Showing papers on "Austenite published in 1977"
232 citations
TL;DR: In this article, the conditions of (Δ∈p/2, T) necessary to induce the γ → α′ phase transformation under low cycle fatigue conditions have been studied in an Fe 18Cr6.5Ni0.19C stainless steel, where the formation of α′ martensite was detected magnetically during testing and by using X-ray measurements at failure.
143 citations
TL;DR: The intrinsic stacking fault energy of a f.c. Alloy was measured for various temperatures in the temperature range 100 −390 K using observations of dislocation nodes by transmission electron microscopy and shear modulus determinations as discussed by the authors.
110 citations
TL;DR: Mossbauer Fe57 spectroscopy allows comparison of Fe−N and Fe−C interstitial solid solutions as discussed by the authors, showing that nitrogen atoms are randomly distributed on octahedral sites in the retained austenite and in the virgin martensite.
Abstract: Mossbauer Fe57 spectroscopy allows comparison of Fe−N and Fe−C interstitial solid solutions. The spectra of Fe−N retained austenite indicate that nitrogen atoms are randomly distributed on octahedral sites in the austenite and in the virgin martensite. On heating, austenite decomposes directly to the equilibrium phases α iron and Fe4N at temperatures above 160°C. Virgin martensite ages at room temperature by local ordering of nitrogen atoms. In that process, three new iron atom environments develop, characteristic of the Fe16N2 (α″) structure. However, the excessive width of the peaks indicate the perfect order of the Fe16N2 precipitate is not achieved, except after very long times. Further aging at 100°C leads to the complete decomposition of the virgin martensite to the discrete phases α iron and Fe16N2. This two phase structure is stable up to 160°C, above which the precipitation of Fe4N occurs. These results are in contrast to Fe−C data. Carbon atoms in retained austenite tend to be far apart in their octahedral sites, and this nonrandom distribution is inherited by the virgin martensite. Fe−C austenite decomposes by the formation of ∈ carbide below 160°C and precipitation of Fe3C above 180°C. The carbon atoms in virgin martensite agglomerate at room temperature and regions of ordered Fe4C are believed to result. Subsequently ∈ carbon is formed at 80°C and Fe3C precipitates above 160°C.1
100 citations
TL;DR: In this paper, the plane-strain fracture toughness and the tensile ultimate and yield strengths of 300M steel were evaluated and shown that substantial improvement in toughness with no loss in strength can be achieved in quenched and tempered steel by austenitizing at 1255 K (1800°F).
Abstract: 300M steel was subjected to a wide range of quenched and tempered heat treatments. The plane-strain fracture toughness and the tensile ultimate and yield strengths were evaluated. Results indicate that substantial improvement in toughness with no loss in strength can be accomplished in quenched and tempered steel by austenitizing at 1255 K (1800°F) or higher. Low fracture toughness in conventionally austenitized 300M steel (1144 K (1600°F)) appears to be caused by undissolved precipitates seen both in the submicrostructure and on the fracture surface which promote failure by quasi-cleavage. These precipitates appeared to dissolve in the range 1200 to 1255 K (1700 to 1800°F).
84 citations
TL;DR: In this paper, the effect of austenite prestrain above the md temperature on the structure and transformation kinetics of the martensitic transformation observed on cooling was determined for a series of Fe-Ni-Cr-C alloys.
Abstract: The effect of austenite prestrain above theMd temperature on the structure and transformation kinetics of the martensitic transformation observed on cooling was determined for a series of Fe-Ni-Cr-C alloys. The alloys exhibited a shift in martensite morphology in the nondeformed state from twinned plate to lath while theMs temperature, carbon content, and austenite grain size were constant. The transformation behavior was observed over the temperature range 0 to -196°C as a function of tensile prestrains performed above theMd temperature. A range of prestrains from 5 pct to 45 pct was investigated. It is concluded that the response of a given alloy to austenite prestrain above theMd temperature can be correlated with the morphology of the martensite observed in the nondeformed, as-quenched state. For the range of prestrains investigated, the transformation of austenite to lath martensite is much more susceptible to stabilization by austenite prestrain above theMd temperature than is the transformation of austenite to plate martensite.
