Showing papers on "Pearlite published in 1993"

Austempering of low manganese ductile irons

Abstract: X-ray diffraction, optical microscopy, and hardness measurements were used to determine the austenitising kinetics and the stage I and stage II austempering kinetics of a low Mn, Cu iron and a low Mn, Ni–Cu iron during austempering at 300, 370, and 440°C after austenitising at 900, 950, and 1000°C. The study of the austenitising kinetics shows that 60 min is sufficient time to produce a constant C austenite content and that the kinetics are influenced strongly by the volume fraction of pearlite in the structure to be austenitised. Decreasing the austenitising temperature is shown to increase the driving force for the stage I reaction but to have only a small effect on the stage II kinetics. This shifts the heat treatment processing window to shorter times and can open a processing window that is closed for higher austenitising temperatures. Decreasing the austenitising temperature results in a more uniform austempered microstructure and reduces the amount of martensite in this structure. Decreasin...

Interphase precipitation in microalloyed engineering steels and model alloy

Abstract: Interphase precipitation of alloy carbide or carbonitride which occurs in association with the transformation interface between austenite and ferrite and between austenite and pearlite in steels can result in a fine particle dispersion that can contribute significantly to strength levels in a wide range of structural and engineering steels. Interphase precipitation has been found to occur in both proeutectoid and pearlitic ferrite, and various morphological aspects have been studied in a range of low carbon and higher carbon steels. Studies of this precipitation reaction are hindered by the fact that the transformation interface is lost upon cooling to room temperature, either by further transformation or by decomposition of the residual austenite phase to martensite. In the present work this has been avoided by developing a model alloy in which the precipitation reaction occurs, but in which the austenite is stabilised to room temperature, thus allowing a detailed examination of the interfacial r...

Influence of the microstructure on the fracture toughness and fracture mechanisms of forging steels microalloyed with titanium with ferrite-pearlite structures

Abstract: Titanium addition to vanadium microalloyed forging steels is one of the ways proposed to improve fracture toughness Fine TiN particles inhibit austenite grain growth after recrystallization at the high temperatures used to forge these steels TiN particles, however, can be formed in the liquid, and as their sizes exceed one micron, they could act as cleavage nucleation sites, impairing the fracture toughness The present work reports fracture toughness results obtained in Ti treated microalloyed forging steels, showing that in coarse microstructures cleavage is nucleated in coarse TiN particles, but that after refining the microstructure, voids originate at the same particles, resulting in ductile rupture

Improvement of fracture toughness of forging steels microalloyed with titanium by accelerated cooling after hot working

Abstract: Ti addition is becoming common practice in the fabrication of many grades of engineering steels. In general it is used with the aim of refining the microstructure through the inhibiting effect to grain coarsening exerted by small TiN precipitates. Although a number of recommendations are made for obtaining the maximum yield of fine TiN precipitates, nonetheless a certain proportion of the precipitate volume fraction is usually in the form of coarse TiN precipitates. Several authors suggest that such coarse TiN particles are simply ineffective in pinning the grain boundaries without impairing other properties. In a recent paper it was shown that these coarse TiN particles act as cleavage nucleation sites, impairing the fracture toughness of steel with coarse ferrite-pearlite microstructures. The present work reports further fracture toughness results and fracture mechanisms for Ti treated microalloyed forging steels. They show that after hot working and accelerated cooling transforming the austenite mainly in an acicular microstructure, ductile rupture results without any cleavage nucleated in the coarse TiN particles, as occurred when the same material had a coarse ferrite-pearlite microstructure.

Application of Hypereutectoid Steel for Development of High Strength Steel Wire

Abstract: Synopsis : The optimum patenting conditions for hypereutectoid steel to obtain a high drawability and a high work hardening rate were studied by metallographic examinations and laboratory drawing. Based on the present results, higher strength steel wire with small diameter has been manufactured on a production basis. 1) Provided that an appropriate cooling rate corresponding to carbon content is secured, the precipitation of thick proeutectoid cementite can be prevented. 2) In the practical patenting temperature range, the cementite plate thickness as well as the pearlite lamellar spacing decreases as the carbon content increases. 3) The work hardening rate during drawing and the delamination resistance are enhanced through elimination of the upper bainite in pearlite. 4) The maximum strength of 0.04mm wire manufactured from 0.96%C-0.2%Si-0.3%Mn-0.2%Cr steel without delamination occurrence has reached to as high as 5.70 GPa.

