Extent Of Cold Work Research Articles

Study of strain induced martensite and its reversal on sensitization behaviour of metastable austenitic stainless steel

PurposeThe purpose of the present study is to investigate the effects of strain-induced martensite (SIM) and its reversal on metastable austenitic stainless steel (MASSs) through the analysis of metallurgical and sensitisation behaviour.Design/methodology/approachIn the present investigation, the samples of Cr-Mn ASS (also known as MASSs) including 15%, 30% and 50% cold worked, solution annealed samples with and without thermal ageing (at 700°C for 3 h) were analysed with the help of X-ray diffraction analysis, microstructure examination and electrochemical behaviour. The scanning electron microscope (SEMJOEL 6380 A) was used to examine the microstructure of the sample, and the double-loop electrochemical potentiokinetic reactivation test was used to determine the degree of sensitisation (DOS) in the samples. The cold worked solution annealed samples without thermal ageing are named as CR15, CR30 and CR50, respectively, and the samples with thermal ageing are named as CR15_TA, CR30_TA and CR50_TA, respectively.FindingsIn CR15, CR30 and CR50 samples, the DOS increased with increase in the extent of cold working, which was attributable to passivation deterioration. Because of the high degree of passivation at the grain boundaries, the DOS of CR15_TA and CR30_TA were practically identical. The DOS in the CR50_TA sample, on the other hand, was lowered due to SIM recovery in the austenite.Originality/valueThe present study sheds light on how to choose the right cold working percentage to avoid sensitisation in MASSs during the fabrication of metal forming components.

Microstructural Studies in Understanding the Role of Metallurgical Parameters on Creep Behaviour of Austenitic Alloys

Studies on creep behaviour of austenitic steels as a function of metallurgical variables like: (a) extent of cold work (b) trace alloying elements (c) choice of joining method indicate the need to understand their role through microstructural studies. As the materials evolve during creep exposure in terms of defect structure and precipitation behaviour, extensive electron microscopy studies were carried out to understand the influence of the above variables. It was observed that cold work shows an increase in creep life as it is varied from 10 to 24 % due to the enhanced prior defect structure providing a complex tangled dislocation structure when the material undergoes creep deformation. The addition of Ti results in enhanced nanoscale precipitation of TiC which was found to influence the creep strength up to 0.23 % of Ti. Employing modified TIG joining over the conventional TIG process it has been found less creep cavitation in the former joint which led to the improvement in creep rupture strength. The paper would discuss in detail of the microchemical variations, microstructural evolution in terms of defect structure and precipitation behaviour on the creep life.

Influence of the Thermomechanical Treatment on the Intergranular Corrosion Susceptibility of Zn-Modified Al-5.1 Wt Pct Mg-0.7 Wt Pct Mn Alloy Sheet

In this study, the effect of thermomechanical treatment on intergranular corrosion (IGC) susceptibility of the Zn-modified Al-5.1 wt pct Mg-0.7 wt pct Mn alloy plates was investigated. The specimens underwent varied amounts of cold work, while final annealing was conducted in the 493 K to 533 K (220 °C to 260 °C) temperature range. It was shown that the extent of cold work, especially at lower temperatures of treatment, had a profound effect on the corrosion resistance of the alloy. Such observation was in direct correlation with the morphology of precipitated ternary grain boundary phase (Al-Mg-Zn). Microstructural characterization showed that, depending on the amount of cold work, different deformation substructures were created, which, in turn, influenced kinetics and the mechanism of precipitation. Wetting of the grain boundaries by the ternary grain boundary phase (Al-Mg-Zn) was a signature of the IGC susceptible state and occurred in the specimens that were subjected to a lower degree of cold work. The specimens that underwent a higher degree of cold work (over 30 pct) showed superior corrosion resistance as a result of ternary grain boundary phase (Al-Mg-Zn) precipitation in the form of discrete particles at the grain boundaries as well as in grain interiors.

