ISSN 0412-1961
CN 21-1139/TG
Started in 1956

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    , Volume 16 Issue 4 Previous Issue    Next Issue
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    EMBRITTLEMENT OF BOLTS MADE OF THE 25Cr2Mo1V STEEL AFTER LONG EXPOSURE AT 540℃
    Qu Zhe;Guo Kexin (K. H. Kuo) Institute of Metal Research; Academia Sinica
    Acta Metall Sin, 1980, 16 (4): 371-487. 
    Abstract   PDF (1319KB) ( 793 )
    Bolts made of the 25Cr2Mo1V steel become gradually embrittled with increas-ing fraction of intercrystalline fracture after long exposure (more than 40000hours) at 540℃. This is found to be caused by the segregation of phosphorus upto 8 at% at austenitic grain boundaries accompanying the depletion of molybdenumin ferrite down to about 0.3% owing to the formation of a molybdenum-contain-ing carbide Fe_3Mo_3C (M_6C). Reheating of the embrittled bolts to 680℃ removes the segregation of phos-phorous at the grain boundaries and therefore also the intercrystalline embrittle-ment. However, the molybdenum content of ferrite is further lowered to about 0.2%and its scavenging effect for phosphorous is thus greatly lost, therefore the embrit-tling tendency of these bolts during reuse is enhanced. Even after requenchingand tempering, the service life of these bolts is still shortened, owing possibly tothe inhomogeniety of molybdenum in austenite not removed by the reaustenitizingtreatment.
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    THE DISTRIBUTION OF BORON IN LOW ALLOY CAST STEELS
    Chu Youyi;He Xinlai;Yu Zongsen;Ou Yuguang Beijing Institute of Iron and Steel Technology and Nei Monggol №. 1 Machine Works
    Acta Metall Sin, 1980, 16 (4): 380-490. 
    Abstract   PDF (3606KB) ( 698 )
    The segregation and distribution of boron varied with heat-treatment in Mn-Mo-B-RE low alloy cast steels has been investigated. The influence of boron con-tent, rare earth additions and other alloying elements such as Mo upon the distri-bution of boron has been studied. It was shown that the boron segregation inthese steels is aggravated with the increase of its content. After norma1 homogeni-zation, the homogeneity of boron may be strongly affected by the segregation ofMo. In certain condition, the boron-bearing phases may precipitate either alongcertain austenite planes or at the grain boundaries to form coarse continuous networks, thus cause brittle fracture. The results also showed that rare earth elementsmay act as a fairly good protective additions for boron.
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    AN EVALUATION OF LONG-TERM PERFORMANCE AND MICROSTRUCTURAL STABILITY OF A 35Ni-15Cr TYPE IRON-BASE SUPERALLOY WITH REDUCED Al+Ti CONTENT
    Guo Jianting;Xu Jiaxun;An Wangyuan Institute of Metal Research; Academia Sinica Harbin Turbine Works
    Acta Metall Sin, 1980, 16 (4): 386-492. 
    Abstract   PDF (3261KB) ( 524 )
    Four-year performance tests on creep and creep-rupture strength under vari-ous stress levels at 700℃ have been carried out for a modified 35Ni-15Cr iron-base superalloy with Al+Ti content reduced from 5 to 3%. It is shown that thehigh temperature properties of this alloy are superior to those of other superalloysof the same type such as ЭИ787, ЭИ437Б, Nimonic 80 and 80A, etc. It seemsthat such an alloy may meet the demands of turbine blade materials for longtime service at 700℃. However, microstructural observations showed that stressingpromotes phase transformation, e. g. γ' phase tends to coarsen directionally whileσ and Laves phases precipitate out much earlier. The results of room temperaturetensile tests after rupture exposure further confirm the acceptability of such alloyas gas turbine blade material for long-term uses.
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    EFFECTS OF RARE EARTH ADDITIONS ON THE COHESION OF OXIDE SCALE IN AN Fe-Cr-Al ALLOY
    Zhang Fuzhong;Sun Chuanyue Baotou Institute of Metallurgy Research and Shanghai Electrical Alloy Plant
    Acta Metall Sin, 1980, 16 (4): 394-400. 
    Abstract   PDF (1034KB) ( 653 )
    In Fe-25Cr-5Al electrical resistance alloy, the presence of 0.103% La, 0.092%Ce, 0.068% mischmetal or 0.25% Yappeared to increase its service life significantlyeither found by accelerated life testing or by isothermal life testing procedurerespectively. There is also a rise in strength of oxide scales formed on the wiresurface.It is found that the distribution of alloying elements in the oxide scale ischanged markedly by the addition of RE. The enrichment of Fe and Cr ions inthe inner layer of the α-Al_2O_3 scale is suppressed, and in Y-containing alloy, theenrichment of Y in the scale causes the formation of Y_3Al_2(AlO_4)_3 phase (YAG).Both may give rise to the improvement of cohesion within the oxide scale whichwould in turn contribute significantly to the increase in service life of the alloy.
