Austenitic Iron Research Articles

Influence of abrasive hardness on the wear resistance of high chromium irons

The resistance to abrasive wear was determined for a series of alloyed white cast irons in a high stress abrasion test which utilizes a specimen in sliding contact with bonded abrasives. These were conducted on silicon carbide, alumina and two sizes of garnet abrasive. The results indicate that the hardness, or type, of abrasive used in the test significantly influenced the wear rate of white irons, i.e. the rate of wear increased with increasing hardness of the abrasive. Also, the results indicate that the type of abrasive used in the test was a significant factor in ranking white irons for resistance to high stress abrasion. When tested on silicon carbide or alumina abrasive, as-cast austenitic irons exhibited lower rates of wear than heat treated martensitic irons; when tested on garnet, an abrasive of lower hardness, those irons with martensitic matrix microstructures exhibited the same or less wear than irons with austenitic matrix microstructures. It was also evident that heat treated irons with martensitic matrix microstructures exhibited varying degrees of resistance to abrasive wear depending on cooling rates and alloy content.

Plastic deformation of austenitic iron at intermediate strain rates

Plastic deformation of austenitic iron at intermediate strain rates

Onset of recrystallization during the tensile deformation of austenitic iron at intermediate strain rates

Onset of recrystallization during the tensile deformation of austenitic iron at intermediate strain rates

Tensile failure of austenitic iron at intermediate strain rates

The basic failure behavior of austenitic iron has been established for the temperature range 950 to 1350°C and the strain-rate range 2.8 x 10-5 to 2.3 x 1(10-2 s-1. Failure in zone-refined iron is determined solely by plastic deformation, leading first to multiple necking, continuing by the exclusive growth of a single neck, and concluding by separation at a point within that neck. With the increasing impurity content of electrolytic iron, Fe-0.05 C and Fe-5.2 Mn, this failure process is interrupted at the lower temperatures by fracture at either second-phase particles or grain boundaries. The regimes of these two fracture modes have been determined as functions of strain rate, deformation temperature, and annealing temperature. Recrystallization is prevalent during the plastic deformation of austenitic iron and influences the necking process to some extent. Recrystallization is more influential as a means of stabilizing arrays of intergranular cracks, thereby allowing the cracks to undergo appreciable plastic deformation during the final stage of failure. The concept of failure diagrams is introduced as a simple means of representing the complex interposition of plastic instability, recrystallization, and fracture during the failure process.

Onset of recrystallization during the tensile deformation of austenitic iron at intermediate strain rates

The onset of recrystallization during the tensile deformation of austenitic iron has been fully documented for the temperature range 950 to 1350°C and strain-rate range 2.8 × 10-5 to 2.3 × 10-2 s-1. Representative materials are zone-refined iron, electrolytic iron, Fe−0.05 C and Fe−5.2 Mn. In general, the strain at the onset of recrystallization decreases with increasing temperature of deformation and decreasing strain rate. The postponement of recrystallization is favored by prior annealing at temperatures above 1200°C and is greatest for the Fe−5.2 Mn alloy; however, for the range of strain rates used, it is difficult to completely eliminate recrystallization. The effects of test conditions on the onset of recrystallization are discussed in terms of a nucleation process that requires a critical amount of stored energy.

Plastic deformation of austenitic iron at intermediate strain rates

The plastic deformation of austenitic iron, represented by a zone-refined iron, an electrolytic iron, an Fe−0.05 C alloy, and an Fe−5.2 Mn alloy, has been documented for the temperature range 950 to 1350°C (1740 to 2460°F) and the strain-rate range 2.8 × 10−5 to 2.3 × 10−2 s−1. The intrusion of recrystallization during deformation restricts the documentation to initial periods of strain usually less than 0.10. The general problem of retaining grain structures representative of polycrystals in specimens annealed at temperatures above 0.95T m is recognized, and a basis for its solution is presented. Chemical composion appears to influence the plastic-flow behavior of austenitic iron primarily through its effect on the grain structure. Thus, the large-grained zone-refined iron is relatively weak, and the difference in behavior between the Fe−0.05 C alloy and the Fe−5.2 Mn alloy is small.

Tracer diffusion of59Fe and51Cr in Fe-17 Wt Pet Cr-12 Wt Pet Ni austenitic alloy

The volume and grain-boundary diffusion of59Fe and51Cr have been studied in an austenitic iron alloy containing 17 wt pct Cr and 12 wt pct Ni. The diffusivities in this alloy of these two tracers and63Ni are compared with their diffusivities in pure iron and in other austenitic stainless steels. For volume diffusion at any particular temperature in the present alloy, Cr is the most rapid while Ni is the slowest, and all three tracers diffuse slower than that reported for pure iron or for other austenitic stainless steels. For grain-boundary transport, Fe diffuses most rapidly above 850°C and Ni diffuses most rapidly below that temperature. The activation energies for both volume and grain-bounary diffusion obey the relationshipQ Ni <Q Cr <Q Fe.

