Showing papers on "Pearlite published in 1985"

Ferrite recrystallization and austenite formation in cold-rolled intercritically annealed steel

Abstract: The recrystallization of ferrite and austenite formation during intercritical annealing were studied in a 0.08C-1.45Mn-0.21Si steel by light and transmission electron microscopy. Normalized specimens were cold rolled 25 and 50 pct and annealed between 650 °C and 760 °C. Recrystallization of the 50 pct deformed ferrite was complete within 30 seconds at 760 °C. Austenite formation initiated concurrently with the ferrite recrystallization and continued beyond complete recrystallization of the ferrite matrix. The recrystallization of the deformed ferrite and the spheroidization of the cementite in the deformed pearlite strongly influence the formation and distribution of austenite produced by intercritical annealing. Austenite forms first at the grain boundaries of unrecrystallized and elongated ferrite grains and the spheroidized cementite colonies associated with ferrite grain boundaries. Spheroidized cementite particles dispersed within recrystallized ferrite grains by deformation and annealing phenomena were the sites for later austenite formation.

A micro‐mechanics analysis for short fatigue crack growth

Abstract: Crack initiation and early growth of fatigue cracks in a fully annealed 0.4% carbon steel was investigated using plastic replicas and torsion loading. In a structure consisting of a 70/30 mixture of pearlite and ferrite the cracks are seen to develop and grow initially along slip bands in the ferrite phase. Energetic considerations lead to the formulation of a model which, while characterizing short crack growth rate, also considers those microstructural variables relevant to fatigue crack initiation and early crack growth. The driving force for crack growth is provided by the energy of the slip band; correspondingly crack growth per cycle is proportional to the strength of the slip band. In the short fatigue crack region, cracks grow initially at a fast rate but deceleration occurs quickly and, depending on the stress level, they either arrest or are temporarily halted at a critical length. This critical length is shown to coincide with the value of the threshold length for crack growth under LEFM conditions.

Kinetics of austenite-ferrite and austenite-pearlite transformations in a 1025 carbon steel

Abstract: Isothermal and continuous-cooling transformation kinetics have been measured dilatometrically for the γ → α+ γ′ and γ′→ P reactions in a 1025 steel. The isothermal transformation of austenite for each reaction was found to fit the Avrami equation after the fraction transformed was normalized to unity at the completion of the reaction and a transformation-start time was determined. The transformation kinetics under isothermal conditions therefore were characterized in terms of then andb parameters from the Avrami equation together with the transformation-start times. The parametern was found to be independent of temperature over the range studied (645 to 760 ‡C) and to have values of 0.99 and 1.33 for the ferrite and pearlite reactions, respectively. This indicates that the nucleation condition is essentially constant and site saturation occurs early in the transformation process. The continuous-cooling experiments were conducted at cooling rates of 2 to 150 ‡C per second to determine the transformation-start times for the ferrite and pearlite reactions and the completion time for transformation to pearlite under CCT conditions. Both reactions were found to obey the Additivity Principle for continuous cooling provided that the incubation (pre-transformation) period was not included in the transformation time. The isothermal transformation data and CCT transformation-start times have been incorporated in a mathematical model to predict continuous-cooling transformation kinetics that agree closely with measurements made at three cooling rates.

Influence of microstructure on fatigue crack initiation in fully pearlitic steels

Abstract: The effect of microstructure on the fatigue crack initiation of fully pearlitic steels was studied through independent variation of the prior austenite grain size, pearlite colony size, and the pearlite interlamellar spacing. Increasing yield strength (controlled by decreasing the pearlite interlamellar spacing) was seen to increase the smooth and notched-bar crack initiation endurance limit. Grain and colony size variations, at constant yield strength, were seen to exhibit no effect on crack initiation. Scanning Electron Microscopy revealed smooth-bar cracks to have initiated at surface inclusions. The influence of the pearlite interlamellar spacing, reflecting a change in the effective slip length, and the differences between notched and smooth-bar fatigue specimens for studying the effects of microstructure on crack initiation are discussed.

