Fine Pearlitic Structure Research Articles

Archaeometric Investigation of the Kunágota-Sword : A Case Study

Among the Early Medieval double-edged swords, excavated in the Carpathian Basin, there are a few which probably have Byzantine origin. The most unique piece of this small but significant group of weapons was unearthed at Kunágota, Southern Hungary. The sword, which has a special sword-guard made of bronze, has been examined by the experts of the Archaeometallurgical Research Group of the University of Miskolc with optical microscopy, SEM-EDS, ED-XRF, and microhardness tests. The primary aim was to study the microstructure of the blade and guard. There was also an important objective of the investigations to explore the possible manufacturing technology. Due to the metallographic examination, it was possible to reconstruct the manufacturing process of the Kunágota-sword. Three samples were taken from the sword for metallographic examination, two of them (K1A and K1B) were collected from the sword-guard and one (K2) from the blade. To summarise the results, it can be established that the basic material of the Kunágota-sword guard is a heterogeneous copper-alloy with high lead content. In the core area of the blade sample a very fine pearlitic structure can be seen. Towards the edge of the blade, a martensitic microstructure can be observed which probably proves a kind of heat treatment of the sword. With the aid of archaeometric investigations, our knowledge related to Byzantine swords can be deepened. Further interesting results can be gained by comparing with the characteristics of other Byzantine swords found of the Carpathian Basin.

Hardening of Steel Through High‐Voltage Low‐Current Energy Input

A novel approach of high‐voltage low‐current energy input is applied for hardening of plain carbon eutectoid steel. Initial fine lamellar pearlitic structure disintegrates into four characteristic regions: lamellar pearlite often containing nucleated cementite spheroids (Region‐I), fragmented cementite lamella in α‐ferrite matrix (Region‐II), submicroscopic cementite particles/clusters dispersed in α‐ferrite matrix (Region‐III), and supersaturated α‐ferrite (Region‐IV). At a particular applied voltage, structural refinement and matrix supersaturation (evolving martensite) progress concomitantly up to 5 min, followed by a reverse trend of coarsening and degeneration of martensite. The refinement effect and martensite‐peak‐broadening effect are augmented with increasing voltage up to 75 kV at which the highest hardness (429 HV) of the steel is achieved with treatment duration of 5 min. While primary hardening effect arises from the martensite region of stratified plate morphology (Region‐IV), a secondary effect of hardening is resulted from the region containing dispersed submicroscopic cementite particles/clusters in α‐ferrite matrix (Region‐III). In addition, in the specimen exhibiting maximum hardening effect (at 75 kV, 5 min), as a unique feature, nanosized cementite particles also appear in Region‐IV being dispersed in martensite matrix so as to provide further effect of dispersion hardening along with martensitic hardening.

Effect of the Microstructure on the Wear Resistance of a Pearlitic Steel

Abstract Despite the experimentation of bainitic and martensitic microstructures in wheel-rail steels, pearlitic microstructure remains dominant in railway track. The wear resistance behavior of bainitic and pearlitic microstructures is still a matter of controversy. In this study, pin-on-disc sliding wear tests were performed to analyze the effects of the microstructure on wear resistance. The AISI 1080 steel was isothermally treated at five temperatures using a dilatometer in order to obtain pearlite, bainite and martensite structures. After these treatments, bainitic and martensitic samples were tempered at 500°C. It was possible to achieve pearlitic specimens with interlamellar spacing ranging from 70 ± 4 nm to 243 ± 9 nm. It was found that the wear resistance increases with decreasing the interlamellar spacing, fine pearlite showed 30% lower mass loss than coarse pearlite. The severe deformation and dislocation accumulation in different depth from the contact surface were analyzed by electron backscattered diffraction technique. The results showed that the first 10 µm depth from the contact surface was severely deformed and a high number of random high-angle boundaries developed due to the large compressive force. Fine pearlitic structure tends to present a better wear performance when compared to bainitic or martensitic structures.

Microstructural and Mechanical Properties Examination of High-Power Diode Laser-Treated R260 Grade Rail Steels Under Different Processing Temperatures

In the present study, high-power diode laser surface treatment was implemented to R260 grade steel with three different processing temperatures (1100 °C, 1200 °C, and 1300 °C) at the laser power of 1750 W and scanning speed of 6 mm/s, in order to identify the effect of various processing temperatures on the mechanical performance. According to the test results, the laser-treated sample at 1300 °C showed much better mechanical performance among the other laser-treated samples. It was found that the laser-treated sample at 1300 °C had about 3 times more surface hardness, a 43 pct increase in yield strength, and a 53 pct increase in toughness value compared to the untreated sample. Microstructural investigations showed that this surface treatment did not only generate a martensitic structure with a certain depth but also provided the formation of a fine pearlitic structure contributing to an increase in the mechanical properties. As a conclusion, it was found that the processing temperature is one of the critical factors affecting the mechanical properties in the laser hardening process. Moreover, the results demonstrated that this treatment method might be an alternative method to enhance the mechanical properties of existing rail steels online without the need for rail disassembly, reducing operational costs.

