Showing papers on "Pearlite published in 1977"

Deformation of pearlite

Abstract: Pearlite with its lamellae oriented mainly parallel to the longitudinal direction was prepared by Bolling's method of transformation in a steep temperature gradient. The Fe-0.7 pct Mn-0.9 pct C pearlite was drawn into wire and also into strip in dies designed to minimize macroscopically nonuniform deformation. Cross sections of the drawn wires and strip were examined by conventional and high-voltage transmission electron microscopy and were analyzed by quantitative metallography for a) average interlamellar spacing, b) distribution of interlamellar spacings, and c) orientation relationship between the cementite lamellae and the slip systems in the ferrite. The strength of pearlite is proportional to the reciprocal square root of the average interlamellar spacing, and the proportionality constant analogous to the Hall-Petch constant (k) is related to the strength of the cementite lamellae. If the stress for the propagation of slip through the cementite is assumed constant, a Hall-Petch type of equation can be derived for the strengthening of the pearlite against slip in the ferrite by piled-up groups of dislocations. Evidence for the plastic deformability of cementite is presented; sufficiently thin cementite plates were fully plastic. The exponential strain hardening of drawn pearlitic wires and of rolled pearlite is explained in terms of locally inhomogenous deformation revealed by the lack of fragmentation of the lamellae.

High strength low alloy structural steels

Abstract: The development of high strength low alloy structural steel has been a remarkable achievement in the field of metallurgy and is of great interest to both the producers and users of structural steels. Higher strength of the steel permits lighter constructions to be made with thinner sections giving rise to steel economy, increase of payload of transport vehicles and a greater utilisation of the design advantages. Of the various techniques available to enhance the properties of structural steels, addition of grain refining and precipitation hardening elements, niobium, vanadium and titanium, to low carbon steels and their controlled rolling or normalising have been found most advantageous. The alloying element required for making these steels is in micro-quantities and a large part of the strength is derived through grain refinement, which also contributes towards toughness. Various factors that control the properties of structural steels such as the effect on strength of the element in solid solution, ferrite grain size, strengthening by precipitation in ferrite, dislocation strengthening and pearlite volume and its fineness, have been discussed. Results of laboratory scale experiments carried out in NML have been summarised. Results of industrial scale trails on the production and controlled rolling of niobium steels carried out in Rourkela Steel Plant have been discussed. (Dr. S.S. Bhatnagar, Shri B.K. Guha, Shri R.K. Sinha; Scientists, National Metallurgical Laboratory. Dr. N.S. Datar, General Superindentent, Rourkela Steel Plant. Dr. R. Chattopadhyay, former Scientist, National Metallurgical Laboratory)

The formation of austenite from mixtures of ferrite and cementite as observed by HVEM

Abstract: The detailed mechanism of the transformation of various mixtures of ferrite and austenite was studied byin situ experiments in a high voltage electron microscope. Various phenomena were observed which seemed to be controlled by the rate of carbon diffusion when the γ/α interface was curved. The effect of manganese was studied by using commercial steels. In agreement with theoretical predictions based upon the local equilibrium model, the dissolution of cementite in ferrite can be more or less prevented by manganese. The effect on the dissolution in austenite is smaller. The reaction from lamellar pearlite to austenite is more complex, the cementite lamellae providing carbon to the austenite but also acting as barriers.

An investigation of the mechanism of splitting which occurs in tensile specimens of high strength low alloy steels

Abstract: A study has been conducted to investigate the metallurgical cause of splitting that is sometimes observed to accompany regular fracture in tensile and Charpy impact specimens. The susceptibility of a steel to tensile specimen splitting (TSS) has been shown to depend on both the composition as well as the processing of Cb (Nb) and V bearing high-strength, low-alloy steels. This study has revealed that Fe3C, either as grain boundary precipitate or in pearlite of a particular distribution, was the microstructural feature which seemed to be responsible for the TSS in the steels investigated. The compositional and processing factors influenced the susceptibility of specimens to TSS by controlling the Fe3C precipitation. There was no correlation between the susceptibility of a microstructure to TSS and its short transverse ductility. This result indicates that the occurrence of splitting in broken tensile or impact specimens is neither related to nor a good predictor of the probability of occurrence of the lamellar tearing that may occur during welding. A mechanism is presented which establishes the link between composition, processing, microstructure, splitting susceptibility and short transverse ductility.

