Showing papers on "Austenite published in 1970"
TL;DR: In this paper, the mechanical properties of several austenitic steels containing γ′ precipitate have been studied and a large increase in proof stress occurs during ageing as a result of particle growth at almost co...
Abstract: The mechanical properties of several austenitic steels containing γ′ precipitate have been studied. A large increase in proof stress occurs during ageing as a result of particle growth at almost co...
217 citations
01 Jun 1970
TL;DR: In this paper, the authors show that during deformation, strain induced γ → ∈ → α transformation occurs with further thermal nucleation of α achieved by aging up to 400°C.
Abstract: Mechanical and thermal-mechanical treatments of 304 stainless steel enables yield strengths of over 200,000 psi to be obtained with elongations better than 10 pct. Electron microscopy, X-ray, and magnetic techniques show that during deformation, strain induced γ → ∈ → α transformation occurs with further thermal nucleation of α achieved by aging up to 400°C. The yield strength is linearly proportional to the amount of ° irrespective of the treatment used to form α. The yield strength is given by αy = 225f + 48.65 ksi, where ƒ is the volume fraction of martensite. Softening occurs by aging at 500°C and above due to a decrease in percent α which may occur by renucleation of γ. The system is an unusual form of composite strengthening; hard martensite particles are formed within the austenite, and the percent α (and thereby the mechanical properties), can be controlled by the mechanical/thermal-mechanical processing.
176 citations
01 May 1970-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this article, the activity of carbon in austenite has been obtained by CO2/CO equilibration of Fe-C alloys in the temperature range 900° to 1400°C.
Abstract: 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.
107 citations
01 Jun 1970
TL;DR: In this paper, the authors measured the resistance of austenite to plastic deformation (austenite flow stress) using a high temperature tensile apparatus and correlated the flow stress with the Ms temperature as determined magnetically during subsequent cooling.
Abstract: The resistance of austenite to plastic deformation (austenite flow stress) was measured using a high temperature tensile apparatus. The flow stress was then correlated with the Ms temperature as determined magnetically during subsequent cooling. In one part of the study, the flow stress of the austenite was varied only by work hardening the austenite, allowing the austenite composition, which is known to affect Ms, to be held constant. A decrease in Ms temperature with increasing austenite flow stress was observed. This observation was supported by the observation of a decrease in the amount of austenite transformed at 25°C. In the other part of the study, a series of alloy steels of different chemical compositions was tested. A decrease in Ms temperature with increasing austenite flow stress was again observed. Strengthening of austenite by plastic deformation was shown not to change the chemical driving force for transformation. The effect of deformation on Ms temperature thus results from its influence on either the nucleation or the growth process. While the effect of austenite deformation on martensite nucleation is uncertain, specific nucleation models can account for only approximately one-third of the nonchemical free energy change which accompanies transformation. A proposal, consistent with the observations, was made that the energy expended for the deformation of austenite during martensite plate growth could reasonably account for a substantial part of the nonchemical free energy change.
77 citations
DOI•
01 Dec 1970TL;DR: In this article, phase transformations in Fe−Mn alloys containing up to 9 pct Mn were studied by optical and electron transmission microscopy and the mechanical properties of all the transformation products were evaluated using tensile and impact testing and are discussed in terms of the observed microstructural features.
Abstract: Phase transformations in Fe−Mn alloys containing up to 9 pct Mn were studied by optical and electron transmission microscopy. Either equiaxed ferrite, massive ferrite, or massive martensite can form on cooling from austenite. The particular type of transformation product formed was found to depend on the alloy content, austenite grain size, and cooling rate. The mechanical properties of all the transformation products were evaluated using tensile and impact testing and are discussed in terms of the observed microstructural features. Yield strength and impact transition temperature were found to be relatively insensitive to manganese content but were strongly influenced by the transformation substructure and grain size of the transformed phase. In martensite it has been shown that the structural unit analogous to grain size in ferrite is the martensite packet size, which in turn is controlled by the prior austenite grain size. The fracture surface of broken impact specimens and the fracture profile were examined by means of electron and optical microscopy techniques. These fractographic observations were correlated with impact test data and microstructural observations of the various transformation products.
