Amount Of Cold Work Research Articles

Microstructure and strength of CuFe in Situ composites after very high drawing strains

Composites consisting of a Cu matrix and a body centred cubic (b.c.c.) phase of fibre morphology have been prepared from rapidly-solidified powders or spray-deposited billets by extrusion and heavy cold drawing. During deformation the b.c.c. phase elongates into ribbons and the microstructure refines, leading to large increases of tensile stresses. The rapid solidification techniques give a fine initial microstructure so that significantly increased strength is observed after a relatively small amount of cold working, whilst after heavy working the material becomes very strong with the microstructure reaching nanoscale dimensions. The dependence of strenth on the extent of prior cold work has been analysed in relation to the evolution of microstructure. There are considerable residual stresses in the materials after drawing which induce a strong Bauschinger effect. The very fine scale of the Fe ribbons at large drawing strains makes them very strong, such that they are still elastically loaded when the composite begins to deform plastically. The yield stress saturates at very high strains as the nanoscale Fe ribbons achieve their ideal strength.

Microstructural corrosion behavior of a cold-worked steel in a sour environment

The effect of cold-working mild steel was investigated on its corrosion characteristics. Pipeline steel was subjected to a mixed sour gas and brine environment. The amount of cold working was varied from 0 to 70% in 10% increments. Surface attack was identified using both light and electron microscopy. Corrosion was measured using an electrochemical technique and a method to separate out hydrogen embrittlement effects is suggested. The corrosive attack was correlated with respect to the underlying microstructure and was monitored as a function of time to determine the microcorrosion mechanisms. The microcorrosive attack of hot-rolled mild steel is a general corrosion process whereas the microcorrosive attack of cold-worked steel is a localized corrosion process. This localized corrosion of coldworked steels is a result of surface deformation slip caused by cold working.

On improving the fatigue life of U-form bellows

Fatigue failure invariably occurs at the root in hydroformed bellows, as the hydroforming process does not cold work the root region and raise yield point there, as it does in other regions. Both elastic and plastic analyses confirm this by predicting that the yield criterion is first satisfied in the root region during deflection. On the other hand, the roll-forming process imparts a substantial amount of cold work to the root of the bellows. A judicious combination of hydroforming and roll-forming processes is examined here therefore as a viable alternative (as opposed to individual routes), to enhance the fatigue life of austenitic steel bellows for low-pressure, low-temperature applications. This combination process has the added merit that bellows with extra-deep convolutions can be formed as replacements to costlier diaphragm-type bellows and for applications having space restrictions. Whilst testing the bellows for fatigue, it is noted that corrugations do not share the total movement equally, this phenomenon appearing to be a major cause for the scatter in values obtained in life tests. Investigation reveals that a correlation exists between this unequal sharing of movement and fatigue life. Based on these observations a new non-destructive stretch test is proposed with which original life estimates can be refined.

冷間加工した純鉄試料における粒界のフラクタル次元

The effects of the amount of cold work on the fractal dimension of grain boundary were investigated using specimens of the commercial pure iron cold-upsetted in the range from 0% to about 85%. The fractal dimension of grain boundary was estimated principally by approximating the length of the grain perimeter (the length of grain boundaries which belonged to a grain) by line segments.The length of the grain perimeter, L, in each specimen decreased with an increase of the scale of the analysis, r, in the range from about 5×10−7m to about 3×10−6m (region I) and above about 1×10−5m (region III) of r, while it showed a constant value, Lp, between about 3×10−6m and about 1×10−5 m of r. Total datum points of several grains were unified by dividing L by Lp and by plotting L⁄Lp against r. The fractal dimension of grain boundary was obtained by using the datum points in region I, since the change in the grain-boundary configuration with cold work was associated with the slip in the grains. The fractal dimension of grain boundary increased from about 1.05 to about 1.15 with increasing amount of cold work in the range from 0% to about 50% of cold reduction, but it was almost constant above 50% cold work. The box-counting method gave a little larger values of the fractal dimension of grain boundary than the coarse-graining using line segments. The shape change of grains with cold work was also examined and interpreted by a simple analysis in this study.

