Showing papers in "Metals technology in 1980"

Gradual changes in residual stress and microstructure during contact fatigue in ball bearings

Abstract: Deep-groove ball bearings have been endurance tested at high stress levels. The purpose of the work was to study the simultaneous generation of residual stresses and occurrence of structural changes owing to cyclic rolling contact fatigue. During the investigation the decomposition of both retained austenite and parent martensite were followed. The residual stresses and the austenite decomposition were measured by an X-ray diffraction technique, using signal averaging. Optical and transmission electron microscopy were used to observe the transformed regions resulting from the martensite decay. Depth profiles of residual stress and of successive structural changes were constructed. The observations are discussed in terms of a qualitative model for residual-stress generation under cyclic rolling contact.

Can a simple heat treatment help to save Detroit

Abstract: Laws passed and regulations approved by the Congress of the USA in recent years require new automobiles in the USA to conform to standards of NOx emission, impact resistance, and fuel consumption which will test to the limit the technological and manufacturing resourcefulness of the American automobile industry Radical changes will have to be made in the materials used Changes in engine design and a reduction in the size of the automobiles will be insufficient Steel is the cheapest acceptable material for many components, but steel will retain its position in the automobile market only if it can be made much stronger (thus reducing the section thickness and weight) without impairing its ductility, formability, weldability, and low cost New steels for automobiles have been developed from the laboratory to full-scale production with astonishing speed in the last three years The most promising of the new steels – ‘dual-phase steels’ – have more than twice the strength of traditional automobile s

Aging effects in copper-based shape-memory alloys

Abstract: In the literature concerned with the martensite transformation in binary and ternary brasses there have been many reports of both variations in the transformation temperatures and anomalously poor ...

Plastic deformation produced during indentation phase of rotary forging

Abstract: The concept of rotary forging in its two basic forms is described and a technique is presented for simulating the indentation phase of the process. Annealed aluminium alloy work pieces of differing height/diameter ratios were indented and examined internally. The approximate shapes of the deformation zones were established by hardness measurements on sections from as-worked samples and by metallographic observations of sections from work pieces which were recrystallized after indenting. Large recrystallized grains define regions which were cold worked by critical amounts during indentation. The three-dimensional shapes of the plastically deformed zones are discussed and the implications are considered in relation to the rotary phase of forging. Mechanisms are suggested for forging faults such as mushrooming of the surface worked by the indenting tool.

Determination of surface heat-transfer coefficients during quenching of steel plates

Abstract: The experimentally determined relationships between temperature and time in quenched steel plates have been used in conjunction with an explicit finite-difference technique to determine the effect of surface temperature on the magnitude of the surface heat-transfer coefficient in water, polymer, and oil quenchants In the case of the water quenchant the results obtained were very sensitive to the degree of oxidation of the specimen surface; this effect was associated with the degree of stability of the vapour blanket produced during the early stages of quenching The polymer quenchant did not possess a clear advantage over water except where the concentration of the latter was as high as 25% In comparison, the values of the surface heat-transfer coefficients obtainedfrom the oil quenchant were very low; this was associated with a relatively short nucleate boiling stage

Characterization of phases in a nickel-aluminium bronze

Abstract: The phases present in an as-cast commercial nickel-aluminium bronze of nominal composition Cu-10Al-5Ni-5Fe have been characterized by optical and electronoptical techniques. Phase distributions andprecipitate morphologies have been studied by optical microscopy, scanning electron microscopy, and transmission electron microscopy. Analytical electron microscopy, both of thin foils and of extraction replicas, has been used to determine the composition of the various intermetallic K-phases.

Fatigue-crack growth in WC–Co hardmetals

Abstract: (1980). Fatigue-crack growth in WC–Co hardmetals. Metals Technology: Vol. 7, No. 1, pp. 83-85.