Effect of Different Cooling Rates on the Corrosion Behavior of High-Carbon Pearlitic Steel

The present work discusses the effect of pearlitic morphology on the corrosion behavior of high-carbon fully pearlitic steel in 3.5% NaCl solution. Four different types of pearlitic steels (furnace-cooled, as-received, air-cooled and forced-air-cooled) consisting of coarse, medium, fine and very fine microstructures, respectively, were tested. Electrochemical behavior of these steels was studied with the help of dynamic and linear polarization and AC impedance spectroscopic tests. The corrosion resistance improved with fineness of the microstructure in general. However, with further reduction in interlamellar spacing beyond a limit, the corrosion resistance reduced slightly. Formation of homogeneous distribution of microgalvanic cells between cementite and ferrite lamellae of fine pearlitic steel improved the corrosion resistance. However, entanglement of the lamellae of pearlite in very fine pearlitic structure as well as breaking of cementite lamellae due to finer pearlitic colonies was attributed to the higher corrosion of the forced-air-cooled steel as compared to the air-cooled steel.

Features of Structure and Property Formation of Rolled Coil for Wire Manufacture

Results are given for research to develop scientifically based process solutions to improve quality characteristics of rolled coils cooled in a two-stage Stelmor line ensuring effective metal microstructure and processing properties for wire and wire products. An increase in welding rod ductility is achieved by limiting the steel’s strengthening element content, effective application of the boron to nitrogen ratio, and optimization of two-stage cooling, ensuring the formation of large ferrite grain size with rolling heat during isothermal soaking, thereby minimizing the formation of non-ductile structural components (bainite and martensite). For high-carbon wire rod used in the manufacture of concrete sleepers, it is necessary to achieve the fine pearlite structure of point 1 (GOST 8233–56) that is provided by alloying steel with boron, vanadium, and/or chromium, and also use of fan cooling. This structure is the optimum from the point of view of metal ductility and strength.

On the significance to use dislocation-density-related constitutive equations to correlate strain hardening with microstructure of metallic alloys: The case of conventional and austempered ductile irons

In order to highlight the importance of selecting the proper constitutive equation of plastic flow in metallic alloys, the strain hardening behaviours of conventional (DI) and austempered ductile irons (ADI) with similar hardness were investigated as study-case. The empirical Hollomon equation and the dislocation-density-related Voce equation were compared. Hollomon equation showed strong limitations in describing the different strain hardening behaviours of DIs and ADIs. Conversely, Voce equation approximated properly all the flow curves, and Voce parameters could describe successfully the different strain hardening behaviours of the two groups of alloys. Voce parameters, rationalised by the Kocks-Mecking-Estrin physical concepts, could also give an insight to the micro-mechanisms that underlie strain hardening, like dislocation density multiplication, dynamic recovery and microstructure features that affect these micro-mechanisms during straining. Through the analysis of Voce parameters it could be highlighted that the DIs strain hardening behaviour was mainly caused by the fine pearlitic structure, consisting of ferritic lamellae with sub-micrometric widths. The improvement of austempered alloys in strength and ductility was related to a significantly lower propensity of ADIs to recover dynamically, which was mainly attributed to the dual phase structure of these alloys. Furthermore, the strain hardening analysis through Voce formalism could identify in ADIs a critical condition of strain hardening rate to be investigated to improve further their ductility, which could not be found with Hollomon equation. The dislocation-density-related Voce equation describes properly the strain hardening behaviour of metallic alloys and give certain correlations between strain hardening behaviour and microstructure.

Effects of Cr Content and Annealing Temperature on Microstructure and Wear Characteristics of Cast Ausferrite Nodular Iron

The effects of Cr content and annealing temperature on abrasive wear characteristics of cast ausferrite nodular iron were investigated with Suga type abrasive wear tester. The surface morphology and Vickers hardness of the tested samples were analyzed by scanning electron microscopy (SEM), digital microscope and Vickers hardness tester. The results show that the cast ausferrite nodular iron could be obtained by alloying with Cr in the as-cast ductile cast iron and permanent mold casting, and the bainite content in the matrix increased with increasing Cr content. However, the decomposition of bainite took place during annealing at 500 °C to 800 °C; especially, at 800 °C, the bainite transformed into a mixture of fine lamellar pearlite and ferrite matrix structure. The wear loss of specimens was reduced with increasing Cr content in the cast ausferrite nodular iron. The wear loss of the sample cast ausferrite nodular iron with 0.4mass% Cr is the least. The wear loss began to increase while the Cr content is 0.6mass%. The wear loss of annealed ductile irons at different annealing temperatures was higher than that of as-cast samples. During the abrasive wear, the shear stress transformed austenite to martensite, and the hardness of specimens increased and the wear resistance of as-cast ductile cast iron was improved.

