Influence of Prior Austenite Deformation and Non-Metallic Inclusions on Ferrite in Low Carbon Steels

 Abstract Effects of prior austenite deformation and non-metallic inclusions on the ferrite nucleation and grain refinement of two kinds of low carbon steels have been studied. The ferrites nucleation on MnS and V(C,N) is observed. The combination of thermal-mechanical processes with adequate amounts of non-metallic inclusions formed in low carbon steels could effectively refine the grain size and the microstructure. Ferrite nucleated on the single MnS or V(C,N) inclusions and complex MnS+V(C,N) inclusion. The proper addition of elements S and V could effectively promote the formation of ferrite and further refinement of ferrite grains.     

Corrosion Behaviour of Chrome–Manganese Austenitic Stainless Steels and AISI 304 Stainless Steel in Chloride Environment

Electrochemical behaviour of chrome–manganese austenitic stainless steels (Cr–Mn ASS) and AISI 304 stainless steel (SS) is evaluated in various chloride (Cl^?) concentrations (Cl^? free to 20,000 ppm) to simulate rural, industrial and marine environment. Potentiodynamic polarization and electrochemical impedance spectroscopy has clearly shown that with increase in Cl^? concentration, the corrosion rate of both Cr–Mn ASS and AISI 304 SS increases and polarization resistance decreases. Comparatively, Cr–Mn ASS is more affected by Cl^? concentration than AISI 304 SS. This is attributed to relatively low Cr content and lack of Ni. The findings have been explained with the help of point defect model. However, in less aggressive environment of up to 100 ppm Cl^? concentration, Cr–Mn ASS may be a candidate material as a cheaper substitute of AISI 304 SS. Ways of improving corrosion resistance of Cr–Mn ASS by alloying with various elements have also been discussed. It is argued that a dedicated effort is needed to improve corrosion resistance of Ni-free or low-Ni Cr–Mn ASS.     

Alloying Design for High WearResistant Cast HotForging Die Steels

The alloying design of cast hotforging die steels was analyzed. The relationship of the life of cast hotforging dies with the failure patterns was studied. The thermal wear resistance was believed to be the key property for the alloying design of cast hotforging die steels. The alloying design parameters were selected and optimized for the cast hotforging die steel with high wear resistance. The wear resistance of the optimized cast die steel was evaluated in comparison with commercial H13 steels and 3Cr2W8V steel. In the new cast hotforging die steel, VC is predominant carbide with Cr and Mo as the main solution elements in αFe. It is found that the cast die steel has significantly lower wear rate than normal H13 steel and 3Cr2W8V steel, almost the same as that of high purity H13 steel. The high wear resistance of the new cast hotforging die steel can be attributed to its reasonable alloying design and nonsensibility to the detrimental function of S and P.     

Effects of Initial Structure and Reversion Temperature on Austenite Nucleation Site in Pearlite and Ferrite–Pearlite

Austenite nucleation sites were investigated in near-eutectoid 0.8 mass pct C steel and hypoeutectoid 0.4 mass pct C steel samples with full pearlite and ferrite–pearlite initial structures, respectively. In particular, the prior austenite grain size had been coarsened to compare grain boundaries in the hierarchical pearlite structure, i.e., the low-angle pearlite colony and high-angle block boundaries with ferrite/pearlite interfaces in the austenite nucleation ability. When the full pearlite in 0.8 mass pct C steel underwent reversion at a relatively low temperature, austenite grains preferentially formed at pearlite block boundaries. Consequently, when the full pearlite with the coarse block structure underwent reversion just above the eutectoid temperature, the reversion took a long time due to the low nucleation density. However, austenite grains densely formed at the pearlite colony boundaries as well, as the reversion temperature became sufficiently high. On the other hand, when ferrite–pearlite in the 0.4 mass pct C steel underwent reversion to austenite, the ferrite/pearlite interface acted as a more preferential austenite nucleation site than the pearlite block boundary even in the case of low-temperature reversion. From these results, it can be concluded that the preferential austenite nucleation site in carbon steels is in the following order: ferrite/pearlite interface?>?pearlite block?>?colony boundaries. In addition, orientation analysis results revealed that ferrite restricts the austenite nucleation more strongly than pearlitic ferrite does, which contributes to the preferential nucleation at ferrite/pearlite interfaces. This suggests that austenite grains formed at a ferrite/pearlite interface tend to have an identical orientation even under high-temperature reversion. Therefore, it is thought that the activation of austenite nucleation within pearlite by increasing the reversion temperature may be effective for rapid austenitization and the grain refinement of austenite structure after the completion of reversion in carbon steels.     