Hardfacing of Nimonic 75 using 2 kW continuouswave CO2 laser

Abstract: The ability of a 2kW continuous-wave CO2 laser locally to melt a substrate allows controlled deposition of surface-hardening alloys. In the present study single tracks of Stellite 12 were applied to a substrate of Nimonic 75. This was achieved by using the defocused laser beam to melt a layer of Stellite 12 powder resting on the substrate. The main process parameters controlling the deposition were identified and an operating chart produced. Track widths in the range 1–4mm with thicknesses of 0·75–1·25mm were obtained using this technique. The maximum rate at which these tracks can be produced is afunction of laser power, laser beam diameter, and the powder thickness. At 2kW a 2mm wide track 1mm thick can be produced at a rate of 22 mms−1. The deposition of coatings over closely defined areas is demonstrated and the advantages, disadvantages, and possiblefuture developments of the process are examined.

Ferrite grain refinement by controlled rolling of lovv-carbon and microalloyed steel

Abstract: A C–Mn steel and two microalloyed steels, one containing niobium and the other vanadium, were subjected to controlled hot rolling followed by cooling in air or vermiculite. The experiments were designed to allow differentiation between cases in which transformation started after the end of rolling and those in which it started in the roll gap during deformation. When transformation began after the end of rolling, austenite grains of the C–Mn steel were refined by recrystallization, while in the microalloyed steels austenite grains were elongated due to the absence of recrystallization. In all three steels ferrite grain refinement originated wholly from changes in size or shape of austenite grains and constancy of the ratio of austenite to ferrite grain sizes. Significant change in the transformation mechanism need not be invoked in order to explain the observed degrees of ferrite grain refinement. On the other hand, when transformation began during rolling, more efficient grain refinement was obta...

Effect of loading path on stressstrain relationships of sheet steel and brass

Abstract: The stress–strain curves of sheet steel and brass determined by uniaxial and balanced biaxial tensile tests after various amounts of predeformation werefound to deviate from those corresponding to monotonic loading. Hill's macroscopic theory of anisotropy cannot explain these anomalies which are of microstructural origin. The results indicate that the dependence of the stress-strain relationships on the loadingpath should be considered as a material property.

Effect of austenitizing temperature on constitution, transformation, and tempering of 9Cr-1Mo steel

Abstract: The effect of solution-treatment (austenitizing) temperature has been investigated on the constitution, transformation, and tempering characteristics of a 9Cr-1 Mo steel. It has been shown that the austenite grain size and phase constitution are markedly influenced by the austenitizing temperature, as also are the transformation characteristics. It has been possible to explain the 15-fold variation in the rate of transformation in terms of the nucleating effect of undissolved carbides or ferrite, and the partitioning of alloying elements to or from the austenite as a function of constitution. Apart from influencing the overall level of hardness obtained on tempering, there was little effect of varying the austenitizing temperature between 900° and 1200°C.

Influences of surface roughness and residual stress on fatigue life of ground steel components

Abstract: An experimental study of the residual stresses and fatigue properties of ground En 31 steel specimens is described. The individual grinding parameters (wheel types and speed, feed, dressing, and lubricant) are grouped into three categories: abusive, conventional, and gentle grinding. In the absence of high temperature-gradients, the mechanical strain in the workpiece is dominant, giving small compressive residual stress and long fatigue life. It is more common, however, for high temperatures to be generated at the surface. Quenching of the bulk steel produces martensite, which is then tempered, and the accompanying volume change can leave high tensile stress in the surface, resulting in greatly reduced fatigue life. Surface roughness is found to be much less important than the residual stress.

Structural and temperature variations during rolling of aluminium slabs

Abstract: A finite-difference technique has been developed to predict the temperature profile during the rolling of aluminium slabs and experimental results are presented which show substantial agreement with the theory. It is shown that such variations affect the mechanisms determining the development of structure and that structural variations exist throughout the slabs on exit from the roll gap. Qualitatively, these variations agree with predicted variations in temperature-compensated strain rate. The effect of Mg as an alloying element is to reduce the possibility of formation of equiaxed subgrains resulting in an elongated substructure.

