Showing papers on "Bainite published in 1994"

Strength of mixtures of bainite and martensite

Abstract: Recently published experimental data demonstrate that the strength of mixed microstructures of tempered bainite and martensite can peak at an intermediate volume fraction of martensite. In the present work, a quantitative interpretation of these observations is achieved by modelling the mechanical properties of bainite and martensite in their tempered states. It is found that the peak in the curve of the strength as a function of the volume fraction of martensite can be attributed to two factors. When bainite forms it enriches the residual austenite with carbon, so that the strength of the subsequent martensite increases. In addition, during its deformation, the strength of the bainite is enhanced via plastic constraint by the surrounding stronger martensite. Taking these effects into account, it is possible to predict accurately both the trends and the absolute values of published experimental data on the strength of mixed microstructures.MST/1901

Transformation Textures in Steels

Abstract: During the hot rolling of steels, the parent austenite phase develops a crystallographic texture. As a result, the material after transformation (ferrite, martensite, acicular ferrite, or bainite ) also acquires a texture which is related in a precise way to the texture of the parent material. The major component of the transformation texture derived from recrystallized austenite is the {001} , which originates from the cube {100} component of the parent texture. The major components of the texture of pancaked austenite are the Bs {110} and Cu {112} , and these give rise, respectively, to the {332} and {113} components in the transformation product. The Goss {110} , Goss/Bs {011} , Bs/S {168} , S{123} , and S/Cu {236} orientations in the deformed austenite also contribute to the formation of the overall transformation texture. Since more than one parent γ orientation can transform into the same bcc orientation, it is sometimes impossible to determine, unambiguously, the origin of particular transformation texture components in the parent γ texture. The intensity of the overall transformation texture can be increased by the addition of Nb, Ti and V to steel, by giving large reductions during controlled rolling, and by using lower finishing temperatures during processing. Among the transformation texture components, the {332} is the most beneficial from the point of view of achieving good deep drawability and improved strength and toughness. The presence of substitutional solutes such as Mn, Ni, Cr or Mo, finer austenite grain sizes and faster cooling rates during transformation increase the intensity of the {332} component. By contrast, the intensity of the {113} component remains relatively insensitive to the above factors.

Effect of Pre-cold-working on Diffusional Reversion of Deformation Induced Martensite in Metastable Austenitic Stainless Steel

Abstract: Metastable austenitic stainless steels undergo deformation induced transformation to bcc martensitic structure during cold-working. The martensite induced reverts to austenite at a relatively low temperature and this leads to the formation of ultra fine austenite grains of less than 1 μm in diameter. In this paper, the effect of pre-cold-working on the morphology of reversed austenite was investigated by means of transmission electron microscopy and tensile test. The alloy used is an Fe-18.08%Cr-8.65%Ni alloy. Since this alloy has metastable austenitic structure at room temperature, it almost transforms to lath-martensite by 50% cold-rolling. Further cold-rolling above 50% deforms transformed martensite itself, and results in the formation of dislocation-cell structure instead of lath-martensitic structure. The diffusional reversion of deformation induced martensite takes place at around 900 K and precold-working to lath-martensite not only promotes the reversion but also gives a large effect on the microstructure of reversed austenite: Reversed arstenite is characterized, in a specimen with 50% pre-cold-working, by the stratum structure of austenite laths and blocks, which looks like a lath-martensitic structure, while in a specimen with heavy pre-cold-working, by the structure of fine equiaxed grains. On the discussion of grain boundary strengthening in the former case, 0.2% proof stress depends not on the lath size but on the block size of reversed austenite.

Stress affected bainitic transformation in a FeCSiMn alloy

Abstract: Isothermal transformation experiments are reported in which the formation of bainitic ferrite occurs under the influences of stresses below the yield strength of the austenite. The response of the transformation was monitored by simultaneously measuring the longitudinal and radial transformation strains. This enabled the dilatational and deviatoric strain components to be deconvoluted from the total transformation strain. The data have been analysed by comparison with a theoretical model for the stress-assisted growth of bainite. The results confirm that the microstructure readily responds to stresses well below the yield strength of the parent phase. Furthermore, those crystallographic variants which are favoured by the stress grow first in the sequence of transformation. Experiments where the stress just exceeds the yield strength are also reported.

