Showing papers on "Austenite published in 1986"
TL;DR: The relationship between phase changes and hydrogen transport parameters was modeled using various assumptions about the microstructure and the effective solubility and diffusivity values were discussed in terms of dislocation trapping and transport as mentioned in this paper.
246 citations
TL;DR: The tensile properties of Fe-high Mn (16 to 36 wt pct Mn) binary alloys were examined in detail at temperatures from 77 to 553 K in this paper.
Abstract: The tensile properties of Fe-high Mn (16 to 36 wt pct Mn) binary alloys were examined in detail at temperatures from 77 to 553 K. The Mn content dependence of the deformation and fracture behavior in this alloy system has been clarified by placing special emphasis on the starting microstructure and its change during deformation. In general, the intrusion of hcp epsilon martensite (e) into austenite (γ) significantly increases the work hardening rate in these alloys by creating strong barriers to further plastic flow. Due to the resulting high work hardening rates, large amounts of e lead to high flow stresses and low ductility. Alloys of 16 to 20 wt pct Mn are of particular interest. While these alloys are thermally stable with respect to bcc α’ martensite formation, 16 to 20 wt pct Mn alloys undergo a deformation induced e →α’ transformation. The martensitic transformation plays two contrasting roles. The stress-induced e→ α’ transformation decreases the initial work hardening rate by reducing locally high internal stress. However, the work hardening rate increases as the accumulated α’ laths become obstacles against succeeding plastic flow. These rather complicated microstructural effects result in a stress-strain curve of anomolous shape. Since both the Ms and Md temperatures for both the e and α’-martensite transformations are strongly dependent on the Mn content, characteristic relationships between the tensile behavior and the Mn content of each alloy are observed.
179 citations
TL;DR: In this article, the effect of hardness on the residual stress in the machined surface of AISI 4340 steel was studied and chips produced during the machining were examined using optical microscope and scanning transmission microscope.
Abstract: The effect of hardness on the residual stress in the machined surface of AISI 4340 steel was studied. Chips produced during the machining also were examined and the surface structure was investigated using optical microscope and scanning transmission microscope. Reflection electron diffraction study revealed the existence of austenite in the white layer of the machined surface together with untempered martensite. The residual stress near the machined surface or hardened steel is a compressive stress, and it changes to tensile stress as the hardness decreases. Chip segmentation was observed when steel with hardness of over Rc 50 was machined.
152 citations
TL;DR: In this article, the microstructural changes, precipitation behavior, and mechanical properties of typical austenitic stainless steels (304 H, 316 H, 321 H, 347 H, and Tempaloy A-1) have been examined after long-term aging.
Abstract: The microstructural changes, precipitation behaviour, and mechanical properties of typical austenitic stainless steels (304 H, 316 H, 321 H, 347 H, and Tempaloy A–1) have been examined after long-term aging. The steels were aged statically in the temperature range 600–800°C for up to 50000 h. The microstructural changes were observed by optical and transmission electron microscopy, and the extracted residue was identified using X-ray analysis. Time–temperature precipitation diagrams were made for each steel. The amount of σ-phase was measured in samples aged at 700°C. The hardness and impact-value changes, and the tensile properties of aged samples were measured.MST/358
96 citations
TL;DR: In this article, the influence of substitutional alloying elements upon the volume free energy change and upon the energies of austenite grain boundaries and nucleus: matrix boundaries was analyzed in terms of the influence.
Abstract: The nucleation kinetics of proeutectoid ferrite allotriomorphs at austenite grain boundaries in Fe-0.5 at. Pct C-3 at. Pct X alloys, where X is successively Mn, Ni, Co, and Si and in an Fe-0.8 at. Pct C-2.5 at. Pct Mo alloy have been measured using previously developed experimental techniques. The results were analyzed in terms of the influence of substitutional alloying elements upon the volume free energy change and upon the energies of austenite grain boundaries and nucleus: matrix boundaries. Classical nucleation theory was employed in conjunction with the pillbox model of the critical nucleus applied during the predecessor study of ferrite nucleation kinetics at grain boundaries in Fe-C alloys. The free energy change associated with nucleation was evaluated from both the Hillert-Staffanson and the Central Atoms Models of interstitial-substitutional solid solutions. The grain boundary concentrations of X determined with a Scanning Auger Microprobe were utilized to calculate the reduction in the austenite grain boundary energy produced by the segregation of alloying elements. Analysis of these data in terms of nucleation theory indicates that much of the influence of X upon ferrite nucleation rate derives from effects upon the volume-free energy change,i.e., upon alterations in the path of theγ/(α + γ) phase boundary. Additional effects arise from reductions in austenite grain boundary energy, with austenite-forming alloying elements being more effective in this regard than ferrite-formers. By difference, the remaining influence of the alloy elements studied evidently results from their ability to diminish the energies of the austenite: ferrite boundaries enclosing the critical nucleus. The role of nucleation kinetics in the formation of a bay in the TTT diagram of Fe-C-Mo alloys is also considered.