Analysis of the Deformation and Damage Mechanisms of Pearlitic Steel by EBSD and “in-situ” SEM Tensile Tests

The processes governing the deformation and damage of C70 pearlitic steel were investigated in nanometer and micrometer scales using electron backscatter diffraction technique and “in-situ” scanning electron microscope tensile testing. The ferrite behavior was identified by “in-situ” x-ray tensile tests. Investigations were carried out on annealed microstructure with two interlamellar spacings of Sp = 170 and Sp = 230 nm. It is shown that pearlite yielding is controlled by the deformation mechanisms occurring in ferrite. Deformation and damage mechanisms were proposed. At low strain, pearlite deforms homogeneously with low misorientation (<5°) inside the pearlite colonies and elongates the cementite plates. At high strain, pearlite deforms heterogeneously in intense localized shear bands inside the more favorably oriented pearlite colonies. Misorientation reaches values up to 15°. Cementite deforms by an offset of lamella along the shear bands. The nucleation of these shear bands occurs at strain level of E 11 = 7% for coarse pearlite and at a higher value for fine pearlite. Damage occurs by brittle fracture of the elongated cementite lamellae parallel to the tensile axis and which are developed by shear micro-cracks along the slip bands. The plastic-induced damage is thus delayed by the fine pearlite structure.

고탄소강의 구상화속도에 미치는 초기 미세조직, 냉간압연 및 온도의 영향

Abstract The spheroidization behavior of cementite in a SK85 high carbon steel was investigated in this study. Fine and coarse pearlite microstructures were obtained by appropriate heat treatments according to the TTT diagram of SK85 high carbon steel. oHot rolled plates of SK85 steel were austenitized at 800 C for 2 hrs and then put directly into a salt bath at either 570 o C or 670 C to obtain a fine pearlite (FP) structure and a coarse pearlite (CP) structure, respectively. Cold rolling was subsequently conducted on those specimens with reduction ratios from 0.2 to 0.4. Spheroidization heat treatments were conducted at the subcritical temperatures of 600 and 720 o C for 1 to 32 hrs to elucidate the effect of initial microstructures, heat treatment temperature, and cold reduction ratios on the cementite spheroidization rate. Spheroidization proceeded with fragmentation of cementite plates, spheroidization of the cementite platelets, and coarsening consecutively. Mechanical fragmentation of cementite by cold rolling expedited the rate of spheroidization. The spheroidization rate of FP was much more rapid than that of CP and the spheriodization rate increased with increases in the cold reduction ratio.

Mechanisms of extrusion wear of medium carbon steel

This study investigated extrusion wear mechanisms and transition of wear mechanisms of medium carbon steel by using a pin-on-disc configuration and micro-analyzing the wear surfaces. In an extrusion wear condition, layers of material on the contact surface of the tested pin were extruded continuously from the interface. Under such a condition, the oxides, mainly Fe3O4 and FeO, on the pin contact surface were very thin at about 2 μm, and likely generated during cooling in air after the wear test. The microstructure of the pin very close to the contact surface was fine pearlite, which was transformed from austenite at the end of the wear test. Compared with the microstructures of the same medium carbon steel cooled in air from a melting state, the debris collected from extrusion wear tests had a fine pearlite structure instead of coarse pearlite and ferrite. Thus, the real contact temperature in extrusion wear did not reach the melting point of medium carbon steel. Such changes of microstructures cannot be found in other types of wear.

Spheroidization Behavior of Cementite in a High Carbon Steel

The effect of initial microstructure, cold reduction ratio, and annealing temperature on the spherodization rate of SK85 high carbon steel sheet was investigated. High carbon steel sheet fabricated by POSCO was soaked at 800oC for 2 hr in a box furnace and then treated at 570oC for 5 min in a salt bath furnace followed by water quenching to obtain a fine pearlite structure. Cold rolling was conducted on the sheets of fine pearlite by reduction ratios of 20, 30, and 40 % and heat treatment for spheroidization was carried out at 600 and 720oC for the various time intervals from 0.1 to 32 hrs. Area fraction of spheroidized cementite was measured with an image analyzer as a function of cold reduction ratios and duration times.

