Transient creep in mild steel and copper at room temperature

Transient creep curves were obtained from mild steel and copper specimens which had been work hardened by cycling. Results are presented in terms of an “overstress” model in which strain rates are related to differences between the actual stress and the corresponding stress-strain point on a quasi-static stress-strain curve. It is further shown that a semi-empirical equation used to describe steady state plastic deformation can be adapted to describe transient behaviour when re-written in terms of the ‘overstress’ rather than the actual stress.     

Dissolution of hydrogen from the gas in steel at room temperature

The purpose of this paper is to show that embrittlement of steel deformed in a hydrogen atmosphere is caused by hydrogen entering the crystal lattice. Tensile tests are made under pure compressed hydrogen gas. It is shown that the hydrogen penetrates steel before any fissures develop. The penetration depends on the time of exposure of fresh surface produced by straining but does not depend directly on the strain rate. The hydrogen distribution vs depth was measured. It agrees with a transient distribution calculated with an apparent solubility (1 cu cm per 100 g at 150 kp per sq cm) and an apparent diffusivity (1.3·10^?7 sq cm per sec).     

Cell structures in polycrystalline copper undergoing cyclic creep at room temperature

Push-pull cyclic tests were carried out on polycrystalline copper specimens between fixed force limits. When a mean stress was superimposed on the cyclic stress, two kinds of cyclic creep were observed, one at low mean stress characterised by relatively symmetrical mechanical hysteresis loops and another at high mean stresses in which hysteresis loops became markedly asymmetric. Examination of the dislocation cell structures provided evidence that such structures change continuously during cycling and deformation proceeds by breakdown of cell walls producing localised areas of high uniform dislocation density from which new cells can form and grow during subsequent cycling before their eventual breakdown. Thus so called steady state cyclic deformation is, in reality, the average effect of a large number of transient deformation events.     

Mo-30Cu合金室温变形组织

对Mo-30Cu合金室温拉伸性能进行了研究,并对其断口进行观察分析.通过对Mo-30Cu合金冷轧实验,研究了不同变形量下组织的变化规律.结果表明:Mo-30Cu合金的断裂以Cu相的韧性断裂为主,并伴随着Mo/Cu界面的分离和Mo晶粒的解理断裂.Mo/Cu界面的分离和Mo晶粒的解理断裂是Mo-30Cu合金室温轧制过程中产生裂纹的主要原因.     

Lattice changes of iron-nitrogen martensite on aging at room temperature

The aging behavior of iron-nitrogen martensite (5.5 at. pct N ≙5.8N/100Fe) at about 297 K was investigated by employing X-ray diffractometry, thereby following, in particular, the changes in the {002} and {200} line profiles. Martensitic specimens were prepared by gaseous nitriding of pure iron in a mixture of NH₃ and H₂, followed by quenching in brine and subsequently in liquid nitrogen. The aging process can be divided into two stages. First, a redistribution of nitrogen atoms in the martensite matrix occurs (aging time < about 40 hours) in three ways: segregation of nitrogen to lattice defects (about 0.07N/100Fe), transfer of a small amount of nitrogen (about 0.06N/100Fe) fromalb- toc-type octahedral interstices, and local enrichment in an ordered way of the majority of the nitrogen atoms (coherent α′’-Fe₁₆N₂ precipitates). Second, formation of incoherent α″-Fe₁₆N₂ takes place (aging time > about 40 hours). Within the range of aging times employed (up to 670 hours), the diffraction by the residual austenite did not change.