Sushil Mishra

Microstructures and Mechanical Properties of as-Drawn and Laboratory Annealed Pearlitic Steel Wires

Near eutectoid fully pearlitic wire rod (5.5 mm diameter) was taken through six stages of wire drawing (drawing strains of 0 to 2.47). The as-drawn (AD) wires were further laboratory annealed (LA) to re-austenitize and reform the pearlite. AD and LA grades, for respective wire diameters, had similar pearlite microstructure: interlamellar spacing (λ) and pearlite alignment with the wire axis. However, LA grade had lower hardness (for both phases) and slightly lower fiber texture and residual stresses in ferrite. Surprisingly, essentially identical tensile yield strengths in AD and LA wires, measured at equivalent spacing, were found. The work hardened AD had, as expected, higher torsional yield strengths and lower tensile and torsional ductilities than LA. In both wires, stronger pearlite alignment gave significantly increased torsional ductility.

Effect of plastic anisotropy on forming behavior of AA-6061 aluminum alloy sheet

AA-6061 (T6) aluminum alloy sheet is used extensively for structural applications in various automotive and aerospace industries due to its excellent mechanical and physical properties. Due to lower formability of this material in age-hardened (T6) condition, forming of complex-shaped components is a major challenge. Forming behavior of the sheet was studied in T6 condition using limit dome height tests by experiment and finite element method for three different sheet directions (rolling direction, inclined direction (ID) and transverse direction). Strain path diagrams were obtained from the experimental limit dome height tests and finite element method simulations from drawing to stretching region, and the results were compared for all the sheet directions. Forming limit diagrams were plotted using strain localization and fracture criteria from experimental and simulated strain path curves. Effect of plastic anisotropy on crack propagation direction was studied using finite element method, and it has been found that the direction of crack propagation was strongly dependent on plastic anisotropy ratio (“r” value) of the sheet in biaxial strain paths.

Microstructural Engineering in Eutectoid Steel: A Technological Possibility?

Eutectoid wire rods were subjected to controlled thermo-mechanical processing (TMP). Both increased cooling rate and applied stress during the austenite-to-pearlite decomposition produced significant changes in the microstructure: major increases in the pearlite’s axial alignment and minor decreases in the interlamellar spacing. The pearlite alignment was correlated with changes in the ferrite crystallographic texture and the state of residual stress. Microstructural engineering, improved axial alignment of pearlite, through controlled TMP gave a fourfold increase in torsional ductility. TMP of eutectoid steel thus appears to have interesting technological possibilities.

Finite Element Analysis-Based Approach for Stress Concentration Factor Calculation

The geometric discontinuity often causes the ‘stress raiser’ or the stress concentration (K t ). The fatigue life of a structure depends on the stress concentration, and hence it is very much required to calculate the ‘K t ’ value correctly. The calculation of exact ‘K t ’ value is cumbersome task. Here a VBA-based tool has been developed to calculate the ‘K t ’ which is well validated with other approach.

Delamination of Pearlitic Steel Wires: The Defining Role of Prior-Drawing Microstructure

This article reports the occasional (<xa010 pct of the actual production) delamination of pearlitic wires subjected to a drawing strain of ~xa02.5. The original wire rods which exhibited post-drawing delamination had noticeably lower axial alignment of the pearlite: 22xa0±xa05xa0pct vs 34xa0±xa04 pct in the nondelaminated wires. Although all wires had similar through-thickness texture and stress gradients, delaminated wires had stronger gradients in composition and higher hardness across the ferrite–cementite interface. Carbide dissolution and formation of supersaturated ferrite were clearly correlated with delamination, which could be effectively mitigated by controlled laboratory annealing at 673xa0K. Direct observations on samples subjected to simple shear revealed significant differences in shear localizations. These were controlled by pearlite morphology and interlamellar spacing. Prior-drawing microstructure of coarse misaligned pearlite thus emerged as a critical factor in the wire drawing-induced delamination of the pearlitic wires.

Microstructural Development Due to Laser Treatment and Its Effect on Machinability of Ti6Al4V Alloy

Application of the laser in machining has been demonstrated to improve the machinability in several metals and alloys. A very high heating and cooling rate during laser treatment tends to modify the microstructure significantly. In some materials, the change in the microstructural features affects the machinability of the materials. In this work, microstructure evolution due to laser treatment and its effect on the machinability of Ti6Al4V was studied using advanced characterization techniques. The microstructure of the surface and subsurface of the cylindrical Ti6Al4V rod was modified using a high-power laser source with varying laser scanning speeds. The laser treatment resulted in three distinctly different microstructures along the radial direction of the rod; these were classified as the lath dominant zone, a mixture of laths with equiaxed grains and equiaxed grains surrounded by bands. Rapid heating and cooling during laser scanning lead to the formation of the martensite phase and local strain development. Further, at the boundaries of laths, compressive twins (57 deg

Limit dome height test of very thin brass sheet considering the scaling effect

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Microstructure Evolution in Three FCC Materials During Limited Dome Height Test

1¯21¯0) were formed because of laser heating. These twins are different from tensile twins (94.8 deg