Study of aged Mg-Sm alloys subjected to severe plastic deformation

The effect of severe plastic deformation by high-pressure torsion on the structure and properties of aged magnesium alloys containing 2.8–5.5 wt % Sm (the maximum solubility of samarium in solid magnesium is 5.8 wt %) are studied. The severe plastic deformation leads to substantial strengthening caused by the formation of a submicrocrystalline structure along with strengthening caused by the decomposition of a supersaturated magnesium-based solid solution.     

Microstructure and crystallographic texture of titanium subjected to combined severe plastic deformation processing

Structural studies of the nanocrystalline titanium powders produced by cryogenic milling followed by severe plastic deformation consolidation are performed. The results obtained are compared with the results obtained for monolithic titanium subjected to severe plastic deformation by torsion.     

Hot cracking susceptibility research in BTW1 austenitic high-manganese wear-resistant steel

Baosteel's first BTW1 austenitic high-manganese wear-resistant steel exhibits strong deformation-induced hardening characteristics.Compared with common low-alloy martensitic wear-resistant steels in the market,it has improved impact wear resistance,hard abrasive wear,erosion wear performance,and impact toughness.The metallurgical properties of such austenitic wear-resistant steel lead to the risk of failure because of hot cracking defects in the welded structure.In wear-resistant applications,evaluating hot cracking susceptibility is necessary to avoid the effect of welding defects.In this study,the Varestraint test is used to quantitatively analyze and evaluate the hot cracking susceptibility of BTW1 austenitic high-manganese wear-resistant steel.The test results show that by controlling the content of impurity elements and grain refinement,BTW1 austenitic high-manganese wear-resistant steel effectively reduces hot cracking tendency and has a low incidence of hot cracking under small strain conditions.The developed matching welding process can effectively avoid the influence of hot cracking susceptibility.     

Reverse transformation of ferrite and pearlite to austenite in an ultrafine-grained low-carbon steel fabricated by severe plastic deformation

Reverse transformation characteristics of a low-carbon steel consisting of ultrafine-grained (UFG) ferrite and severely deformed pearlite by severe plastic deformation were investigated and compared to those of the steel having coarse-grained (CG) ferrite and undeformed pearlite by austenitization and subsequent air cooling. Coarse-grained steel exhibited two serial transformation stages, i.e., pear-lite → austenite followed by ferrite → austenite. Contrarily, UFG steel transformed with the three serial stages, i.e., probably carbon-supersaturated ferrite → austenite, not-fully-dissolved pearlite → austenite, and ferrite → austenite transformations.     

Carbide morphology in steel subjected to cold deformation

Spheroidizing annealing is an important step in the manufacture of metal products by cold upsetting. Deformational and thermal treatment ensures high levels of cementite spheroidization with highly uniform product structure and properties.     

Research of magnesium alloys of the Mg-Sm-Y system subjected to severe plastic deformation and subsequent heat treatment

The effect of severe plastic deformation and subsequent aging on the structure and properties of cast and hardened magnesium alloys containing samarium and yttrium is studied. Severe plastic deformation leads to additional hardening both before and after aging. Hardening is achieved by the formation of nanocrystalline structure in quenched alloys or submicrocrystalline structure in cast alloys. Severe plastic deformation results in the rapid decomposition of a supersaturated magnesium solid solution and additional hardening due to the formation of nano-sized particles of hardening phases.     

Formation of a submicrocrystalline structure in metastable austenitic steels during severe plastic deformation and subsequent heating

The structure and the mechanical properties of metastable austenitic steels after severe plastic deformation by four or six passes of equal-channel angular pressing (ECAP) at a temperature of 400°C are studied. It is shown that ECAP results in strain hardening mainly due to the formation of a submicrocrystalline structure, which is retained after subsequent heating to 500°C.     

Inhomogeneity of the hot deformation of austenitic steel

By high-temperature metallography, the nonuniformity of deformation is studied for 08X18H10T steel with 28% δ ferrite. The mean strain of the ferrite is greater than for the austenite; this difference increases with rise in temperature. Correspondingly, the slip along phase boundaries increases. The hot-microhardness ratio of δ ferrite and austenite declines with increase in test temperature.     

超级奥氏体不锈钢的高温变形行为

 为了研究超级奥氏体不锈钢Cr20Ni24Mo6N钢的高温变形行为,采用Gleeble热模拟试验机进行了等温压缩试验,建立了合金的热加工图。结果表明,当变形温度为1 000～1 200 ℃时,Cr20Ni24Mo6N钢的流变曲线表现出典型的“加工硬化＋动态再结晶软化”特点;Cr20Ni24Mo6N钢的热激活能[Q]为678.656 kJ/mol。通过加工图与微观组织综合分析得出,超级奥氏体不锈钢Cr20Ni24Mo6N的合适热加工工艺为,应变速率10 s－1左右,应变量0.5～0.8,变形温度1 150～1 200 ℃。     

Recrystallization kinetics of a cold rolled dual-phase steel sheet

Determination of the recrystallization kinetics by optical microscopy and hardness test. The activation energy corresponds to that of carbon-diffusion in α Fe. Determination of the recrystallization texture from X-ray pole figures.     