Estimation of nucleation rate and growth rate from time dependence of global microstructural properties during phase transformations

Abstract: An approach has been developed for calculating nucleation and growth rates from the time variation of the volume fraction, surface area, and integral mean curvature of the product phase during a phase transformation. The local growth rate of the product phase can be estimated without any assumption or knowledge regarding the nucleation behavior. The approach is applicable over the complete range of volume fractions(i.e., from zero to one). Practical feasibility of the approach has been demonstrated by deducing the nucleation and growth rates of austenite during austenitization of pearlite in an Fe-0.83 wt pct C alloy at 730 ‡C, 740 ‡C, and 750 ‡C. It is concluded that the local growth rate and nucleation rate of austenite remain constant during an isothermal austenitization of pearlite.

The laser surface-alloying of iron with carbon

Abstract: Observations are reported on the structure of iron, laser surface-alloyed with carbon. Repeated laser surface-melting of iron pre-coated with DAG graphite has produced layers containing up to ∼6 wt % C, showing fine-scale white iron structures. Eutectic regions (interlamellar spacing ∼0.5μm) have been shown by transmission electron microscopy to consist of Fe3C + ferrite, the latter having formed by decomposition of austenite during solid state cooling. Regions of fine pearlite (spacing ∼55 nm) have also been observed. Carbon diffusion into the substrate during alloying produces a zone containing austenite and martensite.

Stresses and phase transformations occurring in quenching of carburized steel gear wheel

Abstract: A method for analysing temperature, metallic structures, stress and strain, and carbon content during the carburized quenching of a steel gear is presented, and the results of calculations using the finite element method are compared with experimentally measured data. Since carburization precedes quenching, a diffusion equation is solved in order to determine the carbon content. Calculated profiles of temperature, stresses, and martensite and pearlite volume fractions during quenching are presented, and the effects of coupling between them are also considered.MST/19

The effect of alloying elements on pearlite growth

Abstract: The model developed by Sharma 1 and Sharmaet al. 2 for the mechanism of pearlite growth in ternary Fe-C-Cr alloys has been extended to other systems. Detailed thermodynamic and semi-empirical kinetic calculations have been carried out to determine pearlite growth rates for a number of Fe-C-X alloys (X = Mn, Cr, Ni, Si) and compared with the experimental data from the literature. It has been shown that the pearlite growth is, in general, controlled by the alloying element boundary diffusion at low supersaturations and carbon volume diffusion at high supersaturations, as predicted by the model. The transition temperature between the two mechanisms is a function of the amount and type of alloying element.

Formation of austenite from a ferrite-pearlite microstructure during intercritical annealing

Abstract: The formation of austenite from a coarse grained ferrite-pearlite microstructure during intercritical annealing was studied. According to the variation of the microhardness values in ferrite and austenite with intercritical annealing time, austenite formation was classified into four stages: (a) austenite growth into pearlite at a slower rate than the dissolution rate of pearlite, (b) subsequent growth of austenite into pearlite and formation of thin film type austenite at ferrite grain boundaries, (c) growth of austenite into ferrite, (d) equilibrium of ferrite and austenite. In particular, plate-like austenite was observed. The experimental results indicated that the growth process of this type austenite was controlled by carbon diffusion in austenite.

Heating and cooling transformation diagrams for the rapid heat treatment of two alloy steels

Abstract: In rapid heat treatments, such as laser and induction hardening, a thin surface layer of austenite is formed on a part during heating After cooling for only a few seconds, this layer transforms into martensite, pearlite, bainite, and/or proeutectoid ferrite/cementite, depending on the cooling rate, dissolved carbon content, homogeneity of the dissolved carbon, austenite grain size, and steel composition In this work, transformation diagrams suitable for rapid heat treatments were determined by dilatometry for two alloy steels, one hypoeutectoid and one hypereutectoid A short austenitizing time after fast heating was used Models for computer calculations of phase transformations with the use of isothermal diagrams are also discussed Calculations of continuous heating diagrams from the isothermal heating diagrams gave good agreement in comparison with the observed diagrams

Machinable ductile or semiductile cast iron and method

Abstract: A method is disclosed which comprises: (a) forming a ferrous alloy melt consisting essentially of by weight, 3-4% carbon, 2.0-3.0% silicon, 0.1-0.9% manganese, up to 0.02% phosphorus, up to 0.002% sulphur, up to 1% contaminants or impurities, 0-0.4% molybdenum, 0-3.0% nickel or copper, and the reminder essentially iron, the melt being subjected to a graphite modifying agent in an amount and for a period of time effective to form either ductile or semiductile iron upon solidification; (b) heat treating the solidification of said melt by austempering to form a matrix consisting substantially of high carbon austenite and ferrite and a cell boundary having unreacted low carbon austenite; (c) heating said austempered iron to a pearlite forming temperature (1200°-1300° F.) and holding (2-5 minutes) at said temperature to permit the unreacted low carbon austenite to form pearlite; and (d) cooling said heat treated iron to room temperature.

