Showing papers on "Pearlite published in 1973"

Diffusional growth limitation and hardenability

Abstract: It has long been recognized that the effects of alloying elements on the hardenability of steels is related directly to their effects on the nucleation and growth kinetics of proeutectoid and eutectoid austenite decomposition products. In the present paper, theoretical and experimental studies of proeutectoid-ferrite and pearlite growth are reviewed for systems of the form Fe-C-X, where X is a substitutional alloying element such as Co, Cr, Mn, Mo, Ni, Si, and so forth. Of principle interest is the limitation which an alloying element X imposes on the corresponding diffusional growth kinetics. Although the agreement between theory and experiment is reasonable for most systems, there remain areas of considerable controversy (e.g., the role of interface diffusion, whether or not local equilibrium is maintained at interfaces and solute segregation to interfaces).

The Crystallography and Nucleation of Pearlite

Abstract: By choice of a suitable iron—manganese—carbon alloy it has been possible to study pearlite nodules growing in austenite, without the austenite transforming on cooling to room temperature. Thin foil electron microscopy has been used to examine the orientation relations between cementite, ferrite and austenite as well as morphological aspects of the transformation. It is shown that one of the classical ferrite—cementite orientation relations found in pearlite (Pitsch—Petch) arises when the pearlite colonies nucleate on ‘clean’ austenite grain boundaries. The other familiar relation (Bagaryatski) arises when the colonies nucleate on pre-existing hyper-eutectoid cementite layers at the austenite grain boundaries. Some observations are made on the mode of nucleation of the pearlite nodules.

Prediction of alloy hardenability from thermodynamic and kinetic data

Abstract: A simple algorithm for the calculation of the hardenability of low alloy eutectoid steels is presented. This involves the semiempirical prediction of concentration-dependent CCT start and pearlite velocity curves using fundamental thermodynamic and kinetic data and current theories of nucleation and growth. The combination of analytic cooling curves with these predictions and a pearlite growth model based on site saturation at grain corners leads to a good prediction of the hardenability of steel 4068, extensively examined by Jominy, and a grain-size dependence which is qualitatively correct. It is also demonstrated via Taylor and binomial expansions of the undercooling within the various kinetic expressions that the hardenability at low alloy concentrations is correctly represented by linear or quadratic addition formulas. At the same time, it is unequivocally demonstrated that Grossman type multiplication formulas are theoretically incorrect. The quadratic terms in the addition formula quantify the so-called “synergistic” effects. The most important positive terms involve an interaction between austenite and ferrite stabilizers. Austenite stabilizers, by depressing the effective temperature of nucleation and diffusional growth processes involving partition of ferrite stabilizers in pearlite, make the latter processes more sluggish. In agreement with long-standing experience, it is concluded that the strongest and most economic hardenability effects can be obtained via mixtures which include both austenite and ferrite stabilizers.

A ductile iron and method of making it

Abstract: For a ductile iron of the type which has been heated, after casting, to its austenization temperature and austenized and subsequently heat-treated isothermally by quenching in a hot bath to start a bainite reaction which is continued until a desired fraction of the austenite have formed into bainite, improved properties are achieved by adding as alloying elements molybdenium 0.10 - 0.26 % and magnanese 0.3 - 1.4 % by weight and preferably also an additional alloying element which promotes the formation of a pearlite micro-structure during casting and, consequently, accelerates the austenization, said additional element consisting of nickel in an amount less than 2.5 % by weight, and tin and/or copper. Preferably said iron contains molybdenium 0.15 - 0.22 % by weight and less than 0.2 % by weight of tin and/or less than 1.0 % by weight of copper.