High toughness low yield ratio, high fatigue strength steel plate and process of producing same

Abstract: A steel plate having a high toughness, low yield ratio and high fatigue strength is provided by preserving the fine metallographical microstructure of martensite or bainite while austenitizing extremely fine portions of the microstructure, and during cooling, dispersing the portions as martensite, retained austenite, cementite or mixture thereof in a tempered martensite or tempered bainite phase.

Diffusion in growth of bainite

Abstract: Edgewise growth rates for Widmanstaetten ferrite and bainite in low alloy steels can be represented with an empirical equation showing proportionality to the square of the supersaturation of the austenite. The proportionality constant has a value in reasonable agreement with the assumption of rate control by carbon diffusion. The growth rates are too low to give a noticeable supersaturation of carbon in the growing ferrite. The experimental B[sub s] for low alloy steels does not seem to be related to the T[sub 0] line, nor does B[sub s] evaluated from the incomplete transformation to bainite for an alloy steel. By assuming rate control by carbon diffusion, the empirical equation can be used to calculate the growth rate under paraequilibrium or no partition, local equilibrium (NPLE) conditions. Experimental growth rates for a similar steel falls in-between. The fact that paraequilibrium does not seem to apply is taken as an indication that the [alpha]/[gamma] interface for Widmanstaetten ferrite and bainite is not of a purely martensitic type.

The γ→α Transformation in Low Carbon Irons

Abstract: The influence of cooling rate on transformation temperatures in low carbon irons is reviewed. Plateaux are obtained in plots of transformation temperature vs.cooling rate. Comparison with later published TTT diagrams show that these plateaux correspond with the nose of 'c' curves on TTT diagrams. This leads to a proposed TTT diagram for iron. Transformations in Fe-Ni, Fe-Cr and Fe-C alloys, and low carbon irons are reviewed. The morphology and kinetics of the individual transformations, namely equi-axed ferrite, massive ferrite, bainitic ferrite, lath (massive) martensite and twinned martensite are then discussed. A recent theoretical treatment of the equi-axed ferrite transformation is summarised. This theory indicates that the kinetics of the equi-axed ferrite transformation is controlled by growth. Correlation is made between microstructures obtained in binary alloys and those obtained in Fe-Nb-C alloys and commercial HSLA steels.

High tensile strength steel sheet having improved formability

Abstract: A high tensile strength, hot or cold rolled steel sheet having improved ductility and hole expandability consists essentially, on a weight basis, of: C: 0.05-0.3%, Si: 2.5% or less, Mn: 0.05-4%, Al: greater than 0.10% and not greater than 2.0% wherein 0.5≦Si(%)+Al(%)≦3.0, optionally one or more of Cu, Ni, Cr, Ca, Zr, rare earth metals (REM), Nb, Ti, and V, and a balance of Fe and inevitable impurites with N being limited to 0.01% or less. The steel sheet has a structure comprising at least 5% by volume of retained austenite in ferrite or in ferrite and bainite. A hot rolled steel sheet is produced by hot rolling with a finish rolling end temperature in the range of 780°-840° C., cooling to a coiling temperature in the range of 300°-450° C. either by rapid cooling to the coiling temperature at a rate of 10°-50° C./sec or by initial rapid cooling to a temperature range of 600°-700° C., then air-cooling for 2-10 seconds, and final rapid cooling to the coiling temperature. A cold rolled steel sheet is produced by hot rolling, cooling to a coiling temperature in the range of 300°-720° C., descaling, cold rolling with a reduction of 30-80%, and annealing. Annealing is performed by heating between the Ac 1 point and the Ac 3 point and cooling such that the temperature is either kept for at least 30 seconds in the range of 550° C. to 350° C. or slowly decreased at a rate of 400° C./min or less in that temperature range.

Titanium-rich mineral phases and the nucleation of bainite

Abstract: Experiments have been conducted to study the nucleation of bainite at interfaces between ceramic compounds of Ti and low-alloy steel. To facilitate this, chemically pure compounds of Ti were pressure-bonded to steel samples. The resulting composite samples were then heattreated to induce transformation and, hence, to compare transformation behavior in the vicinity of the ceramic/steel interface to that within the bulk of the steel. It is found that a variety of Ti oxides are effective in stimulating the nucleation of bainite, whereas TiN is not. The results are interpreted in terms of the crystal structure and chemistry of the Ti compounds.

