ISIJ International
Online ISSN : 1347-5460
Print ISSN : 0915-1559
ISSN-L : 0915-1559
Volume 32 , Issue 11
Showing 1-19 articles out of 19 articles from the selected issue
  • Shuichi Iwadoh, Toshikazu Mori
    1992 Volume 32 Issue 11 Pages 1131-1140
    Published: November 15, 1992
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    As the fundamental tools in the cold rolling, work rolls have been greatly affected on the quality, production cost and productivity. The issue of the technological innovation about work roll manufacturing have been changed from the original, which was concerned with steel making and ingotting techniques for minimizing inclusions, to the next which cope with maximizing the hardening penetration by improving heat treatment and composition designing. In addition, the trend show that the industry is orienting to produce a high anti-wear rolls by increasing alloying elements.
    The improvement of soundness and expansion of hardening depth of roll its self have greatly contributed to the reduction of productivity and production cost of sheet steels by the combination with the innovations of rolling technology such as continuation of tandem mill or hydraulic screw down.
    On the other hand, chasing high anti-wear property caused the problem of regrinding of rolls instead.
    The task from now shall be oriented to reconsidering the factors which restrict the work roll service life returning back to the fundamentals and seeking for the roll performance which suit to each mills own purpose, at the same time developing a regrinding technology which meet to the high performance rolls should be required.
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  • Toshiaki Himemiya, Takateru Umeda, Gouichi Matsunoshita, Yasuo Kimura
    1992 Volume 32 Issue 11 Pages 1141-1149
    Published: November 15, 1992
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    Solidification behavior of high-nickel grain roll materials has been studied experimentally with a unidirectional solidification method. Two specimens were employed; A had the standard chemical composition, and B had the composition which promoted white iron solidification. Solidification structures were observed, and the amount of graphite was measured. The temperature difference between ledeburite (γ+Fe3C) and austenite-graphite (γ+G) eutectic fronts was measured, and there appeared to be a good correlation between this value and the amount of graphite. Then the positions of the two eutectic fronts and the temperature difference were discussed with regard to solidification parameters.
    The results obtained were as follows:
    (1) The critical cooling rate of transition from white to mottled iron in A is 0.12-0.15 K s–1, and for B, it is 0.050-0.067 K s–1.
    (2) The austenite-graphite eutectic front precedes the ledeburite eutectic front at a smaller growth rate, while the latter forms first at a larger growth rate in A. Ledeburite always forms first in B.
    (3) The sequences and temperature difference of both eutectic fronts agree with the results calculated using the Fe-C binary eutectic solidification model.
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  • Yukinori Ono, Noriko Murai, Keisaku Ogi
    1992 Volume 32 Issue 11 Pages 1150-1156
    Published: November 15, 1992
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    The partition coefficients of chromium and carbon to primary austenite were measured on Fe-Cr-C ternary alloys containing 1.1 to 3.6 mass% C and 1.5 to 26 mass% Cr. Each alloy specimen was held for 1 h at a temperature just below the liquidus and then quenched in water cooled copper mold. Partition coefficients were in the range of 0.53 to 0.80 for chromium and 0.25 to 0.38 for carbon. Partition coefficients of third elements to primary austenite were also evaluated on 5 and 15 mass% Cr quaternary alloys. The coefficients of silicon, nickel and copper were larger than unity and increased with an increase in carbon content, while those of molybdenum, manganese and vanadium were smaller than unity and decreased with increasing carbon content of alloy. The partition coefficient of chromium was little influenced by the third elements.
    The partitions of alloying elements between liquid and eutectic phases were evaluated on eutectic alloy specimens with 2, 5, 15 and 30 mass% Cr that were quenched during freezing unidirectionally at 10 mm/h. The irons containing 2 and 5 mass% Cr froze in austenite+(Fe, Cr)3C eutectic, and the 15 and 30 mass% Cr irions crystallized into austenite+(Cr, Fe)7C3 eutectic. In each alloy system chromium, molybdenum, manganese and vanadium were distributed preferentially to eutectic carbide, white silicon and nickel dissolved selectively into eutectic austenite. The partition coefficient of each alloying element to eutectic, defined as the ratio of the average eutectic composition at cell tip to alloy content of liquid near freezing front, were also determined in this study.
