Showing papers on "Pearlite published in 1979"

The process of crack initiation and effective grain size for cleavage fracture in pearlitic eutectoid steel

Abstract: The process of cleavage crack initiation and the character of the effective grain size which controls the fracture toughness of pearlitic eutectoid steel has been investigated using smooth tensile and precracked Charpy impact specimens. The results demonstrated that initial cracking in both specimens was largely the result of shear cracking of pearlite;i.e., localized slip bands in ferrite promoted cracking of the cementite plates, which was then followed by tearing of the adjacent ferrite laths. Such behavior initially results in a fibrous crack. In the tensile specimen, the initiation site was identified as a fibrous region which grew under the applied stress, eventually initiating an unstable cleavage crack. In precracked impact specimens, this critical crack size was much smaller due to the high state of stress near the precrack tip. Fracture mechanics analysis showed that the first one or two dimples formed by the shear cracking process can initiate a cleavage crack. Using thin foil transmission electron microscopy, a cleavage facet was found to be an orientation unit where the ferrites (and the cementites) of contiguous colonies share a common orientation. The size of this orientation unit, which is equal to the cleavage facet size, is controlled by the prior austenite grain size. The influence of austenite grain size on toughness is thus explained by the fact that the austenite grain structure can control the resultant orientation of ferrite and cementite in pearlitic structures.

Influence of carbide thickness on impact transition temperature of ferritic steels

Abstract: A large number of ferrite–pearlite steels have been examined and measurements made of grain size, pearlite volume fraction, degree of precipitation hardening, and thickness of grain-boundary carbid...

Kinetics of the pearlite reaction in Fe−C−Cr

Abstract: Velocity and spacing measurements on the pearlite reaction in three eutectoid alloys of Cr (0.4, 0.9 and 1.8 wt pct) have been recorded and compared with growth and spacing equations based on a variety of thermodynamic and kinetic models. At high temperatures the reaction is controlled by phase boundary diffusion of Cr while at lower temperatures, a local equilibrium no-partition model with kinetic control by carbon diffusion best represents the data. At intermediate temperatures there is a smooth transition rather than a sharp break betwewn the two regimes. There is a discrepancy between theory and experiment on the slope of the spacingvs inverse under cooling plot which can be removed by assuming that the ferrite-cementite epitaxy improves with the addition of chromium.

Pearlite growth kinetics and partitioning in a Cr−Mn eutectoid steel

Abstract: The partitioning of manganese and chromium between cementite and ferrite during the austenite-pearlite transformation in a 1 pct Mn, 1 pct Cr eutectoid steel has been examined using analytical electron microscopy. Simultaneous segregation of both manganese and chromium to cementite was observed to occur at the reaction front for temperatures down to 600°C. Although the extent of partitioning decreased as the temperature was decreased, no-partitioning temperatures were not identified for either element. Calculations based on growth rate and interlamellar spacing measurements made on the alloy supported the view that the partitioning observed was kinetically feasible. Partitioning behind the pearlite front increased with time, and solute distributions which approached the equilibrium values were achieved after a few hours. The lack of experimentally observable no-partition temperatures for the Cr−Mn steel is discussed in the light of previous partitioning studies on eutectoid steels containing chromium or manganese.

The effect of microstructure on fatigue crack propagation in iron-carbon alloys

Abstract: The dependence of fatigue crack growth rate on the cyclic stress intensity factor was determined for six iron-carbon alloys ranging in carbon content from 0.23 to 1.08 wt pct carbon. Both ferrite/pearlite and ferrite/free iron carbide microstructures were studied. Scanning electron microscope fractography studies correlated the fatigue mechanism with microstructure. It was found that when the predominant mode of crack growth was ductile, the crack growth rateda/dN could be related to the cyclic stress intensity factor ΔK by an equation of the formda/dN = (ΔK)m where andm are constants. The constantm was approximately equal to four when the crack growth mechanism presumably was the blunting and resharpening of the crack tip by slip processes. The constantm was greater than four when the crack growth mechanism was void coalescence in the interlamella ferrite of pearlite colonies. The preferred fatigue crack path through the pearlitic alloys was through the free ferrite phase.

The effect of steelmaking on the hydrogen attack of carbon steel

Abstract: Four normalized carbon steels made in different ways (Si-killed, Al-killed, REM-treated, and electroslag refined) were studied to determine the role of differing fine inclusions on the early stages of hydrogen attack (HA). Hydrogen exposures were made at 450°C (6.5 MPa) and 375°C (7.6 MPa). The first stage of HA is shown to be the development of a closely spaced (1 to 2 µm) array of small bubbles over the ferrite/pearlite, or occasionally the ferrite/ferrite boundaries. These bubbles grew together to form tears, primarily in the rolling plane, leading to more rapid expansion normal to this plane than parallel to it. Fracture planes followed high solute layers in banded steel but only rarely if ever did the fine bubbles form on inclusions. At 450°C REM-treated steel was attacked the fastest and Al-killed steel required exposures two to four times as long for attack.