66 citations
TL;DR: In this article, the iron-rich portion of the Fe-Ni-C phase diagram has been determined in the composi-tion range from 0 to 20 wt pct Ni and 0 to 6.67 wt Pct C for four temperatures, 773, 873, 923 and 1003 K. Long term heat treatments were used to grow the ferrite plus austenite assemblages, while slow cooling heat treatments (25 K/h) were used for growing the metal plus carbide assemblage.
Abstract: The iron-rich portion of the Fe-Ni-C phase diagram has been determined in the composi-tion range from 0 to 20 wt pct Ni and 0 to 6.67 wt pct C for four temperatures, 773, 873, 923 and 1003 K. Long term heat treatments were used to grow the ferrite plus austenite assemblages, while slow cooling heat treatments (25 K/h) were used to grow the metal plus carbide assemblages. Other types of heat treatments produced metal plus graphite. The two phase tie-lines and three phase tie-triangles were measured using electron mi-croprobe techniques. In samples where bulk equilibration had not been achieved, tie-lines were obtained by using extrapolated interface compositions, on the assumption of local equilibrium at the interface. The tie-lines lie at higher Ni contents than the equilibrium tie-line through the bulk composition. The tie-line shift was required to produce match-ing growth rates of Ni and C for the carbides. The addition of Ni slightly reduces the solubility of carbon in austenite and decreases the stability of the carbide phase. In addi-tion, the carbide is always Ni-poor relative to the coexisting metal phase(s).
63 citations
TL;DR: In this paper, the formation of carbide in lower bainite was studied in two silicon containing carbon steels by transmission electron microscopy and diffraction techniques Epsilon carbide was identified in the low temperature isothermally transformed bainitic structure.
Abstract: The formation of carbide in lower bainite was studied in two silicon containing carbon steels by transmission electron microscopy and diffraction techniques Epsilon carbide was identified in the low temperature isothermally transformed bainite structure The crystallographic relationship between epsilon carbide and bainitic ferrite was found to follow the Jack orientation relationship,viz, (0001)e l l(011)α, (101l)e l 1(101)α The cementite observed in lower bainite was in the shape of small platelets and obeyed the Isaichev orientation relationship with the bainitic ferrite,viz, (010) cl 1(1-11)α, (103) cl 1 (011)α Direct evidence showing the sequence of carbide formation from aus-tenite in bainite has also been obtained Based on the observations and all the crystallo-graphical features, it is strongly suggested that in silicon containing steels the bainitic carbide precipitated directly from austenite instead of from ferrite at the austenite/fer-rite interface as has been proposed by Kinsman and Aaronson (Ref 1) The uniformity of the carbide distribution is thus envisaged to be the outcome of precipitation at the aus-tenite-ferrite interphase boundary
59 citations
01 Jan 1977
TL;DR: In this paper, the authors present deformation-mechanism maps for ferrous alloys, which combine the understanding of the fundamentals of dislocation mechanics and diffusion theory with the observation of the yielding and creep of commercial steels.
Abstract: The construction of deformation-mechanism maps for ferrous alloys is described. Maps for pure iron, 316 and 304 stainless steel, and a ferritic 1 percent Cr-Mo-V steel are presented, and their use is illustrated. The maps are constructed, as far as possible, from model-based constitutive laws which have been fitted to experimental data. They attempt to combine the understanding of the fundamentals of dislocation mechanics and diffusion theory with the observation of the yielding and creep of commercial steels. In this way we retain some of the predictive power that an understanding of fundamentals permits, while giving a good description of the observed behavior of the alloys.
58 citations
Patent•
18 Apr 1977
TL;DR: The alloys exhibit excellent high temperature strength and oxidation resistance with relatively high aluminum and chromium contents within ranges which are critical to the formation of an aluminum oxide protective film when the alloys are exposed to oxidizing environments at temperatures up to about 1700° F as discussed by the authors.
Abstract: Austenitic iron base alloys containing nickel and with relatively high aluminum and chromium contents within ranges which are critical to the formation of an aluminum oxide protective film when the alloys are exposed to oxidizing environments at temperatures up to about 1700° F. The alloys exhibit excellent high temperature strength and oxidation resistance.