Thermodynamics of acicular ferrite nucleation

Abstract: The thermodynamic driving force necessary to stimulate the nucleation of acicular ferrite and bainite is investigated for a series of high strength weld metals, using a combination of dilatometry, scanning electron microscopy, and thermodynamic calculations. The results indicate that the nucleation of acicular ferrite and bainite can be represented by the same thermodynamic model. It therefore appears that the nucleation mechanism of acicular ferrite on non-metallic inclusions in weld metals is essentially similar to that of bainite at the austenite grain boundaries. Metallographic observations confirm the notion that acicular ferrite is essentially intragranularly nucleated bainite.MST/1897

Bainite nucleation from mineral surfaces

Abstract: Experiments have been conducted to study the nucleation of bainite at interfaces between ceramic compounds and low-alloy steels. To facilitate this, chemically pure mineral powders were pressure bonded to steel samples. The resulting composite samples were then heat treated to induce transformation, and hence compare the transformation behaviour in the vicinity of the ceramic/steel interface to that within the bulk of the steel. It is found that the minerals may be categorised into three groups, according to their observed efficacy in inducing the nucleation of bainite. The dominant reason for the stimulation of bainite nucleation seems to be a chemical interaction between the mineral and the steel. One noteable exception is TiO, which, within the limits of resolution, appears to remain inert, and yet enhances bainite formation.

Modelling reaustenitisation from ferrite/cementite mixtures in FeC steels

Abstract: The formulation of austenite which occurs upon heating low-alloy steels is known as reaustenitisation . Phase transformation theory applicable to the formulation of austenite from ferrite/cementite mixtures in FeC steels is described. The assumption of local equilibrium is made. Diffusion of carbon in cementite and ferrite is ignored. Under these assumptions, the process is controlled by the diffusion in austenite, the growing phase. Exact solutions to the equations to the equations are compared with results obtained using the finite difference method, for one-dimensional growth. It is found that the finite difference method is subjected to numerical inaccuracies which can be considerable. A method to circumvent this problem is described. Reverse time-temperature-transformation diagrams for FeC steels are presented.

Influence of heat treatments on microstructure of austempered ductile iron

Abstract: The influence of temperature and time of austempering on a nodular cast iron austenitised for 30 min at 900°C has been investigated using optical and transmission electron microscopy. The carbon content of the austenite has been evaluated by measuring the lattice parameter via X -ray diffraction. The structure consisted of bainite containing retained austenite, the amount of which increased, and the carbon content of which decreased, with increasing austempering temperature. No carbides were detected in the materials austempered at 300 and 370°C for up to 2 h, which contained only bainite and austenite. After austempering at 410°C and cooling to room temperature a certain amount of martensite was always detected. After long times at this temperature the austenite decomposed to ferrite and complex carbides. Martensite formation seems to be promoted by the decrease in the carbon content of austenite due to the precipitation of ɛ carbide homogeneously within it. During long austempering treatments at...

Formation mechanism of bainitic ferrite in an Fe-2 Pct Si-0.6 Pct C alloy

Abstract: The bainite transformation at 723 K in an Fe-2 pct Si-0.6 pct C alloy (mass pct) was investigated with transmission electron microscopy (TEM) and quantitative metallography to clarify the growth mechanism of the ferritic component of bainite. In early stages of transformation, the bainitic ferrite was carbide free. The laths of bainitic ferrite within a packet were parallel to one another and separated by carbon-enriched retained austenite. The average carbon concentration of the bainitic ferrite was estimated to be 0.19 mass pct at the lowest, indicating that the ferrite was highly supersaturated with respect to carbon. The laths did not thicken during the subsequent isothermal holding, although they were in contact with austenite of which the average carbon concentration was lower than the paraequilibrium value. In the later stage of transformation, large carbide plates formed in the austenite between the laths, resulting in the decrease in the carbon concentration of the austenite. Subsequently, the ferrite with a variant different from the initially formed ferrite in the packet was decomposed for the completion of transformation. The present results indicate that the bainitic ferrite develops by a displacive mechanism rather than a diffusional mechanism.

Morphology of bainite and widmanstätten ferrite

Abstract: Morphology of bainite and Widmanstatten ferrite in various steels has been investigated by means of microstructural and surface relief observations. It was shown that upper and lower bainite should be classified by ferrite morphology,i.e., lathlike or platelike, and that the morphology of cementite precipitation cannot be the index for the classification. Widmanstatten ferrite formed in the upper C-nose where ferrite grain-boundary allotriomorphs nucleate exhibits quite similar appearance with bainitic ferrite that forms in the lower C-nose of bainitic reaction. The only difference between them exists in the fact that Widmanstatten ferrite laths grow in the temperature range where primary ferrite forms and often terminate at a grain boundary ferrite but that bainitic ferrite has its own C-curve at temperatures belowB s and nucleates directly at an austenite grain boundary. The mechanisms for their formations are discussed.

