Showing papers on "Hardening (metallurgy) published in 1975"

Permanent deformation characteristics of subgrade soils due to repeated loading

Abstract: Various procedures are examined for controlling or estimating the contribution of the subgrade to the total permanent deformation that occurs in the pavement structure as a result of repeated traffic loads. The use of layered elastic analysis to estimate the vertical compressive strain at the subgrade surface is suggested as one procedure to control such deformation. A summary of available strain data is included. If these criteria are used for design purposes, the same range in stiffness for the asphalt-bound layer and the same values of Poisson's ration must be used as were used to develop the criteria. Layered elastic analysis is also suggested for estimating the amount of permanent deformation caused by the subgrade. This analysis is based on relationships among permanent strain, applied stress, and number of stress applications based on repeated-load triaxial compression tests; and these relationships are discussed. Data also indicate the importance of stress history effects. Time hardening and strain hardening permit estimates of cumulative loading effects from the results of tests at single stress levels. Although neither method predicts precisely the accumulation of permanent strain under different stress sequences, both bound the measured data and therefore have the potential to assist in the estimation deformation or rutting from cumulative traffic loading.

Prismatic slip in α-titanium single crystals

Abstract: Single crystals of Ti, oriented favorably for prismatic slip and containing two levels of interstitial impurities, have been deformed in tension at temperatures between 78 to 1120 K. The stress-strain curves exhibit three stages of hardening similar to those of Zr and of fcc crystals. The work hardening rate in Stage II, θII/G is lower in Ti than in Zr. From the strain rate dependence of the stress at the onset of Stage III, the stacking fault energy on the prism planes of Ti has been estimated as 0.145 Joules/m2. The relative values of stacking fault energy for Ti and Zr are consistent with a dissociation model which is based on the hcp ai bcc transformation. The thermally activated prismatic slip below 250 K is controlled by the interaction of dislocations with interstitial solute atoms. Above 250 K the dislocation mechanism for plastic flow is not clearly understood.

Precipitation Hardening of Aluminum Alloys

Abstract: The author’s charge was to discuss recent trends in research and development on precipitation hardened aluminum alloys and to indicate where research is needed. This will be done for three areas: fatigue, properties of grain boundaries and interfaces, and stability of precipitates at elevated temperatures. Present strong precipitation hardened aluminum alloys do not have high endurance limits. One problem is that the small GP zones are cut by the dislocations giving rise to highly localized deformation which aids fatigue crack initiation. A duplex structure with relatively large uniformly spaced precipitates to give more homogeneous deformation plus small precipitates to give high yield strength is a promising approach. The structures of precipitation hardened aluminum base alloys are essentially controlled by the stabilities of the various precipitates and the interfacial energies. Precipitates with high interfacial energies tend to precipitate preferentially at grain boundaries giving embrittlement. Low interfacial energy means easy nucleation, a uniform precipitate distribution, and resistance to coarsening at elevated temperatures. For elevated temperature use, the precipitate must be stable at elevated temperatures. Precipitation hardened aluminum alloys do not have good elevated temperature properties because the hardening precipitates normally used, GP zones, are not stable at elevated temperatures. Thus a low interfacial energy, ductile precipitate, which is stable at elevated temperatures, is needed for aluminum. Possibilities for achieving such precipitates will be discussed.

The Secondary Hardening of Tungsten Steels

Abstract: The tempering characteristics of a steel with 2 at.−%W 1.1 at.−%C in the range 500–700°C have been studied and structural changes related to the secondary-hardening phenomenon. The sequence of carbides found both at grain boundaries and in the matrix has been established,and detailed structural observations have been made on the nucleation of W2C and M6C. The ageing behaviour is contrasted with that of a comparable molybdenum steel in which the carbide reactions occur more rapidly. Trace additions of Nb Ti and Ta improve the basic strengthening reaction by providing a fine secondary carbide dispersion which also inhibits the coarsening of the dislocation network. The main carbide dispersion is also refined.