92 citations
TL;DR: In this paper, the microstructure and phase chemistry of a Fe-34Cr-4.5C wt% hardfacing alloy have been investigated using transmission electron microscopy and microanalytical techniques.
Abstract: The microstructure and phase chemistry of a Fe-34Cr-4.5C wt% hardfacing alloy has been investigated using transmission electron microscopy and microanalytical techniques. The microstructure is found to consist of large primary M7C3. carbides in a eutectic mixture of austenite and more M7C3. The results indicate that the microstructure of the undiluted alloy becomes configurationally frozen at a temperature of about 1150° C during deposition by the manual metal arc welding technique. This allows the metastable austenite phase to contain a large chromium concentration (≈ 16 to 17 wt %), thus imparting good corrosion and oxidation resistance. Experimental data on the partitioning of chromium, manganese and silicon between the carbide phases are discussed in the context of the high-temperature stability of the alloy.
67 citations
TL;DR: In this paper, the effects of cathodic hydrogen charging and aging on surface phase transformations were studied in solution treated and cold worked specimens of two austenitic stainless steels, and it was shown that a minimum charging current density is necessary to induce transformation.
Abstract: The effects of cathodic hydrogen charging and aging on surface phase transformations were studied in solution treated and cold worked specimens of two austenitic stainless steels. Quantitative phase evaluation using an X-ray technique has shown that cathodic hydrogen charging and aging can result in a considerable amount of surface transformation toe andα ′ martensites. The extent of this surface transformation differs significantly from deformation-induced transformation at the same temperature, and abnormally high volume fractions ofe martensite are produced by the charging process. A minimum charging current density is necessary to induce transformation. In cold-worked samples, further surface transformation due to hydrogen charging and aging is inhibited by high volume fractions of pre-existing martensite.
61 citations
TL;DR: In this article, a ductility trough was obtained for all the steels and the minimum ductility values were similar, showing that the carbon content above the 0·28% level caused a change in the fracture mode.
Abstract: Hot ductility, measured by reduction in area, has been determined over the temperature range 550–950°C for a series of plain C–Mn steels having the same base composition except for the carbon content, which was in the range 0·04–0·65 wt-%. A ductility trough was obtained for all the steels and minimum ductility values were similar. Raising the carbon content from 0·04 to 0·28 wt–% caused the ductility trough to move to lower temperatures and this was in agreement with the observed changes in transformation temperature. Tensile fracture at the minimum ductility temperature was along thin films of ferrite which formed round the austenite grains – generally by deformation–induced transformation. The softer ferrite allowed strain concentration to cause ductile voiding at the MnS inclusions, and the voids eventually linked up to give intergranular failure. Raising the carbon content above the 0·28% level caused a change in the fracture mode. Instead of the ductility troughs moving to lower temperatures...
59 citations
TL;DR: In this article, phase transformations, solid solution alloying, compound formation, and residual stresses resulting from Ti implantation of AISI 52100 steel are obtained using 57Fe Mossbauer spectroscopy.
Abstract: Information on phase transformations, solid solution alloying, compound formation, and residual stresses resulting from Ti implantation of AISI 52100 steel is obtained using 57Fe Mossbauer spectroscopy. Results show that Ti implantation reduced the near‐surface (0.1 μm) retained austenite content by about 70% or more and evidence is found for an implantation‐induced strain field which extends much deeper than the Ti‐implanted zone. Changes in the near‐surface martensite Mossbauer resonance are attributed to Ti on substitutional sites. Neither of the intermetallic compounds Fe2Ti or FeTi, nor the amorphous Fe–Ti or Fe–Ti–C phases are unambiguously detected. However some features of the data are not explained by Ti and/or C solid solution alloy analysis and this leads to suggestions for a≲10‐nm‐thick amorphous phase layer and surface oxides/carbides. The microstructural modifications are correlated with tribological properties measured on the same specimens. Improvements are attributed to the retained auste...
