Low Temperature Brittleness Research Articles

熱影響部の脆化について(第5報)

It is recognized that the impact-resistance of sharp-notched specimen decreases suddenly at the so-called transition temperature. Below this temperature the fracture shows more brittle than shear one and at low temperatures the shear fracture vanishes. It is important to investigate the properties of welded part at low temperatures.The authors reported in the previous report that there are two brittle zones in the heat-affected zone both in killed and rimmed steels, after testing the distribution of impact resistance when a single bead was deposited on the surface of steel and observing the fracture with X-ray diffraction incthod and microscope.In this report the authors mainly deal with the low temperature brittleness of heat-affected zone of parent plate. Observation of the X-ray diffraction rings of the fractures as well as V-notch Charpy impact resistances are also given.As a result of experiments it has been concluded as follows :1) Weld metal shows somewhat different pattern of the temperature-resistance curve as compared with that of heat-affected zone. In the temperature range above 60°C, the resistance is somewhat inferior, which is ascribed to the precipitation of nitride, but at lower temperatures it is superior to that of heat-affected zone, which may be the effect of low carbon content and small grain size.2) The most brittle part in the heat-affected zone is the one which is affected by the temperature-increase reaching around A transformation point through heat of arc.3) In the temperature range below 30°C, the influence of welding heat vanishes ; so there exists no differences in the impact resistance of parent plate, but the resistance of weld metal is good in this range.

Low temperature embrittlement mechanics deduced from zinc single crystal fracture studies

The most important conclusion of this work is that low temperature brittleness in zinc single crystals is not due to the cessation of slip below a certain temperature. On the contrary slip is quite active, and it is its activity that induces low temperature brittleness: slip causes rotation of the lattice which in turn sets up orientation gradients adjacent to constricted and unslipped regions. At high temperatures these orientation gradients are accommodated by bend-planes, at low temperatures, by cleavage.

Inter-crystalline fracture and twinning of iron at low temperatures

It has been found that small amounts of carbon may strongly influence the ductility and the mode of fracture of iron at low temperatures. Irons containing 0.03 to 0.05 per cent carbon normally exhibit considerable ductility and fracture by trans-crystalline cleavage when tested in tension at −195°C. After decarburization in moist hydrogen the same materials are completely brittle at −195°C and fracture occurs by inter-crystalline cleavage; recarburization restores the original properties and mode of fracture. Incomplete decarburization, which leaves the room temperature properties unaffected, leads to inter-crystalline fractures and brittleness at −195°C, however, the low temperature ductility and trans-crystalline mode of fracture may be restored by homogenization. In explanation of these results it is suggested that the grain boundaries in polycrystalline iron are surfaces of low cleavage strength, and that the resistance to cleavage of these surfaces may be greatly increased by the addition of small amounts of carbon. It has frequently been proposed that the low temperature brittleness of iron may be caused by the formation of deformation twins at low temperatures. A number of observations on twinning in decarburized and carburized irons which were made in the course of this investigation are believed to demonstrate that twinning is a secondary phenomenon and cannot be considered as a cause of low-temperature brittleness.

鋼材の切欠脆性に及ぼす熔接の影響

The authors investigated the effect of welding on the low temperature brittleness of ship steel. Manual and submerged welds were used and the various Charpy impact specimens selected along a line perpendicular to welding beads were tested over a range of temperatures at which the mode of fracture changed from shear to cleavage.The distributions of transition temperatures located off the line of the weld were determined and compared with their metallurgical structures, hardness and temperature distributions.Generally, the fusion zone of a weld showed more extensive notch toughness than others especially at lower temperatures.The test results showed that the brittle zone does not exactly coincide with the heat-affected zone, but was farther located from the weld than the latter.Though the cause is not clarified, it is assumed to be the result of aging phenomena due to thermal cycles.Further inquiry is continued on this point.

ジルコニウム鋼に關する研究(II)

In sequence from the previons reports (TentsutoHagane, May 1951, p. 272283), the eaperiment was made and summarized as follows:(5) Addition of zirconium refines the austenitic grain size of steel and retards the grain growth at high temperatures. (6) 0.50.9% of zirconium into steel has no remarkable effect on A1 point, but slightly lowers A3 point both in heating and cooling conditions. But in most cases these effects are covered by the action of the silicon. (7) In many cases zirconium refines the annealed and normalized structures of steel, but there is no remarkable effect in quenched and tempered structures. (8) Addition of zirconium more than 1% on carbon steel and lowalloyed steel can not expect the improvement of their mechanical properties, but addition of it up to 0.5% improves the mechanical properties of steels in normalized and high temperature tempering conditions. (9) Zirconium raises the toughness of steel at low temperature tempering and shows the temperresistance at high temperature tempering. (10) Zirconium prevents the temper brittleness of lowalloyed etructural steels. (11) The deoxidation with zirconium improves the low temperature brittleness of steel With the indirect effect by improvement of structure, as in the previous report.

An Improved Low-Temperature Brittleness Test

Abstract An improved low-temperature brittleness tester, capable of testing five specimens simultaneously, is described. All machine specifications conform to A.S.T.M. Method D 746-44T. Data are presented which show that many elastomers do not possess a sharp brittle point but are characterized by a distribution of failures over a temperature interval. The improved brittleness tester makes it possible to carry out the necessary statistical study of the distribution of per cent failures versus temperature with a reasonable amount of work. A simple analysis of the resulting distribution curve is presented.

On the Low Temperature Brittleness of Steel

On the Low Temperature Brittleness of Steel

鋼の低温脆性の原因に就て

In charpy machine, the low-temperature impact test was carried out on a series of carbon steels in their various heat treated conditions, and the cause of low-temperature brittleness was systematically investigated.It was found in the test that the sub-zero temperature brittleness is caused by iron carbide in steels, and the critical temperature (the temperature at which the brittleness sets in) varies in a wide range in accordance with the form as well as the quantity of the carbide. An extremely low carbon steel, in the quenched and tempered states, shows the critical temperature below -120°C. The low-temperature brittleness of this steel is an inherent characteristic of ferrite itself, and not due to the carbide which is so small in quantity and exists in an uninfluential form.Steels containing a comparatively higher amount of oxygen show a greater susceptibility to subzero temperature brittleness. The effect of oxygen is particularly remarkable in low carbon steels.

ON THE RELATION BETWEEN STRESS AND STRAIN IN THE IMPACT TEST

The investigation on the relation between stress and strain in the impact test is a very difficult undertaking, so that up to the present, only a few accurate determinations have been published. The author using the same method as that of Korber and Storp with some improvements, obtained the stress-strain curve and investigated some of the problems in the notched-bar impact test. The materials tested were carbon steels containing 0.1,0.3 and 0.5 percent of carbon, and nickelchromium steels. The test-piece used was of the Izod type. The following results were obtained : - (1) A reliable stress-strain curve has been obtained by the present method. (2) In a test-piece of the same material but of different breadths, the energy absorbed is, in general, not proportional to the breadth, but where the thickness is small as compared with the breadth, the proportion between every and breadth nearly holds good. (3) In a case where the shape and the depth of the notch are equal, but the dimensions of the cross section of the test-piece vary in the same ratio, both the energy absorbed and the maximum stress are proportional to the product of the breadth and the square of the effective thickness of the test-piece. (4) The low-temperature brittleness was investigated and it was found that as the temperature falls the maximum stress decreases similary to the energy absorbed. In the case of the static test, the brittleness occurs at a lower temperature than it does in the impact test.