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  • Minoru Ikeda, Takateru Umeda, Ching Ping Tong, Toshio Suzuki, Naotaka ...
    1992 Volume 32 Issue 11 Pages 1157-1162
    Published: November 15, 1992
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    Mo2C was formed as a eutectic in the final stage of solidification of high Cr cast iron containing Mo. This finely dispersed carbide that is harder than Cr7C3 is expected to give good wear resistivity of hot rolls. The effect of addition of Mo up to 10 mass% in 3mass%C-20mass%Cr iron was investigated. With increasing Mo content, tensile strength and fracture toughness decreased monotonically, and hot wear resistivity increased. These effects could be explained by the amount of Mo2C. Fine particles of Mo2C provided crack initiation and growth sites to cause fracture. However they prevented the propagation of wear cracks. Eutectic carbides should be controlled within about 35 vol% considering a balance between mechanical properties and wear resistivity.
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  • Sam Kyu Chang, Dong Gyu Kim, Jin Won Choi
    1992 Volume 32 Issue 11 Pages 1163-1169
    Published: November 15, 1992
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    An experimental study has been made of the effects of alloying elements and austenite destabilization heat treatment on the graphitization in the as-cast and heat treated condition, of a high chromium cast irons containing 3.8%C-11%Cr-2.3%Si-5.5%Ni-1.3%Mn-1.2%Mo as hypereutectic alloy and 3.4%C-7.5%Cr-2.5%Si-1%Mn-1.3%Mo as hypoeutectic alloy. The granular graphites are crystallized in the matrix hypereutectic high chromium cast irons containing copper, phosphorous and vanadium in as-cast state, but the aluminum alloyed melt is solidified with the flake type graphite. The concentrations of graphitizers of silicon, nickel and copper appear higher in the graphite-matrix interface than in the matrix but the concentration of chromium appears very low comparing to that in the matrix. This means that it is possible to substitute copper for nickel which is commonly adopted as a graphitization element in high chromium rolls containing crystallized graphite. Inoculating the hypoeutectic alloys with metallic aluminum and ferrosilicon powder in inoculant dressing process, it is possible to crystallize granular type graphite instead of flake type graphite and increase also the volume of graphite. The number and volume of graphite increase remarkably as the high chromium cast iron containing crystallized graphite are heat treated at 950°C for 90 min. Such an increase of graphite is because a temper carbon and the secondary graphite are precipitated by the first stage graphitization. This result must be considered in dressing the graphite volume fraction in manufacturing high chromium rolls containing crystallized graphite.
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  • Jin Won Choi, Sam Kyu Chang
    1992 Volume 32 Issue 11 Pages 1170-1176
    Published: November 15, 1992
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    To clarify the effect of alloying elements on transformation behavior of destabilization heat treated high chromium cast irons, specimens of high chromium hypoeutectic cast irons containing copper and molybdenum were destabilization heat treated at 900, 1000 and 1100°C for 5×102 to 5×104 sec and then rapidly cooled down to room temperature. As the destabilization heat treatment temperature and soaking time rise, the molybdenum content in the primary dendrite region and the amount of retained austenite are increased, but chromium atoms supersaturated in the primary austenite phase during solidification are precipitated into complex chromium carbides. The presence of copper promotes the attainment of microstructure consisting of discontinuous eutectic carbides. It was observed in the present work that some amount of copper solutes were contained in the secondary carbides precipitated in the copper added cast irons. EDS quantitative analysis showed 5.64% copper. A molybdenum-rich eutectic structure grown in the periphery of eutectic colony appearing a lamellar shape was observed in the 2.8% molybdenum contained cast irons during destabilization heat treatment at 1000°C for 5×102 sec.
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  • Hisashi Hiraoka, Yoshihiro Kataoka, Kouji Yuda, Kazuyuki Taniguchi, Mi ...