59 citations
57 citations
TL;DR: In this paper, the isothermal transformations in five hypereutectoid steels (0.85 to 1.80 wt pct C) have been studied in the temperature range between 623 and 333 K. Two types of lower bainites and a thin plate isothermal martensite were observed.
Abstract: The isothermal transformations in five hypereutectoid steels (0.85 to 1.80 wt pct C) have been studied in the temperature range between 623 and 333 K. Two types of lower bainite and a thin plate isothermal martensite were observed. One of the lower bainites was the conventional lower bainite (CLB) formed at the high temperature range of 623 to 473 K, and the other was the newly named “lower bainite with midrib” (LBm) formed at the lower temperature range of 473 to 423 K. The thin plate isothermal martensite (TIM) was also observed below 373 K. This paper brought LBm into focus. Arrhenius plots (transformation ratevs l/T) for each steel revealed an abrupt change in kinetics at the temperature range between 483 and 443 K. This change was considered to correspond to the transition from CLB to LBm. The following two-stage process for the LBm formation is proposed: at the first stage a TIM is formed, which constitutes a midrib of LBm, and secondly the bainitic decomposition of austenite at TIM/austenite interfaces takes place. That is, an LBm is a composite of isothermal martensite and lower bainite.
TL;DR: In this paper, the nucleation kinetics of proeutectoid ferrite allotriomorphs at the edges of austenite grains in FeC and Fe-C-X alloys, where X is successively Mn, Ni, Co, and Si, were measured using a modification of the techniques previously developed to study nucleation at grain faces.
Abstract: Nucleation kinetics of proeutectoid ferrite allotriomorphs at the edges of austenite grains in Fe-C and Fe-C-X alloys, where X is successively Mn, Ni, Co, and Si, have been measured using a modification of the techniques previously developed to study nucleation at grain faces. Analysis of these data with classical heterogeneous nucleation theory has shown that ferrite nuclei formed at grain edges have low energy interphase boundaries. An equivalent conclusion was reached during our previous studies of ferrite nucleation at austenite grain faces. The influence of alloying elements on nucleation rates was also found to follow a pattern similar to that demonstrated for grain face nucleation.
TL;DR: In this paper, a thermal convection loop with type 316 stainless steel coupons and a Fe-9Cr-1Mo steel loop containing Fe-12Cr- 1MoVW steel specimens were compared for mass loss and surface characterization data.
TL;DR: In this paper, it was found that the erosion rate depends on both the hardness and the ductility of the steel and was associated with a large amount of plastic deformation and that the eroded particles were in the form of small flakes.
TL;DR: The grain structure, inclusion content, and precipitate types were characterized for six heat treatments of a copper-bearing HSLA steel as discussed by the authors, where a higher austenitizing temperature combined with water-quenching resulted in an acicular ferrite microstructure, while lower temperatures produced equiaxed ferrite or ferrite-pearlite structures.
Abstract: The grain structure, inclusion content, and precipitate types were characterized for six heat treatments of a copper-bearing HSLA steel A higher austenitizing temperature combined with water-quenching resulted in an acicular ferrite microstructure, while lower temperatures produced equiaxed ferrite or ferrite-pearlite structures Refinement of equiaxed ferrite was observed in material austenitized at a high enough temperature to dissolve a portion of the carbonitrides, allowing reprecipitation during the austenite-ferrite transformation Age-hardening precipitated body-centered cubic copper clusters; face-centered cubic copper precipitates were observed in overaged material
TL;DR: In this article, the influence of grain size on hot ductility of 0·19 and 0·65wt-%C steels of the C-Mn type has been determined.
Abstract: The influence of grain size on the hot ductility of 0·19 and 0·65wt-%C steels of the C–Mn type has been determined. For the low-carbon steel, a gram Size increase from 70 to 180 μm had only a small influence on hot ductility, as measured by tensile reduction in area values. However, increasing the grain size to 290 μm raised the temperature at which ductility started to fall by 50°C. In the finer grained steels it is believed that the ductility trough starts at the Ar3 temperature when films of ferrite form round the stronger austenite grains. Ductility soon recovers as the temperature is lowered because of a thickening of the ferrite and a consequent reduction of strain concentration at the boundaries, so that only a narrow trough is observed. In coarser grained steels it is considered that deformation induced ferrite can have a pronounced influence on hot ductility over a wide range of temperatures leading to a wide ductility trough. Refining the grain size had an even greater influence on the h...