61 citations
01 Aug 1970
TL;DR: In this paper, a high purity Fe-C alloy of eutectoid composition has been transformed from homogenized austenite in two ways: isothermally and at forced constant-velocity.
Abstract: A high purity Fe-C alloy of eutectoid composition has been transformed from homogenized austenite in two ways: isothermally and at forced constant-velocity. The latter transformation mode, forced over five decades of velocity, produces structures with characteristic dimensions ranging over nearly two orders of magnitude. There is a consistent alignment of the transformation product in the heat-flow direction at all velocities, but the classical pearlite morphology undergoes a microstructural transition at the higher velocities. A spacing-velocity relationship for regular lamellar pearlite was measured as V0.41±o.02λν = constant.
58 citations
01 Jun 1970
TL;DR: In this paper, the heat treatment response of a 350-grade maraging steel, with the nominal composition 18.5 Ni, 12 Co, 4.6 Mo, 1.4 Ti, balance Fe, has been determined in billet and bar form.
Abstract: The heat treatment response of a 350-grade maraging steel, with the nominal composition 18.5 Ni, 12 Co, 4.6 Mo, 1.4 Ti, balance Fe, has been determined in billet and bar form. When aged at temperatures below 900°F, the material was very susceptible to subcritical crack growth, and premature brittle fracture occurred in unnotched tension specimens loaded at a slow strain rate in laboratory air. Fracture mechanics was used to interpret this behavior. The introduction of reverted austenite significantly decreased the strength level but had little effect on fracture toughness. The resistance to brittle fracture of this material is contrasted with that of high-strength steels currently used by the airplane industry.
53 citations
TL;DR: The lattice parameters of a number of iron-carbon alloys have been measured in the austenite field for temperatures up to 1200° C (1473 K) as mentioned in this paper.
Abstract: The 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.
TL;DR: In this paper, the early stages of growth of martensite platelets were observed by means of electron microscopy, and the authors found that very thin martensites were found to be in association with austenite stacking faults.
01 Jun 1970
TL;DR: In this article, the effect of carbon content, grain size, quench rate, and retained austenite on microcracking in Fe-C martensites was investigated.
Abstract: Metallographic analysis was used to study the effect of carbon content, grain size, quench rate, and retained austenite on microcracking in Fe-C martensites. It was found that microcracking is directly related to an increase in the carbon content of the martensite and that there exists a carbon content which corresponds to both the onset of microcracking and the formation of plate martensite. Retained austenite indirectly affects microcracking in that more complete transformation yields more martensite and consequently more microcracking. Grain size changes from 100 to 1200 μ, introduced by varying the austenitizing temperature from 1800° to 2400°F and varying the time at 2000°F for 15 hr, did not affect microcracking or the amount of retained austenite. Finally, the investigation emphasizes that microcracking is a manifestation of the impingement of martensite plates and is not a function of the stress state introduced by the quenching medium.
01 Jul 1970
TL;DR: In this paper, the mechanical properties of a series of stainless steels ranging in composition from 16.5 pct Cr, 5.9 pct Ni to 23.9pct Ni have been determined.
Abstract: The mechanical properties of a series of stainless steels ranging in composition from 16.5 pct Cr, 5.5 pct Ni to 23.9 pct Cr, 2.9 pct Ni have been determined. The series of alloys lie along an approximate 1700°F tie line with room temperature microstructures ranging from 100 pct martensite to 100 pct ferrite. Yield and tensile strengths increased directly with increasing martensite content. In alloys containing on the order of 40 to 60 pet martensite, the presence of a fine dispersion of tougher, albeit stronger, martensite was quite effective in lowering the ductile-to-brittle impact transition temperature.
01 Feb 1970-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: In this paper, a technique has been developed for controlling the grain size of 18 pct Ni maraging steels by thermal treatment alone, which has been applied to two different grades, 250 and 300, of maraging steel, and a large grain size, ASTM 2, was reduced to ASTM 7.