Composite hardfacing of air hardening steel and particles of tungsten carbide

Abstract: A metallurgical composition especially suitable for use as a hardfacing to increase the wear resistance of manufactured articles, such as for example tool joints used in earth drilling operations. This composition has cemented tungsten carbide particles dispersed in a matrix of air hardening alloy steel. Included in the alloy steel are carbon, chromium, molybdenum and vanadium. For weldability, manganese and silicon are added. Also disclosed are suitable ranges of proportions of constituents.

Effect of Various Accelerating Chemical Admixtures on Setting and Strength Development of Concrete

Abstract: A study of the rate of hardening of concretes which contain inorganic accelerators demonstrates the superior performance of calcium chloride. However, there are significant changes in the compressive strength of concretes at various ages when accelerators are employed. Calorimetric studies of cement mortars show the advantages as an accelerator that calcium chloride maintains over other inorganic salts. Also, calorimetric tests demonstrate what appears to be different mechanisms of acceleration between different kinds of accelerators. Differential thermal analysis (DTA) techniques were applied to a study of the effect of calcium chloride and calcium formate on the early stages of hydration of a cement. DTA patterns show definite differences between the function of the accelerators.

Design of strong tough Fe/Mo/C martensitic steels and the effects of cobalt

Abstract: The microstructures and mechanical properties of a series of vacuum melted Fe/(2 to 4) Mo/(0.2 to 0.4) C steels with and without cobalt have been investigated in the as-quenched fully martensitic condition and after quenching and tempering for 1 h at 673 K (400°C) and 873 K (600°C); austenitizing was done at 1473 K (1200°C) in argon. Very good strength and toughness properties were obtained with the Fe/2 Mo/0.4 C alloy in the as-quenched martensitic condition and this is attributed mainly to the absence of internal twinning. The slightly inferior toughness properties compared to Fe/Cr/C steels is attributed to the absence of interlath retained austenite. The two 0.4 pct carbon steels having low Mo contents had approximately one-half the amount of transformation twinning associated with the two 0.4 pct carbon steels having high Mo contents. The plane strain fracture toughness of the steels with less twinning was markedly superior to the toughness of those steels with similar alloy chemistry which had more heavily twinned microstructures. Experiments showed that additions of Co to a given Fe/Mo/C steel raisedM S but did not decrease twinning nor improve toughness. Molybdenum carbide particles were found in all specimens tempered at 673 K (400°C). The Fe/Mo/C system exhibits secondary hardening after tempering at 873 K (600°C). The precipitate is probably Mo2C. This secondary hardening is associated with a reduction in toughness. Additions of Co to Fe/Mo/C steels inhibited or eliminated the secondary hardening effect normally observed. Toughness, however, did not improve and in fact decreased with Co additions.

Correlation of the hot-hardness with the tensile strength of 304 stainless steel to temperatures of 1200°C

Abstract: It is shown that the ultimate tensile strength, σ, of 304 stainless steel can be correlated with hot-hardness measurements at temperatures up to 1200°C using the expression σ = (H/3.0)(n/0.2n) n whereH is the diamond pyramid hardness number andn is the strain hardening coefficient. The strain hardening coefficient was obtained from a Meyer’s hardness coefficient at the room temperature test condition and for test temperatures up to about 0.5T m , from the empirical relationshipn =k/λ. Herek is a constant equal to approximately 0.2 microns and λ is the subgrain dimension of the deformed specimen as obtained by transmission electron microscopy.

Some effects of retained austenife on the fatigue resistance of carburized steel

Abstract: Cyclic deformation properties have been measured for high carbon steels that simulate the surface layers on carburized AISI 4027 steel. The influence of retained austenite is manifested in cyclic hardening and the development of mean compressive stresses. These responses, which are found to vary in direct proportion to the initial retained austenite content, are attributable to deformation-induced transformation. The importance of such cyclic changes is demonstrated by strain-life relations for carburized 4027; specimens with large amounts of retained austenite in the surface layers possess superior fatigue resistance to otherwise identical specimens that are more completely transformed. It is also shown that the benefits of retained austenite diminish as the intrinsic ductility of the fully transformed material increases.