Carbon content of austenite in isothermally transformed 300M steel

Abstract: Published data on the carbon concentration of retained austenite in 300M steel which has been isothermally transformed to bainite have been analysed using phase transformation theory. It is demonstrated that the chemical composition of the austenite can be predicted by assuming that the growth of bainite occurs without any diffusion, but that the excess carbon is partitioned shortly afterwards into the residual austenite.

The influence of thermomechanical treatment on the transformation behaviour of steels

Abstract: The effect of thermomechanical treatment on the γ – α-transformation in steel has been reviewed. It has been shown that the thermo-mechanically conditioned austenite significantly influences the kinetics of transformation due to the differences in the formation of product phases. An enhanced nucleation during the diffusion controlled transformation, as a result of austenite grain refinement and/or austenite strengthening, leads to a substantial refinement of the microstructure (ferrite grains, pearlite nodules). The deformation substructure of austenite may strongly affect the shear mechanism of the diffusionless transformation, which leads to finely fragmented martensite crystals. Such differences in the transformation characteristics result in different formation temperatures of transformation products and so to the changes in CCT diagrams.

Microstructure and fracture of aluminium austempered ductile iron investigated using electron microscopy

Abstract: An unalloyed nodular cast iron, in which the conventional addition of silicon has been replaced by aluminium, has been studied after heat treating in the bainite temperature range. Specimens were austenitised at 950°C for 2 h and then austemperedfor times up to 5 h at either 300 or 400°C. At 400°C the microstructure producedfor austempering times up to 3 h was typical of austempered ductile iron, consisting of carbide free upper bainitic ferrite together with a stable, high carbon enriched retained, reacted, austenite. For longer times, transition carbides are precipitated, initially η carbide in the ferrite, and after 5 h, χ carbide at the austenite/ferrite interfaces by decomposition of the high carbon austenite. Austempering at 300°C produced e carbide in a lower bainitic ferrite together with stable, high carbon retained austenite, for all heat treatment conditions: χ carbide precipitated at the ferrite/austenite interfaces after 5 h austempering. The fracture behaviour of samples austempered ...

Cementite precipitation during tempering of martensite under the influence of an externally applied stress

Abstract: The precipitation of cementite under the influence of an externally applied stress, during the tempering of martensite in steels, is investigated using transmission electron microscopy. The stress appears to favour the development of particular crystallographic variants of cementite in any given plate of martensite. Hence, a Widmanstatten array of cementite particles in a normally tempered sample changes to an array consisting of just one variant in stress-tempered samples. The results are discussed in the context of the mechanism of carbide precipitation during the lower bainite reaction.

Effects of vanadium addition on nucleation and growth of pearlite in high carbon steel

Abstract: The influence of vanadium addition on the microstructure of high carbon steels has been investigated. A careful examination of the initial stages of austenite decomposi~ion has been made, using a r...

Electron microstructure and mechanical properties of silicon and aluminium ductile irons

Abstract: Samples of unalloyed silicon and aluminium spheroidal graphite cast iron have been studied in the austempered condition. Austempering times of up 3 h at 400°C for Al SG and 1 h at 350°C for Si SG gives a typical ADI microstructure consising of carbide-free banitic ferrite and stable, high carbon enriched, retained austenite. This has an attractive combination of elongation and strength. For longer austempering times transition carbides are precipitated in the bainitic ferrite, η-carbide in the upper bainitic range, i.e.400°C for Al SG and 350°C for Si SG, and ϵ-carbide in the lower bainite range. Increasing amounts of transition carbide reduce the ductility and produce a mixed model of fracture. For longer austempring times X-carbide is precipitated at the ferrite/austenite boundaries leading to a more brittle fracture mode.

Wear- and seizure-resistant roll for hot rolling

Abstract: A hot-rolling roll excellent in wear and seizure resistances, which has a composition by weight consisting of 2.0 - 4.0 % of carbon, 0.5 - 4.0 % of silicon, 0.1 - 1.5 % of manganese, 1.0 - 7.0 % chromium, 2.0 - 10 % of molybdenum, 2.0 - 8.0 % of vanadium and the balance consisting of iron and inevitable impurities, a matrix structure consisting essentially of martensite, bainite or pearlite, and a metallographic structure comprising, by areal proportion, 0.5 - 5 % of graphite particles, 0.2 - 10 % of MC-based carbide and at most 40 % of cementite. The roll is well suited for a work roll in the latter stage of the finishing line of a hot strip mill.

