Effects of phosphorous addition on mechanical properties and retained austenite stability of 0.15C−1.5Mn−1.5Al TRIP-aided cold rolled steels

The effects of a P addition on the mechanical properties and austenite stability are investigated for 0.15C−1.5Mn−1.5Al TRIP-aided cold-rolled steels containing 0.05 and 0.1 wt.% of P. The strength and retained austenite fraction are increased by an increment of the P content. The strengthening of P-added TRIP-aided steel partially comes from the solid-solution hardening effect of P, and a higher fraction of strain-induced martensite plays an important role as well. The elongation of steel containing 0.1 wt.% P is diminished compared with that containing 0.05 wt.% P. This is attributed to the lower mechanical stability of retained austenite in TRIP-aided steel containing 0.1 wt.% of P, which inhibits persistent work hardening during deformation.     

Quercetin intake,MATE1 polymorphism,and metabolic syndrome in Korean population: Hallym aging study

Food Science and Biotechnology - Multidrug and toxic compound extrusion transporter-1 (MATE1) is a quercetin transporter. We examined the associations of quercetin intake and polymorphism of MATE1...     

Influence of Al on Microstructure and Mechanical Behavior of Cr-Containing Transformation-Induced Plasticity Steel

Chromium in transformation-induced plasticity (TRIP) steel is known to have a detrimental effect on the mechanical properties by increasing the hardenability of austenite introduced during intercritical heat treatment. In this study, it is suggested that an Al addition can counterbalance the effect of Cr by encouraging ferrite formation during fast cooling and austempering. This contributes to securing the thermal stability of austenite and to retrieving the excellent mechanical properties of TRIP steel even with the addition of Cr.     

Feedrate scheduling for indexable end milling process based on an improved cutting force model

In CNC machining, an optimal process plan is needed for higher productivity and machining performance. This paper proposes a mechanistic cutting force model to perform feedrate scheduling that is useful in process planning for indexable end milling. Indexable end mills, which consist of inserts and a cutter body, have been widely used in the roughing of parts in the mold industry. The geometry and distribution of inserts compose a discontinuous cutting edge on the cutter body, and tool geometry of indexable end mill varies with axial position due to the geometry and distribution of inserts. Thus, an algorithm that calculates tool geometry data at an arbitrary axial position was developed. The developed cutting force model uses cutting-condition-independent cutting force coefficients and considers run out, cutter deflection, geometry variation and size effect for accurate cutting force prediction. Through feedrate scheduling, NC code is optimized to regulate cutting forces at given reference force. Experiments with general NC codes show the effectiveness of feedrate scheduling in process planning.     

Effects of annealing conditions on microstructure and mechanical properties of low carbon, manganese transformation-induced plasticity steel

The effects of annealing conditions on microstructural evolution and mechanical properties have been investigated in low carbon, manganese TRIP (Mn TRIP) steel based on a 0.12C-6Mn-0.5Si-3Al alloy system. The microstructure of cold-rolled sheet subjected to annealing at 760 °C to 800 °C for 30 s to 1800 s consists of a recrystallized ferrite matrix and fine-grained austenite with a phase fraction of 25 % to 35 %. Variation of the annealing conditions remarkably influenced the characteristics of constituent phases and thus affected the tensile strength and elongation. Optimization of microstructural parameters such as grain size and fraction of constituent phases, which control the yield strength, overall work hardening, and the kinetics of strain-induced martensite formation, is thus critical for obtaining an exceptional mechanical balance of the alloy.     

Effects of martensite morphology and tempering on dynamic deformation behavior of dual-phase steels

The effects of martensite morphology and tempering on the quasistatic and dynamic deformation behavior of dual-phase steels were investigated in this study. Dynamic torsional tests were conducted on six steel specimens, which had different martensite morphologies and tempering conditions, using a torsional Kolsky bar, and then the test data were compared via microstructures, tensile properties, and fracture mode. Bulky martensites were mixed with ferrites in the step-quenched (SQ) specimens, but small martensites were well distributed in the ferrite matrix in the intermediate-annealed (IA) specimens. Under a dynamic loading condition, the fracture mode of the SQ specimens was changed from cleavage to ductile fracture as the tempering temperature increased, whereas the IA specimens showed a ductile fracture mode, irrespective of tempering. These phenomena were analyzed in terms of a rule of mixtures applied to composites, microstructural variation, martensite softening and carbon diffusion due to tempering, and adiabatic shear-band formation.     

Time-temperature-precipitation characteristics of high-nitrogen austenitic Fe−18Cr−18Mn−2Mo−0.9N steel

The time-temperature-precipitation (TTP) and corresponding mechanical properties in high-nitrogen austenitic Fe−18Cr−18Mn−2Mo−0.9N steel (all in weight percent) were investigated using electron microscopy and ambient tensile testing. The precipitation reactions can be categorized into three stages: (1) high-temperature region (above 950°C)—mainly coarse grain-boundary (intergranular) Cr₂N; (2) nose-temperature region—integranular Cr₂N→cellular Cr₂N→intragranular Cr₂N+ sigma (σ); and (3) low-temperature region (below 750°C)—intergranular Cr₂N→cellular Cr₂N→ intragranular Cr₂N+σ+chi(χ)+M₇C₃ carbide. After cellular Cr₂N precipitation became dominant above 800°C, yield and tensile strength gradually decreased, whereas elongation abruptly deteriorated with aging time. On the contrary, prolonged aging in the low-temperature regime increased tensile strength, caused by the precipitation of fine χ and M₇C₃ within grains. Based on the analyses of selected area diffraction (SAD) patterns, the crystallographic features of the second phases were analyzed.     

Liquid Zn assisted embrittlement of advanced high strength steels with different microstructures

In the present study, liquid metal embrittlement (LME) phenomenon during high temperature deformation was investigated for 3 grades of Zn-coated high strength automotive steel sheets consisting of different phases. Hot tensile tests were conducted for each alloy to compare their LME sensitivities at temperature ranges between 600 and 900 °C with different strain rates. The results suggest that Zn embrittles all the Fe-alloy system regardless of constituent phases of the steel. As hot tensile temperature and strain rate increase, LME sensitivity increases in every alloy. Furthermore, it is observed that the critical strain, which is experimentally thought to be 0.4% of strain at temperatures over 700 °C, is needed for LME to occur. It is observed via TEM work that Zn diffuses along grain boundaries of the substrate alloy when the specimen is strained at high temperatures. When the specimen is exposed to the strain more than 0.4% at over 700 °C, the segregation level of Zn at grain boundaries seems to become critical, leading to occurrence of LME cracks.