TL;DR: In this article, the fracture toughness of three simple high-purity steels containing between 0.10 and 0.11% carbon was examined after direct transformation of austenite to ferrite by subcritical isothermal transformation in the range 600-800°C and by continuous cooling.
Abstract: Three simple high-purity steels containing between 0.10 and 0.55 wt.-% titanium and 0.02–0.11% carbon have been examined after direct transformation of austenite to ferrite by subcritical isothermal transformation in the range 600–800°C and by continuous cooling. Electron microscopy has shown that titanium carbide occurs in a fine banded form during the γ→α transformation, the dispersion parameters being very dependent on the transformation temperature. The finer dispersions were measured by field ion microscopy. The mechanical properties in tension at room temperature were determined as a function of transformation temperature for the three alloys and compared with the properties obtained by quenching and tempering in the, same temperature range. Fracture toughness measured by a COD test was determined on two titanium steels with 0.26% and 0.48%Ti. The results emphasize the importance of transformation temperature or rate of cooling through the transformation in determining the fracture toughness...
TL;DR: In this paper, both foil and bulk martensites were studied by transmission electron microscopy of Fe-Ni-(C) alloys with subzero Ms temperatures, and the orientation relationship between austenite and martensite in foils is essentially the K-S relationship.
TL;DR: A two-piston splat-quenching technique has been used to prepare splatquenched Fe-Mn alloys with 0 to 20 wt % Mn, and splat quench Fe-Ni-C alloys having a nominal carbon content of 0.1 wt% and 0 to 40 wt%) Ni.
Abstract: A two-piston splat-quenching technique has been used to prepare splat-quenched Fe-Mn alloys with 0 to 20 wt % Mn, and splat-quenched Fe-Ni-C alloys with a nominal carbon content of 0.1 wt % and 0 to 40 wt % Ni. The resulting alloy microstructures have been investigated by a combination of optical and scanning electron microscopy, X-ray diffractometry, and microhardness testing; and the splat-quenched structures have been compared with the microstructures of similar alloys prepared by conventional solid-state quenching. In both alloy systems, splat-quenching produces a very small as-solidified austenite grain size, and a depression of the martensite transformation temperature as shown by an increased tendency to retain austenite to low temperatures. Because of the combination of a small austenite grain size and, therefore, fine scale martensite structure, splat-quenched martensitic alloys of Fe-Mn and Fe-Ni-C exhibit very high microhardness values.
TL;DR: In this paper, a combined investigation of splat-quenched Fe-Cx alloys by resistivity, X-ray diffraction and Mossbauer spectroscopy is presented.
Abstract: The authors present the results of a combined investigation of splat-quenched Fe-Cx (x
TL;DR: In this paper, a model for the nucleation of ferrite on austenite grain boundaries was reexamined using the Cahn-Hoffman construction, which offers a rigorous method of predicting the shape of heterogeneous nuclei.
Abstract: A model for the nucleation of ferrite on austenite grain boundaries proposed by Sharma and Purdy is reexamined using the Cahn-Hoffman construction. The construction, which offers a rigorous method of predicting the shape of heterogeneous nuclei, indicates that the original proposal of a disk shaped nucleus should be modified to that of a spherical segment. Based on currently available thermodynamic and physical data, it is shown that the spherical segment model is very sensitive to the austenite grain boundary interfacial tension. Even small changes in interfacial tension of several mN/m, which could result from the equilibrium absorption of boron into austenite boundaries, is sufficient to delay the austenite transformation by a significant time.
TL;DR: In this article, the effect of grain size on fatigue crack propagation was examined in a high strength steel (Fe-Cr-C) where grain size can be varied considerably without significant change in monotonic and cyclic strength.
Journal Article•
TL;DR: In this paper, the amount of phase transformation vs applied strain was determined by density measurements at various temperatures, assuming that e-platelets form from stacking faults, the volume fraction can be expressed as an implicit function of strain.