Explicit Power Formula for the Darcy–Weisbach Pipe Flow Equation: Application in Optimal Pipeline Design

Although the Darcy–Weisbach equation combined with the Colebrook–White semitheoretical formula for calculating the friction coefficient is a highly accurate generalized pipe-water flow resistance equation, most users prefer the use of simple, explicit power law form formulas. Because of their simplicity (despite their limitations) the purely empirical power formulas of Hazen–Williams and Manning remain the most popular pipe flow resistance equations used in routine hydraulic engineering applications. In this paper, a new simple power law form formula is derived to approximate the generalized Darcy–Weisbach combined with the Colebrook–White equation. The two main pipe flow parameters, such as the discharge (or velocity) and the diameter, appeared explicitly in the proposed formula. The suggested power-form formula compared with the Darcy–Weisbach and Coolbrook–White equation yields a maximum relative error of about ±4.5%. The power-form suggested formula is dimensionally homogeneous and its accuracy is sufficient for practical engineering applications. A correction factor is introduced for the variation of kinematic viscosity with temperature. The usefulness of the formula is demonstrated in an application concerning the optimal design of a delivery pipeline with pumping. The power form of the friction formula facilitates the formulation of the problem leading to the derivation of a simple equation from which the economic diameter is explicitly calculated.     

Effect of Phase-Selective Nanoscale Precipitates on the Bauschinger Effect in Austenitic–Ferritic Duplex Stainless Steels

Metallurgical and Materials Transactions A - The Bauschinger effect in austenitic–ferritic duplex stainless steel 1.4462 was investigated using tension–compression tests combined with...     

Effect of C–N Interaction on Hydrogen Embrittlement of 15Cr–15Mn–4Ni-Based Austenitic Stainless Steels

Hydrogen diffusion and embrittlement in an austenitic steel with 0.2 wt pct carbon and 0.2 wt pct nitrogen were investigated. The simultaneous alloying of both carbon and nitrogen did not reduce hydrogen diffusivity more than single alloying of nitrogen due to the interaction between carbon and nitrogen. During tensile straining, a low density of cracks initiated at the grain boundaries at an early deformation stage. The cracks propagated either along the grain boundaries and twin boundaries, or the paths where ε martensite was concentrated, which resulted in mixed intergranular and transgranular fracture modes. Still, the resistance to hydrogen embrittlement improved in comparison with the single alloying of either carbon or nitrogen due to enhanced austenite stability.

     

Improvement of Strength–Ductility Balance by the Simultaneous Increase in Ferrite and Martensite Strength in Dual-Phase Steels

Metallurgical and Materials Transactions A - This work investigates the effect of increasing both martensite phase and ferrite phase strength on tensile properties and fracture behavior of...     

Constitutive Equations for Flow Behavior of Powder-forged Fe-0.5C-2Cu Steel under Hot Compression

To investigate the hot deformation behavior of powder-forged(P/F)Fe-0.5C-2Cu steel,the hot compression tests were conducted at temperatures ranging from 900to 1 000 ℃ and strain rates from 0.1to 10s-1 using Gleeble-1500thermal simulator.The true stress-true strain curves at different temperatures and strain rates of P/F steel were obtained.It is found that dynamic recovery only occurs as strain rate is 10s-1 at 900℃,and the dynamic recrystallization is the main softening mechanism.The flow stress increases with decreasing temperature and increasing strain rate.The experimental data are employed to develop constitutive equations on the basis of the Arrheniustype equation by introducing the strain with nonlinear fitting.The flow stresses predicted by the proposed constitutive equations are in good agreement with the experimental values,and the correlation coefficient(R2)and the average absolute relative error(AARE)are 0.995 25and 3.07%respectively.These results indicate the proposed constitutive equations can effectively describe the hot deformation behavior of the material.     