Stability of intermetallic aluminides in liquid aluminium and implications for grain refinement

Abstract: The behaviour of intermetallic aluminide particles in liquid aluminium is of importance in view of their postulated role in mechanisms of grain refinement by melt inoculation. The dissolution rates of Al3Ti, Al3Zr, and Al3Nb have been investigatedfor a range of conditions. It is concluded that thermodynamic equilibrium is quickly established in the case of titanium, but takes much longer for niobium, with zirconium apparently exhibiting behaviour intermediate between these two extremes. This result is correlated with observations on grain refinement and the probable mechanisms responsible for these effects are discussed.

Stress-relief heat treatment of submerged-arcvvelded microalloyed steels

Abstract: A wide range of microalloyed steels containing various combinations of Al, Ti, V, Nb, and submerged-arc welded using wires of either high or low Mo additions, were studied in both the as-welded and ...

Strain-rate sensitivity and effects of strain rate in sheet forming

Abstract: The strain-rate dependencies of flow strength and strain-hardening behaviour are particularly important in sheet-forming operations because they influence strain distribution and necking resistance. Measurements made in uniaxial and biaxial tensile tests on low-carbon steels have shown that strain-rate sensitivity is a function of both strain and strain rate, and that it varies with dissolved interstitial solute content. It is concluded that some simple constitutive equations which are commonly used to describe flow-strength–strain-rate relationships do not provide generally reliable bases for predictions of limit strains in sheet-forming operations. Variations in the plastic behaviour of the workpiece material which resultfrom changes in the speed of pressing can have important influences on performance in practical forming operations, but pressing speed–formability relationships are usually complicated by simultaneous changes in process variables such as lubricant behaviour and the extent of def...

Comparison of wear behaviour of single- and multilayer coated carbide cutting tools

Abstract: Single- and multilayer coated inserts were fully characterized by chemical analysis and metallography before monitoring their wear behaviour under high-speed machining conditions when turning annealed En 24 steel. The multilayer insert showed superior behaviour in resisting both flank and crater wear. Examination of worn inserts using Auger electron spectroscopy and scanning electron microscopy indicated that similar wear mechanisms operated for the different coated inserts. The reasons for the improved behaviour of multilayer coatings are discussed.

Replacement of vanadium by niobium in 86–5–2 high-speed tool steels

Abstract: The microstructure and mechanical properties of a series of experimental high-speed steels based on the S6–5–2 (M2) composition have been investigated. In these alloys the 2% vanadium component of the S6–5–2 composition has been partially or completely replaced by niobium additions of up to 3%. It has been shown that niobium-replacement steels have superior cutting properties, which are attributed to the formation of a high volume fraction of niobium-rich carbides. X-ray energy analysis indicates that NbC replaces VC as the MC phase, and niobium changes the chemical composition of the M6C and/or M23C6 carbides. The niobium-replacement grades undergo secondary hardening on tempering, and niobium raises the liquation temperature allowing higher hardening temperatures to be used. Since niobium-rich carbides replace carbides containing the more expensive tungsten, molybdenum, and vanadium alloying elements, it is suggested that niobium could be used to reduce the amounts of these elements needed, and ...

Extrusion limits of Al-5 Mg-O·8 Mn alloy (AA 5456)

Abstract: The factors which determine the success of the extrusion operation may be high-temperature-stress related, surface related, or structure related. These features are reviewed and it is shown that the extrusion pressure cannot be expressed as a simple function of the extrusion ratio but must include a term which expresses pressure dependency as a function of the temperature-compensated strain rate. It is also shown that surface quality and surface recrystallization may also be expressed as a function of the temperature-compensated strain rate. A limit diagram is presented showing the effect of ram speed upon the contracting loci and incorporating recrystallization and surface-quality bounds.

Weldability and hot cracking in thorium-doped iridium alloys.