TL;DR: A metallographic characterization of materials exposed to a flowing lithium environment is presented in this paper, where corrosion behavior is evaluated by measurements of weight loss as a function of time and temperature.
TL;DR: In this article, the corrosion behavior of HT-9 and Fe-9Cr-1Mo steel and austenitic Type 316 stainless steel in a flowing Pb-17 at.% Li environment at temperatures between 371 and 482°C was evaluated by measurement of weight loss as a function of time and temperature.
TL;DR: The causes of embrittlement in several plain carbon-manganese and niobium-treated steels between 800 and 1200 °C have been investigated in this paper, where the size, distribution, and composition of grain boundary precipitates were measured on extraction replicas.
Abstract: The causes of embrittlement in several plain carbon-manganese and niobium-treated steels between 800 and 1200 °C have been investigated. Tensile ductility was measured as a function of temperature and strain rate. Percent elongation and reduction in area were used to characterize the temperature dependence and severity of the ductility loss. The size, distribution, and composition of grain boundary precipitates were measured on extraction replicas. Grain boundary segregation was measured by AES on samples that were deformed at 900 °C before being fractured under ultra-high vacuum at room temperature. Segregation of impurity residual elements and grain boundary precipitation are the primary factors responsible for the observed ductility loss. The embrittlement results in a low ductility fracture which is largely intergranular through the austenite grain boundaries. Segregation of Cu, Sn, and Sb was found on the fracture surfaces of the embrittled samples. High temperature deformation was necessary to produce segregation as no segregation was detected in undeformed samples. Grain boundary precipitation, particularly AIN but also Nb (C,N), contributed to the embrittlement when there was a relatively fine distribution of precipitates along the austenite grain boundaries. The most severe ductility loss occurred when grain boundary precipitation combined with Cu, Sn, and Sb segregation.
TL;DR: In this article, the limits of applicability of the additive principle for the prediction of continuous-cooling transformation kinetics from isothermal transformation data are clarified based on an analysis of recently measured austenite-to-pearlite transformation in a eutectoid, plain-carbon steel.
Abstract: The limits of applicability of the Additivity Principle, necessary for the prediction of continuous-cooling transformation kinetics from isothermal transformation data, are clarified based on an analysis of recently measured austenite-to-pearlite transformation kinetics in a eutectoid, plain-carbon steel. It has been found that additivity holds for the transformation event, exclusive of the incubation period, in this steel. But the isokinetic condition defined by Avrami, and the early site-saturation criteria postulated by Cahn as sufficient conditions for additivity are not satisfied. Thus a new condition, termed “effective site saturation”, is proposed in which the growth of pearlite nucleated early in the transformation dominates the overall kinetics of austenite decomposition. A criterion for effective site saturation has been established.
TL;DR: In this article, the sliding wear behavior of various metastable Fe-Mn-C austenites as well as that of the classic Hadfield steel is investigated using X-ray diffraction, light microscopy and scanning and transmission electron microscopies.
TL;DR: In this paper, the effects of aging treatments on the stress corrosion cracking behavior of Fe8.7Al-29.7Mn-1.04C alloy is discussed.
TL;DR: In this article, a special weld simulation procedure has been adopted to reveal the time exponent in nonisothermal austenite grain growth following particle dissolution at elevated temperatures, and it is concluded that the HAZ grain boundary migration rate is approaching the upper theoretical limit (represented by a time exponent n = 0.5 in the grain growth equation).
TL;DR: In this article, the corrosion behavior of six austenitic alloys and reference Type 316 stainless steel has been examined in a flowing sodium environment at 700°C for up to about 4000 h.
TL;DR: In this paper, the authors identify the conditions in respect of material, loading and environment which may lead to intergranular fracture of 13 wt% chromium steel blades in certain service failures.
Abstract: Fracture of 13 wt% chromium steel blades has been observed to occur in the intergranular mode in certain service failures An attempt has been made in this study to identify the conditions in respect of material, loading and environment which may lead to intergranular fracture Three different materials were subjected to varying heat treatments selected on the basis of fracture characteristics of as-received materials It has been concluded that grain-boundary segregations of impurities and carbide precipitation, intergranular network of delta ferrite at prior austenitic grain boundaries, and a sufficient concentration of NaCl in conjunction with cyclic stress, promote intergranular fracture in a 13 wt% chromium steel
TL;DR: In this article, the influence of precipitated austenite on transgranular hydrogen embrittlement in 55Ni steel was investigated and it was shown that precipitated Austenite decreases the toughness in the presence of hydrogen.
