Experiments were done by spraying urea (NH2CONH2) as its pyrolysis gases at the intervals of 5min onto molten iron containing 0.4 mass% Cu at 1600°C under reduced pressure. If urea amount per each spraying was more than 0.4g, the molten iron was suddenly splashed and slopped over the top of crucible during the experimental run, so that 0.3g of urea was sprayed in the subsequent experiments. Nitrogen concentration of the molten iron increased with increasing the number of urea spraying and the pressure of gas phase. It was 5 to 8 times higher than the concentration in equilibrium with nitrogen gas. The following relationships were found between the rate constant (k) of copper evaporation and the pressure (P in Pa) : In the case of urea spraying, log k = -log P-0.762; without urea spraying, log k = -log P-0.996. These results show that even in the case of urea spraying the evaporation rate of copper was controlled by mass transfer through gaseous film on the surface of the molten iron. It was concluded that acceleration of copper evaporation by urea spraying may be mainly due to the evaporation as Cu(N3)2which has higher vapor pressure than metallic copper. The evaporation rate of copper somewhat decreased in the case of the molten iron containing 0.34 mass% C, because some part of urea was probably consumed by the formation of iron cyanide. Sulfur had little influence on the evaporation rate.
Welded cans for beverages amount to over 1 million cans/year and take an important role in the field bf steel package industry. Under the intense competition among other materials, can cost reduction and high productivity, which usually lead to the worse weldability, must be overcome steadily. Until recently, several authors reported that the static electric contant resistance between welded materials strongly influenced weldability. However, the static contact resistance could not be the index of the dynamic high speed welding. The weldability using high speed seam welder was hardly experimented and discussed quantitatively because the dynamic electric resistance could not be divided into the contact resistance and the bulk resistance. In this report, the effects of the main parameters on weldability, namely tin coating weight, steel thickness and welding speed, were investigated in connection with the equivalent contact resistance by subtracting the calculated bulk resistance from the measured total resistance during high speed welding. It made clear that the contact length between material and electrode correlates with the available welding current range. The weldability deteriorated with the decrease of tin coating weight and the decrease of steel thickness because of the increased contact resistance and with the increase of welding speed because of the increased discontinuity of HAZ pattern.
We propose a new method for estimating the AE (or elastic wave) source wave in the delayed fracture of a finite specimen (NACE-TM0177) by using the experimental transfer functions of medium and/or AE transducer. A laser induced dielectric break-down of silicon grease was utilized to examine the frequency resolution of the AE system employed. Due to the limited frequency resolution of the system and the reflected waves, the accurate source analysis of micro-fracture was limited to a relatively slower crack generation with the rise time longer than 0.5μs. Crack generation rate in the delayed fracture of QT-treated SCM 440 alloy with tensile strength of 1323 and 1500 MPa was estimated to change from 50 m/s ( effective rate : 145m/s) to 170 m/s (490 m/s), depending on both the strength of material and hydrogen concentration in front of notch.
Glow discharge mass spectrometry (GDMS) which has mainly been developed for bulk samples was applied to powder samples. Powders were pressed on a pure In sheet and mounted on a discharge cell for disk-shaped samples. The discharge condition commonly used for bulk samples was employed. The surface contamination was removed by presputtering for 60 minutes. The size of particle and the density of the powder pressed on the In sheet do not affect the ratios of ion currents of analyzed elements to that of the matrix element. The relative sensitivity factors (RSFs) for 21 elements (isotopes) have been determined for Fe-based powders. The RSFs for powders are almost equal to those for Fe-based alloys with disk shape. The relative error of analytical values by GDMS to the chemically analyzed values was about 25% in average for trace elements of concentration less than 10ppm and smaller for elements of the higher concentrations.
The properties of the commercially pure titanium seamless pipe, manufactured by the inclined rolling, process, was investigated in comparison with the pipe by the conventional hot extrusion process. The results were as follows. ( 1 ) The titanium pipe without surface defects was successfully manufactured by the inclined rolling process. The pipe, reheated and finish rolled in the alpha phase temperature, had a good surface properties and equiaxed structure after annealing heat treatment. ( 2 ) Post annealed tensile properties of the rolled pipes satisfied the ASTM specification regardless of the reheating temperatures. The tensile properties of the rolled pipes, which were reheated in alpha phase region, were almost equivalent to that of the extruded pipe. ( 3 ) Texture formed in the rolled pipe was similar to that of formed in the rolled plate when the pipes were reheated and finish rolled in alpha phase region. On the other hand, the texture in the rolled pipes which were reheated and finish rolled in beta phase region was transformed type. The (0002) reflection was strongly accumulated in the extrusion and the transverse directions in the extruded pipe. ( 4 ) Longitudinal strength of rolled pipe, reheated and finish rolled in beta phase region, was higher than that of the pipes reheated in alpha phase region, due to the accumulation of (0002) direction along rolling direction.