Investigation of stress corrosion susceptibility of duplex (α + γ) stainless steel in a hot chloride solution

The stress corrosion susceptibility of 25Cr–6Ni–3Mo duplex stainless steel (alloy 255, UNS S32550) in boiling 35% MgCl2 solution has been examined in terms of the relationship between the critical cracking potential Ecc for duplex stainless steel. Mill-annealed alloy 255 loaded to 90% of the yield strength in a boiling MgCl2 solution is immune to stress corrosion cracking (SCC) at the open circuit corrosion potential (Ecc = − 470 mV vs. standard colomel electrode (SCE)); however, the susceptibility is induced by anodic polarization, exhibiting a critical potential (Ecc = − 335 mV vs. SCE) that is 135 mV more positive than the corrosion potential. A small amount of cold work significantly increases the susceptibility to SCC by shifting Ecc in the negative direction without any effect on Eoc. Ecc for mill-annealed alloy 255 is shown to be a potential for crack initiation and varies from −335 to −380 mV vs. SCE, depending on the microstructural and loading conditions. For alloy 255, the minimum potential for crack propagation is constant at −380 mV, irrespective of any cold work and the loading mode. The potential (−380 mV) is indeed a critical potential, capable of passivating growing cracks completely, and is found to correspond to the repassivation potential for growing pits that is determined from the cyclic polarization curve measured at a slow scan rate in the unstressed state.

Effect of Cold Work and Aging Upon the Properties of a Ni-Mo-Cr Fastener Alloy

HAYNES® alloy 242 is a promising new Ni-Mo-Cr alloy for high-strength, high-temperature aerospace fastener applications. Age-hardenable by virtue of a long-range-order strengthening mechanism, 242™ alloy is capable of developing very high strength, particularly in the cold-worked condition. A key difference from other fastener materials is its attendant good ductility. The relationship between the amount of cold work, aging temperature and time, and the properties of this alloy has not been previously explored in detail. In the present work, the nature of the interaction between cold work and aging will be examined, and the properties of the material relevant to aerospace fastener applications will be described.

高張力鋼の内部摩擦におよぼす結晶粒径，微細組織と冷間加工の影響

Effects of grain size, microstructure and cold work on the internal friction were investigated using a commercial high-tensile strength steel HT 80.The internal friction increased with decreasing grain size in the heat-treated specimens for both ferrite-pearlite and sorbite structures, while it did not exhibit any detectable grain-size dependence in the cold worked and heat-treated (recrystallized) specimens. At small strain amplitudes, the internal friction was larger in the heat-treated specimens with ferrite-pearlite structure than those with sorbite structure, irrespective of grain size. But, the internal friction was larger in the latter specimens at larger strain amplitudes and at larger grain sizes. The internal friction of the high-tensile strength steel in this case was principally attributed to the magneto-mechanical hysteresis loss and the viscous flow at grain boundaries and ferrite-pearlite phase boundaries.The internal friction and the hardness increased with increasing amount of cold work. The increase of internal friction was larger at larger amounts of cold work and at larger strain amplitudes.

Effect of ageing on the microstructural stability of cold-worked titanium-modified 15Cr-15Ni—2.5Mo austenitic stainless steel

A titanium-modified 15Cr-15Ni-2.5Mo austenitic stainless steel conforming to ASTM A 771 (UNS S 38660), commercially called Alloy D9, is being indigenously developed for application as material for the fuel clad and the hexagonal wrapper for fuel subassemblies of the Prototype Fast Breeder Reactor. As this material would be used in the cold-worked condition and would be subjected to prolonged exposure to elevated service temperatures, the effect of ageing on the microstructural stability was studied as a function of the amount of cold work. The material was given 2.5–30% prior cold work and then aged at temperatures in the range 923 to 1173 K for times ranging from 0.25 to 1000 h. Hardness measurements made before and after ageing were correlated with the Larson-Miller parameter to determine the highest stable prior cold-work level. Optical microscopy was used to study the microstructural changes. The influence of prolonged exposure for two and three years at the operating temperatures of clad and wrapper, on the elevated temperature tensile properties of a 20% prior cold-worked Alloy D9 was also studied through accelerated ageing treatments based on the present parametric approach.

Effects of heat treatments on the stress corrosion cracking of alloy 600 in high temperature waters

The effects of low temperature ageing treatments on the susceptibility of alloy 600 to stress corrosion cracking in simulated primary side nuclear reactor water have been studied by a variety of techniques. Chromium depletion at grain boundaries was assessed by Electrochemical Potentiokinetic Reactivation (EPR) and polythionic acid tests while cracking was investigated using U bend, constant strain tensile and slow strain rate tests. The susceptibility to cracking was increased by annealing at 925°C after a small amount of cold work and further enhanced by ageing for 60 h at 450°C. The activation energy for cracking is in the region of 190 kJ/mol, which indicates that marked cracking is only likely at relatively high temperatures in water.

