Normal Hardening Research Articles

THE CHANGE IN DEFORMATION CHARACTERISTICS OF CONCRETE MONOLITHIC HIGH-RISE BUILDINGS

In the article results of studies of deformation features of concrete on actuate cement for monolithic high-altitude buildings are presented. It is shown that in construction of the high-altitude monolithic buildings in a summer period of a year one should take into account the character of changing the concrete elasticity and plasticity in time, which differs from the same indices for the concrete of normal hardening.

Experimental evaluation of wrinkling limit diagrams for aluminium alloy 5052 sheets annealed at different temperatures

The sheet-metal-forming operations are principal processes in the automotive industry. Aluminium alloy 5052 sheet is a widely used material in the automotive industry. With the aim of finding the safe working strains for this metal under various forming processes, a set of wrinkling limit diagrams in terms of strain and strain increment ratios and a forming limit diagram with a wrinkling limit curve superimposed have been constructed for the same sheet metal with 2.0 mm thickness annealed at four different temperatures. It has been found that the onset of wrinkling takes place when the ratio (dε r/dε θ) of strain increments or the ratio (ε r/ε θ) of strain reaches a critical value during the drawing process. Further it was observed that, the higher the annealing temperature, the greater was the safe strain region, because of higher normal anisotropy and strain hardening index values.

Effect of Post-Weld Straining on Temper-Rolled Austenitic Stainless Steel Welds

Temper-rolling increases the mechanical strength in metastable austenitic stainless steels of 1.4310 (AISI 301) type. However, these grades are subject to local softening in the weld region after welding. This loss has been characterised for various temper-rolled conditions after GMAW, GTAW and Nd:YAG laser welding. Different levels of post-weld straining were applied across the welds in an attempt to restore the strength by a combination of normal work hardening and hardening due to martensite formation. The martensite transformation in this type of steel can be used for improved formability, so called transformation induced plasticity (TRIP). The effects of post-weld straining of the weldment were evaluated for each welding method and material by means of hardness profiles, tensile tests and optical strain measurements. The extent of strength loss and compensation found, with and without weld bead reinforcement has been assessed. The results are discussed in terms of differences between welding methods, the behaviour of individual regions in the weldments and practical applications. Laser welds gave the highest strength in the as-welded condition while GTA welded joints were the most ductile and showed the greatest potential for strength restoration by post-weld straining. For GMAW the filler metal determined the strength level of the joint. Fatigue test results of as-welded GMA specimens are reported.

Cyclic deformation behaviour of a nickel base alloy at elevated temperature

Low cycle fatigue tests for a hot extruded Nickel base alloy tube material have been performed at room temperature and at 204°C. The alloy shows a normal hardening and softening cyclic stress-strain response at room temperature. At 204°C, however, the cyclic stress-strain response shows a strain hardening first, followed by a relatively stable stress and finally a secondary cyclic strain hardening. This stable stress disappears with increasing strain amplitude. The mechanisms of the secondary cyclic strain hardening have also been investigated by transmission electron microscopy (TEM). Besides dislocation multiplication, interactions between stacking faults and moving dislocations and between interstitial atoms and moving dislocations could also contributed to this secondary cyclic strain hardening. The formation of micro-twins during cyclic loading at 204°C and its influence on the cyclic stress-strain response were also discussed.

Nucleation of kink pairs on partial dislocations: A new model for solution hardening and softening