Banding and the nature of large, irregular pearlite nodules in a hot-rolled low-alloy plate steel: A second report

Abstract: The microstructure of a hot-rolled low-carbon plate steel has been examined using a combination of light microscopy and scanning electron microscopy. It has been found that in the hot-rolled condition, the microstructure consists of alternate bands of ferrite and pearlite, together with relatively large, irregular pearlite nodules. These large nodules were found to be comprised of pearlite, intragranularly nucleated ferrite (both Widmanstatten and idiomorphic), together with carbide-deficient and/or carbide-free regions. It is argued that the carbide-deficient and carbide-free regions form as a result of the premature initiation of the pearlite reaction, i.e. pearlite forms prior to the body of the austenite grains attaining the eutectoid composition. In order to model the formation of the banded structure, specimens were reaustenitized at 1050 °C for 10 min and furnace cooled. This heat-treatment cycle produced an austenite grain size which was less than the chemical banding wavelength. A model for the decomposition of austenite, under these conditions, is presented.

Scatter in small crack propagation and fatigue behaviour in carbon steels

Abstract: In order to investigate the physical basis of scatter in fatigue behaviour, rotatory bending of smooth fatigue specimens was carried out using two steels with different microstructures (ferrite/pearlite and tempered martensite). Fifteen or sixteen specimens were fatigued at each stress, and the initiation and propagation behaviour of a crack which led to the final fracture were examined for all the specimens. The emphasis was to investigate the scatter characteristics of fatigue behaviour based on the scatter of small crack propagation data. The data were analysed by assuming the Weibull distribution, and a statistical investigation of the physical basis of scatter was performed, i.e. the distributions for fatigue life, crack propagation life and growth rate of small cracks were established and the relation between the scatter in those distributions was studied.

A transmission electron microscopy study of copper precipitation in the cementite phase of hypereutectoid alloy steels

Abstract: The precipitation of copper has been detected and studied in three of the main decomposition products of austenite: allotriomorphic grain-boundary cementite, pearlitic cementite, and Widmanstatten cementite plates. The investigation has been carried out on two high-alloy hypereutectoid steels containing copper contents of 1.0 and 2.5 wt pct. The main advantage of these high-alloy steels is that the parent austenite phase remains stable upon cooling to room temperature, thus preserving the parent phase and the parent/product interfaces in the microstructure for subsequent examination. Transmission electron microscopy (TEM) revealed that the copper precipitation occurs in proeutectoid allotriomorphic grain-boundary cementite in association with the transformation interface. The copper particles were dispersed in the form of rows (or sheets) within the allotriomorphs of cementite. Evidence for copper precipitate particles nucleated at structural features imaged at the growth interface was also obtained. Copper precipitation was found to occur in both the ferrite and cementite lamellae of pearlite, and again, examination of partially decomposed structures revealed copper particles nucleated at the austenite/pearlite transformation interface. In addition, copper particles were also observed at the ferrite/cementite interface of pearlite. Copper precipitation observed in Widmanstatten cementite plates revealed a precipitate-free midrib region in the plates and a higher concentration of copper particles toward the broad faces of the plate. Copper particles were also found located at coarse linear interface defects at the broad faces of the plate.

Austempering of low manganese ductile irons. II: Influence of austenitising temperature

Abstract: X-ray diffraction, optical microscopy, and hardness measurements were used to determine the austenitising kinetics and the stage I and stage II austempering kinetics of a low Mn, Cu iron and a low Mn, Ni-Cu iron during austempering at 300, 370, and 440 o C after austenitising at 900, 950, and 1000 o C. The study of the austenitising kinetics shows that 60 min is sufficient time to produce a constant C austenite content and that the kinetics are influenced strongly by the volume fraction of pearlite in the structure to be austenitised. Decreasing the austenitising temperature is shown to increase the driving force for the stage I reaction but to have only a small effect on the stage II kinetics

Tensile and Fatigue Behaviour of Phosphorus Alloyed Sintered Steels

Abstract: Phosphorus alloyed sintered steels of chemical composition in the range 0·25–0·7 wt-%C and 0·45–0·8 wt-%P produce alloys with pore morphologies characterised by shape factors varying between 0·52 and 0·68 and microstructures characterised by different percentages of phases with high (pearlite and phosphorus rich ferrite) and low (low phosphorus ferrite) hardness. The results of tensile tests show that microstructure plays a major part in determining mechanical properties. In particular, while tensile strength is improved when high hardness constituents predominate, ductility requires an optimal composite microstructure. This is discussed in relation to the deformation and fracture behaviour of the alloys, by means of an extensive fracto graphic analysis. The results of fatigue testing show that the alloy Fe–0·7C–0·8P, characterised by a predominantly pearlitic microstructure, has a lower fatigue limit than the alloy Fe-0·25C–0·6P which is predominantly ferritic, although the former has a higher te...