The spheroidization of pearlite

Abstract: In a current publication we show that the kinetics of spheroidization of a deformed Al-CuAl2 eutectic can be explained by a simple geometric model based on Mullins's analysis of thermal grooving of grain boundaries. For this particular eutectic the kinetics are controlled by rapid interface diffusion, but in other systems the controlling rate could be volume diffusion in either phase or a slow interface reaction. In this Note we demonstrate that the same model provides a reasonable figure for the rate of spheroidization of pearlite in cold-worked and annealed, and hot-fatigued eutectoid steels.

Unidirectional transformation of Fe-0.8C-Co alloys: Part I. Process per structure relationships and the significance of pearlite interlamellar spacing measurements

Abstract: Fe-0.8C-Co alloys have been unidirectionally transformed by translation through a temperature gradient which establishes a single interface between the austenite and pearlite phases. A comparison between the temperature gradient calculated to maintain a single planar interface by preventing nucleation ahead of the interface and that actually required in the experiment led to the conclusion that the temperature gradient must retard the nucleation of pearlite. The relationship between interface morphology and the resultant pearlitic microstructure was examined, and comparisons made with more familiar pearlite structures produced by conventional isothermal heat treatments. The degree of alignment of the pearlite lamellae was analyzed metallographically and found to be predominantly within 12 deg of the growth direction. A detailed analysis of interlamellar spacing measurements as a function of growth velocity established that pearlite can possess a wide range of interlamellar spacings at any constant growth velocity and that this range seems to be dependent on growth velocity.

Method of making a steel wire adapted for cold drawing

Abstract: A steel wire after coming from the mill is brought to a temperature between 850° and 910° C. This is followed by multi-stage water-cooling of the wire in such a manner that the surface of the wire is cooled to below the martensite start temperature while austenite is retained in the core of the wire. The heat retained in the core of the wire serves to partially temper the martensite formed at the surface of the wire. The wire is coiled while the temperature remains substantially constant so that the retained austenite in the core of the wire undergoes an isothermal transformation to fine pearlite. The heat of transformation serves to complete tempering of the martensite. After coiling, the wire is air-cooled to room temperature. The final wire exhibits a structure consisting of an outer layer of tempered martensite and a core of fine pearlite. This structure imparts excellent cold-working characteristics to the wire.

Unidirectional transformation of Fe-0.8C-Co alloys: Part II. Kinetics of the eutectoid reaction

Abstract: Unidirectional transformation techniques have been applied to a study of the kinetics of eutectoid growth in Fe-0.8C-Co alloys. The technique readily yielded kinetic data which it is shown could be used to indicate the rate controlling process for pearlitic growth. Accurate measurements of interlamellar spacing (λ) could be made at controlled growth rates (V) and analyzed in terms of the expressionVλn, where the exponentn can indicate the rate controlling process. The results obtained by unidirectional transformation were compared with those achieved by conventional isothermal transformation, both to aid in the initial interpretation of the more unfamiliarV:λ data and also to show that the two different experimental routes lead to equivalent kinetic data. Analysis of the results obtained for Fe-0.8C-Co alloys suggested control by interfacial diffusion of carbon at high growth rates (n=3) changing towards volume diffusion of carbon at lower growth rates (n=2), but also revealed an unexpected region at very slow growth rates (n=4). This anomalous region could be explained in terms of the partitioning of cobalt as the growth rate decreased. It was also shown that cobalt additions decreased the pearlite interlamellar spacing at constant undercooling or growth rate.

Cast alloy for composite roll shell

Abstract: PURPOSE: To considerably improve the wear resistance of an alloy by restricting the component ratio of the alloy and heat treatment temps. to form a nearly white pig iron-like matrix in which granular pearlite and sorbite occupy more than 50%, and by limiting the amt. of carbides precipitated in the matrix. CONSTITUTION: An alloy is refined consisting of, by wt., C; 2W3%, Si; 0.4W1.5%, Mn; 0.4W2%, Ni; 1.5W4%, Cr; 0.8W3%, Mo; 0.5W2%, one or more out of V, Nb, Ti, Zr and W; 0.5W3.5% and the balance Fe practically. The alloy is subjected to diffusion heat treatment, hardening normalizing heat treatment, spheroidizing heat treatment and tempering strain relieving heat treatment in each suitable temp. range to form a nearly white pig iron-like matrix in which sorbite of high toughness and granular pearlite occupy more than 50%, and fine graphite is hardly precipitated. At the same time, the content of Fe type carbide is reduced to 30W50%, and the carbide is finely granulated and dispersed. 2W10% of V, Ti, Zr and Nb carbides of high hardness are further precipitated. Thus, the wear resistance of the alloy can be enhanced considerably. COPYRIGHT: (C)1979,JPO&Japio