Corrosion behavior of cold-worked austenitic stainless steels in liquid lead–bismuth eutectic

The effect of cold working on the corrosion behavior of austenitic stainless steels in liquid lead–bismuth eutectic (LBE) was studied to develop accelerator-driven systems for the transmutation of long-lived radioactive wastes and lead–bismuth cooled fast reactors. Corrosion tests on solution-treated, 20% cold-worked and 50% cold-worked 316SS and JPCA (15Cr–15Ni–Ti) were conducted in oxygen-controlled LBE. Slight ferritization caused by Ni dissolution and Pb–Bi penetration were observed for all specimens in the corrosion test conducted at 500°C for 1000h in liquid LBE with an intermediate oxygen concentration (1.4×10−7wt.%). In the corrosion test performed at 550°C for 1000h in liquid LBE with a low oxygen concentration (4.2×10−9wt.%), the depth of the ferritization of 316SS and JPCA increased with the extent of cold working. Only oxidation was observed in the corrosion test that was performed at 550°C for 1000h in liquid LBE with a high oxygen concentration (approximately 10−5wt.%). Cold working accelerated the formation of the double layer oxide and increased the thickness of the oxide layer slightly. In contrast, the ferritization accompanied by Pb–Bi penetration was widely observed with oxidation for all specimens corrosion tested at 550°C for 3000h under the high-oxygen condition. Cold working increased the depth of the ferritization of 316SS and JPCA. It is considered that cold working accelerated the ferritization and Pb–Bi penetration through the enhanced dissolution of Ni into LBE due to an increase in the dislocation density under conditions in which the protective oxide layer was not formed in liquid LBE.

Recrystallization and fission-gas-bubble swelling of U–Mo fuel

At high burnup, U–Mo fuel exhibits some form of recrystallization, by which fuel grains are subdivided. The effect of grain subdivision is to effectively enhance fission gas bubble (FGB) swelling due to increased grain boundaries. Inter-granular FGB swelling, i.e., FGB formation and growth at the grain boundaries, is much larger than the intra-granular FGB swelling. Recrystallized fuel volume fractions of U–Mo fuels irradiated to fission densities reaching 5.7×1021f/cm3 were measured. Analytical expressions of recrystallization kinetics of U–Mo fuel during irradiation have been developed through the usage of the Avrami equation, a phenomenological equation which is also used to describe similar typical transformation reactions, such as new phase formation. In this work, we present a novel FGB swelling model of U–Mo fuel that is expressed in terms of Mo content, extent of cold work (fuel powder fabrication method), and fission density.

Effect of substrate structure on properties of nitrided layers formed on pure iron

PurposeThis paper aims to investigate the structure and scratch resistance properties of gas nitrided pure iron samples.Design/methodology/approachThe effects of material strain hardening and amount of grain boundaries exposed on nitriding surface were evaluated by cold rolling the starting samples to different reduction levels before gas nitriding.FindingsThe study finds that nitriding without any prior cold rolling produced a comparatively wide compound layer with a large fraction of porous zone featuring low scratch hardness values but no evidence of damage. On the contrary, cold rolling before nitriding led to a more irregular and thinner compound layer with reduced amount of porous zone and much finer nitrides in the diffusion zone. Scratch hardness was increased but failure mechanism changed by generation of conformal cracks within the track groove and the appearance of discontinuous spallation at high loads.Originality/valueOne of the issues of great industrial importance concerning nitriding of steels is the need to predict the extent of the nitrided layer in products showing small variations in microstructure or in extent of cold working due to complex manufacturing cycles. Despite the practical importance, relatively little information is available in literature about these issues. The present paper is therefore aimed at investigating the structure and mechanical properties of pure iron samples, gas nitrided with different amounts of cold working and microstructural conditions.