Magnetic and electromagnetic inspection of mechanical properties of high-carbon steel with an initial fine-pearlite structure subjected to high-temperature annealing

We study the possibilities of applying the measurements of major and minor magnetic hysteresis loops and electrical and eddy-current parameters for estimating changes in the strength and plastic characteristics of the high-carbon steel У 10 (with 1.03 wt % C) with a fine-pearlite structure during annealing at 650°C for 10–300 min. We analyze the correlations between the mechanical and physical properties of this steel with pearlite structures differing in morphology and imperfection of cementite, as well as the levels of solid-solution hardening and microdistortions of the ferrite-component lattice.

ＭｏおよびＷ合金鋳鉄溶製とレーザによる表面改質−鋳鉄の耐摩耗性向上を目的としたレーザ表面改質（第３報）−

Cast iron has been widely used for the parts of sliding wear such as cylinder bores of motor engines because of its high resistance, which is mainly due to the fine pearlite structure and the existence of graphite acting as a solid lubricant. These features are derived from the rich carbon content (3-4 mass%). However, under severe sliding conditions such as those in high-power motor engines or exhaust-gas recycle (EGR) engines, cast iron without any treatment is not sufficient for wear resistance. In this study, iron casting with Mo-alloyed and W-alloyed was presented. Effects of the alloying of these metals on the microstructure, the hardness and the wear resistance were studied. Furthermore, surface modification by laser melting was carried out to obtain a chilled microstructure, that is, a non-equilibrium phase. The difference between the equilibrium and the non-equilibrium phases was examined for the tribological characateristics. 3% Mo-alloyed, 8% Mo-alloyed and 8% W-alloyed cast iron with laser melting showed high wear resistance ; on the other hand 16% Mo-alloyed cast iron as cast showed high wear resistance.

Characterization of very fine pearlitic structure using ultrasonic attenuation technique: Kopec, B. Ultrasonics international 87, conference proceedings, London (United Kingdom), 6–9 Jul. 1987. pp. 353–358. Butterworth and Co. (Publishers) Ltd., Guildford, Surrey (1987)

Characterization of very fine pearlitic structure using ultrasonic attenuation technique: Kopec, B. Ultrasonics international 87, conference proceedings, London (United Kingdom), 6–9 Jul. 1987. pp. 353–358. Butterworth and Co. (Publishers) Ltd., Guildford, Surrey (1987)

Characterization of the compression properties of rail steels at high temperatures and strain rates

This paper describes a study of the mechanical behaviour of several rail steels at elevated temperatures and strain rates exceeding 10 3 s −1. Dynamic compression testing was performed at high strain rates on several plain carbon and low alloy eutectoid rail steels in the temperature range 25–680 °C using a modified version of the direct impact Hopkinson bar to generate adiabatic stress-strain curves. It was found that the flow stress dependences on the initial testing temperature and interlamellar spacing of pearlite at high strain rates and 25 °C follow the same established trends reported for the low strain rate regime. Impacts at low deformation temperatures (25–180 °C) were found to induce localized catastrophic shearing at the strain rate tested in steels with a fine pearlitic structure.

Characterization of very fine pearlitic structure using ultrasonic attenuation technique: Kopec, B. Ultrasonics international 87, conference proceedings, London (United Kingdom), 6–9 Jul. 1987. pp. 353–358. Butterworth and Co. (Publishers) Ltd., Guildford, Surrey (1987)

Characterization of very fine pearlitic structure using ultrasonic attenuation technique: Kopec, B. Ultrasonics international 87, conference proceedings, London (United Kingdom), 6–9 Jul. 1987. pp. 353–358. Butterworth and Co. (Publishers) Ltd., Guildford, Surrey (1987)

Characterization of very fine pearlitic structure using ultrasonic attenuation technique

Characterization of very fine pearlitic structure using ultrasonic attenuation technique

Use of X-Ray Diffraction with the Gaussian Curve Method to Evaluate the Hardening in Quenched Steels

Abstract An X-ray diffraction line will broaden considerably when steels transform to martensite on quenching. Slack quenched steels contain a mixed martensite and fine pearlite structure which produces an anomalous diffraction line profile with a sharp peak superimposed on a broad base. The sharpness of the diffraction line peak can be measured by using a constant of the Gaussian curve fitted to the peak. This constant (denoted GCP) for completely hardened steels increases with increasing carbon content up to 0.7 wt% carbon. At higher carbon contents, the GCP becomes almost constant. Also, the GCP increases with increasing hardness along a single curve independently of carbon content. The GCP for the slack quenched steels is smaller than that for the completely hardened steels. Extent of hardening of the slack quenched steels having a sharp diffraction line peak can be evaluated rapidly and nondestructively by comparing their GCP value with that for the completely hardened steels.