Nucleation and motion of kink pairs on partial dislocations are examined by elasticity theory for materials with a high Peierls stress. Two approaches are used: one considers the change in average stacking-fault energy (SFE) due to alloying elements and the other considers the change in local SFE due to a nearby solute atom. Both approaches highlight the role of SFE on kink nucleation, propagation and annihilation and both furnish strain rate as a function of stress, temperature and SFE. Model predictions are compared with yield stress data for two systems: firstly, an intermetallic, MoSi2, which softens for alloying elements (V, Nb, Cr and Al) that decrease the SFE and hardens for Re additions that increase the SFE; secondly, a ceramic oxide, MgO-Al2O3 spinel, which softens with increasing addition of excess alumina and at the same time exhibits a decrease in SFE. The average SFE approach agrees qualitatively with the data while quantitative agreement is obtained with the local SFE approach. The possibility is considered that the model applies to other materials, such as TiAl, HfV2 and Fe3Al, which show softening with certain alloying additions. One requirement is that the dislocations are dissociated more than a few atomic distances; otherwise kink nucleation occurs on the perfect dislocation (or simultaneously on both partials). Hence the model does not apply to materials such as bcc metals which only have a core dissociation. Normal hardening effects of solutes from size and modulus misfits are additive with any softening effects from a decrease in SFE and so may mask the latter, as occurs for W additions to MoSi2.

Numerical analysis of effect of material and processing parameters on thickness distribution during superplastic die bulging of cavity sensitive materials

The superplastic bulging of circular sheets clamped against axisymmetrical cylindrical dies has been analysed numerically by means of a rigid–viscoplastic finite element method, in which four node quadrilateral isoparametric elements are used with a Newton–Raphson non­linear solution scheme. Both effects of normal anisotropy and strain hardening in the material are considered and a modified Coulomb friction law is adopted. At the same time, the yield criterion suited for the superplastic forming process and the cavity damage evolution model deduced from continuum damage mechanics are applied to a finite element formulation. The influences of material parameters (the strain rate sensitivity exponent m, the strain hardening exponent n, the coefficient of normal anisotropy R) and processing parameters (pressure cycle, lubrication condition, die geometry) on the inhomogeneity of the thickness distribution are studied and discussed. A selection of the simulated results is compared with the experimental results, with good agreement.

Hydration of C 3A and C 2 (A,F) - separated from sulphate-resisting and white portland cement - under conditions of normal hardening and heat treatment

With the preparations of C 3A and C 2(A,F) obtained after the extraction of silicates with salicylic acid from two technical cements the hydration and its products were examined. All methods used - X-ray diffraction to observe the decrease of C 3A and C 2 (A,F) during the hydration, thermoanalytical determination of forming sulphate hydrates and determination of combined water based on ignition loss - show the more rapid hydration of C 2 (A,F) than those of C 3A.

Influence of isothermal hardening on the sliding wear behaviour of 52100 bearing steel

In this paper, the characteristics of the dry sliding wear of 52100 steel after normal hardening and after isothermal hardening treatments are studied by comparative testing. The results indicate that the changing of the sliding conditions causes a transition of the wear mechanism. Compared to the normal hardening treatment, isothermal hardening leads to the appearance of a wear rate transition when load and speed are increased. Also, examination of the specimen shows that the microstructures in the wear surface layers change with test conditions. This is related to the occurrence of the α-γ phase transformation during the wear process.

Laser hardening of TiN-coated steel

The surface hardness of hardened carburizing steel is about the same as that required for the substrate of hard physically vapour-deposited coatings in practical applications. Accordingly, by changing the normal hardening- coating sequence to the reverse sequence coating-hardening, it should be possible to obtain usable hard coatings also on carburizing steels.This idea was studied in the present work. The hardening treatment was performed with radiation from a 2.5 kW CO2 laser using different beam scanning velocities and laser power densities. The tracks of the beam on the TiN-coated carburized steel samples were studied with regard to substrate hardness, hardening depth and microstructure. The coating was studied using scratch tests to determine the critical load and possible adhesion defects.It was found that the hardness of the substrate was excellent and the maximum depth of hardening was 0.4 – 0.5 mm. The coating showed good adhesion provided that overheating was avoided, excessive laser power densities or insufficient beam velocities resulting in circular detachments of the coating and finally in incipient melting. The first signs of these detrimental phenomena appeared in the neighbourhood of sample edges where dissipation of absorbed heat was, for geometrical reasons, more restricted than in the middle parts of the sample. On the basis of the thermal expansion coefficients for steel and the coating some estimates were made concerning the stress relations between the coating and the substrate during a hardening cycle. It seems that compressive stresses are the probable reason for the detachments.