Time–Temperature–Precipitation Relations for Nitrides and Evaluation of Internal Oxidation Theory for Nitridation of Austenitic Stainless Steel

Metallurgical and Materials Transactions A - Internal nitridation kinetics were determined for a UNS N08810/800H alloy using a general model of the form $$x^{n}=kt$$ . Nitridation behavior was...     

Analytical Solution for Biot Flow–Induced Damping in Saturated Soil during Shear Wave Excitations

This paper presents a theoretical study of Biot flow–induced damping in saturated soil during shear wave excitations. The solid skeleton is treated as equivalent linear. Biot flow–induced damping is evaluated for the cases of resonant column tests and site response analysis, based on the spectral response of a soil column/layer under harmonic torsional/horizontal excitations. Closed-form analytical solutions indicate that Biot flow–induced damping is hydraulic conductivity and frequency dependant. At the first resonance in a resonant column test, Biot flow–induced damping is dependent on a dimensionless hydraulic conductivity parameter K. For K within the range of 0.01 to 100, corresponding to coarse sands and clean gravels, Biot flow–induced damping may have an important contribution to total soil damping, especially at small strain levels. For site response analysis, Biot flow–induced damping should be considered for coarse sands and clean gravels, but can be practically neglected for fine sands, silts, and clays. The effects of soil porosity, mass coupling, and non-Poiseuille flow on Biot flow–induced damping are discussed.     

Effects of Adsorbed Water Layer in Predicting Saturated Hydraulic Conductivity for Clays with Kozeny–Carman Equation

Saturated hydraulic conductivity for clays predicted using the conventional Kozeny–Carman equation is scalar and found to diverge significantly from measured values. The divergence is consistent and systematic requiring a mathematical derivation of the formula using first principles. The incorporation of the physical characteristics of the adsorbed water layer surrounding a clay particle results in a generalized Kozeny–Carman equation with two new parameters. The porosity correction factor gives the effective porosity taking into account the thickness of the adsorbed water layer and the mass specific surface area of the clay. The second parameter is shown to depend on the interparticle contact area and the interparticle contact stress. The ability of the proposed physically based generalized Kozeny–Carman equation to explain the results from some of the published laboratory permeability tests is tested. The paper results in a new theoretical framework to model changes in saturated hydraulic conductivity in clays where the soil profile is compacting as a result of changes in pore-water pressure and or externally applied loads.     

Features of the Effect of Microstructure Characteristics on Corrosion Resistance of Cold-Rolled High-Strength Low-Alloy Steels (HSLA) Grade 260–300 for Automobile Building

Metallurgist - An experimental study is conducted on the effect of production parameters on the corrosion resistance of cold-rolled high-strength low-alloy steels (HSLA) grade 260–300,...     

Study of the Effect of Microstructure Characteristics on Corrosion Resistance of Cold-Rolled Micro-Alloyed Sheet Steels (Hsla) of Strength Classes 340–420 for Automobile Building

Metallurgist - The effect of microstructure characteristics and also production regimes on corrosion resistance of cold rolled high-strength low-alloy steels (HSLA) grades 340 and 420 is studied....     

Link between the Semi-empirical Andrade and Schytil Equations and the Statistical-Mechanical Born–Green Equation for Viscosity and Surface Tension of Pure Liquid Metals

The semi-empirical Andrade and Schytil equations are revisited for the melting point dynamic viscosity and surface tension of pure liquid metals. Both equations are derived in modified forms, with easy-to-use, dimensionless semi-empirical parameters. The modified equations are used to reproduce the theoretical equation of Born–Green on the ratio of surface tension and viscosity of pure liquid metals.