Effect of Cold Working and Heat Treatment on Recrystallization, Mechanical Properties and Microstructure of High Strength Ti15V3Al3Cr3Sn (Ti-Beta) Alloy

Ti15V3Al3Cr3Sn (Ti-15-3-3-3) alloy is a highly cold formable metastable beta alloy and attains very high strength by proper selection of cold working and heat treatment cycles. Due to the presence of softer BCC beta phase at ambient temperature in solution treated condition, this alloy is highly cold workable; to as much as 90% without need of any intermediate annealing. In the present work, cold working up to 83% was imparted to the sheet. Subsequently, cold worked sheet was solution annealed at various temperatures. Cold worked and solution annealed samples were provided with two types of aging cycles: 482°C/16hrs/AC (STA-1) and 538°C/8hrs/AC (STA-2). Hardness measurement, tensile property and microstructural evaluation in cold worked (CW), CW plus solution annealed (CWSA) and CWSA plus aged conditions were carriedout. Recrystallization temperature has been observed to be dependent on extent of cold working. Tensile properties are higher for STA-1 cycle as compared to STA-2 cycle. Hardness values in cold worked condition are higher than solution annealed samples whereas for cold worked and STA samples, an increase in hardness w.r.t. to annealed values has been observed. Corresponding volume fraction of alpha precipitates is found to be more with STA-1 cycle than STA-2 cycle. Also, distribution of the precipitates with STA-1 cycle is observed to be more uniform than STA-2 cycle. The present paper discusses the effect of cold working on recrystallization, mechanical properties and microstructure in Ti-15-3-3-3 beta alloy.

Effect of Deformation on the Mechanical and Electrical Properties of Aluminum-Magnesium Alloy

This paper presents the effect of deformation on the tensile strength, toughness, hardness and electrical resistance of aluminum 6063 alloy. Cast samples were cold rolled in the range of 0-24 percent thickness reduction and subjected to mechanical (static, dynamic) and electrical resistance tests. Results show significant improvement in hardness and electrical resistance properties of the alloy. The nature, amount and distribution of the secondary phase, Mg2Si, particles precipitated within the matrix which was influenced by the extent of cold-work, are responsible for the observed behaviour. The resistance of the alloy also depends on the degree of cold work carried out prior to use.

Three-dimensional stress distribution around cold expanded holes in aluminium alloys

Aluminium alloy 6082 (HE30) and aluminium-lithium alloys 8090 and 2091 were examined after holes were cut and cold-expanded by means of an oversized mandrel. The extent of cold working was analysed by two techniques, namely neutron diffraction (ND) and the Sachs cutting method (SM). While the former requires neutron diffraction facilities and is a non-destructive measurement technique, the latter is based on the removal of small layers of material from the inside of the expanded hole while recording the apparent change in strain by the removal of the layer. The stress distributions analysed by ND are compared with the method of Sachs and the results are discussed with respect to distances over which the state of stress changes from compression to tension. These changes are significant in explaining the improvement of service life in mechanical fastener holes from the process of cold expansion. In all alloys examined it was found that the improved fatigue performance was a function of the degree of expansion. All alloys exhibited a maximum in expansion beyond which fatigue life deteriorated. This was due to crack initiation during excessive hole enlargement exceeding the yield strength of the alloys. Crack initiation usually started from inside the hole of the fastener but always perpendicular to the applied load. The initial stages of growth occurred perpendicularly over a short distance but further growth occurred on a plane with normals inclined at about 55–60° to the tensile axis. This behaviour was due to the presence of texture development in the alloys which is beneficial to the resistance of both fatigue crack initiation and propagation.

Deformation, twinning and thermo-mechanical strengthening of Ti 50Ni 47Fe 3

The dislocation Burgers vectors for the B2 intermetallic compound, Ti 50Ni 47Fe 3, are shown to be the 〈010〉 type, which provide this alloy with only three independent slip systems. However, concurrent dislocation slip and mechanical twinning on {114} planes affords the polycrystalline material with greater than 50% room temperature ductility. Individual twins do not grow greater than 50–150 nm in width, and the twinning density increases with the extent of cold working. Annealing a cold worked structure, comprised of mechanical twins and dislocations, results in the formation of subgrains with a size limited by the width of the twins. Greater cold working produces a finer twin spacing and, subsequently after annealing, a refined subgrain size which in turn brings about an improved combination of yield strength and ductility.