is not influenced by the variation of operating conditions (normal load, sliding velocity, and relative humidity).

Influence of Previous Structure on Laser Surface Hardening of AISI 1045 Steel.

The effect of laser surface hardening was studied in an AISI 1045 steel with different microstructures: ferrite and pearlite, or with carbides dispersed in the ferritic matrix produced by martensite tempering at 180, 450, 600 and 660°C.The laser treatments were carried out working with a 10×10 mm square beam of uniform power density and 1.5, 2.5 and 5 kW output power. The scan rates permitted temperatures to range from those at the austenitization start to the melting point of the material.The depths of the zones of affected material were revealed by metallographic observation and Vickers hardness measurement. The results suggest that the initial structure of the steel has a considerable influence on laser surface hardening effect. The differences are manifested in the depths of the distinct heat affected zones and in the obtained microstructures.

Friction, wear and service properties of i-C coatings on steel

We have developed a high-accuracy test unit that permits the testing of wear of coatings by a flux of solids. The unit features the following advantages: • - Special abrasive particle collectors are provided which enable one to determine accurately the number of particles that have caused the wear of a given specimen; • - Spatial homogeneity of the particle effect on a specimen is ensured, owing to scanning a particle jet perpendicular to the plane of its rotation. Friction studies and tests of i-C diamond-like coatings (DLCs) in a flux of solids have shown that the surface hardening effect is determined by the adhesion of coating to the substrate and by the critical degree of plastic deformation at the substrate coat interface. On the basis of the tests performed, a procedure of applying surface-hardening i-C DLCs on various tools has been developed which permits the operational life of tools to be extended considerably.

Effect of surface roughness and surface hardening of 45 steel on the tribotechnical properties of antifriction friction pairs based on iron

Effect of surface roughness and surface hardening of 45 steel on the tribotechnical properties of antifriction friction pairs based on iron

The effects of surface hardening on fracture toughness of carburized steel

This research program was carried out to evaluate the effects of surface hardening on the fracture toughness of carburized steel. The materials AISI 8620 steel was machined into compact-tension (CT) specimens. The specimens were pack carburized at 930°C (1706°F) for different periods of time, cooled to ambient temperature and subsequently tempered at various temperatures for one hour. The fractured specimens were examined by hardness tests, metallography, X-ray diffraction analysis for retained austenite in the case, and scanning electron microscope fractographic analysis of the fracture surfaces. The experimental results revealed that theKIC values of the carburized, AISI 8620 steels were improved by the increase in case depth. Martensitic/tempered-martensitic structure in the case was the major constituent contributing to the improved toughness. The amount of retained austenite at the case increased as the thickness of the hardened layer increased. But retained austenite as well as large grain size were found to have adverse effects on fracture toughness of the carburized steel. The tempering temperature of 500°C (932°F) provided maximumKIC values. Higher tempering temperatures resulted in sharp decrease of fracture, toughness values.

Properties of SbCl5-doped PPP/PPS composites

Microindentation hardness is used to characterize the surface mechanical behaviour of two series of sintered PPP/PPS composites in a wide range of compositions. This work complements a previous electrical conductivity study carried out to determine the insulator-conductor transition within these materials. The influence of annealing the PPP-phase at 400° C before sintering the composites is discussed with reference to the additivity of hardness values of the single components PPP and PPS. The hardening of these composites upon doping with SbCl5 is investigated in the light of the morphology of sintered materials. The elastic release of the material and the creep behaviour under the indenter are examined in terms of the porosity of the samples and of the dopant penetration within the material. In the case of compact materials, the hardness is found to increase due to a doping-induced surface-hardening effect. The hardness increase in porous materials responds to an inclusion of the dopant species within the material volume.

Effect of surface hardening in zone of stress concentration on the tendency of carbon steel to brittle fracture

With a stress concentrator present in specimens, laser hardening offers advantages over casehardening.

Wear Behavior of Laser Surface-Hardened Gray and Ductile Cast Irons. Part 2—Erosive Wear

A 1.2-kW, continuous wave, CO2-gas laser was used to transformation harden or melt the surface of gray and ductile cast irons. Effects of surface-hardened layers on solid particle erosion showed that the erosion rate decreased with an increase in surface hardness and case depth. The order of matrix microstructures that increased the erosion rate were ledeburite, tempered martensite, and pearlite. These results were opposite to those observed in bulk-hardened alloys. Erosion mechanisms of brittle, gray iron included micromachining in the untreated condition and grain boundary cracking in the laser-treated condition. In contrast, erosion modes of ductile iron were plastic flow followed by cracking in the untreated condition and platelet formation and fatigue in the laser-treated conditions. The beneficial effects of surface hardening on erosion were examined and discussed.

塗装鋼板の塗膜性能に対する微細無機添加物の効果

The effect of inorganic additional substances on the coated films was investigated in order to obtain the anti-abrasion precoated steel sheet having good formability. The finely grinded glass fibers and glass flakes were found to be very effective for the above mentioned purposes, but other inorganic materials such as SiO2 powder or CaSiO3 powder afforded only surface-hardening effect of precoated films. Almost all kinds of paints except those composed of fluorocarbon polymers were applicable for this anti-abrasion precoated steel sheet, and the effective content of the glass fibers or glass flakes in paints was found to be 15-20%, considering the surface hardness and the formability of the precoated films and the coating workability in the continuous coating lines.

