Lower Rolling Temperature Research Articles

アルミニウム合金の温間圧延における組織変化

Micro-structural change in 1100, 3004, 5052 and 5082 aliminum alloys due to single pass rolling at temperature betwean 50°C and 350°C has been investigated. Dynamic recovery during rolling was influenced by both rolling temperature and Mg content. In the alloys containing Mg, finer subgrain size and existence of dislocations in subgrains were found, though no subgrain formation were observed in 5052 and 5082 alloys at lower rolling temperature, due to inhibited migration of dislocations. After rolling, hardness decreased due to the static recovery, while recrystallization occured at elevated temperature. In the alloys containing Mg, the recrystallization was accelerated by high density of dislocations which were introduced during rolling.

Influence of warm working and tempering on fissure formation

The influence of warm working and tempering on the formation of fissures on the fractured faces of Charpy V-notch samples has been examined for a variety of ferrite–pearlite steels and iron alloys which had been rolled in the temperature range 600–400°C and tempered in the range 600–725°C. In accordance with fissures being initiated by the ease of intergranular failure along the ferrite grain boundaries, the number of deep fissures produced on warm working increased with the degree of grain boundary alignment in the rolling direction and the grain aspect ratio (maximum grain diameter/minimum grain diameter). Pearlite banding and the presence of grain boundary carbides were found not to influence the number of fissures formed, fissuring behaviour being the same for the Fe–Mn alloys and plain C–Mn steels. The presence of low levels of S and P also did not influence fissure formation. At a given average grain aspect ratio it was found that the introduction of a two phase rolling sequence (760–720°C) into the rolling schedule encouraged fissure formation. This is probably due to a small number of elongated grains not recrystallising during the two phase rolling sequence and being further elongated at the lower rolling temperatures, combined with a greater alignment of the ferrite boundaries in the rolling direction. By rolling the steels and Fe alloys with the same reduction at temperatures insufficient to allow recrystallisation (600–400°C), it has been possible to keep the aspect ratio constant and vary the dislocation density. At constant aspect ratio, increasing the dislocation density by warm working increased the number of deep fissures formed. On the basis of these results, it is suggested that the weakness at the grain boundaries which gives rise to these fissures may be caused by dislocation interaction with the boundary together with boundary alignment giving a well defined crack path. Subsequent tempering at 600°C which allowed some recovery to take place without grain boundary movement did not reduce the number of fissures. Fissuring was only removed when the tempering temperature was high enough to allow grain boundary movement.MST/769

Deformation processes in hot worked copper and α brass

The generation of the fine grained, dynamically recrystallized microstructure has been studied in hot rolled copper and α brasses and in 70:30 brass deformed by hot torsion. The new grains, which developed preferentially at grain boundaries and inhomogeneities of deformation, contained none of the deformation features present in unrecrystallized parts of the microstructure. This observation is contrary to theories of dynamic recrystallization which imply that the microstructure contains a spectrum of grains ranging from just recrystallized to severely deformed. Texture studies showed cold rolled textures at low rolling temperatures but in the case of copper the texture became quite flat after rolling at 350 and 425 °C. Flat textures were associated with a minimum grain size. At higher rolling temperatures the textures were again typical of cold rolled material. It is suggested that while normal slip processes are operating at all temperatures there is an additional contribution from grain boundary deformation processes associated with fine grained microstructures. Such processes would account for the absence of normal deformation features from dynamically recrystallized microstructures.

On the origin of equiaxed austenite grains that result from the hot rolling of steel

An investigation has been conducted into the influence of hot rolling on the microstructure of austenite in both a low alloy (transformable) and an austenitic stainless steel. Specimens of each steel were reheated and then given a single 50 pct reduction at various temperatures, after which the specimens were water quenched. The specimens were analyzed using optical, transmission electron and X-ray metallography. The results of these experiments showed that both steels exhibited equiaxed grains after high temperature rolling, elongated grains after low temperature rolling and a mixture of both types of grains after rolling at intermediate temperatures. One of the principal goals of this work was to study the origin of the equiaxed grains that result from high temperature rolling. Information obtained from dislocation observations and texture analysis has led to the conclusion that the mechanism most likely responsible for the equiaxed grains in as-rolled austenite is dynamic recrystallization.