    1992 Volume 32 Issue 11 Pages 1177-1183
    Published: November 15, 1992
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    High-chromium (Hi-Cr) iron rolls have good wear resistance, but have certain disadvantages in their application to roughing mills. The influence of C and Cr contents on material and mechanical properties were examined.
    The dendritic structure of the material changes with C and Cr contents, with the structure of lower C and Cr steel being larger than that of higher C and Cr iron. Hot hardness and wear resistance do not depend on C and Cr contents, while the mechanical wear of these materials decreases with increasing hardness. The thermal shock resistance decreases with decreasing Cr content.
    Using Hi-Cr steel rolls instead of Hi-Cr iron rolls in a hot strip roughing mill, accidental slippage was prevented by their rougher surface and better performance obtained by increasing hardness.
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  • Kunio Goto, Yukio Matsuda, Kohichi Sakamoto, Yoshihito Sugimoto
    1992 Volume 32 Issue 11 Pages 1184-1189
    Published: November 15, 1992
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    Work roll life of hot rolling mills is strongly affected by roll material. Recently, high-carbon high speed steel rolls have been developed to improve further work roll life.
    In this paper, relationship between basic characteristics of roll and microstructure in high-carbon high speed steels were investigated. After specimens with the several chemical compositions made by casting, forging, and powder process were prepared, wear test, friction test, heat crack test, flexure test were conducted.
    Consequently, it was revealed that basic characteristics of roll were strongly dependent upon the amount, shape, size of carbide, that is, wear resistance mainly increases with an increase in the amount of carbide, seizure resistance increases as the size of carbide is larger except at a large amount of carbide, heat crack resistance and toughness increase as the shape of carbide is the more spherical and the size of that is the smaller.
    Moreover, it became clear from the above results that 3.0wt%C-10.0wt%V high speed steel made by powder process is one of the most desirable roll material as has a large amount of fine spherical carbide.
    As a result of model rolling test, it was found that wear resistance of the above material is about five times that of high Cr cast iron.
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  • Toshihiro Kudo, Suguru Kawashima, Ryurou Kurahashi
    1992 Volume 32 Issue 11 Pages 1190-1193
    Published: November 15, 1992
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    Monobloc type durable rolls of over 10000 kg have been developed by ingot metallurgy for hot rolling mills, and the metallurgy and the manufacturing process of the roll are described. The microstructure of the roll consists of hard primary carbides, mainly vanadium rich MC, embedded in the highly tempered matrix. The characteristics of the roll which relate to the performance expected for a durable roll are also explained.
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  • Yoshikazu Sano, Toshiyuki Hattori, Michio Haga
    1992 Volume 32 Issue 11 Pages 1194-1201
    Published: November 15, 1992
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    In the field of hot strip mill finishing train, the demands for not only high quality of sheet product shape and sheet surface condition but also high productivity and energy saving in rolling are increasing. In this circumstance, we have developed completely new type compound roll which is composed of high-carbon high speed steel of outer shell and forged steel of core material to meet the requirement of high reliability as well as high wear resistance.
    After many experiments, the first trial of this new compound high-carbon high speed steel rolls was made in 1987 in finishing train of hot strip mill. Since then more than one hundred fifty new compound rolls have been used in hot strip mill finishing train. These new compound rolls are contributing the high productivity of rolling and the improvement of sheet products.
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  • Mitsuo Hashimoto, Seizi Otomo, Kouichiro Yoshida, Kazuo Kimura, Ryurou ...
    1992 Volume 32 Issue 11 Pages 1202-1210
    Published: November 15, 1992
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    In response to severe quality requirements resulting from remarkable progress in rolling techniques, composite type high performance roll was developed. With the adoption of this method, tough core metal, fine structure and high alloy at shell metal can be obtained with ease. Rolls with shell metal of high speed tool steel used as finishing work roll for hot strip mill showed outstanding results in wear resistance, surface roughening resistance and toughness. Consequently, conditions restricted by rolls in steel rolling mills are markedly relieved, rolled products of high grade can be produced and productivity is improved.