Spheroidizing heat treatment method for high carbon- chromium-molybdenum bearing steel

Abstract: PURPOSE:To perfectly spherodize metal carbides in the structure of a high carbon Cr-Mo bearing steel by repeatedly annealing the steel under specific conditions CONSTITUTION:A high carbon Cr-Mo steel contg C; 080-120%, Si; 010-080%, Mn<20%, Cr; 1-2% and Mo; 01-10% is refined in a high frequency furnace or the like and cast into an ingot The ingot is forged and drawn to a bearing round bar of uniform pearlite structure The bar is then heated to a temp from the Acid point (742 degC of the steel to the Acie point (776 degC), held for about 1hr, slowly cooled from the Arib point (710 degC) to the Arie point (660 degC) at a very slow cooling rate of 10 degC/hr, and held at 650 degC for 1hr The annealing is repeated 4 times or more By the treatment metal carbides in the structure are spheroidized and become few spherical carbides of large diameter, and hence the wear resistance and hardenability of the bearing steel are enhanced

High duty ductile case iron and its heat treatment method

Abstract: A ductile cast iron having a high tensile strength as well as a high elongation due to its matrix structure of finely mixed ferrite and pearlite grains obtained by the heat treatment. The material is pearlitic ductile cast iron and may be of ordinary ductile cast iron composition with the only exception that the manganese content being substantially less than 1%. A method of heat treatment for obtaining such a ductile cast iron, which is composed substantially of heating the material rapidly to form ferrite, austenite and graphite co-existing structure, and air cooling the same to change that structure into the above mentioned matrix structure.

Characteristics of graphite and cast iron particle dissolution in iron during sintering

Abstract: 1. The dissolution of graphite in iron may take place with the formation of a liquid phase; the temperature at which this phase appears is determined by the amount of ash impurities in the graphite. 2. The pearlite produced as a result of impregnation of iron with carbon forms discrete fields arranged in directions of preferential diffusion of carbon into iron rather than a continuous zone around the periphery of the impregnation source. 3. The appearance of a large quantity of a liquid phase accompanying the sintering of iron with a high-ash graphite is chiefly responsible for the formation of structurally free cementite.

HSLA Metallurgy in Europe

Abstract: A look at high strength low alloy steels from the European viewpoint: metallurgical factors, economic constraints and future development trends

Steel of excellent sr embrittlement resistance

Abstract: PURPOSE: To minimize embrittlement of steel SR (strain relief annealing) treatment and impart strength, notch toughness, etc. suitable for various kinds of welded structures to the steel by specifying each vol. ratio of ferrite and pearlite as the structure of a more than 30mm thick plate before SR treatment. COPYRIGHT: (C)1978,JPO&Japio

Pearlite-reduced HSLA steels for line pipe

Abstract: The rapid progress in understanding the metallurgy of ferrite-pearlite steels has led to the development of high-strength, tough pearlite-reduced steels capable of meeting stringent Arctic line pipe specifications The classical Nb or Nb-V pearlite-reduced steels may be used in cold climates although it appears that heavy controlled-rolling schedules are required to produce X70 properties in heavy-wall (19-mm) pipe These steels have been shown to provide a dequate properties in thinner sections Recent commercial experience with a molybdenum-modified pearlite-reduced steel has confirmed the laboratory results for longitudinally welded pipe reported in the present paper The Mo-Nb steel exhibited a yield strength in excess of 480 MPa, coupled with good toughness in a 197-mm-thick wall pipe This steel was not subjected to heavy controlled rolling and the finish-rolling temperature was 760°C Spiral-welded X70 pipe has been commercially produced using the Mo-Nb pearlite-reduced steel, and laboratory results predict that a pipe yield strength of at least 540 MPa should be attainable in similar steel compositions when tested to API specifications The probable introduction of new processing techniques, eg, water cooling, either during rolling or after rolling, will undoubtedly upgrade pearlite-reduced steels for application under more demanding conditions