Abstract: Modified iridium alloys containing ≥ 100ppm Th were found to be very susceptible to cracking during gas tungsten-arc and electron-beam welding. However, the electron-beam welding process showed greater promise of success in welding these alloys, in particular Ir–0·3W doped with 200ppm Th and 50ppm Al. The weld ability of this particular alloy was extremely sensitive to the welding parameters, such as beam-focus condition and welding speed, and the resulting fusion-zone structure. At low speeds successful electron-beam welds were made over a narrow range of beam-focus conditions. However, at high speeds successful welds can be made over an extended range of focus conditions. The fusion-zone grain structure is also a strong function of welding speed and focus condition. Weld-metal cracking was found to be caused by the combined effects of heat-affected-zone liquation cracking and solidification cracking. Scanning electron microscopic analysis of the fractured surface revealed patches of low-melting...

Precipitation in some Cu-Ni-Cr alloys

Abstract: An investigation has been made of the precipitation reaction in a series of Cu-Ni-Cr alloys which lie within the ternary miscibility gap. Symmetrical alloys, with a composition near the centre of the miscibility gap, decomposed by a spinodal mechanism to form a highly interconnected microstructure aligned along . In asymmetrical alloys near the edge of the miscibility gap, phase separation occurred by nucleation and growth and discrete particles were formed. In the symmetrical alloys the initial stages of aging were associated with a rapid increase in hardness while the wavelength of the composition modulations remained constant. An interconnected microstructure rapidly evolved, and as coarsening proceeded the ‘effective wavelength’ increased but the hardness remained constant. Temperature-cycling experiments were carried out in which the amplitude of the composition modulations in the interconnected structure was varied while the effective wavelength was kept constant. These experiments prov...

Effect of section geometry on extrudability of Al–Cu–Mn alloy

Abstract: Most aluminium alloys are produced in complex shapes and hence it is important to investigate the effect of geometry on extrudability. Results of extrusion experiments which show that shape geometry appears to alter the relationship between the temperature-compensated strain rate and the hyperbolic sine stress function are presented. It is suggested that this anomaly is the result of inconsistencies in calculation of strain rate and temperature and a correction factor is proposed to relate extrusion experiments to a simple torsion test. It is shown that this correction factor can be related to the logarithm of a modified extrusion ratio. It is concluded that extruded structure, and hence some properties, may be predicted for shaped as well as rod extrudates.

Relative plasticity of manganese sulphide inclusions during rolling of some industrial steels

Abstract: 16 mm thick plates were rolled from slabs of four different steels in the temperature range 1200°–790°C. The length of manganese sulphide inclusions was assessed on longitudinal sections and the index of relative plasticity calculated. Results show that incomplete recrystallization of austenite between rolling passes increases the relative plasticity of manganese sulphide inclusions much more than solution hardening. Rolling of steel in the temperature range of high relative plasticity can double the length of inclusions on the longitudinal section. Partial transformation of austenite to ferrite during rolling decreases the relative plasticity of manganese sulphide inclusions in a limited temperature range.

Bauschinger effect in structural steels and role in fabrication of line pipe: Part 1 analysis of Bauschinger effect in structural steels

Abstract: During the plastic deformation of a two-phase system containing hard particles it is important to determine the extent to which these particles support unrelaxed plastic strains. The amount of unrelaxed strain can be determined, in principle, from measurements of the behaviour of the material during reverse flow. The existence of unrelaxed plastic strains can give rise to internal stresses which not only aid flow in the reverse direction but also contribute to dimensional instabilities and to the nucleation of voids at second-phase particles. The present work illustrates that for well characterized structural materials such as carbon steels containing dispersions of cementite particles the above processes can be described in a quantitative manner based on models of heterogeneous deformation. In addition, the work indicates that for structural steels containing distributions of transformation products such as martensite and retained austenite similar conclusions can be drawn and many important face...