The partitioning of alloying elements in vacuum arc remelted, Pd-modified PH 13-8 Mo alloys

The partitioning of alloying elements in as-solidified PH 13-8 Mo stainless steel containing up to 1.02 wt pct Pd has been investigated. The as-solidified structure is composed of two major phases, martensite and ferrite. Electron probe microanalysis reveals that Mo, Cr, and Al partition to the ferrite phase while Fe, Ni, Mn, and Pd partition to the martensite (prior austenite) during solidification and cooling from the solidus. In addition to bulk segregation between phases, precipitation of the intermetallic, PdAI, in the retained ferrite is observed. Precipitation of the normal hardening phase, β-NiAl, is also observed in the retained ferrite. Partition ratios of the various alloying elements are determined and are compared with those observed previously in duplex Fe-Cr-Ni stainless steel solidification structures. The martensite start temperature (Ms) was observed to decrease with increasing Pd concentration.

Structural transformations in heat treatment of chrome-molybdenumvanadium tool steels

1. During an isothermal hold of the supercooled austenite of types 65Kh6M1.5F3B and 65Kh6M3F3B chrome—molybdenum—vanadium steels in the area of subcritical temperatures (560–680°C) concentration microinhomogeneities or zones occur in it, which causes an increase in hardness and a reduction in specific electrical resistance of the martensite formed in further cooling. The substructure of the martensite does not depend upon the form of hardening. 2. The general character of the change in properties in tempering of hardened chrome—molybdenum—vanadium steels does not depend upon the preceding hardening cycle. However, after isothermal hardening the decrease in hardness in tempering at 300–400°C is less intense than after normal hardening. An increase in the isothermal hold time strenthens this effect. 3. The tempering temperature corresponding to the effect of secondary hardening does not depend upon the preceding hardening cycle while the increase in hardness is greatest after isothermal hardening. 4. The increased hardness of the steel after isothermal hardening and tempering at 530–540°C in comparison with the hardness after normal hardening and a similar temper is the martensite matrix. 5. Between the structural condition of chrome—molybdenum—vanadium steels after hardening and tempering, the hardness level, and tool life there is a correlation relationship. The life of certain forms of tools of 65Kh6M3F3B steel after isothermal hardening and tempering is under certain conditions close to the life of similar tools of R6M5 steel.

ＢＭＣ射出成形品のウェルド形成機構

In injection molding, the weld is formed when the flow of molding compound is injected through multi-gate or is separated by an insert followed by confluent in a cavity. Most studies on weld are concerned with strength, and little work deals with the formation and the hardening mechanism of weld. Then, the mechanism of weld formation was investigated for injection molding of Bulk Molding Compound (BMC). Forming a weld by an insert in a cavity, the behavior of a flow front and the temperature profile in the contact surface of weld were observed. The main results are as follows: The BMC being the first to flow into a cavity forms the weld after being in contact with an insert for a little while, which makes the temperature of flow front high. According, adhesion at weld becomes poor and the strength to be low. During the cross-linking reaction of resin, the reaction between radical and oxygen in air disturbs the normal hardening reaction of resin at the contact surface of weld.

High-temperature flow and aging behaviour of oxygen-enriched Zircaloy-2 and Zr-2-5 Nb

AbstractAn oxygen-enriched Zircaloy-2 alloy (4180 ppm 0) and an industrial grade of Zr-2.5Nb were hot compressed in the temperature range 750–1000°C at constant true-strain rates in the range 10−4 to 10−1 S−1. Significant yield drops were detected in the Zircaloy-2 followed by normal work hardening. The magnitude of the yield drop increased with temperature and therefore with β-phase fraction, and a strong but slow strain-aging response was observed at 1000°C. By contrast, the Zr-2.5Nb alloy displayed flow softening in the (α+β)-phase field, changing to normal flow in the single-phase β region. The amount of flow softening decreased with an increase in the β-phase fraction and is ascribed to the coarsening of the fine Widmanstatten or martensitic structure produced by the prior heat treatment, leading to an equiaxed structure at large strains. The comparatively weak strain-aging effect and the relatively fast aging kinetics in the Zr-2.5Nb alloy suggest the involvement of Nb-rich clusters in this material...