Method for producing a high strength bolt

Abstract: A method for producing a high strength bolt from a carbon steel or a low alloy steel material, which comprises the steps of subjecting said material, in turn, to cold working at the reduction-of-area percentage of 10 percent and over rapid heating to a temperature range from 450 DEG C to A1 transformation point, warm-forming to a bolt shape and air-cooling or cooling at a cooling rate higher than that of the air-cooling. The steel material adapted for use herein includes a steel having a pearlite structure or a tempered martensite structure, and particularly the steel having the latter structure presents excellent resistance to the delayed rupture phenomenon with an accompanied high tensile strength of over 100 kg/mm2, particularly, in the range from 130 to 140 kg/mm2 and over.

The kinetics of isothermal and isovelocity pearlite growth in Cu-Al eutectoid alloy

Abstract: Measurements of pearlite growth rate and inter lamellar spacing have been made on isothermally transformed specimens of Cu-11.8 wt pct Al eutectoid alloy. Growth rates which have been calculated on the assumption that volume diffusion in the parent β phase is the rate-controlling process show excellent agreement with the measured values. Directional control of eutectoid growth by translating specimens through steep temperature gradients resulted in the formation of aligned lamellar structures, and the effect of variations in imposed velocity and temperature gradient on alignment has been examined. A comparison of the kinetics of the two modes of transformation has shown that isothermal and isovelocity pearlite growth in this alloy may be readily interrelated. Analysis of the isovelocity growth data supports the conclusion that growth is controlled by volume diffusion.

Effect of cooling rate and alloying on the

Abstract: The pearlitic hardenability of a high-purity Fe-0.8 pct C alloy and zone-refined iron binary alloys containing Mn, Ni, Si, Mo, or Co was studied by means of hot-stage microscopy. The binary alloys were carburized in a gradient furnace to produce eutectoid compositions, thus eliminating proeutectoid phases. A special technique based on hot-stage microscopy was used to study the effect of cooling rate (10°F/min to 25,000°F/min) on the transformation of austenite and provided data for the construction of continuous cooling-transformation diagrams. From these diagrams critical cooling rates were obtained for hardenability calculations. It was found that molybdenum is the most effective element, followed by Si, Ni, Co, and Mn, in suppressing the pearlite transformation,i.e., in increasing the hardenability of the alloys studied. The alloying additions were grouped into two classes according to their effect on hardenability: α-stabilizers (Mo and Si) and γ-stabilizers (Ni, Co, Mn), with the α-stabilizers being the more effective in improving hardenability.

Processing pearlite to obtain metal silicates

Abstract: Processing of pearlite by treating the same with an alkaline solution having a concentration of 40-140 g/l taken in an amount which brings the ratio of the liquid and solid phases to (0.7-1.5) : 1 and then separating by filtration the water glass, obtained in the process of heat treatment, from the residue formed.

As-worked bainitic ferrous alloy and method

Abstract: THIS INVENTION RELATES TO AN AS-WORKED BIANITIC FERROUS ALLOY AND TO A NOVEL METHOD OF PROCESSING SAME TO OBTAIN OPTIMUM STRENGTH AND TOUGHNESS. MORE PARTICULARLY, THIS INVENTION IS DIRECTED TO THE HOT WORKING CYCLE OF A FERROUS ALLOY CHARACTERIZED BY AN I-T DIAGRAM OR S CURVE HAVING A DOUBLE NOSE OR A PEARLITE TRANSFORMATION KNEE OF THE BEGINNING CURVE ABOVE A BROAD BIANITIC BAY REGION. SUCH AN ALLOY IS HEATED TO AN AUSTENITIZING TEMPERATURE OF ABOUT 1500* TO 2200*F., AND SUBJECTED TO A PLURALITY OF WORKING OPERATIONS AT SUCCESSIVELY LOWER TEMPERATURES, WHERE THE FINAL WORKING OPERATION IS CONDUCTED AFTER THE BEGINNING OF THE AUSTENITE TRANSFORMATION TO BAINITE AND BEFORE THE COMPLETE TRANSFORMATION THEREOF.