The round circular wires are mainly net-shaped into various profiled wires by rolling or drawing, to be further worked for electronic parts, springs, piston rings and rails. These processes require a large number of mill stands, roll passes or dies. Authors have developed a new type of compact continuous mill named the satellite mill. In this satellite mill rolling, longitudinal compressive stress significantly decreases the elongation and promotes transverse metal flow. This elongation-constrained effect of the satellite mill was confirmed in the previous study for rolling of flat and T-shaped profiled wires using open passes. In this study, the satellite mill with closed passes is applied to production of U-shaped and H-shaped profiled wires. The obtained rolling characteristics and hardness are compared with those by a conventional rolling method. It is shown that the satellite-mill rolling is able to form much higher ribs in products than a conventional rolling method and has advantage in the ability to fill the metal into the roll grooves. The elongation-constrained effect is more enhanced in using closed passes than open passes. This type of mill is considered to be suitable for production of profiled wires with complex cross sections.
The aim of this study is to clarify the effect of P on the microstructure of Al-free galvanized coatings. Fe-0.093wt%P binary alloy was galvanized using zinc bath without Al. It was found that P homogenizes the microstructure of galvanized coatings. Over a large part of the stereographic triangle extending from the (111) αcorner, where react diffusion is suppressed compared with that on other Fe planes, the intermetallic layer formed on Fe-P substrates is thicker than that on Fe substrates. On the Fe planes occupying the remainder of the triangle, the intermetallic layer on Fe-P is thinner than that on Fe. On Fe-P, FeZn13(ζ) crystals randomly orient even on the Fe planes near (111) a where ζ crystals are formed heteroepitaxially with respect to underlying Fe substrates. The reason for that the intermetallic layer on Fe-P planes near (111) αis thicker than that on Fe planes near (111)αmay, therefore, lie in the grain boundary structure in ζ crystals. High angle boundaries in ζ crystals on Fe-P may allow high diffusivity of Zn toward substrates with eventual formation of thicker intermetallic, whereas low angleζboundaries on Fe planes near (111) α suppress the Zn diffusivity, which consequently retards the growth of the intermetallic layer.
The development and phase transformations of Al2O3 scales formed on Al-deposited Fe-Cr-Al foil and Fe-20Cr-5Al foil have been studied during the oxidation at 1173K in air using TEM, SEM and XRD. The both kinds of foils had very similar chemical compositions, however the oxidation started on a surface of high Al content for the Al-deposited foil. The scale formed on it has a two-layer structure during the initial oxidation period : the outer layer consists of γ-Al2O3 and the inner layer of mainly fine-grain θ-Al2O3. The phase transformation from γ to θ takes place at the scale / substrate interface. As oxidation proceeds needle-like crystals start to grow at the interface of the two layers, pass through the outer layer, and extended out from the scale surface. They consist of twin crystals of γ-Al2O3, some of which transform to θ-Al2O3, with twin boundaries parallel to their growth directions. It is proposed that the twin boundaries provide fast diffusion paths for Al cations. During the growth of needle-like crystals, the inner layer consists of fine-grain θ-Al2O3. After about 180ks oxidation α-Al2O3 grains nucleate at the scale / substrate interface and after about 360ks the major part of the scale transform to α-Al2O3. Its grain size is 1 to 2, μ m and thus one or two grains occupy the scale thickness. Small voids are formed within α-Al2O3 grains. This is attributable to volume decrease by about 12% accompanying the θ to α transformation. Contrary to the Al-deposited foil, scales formed on the Fe-20Cr-5Al foil transform to α-Al2O3 in short periods.