Structures of machined steel chips

Abstract: Transmission electron microscopy studies have been carried out on the structures of chips formed during the high-speed machining of steel. The chip bodies, which reached temperatures of ~300°C during machining, had a pearlitic-ferritic structure with very fine, elongated, parallel-sided ferrite cells. The structure of the flow zone, which attained a maximum temperature of ~900°C, consisted, in all cases, of equiaxed ferritic cells, 0·5–1·5 μm dia., with dislocation tangles in many cell boundaries, but few internal dislocations. No pearlite was observed in the flow zone, but initially pearlitic areas showed cementite networks at cell boundaries and very small cementite particles. Coarse cementite particles in spheroidized steel remained largely intact in the flow zone. Textures developed in the flow zone and in the chip body were ferrite shear textures. The flow zone is a thermoplastic instability, and this work suggests that the observed fine, equiaxed cell structures have the characteristic of pe...

Manufacture of hot rolled steel stock

Abstract: PURPOSE:To improve not rolling efficiency end yield and to reduce cost, by combining particle diameter forecast contg. forecast of hardness of each microstructure and forecast of structural vol. ratio, and suitably selecting component and manufacturing condition. CONSTITUTION:In case of obtaining products by rolling conventional carbon steel at the temp. higher than Ar3 transformation temp., then cooling the plate, at first, an austenite grain diameter dgamma, and a residual stress quantity epsilon just before starting cooling are calculated from component, heating and rolling conditions. Next, vol. ratio of each structuer (ferrite, pearlite, bainite and martensite), hardness and grain diameter after end of cooling are calculated from cooling condition, dgamma, and epsilon thereafter. Further, material quality of the final hot rolled steel stock is calculated from these microstructures (vol. ratio, hardness and grain diameter of structure), and at least manufacturing conditions (component, heating condition, rolling condition and cooling condition) are controlled so that the material quality becomes the desired one. In this way, the material quality is accurately estimated and the hot rolled steel stock having accurately controlled quality is manufactured.

Spheroidal graphite cast iron casting and its manufacture

Abstract: PURPOSE: To obtain a cast iron casting having superior fatigue strength, excelling in workability, and having a matrix structure consisting of fine pearlite structure by controlling the austenitizing temp. at normalizing as well as the Mn quantity of the titled cast iron casting having a specific composition. CONSTITUTION: The molten metal consisting of, by weight, 3.0W4.0% C, 1.5W2.5% Si, ≤0.4% Mn, 0.01W0.08% Mg, ≤0.15% P, ≤0.03% S, and the balance Fe is cast in a mold, which is drawn from the mold at the A 1 transformation point or above, heated and held at the temp. right above the A 1 transformation point, e.g., about 800W850°C, and then cooled rapidly to produce the spheroidal graphite cast iron casting having a fine pearlite structure. This casting excels in workability as well as in toughness. COPYRIGHT: (C)1986,JPO&Japio

Iron sintered alloy for valve sheet

Abstract: PURPOSE:To obtain an iron sintered alloy for valve sheet in which wear resistance is improved, injury of opposed material is decreased, by dispersing uniformly fine hard particles of a specified compsn. in Fe-C matrix structure composed mainly of pearlite structure. CONSTITUTION:Alloy powder for the hard particles consisting of 1.0-2.0% C, 5.0-20.0% Cr, 0.2-3.0% Mo, 0.1-1.0% V and substantially the balance Fe is added to iron powder for the matrix structure composed mainly of pearlite structure consisting of 0.5-2.0wt% C, 0.25-4.0% Cr, 0.1-0.6% Mo, 0.05-0.2% V and substantially the balance Fe. Furthermore, graphite powder, zinc stearate, etc. are added thereto, these powders are compacted, then sintered. In this way, the hard particles having 40-150mu average particle diameter, Hv 300-700 hardness are dispersed uniformly in 5-20% range. Further, the hard particles are joined firmly with matrix structure to form the titled sintered alloy.