Observations concerning transformation interfaces in steels

Abstract: The transformation interfaces of pearlite, allotriomorphic cementite, M[sub 23]C[sub 6], and Widmanstaetten cementite plates in high-Mn high-C alloy steels have been studied by TEM. Linear striations in the interface have been analyzed and related to intersections with stacking faults in the parent austenite phase. Emphasis is given to the pearlite interface where it is found that the striations at the interface increased as a result of thermomechanical treatment of the austenite prior to isothermal transformation, consistent with an increased density of planar defects. The effect of heat treatment, and Si alloying additions, are also considered. Both conventional and in situ TEM of the pearlite interface showed that the linear defects stretched across both ferrite and cementite phases at the pearlite interface, apparently without any deviation or change in image contrast. The results are compared with similar ones made of the static [gamma]/[alpha] interphase boundaries in duplex stainless steel. The effect of prior deformation structure in the parent austenite on the growth and interface structure of Widmanstaetten cementite plates has also been considered.

Production of high toughness rail having pearlite metallic structure

Abstract: PURPOSE:To produce a high toughness rail by imparting toughness to a high carbon steel, excellent in strength and wear resistance and having a pearlitic structure. CONSTITUTION:At the time of rolling a steel contg. 0.6 to 1.00% C to form into a rail, three passes of continuous rolling are performed in the finish rolling at temp. range of 850 to 1000 deg.C, at area reduction rate of 5 to 30% for each pass and with interpass time of <=8sec and then air cooling or accelerated cooling is executed. Based on the knowledge that, concerning a high carbon steel, austenitic grains are easy to recrystallize, and immediately after rolling, recrystallized grains close to dynamic recrystallized grains are produced, rolling is executed by the same method, by which fine rolling recrystallized grains can be obtd. to remarkably improve the roughness of the pearlitic steel.

Effects of alloying elements upon the eutectoid transformation in as-cast spheroidal graphite cast iron

Abstract: Detailed experimental results related to the growth of ferrite and pearlite during austenite decomposition in S.G. cast iron are presented. They have been obtained by means of quenching samples during directional freezing and by differential thermal analysis. The kinetics of austenite decomposition has been quantitatively measured in both cases. The effect of cooling rate, nodule count and alloying with low level of copper and/or manganese was investigated. The present results related to the effect of cooling rate and nodule count are in full agreement with the literature on the eutectoid transformation in S.G. cast iron. An increase of the former or a decrease of the latter shifts the kinetics curves for austenite decomposition towards lower temperatures. Moreover, it was found that adding manganese results in a significant increase in the ratee of pearlite and ferrite formation

Manufacture of steel material for bearing having excellent spheroidizing characteristic

Abstract: PURPOSE: To provide a method for manufacturing a steel material for bearing which can obtain the uniform spheroidal carbide structure without containing coarse flaky carbide by the ordinary spheroidizing and has excellent cold- workability after annealing and rolling fatigue resistant characteristic in the bearing parts executing the quenching and the tempering treatment. CONSTITUTION: At the time of hot-rolling the steel containing 0.8-1.2% C and the other specific composition, the rolling is executed in the specific rolling condition having an intermediate cooling, in which after rolling, immediately the steel material temp. is cooled so as to become once Ms point-700°C, and making the steel material temp. at the outlet side of the finish rolling at 700-880°C. After finish-rolling, this steel material is rapidly cooled at 550-700°C, and thereafter cooled to ≥450°C at 0.05-1°C/sec average cooling velocity. By this method, the steel material for bearing having excellent spheroidizing- characteristic composed of substantially proeutectoid cementite and pearlite in the structure can be manufactured. COPYRIGHT: (C)1994,JPO

High tensile steel sheet having excellent stretch flanging formability

Abstract: A high tensile steel sheet excelling in workability and stretch flanging formability, which is of a composite texture composed of a ferrite phase and a 2nd phase selected from the group consisting of martensite, bainite, pearlite, retained austenite and cold-transformed ferrite, wherein the volume fraction of the 2nd phase is not less than about 1.3 times higher at an outer region of the steel sheet than the volume fraction of the 2nd phase in a central region of the sheet thickness.