The influence of thermome chanical working on the quantity of residual austenite

1. The residual austenite content in the investigated complex chromium alloy steels is less after thermomechanical working with a large reduction in rolling at metastable condition temperatures than after normal hardening. 2. The stability of the residual austenite against subsequent tempers or cold treatments is less after thermomechanical treatment than after normal hardening.

The influence of the deformation of austenite on the properties of nickel steels

1. The tendency of the martensite of the investigated steels to decomposition changes substantially with thermomechanical working and also after rehardening in comparison with normal hardening. 2. The influence of deformation on the composition of the martensite is determined by the substructure created during thermomechanical working and by the preservation of it during subsequent repeated heating.

Phospholipid, protein, and nucleic acid increases in protoplasm and membrane structures associated with development of extreme freezing resistance in black locust tree cells

Summary o 1. Increases in polar lipids (principally phospholipids) and lipoproteins without changes in total lipids are shown to occur in the living bark cells of the black locust tree during development of extreme freezing resistance or hardiness in autumn, and it is suggested that a process of membrane replication is occurring as part of the mechanism of resistance. 2. Electron and light microscope studies with fixed cells confirm earlier chemical and cytological studies in indicating that this membrane replication is, under normal hardening conditions in autumn, a part of a process of whole protoplasmic augmentation occurring at this time. 3. Events occurring under two sets of circumstances a) and b) would suggest that a condition of hardiness associated with phospholipid increases and presumably membrane replication can be disengaged from the condition related to whole protoplasmic augmentation: a) In autumn under conditions of starvation established by girdling or isolation of bark its is shown that cytoplasmic augmentation (as indicated cytologically or in amounts of soluble protein and nucleic acid in the cells) can be arrested while phospholipid synthesis and a limited degree of hardening proceed. b) In spring an early drop in hardiness is associated with dissolution of membrane containing organelles well before a decrease in soluble protein component of the cytoplasm occurs. 4. Membrane replication appears to be a vital factor in the hardiness of tree cells but in view of the fact a) that extreme freezing resistance is never achieved without supplementation of the phospholipid changes with whole cytoplasmic augmentation (increase in soluble protein, etc.), b) that graded levels of freezing resistance can be produced according to different degrees of starvation and augmentation of cytoplasm, and c) that some hardening occurs during starch to sugar conversion, it is suggested that normal hardening is a composite of three principal processes which include membrane replication, membrane replication in association with whole protoplasmic angmentation, and starch to sugar conversion.

The Imaginal Ecdysis of Blowflies. The Control of Cuticuar Hardening and Darkening

ABSTRACT Blood transfusion experiments show that normal hardening and darkening at the imaginal ecdysis of Calliphora eryihrocephala(Meigen) is brought about by the release into the blood of an active factor. Introduction of this factor into a newly emerged fly some 35 min. prior to the time at which it would normally be released is sufficient to prlivent expansion. The factor is normally released some 45 min. before the appearance of the first signs of darkening and between 3 and 15 min. after the fly has reached conditions suitable for expansion, that is at about the time of initiation of air-pumping. Decapitation at emergence will prlivent the initiation of normal hardening and darkening but not of secondary darkening. Evidently the head is concerned in the release or the control of the release of the blood-borne darkening factor. The critical period for the prlivention of normal hardening and darkening by decapitation lies between 3 and 15 min. after the fly has reached conditions suitable for expansion. Isolated abdomina behave in a manner similar to decapitated flies but their reactions are complicated by secondary darkening associated with damage. Flies deprived of their abdomina will expand at least partially but the rate of their hardening and darkening is reduced. Damage reactions resembling secondary darkening in digging flies are more extensive after damage to internal organs such as the gut than to superficial organs such as the body wall. Allowing for the effects of secondary darkening it is possible to demonstrate the occurrence of the blood-borne darkening factor by means of ligatures placed at emergence between the thorax and the abdomen. Under these conditions only the head and thorax exhibit normal darkening.