Drift in film thickness uniformity arising from sputtering target recrystallization

Crystallographic texture in sputtering targets determines the emission trajectory of the sputtered atoms and significantly influences the film thickness uniformity chracteristics of the sputtering source. Therefore, it is important that the target’s crystallographic texture remain stable at the operating temperature over the entire life of the target. Measurements of drift in deposited aluminum film thickness uniformity are reported and shown to be due to target recrystallization. X‐ray diffraction pole figure measurements are used to determine the crystallographic texture of the sputtering target. During sputtering strong initial 〈110〉 target textures rotate into 〈100〉 ‘‘cube’’ target textures as the target recrystallizes, degrading the deposited film thickness uniformity. The target operating temperature is varied independent of the sputtering system operating power by changing the target cooling conditions. Increasing the amount of cold work in the target prior to sputtering or increasing the target operating temperature increases the propensity for the target to undergo recrystallization. Target recrystallization can be a significant source of thickness uniformity variation in production sputtering operations.

The effects of pre-ageing on a thermomechanically treated 6201 aluminium alloy

The effects of pre-ageing on the tensile properties of a thermomechanically treated 6201 aluminium alloy were examined. It was found that the pre-ageing effects can be either beneficial or detrimental depending on the amount of cold work applied prior to final ageing. The pre-ageing performed was at 135° C for 30 min. The final ageing was at 140° C for various time periods. Pre-ageing combined with 60% cold work improves the tensile properties. However, pre-ageing combined with 80% cold work shows a detrimental effect on the tensile properties of 6201 alloy. The mechanisms are explained in terms of transmission electron microscopy.

Creep and Yield Loci of Zircaloy Cladding at Elevated Temperatures

Crystal plastic models are applied to textured Zircaloy in order to explain the recent experimental results on yield and creep loci by Suzuki et al. Crystallite orientation distribution functions were developed using texture pole figures obtained on cold‐worked stress‐relieved and recrystallized Zircaloy‐4 tubings. The model predictions are in good agreement with experimental loci, and clearly point out the predominance of prism slip contribution for recrystallized material while the contribution of the basal slip increased as the amount of cold work increased.

The corrosion/hydriding behavior of Zr-2.5 wt pct Nb nuclear reactor pressure tubing in pressurized Lithiated Water (pH 12.3) at 300 °C

The corrosion/hydriding behavior of Zr-2.5 wt pct Nb nuclear reactor pressure tubing has been studied in two metallurgical conditions, namely cold worked or heat treated. Two different corrosion tests were used, for total exposure times of up to 2000 hours. The study involved weight gain measurements and hydrogen pickup analyses, x-ray diffraction identification of oxides and hydrides, optical microscopy of oxides and hydrides, and TEM and SEM examination of the thin film oxides. The corrosion of the tubing follows a parabolic rate law in the pretransition period, which then changes to linear kinetics after the breakaway point. The monoclinic oxide was the predominant phase found in the oxide, while the γ-hydride (ZrH) was the predominant hydride phase in the metal. Comparison of the behavior of the coldworked and the heattreated material would suggest that a certain amount of cold work is beneficial in order to strengthen the metal and its oxide, to avoid lateral detachment of the oxide and to avoid the formation of radial (throughwall) hydrides.

Effects of cold-working on pinning behaviour and critical current densities in NbTi-based superconductors

Abstract The effects of cold-working on high-field pinning behaviour at 1·8 K and 4·2 K have been studied for multifilamentary NbTi, NbTiHf and NbTiTa superconductors, which were subjected to cold-working, heat treatment and cold-working, in sequence. It is found that the cold-working, either before or after heat treatment, shifts the peak in pinning force density to a higher field, while the maximum pinning force value is first increased with increasing amount of cold-working, and then decreased. This result can not be predicted by existing pinning theories, and we conclude that for pinning behaviour induced by cold-working, not only the introduction of pinning centres but also their size and spacing must be taken into account.

Ultrasonic angle-beam inspection through the cold-worked layer in railroad rail

The ultrasonic angle-beam shear wave technique is widely used for rail flaw detection. The shear wave (SV) refraction angle is shown in this paper to be affected by the mechanical properties of the cold-worked zone on the rail head. In general, a greater amount of cold-work in the head causes a proportionate decrease in the shear wave speed in the upper layer and this decrease in speed causes a predictable change in the entrance angle for the inspection shear wave. Experimental measurements on 12 actual rail samples have shown that the deviation from the expected refraction angle is least when the beam entrance ( ie refraction) angle is in the 52° to 60° range.