Abstract: This work was undertaken to test the influence of precipitated austenite on transgranular hydrogen embrittlement in 55Ni steel Prior work has shown that the mechanism of transgranular hydrogen embrittlement in this steel is interlath separation Since the austenite that forms during the tempering of 55Ni steel precipitates on the martenite lath boundaries, it was hypothesized that the austenite might have a beneficial effect The experimental results show, however, that the precipitated austenite decreases the toughness in the presence of hydrogen The apparent mechanism is straightforward The precipitated austenite transforms to martensite in the strain field ahead of the crack tip Interlath cracks appear at the periphery of the fresh martensite particles They are apparently caused by the volume change that accompanies the martensite transformation, which imposes a tension across the lath boundary The interlath cracks link together to form the macroscopic fracture
TL;DR: In this paper, phase equilibria in the Fe rich portion of the Fe-C-B ternary system were analyzed on the basis of the solubility data on Fe-B system by Cameron and Morral.
Abstract: Phase equilibria in the Fe rich portion of the Fe-C-B ternary system were analyzed on the basis of the solubility data on Fe-B system by Cameron and Morral. The Gibbs energy of solution phases was approximated by the interstitial model, assuming C and B to be interstitial atoms. The influence of ferromagnetism on the Gibbs energy of ferrite was also taken into account. The effect of B addition on the pure austenite field was calculated precisely, and it was confirmed that the equilibrium distribution coefficient of B between liquid and austenite is much smaller than that evaluated previously.
TL;DR: In this article, the authors investigated the stress corrosion cracking behavior of the duplex Fe-10 Al-29 Mn-0.4 C alloy having two phases (α andγ) in an aqueous 20% NaCl solution.
Abstract: The stress corrosion cracking behaviour of the duplex Fe-10 Al-29 Mn-0.4 C alloy having two phases (α andγ) in an aqueous 20% NaCl solution (100° C) has been investigated using both the static constant load and dynamic slow strain rate tests. The constant load test shows that the duplex alloy investigated is immune to stress corrosion cracking in a 20% NaCl solution. However, the slow strain-rate test reveals that this alloy is susceptible to stress corrosion cracking at the stabilized corrosion potential, and also at potentials anodic and cathodic to this potential. Furthermore, the metallographic cross section of this duplex alloy after slow strainrate testing shows that the secondary cracks propagate transgranularly through the ferrite grains at and above the stabilized corrosion potential. However, the cracks propagate transgranularly in both the ferrite and austenite grains and also at the austenite-ferrite grain boundaries when the applied potential is cathodic to the stabilized corrosion potential.
TL;DR: In this paper, the structure and properties of ion-nitrided layers on several stainless steels, 410 martensitic stainless steel, 430 ferritic stainless steel and 321 austenitic steel, has been studied under varying process conditions with microhardness-depth correlations, optical microscopy and transmission electron microscopy.
Abstract: The structure and properties of ion-nitrided layers on several stainless steels, 410 martensitic stainless steel, 430 ferritic stainless steel and 321 austenitic stainless steel, has been studied under varying process conditions with microhardness-depth correlations, optical microscopy and transmission electron microscopy. The process variables studied include time (2 to 10 h) and temperature (400 to 600° C). The highest case depth values and hardness levels were observed in martensitic stainless steels. The lowest case depths were observed in austenitic stainless steel. In general, the behaviour of matensitic and ferritic stainless steels were similar. All three steels showed increasing case depths and decreasing surface hardnesses with increasing ion-nitriding temperatures and times. Nitriding depth was found to be parabolic with ion nitriding time in all three steels at all ion-nitriding temperatures investigated, the nitriding reaction being faster in martensitic stainless steel than the others. Electron microscopy showed that almost no structural difference arises in the core of ferritic and austenitic stainless steels whereas recrystallization of the martensitic structure was observed in the core of martensitic steel following ion nitriding. Electron microscopy results also showed that ion nitriding produces platelets or disc-shaped precipitates on {001} matrix planes, coherent with the matrix. These platelets showed a striated morphology which is thought to be the result of the elastic strain in the matrix.
TL;DR: In this article, a torsion simulation of industrial hot working was conducted to evaluate the deformation properties of carbon, microalloyed, tool and γ stainless steels.