The Imaginal Ecdysis of Blowflies. Detection of the Blood-Borne Darkening Factor and Determination of Some of Its Properties

ABSTRACT At the imaginal ecdysis of Calliphora erythrocephala (Meigen) the initiation of normal hardening and darkening is brought about by the release into the blood of an active factor (Cottrell, 1962b). The darkening factor can be detected in fly blood by injecting it into flies decapitated at the moment of emergence. Blood taken from flies at the moment of emergence or 24 hr. after expansion produces little or no reaction, although blood taken between 3 min. and 10 hr. after emergence shows darkening activity. However, extracts of other tissues and many chemicals will also induce darkening though probably unspecifically through damage effects. The assay can therefore be used certainly only for detecting activity in fly blood. The blood-borne darkening factor of blowflies will withstand boiling for 10 min. or drying at 120° C. for 20 min., but it does not retain its activity when kept in solution at room temperature for more than 24 hr. It is non-dialysable, relatively insoluble in organic solvents and is inactivated by ethyl alcohol and the bacterial protease subtilisin. It is probably proteinaceous and is certainly not tyrosine or any of the phenolic compounds at present thought to act as the precursors of the tanning agent. The blood-borne factor of different blowflies (Calliphora, Sarcophaga and Lucilia) is not species-specific and there is some inconclusive evidence that a similar factor is present at the ecdysis of Schistocerca.

Rapid method for detecting the presence of deleterious organic matter in soil‐cement

AbstractThe use of cement‐stabilised soils for constructing road bases is dependent upon the availability of soils which are free from organic matter. This organic matter can prevent the normal hardening of the cement. A simple, reliable test for detecting the presence of organic matter is described, which is based on the measurement of the pH of the soil‐cement mixture 1 h. after being mixed.A study was made of the factors that required control so that only the type of soil would affect the pH results under the conditions of the test. Under these standardised conditions it was found that the pH of the soil‐cement in the early stages of hydration was related to its later compressive strength. It was concluded that the measurement of the pH of soil‐cement could be used to find the presence of deleterious organic matter in soils.

Beitrag zur kenntnis des verschleisswiderstandes von gusseisen mit zwischenstufengefüge

The structure and properties of two grades of cast iron with flake graphite have been investigated after isothermal transformation in the “tempering” range of bainitic hardening. They were compared as regards structure and properties with the same grades of cast iron after a normal hardening and tempering, i.e. oil quenching resulting in a martensitic structure, followed by tempering until the same Brinell hardness is reached as with the bainitic hardening. Comparison was also made with the martensitic, untempered condition. It was found that isothermal transformation, but only in the lower bainitic hardening range (350°C), gives a favourable ratio between toughness and hardness. Particularly when comparing the wear-resistance, the superiority of this bainitic-hardened cast iron over the normally hardened and tempered cast iron was established. These comparative experiments were carried out with a specially constructed wear-testing machine, designed to take into account the influence of the cold-working of the surface zone as an important component of the wear process. Our data confirm in principle the results reported in the literature and emphasize once more the importance of residual austenite present in the Bainite and its subsequent transformation into martensite by cold-working during the wear process. This structure, together with the comparatively high value of toughness of this grade of cast iron, is responsible for the superior wear-resistance of bainitic iron. However, this superiority becomes apparent only over a comparatively small range of the bainitic hardening process.