• Transactions of Materials Processing
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• v.23 no.6
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• pp.345-350
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• 2014

The current study elucidates the effects of cementite spheroidization and pro-eutectoid ferrite on the sliding wear resistance in medium carbon (0.45wt%C) and high carbon (1wt%C) steels. Both steels were initially heat treated to obtain a fully pearlite or ferrite + pearlite microstructure. Spheroidizing heat treatments were performed on both steels to spheroidize the pearlitic cementite. Sliding wear tests were conducted using a pin-on-disk wear tester with the steel specimens as the disk and an alumina ($Al_2O_3$) ball as the pin. The sliding wear tests were carried out at room temperature in air with humidity of $40{\pm}2%$. Adapted sliding distance and applied load was 300m and 100N, respectively. Sliding speed was 0.1m/s and the wear-track radius was 9 mm. Worn surfaces and cross-sections of the wear track were examined using an SEM. Micro Vickers hardness of the wear-track subsurface was measured as a function of depth from the worn surface. Hardness and sliding-wear resistance of both steel decreased with increased spheroidization of the cementite. The decrease was more significant in the fully pearlitic steel (1wt%C steel). The steel with the pro-eutectoid ferrite showed relatively higher wear resistance compared to the spheroidized pearlitic steel.

• Applied Microscopy
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• v.25 no.3
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• pp.90-98
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• 1995

In the Fe-Si system, a mixture of a($Fe_{2}Si_5$) - and ${\epsilon}$(FeSi)-composition powders was sintered and heat-treated subsequently at various temperatures and time to get thermoelectric ${\beta}$-phase($FeSi_2$) compacts. The different transformational sequences depending on the heat treating temperature were found through the investigation into phase transformation and microstructural development. That is, a rapid eutectoid decomposition of ${\alpha}{\to}{\beta}+Si$ occurred together with a accompanying slow reaction between the dispersed Si formed by above decomposition and the preexisted ${\epsilon}$ phase at temperatures below $830^{\circ}C$. The unreacted Si and the micropores formed due to the density change upon the transformation coarsened as heat treating time elapsed. At temperatures above $880^{\circ}C$, however, transformation was proceeded by a peritectoid reaction of ${\alpha}+{\epsilon}{\to}{\beta}$. It took at least 200min. to achieve 90% volume fracion of transformed ${\beta}$ phase, and the growth of micro-pores was also observed in this transformational sequence with prolonged heat treating time.

• Economic and Environmental Geology
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• v.8 no.1
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• pp.1-23
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• 1975

The subject of this study deals with phase relations between stannite ($Cu_2FeSnS_4$) and sphalerite (${\beta}-ZnS$)/wurtzite (${\alpha}-ZnS$). The phase relations were systematically investigated from liquidus temperature to $400^{\circ}C$ under controlled conditions. ${\beta}-stannite$ (tetragonal) is stable up to $706{\pm}5^{\circ}C$, where it inverts to a high-temperature polymorph ${\alpha}-stannite$ (cubic) melting congruently at $867{\pm}5^{\circ}C$. Sphalerite (cubic, ${\beta}-ZnS$) inverts at $1013{\pm}3^{\circ}C$ to wurtzite, which is the hexagonal hightemperature polymorph of ZnS. Between ${\alpha}-stannite$ and sphalerite a complete solid solution series exists above approximately $870^{\circ}C$ up to solidus temperature. The melting temperature of ${\alpha}-stannite$ rises towards sphalerite and reaches a maximum at $1074{\pm}3^{\circ}C$, which is the peritectic with the composition of 91 wt. % sphalerite and 9 wt. % ${\alpha}-stannite$. At this temperature, wurtzite takes only 5wt. % ${\alpha}-stannite$ in solid solution which decreases with increasing temperature. The inverson temperature of ${\alpha}/{\beta}-stannite$ is lowered with increasing amounts of sphalerite in solid solution down to $614{\pm}7^{\circ}C$, which is the eutectoid with the composition of 13 wt. % sphalerite and 87 wt. % ${\alpha}-stannite$. Here, ${\beta}-stannite$ contains only 10wt. % sphalerite in solid solution. With decreasing temperature, the ranges of the solid solution on both sides of the system narrow. The phase relations in the above pure system changed due to the FeS impurities in the sphalerite solid solution. The eutectoid increased from $614{\pm}7^{\circ}C$ up to $695{\pm}5^{\circ}C$ (5 wt. % FeS) and $700{\pm}5^{\circ}C$ (10wt. % FeS), while the peritectic decreased from $1074{\pm}3^{\circ}C$ down to $1036{\pm}3^{\circ}C$ (wt. %FeS) and $987{\pm}3^{\circ}C$ (10wt. %FeS). A most notable change is the appearance of non-binary regions. An important feature is the combination of this study system with the experimental results reported by Sprinfer (1972). If a stannite-kesterite solid solution is used in the place of stannite as a bulk composition, the inversion temperature is lowered to less than $400^{\circ}C$ which belongs to temperatures of the hydrothermal region.

• Transactions of Materials Processing
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• v.19 no.1
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• pp.25-31
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• 2010

To achieve desired microstructure and mechanical property of a manufacturing product, heat treatment process is applied as a secondary process after forging. Especially, quenching process is used for improving strength, hardness, and wear resistance since phase transformation occurs owing to rapid heat transfer from the surface of the specimen. In the present paper, a study on surface temperature measurement for water quenching of eutectoid steel was investigated. In order to determine the temperature history in experiments, three different measuring schemes were used by varying installation techniques of K-type thermocouples. Depending on the measured temperature distribution at the surface of the specimen, convective heat transfer coefficients were numerically determined as a function of temperature by the inverse finite element analysis considering the latent heat generation due to phase transformation. Based on the inversely determined convective heat transfer coefficient, temperature, phase, and hardness distributions in the specimen after water quenching were numerically predicted. By comparing the experimental and computational hardness distribution at three different locations in the specimen, the best temperature measuring scheme was determined. This work clearly demonstrates the effect of temperature measurement on the final mechanical property in terms of hardness distribution.