Thermodynamics and kinetics of the formation of widmanstätten ferrite plates in ferrous alloys

Abstract: Experimental data on the formation of Widmanstatten/bainitic ferrite in ferrous alloys(i.e., the Widmanstatten start temperature, partition of alloying elements, incomplete transformation, lengthening kinetics,etc.) are examined on the basis of thermodynamic calculations and kinetic analyses. A morphological change of ferrite from grain-boundary allotriomorph to Widmanstatten plate occurs well above theT 0 temperature, except in high Mn and Ni alloys, but does so in the regime of carbon diffusion control in all alloys. Under the assumption that the plate tip consists of a pair of ledges of the height equal to the tip radius, the reported lengthening kinetics of ferrite plates can be accounted for very well by the diffusion-controlled motion of these ledges in a wide range of carbon supersaturation. It is also shown that the transformation stasis (incomplete transformation) observed below the kinetically definedB s in some iron alloys cannot be unequivocally attributed to either the completion of the precipitation of no-partitioned ferrite or the loss of the driving force for subsequent shear transformation.

Observations of plate martensite in a low carbon steel

Abstract: It has long been known that there are two predominant morphologies of martensite in steels. These morphologies are currently referred to as plate martensite and lath martensite and are primarily distinguished by the size and shape of individual martensite grains. Plate martensite is typically several microns thick and tens of microns in diameter, while lath martensite is typically less than one-half micron thick, a few microns wide, and tens of microns long. This paper presents evidence of a coarse plate-shaped martensite morphology in a commercial HSLA-100 steel which contains only 0.07% carbon. This morphology was discovered during microstructural characterization of specimens thermally cycled to simulate weld heat affected zones in a steel plate and was reproduced in other specimens subjected to a quench and temper heat treatment.

Experimental study of the eutectoid transformation in spheroidal graphite cast iron

Abstract: The decomposition of austenite to ferrite + graphite or to pearlite in spheroidal graphite cast iron is known to depend on a number of factors amongst which are the cooling rate and microsegregation of alloying elements (Si, Mn, Cu,...) issued from the solidification step. This present study was undertaken in order to deepen the understanding of the effect of alloying with low levels of Mn and/or Cu on the eutectoid reaction. For this purpose, differential thermal analyses were carried out where samples were subjected to a short homogenization treatment designed to smooth out the microsegregations. The effect of the cooling rate on the temperature of the onset of the growth of ferrite and pearlite and on the overall growth kinetics was investigated. A description of the conditions for the growth of ferrite and of pearlite is given and shows that the reactions can develop only when the temperature of the metal is below the lower boundary of the related ferrite + austenite + graphite or ferrite + austenite + cementite tri-phasic domain. The experimental results might then be conveniently understood when the appropriate reference temperature is used to express the effect of the cooling rate on the undercooling of the reaction. The effect of the cooling rate on the temperature of the onset of the ferrite growth is thus found to be alike what is observed for the eutectic reaction, with a measured undercooling which can be extrapolated to a zero value when the cooling rate is zero. Concerning pearlite, it is found that its growth undercooling takes values which are in agreement with similar data obtained on silicon steels

Method of preparing a high strength dual phase steel plate with superior toughness and weldability (LAW219)

Abstract: A high strength steel composition comprising ferrite and martensite/bainite phases, the ferrite phase having primarily vanadium and niobium carbide or carbonitride precipitates, is prepared by a first rolling above the austenite recrystallization temperature, a second rolling below the austenite recrystallization temperature; cooling between the Ar 3 transformation point and 500° C.; and water cooling to below about 400° C.

Process for producing hot forging steel with excellent fatigue strength, yield strength and cuttability.

Abstract: A process for producing a hot forging steel of ferrite plus bainite type which comprises hot forging a steel material containing, on the weight basis, 0.10-0.35 % of carbon, 0.15-2.00 % of silicon, 0.40-2.00 % of manganese, 0.03-0.10 % of sulfur, 0.0005-0.05 % of aluminum, 0.003-0.05 % of titanium, 0.0020-0.0070 % of nitrogen and 0.30-0.70 % of vanadium and further containing one or more elements selected from among chromium, molybdenum, niobium, lead and calcium each in a specified amount, cooling the steel in such a manner that the ferrite plus bainite structure will account for at least 80 % of the metallographic structure after transformation, and then conducting aging at a temperature of 200 to 700 °C. This process permits the production of a hot forging steel with sufficient fatigue strength, yield strength and cuttability, and thus has an extremely great industrial effect.

