Pearlite Colonies Research Articles

Formation of a Transition Zone Structure in Welded Joints between Dissimilar Steels

The results of structural research of welded joints between pearlitic high-carbon steel and austenitic chrome-nickel steel obtained by contact welding are presented. As a result of the diffusion process and mechanical mixing of steels local alloyed areas surrounded by pearlitic colonies of high-carbon steel are formed in the transition zone of the weld. The transmission electron microscopy (TEM) has been employed. The formation of the austenitic-martensitic microstructure occurs due to reducing the amount of alloying elements in local areas as compared to the original austenitic chrome-nickel steel chemical composition. Both austenite and martensite have crystallographic characteristics with the following orientation relationships: [211] γ-Fe || [011] α-Fe; [11-1] γ-Fe || [-110] α-Fe. The presence of high-strength local regions in the transition area may lead to a significant reduction in сrack resistance of dissimilar steels welded joints.

Metallographic study of construction materials with atomic force microscopy method

The results of atomic force microscopy (AFM) investigation of the micro- and nanostructure of 09G2S steel are presented. The method was developed for investigation of construction steel with AFM which allowed improving the quality and reliability of metallographic studies. Identification of the phase state of a material and determination of such microstructure parameters as grain size, pearlite fraction, the size of pearlite colonies, pearlite structural characteristics, and the width of intergrain boundary areas were performed on the basis of AFM images of 09G2S steel.

Microstructure and Mechanical Properties of Ductile Cast Iron in Lost Foam Casting with Vibration

The microstructures and mechanical properties of the ductile cast iron (Dl) specimens obtained by lost foam casting (LFC) with and without vibration were investigated. The results indicate that the number of the graphite nodule increases from 173 mm−2 of the specimens produced by LFC without vibration to 334 mm−2 of the specimens produced by LFC with vibration, and the thickness of the ferrite shell increases. Meanwhile, the amount of the carbides decreases in the specimens produced by LFC with vibration and the granule structure then forms. These are mainly attributed to the “crystal shower” caused by the vibration. In addition, the tensile strength and elongation of DI specimens produced by LFC with vibration are improved due to the dispersion-strengthening of refined carbide and pearlite colony, uniform distribution of the graphite nodule, and increase of the amount of dimples and tearing edges.

Structure and Mechanical Properties of Cu-Alloyed Cast Iron

The effect of Cu addition on structure and mechanical properties of the gray cast iron is studied. Copper is showed to affect the graphitization process. Copper content increase up to 6 ... 7 wt. % reduces the depth of the chill layer.With further increase of coppercontent the alloys tendency to chilling effectincreases.When the cast ironcontains from 0 to ~ 7% Cu, inclusions can’t be detected using only optical microscopy. In the cast iron with 14.7% Cu, distribution of inclusions has two peaks: 30 ... 40 ... 150 microns and 160 microns. Out-of-shape cupric inclusions of the size of ~ 1 micron are detected in the ledeburite cementite.Submicron inclusions are observed in the lamellar pearlite colonies. With increase of copper content up to ~ 7 wt. % cast iron hardness and microhardness of pearlite increases.

Finite Element Analyses of Elasto-Plastic Deformation in Pearlite Lamellar and Colony Structures

Elasto-plastic tensile deformations in pearlite lamellar and two-colony structures are studied by finite element analyses to investigate the effects of lamellar thickness ratio and difference of lamellae orientation of two colonies in pearlite microstructure. The results obtained from plastic strain distributions in lamellar and colony structures show that plastic deformation in cementite lamellar stabilized when ferrite lamellar is thicker than cementite lamellar thickness and plastic strain concentrates when the difference between cementite lamellar orientation in two colonies are larger than 45°.

Study on the Microstructure Control and the Variation of Mechanical Properties of Pearlitic Steel

The effect of austenitizing temperatures and isothermal transformation temperatures on microstructure size and mechanical properties of 70 steel was studied. The experimental results show that the grain size increases with the increasing of austenitizing temperature. And the tensile strength increased with isothermal temperature decreasing. The grain size has a great influence on tensile strength. The strength increase of the samples with fine grain is greater than the samples with coarse grain. With the decreasing of isothermal temperature, the pearlite colony size and interlamellar spacing decreases and the reduction of area of the specimens increase.

Effect of Reserved Texture on Mechanical Properties of Cold Drawn Pearlitic Steel Wire

In this paper, pearlitic steel wire with/without reserved texture were investigated with the help of mechanical test system, scanning electron microscope (SEM) and XRD. Experimental result shows that: Tensile strength of two wire are almost same. After cold drawn tensile strength of wire with reserved texture are higher than tensile strength of the without one. Before cold drawn, two wires have same microstructure of isometric pearlite and after drawing the wire with reserved texture has less shear deformed pearlitic colony. Intensity of <110> fiber texture in the wire with reserved texture are stronger than the without one at all strains. The stronger <110> texture mean the orientation of α-ferrite lamella were more closely and improve working hardening rate of pearlitic wire.

