Effect of elasto-plastic compatibility of grains on the void initiation criteria in low carbon steel

The present study evidences the role of ferrite grain size distributions on the occurrence of void initiation in a low carbon steel. Various thermomechanical treatments were done to create ultrafine, bimodal and coarse range of ferrite grain distributions. A two parameter characterization of probable void initiation sites is proposed; elastic modulus difference and difference in Schmid factor of the grains surrounding the void. All microstructures were categorized based on the ability to ease or resist void nucleation. For coarse grains, elastic modulus difference as well as the Schmid factor difference is highest, intermediate for ultrafine and lowest for bimodal microstructure.Comment: 10 pages, 4 figure

Effect of alloy treatment and coiling temperature on microstructure and bending performance of ultra-high strength strip steel

Two different high strength B-containing microalloyed steel strips produced in industrial processing conditions, one treated with Ti and the other treated with Al, processed by controlled rolling, accelerated cooling and coiling in two different temperatures ranges [723 K to 733 K (450 °C to 460 °C)] and [633 K to 653 K (360 °C to 380 °C)] were subjected to bend testing. The Ti treated steel coiled at the higher temperature 733 K (460 °C) showed the best bending performance. The relatively softer (tensile strength of and even {112} in the sub-surface region as well as uniformity of through thickness texture of the rolled sheet improve the bendability. In the presence of crack initiators, like coarse and brittle TiN particles found in the Ti treated steel, a harder microstructure and the presence of Cube and Goss texture in the sub-surface layer, seen for the lower coiling temperature can cause local transgranular cleavage cracking. Finally the post-uniform elongation obtained from tensile testing and bendability follow a good correlation

Sorting of Bio-cells through a Symmetric Serpentine Microchannel

Sorting target bio-cells like RBC, WBC, and CTCs from complex samples into a high-purity product is challenging yet essential for downstream cell biology research and clinical diagnostics. Conventional active particle sorting approaches include centrifugation and fluorescent activated cell sorting (FACS), both of which may cause contamination and loss of target cells. On the contrary, the rising field of inertial microfluidics brought light to label-free passive particle sorting, which also eliminates potential cell-damaging procedures.</p

Effect of thermomechanical processing on microstructural evolution in precipitation strengthened ferrite steel

The present study is focused on processing simulation in Gleeble® to understand the effect of thermomechanical processing parameters, especially thin-slab casting rolling (TSCR) process, on the ferrite grain structure and precipitation in a nano-precipitation strengthened ferritic steel. The double-hit compression test confirmed that heavy deformation in the range of 900–850 °C can accumulate sufficient strain in deformed austenite that is required to achieve significant ferrite grain refinement. Subsequent simulation of conventional hot-strip mill processing route showed fully ferritic microstructure upon isothermal holding at and above 650 °C (for coiling simulation). Holding at lower temperatures (≤ 600 °C) generate pearlite and bainite, which are undesirable for formability. Finally a TSCR-type of processing schedule is applied maintaining a constant deformation temperature (870 °C) and isothermal holding temperature (650 °C) to understand the effect of equalization entry temperature (Teet). A low equalization entry temperature (900 °C) was found to be beneficial to generate fine ferrite grains with fine precipitates during processing by TSCR route which is a novel finding

Processing of Ultrafine-Grained Steels by Warm Rolling and Annealing

Low-carbon microalloyed steel was subjected to warm rolling followed by rapid transformation annealing (RTA) at 800-850 C and subcritical annealing (SCA) at 600 C to develop ultrafine ferrite grain structures (UFFG) with grain size less than 3 lm. The present study investigated the influence of light (40%) and heavy (80%) warm rolling deformation (LWR and HWR) applied during the finishing pass of two-pass rolling schedules on the microstructural evolution after rolling and subsequent annealing treatments. RTA treatment of HWR sample at a lower intercritical temperature for an optimum duration (800 C, 30 s) developed UFFG-martensite dual-phase structure that offered the best combination of strength (YS 900 MPa and UTS 1200 MPa) and ductility (25% elongation). The SCA treatment provided sufficient time to achieve a uniform distribution of carbide particles throughout the ferrite matrix. SCA treatment of HWR at 600 C for 4 h developed UFFG-carbide structure achieving YS of 800 MPa with 20% ductility. The SCA of LWR resulted in coarser ferrite grain structures (grain size > 5 lm) having higher ductility (more than 30%) but lower strength (UTS of 400-550 MPa) as compared to RTA

