An experimental and theoretical study of heat-affected zone austenite reformation in three duplex stainless steels

Three duplex grades, one molybdenum-free, one 22Cr type, and one super duplex grade, have been subjected to weld simulation treatments, and the resulting microstructures have been quantified by automatic image analysis techniques. Substantial differences between the duplex grades were observed with an increased ability to reform austenite with increased alloying content. A theoretical model has been applied, based upon the paraequilibrium concept elaborated by Hillert, and the paraequilibrium compositions of individual phases were calculated as a function of temperature using the THERMOCALC database. A model based on Cahns theory of grain boundary nucleated reactions has also been utilized to calculate the kinetics of the reaction. By using this model, the grain size effects could be included in the treatment. The results of the calculations were compared with experimental data, and the experimental results were reproduced using the same parameter set for the three materials, with the exception of the diffusion coefficient values which had to be adjusted. This adjustment has in a later study been verified experimentally. The results validate the model used and the physical relevance of using the paraequilibrium model. The appropriateness of a paraequilibrium approach is also supported by experimental evidence from weld metal compositions. It is shown that the nitrogen content of the alloys plays an important role, and a higher nitrogen content results in more efficient austenite reformation. This implies that the alloy nitrogen compositions should lie close to the upper specification limits for these materials and nitrogen losses should be avoided on welding since the material properties, both mechanical and corrosive, are strongly related to the austenite-ferrite phase ratio.     

Thermodynamics of carbon in austenite and Fe-Mo austenite

A Cahn Electrobalance has been used to determine directly and very accurately the carbon content of iron, iron-0.48 wt pct molybdenum and iron-1.16 wt pct molybdenum specimens which were equilibrated with a series of methane-hydrogen gas mixtures of constant composition. The equilibria investigated involved the austenite phases of the alloys at 783, 813 and 848‡C. The experimental results permit direct calculation of the activities of carbon in the samples, relative to graphite as unity, and of the enthalpy and entropy of solution of carbon. The results are compared with the experimental measurements of a number of other investigators. The results are in excellent agreement with those of Smith and Schenck and Kaiser for the Fe-C system at 800‡C, and indicate -H _C ^/M values of 9700 ± 500 cal/mole for pure Fe, 10,030 ± 500 cal/mole for an Fe-0.48 wt pct Mo alloy, and 10,150 ± 500 cal/mole for an Fe-1.16 wt pct Mo alloy. The effect of molybdenum in austenite is to decrease the activity coefficient of carbon in austenite.     

Thermodynamics of carbon in austenite and Fe-Mo austenite

A Cahn Electrobalance has been used to determine directly and very accurately the carbon content of iron, iron-0.48 wt pct molybdenum and iron-1.16 wt pct molybdenum specimens which were equilibrated with a series of methane-hydrogen gas mixtures of constant composition. The equilibria investigated involved the austenite phases of the alloys at 783, 813 and 848‡C. The experimental results permit direct calculation of the activities of carbon in the samples, relative to graphite as unity, and of the enthalpy and entropy of solution of carbon. The results are compared with the experimental measurements of a number of other investigators. The results are in excellent agreement with those of Smith and Schenck and Kaiser for the Fe-C system at 800‡C, and indicate -H _C ^/M values of 9700 ± 500 cal/mole for pure Fe, 10,030 ± 500 cal/mole for an Fe-0.48 wt pct Mo alloy, and 10,150 ± 500 cal/mole for an Fe-1.16 wt pct Mo alloy. The effect of molybdenum in austenite is to decrease the activity coefficient of carbon in austenite.     