Thermodynamics and phase equilibria for the Fe−C−Cr system in the vicinity of the eutectoid temperature

Abstract: The low chromium Fe−C−Cr phase equilibria pertinent to the eutectoid transformation of austenite have been modeled and calculated from published thermodynamic information and verified through a series of selected equilibration experiments. In particular, α-γ, α-cm and γ-cm partition coefficients have been measured within the range 700 to 770°C and compared with austenite and carbide models proposed by Hillert and coworkers. While the theoretical-empirical closure is not perfect, the models are proven to be completely adequate for incorporation within the kinetic description of the corresponding ternary pearlite reaction.

On the Yield and Flow Stress of Lamellar Pearlite

Abstract: The experimental (macroscopic) values for the yield and flow stress of fully pearlitic eutectoid carbon steel may be represented by a linear function of either, the inverse of the true interlamellar spacing or its square root. The latter representation determines, however, a negative zero-intercept ordinate in the case of the yield stress. Different theoretical models may be contemplated for the critical resolved shear stress (CRSS) of pearlitic ferrite. Most of them give way to inverse proportionality relationships between the CRSS and either, the apparent interlamellar spacing on the slip plane considered or its square root. A quantitative comparison between the results of non pile-up models and the experimental values of the yield stress is made in this paper, making use of the value of an orientation factor appropiate to pearlitic ferrite obtained previously (Gil Sevillano, Van Houtte and Aernoudt, 1978). Experimental values for the flow stress of pearlite after large strains are also interpreted in this way. The paper stresses the plausibility of non pile-up models against the more widely accepted pile-up models for the yield and flow stress of pearlite.

Tough and hard spheroidal graphite cast iron and its manufacture

Abstract: PURPOSE: To manufacture a product having excellent machinability, by quenching spheroidal graphite cast iron having pearlite matrix structure of specific component from A 1 transformation range by oil or air cooling to form fine mixed structure consisting of two phases, ferrite and martensite. CONSTITUTION: The matrix consists of 3.1W4.1% C, 2.1W3.2% Si, ≤1.0% Mn, ≤0.15% P, ≤0.03% S, and one or more members among Cu, Ni, Mo in quantities ≤1.5% Cu, ≤2.5% Ni, and ≤0.5% Mo. The elements for spheroidizing graphite is ≤0.1% one or more members among Mg, Ca, Ce, and Y, the balance being Fe and inevitable impurities. Matrix contg. ≥75% area ratio of pearlite is heated to form a structure where ferrite, austenite, and graphite coexist, then quenched to convert the austenite into martensite to form a matrix of mixed structure composed of ferrite and martensite having ≤15μ mean crystal particle diameter. The matrix is tempered to the structure where graphite is crystallized in the matrix of fine structure consisting of ferrite and tempered martensite or tempered troostite. COPYRIGHT: (C)1981,JPO&Japio

Factors affecting the inherent hardenability of steel

Abstract: The hardenability of a steel depends upon the actual rate at which its austenite transforms to fine pearlite at the particular temperature at which this reaction sets in most promptly. The precise temperature at which this transformation rate is greatest depends upon the composition of the steel; in any case, it is this maximum rate at temperatures near 950 degrees Fahr. (500 degrees Cent.), which determines the critical quenching speed which must be exceeded if the steel is to be hardened. This maximum rate of austenite transformation to products other than martensite is in turn largely determined by the condition of the austenite at the moment of quenching with respect to two factors:

Abrasion resistant iron based sintered alloy material

Abstract: PURPOSE: To enhance abrasion resistance under severe use conditions by a method wherein ferromolybdenum particles are uniformly distributed into mixed base structure of pearlite, bainite, and martensite, and the surface ratio of the four elements is specified. CONSTITUTION: Ferromolybdenum particles are uniformly distributed into mixed base structure consisting of pearlite, bainite, and martensite. The mixed base structure is given a surface ratio of 20W50% for pearlite, 15W40% for bainite, 15W40% for martensite, and 3W20% for ferromolybdenum particles. This iron based sintered alloy consists of C; 0.8W1.5%, Ni: 1.5W4%, Cu: 0.5W2%, Mo: 2.5W6.5%, and the remaining Fe. The alloy develops excellent abrasion resistance when used as sliding material for internal combustion engines, valve seats, or valves. COPYRIGHT: (C)1980,JPO&Japio