Abstract: The kinetics of the strain-induced γ (fcc)→e (hcp) transformationi.e. the amount of phase transformationvs applied strain were determined by density measurements at various temperatures. The transformation curve has a sigmoidal shape and approaches saturation below 100 pct transformation. Assuming that e-platelets form from stacking faults, the volume fraction can be expressed as an implicit function of strain. The saturation value is constant and can be evaluated from quantitative metallography. The approach to saturation is determined by only one temperature-dependent parameter related to the stacking fault energy. Good agreement with experimental results was obtained. The model was also applied to transformation kinetics after a prestrain inducing both slip and twinning. The prestrain stabilizes austenite with respect to the strain-induced transformation through a block-refining of austenite by the substructure. In addition the nucleation is enhanced through the introduction of stacking faults. This effect vanishes at high applied strains but causes the shape of the transformation curve to become parabolic. It is concluded that decreasing the size of the e platelets provides a simple means for reducing the temperature dependence of the transformation kinetics.
TL;DR: In this paper, high-resolution boron autoradiography and a literature survey have enabled an assessment to be made of the location of the small amounts of BORON (0.002-0.005%) added to alloy steels.
Abstract: High-resolution boron autoradiography and a literature survey have enabled an assessment to be made of the location of the small amounts of boron (0.002–0.005%) added to alloy steels. It has been shown that boron readily segregates to fcc carbides to give boro-carbides such as M23(BC)6 and V4(BC)3, and that metal borides are not formed in steels with this level of boron addition. Boron also segregates to austenite grain boundaries on slow cooling low-alloy steels below 980°C. Grain-boundary segregation thus occurs in ½%Mo–B bainitic steels as predicted by some harden ability theories. However, quenched and tempered Cr-Mo-V creep-resisting steels do not have boron at the austenite boundaries and the boron does not segregate to the boundaries even after creep testing for > 16 000 h at 550°C. The observed microstructural effects have been related to mechanical properties and interpreted in terms of vacancy–boron interactions.
TL;DR: In this article, the carbide/austenite equilibria were studied experimentally in the alloy systems Fe-Mo-Cr-C, FeMo-Ni-C and Fe-CrNi-Mn-C in the temperature range 1173 to 1373 K. The carbides were identified by microscopic examination after etching and X-ray analysis of carbide residues obtained by electrolytic extraction.
Abstract: The carbide/austenite equilibria were studied experimentally in the alloy systems Fe-Mo-Cr-C, Fe-Mo-Ni-C, Fe-Mo-Mn-C, Fe-Cr-Mn-C, Fe-Cr-Ni-C and Fe-Cr-Ni-Mn-C in the temperature range 1173 to 1373 K. The carbides were identified by microscopic examination after etching and by X-ray analysis of carbide residues obtained by electrolytic extraction. The alloy contents in the individual phases were measured with a microprobe technique. The partitioning of the alloying elements were evaluated and phase diagrams at constant temperature and carbon activity were constructed from the experimental information.
TL;DR: In this paper, the effect of austenite yield strength on the transformation to martensite was investigated in Fe-10 pct Ni-0.6 pct C alloys.
Abstract: The effect of austenite yield strength on the transformation to martensite was investigated in Fe-10 pct Ni-0.6 pct C alloys. The strength of the austenite was varied by 1) additions of yttrium oxide particles to the base alloy and 2) changing the austenitizing temperature. The austenite strength was measured at three temperatures above theM
s temperature and the data extrapolated to the experimentally determinedM
s temperature. It is shown that the austenite yield strength is determined primarily by the austenite grain size and that the yttrium oxide additions influence the effect of austenitizing temperature on grain size. As the austenite yield strength increases, both theM
s temperature and the amount of transformation product at room temperature decrease. The effect of austenitizing temperature on the transformation is to determine the austenite grain size. The results are consistent with the proposal1 that the energy required to overcome the resistance of the austenite to plastic deformation is a substantial portion of the non-chemical free energy or restraining force opposing the transformation to martensite.
TL;DR: The maximum elongation temperature (MET), the temperature at which the major principal strain is maximum, determined from tests in uniaxial tension, is usually quoted The authors confirm that formation of sufficient martensite in the region of incipient instability close to the instability strain is responsible for increased tensile ductility, but there is no unique MET for a given steel It depends, critically, on the rate of loading.