Experimental evidence for pretransitional fluctuations and domain movements

A review is given of the observation techniques by electron microscopy and electron diffraction which allow information to be obtained on phase transitions and pretransitional phenomena in solids. The review is illustrated with a few examples of different types of transitions. The α→ β phase transition in quartz is discussed in some more detail. It is shown that in this case defect mobility is responsible for the observed pretransitional phenomena. Observations are reported of shimmering phenomena in two alloy systems: CuZnAl and a γ-brass (Cu₄A₁₉). The experimental conditions of appearance of the phenomena in these different systems are compared and related with possible physical origins. This paper is based on a presentation made at a symposium on “Pretransformation Phenomena, Fluctuations and Related Effects” held at the annual meeting of The Metallurgical Society of AIME, New Orleans, Louisiana, February 18–22, 1979, under the sponsorship of the Structures Activity, Materials Science Division, ASM.     

Experimental evidence for fatigue during sliding wear

Metallurgical and Materials Transactions A -     

Solubility product for niobium carbide in austenite

The solubility product for NbC_0.87 has been experimentally determined between 950° and 1250 °C by gas equilibration and extraction methods. The new relation log₁₀[pct Nb] [pct C]^0.87 = 3.4 − 7920/T on a weight percent basis has been evaluated from the data. This is in good agreement with a compendium of measurements from the literature. The data do not yet justify an analysis which takes account of a variable stoichiometry.     

Experimental evidence for Moraxella-induced penicillin neutralization in pneumococcal pneumonia

Resistance of microorganisms to antimicrobial agents is an increasing problem in the treatment of infectious diseases. In mixed infections, an interesting development can arise when one organism protects another from being killed by an antibiotic. Unfortunately, in the case of respiratory tract infections, experimental evidence of this development is poor. In this study, mice intranasally infected with a lethal number of pneumococci and treated with a curative dose of penicillin or amoxicillin died from pneumococcal pneumonia when they were coinoculated with beta-lactamase-producing Moraxella catarrhalis. beta-lactamase-negative M. catarrhalis did not show a similar indirect pathogenic effect. Treatment with a combination of amoxicillin and the beta-lactamase inhibitor clavulanic acid was not affected by beta-lactamase-producing M. catarrhalis. These findings help explain antibiotic failure in respiratory tract infections, even though the causative microorganism is sensitive to the antibiotic in vitro.     

Experimental determination of the stability of retained austenite in low alloy TRIP steels

The stability of retained austenite is the most important parameter controlling the transformation plasticity effects in multiphase low alloy TRIP steels. In this work the thermodynamic stability of the retained austenite has been determined experimentally by measuring the M^σ_s temperature as a function of bainite isothermal transformation (BIT) temperature and time in two low alloy TRIP steels. A single-specimen temperature-variable tension test technique (SS-TV-TT) has been employed, which allowed to link the appearance of yield points in the stress-strain curve with the mechanically-induced martensitic transformation of the retained austenite. The results indicated that the M^σ_S temperature varies with BIT temperature and time. Higher austenite stability is associated with a BIT temperature of 400°C rather than 375°C. In addition, the chemical stabilization of the retained austenite associated with carbon enrichment from the growing bainite is lowered at short BIT times. This stability drop is due to carbide precipitation and comes earlier in the Nb-containing steel. At longer BIT times the retained austenite dispersion becomes finer and its stability rises due to size stabilization. The experimental results are in good agreement with model predictions within the range of anticipated carbon enrichment of the retained austenite and measured austenite particle size.     

Negotiation behavior and outcomes: Empirical evidence and theoretical issues.

This article examines the ability of the individual differences, motivational, and cognitive approaches of negotiation to account for empirical research on dyadic negotiation. Investigators have typically focused on objective, economic measures of performance. However, social-psychological measures are important because negotiators often do not have the information necessary to make accurate judgments of the bargaining situation. Negotiators' judgments are biased, and biases are associated with inefficient performance. Personality and individual differences appear to play a minimal role in determining bargaining behavior; their impact may be dampened by several factors, such as homogeneity of S samples, situational constraints, and self-selection processes. Motivational and cognitive models provide compelling accounts of negotiation behavior. A psychological theory of negotiation should begin at the level of the individual negotiator and should integrate features of motivational and cognitive models. (PsycINFO Database Record (c) 2010 APA, all rights reserved)