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    EFFECT OF RARE EARTH ADDITIONS ON THE SCALE MORPHOLOGY OF AN Fe-Cr-Al ALLOY
    Li Pei;Luo Jiqun Baotou Institute of Metallurgy Research
    Acta Metall Sin, 1980, 16 (4): 401-496. 
    Abstract   PDF (4050KB) ( 615 )
    Scales on Fe-23Cr-6Al alloy wrinkle rapidly in air at 1300℃. Cavities andvoids are formed at the scale/substrate interface. For pre-polished specimens, cav-ities are found at the grain boundaries on the metal surface in the form of net-work, and voids occur at places originally occupied by inclusions and carbides.For alloys containing 0.15% La, 0.15% Ce or 0.60% Y, the scales are flat andfree from cavities and voids at the scale/substrate interface. The grains in theinner layer of the scale are columnar in form and adhere tightly to each other.It is considered that the capability of the RE in suppressing the formation of hotcorrosion pits on the alloy surface during the early stage of oxidation and inreducing the creep deformation due to the growth stress in the scale may accountfor the fact that RE addition inhibits the formation of cavities and voids at thescale/substrate interface and improves the adhesion between the scale and the sub-strate.
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    SEM INVESTIGATION ON HIGH TEMPERATURE OXIDATION OF Fe-23Cr-6Al ALLOYS (WITHOR WITHOUT La, Ce AND Y ADDITIONS)
    Mao Xiaoyu
    Acta Metall Sin, 1980, 16 (4): 406-498. 
    Abstract   PDF (2221KB) ( 868 )
    High temperature oxidation of Fe-23Cr-6Al alloys with and without La, Ceand Y additions at 1300℃ in air has been studied using SEM with a wavelengthdispersive X-ray spectrometer. It is shown that the presence of the cavities formedby the condensation of vacancies caused by the outward diffusion cations resultsin a local detachment at the oxide/substrate interface. This may mainly be respon-sible for the poor oxide adhesion of the alloy without RE. The addition of REchanges the mechanism of growth of the oxide, thus accounts for the improve-ments in oxide adhesion.
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    AN INVESTIGATION OF RESIDUAL STRESS OF OXIDE SCALE AFFECTED BY THE ADDITION OF RARE EARTH ELEMENTS IN Fe-Cr-Al ALLOY AT 1200 AND 1350℃
    Zhang Lixin;Li Liguang;Yin Yaode;Zhao Qi;Zhang Bingshen
    Acta Metall Sin, 1980, 16 (4): 411-419. 
    Abstract   PDF (756KB) ( 585 )
    The residual stress of oxide scale formed at 1200 and 1350℃ in Fe-Cr-Alalloys with the addition of 0.5% Y or 0.15% (La+Ce) has been studied by usingthe internal standard method of X-ray diffraction. The results indicate that theoxide scales have residual compressive stresses and the rare earth elements showan effect on them. The residual compressive stresses in alloys free from rare earthelements are less than 100 kgf/mm~2, in alloys with La and Ce, more than 200kgf/mm~2, and in alloys with Y, more than 300 kgf/mm~2. It is obvious that theadherence of oxide scale is influenced by the value of residual compressive stress. According to the experiments result of Mar, it is thought that the spalling(residual stress) of oxide scale is related to its preferred orientation. In. order toprove this relationship, a texture parameter [P]_A showing the degree of preferredorientation of α-Al_?O_3 scale is defined as follows:[P]_A=P_(0001)+P_(0118)+P_(1129)+P_(10110)P_(hkil) is the texture parameter of inverse pole-figure of α-Al_2O_3 within a strongpole range of 20°. It has been found that the adherence of oxide scale is bad at[P]<6.5 and good at [P]_A>6.5, and the rare earth elements improve the adher-ence of oxide scale through their effect in increasing the degree of preferredorientation of the oxide scale.
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    THERMODYNAMICS OF THE MARTENSITIC TRANSFORMATION IN Fe-X SYSTEMS
    Xu Zuyao (T. Y. Hsu) Shanghai Jiaotong University
    Acta Metall Sin, 1980, 16 (4): 420-425. 
