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An HSS roll and a Ni-grain roll, commercially manufactured in a centrifugal casting method, were used in this study. CommunicationsTheir chemical compositions (as per input constituents) are listed in Table I. The specimens were cut from the shell part of commercially cast rolls. The HSS roll specimens Phase Analysis of Two Steel Work experienced a series of heat treatment, i.e., austenitization, Rolls Using Mössbauer Spectroscopy air cooling, and double tempering, and were taken at intermediate stages, such as (1) after austenitization at 1050 ЊC for SEI JIN OH, SOON-JU KWON, HONGSUG OH, 1 hour followed by air cooling, (2) after first tempering at SUNGHAK LEE, and KEUN CHUL HWANG 540 ЊC for 1 hour, and (3) after second tempering at the same condition. By the first tempering, a large amount of Responding to an increasing demand lately in the hot retained austenite is removed. The second tempering rolling process to produce rolled steel plates with homogeincreases fracture toughness by transforming martensite to neous thickness and even surface and to improve the productempered martensite. [6] The Ni-grain roll specimens were tivity, continuous studies on developing rolls with enhanced subjected to the stress-relief treatment only at 450 ЊC for 15 properties in wear resistance, strength, fracture toughness, to 30 minutes after casting without austenitization. The heatand thermal fatigue have been made. [1][2][3][4] Because rolls are treatment time of the specimens was decided according to cast in large sizes and cannot go through a subsequent hot that of large commercial rolls. deformation process, the cast structure composed of coarse After polishing and etching the roll specimens, their carbides is retained, and the matrix alone is transformed microstructures were examined by an optical microscope into tempered martensite by austenitization and tempering and SEM. The fractions of various carbides and graphites treatments. [5] Heat-treated rolls are affected by various facpresent in the roll specimens were measured using an image tors such as chemical composition, casting condition, and analyzer. Hardness of the matrix was measured by a Vickers heat-treatment condition, and thus have a complex structure hardness tester under a 25-g load, and hardness of the overall with many phases such as carbides, tempered martensite, bulk was measured by a Rockwell hardness tester (C scale). austenite, pearlite, and graphite. [6] Although most coarse X-ray diffractograms were taken in the 2 range of 30 carbides are not influenced by heat treatment, retained austo 100 deg using a monochromatic Cu K ␣ radiation. The tenite formed after austenitization seriously deteriorates diffractometer (Rigaku, D/MAX 3-C) was equipped with a hardness and wear resistance. Therefore, it is required to graphite monochromator and operated at a voltage of 40 kV carefully analyze the microstructural changes varying with and at a current of 40 mA. After calculating the exact angle the casting and heat-treatment conditions, together with parof peaks ...
An HSS roll and a Ni-grain roll, commercially manufactured in a centrifugal casting method, were used in this study. CommunicationsTheir chemical compositions (as per input constituents) are listed in Table I. The specimens were cut from the shell part of commercially cast rolls. The HSS roll specimens Phase Analysis of Two Steel Work experienced a series of heat treatment, i.e., austenitization, Rolls Using Mössbauer Spectroscopy air cooling, and double tempering, and were taken at intermediate stages, such as (1) after austenitization at 1050 ЊC for SEI JIN OH, SOON-JU KWON, HONGSUG OH, 1 hour followed by air cooling, (2) after first tempering at SUNGHAK LEE, and KEUN CHUL HWANG 540 ЊC for 1 hour, and (3) after second tempering at the same condition. By the first tempering, a large amount of Responding to an increasing demand lately in the hot retained austenite is removed. The second tempering rolling process to produce rolled steel plates with homogeincreases fracture toughness by transforming martensite to neous thickness and even surface and to improve the productempered martensite. [6] The Ni-grain roll specimens were tivity, continuous studies on developing rolls with enhanced subjected to the stress-relief treatment only at 450 ЊC for 15 properties in wear resistance, strength, fracture toughness, to 30 minutes after casting without austenitization. The heatand thermal fatigue have been made. [1][2][3][4] Because rolls are treatment time of the specimens was decided according to cast in large sizes and cannot go through a subsequent hot that of large commercial rolls. deformation process, the cast structure composed of coarse After polishing and etching the roll specimens, their carbides is retained, and the matrix alone is transformed microstructures were examined by an optical microscope into tempered martensite by austenitization and tempering and SEM. The fractions of various carbides and graphites treatments. [5] Heat-treated rolls are affected by various facpresent in the roll specimens were measured using an image tors such as chemical composition, casting condition, and analyzer. Hardness of the matrix was measured by a Vickers heat-treatment condition, and thus have a complex structure hardness tester under a 25-g load, and hardness of the overall with many phases such as carbides, tempered martensite, bulk was measured by a Rockwell hardness tester (C scale). austenite, pearlite, and graphite. [6] Although most coarse X-ray diffractograms were taken in the 2 range of 30 carbides are not influenced by heat treatment, retained austo 100 deg using a monochromatic Cu K ␣ radiation. The tenite formed after austenitization seriously deteriorates diffractometer (Rigaku, D/MAX 3-C) was equipped with a hardness and wear resistance. Therefore, it is required to graphite monochromator and operated at a voltage of 40 kV carefully analyze the microstructural changes varying with and at a current of 40 mA. After calculating the exact angle the casting and heat-treatment conditions, together with parof peaks ...
In this study, microstructures of a heat-affected zone (HAZ) of an SA 508 steel were identified by Mössbauer spectroscopy in conjunction with microscopic observations, and were correlated with fracture toughness. Specimens with the peak temperature raised to 1350 ЊC showed mostly martensite. With the peak temperature raised to 900 ЊC, the martensite fraction was reduced, while bainite or martensite islands were formed because of the slow cooling from the lower austenite region and the increase in the prior austenite grain size. As the martensite fraction present inside the HAZ increased, hardness and strength tended to increase, whereas fracture toughness decreased. The microstructures were not changed much from the base metal because of the minor tempering effect when it was raised to 650 ЊC or 700 ЊC. However, fracture toughness of the subcritical HAZ with the peak temperature raised to 650 ЊC to 700 ЊC was seriously reduced after postweld heat treatment (PWHT) because carbide particles were of primary importance in initiating voids. Thus, the most important microstructural factors affecting fracture toughness were the martensite fraction before PWHT and the carbide fraction after PWHT.
Surface composites reinforced with TiC particulates were fabricated by high-energy electron-beam irradiation. In order to investigate the effects of flux addition on the TiC dispersion in surface composite layers, four kinds of powder mixtures were made by mixing TiC with 5, 10, 20, and 40 wt pct of the flux components (MgO-CaO). To fabricate TiC-reinforced surface composites, the TiC-flux mixtures were deposited evenly on a plain carbon steel substrate, which was subjected to electronbeam irradiation. Microstructural analysis was conducted using X-ray diffraction and Mössbauer spectroscopy as well as optical and scanning electron microscopy. The microstructure of the surface composites was composed of a melted region, an interfacial region, a coarse-grained heat-affected zone (HAZ), a fine-grained HAZ, and an unaltered original substrate region. TiC agglomerates and residual pores were found in the melted region of materials processed without flux, but the number of agglomerates and pores was significantly decreased in materials processed with a considerable amount of flux. As a result of irradiation, TiC particles were homogeneously distributed throughout the melted region of 2.5 mm in thickness, whose hardness was greatly increased. The optimum flux amount, which resulted in surface composites containing homogeneously dispersed TiC particles, was found to be in the range of 10 to 20 pct to obtain excellent surface composites.
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