Cast iron for rocker arm

Abstract: PURPOSE:To provide the titled cast iron having excellent resistance to wear, scuffing, etc. by consisting said iron of sepcifically composed C, Si, Cr, W, V, Mo, Co and Fe and dispersing and crystallizing carbide into the matrix consisting of structure such as austenite or the like. CONSTITUTION:A cast iron for a rocker arm is a cast iron consisting of 0.5- 4wt% C, 0.1-2.0% Si, 0.5-35% Cr, 0.05-20.0% W, 0.03-10.0% V, 0.05-15.0% Mo, 1.0-10.0% Co and the balance substantially Fe, which Fe is incorporated at >=10%. Said cast iron has the structure dispersed and crystallized with carbide in the matrix consisting of the structure contg. the phase of at least >=1 kind among austenite, martensite, bainite and pearlite. The above-mentioned cast iron is highly resistant to wear and scuffing and decreases damage on the mating material to be slided with when said cast iron is used not only for unleaded gasoline but for high lead gasoline as well.

Transformation of austenite into granular pearlite in carbon and alloy steels

Abstract: 1. A granular pearlite structure in steel may be obtained directly from homogeneous austenite during isothermal decomposition after previously thermally cycling it at temperatures of the subcritical region. 2. During thermal cycling, alternating thermal stresses of considerable absolute value arise in austenite, and this leads to its plastic deformation. During plastic (thermoplastic) deformation of homogeneous austenite, even with small degrees (up to 1%) preceding eutectoid transformation, conditions are also created for transformation (a typical dislocation structure) with which the energy factor prevails over the kinetic factor, and decomposition of homogeneous austenite is realized with formation of a granular pearlite structure. 3. By means of TCT in the stream of a rolling mill it is possible to obtain a finely dispersed granular pearlite structure in rolled material 6.5–18 mm in diameter. Use of this rolled material makes it possible, as a result of shortening the duration or completely excluding the spheroidizing anneal, to simplify the production cycle of tool wire and gauge steel for cold upsetting.

Sintered alloy material for valve seat

Abstract: PURPOSE:To obtain the titled sintered alloy material having low porosity and superior various characteristics such as superior resistance to wear, corrosion and falling by providing a specified composition consisting of C, Cu, Mo and Fe, and forming a structure having dense pearlite as the matrix CONSTITUTION:This sintered alloy material for a valve seat for an internal- combustion engine has a composition consisting of, by weight, 09-16% C, 10-30% Cu, 03-08% Mo and the balance Fe with inevitable impurities or further contg 02-05% P The porosity of the alloy material is <=120%, and the structure has dense pearlite as the matrix The alloy material has superior resistance to corrosion by S, Cl, Br, etc in fuel and lubricating oil, and it also has superior resistance to wear and falling

Manufacture of wire rod for wire having high strength as well as weatherability

Abstract: PURPOSE:To obtain the wire rod for wires having high strength as well as improved weatherability by incorporating Cu and the like to high carbon steel having a prescribed composition and carrying out holding heat treatment at specific temp. after the ferrite + pearlite transformation. CONSTITUTION:The steel containing 0.5-1.0% C, 0.1-2.0% Si, 0.3-1.2% Mn, 0.2-2% Cu, and if necessary, 0.01-0.30% V, 0.2-1.0% Cr, and 0.01-0.1% Al is manufactured. This billet or ingot is hot-rolled into wire rods, which are cooled from the austenite zone to be subjected to ferrite+pearlite transforma tion, and are then subjected to holding heat treatment at 400-500 deg.C for 5min-10hr. In this way, the highly strengthened wire rod for wires having increased corrosion resistance can be obtained, accordingly the wire rods suit ably used for PC concrete buildings, springs, etc., can be manufactured at low cost.