Metal processing by severe plastic deformation

The mechanics of severe plastic deformation (SPD) is considered. Unlike steady-state plastic flows with the continuous evolution of dislocation structures, the SPD-induced microlocalization strongly depends on the deformation mode. The quantitative characteristic of a deformation mode is determined by the distribution of strain rates over the principal directions of a continuum shear and corresponds to the limiting states of pure shear and simple shear. Simple models of SPD mesomechanics demonstrate that a deformation mode affects a transition to localization, localization in shear bands, and rotational localization. The simple shear mode is shown to correspond to the optimum scheme of plastic structure formation, including the development of high-angle boundaries and grain refinement. Various SPD processes are analyzed in terms of simple shear.     

Short-range ordering kinetics in 316 austenitic stainless steel

In situ measurements are reported of electrical resistance changes in 316 austenitic stainless steel after abruptly raising or lowering temperature in the range from 440 °C to 550 °C subsequent to equilibration. These changes are found to be reproducible and have a magnitude roughly proportional to the temperature change. They are believed to be manifestations of approach toward a new state of shortrange order at the new temperature. Analysis of the kinetics indicates that very nearly a simple first-order reaction is involved. The rate constants were found to have an activation energy of 3.18 ± 0.40 eV. By analogy with the Zener relaxation, the temperature-change-induced short-range order which we observe is also believed to result from local atomic rearrangements in which an average atom makes a relatively small (<10) number of jumps. Good agreement between our measured relaxation rates and those calculated from extrapolated diffusion studies for iron, chromium, and nickel in comparable alloys tends to substantiate the hypothesis that average atomic jump rates are being measured.     

Structure and mechanical properties of iron subjected to surface severe plastic deformation by friction: I. Structure formation

Depth-sensing indentation is used to study the effect of grain refinement to submicro- and nanograins on the mechanical properties (hardness, plasticity, Young’s modulus) of armco iron subjected to severe plastic deformation by attrition in argon. In contrast to fcc metals, where the hardness increases and the plasticity decreases as the grain size decreases to 20 nm, the hardness of bcc iron decreases from 5.8 to 3.7 GPa and plasticity δ _A increases from 0.82 to 0.87 as the grain size decreases from 50 to 20 nm.     

Character of plastic deformation in niobium carbide powders subjected to vibratory milling

Conclusions A study of the fine-structure parameters of niobium carbide powders has shown that nonstoichiometric carbides are more brittle than stoichiometric niobium carbide. This is due, firstly, to the formation of vacancy complexes in carbon-deficient sublattices and to the generation of Frank dislocations, which markedly hinder the motion of existing and nucleation of new dislocations, and, secondly, to the increase in Peierls-Nabarro forces brought about by a fall in the carbon content of niobium carbide.Translated from Poroshkovaya Metallurgiya, No. 3(171), pp. 7–11, March, 1977.     

The deformation kinetics theory of the stress dependence of plastic deformation

The fact that plastic deformation is controlled by thermally activated processes leads to the physically rigorous conclusions that the mechanisms are defined either by a single rate constant or by the kinetics combination of rate constants. For the determination of the kinetics—that is, for the establishment of the functional relation of the stress dependence of the work, experiments have to be carried out. When the test results are plotted in the coordinate systems of logarithm of strain rate vs linear stress, also logarithm of strain rate versus linear reciprocal temperature, the behavior exhibited by the two plots defines the nature of the stress dependence of the work. The kinetics analysis of the two representations leads to the functional expression of the constitutive law in physically exact and rigorous expressions. Applications to typical mechanisms are discussed: plasticity limited by discrete obstacles; lattice diffusion controlled creep; dislocation core diffusion controlled creep; plasticity limited by lattice resistance.     

Effect of severe plastic deformation on the phase and structural transformations and mechanical properties of metastable austenitic Ti-Ni alloys

The effect of deformation under pressure and severe plastic torsional deformation (SPTD) on the structure and mechanic properties of Ti-Ni alloys is studied. It is found that, as an external load is applied, metastable austenitic alloys of the Ti-Ni system undergo the B2 → B19′ transformation. The SPTD Ti-Ni alloys are characterized by high mechanical properties and high thermal stability of their nanostructured state and properties.     

Effects of tantalum on austenitic transformation kinetics of RAFM steel

The RAFM (reduced activation ferritic/martensitic) steels containing different tantalum contents (0 wt.％,0.027 wt.％,0.073 wt.％) were designed and cast.Differential scanning calorimetry and optical microscopy were employed to explore the influence of tantalum content on the austenitic transformation of RAFM steels.The austenitic transformation kinetics was described by a phase-transformation model.The model,involving site saturation nucleation,diffusion-controlled growth and impingement correction,was established based on the classical Johnson-Mehl-Avrami-Kolmogorov model.The phase-transformation kinetics parameters,including D0 (pre-exponential factor for diffusion) and Qd (activation energy for diffusion),were calculated by fitting the experimental data and the kinetic model.The results indicated that the average grain size is decreased with the increase of tantalum.The values of Ac1 and Ac3 (onset and finish temperature of austenitic transformation,respectively) are increased by increasing the tantalum content.The increase of tantalum caused the decrease of D0.However,Qd is increased with the increase of tantalum.In addition,as a carbides forming element,tantalum would reduce the carbon diffusion coefficient and slow down the austenitic transformation rate.