Showing papers on "Pearlite published in 1972"

The pearlite reaction

Abstract: A critical appraisal of theory and experiments for both isothermal and forced velocity pearlite is presented. It is concluded for binary systems that both the theoretical models for volume diffusion and boundary diffusion control are well-advanced and adequate for the purposes of experimental test. However, some ambiguity remains in the boundary diffusion model with respect to the thermodynamics of the boundary ”phase” region, so it is still not possible to predict absolute rates of transformation. The theoretical problem for ternary pearlites is also well understood, although rigorous theory seems intractable. A new perturbation procedure for definition of the optimal steady-state spacing is presented and amplified for both isothermal and forced velocity pearlite, and for both volume and boundary diffusion models. In terms of the critical spacing Sc for isothermal pearlite and the spacing at minimum undercooling Sm for forced velocity pearlite the predicted stability points are as follows: {fx2777-1} For isothermal pearlite these perturbation results correspond closely to the state of maximum entropy production rate while for forced velocity pearlite the correspondence is also satisfactory. A detailed analysis of the data leads us to reaffirm the author’s conclusions that the eutectoid reactions in Cu-12 pct Al and some related ternary alloys reported by Asundi and West are controlled by volume diffusion and that the eutectoid reaction in Al-78 Zn reported by Cheetham and Ridley is controlled by boundary diffusion. We conclude further after careful analysis that the pearlite reaction in Fe-0.8 C is controlled for the higher temperatures by volume diffusion of carbon in austenite. We are also led to state that the pearlite transformations in Fe-C-Mn and Fe-C-Ni occur for the most part in a nopartition regime and are therefore controlled by volume diffusion of carbon in austenite, while the transformations in Fe-C-Cr and Fe-C-Mo, being forced by thermodynamics to sustain partition of chromium and molybdenum, are controlled by phase boundary diffusion of the latter elements. nt]mis|M. P. PULS, formerly Postdoctoral Fellow, Department of Metallurgy and Materials Science, McMaster University, Hamilton, Ontario, Canada

Ferrite and bainite in alloy steels

Abstract: The addition of alloying elements even in small concentrations can alter the properties and structure of ferrite and bainite. The various morphologies of ferrite-carbide aggregates are surveyed including alloy pearlite, fibrous carbide eutectoids and precipitation of fine alloy carbides atγ-α interfaces. Modern ideas on the morphology and growth kinetics of ferrite and upper and lower bainite are also summarized. Using this information, an attempt is made to rationalize subcritical transformations of austenite in low alloy steels. Basic factors influencing the strength of alloy ferrites are discussed, leading to an examination of structure-mechanical property relationships in ferrite and bainite. Finally the exploitation of the ferrite and bainite reactions to produce useful alloy steels by direct transformation of austenite is explored.

Fracture of steels containing pearlite

Abstract: The relative effects of pearlite and spherodite on ductile, cleavage, and fatigue failure are summarized. Neither the cleavage strength nor the fatigue endurance limit appear to depend directly on cementite contentper se. Spherodized steels cleave less readily than ferrite/pearlite steels. Ductile fracture resistance is lowered considerably by both types of cementite, pearlite being more deleterious. Ferrite/pearlite steels appear to exhibit slower fatigue crack growth rates at low stress intensity levels than high strength steels. At high stress intensity levels the behavior is reversed. Slip-incuded cracking of carbide lamellae appears easier than that of spherodized carbides. In ductile fracture situations the crack spreads progressively through a pearlite colony via preferential cracking of carbides and rupture of the intervening ferrite accompanied by large local shear strains. Fatigue fracture proceeds with formation of frequent branches, preferentially along the pearlite colony interface.

The stability of lamellar structures

Abstract: The thermal stability of lamellar structures under creep or hot-working conditions is considered. It is suggested that the microstructural stability of the two-phase alloy can be altered by the introduction of boundaries formed by deformation and recovery processes. Expressions are derived for the rate of growth at triple points formed in this way. These expressions are related to the stability of unidirectionally grown eutectics under creep conditions, and spheroidization observed under hot working conditions. Under certain limiting conditions the results reduced to those of Mullins for “grooving” at grain boundary-free surface junctions by volume and surface diffusion.

The Influence of Deformation on the Spheroidization and Coarsening of Pearlite

Abstract: It is well known that the spheroidization of pearlite in eutectoid steels can be greatly accelerated by deformation either before or during annealing. An investigation of the phenomenon by electron microscopy is described and several factors influencing the spheroidization process are reported. Some of the observations confirm suggestions made by earlier workers but other mechanisms are also proposed. In particular, the ability of the cementite to undergo considerable plastic strain at all temperatures investigated is shown to be an essential feature of the acceleration of spheroidization by deformation.

Continuous heat treating process for low carbon structural steels in bar form

Abstract: An improvement in a process for preparing a structural steel having a maximum carbon content of 0.26 weight percent, the balance comprising iron, wherein the steel is continuously heated with the use of rapid heating, followed by quenching, the improvement comprising heating the steel only in its shell to a temperature between A cl and 1,300°C such that the core heats up at an average rate of at least 100°C/sec. up to a temperature between incipient pearlite transformation (A cl ) and 900°C, and thereafter, but prior to the attainment of equilibrium with respect to the carbon content, quenching said steel.