Abstract: A technique has been developed for controlling the austenitic grain size of 18 pct Ni maraging steels by thermal treatment alone. This treatment has been applied to two different grades, 250 and 300, of maraging steel, and a large grain size, ASTM 2, was reduced to ASTM 7 in both cases. The process of grain size refinement requires thermal cycling from a temperature belowM
f to a temperature considerably above the austenitizing temperature. The minimum austenitic grain size attainable depends on the prior strain in the material as well as the thermal treatment. While significant grain size refinement can be attained by one cycle to the proper temperature, the attainment of the minimum uniform grain size requires several cycles. The effects of austenitic grain size on tensile properties have been investigated both at room temperature and at elevated temperatures. The prior austenitic grain size has a small but measurable effect on the mechanical behavior of aged material at room temperature. The austenitic grain size has a significant effect on the ultimate tensile strength at 1600°F.
TL;DR: In this paper, the authors examined the stress corrosion cracking of Type 304 austenitic stainless steels and alloys containing additions of Cu, Co, Ni, and Si in MgCl2 boiling at 154 C (310 F) by scanning electron microscopy.
Abstract: The stress corrosion cracking of Type 304 austenitic stainless steels and alloys containing additions of Cu, Co, Ni, and Si in MgCl2 boiling at 154 C (310 F) has been examined fractographically by scanning electron microscopy. Type 304 steels and alloys containing Co and Cu exhibit mainly a coalescing pattern of cracking as a result of multiple crack nucleation and some flat crystallographic regions. Alloys containing Ni and Si exhibit mainly flat fractures with some coalescence. Since the type of fracture observed is not dependent upon the stacking fault energy it is suggested that the principle effect is chemical: Crack nucleation is rendered difficult by additions of Ni and Si and the rate of propagation is lowered. Stress corrosion fracture in autoclave conditions appears to be similar. Some intergranular stress corrosion cracking occurred in all the alloys examined.
01 May 1970-Metallurgical and Materials Transactions B-process Metallurgy and Materials Processing Science
TL;DR: The most important parameter in the theoretical activity equation is the pairwise binding energy Δe between two nearest-neighbor solute atoms as mentioned in this paper, which is independent of both temperature and composition.
Abstract: The recent extensive data for the variation with temperature and composition of the activity of carbon in austenite has been analyzed using a quasichemical model for interstitial solid solutions. The most important parameter in the theoretical activity equation is the pairwise binding energy Δe between two nearest-neighbor solute atoms. A computer fitting method has shown that the new activity data for austenite, which spans a temperature range from 900° to 1400°C and compositions ranging from very dilute up to the limiting composition of the phase boundary, are compatible with the theoretical model with a Δe-value of -2 kcals per mole which is independent of both temperature and composition.
TL;DR: In this paper, the structural changes taking place in a commercial AISI Type 310 steel at temperatures in the range 650° to 950°C have been examined for times of up to 900 hours by means of optical metallographic techniques.
01 Jun 1970
TL;DR: In this article, the effect of thermomechanical treatment on the tensile properties of metastable manganese austenites was determined, and deformation-induced transformation characteristics were analyzed by X-ray diffraction and by data derived from stress-strain curves.
Abstract: The effect of thermomechanical treatment on the tensile properties of metastable manganese austenites was determined, and deformation-induced transformation characteristics were analyzed by X-ray diffraction and by data derived from stress-strain curves. An improved combination of tensile strength and ductility is obtained through a processing treatment entailing ausforming and deformation-induced transformation. The two treatments are very strongly interrelated, the first imposing some limiting factors on the latter. After small ausforming deformation, the strain-induced austenite-to-martensite transformation at room temperature is slightly stimulated, but additional increments of austenite deformation have a strong retarding effect. It is concluded that the formation of a strong martensite in a work-hardened austenite matrix is most effective in enhancing strength and ductility.
TL;DR: For comparison with carbon austenite, this article proposed a solute-solute binding energy derivation from experimental data for comparison with CO 2, and showed that CO 2 is more stable than CO 2.
Patent•
23 Dec 1970
TL;DR: An austenitic-ferritic stainless steel consisting essentially of up to about 0.06 percent carbon, about 4.0 to less than 11.0 percent manganese, about 19 to about 24 percent chromium, 0.12 to 0.26 percent nitrogen, nickel, and iron, with a balance between 10 percent and 50 percent austenite, is stable as discussed by the authors.