High tensile band stock and its production

Abstract: PURPOSE: To produce a band stock having excellent strength and ductility with high efficiency without pollution by hot rolling and cold rolling a steel contg. C and Mn at a specific ratio each then subjecting the steel to continuous annealing and slitting under specific conditions. CONSTITUTION: The steel consisting, by weight, 0.25W0.60% C, 0.5W1.50% Mn and the balance Fe and inevitable impurities is subjected to the hot rolling and cold rolling by the conventional practice. The steel is then annealed in an annealing temp. range of the A c3 transformation point W (A c3 transformation point + 100°C) at a cooling rate of 10W50°C/sec and thereafter the steel sheet is slit to a desired width to form the band stock. Such band stock consists of 10% area rate of ferrite and the balance having the independent or mixed structure of bentonite, fine pearlite or martensite and has ≥80kgf/mm 2 tensile strength. The high tensile band stock having the goo ductibility is thus efficiently produced. COPYRIGHT: (C)1987,JPO&Japio

Fracture-toughness testing of ductile cast irons

Abstract: The fracture toughness of ferritic, spheroidal graphite ductile cast iron has been measured by a single specimen J-integral technique. Two ductile cast irons were investigated; they had similar volume fractions of graphite, graphite nodule sizes, and ferrite grain sizes. One, however, contained approximately 15% pearlite, while the other had less than 1% pearlite. The alloy with greater pearlite content exhibited higher strength and higher ductile-to-brittle transition temperature. Although cast irons are generally perceived as being low in toughness, the toughness values measured on fully ferritic nodular iron were quite high (K/sub IC/ = 80 to 106 MPa..sqrt.. m or 73 to 96 ksi..sqrt.. in from -80 to 25/sup 0/C).

Heat resistant cast iron

Abstract: PURPOSE:To improve the heat check resistance and durability of cast iron and to make the cast iron suitable for use as the material of a cylinder head by adding very small amounts of Cr, Mo, V and Ni+Cu to the cast iron and forming a pearlite structure. CONSTITUTION:This cast iron consists of, by weight, 3.5-3.9% C, 1.7-2.2% Si, 0.5-1.0% Mn, 0.1-0.5% Cr, 0.2-1.0% Mo, 0.1-0.4% V, 0.2-2.0% Ni+Cu and the balance Fe with inevitable impurities. By the composition, a low Young's modulus, a high yield point at high temp. and superior heat conductivity are provided, and a pearlite matrix structure which is stable at high temp. is formed. Since the heat check resistance and durability of the cast iron are improved by the composition, the cast iron can be used as a material for a cylinder for a diesel engine used under severe thermal load, and the cost can be reduced.

Spheroidal graphite cast iron caliber roll having excellent resistance to crack and wear and its production

Abstract: PURPOSE:To provide a titled roll having excellent resistance to crack and wear by forming the working layer of a roll consisting of a specified chemical compsn. and contg. a caliber part into the matrix structure which prevents the precipitation of ferrite as far as possible and has the dense pearlite structure. CONSTITUTION:The chemical compsn. consists, by wt%, of 3.0-3.8% C, 1.5- 2.5% Si, 0.2-1.0% Mn, =55kg/mm. . The hardness of the base part 2 of the caliber is higher by 2-10HS than the hardness in the same diameter position of a flange part 3. The quantity of the cementite in the matrix structure of the part 2 is approximately equal to the quantity of the cementite in the same diameter position of the part 3.

Working heat treating method for steel

Abstract: PURPOSE: To produce superplasticity and to obtain a practicable steel by subjecting a hypereutectic steel to heating to a specified temp., rapid cooling, cold working and heating to a specified temp. to form a structure consisting of fine ferrite grains and spheroidal cementite. CONSTITUTION: A hypereutectic steel is heated to a temp. above the A 3 point and rapidly cooled to form a structure contg. a large amount of carbide in the matrix as solid soln. such as a martensite or bainite structure. The heated steel may be slowly cooled to form a pearlite structure. The steel is then cold or warm worked at about 100°CWA 1 point and heated to a temp. just below the A 1 point to form a structure consisting of fine ferrite grains and spheroidal cementite. Thus, superplasticity is provided to a practical hypereutectic steel such as a bearing steel. COPYRIGHT: (C)1986,JPO&Japio