Effect of spark hardening on life of hot-forging dies

The effect of surface hardening by spark deposition of tungsten carbide on the life of hot-forging dies was assessed by Weibull analysis for several pinion punch dies. It was found that the coating was beneficial to die life if those factors which contributed to long die life governed the die behaviour whereas the coating was detrimental if those factors which contributed to short die life were governing the behaviour. The results showed that better temperature control of the billet heating arrangements produced significant improvements in the die life.

Effect of surface hardening on the kinetics of fracture of gray alloy cast iron

Effect of surface hardening on the kinetics of fracture of gray alloy cast iron

Effects of notches and surface hardening on the early growth of fatigue cracks

The majority of fatigue-crack growth data for specimens containing surface-hardened layers is in the form of S/N curves. In hardened specimens, however, many factors, such as residual stress levels in ‘case' and ‘core', relaxation of these stresses by specimen distortion during hardening, and microstructural and (in some cases) chemical variations, affect the processes of initiation and growth. In addition, it may happen that the effect of these factors on initiation and on propagation of a fatigue crack is not the same. The present paper describes experiments involving the monitoring of short fatigue cracks which grow from machined notches through hardened surface layers of different kinds, and examines the effects of residual stresses as the crack extends into the ‘core’ material. Observations of crack-growth rates in the important situation of an asymmetrically hardened component show the effects of specimen distortion in relaxing residual stresses, and in some situations permit an estimate to be made of the variation of residual stress throughout the hardened layer. In addition, there is described a means of correcting for the effect of notch shape on the growth rate of a short fatigue crack.

Mechanical properties of carbon fibers coated with refractory carbides

The internal friction method has been used to investigate the protective function of barrier coatings of silicon and zirconium carbide. The effect of the thickness of the coating on the mechanical characteristics of carbon fibers and their oxidation resistance is examined. The optimal coating thickness is established. A surface hardening effect of the coatings has been detected.

The effect of an air environment on the creep and rupture behavior of a nickel-base high temperature alloy

The behavior of wrought and cast polycrystalline Udimet 700 tested in static tension at 1200 K (1700†F) has been determined. An air environment decreases rupture life and ductility, except in very coarse-grained cast specimens, because of premature failure by stress-assisted grain boundary oxidation and cracking. In very coarse-grained cast specimens greater life and ductility are found in air than in vacuum, presumably due to the paucity of transverse grain boundaries and to some type of surface hardening effect. Wrought specimens exhibit greater grain boundary sliding, hence more cracking, shorter life, and lower ductility, than cast specimens in any environment. This is attributed to differences in grain boundary topography.

Effect of surface hardening and environment on certain properties of monolayer compositions based on aluminum and tin

Effect of surface hardening and environment on certain properties of monolayer compositions based on aluminum and tin

Effect of mechanical surface hardening on the low-cycle fatigue strength of titanium alloys

1. Surface hardening effectively increases the low-cycle fatigue strength of titanium alloy VT3-1 particularly with stress concentrators. 2. Hardening a notch by burnishing substantially increases the fatigue limit under load to a value corresponding to the yield strength of the material and may completely eliminate the unfavorable effect of the concentrator. 3. Hardening of the area near the stress concentrator without hardening the notch itself has comparatively little effect.

The surface layer of surface-hardened parts of heat-resisting alloys

The effect of surface hardening by cold working depends mainly on the stability of residual compressive stresses. The residual stresses decrease greatly in the first hours at elevated temperature and then change slowly. The time that the effect of surface hardening is retained in heat-resisting alloys can be determined approximately — from the decoration of the structure with dislocations — by metallographic examination.

Effect of surface hardening of carbon steel by high frequency induction heating on its susceptibility to stress corrosion cracking

It was demonstrated that the conditional static corrosion-fatigue limit of steel 40Kh under stress-corrosion conditions depends on the depth of surface quench-hardened layer and on the initial structure of the steel.

Electrical Industry and Research

SEVERAL notable developments have taken place in the research laboratories of the Metropolitan Vickers Electrical Co., Ltd., during the past year. The investigations on the ‘creep’ or deformation of metals under stress at high temperatures have led to definite results which are of importance in mechanical engineering. It has been proved that even at the lower stresses and temperatures of turbine practice steels cannot be regarded as permanently elastic materials. They are subject to gradual stretch or other permanent distortion. A quick method of testing steels has been developed in the laboratories, and thoy can now be placed in order of merit after a duration test of only a few days.‘Creep’ tests as ordinarily applied may last for months. A particular sample was subjected to test for twelve months and was found to creep at the rate of one part in a hundred million per hour. For the next two months, however, after the year was completed, it only increased at a tenth of this rate. The limit of sensitivity of the apparatus has now been reached, but it is not yet possible to say definitely that creep has ceased. If we consider a turbine cylinder 100 inches in diameter and subject to a rate of increase of one part in a hundred million per hour over a period of ten years, its diameter would have increased by nearly one-tenth of an inch, and this increase would seriously limit the life of the turbine. Other useful mechanical researches are being made in the laboratory as to the effect of surface hardening on the fatigue resistance of gear-wheel teeth. The results obtained are of great use in designing the best driving gears for electric trams and locomotives.