Effect of cold work on recrystallization behavior and grain size distribution in titanium

The effect of cold work in the range of 21.9 pct to 94.2 pct reduction in area by swaging on the recrystallization behavior and grain size distribution in Ti (0.2 pct Oeq) was investigated. In keeping with commonly observed behavior, increasing amounts of cold work lead to an increase in hardness prior to annealing and a decrease in the subsequent recrystallization temperature and grain size. Also, there occurred for the recrystallized grains a decrease in the standard deviation of the grain volume distribution In Σv deduced from the one-dimensional linear intercept measurements. The decrease in In Σv with cold work in swaged Ti is in good accord with that reported by Rhines and Patterson following uniaxial deformation of Al. Considering the results for both Al and Ti, it appears that the largest decrease in In Σv occurs for true strains up to R ~0.5, the change with larger strains being more gradual. The reason for the decrease in In Σv with increased cold work is not completely clear. The increased rate of grain growth with reduction in amount of cold work can be understood in terms of the larger number of three-edged grain faces which occur with the greater spread in the recrystallized grain volume distribution.

Creep of mild steel at low temperatures

Creep data for mild steel at low temperatures (360–400°C) have been analysed and it has been found that the creep behaviour is similar to that at higher temperatures. The variation of secondary creep rate with stress and temperature, in the temperature range (360–538°C) may be described by two equations with a transition stress. This transition stress is 410 MPa at 360°C. For low stresses the creep equation is given by ε s = 250 σ 3.7 exp{−(2.17 × 10 5/ RT)} . Material response to stress is highly dependent on the amount of cold work; secondary creep rate decreases with increasing prior deformation.

Effects of fabrication parameters on the properties of cold-worked 316 stainless steel tubing

Fuel cladding tube of cold-worked type 316 stainless steel for use in a liquid-metal fastbreeder reactor has been fabricated to study the effects of the intermediate fabrication processes and the final cold-working conditions on its mechanical properties. The amount of cold work is usually specified by the reduction of the cross sectional area: results in this work, however, indicate that the mechanical properties of tubes after final drawing depend on both the reduction of the cross sectional area ( W) and the strain-ratio parameter ( Q ϵ ) at final drawing. The strain-ratio parameter Q ϵ as defined as Q ϵ = ln(t/t 0)/ ln( d/ d 0) , where t 0 and t are the thickness before and after the final cold work and d 0 and d are the mean diameter before and after the final cold work. With constant W, the strength decreases as Q ϵ increases from 0 to 1, and then increases as Q ϵ increases beyond 1. With constant Q ϵ , the strength increases as W increases. These phenomena can be explained by considering the effective strain, which can be determined from W and Q ϵ in the final plug drawing. From this study, it is concluded that the amount of cold work of tubular products should be specified by parameters — such as effective strain — that include the factors W and Q ϵ .

The relationship between mechanical properties and structure in rolled polypropylene

AbstractThe relationship between mechanical properties and fine structure has been studied in polypropylene rolled both unidirectionally and biaxially (cross rolled). In unidirectionally rolled samples, a complex dependence with cold work is observed with a substantial change being observed at about 50 percent cold work. At 70 percent cold work, the yield strength and tensile strength increase substantially in the roll direction as compared with the starting billet but decrease only slightly in the transverse direction. Above 50 percent cold work, Young's modulus increases rapidly in the roll direction with a smaller increase in the transverse direction. The elongation to freak decreases in the roll direction but increases in the transverse direction. A striking feature is the large increase in ductility due to a small amount of cold work (ca., 10‐20 percent). Analogous property changes are observed for cross rolled samples although no significant variation with direction in the sheet was found. The complex property changes are accompanied by complex changes in the molecular orientation as observed by wide angle X‐ray pole figures and by changes in the morphology as observed with small angle x‐ray scattering. These changes are interpreted in terms of a model incorporating tilting both of lamellae and of chain stems within the lamellae at early stages of rolling followed by breakup of lamellae and molecular rearrangement at later stages.

A LOW TEMPERATURE COLD WORK INTERNAL-FRICTION PEAK IN Al-0.5 Wt % Ga

An internal friction peak (around - 84° C, f = 0.8 hz) was observed in Al-0.5 wt % (0.19 at %) Ga cold-drawn to 12% reduction in area at 20°C. This peak was stable when measurements were taken below 20°C with decending and ascending temperatures and the height of the peak decreased after an anneal at elevated temperatures. It disappeared completely after an anneal at 200°C. The peak height first increased and then decreased with the amount of cold-working at 20° C and a 12% reduction in area seems to be close to the optimum amount of cold-working. The activation enthalpy associated with this internal friction peak measured with the method of changing of frequency is 0.85 ± 0.05 eV. A dislocation-kink dragging model is suggested in which the mobile agents that interact with dislocation kinks are Ga atom-vacancy pairs. The effect of the temperature of previous deformation on the behavior of the internal friction peak is discussed. It is contemplated that the broadening of the peak when the previous plastic deformation was made at -196°C may be due to the formation of Ga atom-divacancy pairs.