Influence of grain boundaries on fissure formation during impact testing of ferritic stainless steels

Abstract: In the hot-rolled conditions (Fig.l), the microstructure of the steels consisted of elongated coarse ferritic grains (~220fLm long x 40fLm thick), with elongated thin martensitic grains and grain-boundary carbides at the ferrite grain boundaries. Tempering at 750°C produced no change in the ferrite and resulted in the martensite tempering to a fine dispersion of carbides (Fig.2). Normalizing at 950°C caused the martensitic areas to transform to Y which on cooling retransformed to give martensite islands which have a more equiaxed appearance (Fig.3). The volume fraction of the second phase was greater than for the hot-rolled condition but the difference was small (~3 %), suggesting that the major effect of this heat treatment was to change the shape of the martensitic areas. The ferrite/ martensite grain boundaries can now be seen to be broken up (see Figs. 1-3), the boundary having changed from planar to undulating. Tensile results (Table 2) showed th~t whereas the 0·2% proof stress (the steels are·'non-straln The ferritic stainless steel examined had the composition given in Table 1. The steel had been hot rolled to 25mm plate and was examined in three conditions: (i) hot rolled (ii) hot rolled and tempered at 750°C. for 1h and air cooled (iii) hot rolled and normalized for 1h at 950°C. Longitudinal Charpy V-notch impact transition curves were obtained for the three conditions (testpieces notched in the through-thickness direction). Longitudinal tensile testpieces 4·4mm dia. with a 16mm gauge length were also obtained and tested on an Instron machine at a crosshead speed of 0·5mmmin -1. Microhardness measurements were taken within the ferrite grains using a 50g load, and the grain elongation of the ferritic grains in the rolling direction was measured by the method of mean linear intercept. The fracture appearance was examined and photographs taken of the fissures. Impact testpieces of controlled-rolled steels notched in the through-thickness direction often reveal fissures on the fracture surfaces after breaking, the fissures forming parallel to the plate surfaces. There appear, therefore, to be 'planes of weakness' in these steels parallel to the rolling plane which fracture ahead of the notch to form fissures, which by relieving the triaxial stress system associated with a notch reduce the possibility of brittle fracture. 1 A considerable amount of work2-6 has been carried out in recent years into the origin of these splits or' fissures and it is noticeable that the controlled-rolled ferrite-pearlite steels which give rise to fissures generally have elongated ferrite grains and a preferred orientation as a result of deformation in the ferrite temperature range. Both these factors, indeed, have been quoted as playing a part in controlling fissure formation since normalizing generally prevents their formation.2,6 However, work by Mintz et a1.7 has shown that grain shape rather than texture is the important factor in controlling fissure formation and this has been substantiated further by the recent metallographic observations of Morrison et al.2 In the latter work, the fissures were observed to nucleate at seCond-phase particles, generally non-metallic inclusions, in both controlled-rolled and normalized steels. However, whereas in normalized steels the holes associated with second-phase particles became blunted, those in the controlled-rolled steel were able to initiate cracks which propagated in a brittle manner giving the characteristic appearance of fissures. The growth of a crack large enough to propagate in a brittle manner appeared to take place by intergranular decohesion. Although inclusions are favoured initiation sites, fissure formation has been shown not to be critically dependent on the cleanliness of the steel, sufficient inclusions always being present to initiate a crack even in the cleanest of steels.5,8 The critical event appears to be the ability to decohese a grain boundary for a sufficiently long enough length to promote brittle fracture. It would therefore be expected that the longer and more closely aligned are the ferrite grain boundaries, the easier it would be to decohese along them. It is not surprising, therefore, that the tendency to fissure formation increases with increase in grain elongation. 2,3, 7 For example, normalized steels which have equiaxed grains do not give rise to fissures and it is only after the grains have been elongated to a critical amount that fissures are first observed. 6, 7 Increasing the dislocation density by warm w,orking has also been shown to favour their formation 7 and, because of this, it has be((n suggested that raising the strength of the grain matrix concentrates the strain on to the grain boundaries thereby encouraging decohesion. However, the reason for the apparent weakness of the grain-boundary regions after warm working is by no means clear and further studies are required. During a recent study into the impact behaviour of Fe-13Cr ferritic steels, some interesting observations were made with regard to the manner in which grain boundaries

Glass-lubricated hot extrusion of stainless steel

Abstract: Experimental extrusion has been carried out on type 321 and type 316 stainless steels to study the influence of temperature, ram speed, extrusion ratio, die design, and several different compositions of glass lubricants on extrusion pressure–distance curves and on the surface quality of the extruded products. The choice of billet/container lubricant has a marked effect on the shape of the pressure–distance curves by influencing both the effective coefficient of friction and the heat-transfer coefficient. Temperature, extrusion ratio, and die lubricant mainly influence the level of the pressure–distance curve. The surface quality of the extruded product, assessed in terms of scoring and roughness, varies widely with extrusion conditions but does not appear to correlate directly with the efficiency of lubrication, as judged from the pressure curves. The best surface quality is obtained with/ast extrusion speed and temperatures low in the normal reheating range, as defined by the extrusion limit diagram.