The “Central Atoms” model of multicomponent interstitial solutions and its applications to carbon and nitrogen in iron alloys

The “Central Atoms” model has been generalized to multicomponent interstitial solutions. The probabilities of various configurations in the nearest neighbor shell of an atom have been calculated and the thermodynamic properties of the mixture deduced. At a given temperature, the effect of an alloying element on the interstitial solute under consideration is analyzed in terms of a single parameter describing the bonding between the two kinds of atoms. The expressions of first and second order free energy interaction coefficients have been deduced. The model has been applied to carbon in austenitic and liquid iron alloys and describes successfully its activity at both low and high concentrations. In particular, interaction coefficients defined at infinite dilution can be satisfactorily predicted from the solubility of graphite. The solubility of nitrogen in multicomponent iron alloys at 1600°C was also calculated satisfactorily through the model.

ALMANITE WSH

Abstract ALMANITE WSH is an austenitic nodular iron possessing superior tensile strength, toughness and ability to work harden under conditions of severe pounding impact. It is recommended for crusher liners, hammers, grinding balls, etc. This datasheet provides information on composition, physical properties, hardness, elasticity, and tensile properties as well as fracture toughness. It also includes information on casting, heat treating, machining, and surface treatment. Filing Code: CI-40. Producer or source: Meehanite Metal Corporation.

THE PARTICLE-TO-MATRIX BOND IN DISPERSION-HARDENED AUSTENITIC AND FERRITIC IRON ALLOYS

The bonding strength, or ‘work of adhesion’, W, between particle and matrix in a number of austenitic and ferritic iron alloys has been determined from electron micrographs of the solid/solid contact angle, θ, at cavities formed by cold working and annealing. The critical strain to bring about cavitation, ec, was measured by plotting the strain corresponding to a sudden fall in rate of work-hardening. In deriving an equation to predict ec, account must be taken of the dependence of the equilibrium shape of the cavity on θ. Good correlation between experimental and predicted ec, as a function of W, was found. Brittle fracture of the matrix is likely to occur if θ is very low and the volume fraction is high. A criterion for brittle fracture, based on θ, is suggested which successfully predicts brittle fracture in one of the alloys studied.

低合金鋼のオーステナイトにおけるニオブ炭化物およびニオブ窒化物の溶解度

The solubilities of niobium carbide and nitride in iron austenite containing about 3%Ni and 1.5%Cr or 3%Ni, 1.5%Cr, 1%Mn and 0.4%Si have been measured by the method of equilibration with methane-hydrogen mixture gas or nitrogen.The measured values of the solubility products of niobium carbide and nitride in the low-alloyed iron austenite agree approximately well with the calculated values obtained by adding arithmetically the part dependent on the content of alloying element in the logarithms of the solubility products of them in iron austenite containing each one of the elements. The results support the thermodynamic consideration on the solubility products of compounds in the multi-component solution.

The formation of Hcp and Bcc phases in austenitic iron alloys

The formation of the hcp (∈) and bcc (α) structures in pure iron under high pressure conditions, as well as the morphological and crystallographic aspects of martensitic transformation to these structures at atmospheric pressure in iron alloys, are reviewed., It is concluded that the unique features of α- or lath martensite formation are not dependent upon the presence of the ∈ phase. Application of the phenomenological theory of martensitic transformation has not successfully rationalized the crystallography of lath-martensite. The criterion for ∈- and α-phase formation is established using the regular solution approximation and appropriate lattice stability parameters. In particular, the ∈ phase can be formed in Fe−Ni−Cr compositions through stress-induced transformation attending α-martensite formation. Further consideration suggests that the ∈→α transformation is not expected at atmospheric pressure at temperatures below approximately 500°K in the alloys considered. Thus, two martensitic transformations, γ→∈ and γ→α, can occur jointly in certain alloys.

The low temperature properties of austenitic cast irons

The tensile strengths of austenitic flake and nodular graphite irons increase rapidly with falling temperatures in the range 295 to 75 K. An initial increase in elongation may be observed, but when martensite is formed on cooling, elongation values decrease rapidly. The proof stress values for stable austenitic irons increase with falling temperature. The notched impact values of austenitic flake graphite irons show little variation with temperature. The impact values of austenitic nodular graphite irons, on the other hand, may show an initial increase, or remain constant with falling temperature, until the formation of martensite causes a rapid decrease. Some austenitic irons show a progressive decrease in elongation and impact value at temperatures below room temperature (295 K), although the austenite remains stable.

