Pressure-Induced Free Dislocations in Iron

Yajima, Masami; Ishii, Mitsuru

doi:10.2320/jinstmet1952.32.8_697

Cited by 4 publications

(3 citation statements)

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“… Experimental data on the hydrogen solubility in pure liquid iron at 1 bar H 2 as function of temperature 2, 15–24. The straight line is from a thermodynamic evaluation by Zinkevich et al 28.…”

Section: Hydrogen Solubility Using Dilute Solution Theorymentioning

confidence: 99%

Determination of Hydrogen Solubility in Fe–Mn–C Melts

Lob

Senk

Hallstedt

2011

steel research int.

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High manganese steels are supposed to be sensitive to hydrogen embrittlement. This can be explained by increased hydrogen solubility in comparison to unalloyed steels. To minimise hydrogen pick up during melting operations, it is necessary to know accurately the hydrogen solubility as function of hydrogen partial pressure, temperature and Mn content. In this work in situ measurements of hydrogen content at 12, 18 and 23 wt.% Mn (and 0.6 wt.% C) using the Hydris 1 system are compared to pin-tube measurements. Below about 7 ppm [H] both methods gave the same results and above 7 ppm [H] the in situ measurement showed slightly higher hydrogen contents because some hydrogen is lost during quenching with the pin-tube method. The measured solubilities were compared with thermodynamic calculations. Using dilute solution theory with data developed for alloyed Fe-based melts with up to 10 wt.% Mn gives reasonable results except that the hydrogen solubility is slighltly underestimated for the presently investigated Mn contents. This could be compensated by using an interaction parameter of e Mn H ¼ -0.004 instead of e Mn H ¼ -0.0012. A Calphad type extrapolation from the binary Fe-H, Mn-H and Fe-Mn systems gave results very close to the experimental ones. This work is a contribution from the collaborative research centre SFB 761 ''Steel -ab initio''.

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Section: Hydrogen Solubility Using Dilute Solution Theorymentioning

confidence: 99%

Determination of Hydrogen Solubility in Fe–Mn–C Melts

Lob

Senk

Hallstedt

2011

steel research int.

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“…Much evidence has been given that pressurization introduces dislocations in Fe-Oz [7], Fe-C [8], Cr [9], in which elastic stress concentration takes place at the surface of particles of second phases under hydrostatic pressure and plastic relaxation occurs around the second Pressurization on the pseudo-brittleness in an Fe-0 2 alloy 5 stress, d grain size, and a, Ky constants, and proposed a new formula in which the parameter Ky was expressed as a function of the pressure-induced free dislocations. The disappearance of pseudo-brittleness by pressurization in iron used here may be explained as the consequence of the increase of the initial free dislocations by the same treatment.…”

Section: Discussionmentioning

confidence: 99%

The effect of pressurization on the pseudo-brittleness in an iron oxygen alloy

Yajima

Ishii

1969

Int J Fract

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Free grained iron containing 600 ppm oxygen is fairly brittle below room temperature. The brittleness essentially comes from the difficulty for the Lfiders band to initiate and propagate in fine grained specimens at the reqmred velocity and fracture occurs m the severely strained region wathin and near the band front, before deformation propagates through a specimen.Pressurization at several thousand atmospheres, which introduces free dislocations into a specimen, removes the brittleness and increases the elongation at low temperatures. It is shown that the pressure-reduced dislocations modify the stress dependence of the band velocity and increase the band velocity at a given stress. In~oducfionIn an impact tensile test coarse grained iron and steel show sufficient elongation while fine grained specimens fracture with very tittle elongations [1]. This is quite different from the case of a static tensile test in which finer gained specimens show larger elongation. It seems that the brittleness of fine grained specimens in an impact tensile test is not explained by the well known effects of grain size, strain rate and temperature on the fracture of iron and steel. It was confirmed that the brittleness in these cases essentially comes from the difficulty for the Liiders band to propagate in fine grained specimens at the required velocity, and fracture occurs in the severely strained region within and near the band front before deformation propagates throughout a specimen. It was also confirmed that these specimens having little elongation always fractured in ductile manner by drawing down with high reduction in area. In this sense Sakui and Moil [1] called such a phenomenon in an impact tensile test "pseudo-brittleness fracture".The velocity of propagation of the Lfiders bands is known to be sensitively dependent on either the test conditions [2] or material variables of grain size and matrix [3]. Recently, the present authors [4,5] have shown that pressurization at several thousand atmospheres, which is assumed to introduce free dislocations into material, makes it easy for the Lfiders band to initiate and propagate in iron, making the yield more homogeneous. This observation leads us to the expectation that pressurization or the pressure-induced free dislocations may remarkably affect the appearance of pseudo-brittleness in iron and steel. In this paper it will be shown that pseudo-brittleness generally appears just below room temperature in a fine grained Fe-O2 alloy even in static tensile test, and that pressurization removes the phenomenon and increases the elongation at low temperatures. The qualitative expression of the velocity of the Lfiders bands as a function of initial free dislocation density will also be given.

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“…In some materials changes in mechanical properties such as hardness and yield stress are observed when they are tested at atmospheric pressure after being kept under hydrostatic pressure. This phenomenon is called the effect of pressurizing or pressure cycling and has been studied with pure iron (2), zinc(3), beryllium(4), chromium (5), Cr-Mo alloy (6), etc. This effect is thought to appear as the result of microscopic plastic deformation due to the shear stress generated under hydrostatic pressure when the material contains elastic discontinuity.…”

Section: Introductionmentioning

confidence: 99%

Electron Microscope Observation of Dislocation Structure in Pressurized Tough Pitch Copper

1973

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Annealed tough pitch copper containing Cu20 inclusion particles has been pressurized under various pressures up to 15000 kg/cm2 at room temperature and the dislocation structure formed by pressurizing has been studied by means of transmission electron microscopy. The results obtained are as follows: (1) The critical pressure required to generate dislocations and to form tangled dislocations around a Cu2O particle depends strongly on the particle diameter. The relation between the critical pressure and the particle diameter agrees well with the theory of Ashby et al. (2) The tangled dislocations show regular structures whose shape changes with the orientation of the foil specimen. This phenomenon is successfully explained by a mechanism of the tangle formation through the interaction between the dislocations generated on the surface of an inclusion particle. (3) The maximum range D of the dislocation tangle is proportional to the diameter of the inclusion particle d and increases with increasing pressure. The value of the ratio Did is about 3 at 5000 kg/cm2 and about 7 at 15000 kg/cm2. (4) The dislocation tangles formed around the inclusion particles act as obstacles to the motion of dislocations when a pressurized specimen is deformed and causes the change of its mechanical properties.

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Pressure-Induced Free Dislocations in Iron

Cited by 4 publications

References 0 publications

Determination of Hydrogen Solubility in Fe–Mn–C Melts

Determination of Hydrogen Solubility in Fe–Mn–C Melts

The effect of pressurization on the pseudo-brittleness in an iron oxygen alloy

Electron Microscope Observation of Dislocation Structure in Pressurized Tough Pitch Copper

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