Shaping the structure during rolling and isothermal annealing, and its influence on the mechanical characteristics of high-carbon steel

Rail sections made of pearlitic steels used in the construction of turnouts and railroads must have appropriate mechanical and fatigue characteristics as well as high resistance to abrasive wear. The paper discusses the influence of temperature at the end of rolling and isothermal annealing on the morphology of pearlite and the mechanical properties of steel R260. Properties of sections were evaluated in a statistic tensile and impact test, while that of the microstructure by using a scanning microscope. For a quantitative analysis of pearlite colonies, the “MET-Ilo v.3.5” computer program was used. The influence of the morphology of pearlite on the impact strength of KCU in the temperature range from −80°C to 100°C was also determined. It was demonstrated that in the above-mentioned processes the properties of the steel may be controlled within a wide range by changing the pearlite morphology parameter in the material.

Deformation bands in fully pearlitic steel during wire drawing

The deformation of fully pearlitic steels during wire drawing has been investigated for both longitudinal section and transverse section by back-scattered electron imaging (BSEI), electron back-scattered diffraction (EBSD), and transmission electron microscope (TEM). The results show that a large number of deformation bands (DBs) composed of a mixture of kink-like bands and shear-like bands were observed both in the longitudinal section and the traverse section of the drawn wires. The formation of such bands involves two aspects: heterogeneous deformation in the scale of pearlite colonies and instability of ferrite-cementite interfaces due to stress concentration during wire drawing. The development of such bands in fully pearlitic steels dominates the formation of metallographic texture, reduces the pearlite interlamellar spacing and promotes the development of fiber crystalline texture of ferrite matrix during wire drawing.

Reverse Transformation from Ferrite/Pearlite to Austenite and Its Influence on Structure Inheritance in Spring Steel 60Si2MnA

Reverse transformation at 725–800°C × 0–35 s from a ferrite/pearlite to austenite was investigated in spring steel 60Si2MnA with various pearlite fineness obtained by isothermal transformation. Then, its influence on the structure inheritance in the spring steel during heat treatment process was discussed. The results indicated that various pearlite fineness influences clearly start temperature of the reverse transformation. Austenite preferentially nucleates at the ferrite/cementite interface within pearlite, the neighboring pearlite colony boundary and the proeutectoid ferrite/pearlite boundary during the reverse transformation process. And the angle between pearlite lamellae and austenite growth direction has an important influence on austenite growth rate. Besides, the ferrite/pearlitic structure has structure inheritance phenomenon, because various hot-rolled microstructure affect the austenite nucleation and growth during heat treatment process.

Microstructure evolution and mechanical properties of eutectoid steel with ultrafine or fine (ferrite+cementite) structure

Eutectoid steel with the ultrafine or fine-grained ferrite (α)+cementite (θ) particles structure was formed by hot deformation of undercooled austenite at 0.1s−1 or 5s−1 at 650°C using a Gleeble 1500 hot simulator and subsequent annealing. The microstructural evolution of fine (α+θ) structure was investigated by means of a scanning electronic microscope, electron backscattered diffraction and transmission electron microscope, and the mechanical properties of fine (α+θ) steel were analyzed in comparison with that of ultrafine (α+θ) steel. The results show that only dynamic transformation of undercooled austenite into proeutectoid ferrite occurs during hot deformation at 650°C at 5s−1. During water quenching, lamellar pearlite with small colony sizes is formed and the average size of pearlite colonies decreases with increasing the strain. By subsequent annealing at 650°C for 30min, the spheroidization of lamellar pearlite takes place, resulting in the formation of fine (α+θ) structure consisting of ferrite matrix with the average size of about 4.9μm and fine cementite particles mainly within ferrite grains. In comparison with ultrafine (α+θ) steel consisting of ferrite matrix with the average size of about 1.8μm and relatively large cementite particles mostly located at grain boundaries, the yield strength, tensile strength, uniform elongation, total elongation and work-hardening capability of fine (α+θ) steel improve markedly.

131 パーライトコロニー界面近傍に生ずる弾塑性変形の三次元有限要素解析(材料力学III)

131 パーライトコロニー界面近傍に生ずる弾塑性変形の三次元有限要素解析(材料力学III)

パーライトコロニー構造における弾塑性変形の有限要素解析

パーライトコロニー構造における弾塑性変形の有限要素解析

Kinetics of austenite decomposition in manganese-based steel

In this work, pearlite formation in undeformed and deformed austenitic manganese-based steel is investigated by means of in situ magnetization measurements and optical and scanning electron microscopy. The metastable austenitic microstructure partially transforms to pearlite upon isothermal aging in the temperature range 500–600°C on a time scale of tens of hours. The observed transformation kinetics and microstructure development are interpreted in terms of the nucleation and growth of pearlite colonies. Preferential nucleation sites for pearlite formation are grain boundaries, and prior plastic deformation increases the density of nucleation sites. Manganese partitioning between the ferrite and cementite lamellae in pearlite appears to control the growth rate, and is the underlying reason for the slow transformation kinetics.