Ａｌ‐１０％Ｍｇ合金の圧延における二枚板の発生とその防止

The Al-10%Mg alloy slabs having various thickness were hot rolled at various rolling temperatures. Electron microfractography was made on the fractured surfaces in alligatoring to examine causes of alligatoring. The fractographs were compared with those of Charpy impact specimens tested at high temperatures. There are two types of alligatoring: One is connected with hot shortness of material itself and occurs at high rolling temperatures. The other is owing to the nonuniform deformation and occurs at relatively low rolling temperatures at about 50% reduction. An effective prevention for the latter, the inserted bolt method is proposed, in which the tails of the rolling material are mechanically reinforced.

Einfluss Der Verformung Bei 77°K Auf Die Elektrochemischen Eigenschaften Der Oberfläche Von Nickeleinkristallen

Monocrystalline nickel with a (110 surface orientation was deformed during rolling in liquid nitrogen in a low-temperature rolling installation. The degree of deformation constituted 9, 23, 40 and 83 per cent. Plarization curves of deformed single crystal nickel showed that anodic oxidation processes depend on the degree of metal deformation. With the increase in degree of deformation the transition of monocrystalline nickel to the passive state is facilitated. It is evident from the deceleration of the dissolution rate in the region of the active state of the surface, from the decrease of critical passivation current as well as from the shifting of critical passivation potential towards the less noble values. Electron microscopic investigation has shown that the growth of the deformation degree results in an accumulation of faults in the crystal lattice. The growth of single crystal nickel susceptibility to passivation with the increase of deformation degree can be explained by the fact that growth of dislocation density leads to the increase of the number of nickel-oxygen compounds formation centres.

Effect of low-temperature rolling on the specific electrical resistance of nickel-chromium alloys

Effect of low-temperature rolling on the specific electrical resistance of nickel-chromium alloys

Zur kinetik der rekristallisation von kupfer nach tieftemperaturverformung

The recrystallization kinetics after deformation at room temperature and particularly at liquid air temperature were investigated for 99.99% and 99.999% copper after 95% rolling. The progress of recrystallization was investigated in the temperature range up to 150°C by observing the micro-hardness, the number of sharp Laue reflexes, the fraction of recrystallized polished section area, and the fraction of rolling and recrystallization textures which may be deduced from the pole figures. It was found that after deformation in liquid air the rate of recrystallization was larger by a factor of about 1000 as compared with room temperature deformation. This had the consequence that 99.99 % copper recrystallized after low temperature rolling completely during room temperature aging for a few days. From the half life times of the recrystallization, activation energies of 24.9 kcal/mol and 17.8 kcal/mol were deduced for deformation at room temperature and at low temperatures, respectively.This effect is surprising in view of the fact that the driving force for grain boundary motion may be increased by low temperature deformations by a factor of not more than 10. From the various attempts of interpretation, the most probable one assumes that the vacancies generated by low temperature deformation do not anneal spontaneously as in the case of room temperature deformation, but are rather picked up by the migrating grain boundary and consequently increase the mobility of the latter.

熱間圧延した際のMn, SiおよびSi-Mn各単独脱酸鋼中の介在物の挙動

This study was carried out to get fundamental informations on nonmetallic inclusions in order to make clear the relation betwee nonmetallic inclusions and properties of steel.To. study the behaviour of Mn oxide, Si oxide and manganese silicate in steel, electrolytic iron was melted in a high frequency induction furnace with varied addition of manganese, silicon or silicomanganese.Two kinds of rolling temperature (1250-1000°and below 1000°) and two kinds of rolling ratio (9 and 36) were selected.X-ray probe microanalyser was used to identifyinclusions and the eyepiece with micrometer was used to measure microscopically the quantity of inclusion deformation.The results were mainly as follows:It appears that inclusions are classified into two typesaccording to course of formation, size, composition and distribution, namely: largeinclusions (5-25μ) and small inclusions (>5μ).Quantity of inclusion deformation increases as the volume of inclusion increases and rolling ratio becomes large.But the proportion of quantity of inclusion deformation to that of steel deformation decreases with increasing rolling ratio.In this experiment inclusions except sulfide, Mn silicate and silica are easier to deform at low rolling temperature than at high rolling temperature.In cases of sulfide and Mn silicate, the quantity of deformation is large at high rolling temperature.Quantity of deformation of inclusions which is produced by manganese deoxidation increases gradually with added manganese content.Quantity of deformation of inclusions in steel deoxidized with silicon increases rapidly with added silicon content, but it decreases rapidly as soon as SiO2 begins to form and they are scarcely defo rmed by rolling. In case of inclusions in steel deoxidized with silicomanganese, the quantity of deformation increases with increasing added silicomanganese content.This deformation depends mainly on that of manganesesilicate.