Stabilization of retained austenite due to partial martensitic transformations

Abstract: Laboratory of Engineering Materials, Helsinki University of Technology, SF-02150, Espoo 15, Finland (Received 20 December 1993) A~traet--The stabilization effect of retained austenite has been studied using Fe-Ni~C alloys with M s temperatures below 0°C via a two-step cooling procedure, i.e. the samples were first cooled to a temperature (Ta) below M s temperature and then heated to room temperature (RT), after being held at RT for a while, the samples were recooled to low temperatures (23 or 82 K) and then heated to RT. It was found that, during the second step of cooling, the martensitic transformation occurred at a temperature of M ~ which was lower than 1",. With increasing the amount of martensite formed during the first cooling, the difference in the martensitic transformation starting temperatures, AMs = Ms - M ~, increased. The mechanism of the stabilization of retained austenite during the second step of cooling is proposed to be mainly due to the inhibition effect produced by the previously formed martensite. The aging processes, which retard the growth of the previously formed martensite plates and reduce the number of the available nucleation sites, are the necessary conditions for the above mechanism to operate. By simplifying the internal resisting stress acting on the retained austenite due to the existence of martensite phase as a hydrostatic compressive stress, which increases with increasing the amount of martensite, the change in AM s is discussed from a thermodynamic point of view. 1. INTRODUCTION Kinsman and Shyne [8, 9] can be used successfully in explaining the kinetics of the stabilization of retained austenite at and above RT. Studies performed at The athermal transformation of martensite is sub-zero temperatures have shown that the stabiliz- independent of time, i.e. when austenite is cooled ation of retained austenite can also develop rapidly in below the Ms temperature at which martensitic trans- high Ni-steels at temperatures as low as -90°C formation starts, the athermal transformation of [10-12], where significant diffusion of carbon atoms austenite to martensite proceeds only when the should not occur in short time. This result shows temperature decreases. It is well known that, if cool- clearly the inability of the earlier theories in explain- ing is arrested at a temperature of Z~ within the ing the stabilization of retained austenite at low martensitic transformation range and the sample is temperatures. Although some researchers have allowed to age at the temperature T~ or a higher related the stabilization of retained austenite to the temperature, the retained austenite can be stabilized, stress relaxation in the surroundings of the previously and further transformation can occur only upon formed martensite plates [3, 4] and some earlier additional cooling below the arrest temperature [1-7]. works [4, 11] have shown that the degree of the This phenomenon has long been attributed to the stabilization of retained austenite varies with the diffusion and segregation processes of interstitial amount of the previously formed martensite, the real solute atoms either to dislocations in the austenite or effects of the previously formed martensite on the to the interfaces between austenite and martensite stabilization of retained austenite are still not yet fully phases [5-7]. Kinsman and Shyne have proposed a understood. model which attributes the stabilization of retained In the present study the stabilization of retained austenite to the diffusion of carbon atoms to austenite in Fe-Ni-C alloys with M S temperature austenite-martensite phase boundaries [8,9]. How- lower than 0°C was studied by using a magnetic ever, it has to be noted that most of the earlier studies susceptibility measurement technique. The effects of have been performed with alloys having M s tempera- both aging and the previously formed martensite on tures higher than room temperature (RT) and with the stabilization of retained austenite are clarified. A both the arrest and the aging temperatures above RT. thermodynamical analysis of the effects of the Since the diffusion of carbon atoms has played a previously formed martensite on the stabilization of predominant role in the earlier studies, the theories of retained austenite is also performed. 4117

Real time neutron transmission investigation of the austenite-bainite transformation in grey iron

Abstract: The first successful application of a new method to investigate phase transformations in real time, like the decomposition of austenite into bainite in grey iron, is described. During the ongoing transformation, transmission spectra of thermal neutrons, which contain Bragg edges corresponding to the crystal structure of the transforming phases, are recorded. By evaluating the height of these Bragg edges, which is a measure of the volume fraction of the phase, at different transformation times, the transformation can be followed in-situ in a time resolved manner. The method is compared to other previously used methods (micrographs, dilatometry, diffraction techniques); also a summary and an outlook are given.