Effect of pre-IC annealing treatments on the final microstructure and work hardening behavior of a dual-phase steel

This paper investigates the relationship between the microstructure and the work hardening behavior of a dual-phase (DP) steel. Various DP microstructures were systematically produced by application of different pre-IC annealing heat treatments as well as changing the IC annealing temperature. It was found that various austenite nucleation sites such as grain boundaries, prior pearlite colonies, martensite particles and cementite particles, have different nucleation and growth effectiveness which significantly influences the microstructure after IC annealing. Following a quantitative analysis of all microstructures, the effect of microstructural parameters including martensite particle size, volume fraction as well as their spatial distribution and morphology, on the mechanical behavior of DP steels is examined by considering true work hardening rate, instantaneous work hardening rate and the dislocation annihilation factor from the Kocks–Mecking analysis. These analyses reveal that at constant ratios of volume fraction to size of martensite particles, there are significant differences in all the three work hardening parameters. It is proposed that these observations are due to the effects of morphology and spatial distribution of martensite particles. Furthermore, it was shown that the contribution of martensite particles to work hardening behavior, via geometrically necessary dislocations, is only significant at the early stages of deformation.

Effect of Microstructure on Mechanical Properties of High Carbon Steel Wire Rod

In this study, the effect of pearlite microstructure on mechanical properties has been analyzed.The high carbon steel wire rods were treated by traditional salt-bath isothermal heat treatment and a new process, respectively. The microstructures and mechanical properties of the wire rods were tested with SEM and Instron 8501. The results shown that with the decrease of the isothermal holding temperature, the pearlite interlamellar spacing and pearlite colony size decreased and the mechanical properties of the wire rod increased. Especially the interlamellar spacing and pearlite colony size were decreased by new heat treatment observably. With the new treatment, the reductions of area increase.

Proposal for an engineering definition of a fatigue crack initiation unit for evaluating the fatigue limit on the basis of crystallographic analysis of pearlitic steel

In this study, in order to define a fatigue crack initiation unit, the relationship between the fatigue crack initiation process and the crystal structure in the pearlitic steel used for railroad rails was examined and fatigue tests, focusing on crack initiation, were performed. The fracture surfaces were analyzed using a scanning electron microscope (SEM) and electron backscatter diffraction (EBSD). The crystal structure of the pearlitic steel is composed of “pearlitic colonies” that have the same lamellar structure direction and “pearlitic blocks” that have the same ferrite crystal direction. The SEM and EBSD results revealed that the crack initiation depends on the pearlitic colonies. Therefore, we defined the characteristic dimension for fatigue crack initiation as the pearlitic colony size. However, for safety purposes, the pearlitic block size should be considered the engineering definition of the fatigue crack initiation unit, since decreasing the pearlitic block size should cause an improvement in the fatigue limit of pearlitic steel.

Effect of Prior Austenite Grain Size on Pearlite Transformation in a Hypoeuctectoid Fe-C-Mn Steel

The aim of this work is to evaluate the influence of the prior austenite grain size (AGS) on the austenite-to-pearlite isothermal decomposition in a Fe-C-Mn hypoeutectoid steel. Due to the strong influence, grain boundaries have on pearlite transformation kinetics, morphological aspects of pearlite from two conditions with very different AGS were studied and characterized. Results allow us to conclude that the formation of pearlite and ferrite are favored for small AGS values, whereas a larger AGS led to an increase in the total amount of pearlite volume fraction. Furthermore, the average size of pearlitic colonies increased with increasing AGS, and it appears that the interlamellar spacing of the pearlite does not depend on AGS, but instead, is controlled by the isothermal decomposition temperature. Finally, it was observed that the ratio between lamellar thickness of ferrite and cementite depended on AGS.

Effects of Cooling Rate on Microstructure and Properties of Nb-Ti Micro-Alloyed Steel

Continuous cooling transformation (CCT) curves of deformed austenite (A) of Nb-Ti microalloying high strength steel were measured using Gleeble-3800 thermo-mechanical simulator, and corresponding transformation and structure were analyzed, and the effects of cooling rate on the tested steels mechanical property were studied. The resultes showed that the Ar3 transformation point decreased with increasing cooling rate after hot-rolling. The morphology of ferrite (F) grains changed from polygonal to lath, and the pearlite (P) colonies became more fine with increasing cooling rate. The quantity of ferrite and pearlite decreased, and the quantity of bainite (B) and martensite (M) increased. Then the hardness of Nb-Ti micro-alloyed steel is increased along with the increasing cooling rate, which may owing to the reasons that the hardness of ferrite and pearlite is far smaller than that of bainite and martensite, and the grain refinement causes the hardness increasing.

Structure levels of pearlite deformation in carbon steel of eutectoid composition

The structure of eutectoid steel 80 has been studied at various stages of producing high-strength large-diameter reinforcing bars using transmission and scanning electron microscopy. Peculiar features of structural state have been revealed by the scale factor. It has been demonstrated that the stage of intensive strengthening does not exist at the initial steps of drawing a large-diameter wire. Using EBSD it has been established that, in the course of drawing, within the limits of the former austenite grain, a conglomerate is formed that consists of pearlitic colonies with the single orientation of the ferrite constituent along the {100} cleavage plane, which causes the poor technological plasticity of the studied steel.