オーステナイト鉄中におけるニオブ窒化物の固溶-析出反応におよぼすMn, Si, CrおよびNiの影響

オーステナイト鉄中におけるニオブ窒化物の固溶-析出反応におよぼすMn, Si, CrおよびNiの影響

オーステナイト鉄中におけるニオブ炭化物の固溶-析出反応におよぼすMn,Si,CrおよびNiの影響

オーステナイト鉄中におけるニオブ炭化物の固溶-析出反応におよぼすMn,Si,CrおよびNiの影響

Thermodynamics of austenitic Fe-C alloys

New data on the activity of carbon in austenite have been obtained by CO2/CO equilibration of Fe-C alloys in the temperature range 900° to 1400°C. Equations for the thermodynamic properties of carbon and iron in austenite are obtained from the data combined with selected data from the literature. A slightly modified phase diagram is presented. The stability of cementite is also determined from data published earlier and the results of the present study. Parameters of the various models of the behavior of carbon in austenite taken from the literature are also calculated from the data.

高圧窒素ガスのオーステナイト鉄への溶解度および鉄-窒素系侵入型固溶体の熱力学的性質

Studies on the equilibrium between austenitic iron and nitrogen under various conditions of the maximum pressure of 920 kg/cm2 and the temperature range of 950°∼1300°C were carried out using a high temperature-high pressure equipment. It was shown that the concentration of nitrogen in austenite deviates from Sieverts’ law with increasing pressure. The cause for such discrepancy was considered thermodynamically and statistically. That is, the experimental result can reasonably be explained from the geometrical consideration that the chemical potential of a nitrogen atom in austenite with a high nitrogen content, departs remarkably from the value for the ideal random interstitial solid solution, since each interstitial atom added excludes other interstitial atoms from the seven adjacent sites. Thus, the activity of nitrogen in austenitic iron can be expressed by the following equations:(This article is not displayable. Please see full text pdf.)

Partial Molar Volumes from High-Temperature Lattice Parameters of Iron–Carbon Austenites

AbstractThe lattice parameters of a number of iron–carbon alloys have been measured in the austenite field for temperatures up to 1200° C (1473 K). By extrapolation and interpolation of these data the variation with carbon concentration of the lattice parameter of austenite has been determined for a wide range of temperatures, and used to calculate partial molar volumes of iron and carbon in austenite. Both partial molar quantities show little variation with composition but V c, γ decreases with increasing temperature, while V Fe, γ increases. The values obtained for the partial molar volume of carbon in austenite are appreciably lower than those cited earlier. It is probable that the differences previously reported between the measured and calculated effect of pressure on the composition of austenite in equilibrium with cementite at 727° C (1000 K), are due primarily to the use in the calculations of too high a value for the partial molar volume of carbon in austenite.

Oxidation and Decarburization Kinetics of Iron‐Carbon Alloys

The early stages of the oxidation‐decarburization kinetics have been investigated for austenitic iron alloys of carbon contents 0.23–1.07 w/o exposed to carbon dioxide‐carbon monoxide atmospheres at the temperature of 950°C. Complex reaction behavior was observed for these alloys in the range 10–100 v/o carbon dioxide. The initial selective oxidation of carbon from sheet specimens exhibited linear kinetics. During late stage scale growth of wustite crystals, decarburization occurred by gaseous transport of carbon oxides through pores in the oxide. An oxidation‐decarburization model based on surface controlled reaction steps accounted most adequately for decarburization and wustite formation before onset of control by diffusion processes.

DIRECT ELECTRIC-FIELD ELECTROTRANSPORT OF CARBON AND NITROGEN IN IRON AND IRON ALLOYS

The interstitial mobility of carbon and nitrogen in austenite iron is determined from diffusion experiments carried out in a direct electric field. Diffusion-penetration curves are obtained, using a microhardness technique, and related to the "apparent charge" of the solutes by the Einstein equation. The apparent charge of carbon is positive, increasing from +8.6 ± 1.0 at 950 °C to +13.7 ± 1.7 at 842 °C. The apparent charge of nitrogen is negative, increasing from −8.3 ± 1.0 at 1 000 °C to −14.1 ± 1.7 at 922 °C. Positive Hall coefficients are found for both systems at 925 °C. The effect of 4% manganese in iron is to increase the apparent charge of carbon to ~ +9.3, while 2% silicon in iron decreases the apparent charge of carbon to ~ +4.7 at 950 °C. The results obtained are discussed in relation to the band structure of the alloys and the effect of electron or "hole" momentum transfer to the lattice. A possible alternative mechanism is also proposed which could contribute to the high apparent charge obtained for the solutes.