• Corrosion Science and Technology
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• v.13 no.3
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• pp.102-106
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• 2014

Nickel electrodeposition from sulfamate bath has several benefits such as low internal stress, high current density and good ductility. In nickel deposited layers, sulfur induces high temperature embrittlement, as Ni-S compound has a low melting temperature. To overcome high temperature embrittlement problem, adding manganese is one of the good methods. Manganese makes Mn-S compound having a high melting temperature above $1500^{\circ}C$. In this work, the mechanical properties of Ni-Mn deposited layers were investigated by using various process variables such as concentration of Mn$(NH_2SO_3)_2$, current density, and bath temperature. As the Mn content of electrodeposited layers was increased, internal stress and hardness were increased. By increasing current density, internal stress increased, but hardness decreased. With increasing the bath temperature from 55 to $70^{\circ}C$, internal stress of Ni deposit layers decreased, but hardness didn't change by bath temperature. It was likely that eutectoid manganese led to lattice deformation, and the lattice deformation increased hardness and internal stress in Ni-Mn layers. Increasing current density and decreasing bath temperature would increase a mount of $H_2$ absorption, which was a cause for the rise of internal stress.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.173-176
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• 2009

A great emphasis has been placed on the design of heat treatment process to achieve desired microstructure and mechanical property of final product. In this study, finite element analysis was carried out to predict temperature, microstructure and hardness of eutectoid steel after water quenching. Convective heat transfer coefficients were determined by inverse analysis using surface temperatures measured with three different installation methods of thermocouples. Finally, the effect of convective heat transfer coefficients on the prediction of temperature history and hardness was analyzed by comparing experimental and simulation results.

• Journal of Korea Foundry Society
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• v.8 no.3
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• pp.310-321
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• 1988

This study is aimed to investigate the effects of the multi-phase(ferrite-bainite-martensite) on the strengthening and toughening in ductile cast iron. All the specimen were austenitized at eutectoid transformation temperature range(${\alpha}+{\gamma}$) for 1hr and austempered at $300^{\circ}C$ and $400^{\circ}C$ for various holding time, and then quenched in iced water for multi - phase (${\alpha}-B-M$). When the volume fraction of martensite is below 15%, excellent maximum fracture load can be obtained due to strengthening by the fine martensite, but, with increasing of volume fraction over 15%, it was decreased drastically. The martensite size became finer and the shape of it changed from bar to spherical type with increasing of austempering holding time. The higher the austenitizing temperature is, the more preferential is the formation of austenite phase around the graphite nodules improving strength and toughness of austempered ductile cast iron.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.120-123
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• 2007

The effects of annealing condition on the occurrence of the delamination in cold drawn hyper-eutectoid steel wires, were investigated. Annealing treatment was performed on cold drawn steel wires for temperature range of $425^{\circ}C\sim500^{\circ}C$ with the variation of annealing time from 30sec to 15min. The increase of annealing temperature and time would cause the decrease of tensile strength and the increase of ductility. However, the occurrence of the delamination, representing torsional ductility, showed the different way from the variation of ductility.

• Korean Journal of Materials Research
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• v.25 no.9
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• pp.497-502
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• 2015

The hardenability of boron steel specimens with different molybdenum and chromium contents was investigated using dilatometry and microstructural observations, and then was quantitatively measured at a critical cooling rate corresponding to 90 % martensite hardness obtained from a hardness distribution plotted as a function of cooling rate. Based on the results, the effect of an austenitizing temperature on the hardenability and tensile properties was discussed in terms of segregation and precipitation behavior of boron atoms at austenite grain boundaries. The molybdenum addition completely suppressed the formation of pro-eutectoid ferrite even at the slowest cooling rate of $0.2^{\circ}C/s$, while the chromium addition did at the cooling rates above $3^{\circ}C/s$. On the other hand, the hardenability of the molybdenum-added boron steel specimens decreased with an increasing austenitizing temperature. This is associated with the preferred precipitation of boron atoms since a considerable number of boron atoms could be concentrated along austenite grain boundaries by a non-equilibrium segregation mechanism. The secondary ion mass spectroscopy results showed that boron atoms were mostly segregated at austenite grain boundaries without noticeable precipitation at higher austenitization temperatures, while they formed as precipitates at lower austenitization temperatures, particularly in the molybdenum-added boron steel specimens.

• Journal of the Korean Society for Heat Treatment
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• v.36 no.4
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• pp.230-236
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• 2023

The current study deals with the effect of cooling rate and temperature for annealing on medium-carbon Cr-Mo alloy steel, especially for cold heading quality wire rod, to derive the optimum micro-structures for plastic deformation. This is to optimize the spheroidization heat treatment conditions for softening the material. Heat treatment was performed under seven different conditions at a temperature between A_c1 and A_c3, mostly within 720℃ to 760℃, and the main variables at this time were temperature, retention time and cooling rate. Microstructure and phase changes were observed for each test condition, and it was confirmed that they were greatly affected by the cooling rate. It was also confirmed that the cooling rate was changed in the range of 0.1℃/min to 5℃/min and affected by phase deformation and spheroidization fraction. The larger the spheroidization fraction, the lower the hardness, which is associated with the increasing connection of ferrite phases.