Structure and properties of low-pearlite steel

Abstract: 1. In terms of increasing stability of austenite the steels investigated can be arranged in the following order: 08G2S; 08G2S+0.03% V; 08G2S+0.05% Nb; 08G2S+0.02% Nb+0.03% V. 2. The increase in the strength of steels 08G2S, 08G2SB, and 08G2SF and the increase of their cold resistance when the final rolling temperature is lowered to 700° are due to refining of the grains and the substructure and also to slowing down of ferrite recrystallization. Raising the final rolling temperature leads to a coarser substructure and intensive recrystallization. 3. The increase in the strength of 08G2S steels microalloyed with vanadium or niobium is higher than for the unalloyed steel due to the precipitation of carbonitrides of these elements. Niobium is more effective in this respect. 4. The notch toughness is highest for 08G2S steel with carbonitride hardening after final rolling at a temperature in the upper range of the austenite region.

Effect of carbon and the microstructure on the hardening of steel during cold deformation

Abstract: 1. The carbon content and the shape of cementite in the steel (lamellar or granular) have a substantial effect on the flow stress during cold plastic deformation. The formulas obtained in this work make it possible to determine this value quantitatively. 2. The flow stress of steels with a structure of divorced pearlite is lower than that of steel with lamellar pearlite, the difference increasing with the carbon content of the steel, i.e., with increasing amounts of pearlite in the structure.

Heat resistant cast iron - alloyed with (scrap) nickel-base alloy is used as car exhaust manifold

Abstract: Cast iron is given improved heat resistance by adding to the liquid iron, before casting, 0.5-8% (1-2%) of a Ni-base high temp. alloy in the form of scrap, as well as Mo to give an Mo content of 0.25%. The alloy is also inoculated before casting using known agents, and the casting is heat treated at a temp. above the pearlite transformation, at about 800 degrees C before mechanical treatment.

Steel rings for bearings prodn. - by centrifugal casting with controlled cooling, and heating, followed by rolling to shape

Abstract: The prodn. of ring-shaped workpieces of hypereutectoid steel, which after hardening, contains low C martensite with a dislocation substructure, comprises cooling the hollow ingot, or a section of the ingot, obtd. by centrifugal casting, from the casting temp. to is not >100 degrees below the eutectoid transformation, and re-heating the casting to is not >100 degrees C. above the temp. of the eutectoid transformation. After a spheroidal pearlite structure is obtained, the temp. is raised to is not >1150 degrees C, followed by forming a semi-finished product, e.g. by rolling, and finally applying a hardening and annealing treatment. Method utilizes fully the thermal energy supplied by the centrifugal casting of the ring, being sufficient for the subsequent forming and heat treatment, which gives a saving in time.

Relaxation resistance of carbon steels in relation to the structure

Abstract: 1. The strength and ductility of steels at 20° decrease with increasing amounts of Widmanstatten structure and increasing grain sizes. However, the strength characteristics of steels with Widmanstatten structure are higher, and the ductility lower, than for steels with the same grain size but rounded grains, with coarser pearlite and ferrite supersaturated with carbon. 2. When the Widmanstatten structure exceeds grade 3 the relaxation resistance at 430° increases, mainly due to larger grain sizes. At higher grdes of Widmanstatten structure the relaxation resistance decreases.

Effect of strengthening and embrittlement on the dissipation of energy in the deformation-aging of casing steels for atomic plants

Abstract: 1. In the original undeformed condition the primary mechanism for dissipation of energy in Cr−Ni−Mo−V and Mn−Ni−Mo pearlite casing steels is magnetomechanical hysteresis. 2. Plastic deformation almost completely suppresses magnetomechanical hysteresis and then the primary mechanism for the dissipation of energy is the mechanism of microplastic deformations. 3. For the investigated class of steels the composite characteristics of dissipation of energy were determined. These have a correlation relationship with the criteria for determining the tendency of steels toward deformation aging obtained on the basis of the results of mechanical tests. 4. A close correlation relationship was obtained only for the characteristics of damping determined without the application of a magnetic field. 5. With an increase in tempering time there is a decrease in the tendency of casing steels toward aging and an increase in their tendency toward deformation strengthening. 6. With an increase in the ductility of the investigated steels in the original condition there is an increase in the contribution of work hardening to embrittlement in deformation aging.