Potential uses of rapidly solidified alloys in gas turbine engines

Abstract: The benefit of rapid solidification was studied relative to the development of new superalloy compositions for appcation in the hot sections of the gas turbine. Centrifugal atomization ofliquid metal into powder droplets and subsequent freezing by forced convective cooling was used to produce experimental alloys in a rapidly solidified form. Metalworking techniques common to powder-metallurgy processing were used, in turn, to produce bulk stock for test and evaluation. Results with the precipitation-hardening class of superalloys showed that higher concentrations of alloying additions than possible with conventional solidification practices could be achieved by rapid solidification without onset of macrosegregation or deleterious solidification compoundformation. It was found also that certain groups of alloys within this class responded effectively to abnormal grain growth which was controllable to produce aligned crystallographic structures. These combined characteristics were used to develop an...

Magnetic properties of amorphous materials

Abstract: The magnetic properties of the amorphous alloys containing 75–85 at.-% transition metals and 15–25 at.-%.metalloids (P, C, B, Si) are reviewed. Attention is centred on the strongly ferromagnetic alloys, and on magnetic properties that are influenced by changes in structure brought about by annealing treatments that do not cause crystallization. A conceptual distinction is made between compositional short-range ordering and topological short-range ordering in the amorphous state: compositional ordering involves primarily changes in the chemical identity of nearest-neighbour atoms, while topological ordering involves a long-range cooperative motion of atoms over small distances, without significant changes in nearest-neighbour identity. Probable directions for the engineering applications of these materials are also discussed, especially their use in power transformers because of their very low magnetic losses andpotentially low production cost.

Melting, degassing, and casting characteristics of Al-11·8Si alloys containing dispersion of copper-coated graphite particles

Abstract: The effects of additions of copper-coated graphite particles on the spiral fluidity, casting fluidity, and hot-tearing characteristics of Al-11·8Si alloys were studied. The remelting and degassing characteristics of aluminium-graphite-particle composites made from copper-coated graphite particles are also reported. Spiral fluidity and casting fluidity of Al-11·8Si alloys decreases with an increase in the amount of suspended graphite particles of a given size and shape, and a decrease in the particle size or sphericity for a given vol.-%. Regression equations relating spiral and casting fluidity to surface area of suspended graphite particles have been derived. The decrease in spiral and casting fluidity of Al-11·8Si alloys owing to additions of copper-coated graphite particles is attributed to an increase in the effective viscosity of the melt. Additions of up to 4 wt-% of copper-coated graphite particles do not increase significantly the hot-tearing tendency of Al-11·8Si alloys. Degassing of Al-1...

Creep deformation and rupture of butt-welded tubes of cold-worked AISI 316 steel

Abstract: Tubes of AISI316 steel 20% cold-worked and TIG welded without filler metal were creep tested under internal pressure. The creep deformation was concentrated mainly in the weld metal and the heat-affected zone (HAZ). The failure was a result of the formation of axial cracks in the HAZ, a few millimetres from the fusion boundary. The rupture stresses (hoop stresses) of the tubes were about 5% lower than those of uniaxially tested simulated HAZs and about 25% lower than those of the parent metal. The creep ductility was only about 1·5%, which was much less than the unaxial elongation of the cold-worked parent metal. To explain the creep-deformation and rupture behaviour a model for thin-walled tubes was used with uniaxial creep data on simulated HAZs and parent metal. The model gave a good description of the observed creep rates, rupture times, position and orientation of cracks, and a rupture ductility of the right order of magnitude. For the rupture properties a failure criterion based on the maxim...