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  • Yoshio Oike, Junji Sato, Kazuhiko Minami, Kunihiko Yoshitake, Shigeo Y ...
    1992 Volume 32 Issue 11 Pages 1211-1215
    Published: November 15, 1992
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    The relationship between the strip surface flaw occurrence and rolling conditions in upstream stands together with the chemical compositions of rolled material are examined in the skinpass mill line. The ratio of the mean rolling pressure and the work roll surface in roll bite has a good correlation with the occurrence of the strip surface flaw. The strip surface flaw occurs frequently when the ratio exceeds the threshold value fixed by the chemical compositions of rolled strips. A slight addition of Si to Al-killed steel reduces remarkably the occurrence of the strip surface flaw. In order to clarify this phenomena, the influence of Si content on the behavior of scale formed on strip surface is investigated through laboratory tests. Moreover, the influence of the friction coefficient on the velocity difference between roll surface and strip surface is calculated by rigid-plastic FEM, as the friction coefficient changes with Si content.
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  • Osamu Kato, Hiroyasu Yamamoto, Matsuo Ataka, Koe Nakajima
    1992 Volume 32 Issue 11 Pages 1216-1220
    Published: November 15, 1992
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    Investigation of mechanisms of the surface deterioration of the roll for the hot strip rolling is very important for the development of the new roll material. Then, several experiments are conducted based upon results obtained by earlier investigations, and considerations concerning it are given.
    The experiments are a rolling/sliding friction test at high temperature and a rolling contact fatigue test using specimens previously incurring thermal fatigue. The surface and its cross section of tested disks are examined carefully by a scanning electron microscope and an optical microscope.
    Regarding the wear, abrasion of the matrix at high temperature is probably one of the main mechanisms. And regarding the surface roughening, the rolling contact fatigue of the material that has previously incurred perpendicular crack is probably one of the main mechanisms.
    However, these models of the surface deterioration mechanisms should be refined in future, as it is very important problems for a rolling tribology.
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  • Jae Hwa Ryu, Ohjoon Kwon, Pil Jong Lee, Yong Min Kim
    1992 Volume 32 Issue 11 Pages 1221-1223
    Published: November 15, 1992
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    Effects of the service conditions on the roll surface deterioration in the front finishing stands of hot strip mill were analysed by observing the roll surface after each roll change and by calculating the roll surface temperature and the heat penetration depth. The roll surface temperature was varied with the rolling conditions and the steel grades rolled. The heat penetration depth was greatest at the F1 stand, and was gradually decreased in the latter stands. The roll surface deterioration was greatest at the F2 stand, which was thought to be due to the severe thermal fatigue of the F2 rolls. A parameter representing the thermal fatigue damage was developed by considering the effects fo roll surface temperature and heat penetration depth on the degradation of the roll surface. It was found that the parameter had a good correlation with the degree of the observed roll surface breakdown.
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  • Tatsumi Kimura, Masatake Ishii, Keniti Amano, Syuzo Ueda, Yutaka Oka, ...
    1992 Volume 32 Issue 11 Pages 1224-1231
    Published: November 15, 1992
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    Secondary hardening characteristics and those effects on a wear and a thermal shock resistance of the 5%Cr-2%Mo-1%V steel roll for cold strip mill were studied.
    The secondary hardening by a tempering was induced both by the precipitation of carbide during holding stage and by the transformation of retained austenite to a fresh martensite (FM) during the cooling stage.
    The increase in FM volume % raised the hardness in secondary hardening. The hardness of FM was calculated as Hv935. The wear and thermal shock resistance decreased as the volume % of FM increased. This is due to the preferential carbide precipitation on grain boundaries.
    On the practical viewpoint, the suitable micro-structure for the work roll is the tempered martensite containing a 20% of FM. The work roll showed an excellent wear and thermal shock resistance compared to the conventional roll tempered at low temperature.