High strength rail excellent in toughness and ductility and its production

Abstract: PURPOSE:To obtain a rail steel excellent in toughness and ductility by subjecting a heated steel bloom, which has a composition containing specific amounts of C, Si, Mn, S, Cr, etc., and to which deoxidizing treatment is applied, to cooling under prescribed conditions and forming pearlite where V nitride precipitated on MnS is used as a nucleus. CONSTITUTION:A steel, which has a composition consisting of, by weight, 0.55-0.85% C, 0.2-1.2% Si, 0.5-1.5% Mn, 0.006-0.035% S, 0.1-1% Cr, 0.01-1% V, 0.0005-0.03% N, and the balance Fe and is deoxidized by the addition of Mn and/or Si, is refined. At the time of applying cooling, from an austenite region temp., to the head or further bottom part of a rail prepared by subjecting a bloom of this steel to hot rolling, etc., cooling is done through the temp. region between 700 and 500 deg.C at (1 to 5) deg.C/sec cooling rate. By the above procedure, pearlite where V nitride precipitated on MnS in an austenite grain is used as a nucleus can be formed.

On the ledge mechanism of pearlite growth: The Cu-Al lamellar eutectoid

Abstract: Recently the classical views of pearlite growth were challenged by a series of studies of the three heterophase boundaries present in growing lamellar eutectoids. The ferrite/cementite boundary was found to contain linear defects (direction steps), which maintained a micro-habit plane between the pearlitic phases, in both Fe-C and Fe-C-Mn steels. Observations of the ferrite/austenite and cementite/austenite growth interfaces revealed the presence of facets and growth ledges. From these observations Hackney and Shiflet proposed that pearlite grows from the parent austenite by a co-operative ledge mechanism. The motion of ledges on the growth interface determines the position of the triple points and hence the introduction of direction steps into the inter-lamellar boundary. Further observations have indirectly supported this ledge mechanism of pearlite growth. Direction steps have also been observed at the inter-lamellar boundaries in Cu-Be and Fe-Ti pearlites. This work aims to show that features of the lamellar eutectoid ([beta] [r arrow] [alpha] + [gamma]) in a Cu-11.95 wt%Al alloy can be readily rationalized in terms of a co-operative ledge mechanism.

The effect of boron addition on the tensile properties of control-rolled and normalized C-Mn steels

Abstract: Control-rolled and normalized C-Mn steels with and without boron alloying at two finish rolling temperatures of 800 °C and 1000°C were studied with respect to their tensile properties in order to investigate the role of boron in enhancing the strength of these materials. It was found that in boron steels ultimate tensile strength increased and impact transition temperature decreased owing to a decrease in grain size and an increase in pearlite fraction at both the finish rolling temperatures.

Effects of heat treatment cycle on equilibrium between ferrite and austenite during intercritical annealing

Abstract: A steel containing 0.2% C, 0.98% Mn, 0.46% Si and 0.47% Cr was intercritically annealed at 750, 770, 790 and 810 °C for 15 minutes and quenched to room temperature to produce dual-phase containing ferrite and martensite. Three heat-treatment cycles—IN aIQ and IA—were applied to the steel such that the structure at the beginning of intercritical annealing consisted of pearlite, martensite and austenite respectively. During intercritical annealing the steel first approaches partial equilibrium state is attained. The steel remains in that state uop to 770 °C, but above 770 °C departs from that state early during annealing because of partitioning of substitutional solutes. In the IN and IA cycles, the transformation rates are too slow for the partial equilibrium state to be attained in 15 minutes. In the case of the IA cycle, the departure from the partial equilibrium state increases with an increase in annealing temperature because of a decrease in the transformation rate with an increase in temperature.