Effect of hot rolling temperature on the grain size of aluminium sheets with various purities

Effects of hot rolling temperatures on recrystallized grain size of aluminium sheets have already been studied by many investigators, and it is generally known that the higher the hot rolling temperature rises, the finer does the grain size grow. However, these investigations were carried out on aluminium of commercial purity, such as 99.0-99.5% aluminium, and few or no systematic studies on aluminium of a wide range of purity.Therefore, this work is undertaken to determine the effect of the hot rolling temperature on the recrystallized grain size of 99.1-99.99% pure aluminium sheets, hot rolled at the starting temperature of 400°C (finishing 340 °C), 500°C(finishing 400°C) and 600°C (finishing 450°C) respectively and cold rolled without interannealing.The results obtained are as follows:1) A high hot rolling temperature gives a fine recrystallized grain size in aluminium of lower purity than 99.9%, whereas it has a little effect on a grain size in 99.9% aluminium as well as in 99.99% aluminium having a cold reduction lower than approximately 85%, As regards 99.99% aluminium with a cold reduction higher than approximately 85%, when hot rolling temperature is high, the recrystallized grain size becoms large in case of a rapid heating rate in annealing, while the grain size becomes fine in case of a slow heating rate.2) With 99.99% aluminium hot rolled at a high temperature, a recrystallized grain size increases sharply at a cold reduction over 85%, in case of a rapid heating rate in annealing, and this phenomenon shifts to a high cold reduction in the case of a slow heating rate.3) As regards 99.99% aluminium with a cold reduction in excess of 85%, a rapid heating rate gives a large recrystallized grain size at a high hot rolling temperature, but a grain size of sheet heated at a very rapid rate as treated in a salt bath is comparable to that of sheet at a very slow heating rate.Whereas, a rapid heating rate gives a fine recrystallized grain size at a low hot rolling temperature.4) A hot rolling temperature also has an influence upon a recrystallization temperature. In the case of 99.99% aluminium, a low hot rolling temperature always goes with a low recrystallization temperature. This tendency becomes less pronounced as the purity of aluminium decreases. However, it again becomes marked with 99.1% aluminium. This apparently is attributable, unlike 99.99% aluminium, to a difference in the amount of cold work due to a difference in the degree of recrystallization on a hot rolled sheet.

Preferred orientation in α-uranium

The preferred orientation of uranium rolled in the α-range has been investigated by X-ray diffraction using a spherical specimen in the Geiger counter spectrometer. Complete figures of the principal pole distributions have been obtained without absorption correction. At low rolling temperatures, a texture is obtained having principal pole maxima corresponding to a single unit cell orientation. The (001) and (100) pole maxima lie in the plane normal to the rolling direction at 30 and 60 degrees respectively to the compression axis; the (010) pole maximum is parallel to the rolling direction. At higher rolling temperatures near the recrystallization point a duplex texture is obtained, having a common (001) pole maximum at 20 degrees to the compression axis, and having the (010) and 110) poles parallel to the rolling direction. The unit cell probability distribution has been derived using two principal pole distributions, and from this the inverse pole figures have been calculated, giving the distributions of the compression axis and of the rolling direction over the unit cell. A direct comparison of the rolling figures predicted by Calnan and Clews is obtained from the inverse pole figures. Good agreement is obtained with the figures predicted for rolling at low temperatures where deformation occurs predominantly by twinning with a small amount of slip. The rolling figures obtained at high temperatures giving the duplex texture are not in agreement with Calnan and Clews. A treatment of the deformation of α-uranium during tension, compression and rolling is described, using the glide mechanisms determined by Cahn, which is compatible with both the low- and high-temperature textures. The reorientation of the (010) axial and the duplex (010)-(110) axial textures upon recrystallization has been investigated. The (010) texture is shown to be relatively stable under recrystallization. The duplex texture undergoes reorientation to give a single component texture having the (151) pole axial. A (100) pole maximum occurs along the rolling direction which is shown to be due to overlapping of four symmetric components.