Normal and dwell fatigue behavior of a near-alpha titanium alloy - IMI 834

Dwell sensitivity of titanium alloys at ambient temperature (~250 C) is a well-known phenomenon, although the question about the exact micromechanical reasons responsible for this still remains open. In this work, the normal and dwell fatigue response of a near-alpha titanium alloy, IMI 834, is studied. Samples with three different microstructures, namely, fully lamellar, fully equiaxed and bimodal, are evaluated for their dwell fatigue behaviors. A reduction in fatigue life by at least an order of magnitude is seen in all the three microstructures. Large plastic strain accumulation (almost equal to the monotonic ductility) was observed during the dwell fatigue loading condition and this is held responsible for this large debit in fatigue life. The normal fatigue lives decreased in the order, bimodal > fully equiaxed > fully lamellar, while the dwell fatigue lives decreased in the order, fully equiaxed > fully lamellar > bimodal. Bimodal microstructure showed a dwell fatigue debit of 17, while fully lamellar and fully equiaxed showed a debit of 9 and 10, respectively

Insights into the stability of retained austenite during wear

Transformation-induced plasticity mechanism is a very interesting phenomenon wherein a certain amount of austenite, which is thermally stable at room temperature but can be transformed to martensite during deformation, is retained in the microstructure. The amount of deformation (either by tensile, compressive or shear) that the austenite regions can withstand before they transform to martensite depends on their stability which is a function of the chemical-free energy and the severity of straining. In the current work, a bainitic steel with some retained austenite (RA), exposed to sliding wear in a pin-on-disc wear testing machine, was considered for the study. This paper aims to quantify the shear strain developed in the deformed subsurface region due to wear by using a simple image digitisation technique, and the stability aspect of RA for a complicated deformation mechanism like wear was studied considering the thermodynamics of austenite to ferrite transformations

Comparison Between Different Processing Schedules for the Development of Ultrafine-Grained Dual-Phase Steel

A comparative study was carried out on the development of ultrafine-grained dual-phase (DP) (ferrite-martensite) structures in a low-carbon microalloyed steel processed using two thermomechanical processing routes, (i) intercritical deformation and (ii) warm-deformation and intercritical annealing. The samples were deformed using Gleeble3500(A (R)) simulator, maintaining a constant total strain (epsilon = 1) and strain rate ( = 1/s). Evolution of microstructure and micro-texture was investigated by SEM, TEM, and EBSD. Ultrafine-grained DP structures could be formed by careful selection of deformation temperature, T (def) (for intercritical deformation) or annealing temperature, T (anneal) (for warm-deformation and annealing). Overall, the ferrite grain sizes ranged from 1.5 to 4.0 mu m, and the sizes and fractions of the uniformly distributed fine-martensitic islands ranged from 1.5 to 3.0 mu m and 15 to 45 pct, respectively. Dynamic strain-induced austenite-to-ferrite transformation followed by continuous (dynamic) recrystallization of the ferrite dictated the grain refinement during intercritical deformation, while, continuous (static) recrystallization by pronounced recovery dictated the grain refinement during the warm-deformation and the annealing. Regarding intercritical deformation, the samples cooled to T (def) indicated finer grain size compared with the samples heated to T (def), which are explained in terms of the effects of strain partitioning on the ferrite and the heating during deformation. Alpha-fiber components dominated the texture in all the samples, and the fraction of high-angle boundaries (with > 15 deg misorientation) increased with the increasing T (def) or T (anneal), depending on the processing schedule. Fine carbide particles, microalloyed precipitates and austenitic islands played important roles in defining the mechanism of grain refinement that involved retarding conventional ferrite recrystallization and ferrite grain growth. With regard to the intercritical deformation, warm-deformation followed by annealing is a simpler process to control in the rolling mill; however, the need for high-power rolling mill and controlled annealing facility imposes industrial challenge