Abstract: An austenitic-ferritic stainless steel consisting essentially of up to about 0.06 percent carbon, about 4.0 to less than 11.0 percent manganese, about 19 to about 24 percent chromium, about 0.12 to about 0.26 percent nitrogen, nickel up to about 3.0 percent, and remainder substantially iron except for incidental impurities. The austenite-ferrite balance, ranging between 10 percent and 50 percent austenite, is stable, and the steel exhibits high toughness, corrosion resistance and excellent weldability.
TL;DR: In this paper, Niobium-free steel was applied to 20 Cr/25 Ni steel and denuded zones were formed near grain boundaries, which caused the strain to be concentrated in grain boundary regions during creep, leading to the formation of surface and wedge-cracks at grain boundaries.
Abstract: Stabilisation of 20 Cr/25 Ni steel by niobium not only increased the creep resistance but eliminated the tendency for cracking and thereby enhanced the ductility. No change in density was detected in fine-grained specimens solution-treated at 1000° C until well into tertiary creep, and elongations of 75 to 150% were obtained. After a solution-treatment at 1250° C the creep resistance was further increased and denuded zones were formed near grain boundaries. This caused the strain to be concentrated in grain boundary regions during creep, leading to the formation of both surface- and wedge-cracks at grain boundaries. However, in contrast to a niobium-free steel, these did not nucleate until the end of the secondary creep.
TL;DR: In this paper, the development of cavitation during creep has been examined in an unstabilised 20 Cr/25 Ni austenitic stainless steel, using precise density measurements as an indicator of the level of cavitations.
Abstract: The development of cavitation during creep has been examined in an unstabilised 20 Cr/25 Ni austenitic stainless steel, using precise density measurements as an indicator of the level of cavitation. The change in density was proportional to the duration of creep to the power of 3.0 increasing to 4 to 5 just before fracture, and this time exponent was not affected by either grain size or irradiation. Metallographic examination showed that wedge-cracks were the predominant mode of cavitation and helium bubble growth in irradiated specimens increased the rate of crack propagation, thus reducing the ductility. A simple model for the growth of triple-point cracks is used to explain the experimentally observed changes in density.
TL;DR: Mossbauer effect measurements of the temperature dependence of the hyperfine field for several austentic stainless steels are reported in this article, where a broadening of the single linewidth occurred for each specimen at a temperature near its transition temperature.
Abstract: Mossbauer‐effect measurements of the temperature dependence of the hyperfine field for several austentic stainless steels are reported. Antiferromagnetic transitions were observed for all specimens in the temperature range below 56°K. In addition, a broadening of the single linewidth occurred for each specimen at a temperature near its transition temperature. The transition temperature is interpreted to be a measure of the Neel temperature of antiferromagnetic γ‐phase iron.
Patent•
14 Oct 1970
TL;DR: A bearing steel consisting of 0.55 to 0.78 percent of carbon, 0.50 to 2.00 percent of chromium and 0.10 to 1.15 percent of manganese, with the balance iron having been spheroidized during annealing, and afterward, heated to an austenitizing temperature ranging from about 810 DEG to 870 DEG C..
Abstract: A bearing steel consisting of 0.55 to 0.78 percent of carbon, 0.50 to 2.00 percent of chromium, 0.10 to 1.15 percent of manganese and 1.00 to 2.00 percent of silicon by weight with the balance iron, said steel having been spheroidized during annealing, and afterward, heated to an austenitizing temperature ranging from about 810 DEG to 870 DEG C. for a period of about 30 minutes to dissolve 0.35 to 0.55 percent by weight of carbon into austenite retaining 3 to 6 percent by weight of undissolved spheroidized iron carbide, liquid quenched and tempered at about 150 DEG C.
TL;DR: In this paper, a theoretical model of neutron damage in austenitic steel was adjusted with available creep-strain data for irradiated at temperatures below ∼ 400°C, yielding a damage function for the neutron-energy dependence of irradiation-induced creep strain.