Improvement of fatigue life of 1080 steel by thermomechanical processing

Abstract: — Many thermomechanical treatments (TMT) have been applied in the past to alloys in order to improve the balance between various static mechanical properties. The current research has applied a given type of TMT to the improvement of fatigue behavior in eutectoid steel. The TMT involved the cold rolling of annealed eutectoid steel to a reduction in thickness of 75% followed by rapid heating in liquid lead to a temperature just above the A1 temperature for a short time period and an air cool to room temperature. This type of TMT produces very oriented cementite in recrystallized ferrite. Plane bending cantilever fatigue tests with constant maximum load were run at 30 Hz and zero mean stress (R=−1·0). In terms of S–N fatigue curves the annealed condition is inferior to both the TMT and cold rolled conditions, however, there is no apparent advantage of the TMT over the cold rolled condition. There is, however, a considerable advantage in the TMT which becomes evident with normalization of all S–N curves with respect to the ultimate tensile strength. One thus finds that the TMT is quite superior, on an equivalent strength basis, to both the cold rolled and annealed conditions. The same was true on a basis of hardness normalization. This means that by TMT one can produce fatigue properties in a material of much higher formability which are equivalent to or better than those in a cold rolled material. Samples oriented in the cross-roll direction had total fatigue lives longer than for those oriented in the roll direction. This is explained in terms of mechanical fibering of pearlite colonies and inclusions, and by a crystallographic texturing of the ferrite matrix. TMT strength is a result of austenite grain size refinement, reduction of interlamellar spacing, fiber strengthening and both solid solution and precipitate hardening.

Manufacture of direct patenting wire rod

Abstract: PURPOSE:To manufacture a direct patenting high carbon steel wire rod with superior drawability by hot rolling a high carbon steel billet under specified conditions and subjecting the resulting wire rod to controlled cooling to form uniform fine pearlite structure. CONSTITUTION:A high carbon steel billet contg. C 0.6-1.0%, Si<2.0%, Mn 0.3-1.4% and Al 0.02-0.1% or further contg. Cr<1.5% is heated to such a relatively low temp. as 1,050 deg.C or below to fix N2 having a harmful effect on ductility as undissolved nitride. When this billet is worked into a wire rod by hot rolling, rolling from middle stand to finish stand or at finish stand is carried out at such a low temp. as about 900 deg.C or below to further enhance the ductility of the rod. The rolled rod is then subjected to appropriate controlled cooling between the final hot finish rolling and coiling to form fine pearlite structure.

Vanadium high-strength low-alloy steels for low-temperature use

Abstract: High-strength low-alloy (HSLA) steels having low impact transition temperature are possible substitutes for costlier 2 1/2% and 3 1/2% nickel steels. The effects of solid solution strengthening, grain size and precipitation in ferrite on the strength and toughness of low-carbon steels and the special advantages of vanadium as an alloying element in HSLA steels, are discussed. An investigation has been carried out with 1.5% manganese low-carbon steels containing vanadium in the range 0.12% to 0.29% and 0.013% to 0.017% nitrogen. Room temperature tensile and sub-zero temperature impact tests down to−100° C, and a metallographic study to determine the grain sizes and pearlite contents of the steels normalized at different temperatures, have been carried out. Calculations are made with empirical equations for yield and tensile strengths and the values obtained are compared with those experimentally observed. The solubility products of vanadium carbide and vanadium nitride are calculated and compared with available data to throw light on the mechanism of strengthening of the steels.

A Study on Fatigue Crack Propagation of Rail Steels

Abstract: The characteristics of fatigue crack propagation and the effects of metallurgical factors on them were investigated on various rail steels and experimentally produced eutectoid steel plates. The fatigue crack propagation rate is affected by residual stress and stress ratio, but is little affected by chemical compositions, austenite grain size and mechanical properties. Fatigue crack of eutectoid steels seems to propagate around or across the pearlite block as a pass unit.

Mechanism of solid-state eutectoid transformation in an aluminium-zinc alloy

Abstract: The growth rate of pearlite during isothermal transformation of an aluminium-zinc eutectoid has been determined experimentally. Different theoretical models, assuming either volume or boundary diffusion of zinc to be a rate controlling mechanism for the eutectoid transformation, have been applied. With volume diffusion models, the calculated growth rates were lower than the experimental growth rates by a factor of three orders of magnitude. Reasonable agreement between the calculated and experimental growth rates has been obtained on applying the boundary diffusion models. The activation energy for boundary diffusion of zinc in the aluminium-zinc alloy was estimated to be ≅11.6 kcals/mole.