TL;DR: In this article, the authors report that low-alloy steels tempered between 320 to 525/sup 0/C are embrittled by the segregation of impurity and alloy elements to the grain boundaries.
Abstract: Recent work with emphasis on the direct measurement of segregation of impurities and alloying elements as they relate to temper embrittlement of low-alloy steels is reported. Low-alloy steels tempered between 320 to 525/sup 0/C are embrittled by the segregation of impurity and alloy elements to the grain boundaries. Segregation occurs during tempering. Segregation in austenite is not important. Alloy elements promote impurity segregation. Embrittlement occurs by the reduction of cohesion at the grain boundaries. Antimony and tin are most effective embrittlers. Carbon and boron enhance ductility. (FS)
TL;DR: In this paper, the behavior of metallic second phases of stainless steels has been investigated in all systems, and 475 C embrittlement of ferritic and martensitic steels is treated.
Abstract: This paper considers how metallic second phases influence the behavior of austenitic, ferritic, and martensitic stainless steels. Among the cases considered are ferrite and martensite in austenitic steels, austenite and martensite in ferritic alloys, and austenite and ferrite in martensitic steels. Sigma is discussed in all systems, and 475 C embrittlement of ferritic and martensitic steels is treated. The problem of “invisible” phases is discussed.
01 Nov 1977
TL;DR: In this paper, an improved transition weld joint between stainless steel and ferritic steel piping was developed to circumvent the failures and concerns with joints made by existing technology, and Alloy 800H was selected as an appropriate intermediate material for this application.
Abstract: The objective of this study was to develop an improved transition weld joint between stainless steel and ferritic steel piping to circumvent the failures and concerns with joints made by existing technology. The primary concern of mismatch in coefficients of thermal expansion between the ferritic and austenitic steels and the high stresses that it imposes at the interface between ferritic steel and weld metal led to an extensive elastic stress analysis involving base metal combinations, filler metals, and weld joint geometries. This analysis indicated that, for pipe welds, joint stress could be reduced considerably by using a transition material with an intermediate coefficient of thermal expansion between the 2 1/4 Cr-1 Mo ferritic steel and the austenitic stainless steel. Alloy 800H was selected as an appropriate intermediate material for this application.
TL;DR: In this article, the compressive flow stress and rate of work hardening of quenched and tempered AISI 52100 steel were measured for a variety of heat treatments.
Abstract: The compressive flow stress and rate of work hardening of quenched and tempered AISI 52100 steel were measured for a variety of heat treatments. Both the flow stress and the work hardening index,n, increase with decreasing tempering temperature. Flow stresses increase initially with increasing austenitizing temperature,Ta, then decrease with a further increase inTa as the amount of retained austenite increases.n tends to increase asTa increases. In specimens temperared to eliminate retained austenite,n decreases to near zero as the strain increases. This behavior appears to be characteristic of tempered martensite. When less than 10 pct retained austenite is present,n still decreases with increasing strain, but witn n ore than about 15 pct retained austenite,n increases with strain. Heat treatments which refine the primary carbides increase the flow stress forTa≤840°C. Since fine primary carbides lead to more retained austenite at a givenTa, n tends to be greater when primary carbides are refined. For one heat treatment, the retained austenite content was measured by an X-ray method as a function of plastic strain. From changes in the relative intensities of austenite reflections, it was found that austenite crystals most favorably oriented for deformation in compression transform most readily to martensite on straining.
Patent•
24 Aug 1977TL;DR: A high strength, tough alloy steel is formed by heating the steel to a temperature in the austenite range (1000°-1100° C) to form a homogeneous austenitic phase and then cooling the steel.
Abstract: A high strength, tough alloy steel is formed by heating the steel to a temperature in the austenite range (1000°-1100° C.) to form a homogeneous austenite phase and then cooling the steel to form a microstructure of uniformly dispersed dislocated martensite separated by continuous thin boundary films of stabilized retained austenite. The steel includes 0.2-0.35 weight % carbon, at least 1% and preferably 3-4.5% chromium, and at least one other substitutional alloying element, preferably manganese or nickel. The austenite film is stable to subsequent heat treatment as by tempering (below 300° C.) and reforms to a stable film after austenite grain refinement.