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  • Akira Azushima, Yasuhiro Morita
    1992 Volume 32 Issue 11 Pages 1232-1237
    Published: November 15, 1992
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    The lubrication characteristics of surface treated rolls of the chromium plated roll, the TiN coated PVD (Physical Vapor Deposition) roll and the VC coated TRD (Thermo-Reactive Deposition) roll are examined by using the simulation testing machine developed by the author. The coefficient of fraction is measured in order to evaluate the lubricity, and the occurrence of the friction pick up is observed in order to evaluate the anti-seizure property changing rolling speed and reduction in thickness. The experimental results are compared with that of the conventional roll and the conclusions obtained are as follows; (1) the coefficients of friction of the VC coated TRD roll are about half of that of other rolls, (2) the limitation reduction when the friction pick up occurs is significantly greater than that of the conventional roll.
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  • Shigeki Shimizu, Kenichi Aoki, Makoto Kobayashi, Teruhiro Saito, Yasuh ...
    1992 Volume 32 Issue 11 Pages 1238-1243
    Published: November 15, 1992
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    One of the important factors in cold rolling is the friction coefficient between strip and work roll. Friction coefficient has a close relationship with surface roughness of the work roll. Therefore, highly wear-resistant work rolls with small diminution of roll surface roughness due to slippage in the bite between strip and rolls have been required for stable rolling operations. In order to meet the need for optimum degree of roughness of work rolls, a new roll with minute and uniformly-distributed titanium carbo-nitrides (hereafter Ti-roll) has been developed. Presumably as a result of such hard titanium carbo-nitrides becoming detached, a new improved roughness profile can be continuously generated on the roll surface while rolling. Actual use of the Ti-roll in cold rolling not only showed the small change in surface roughness of work rolls, but made higher production sure due to higher line speeds in the early stage of the work roll service life, as well as to longer overall roll-life.
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  • Masaki Shimizu, Osamu Shitamura, Shusuke Matsuo, Toshio Kamata, Yasuo ...
    1992 Volume 32 Issue 11 Pages 1244-1249
    Published: November 15, 1992
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    Recently work rolls for cold rolling mill have been required for higher toughness because of remarkable progress in rolling mill, in addition, demands for higher wear resistance of rolls and lower damage of rolls in the accident of rolling have been increasing more and more. The new composite roll by the rotational electroslag remelting (ESR) bimetallic method was developed in order to satisfy such various demands at the same time.
    The rotational ESR bimetallic method is a producing method of composite ingots, in which a pipe shaped electrode is electroslag remelted in a gap between a mold and a core rotating synchronously and forms an outer layer around a core. By this bimetallic method, it is possible to manufacture a composite ingot with highly concentric boundary and outer layer of extremely uniform thickness. Because the boundary is sound and strong enough to endure at severe heat treatment and hard rolling condition, in addition, various materials such as high speed steel or high chromium iron can be applied to the outer layer with sound boundary, it becomes possible to improve remarkably roll properties. This new composite rolls with the outer layer of high speed steel obtained three to five times higher wear resistance than conventional rolls in commercial cold rolling, and the damage in the accident of rolling could be decreased remarkably.
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  • Takahiko Ohkohchi, Ken-ichi Yasuda, Mitsuo Nakagawa
    1992 Volume 32 Issue 11 Pages 1250-1257
    Published: November 15, 1992
    Released: May 31, 2007
    JOURNALS FREE ACCESS
    The use of ceramics has been studied to provide rolling performance levels that conventional steel rolls can never attain. Sialon was selected as the most suitable roll material for cold rolling. Its characteristics and performance in cold rolling were evaluated.
    Mechanical properties, especially flexural strength, were lower than for steel rolls. However, sialon rolls were found to be sufficiently durable for industrial applications, and they were superior in wear resistance to steel rolls.
    Excellent strip rolling capability was demonstrated during experimental rolling. High Young's modulus and smooth surface enable the ceramic rolls to produce a minimum thickness 2/3 that obtained with steel rolls. Roll coating was negligible on the sialon rolls because of the low adhesivity to metal. Thus, strips had a glossy surface and rolling conditions were stable.
    Other advantages over conventional rolls, including fewer rolling passes, fewer roll changes, flexible strip width change, and longer re-grinding intervals, were demonstrated in commercial rolling.
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