Steel excellent in fatigue crack propagating property in wet hydrogen sulfide environment

Abstract: PURPOSE: To provide steel having properties in which fatigue cracks are hard to propagate in the case of use in a wet hydrogen sulfide environment. CONSTITUTION: This steel has a compen. contg. 0.01 to 0.2% C, 0.1 to 0.6% Si, 0.3 to 2.0% Mn and 0.01 to 0.1% sol.Al. Its structure is constituted of a mixed one of a primary phase of ferrite and a secondary phase of bainite and/or pearlite, and the average grain size of the ferrite is regulated to ≤20μm. The steel may be incorporated with one or more kinds of components selected from either or both of the following two groups: a primary group; 0.1 to 1.0% Cu, 0.1 to 2.0% Cr, 0.05 to 0.5% Ni and 0.01 to 0.5% Mo and a secondary group; 0.01 to 0.1% Nb, 0.01 to 0.1% Ti and 0.01 to 0.1% V. COPYRIGHT: (C)1994,JPO

The influence of pearlite on magneto-acoustic emission in plain carbon steels

Abstract: The present study utilizes pulse height distribution analysis to investigate the relationship between magneto-acoustic emission (MAE) and pearlite (carbon) content in iron and plain carbon steel. All of the samples were found to display the same basic features in the pulse height distribution—(1) a primary peak, attributed to 90° domain wall motion, and (2) a secondary peak, which became more pronounced at higher fields and was believed to be associated with domain magnetization vector rotation. In iron, the rotation component of MAE was dominant even at low levels of magnetization. In contrast, a fully pearlitic sample exhibited MAE produced primarily by 90° domain wall motion. Distributions from samples having “intermediate” compositions (containing both ferrite and pearlite) resembled one another more than either of the two “pure” component samples, suggesting a strong interaction between 90° domain wall processes and the ferrite/pearlite boundary.

Resolution of the Hall-Petch equation and comparison with the experimental results of three vanadium-titanium microalloyed steels

Abstract: Results obtained when increasing quantities of titanium are added to a vanadium microalloyed steel are reported. Starting with the TEM study of the particles and pearlite, the theoretical equations of Gladman, Kouwenhoven, Licka and Burnett were applied to a connecting rod manufactured with three medium carbon steels in order to calculate the yield strength and the impact transition temperature (ITT). Through a comparison of the theoretical and experimental results, it was concluded that Gladman's equation is the best equation for obtaining more realistic results in this kind of microalloyed steel.

Segregation of rare earth during isothermal transformation in low carbon steels

Abstract: The distribution of rare earth elements (RE) in steel is a significant topic tied to its application. It has been known that there is segregation of RE in austenite grain boundary. Liu and Hsu supposed that RE might segregate at interphase boundaries and influence the kinetics of isothermal transformation. In this investigation, the segregation of RE in proeutectoid ferrite, pearlite and granular bainite, combined with its effect on their kinetics in two low carbon steels is studied by means of SEM-EDAX.

Producing steel sheet having high tensile strength and excellent stretch flanging formability

Abstract: of EP0559225A high tensile steel sheet excelling in workability and stretch flanging formability, which is of a composite texture composed of a ferrite phase and a 2nd phase selected from the group consisting of martensite, bainite, pearlite, retained austenite and cold-transformed ferrite, wherein the volume fraction of the 2nd phase is not less than about 1.3 times higher at an outer region of the steel sheet than the volume fraction of the 2nd phase in a central region of the sheet thickness.

Production of high strength and high toughness hyper-eutectoid steel wire

Abstract: PURPOSE:To produce a high strength and high toughness hyper-eutectoid steel wire by subjecting hyper-eutectoid steel having a specified compsn. to hot rolling into wire rod, thereafter subjecting it to patenting treatment and furthermore executing cold wire drawing at a specified wire drawing draft. CONSTITUTION:The continuously cast slab of hyper-eutectoid steel contg., by weight, 0.9 to 1.2% C, 0.5 to 1.5% Si, 0.2 to 1.0% Mn, 0.02 to 0.05% Al and 0.003 to 0.0l5% N or furthermore contg. specified small amounts of at least one kind among Cr, Ni, Co and W or at least one kind among V, Nb and Ti is subjected to hot rolling into wire rod. Immediately after that or after reaustenitization, it is subjected to lead patenting treatment, so that the essence of the structure will be formed of fine pearlite and the precipitation of pro-eutectoid cementite in the central area from the central part of the wire rod to =145kgf/mm tensile strength. This steel element wire is subjected to cold wire drawing at 70 to 90% wire drawing draft, by which the high strength and high toughness hyper-eutectoid steel wire rod having 4 to 8mm wire diameter >=200kgf/mm tensile strength and >=30% fracture reduction of area can be produced.