Production of rod steel without thermal refining

Abstract: PURPOSE:In low carbon steel containing an adequate amount of Cu, Mn and the like, a hot-rolling condition is specified on rolling temperature, processing quantity, cooling rate and others, to provide material as rolled with the same mechanical property as when thermal refining is conducted. CONSTITUTION:A low-carbon steel and like material containing C:0.25-0.6% and Mn:1.5% or less, is rolled at a rolling temperature of 850-1050 deg.C, in a processing quantity of 30% or higher and a final finishing temperature of 850-950 deg.C, and cooled at a normal rate of 0.3-5 deg.C/sec. The above-described composition for low- carbon steel and condition for rolling provide rolled material having structure with pearlite colony of finer grain No.6 or higher, compared with conventional grain of No.4-5 or so. The process while eliminating annealing operation, provides low-carbon steel and the like with an enhanced machanical property, particulary yield- strength ratio, ductility and toughness together with machinability and cold-process property.

Production of low temperature steel

Abstract: PURPOSE:A low carbon high manganese steel containing a minor amount of Nb is adjustedly cooled in annealing process, thereby to economically provide a steel for low temperature use, having an excellent strength, low-temperature toughness, and weldability. CONSTITUTION:A low carbon high manganese steel containing C<0.16%, Si: 0.10 to 1.0%, Mn<2.0%, P<0.035%, S<0.03%, Nb: 0.02 to 0.1%, sol Al: 0.01 to 0.09% is heated to a temperature of 880 to 950 deg.C. In annealing process, cooling rate is controlled in a range of 3 to 4 deg.C/sec from ferrite modification starting temperature 800 deg.C to ferrite modification finishing temperature 550 deg.C. In such process, large grain pearlite formation and bainite structure are effectively prevented, resulting in pearlite structure containing ferrite microstructure. As such, the so obtained steel material is excellent in strength, weldability, and low-temperature toughness. Beside, the steel is less expensive than conventional low-temperature steel since it contains no Ni component.

Effect of interlamellar spacing of pearlite on the attenuation of ultrasound

Abstract: The attenuation of ultrasound was studied in samples of pearlitic steel taken from railway wheels containing between 0.53 and 0.61% carbon. A strong dependence of ultrasonic attenuation on grain size was observed; in addition a relationship was shown between the interlamellar spacing of pearlite in the steel and the attenuation coefficient. The scattering losses in the Rayleigh zone of the pearlitic/ferritic steel were found to be proportional to the spacing of the cementite lamellae in the pearlitic structure.

Process for heat treatment of steel

Abstract: The present invention provides a process for the heat treatment of steel, wherein a rail is quenched entirely or in their head portion from a temperature which is in the austenite range in water at at least 80.degree.C to at least a temperature at which pearlite transformation is completed, the composition of the steel being such that a very fine pearlitic structure is obtained in the quenched steel.

Preparation of high strength bolt superior in delayed cracking resisting property

Abstract: PURPOSE:To cheaply obtain the above mentioned high strength bolt, by carrying out hot thread rolling, after carrying out a fixed cold drawing processing of pearlite steel wire rod containing a specific extent carbon. CONSTITUTION:Head part is formed by hot thread rolling using piano wire rod or hard steel wire rod of pearlite steel containing 0.6-0.85% of C after carrying out cold drawing processing being reduction ratio more than about [180-210X C(%)]%. Hereby, high strength bolt is able to cheaply obtain having delayed cracking resisting property being equal to maraging steel and strength more than about 120-130 Kg/mm .

The mechanism of deformation of pearlite

Abstract: Pearlite is a two phase structure of iron and cementite (Fe3C) which forms as colonies with a lamellar morphology When fully pearlitic wires are drawn the lamellae rotate until they are all oriented along the axis of the wire Such wires have enormous strengths and are used eg for lifts, cranes, ski-lifts, etc The basis of these wires' great strength is not fully understood and in this work dynamic deformation experiments are carried out in the electron microscope in an attempt to elucidate the deformation mechanims

Crack Propagation in Coarse Two-phase Steels

Abstract: Crack propagation in binary Fe-C alloys with ferrite-pearlite has been studied. Major structure variables are volume fraction of pearlite, grain size and the ratio between the yield stresses of the constituents. The crack growth rate has a very strong sensitivity to the grain size in ferrite-rich materials. In pure pearlite, a regular lamellar structure offers better crack resistance. Ferrite-pearlite phase mixtures reduce crack growth rate remarkably, more pronounced the larger the grain size. This is associated with an enlarged plastic zone around the crack tip. Generally, the influence of microstructure is largest at lower stress intensity ranges. Fractographic observations indicate ductile fractures in most cases.