Method of making steel cartridge cases

Abstract: A cartridge case is formed from C1008 steel strip. The cartridge case is heated in a carbon rich atmosphere to increase the carbon content of the steel to approximately 0.55% and is furnace cooled so that it has a ferrite and pearlite structure and exhibits a uniform hardness and has a tensile strength similar to that of a brass cartridge case.

Production of low alloy steel wire

Abstract: Low alloy steel rod is given a pearlite structure and is then cold-drawn to initiate work hardening. The rod is then drawn through a die producing a reduction in area of between 10 and 40 percent. The wire leaving the die is heated to 300*-450*C and then forcibly cooled.

Phase transformational kinetics and hardenability of low-carbon, boron-treated steels

Abstract: The phase transformations and hardenability of 0.1 pct C boron-treated and boron-free steels containing Mn, Cr, Ni, or Cr plus Ni, and up to 1 pct Mo were studied. Continuous cooling transformation diagrams, hardenability characteristics, and diagrams of the ferrite start half-cooling time vs alloying were established. An unalloyed 0.1 pct C steel transforms diffusionally in the ferritic-pearlitic range when cooled from an austenitizing temperature, with a negligible contribution of the intermediate (bainitic) transformation occurring at very high rates of cooling. Molybdenum extends the range of the bainitic transformation and markedly delays the decomposition of austenite in the ferritic-pearlitic range. Boron treatment of the unalloyed (molybdenum-free) 0.1 pct C steel permits bainite formation over a wider range of fast cooling programs. At lower rates of cooling, the steel transforms diffusionally into ferrite and pearlite . Alloying additions of Mn, Cr, or Ni result in a slightly higher proportion of the bainitic transformation, which may occur over a wider range of cooling programs. When both nickel and chromium are present, a modest synergistic effect on the delay of the ferritic-pearlitic transformation may be noted. Introduction of molybdenum into all of the boron-treated 0.1 pct C steels strongly delays the decomposition of austenite into ferrite-pearlite structures and vastly expands the range of cooling programs that result in the formation of bainitic structures. In this important action, molybdenum is assisted to a smaller degree by alloying additions of manganese and chromium, and to a greater degree by nickel and chromium plus nickel. In all the steels studied, the alloying elements lower the temperatures of the bainitic transformation, thereby explaining, at least partly, the somewhat higher hardness for any specified cooling program. The observed beneficial effects of boron, molybdenum, and other alloying elements on the phase transformational behavior on continuous cooling are reflected in terms of higher hardenability.

Effect of the Pearlitic Structures on the Wear of 0.89%C Carbon Steel at Ambient Temperature to 800°C

Abstract: In this experiment the effects of the lamellar and globular pearlites and their combinations on the wear of carbon steel were studied in the temperature range from ambient temperature to 800°C. Therefor 0.89%C carbon steel was used as a fixed spescimen and 0.64%C carbon steel as a rotating one. The wear test machine was Dr. Okoshi's Rapid Wear Testing Machine which is the same as the one used in the last report. On the other hand the oxidation property at 200°C and the hardness at each test temperature were measured, and under consideration of these results the behaviour of wear phenomena was discussed. Further the results which one of the present authors obtained in the earlier experiment were again discussed. The results in this report show that the maximum values of wear rate at ambient temperature and 800°C were greater on the lamellar pearlite than on the globular. This is caused by the difference of the pearlitic structures, which changed not only the mechanical property but also the oxidation property of the carbon steel that is the same carbon steel.

Kinetics of isothermal transformation of austenite in hot rolled carbon steels

Abstract: 1. Hot deformation accelerates precipitation of excess ferrite and the pearlitic transformation in steels 40 and U8. With decreasing transformation temperatures this accelerating effect of deformation gradually decreases. Hot deformation of steel U8 slows down the transformation in the bainitic region. 2. The difference in the rate of decomposition of deformed and undeformed austenite increases with the austenitizing temperature. 3. Hot deformation prevents the formation of Widmanstatten ferrite and refines the ferrite and pearlite grains; the dispersity of pearlite remains unchanged in this case.