The oxidation of an Fe-36%Ni alloy (invar type alloy) is investigated at temperatures between 1000K and 1300K in air under tensile stress conditions using metallographic, electron probe microanalysis, and X-ray diffraction techniques. The oxide scales consist of an external scale and a subscale which has an intragranular oxidation zone and an intergranular oxidation zone. The oxide phases in each scale are identified as FeO, Fe3O4, and Fe2O3 and FeO and Fe3O4, respectively. The oxide phases do not depend on the magnitude of tensile stress within 14.7MPa, but the growth rates of scales depend on remarkably. The growth rates of the intragranular oxidation zone increase (below 1100K) or decrease (above 1200K) with increasing tensile stress, but those of the intergranular oxidation zone increase (above 1200K) with increasing tensile stress. The formation of intergranular oxide is promoted not only in the direction of depth from a surface, but also in the width (thickness) of oxide with increasing tensile stress. The stress accelerated grain boundary oxidation (SAGBO) in this alloy is confirmed distinctly
Effects of reheating temperature, corresponding to austenite single phase or ferrite-austenite two-phase region, on chemical and quantitative changes in Martensite and Austenite (M-A) constituents in a low alloy steel were examined. Reheating to austenite single phase results in bainite microstructure containing M-A constituents. Enrichment of carbon in the M-A constituents is observed. Any substantial difference in Mn content between the M-A constituents and surroundings is not observed. T0 temperature of the steel which chemistry is equal to the M-A constituents is close to the bainite transformation finishing temperature. When the steel is reheated in the two-phase region, M-A constituents are observed in ferrite and reveal higher carbon and Mn contents than the ferrite. Carbon content of the M-A constituents decreases and Mn content increases with increasing holding time of reheating at the two-phase region. The MA constituents observed in the materials reheated to austenite single phase region show higher carbon content than those in the steel reheated to ferrite and austenite two phase region.
The method of surface observation for creep voids was discussed for SUS304H, 316H and 321H austenitic stainless steels, comparing with cross sectional observation. The creep tests were carried out up to about 60000h at 600-750°C. After machining, the surface of the specimen was polished and etched, then the microstructures of the specimen surface were metallographically observed by optical microscope as a function of depth from the surface and compared with those of vertical section (stress direction of specimen). The precipitation free zone of σ phase was observed beneath the specimen surface and its depth was about 60μm after about 20000h at 700°C. The observation of σ phase precipitates along grain boundaries is important to the evaluation of creep damage for austenitic stainless steels, because σ phase has roles to accelerate the nucleation and growth of creep voids. The polishing of specimen surface up to 70μm in depth lead the same microstructure as that at the vertical section of the center part of specimen. For SUS321H steel, the surface cracks were formed at the grain boundaries of specimen surface and propagated into the inner part of specimen. The length of the surface cracks observed after polishing the surface layer was about twice of that observed at vertical section.
Microstructural change during isothermal aging has been investigated in 13%Mn-0.9%C and 22%Mn-0:6%C steels by means of optical and electron microscopy and X-ray diffractometry. High manganese austenitic steels undergo three kinds of reactions during isothermal aging ;(1) grain boundary precipitation of carbide, (2)precipitation of platelet carbide within austenite(γ) grains and (3)formation of lamellar structure through eutectoid transformation (γ→ferrite(α)+carbide).In 13%Mn-0.9%C steel, all of the reactions occur and the carbide concerning the reactions is M3C in any case. On the other hand, in 22%Mn-0.6%C steel, only two of them occur ; grain boundary precipitation of M23C6 carbide (not M3C) and the eutectoid transformation (γ→α+M3C). Besides, both of the two reactions in 22%Mn-0.6%C steel were effectively suppressed due to the chemical composition ; high Mn and low C content. Eutectoid transformation proceeds by being supplied carbon from untransformedγ, so that this results in the shortage of carbon in untransformedγduring isothermal aging and theγphase undergoesγ→ε(hcp) martensitic transformation on the following cooling.
In order to improve the performance of sintered high-speed-steels by increasing carbide fractions and carbon contents and to clarify the limits of their addition, several properties of high-speed-steels having higher carbide fraction and carbon content than conventional ones have been investigated. Carbide fractions were controlled by changing the W, Mo and V contents of atomized powder. Specimens were prepared by vacuum sintering of cold-compacted water atomized powder consisting of fine solidification structure. The upper limit of carbide fraction was found to be about 43 area%, because the bending strength decreased with the formation of network carbide structure. The upper limit of carbon balance (Cbal), converted into carbon content, was about 0.15, because above 0.15, the tempered hardness decreased with the increase in retained austenite, and, the bending strength decreased with coarsening of carbides after sintering. The chemical compositions of 2.8C-13W-11Mo-8V-8Co and 3.2C-12W-8Mo-10V-9Co showed superior performance to conventional high-speed-steels.