High-temperature plasticity of carbon steels

Abstract: 1. A relationship was found between the change in the plasticity and strength of carbon steels and the structure of divorced pearlite at subcritical and critical temperatures. Up to 600°C the plasticity changes little, while the strength decreases. Above 600°C the plasticity increases sharply, reaching a peak at Ac1 (beginning of the transformation) and then decreases sharply, while the strength increases or remains unchanged. At Ac3 in hypoeutectoid steel or Ac1 (end of the transformation) in hypereutectoid steel the plasticity is minimal. With further increase in temperature the plasticity increases. 2. The increase in plasticity at 600–730°C is explained by recrystallization of α phase, and the reduction of the plasticity in the critical range is explained by the difference in the plasticity of the α and γ phases and the difference in recrystallization rates. 3. The plasticity of steels with lamellar pearlite has no extremal values and increases monotonically in the range of phase transformations, which results from the small difference in the properties of lamellar pearlite and austenite. 4. In alloys with austenitic and ferritic structures that do not undergo transformations no anomalous change in plasticity was observed.

Some recollections, early observations of phase transformations-micromorphology

Abstract: Reminiscing, the author briefly mentions some of his early contributions, including 1) the X-ray discovery of substitutional solid solutions, ordered solid solutions, and retained austenite; 2) determination of the time for isothermal transformation of austenite in certain carbon steels at a variety of temperatures; and 3) discovery of the looped austenitic field in the system, Fe-Cr. He then recounts in greater detail his demonstration (1930–34), with E. S. Davenport, that the superiority of forged automotive components of quenched and tempered low-alloy steel over their plain carbon steel counterparts lay in their microstructure: the alloying elements delayed the transformation of austenite, ensured full conversion to martensite, and thus provided adequate hardenability.

A Study on the Impact Fatigue of Carbon Steels

Abstract: It is very important that the behavior of structurals will be studied under repeated impact loads, but there have been few papers hitherto published about impact fatigue since few efficient impact fatigue testing machines have been made available.So, we devised a new rotating disk type impact fatigue testing machine, of which the impact velocity and the number of impacts per minute were 5.5m/sec and 600 respectively, and studied the effects of microstructure on the impact fatigue lives.The 0.24% carbon steels, and 0.85% carbon steels with lamellar and spheroidal pearlite structure were used, of which some were annealed while others were left as they were when obtained.The results obtained are as follows.(1) The impact fatigue lives of 0.24% carbon steels were longer than those of 0.85% carbon steels, and the slopes of S-N curves of the former were steeper than those of the latter.(2) The impact fatigue life of the annealed 0.24% carbon steel was longer than that of the 0.24% carbon steel that was left as it was.(3) The impact fatigue life of 0.85% carbon steel with lamellar pearlite structure was almost the same as that of 0.85% carbon steel with spheroidal pearlite structure.

Effect of dendritic segregation of manganese on the transformation of austenite in steel

Abstract: 1. We investigated the effect of manganese (0.58–2.45%) on the transformation of austenite under isothermal conditions after solidification and homogenizing annealing. 2. In the presence of manganese segregation the pearlite and bainite transformations in steel with 0.58–2.45% Mn occur over a longer time period and wider temperature range than in the homogenized steels. 3. The isothermal transformation of austenite begins in the axial sections of dendrites with a low stability due to the low concentration of manganese. Austenite later decomposes in sections between branches that are rich in manganese.

Residual stresses in centrifugally-cast iron pipe

Abstract: 1. The values of the residual stresses and the strength of centrifugally cast pipe depend greatly on the silicon content and the heat treatment. An elevated silicon content (over 2.5%) lowers the strength and raises the residual stresses. 2. Partial annealing of the pipe should be avoided, since the presence of structurally free cementite in combination with the ferrite matrix favors substantial residual stresses in the castings. 3. Pipe with 1.8–2.2% Si should be normalized. The presence of pearlite in the structure makes the pipe less susceptible to cracking.

Weld compsn - for low pearlite, gas-shielded or submerged arc welds

Abstract: The deposit is produced using core-filled or solid welding wires and contains, after fusion but without mixing with parent materials, 0.03-0.06% C, 0.30-0.45% Si, 1.6-2.0% Mn, 0.02% each of P and S, and 1.5% Mo, 0.06% Nb, 0.2% V, and 0.03% N. The deposit has a low pearlite content and, by working the cooling weld, a fine-grained structure.

Hydrogen permeability of annealed and deformed carbon steels with a lamellar pearlite structure

Abstract: Tests were carried out on specimens of carbonyl iron and St. 20, St. 40, U8, and U12 carbon steels with a lamellar pearlite structure. It was established that the structure sensitivity of hydrogen permeability of steel is relatively low at elevated temperatures (t>tcr) and extremely high at low temperatures (t