Residual Thermal Stresses in a Solid Sphere Cast From a Thermosetting Material

Abstract: Expressions are developed for the residual thermal stresses in a solid sphere cast from a chemically hardening thermosetting material in a rigid spherical mold. The description of the heat generation rate and temperature variation is derived from a first-order chemical reaction. Solidification is described by the continuous transformation of the material from an inviscid liquidlike state into an elastic solid, with intermediate properties determined by the degree of chemical reaction. Residual stress components are obtained as functions of the parameters of the hardening process and the properties of the hardening material. Variation of the residual stresses with a nondimensionalized reaction rate parameter and the relative compressibility of the hardened material is discussed in detail.

Effect of „Forest” Dislocations in the {1122} 〈1123〉 system on hardening in Mg single crystals under basal slip

Abstract: Experimental results are given of the dependence of work hardening parameters (critical shear stress, τc, work hardening coefficient, θA, and stage length ϵA at easy glide) in Mg crystals under basal slip on the density of pyramidal dislocations ϱf of various kinds. A relation between the kind of basal–pyramidal dislocation interaction is found and its effect on the above-mentioned hardening parameters is shown. The influence of interaction type depends on the quantity of energy gain in this interaction. ]Russian Text Ignored].

Ternary solution-hardening of copper single crystals

Abstract: The hardening of copper by two solute additions, germanium and silicon, has been measured in the plateau range. The results fit the predictions of a theory of Labusoh, and perhaps a180 one of Fleischer. They do not agree as well with a much-used computer interpolation formula.

Method for heat treating by induced current

Abstract: Steel workpieces, such as thread-forming screws and bolts, tapping tools, and the like, are hardened in localized areas to controlled depths of hardening by utilizing loose electromagnetic coupling between the workpiece and the induction coil. The loose coupling reduces the criticality of the positional relationship between the workpiece and coil and also allows unidirectional axial through-feed of headed workpieces. A high degree of symmetry of hardening around each piece and uniformity of hardening from piece to piece at high production speeds is accomplished.

On solid solution hardening in the zirconium-oxygen system

Abstract: Zirconium-oxygen alloys containing between 0.02 and 1.05 at.% oxygen were prepared by engassing β-Zr at 1500°C followed by an anneal at 800°C. Conventional stress-strain measurements as well as strain-rate-change tests were made. The yield point was determined in the range from 77 to 500 K for wire samples with an α-Zr bamboo structure, and the hardening coefficient, Ar/AC, was found to vary from 0.52 m at 77 K to 0.36 μ at 300 K. Observations with the electron microscope under weak-beam conditions demonstrated the presence of clusters inside the Zr matrix. For the temperature range 0–500 K, two rate-controlling mechanisms are indicated. Below approximately 300 K, the flow stress is composed of a temperature dependent component, caused by the interaction between dislocations and single, interstitial oxygen atoms, and a temperature-independent contribution due to an interaction with stable oxygen clusters. Above about 300 K, the onset of plastic deformation is determined by the overcoming of clusters.

The role of electron concentration in softening and hardening of ternary molybdenum alloys

Abstract: Effects of various combinations of hafnium, tantalum, rhenium, osmium, iridium, and platinum in ternary molybdenum alloys on alloy softening and hardening were determined. Hardness tests were conducted at four test temperatures over the temperature range 77 to 411 K. Results showed that hardness data for ternary molybdenum alloys could be correlated with anticipated results from binary data based upon expressions involving the number of s and d electrons contributed by the solute elements. The correlation indicated that electron concentration plays a dominant role in controlling the hardness of ternary molybdenum alloys.

Measurement of the mechanical state of a low alloy steel at elevated temperature

Abstract: Load relaxation tests on a Cr-Mo-V steel are used to generate stress-strain rate curves at high temperature. It is shown that the mechanical state as described by these curves is sensitive to the deformation history, such that the alloy undergoes a hardening and subsequent softening as strain is accumulated. However, these changes are quite small in successive tests and it is shown that results at different temperatures can be made to coincide by a suitable translation of the strain rate scale at nearly constant mechanical state. The result is a stress-strain rate curve over about twelve orders of magnitude in strain rate so that initial creep rates at stresses far beyond the range covered at each temperature can be estimated.