    Abstract   PDF (427KB) ( 892 )
    Similar to the treatment in Fe-C alloy by the author, the thermodynamicapproach of martensitic transformation is conducted in Fe-Ni, Fe-Cr, Fe-Mn andFe-Si systems which are regarded as regular solutions. The M_s and the drivingforce of the transformation at M_s are obtained and consequently the thermody-namic properties of fcc→bcc can be generalized. Like in Fe-C, the driving forcein Fe-X systems increases with the lowering of M_s, but the slope of incrementvaries with the different effect of alloying elements on T_0 temperature and thestrengthening of austenite. These two factors also govern the effect of alloy element onM_s. The driving force in each Fe-X system might be at least 282 cal/mole.This corrects the unrelevant concept which has been widely accepted as long astwenty years. The M_s of pure iron extrapolated from that of Fe-X is 800K,consistent with that of Fe-C, which clarifies the contradictory aspect previouslypresented.
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    THERMODYNAMICS OF THE MARTENSITIC TRANSFORMATION IN Fe-X-C SYSTEMS
    Xu Zuyao (T. Y. Hsu) Shanghai Jiaotong University
    Acta Metall Sin, 1980, 16 (4): 426-429. 
    Abstract   PDF (301KB) ( 554 )
    The △G_(Fe-X-C)~(γ→α) in the martensitic transformation in Fe-X-C system is sugges-ted as: △G_(Fe-X-C)~(γ→α)=x_(Fe)△G_(Fe-X-C)~(γ→α)+x_C RT lnγ_C~α/γ_C~γ+x_i△G_i~(γ→α) +△Ω~(γ→α)where γ_C~α and γ_C~γ are activity of carbon in Fe-X-C ferrite and austenite respec-tively. The M_s of Fe-Ni-C and Fe-Cr-C obtained in present work are in goodagreement with the experimental results, showing that the above equation inavailable and convenient for application. The M_s of Fe-X-C system mainlydepends upon the activity of carbon in Fe-X-C and the strengthening effect onaustenite and carbon play an important role to determine the driving force of themartensite transformation in Fe-X-C.
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    THERMODYNAMICS OF THE MARTENSITIC TRANSFORMATION β(γ)→ε
    Xu Zuyao (T. Y. Hsu) Shanghai Jiaotong University
    Acta Metall Sin, 1980, 16 (4): 430-434. 
    Abstract   PDF (320KB) ( 642 )
    The stacking-fault energy (SFE) at M_s temperature in Co, Co-14Ni and Co-3.5Cu alloys are given and the nucleation mechanism of ε-martensite is discussedwith respect to their driving forces. The transformation barrier in pole mechanismmight include the SFE of parent phase as well as the interaction energy betweenimperfect dislocations, the driving force pushes the dislocations to glide with aspeed about 0.4 of that of sound that provides the dynamic energy to overcomethe transformation barrier. The Seeger's pole mechanism may be effective for themetals with higher SFE like Co, but inavailable for the Co-14Ni and Co-3.5Cualloys with low SFE in 10~(-1) order of magnitude in which the spontaneous nu-cleation of fault will be applicable.
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    DETERMINATION OF DIFFUSION COEFFICIENT OF CARBON IN LIQUID IRON
    Han Qiyong;Han Tongfu;Wang Jian Beijing Institute of Iron and Steel Technology
    Acta Metall Sin, 1980, 16 (4): 435-441. 
    Abstract   PDF (944KB) ( 792 )
    The diffusion coefficient of carbon in liquid iron has been determined byrotating disk method in the temperature range of 1550--1680℃ under argonatmosphere, the temperature dependence of diffusion coefficient being D=4.76 exp(-38000/RT). It was shown that in the case of either complete deoxidation orwithout any deoxidation, the reaction between solid carbon and liquid iron usu-ally lies in the region of diffusion kinetics. In the former case, the diffusion ofcarbon is the rate controlling factor of the reaction. While in the latter case, theoverall reaction consists of two parallel processes-the solution of carbon andthe reaction of solid carbon with the oxygen in liquid iron. The reaction rate isthen controlled by the diffusion of both carbon and oxygen.
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    STUDIES ON THE KINETICS OF Cu DISSOLUTION IN AQUEOUS AMMONIACAL SOLUTION
    Xia Guangxiang;Hu Zhongwu Institute of Chemical Metallurgy; Academia Sinica
    Acta Metall Sin, 1980, 16 (4): 442-453. 
    Abstract   PDF (927KB) ( 730 )
    Studies on the kinetics of copper dissolution in aqueous ammoniacal solutionsaturated with oxygen-nitrogen mixtures of different composition under ambientpressure have been carried out. The reaction of copper dissolution is electrochemi-cal in nature. When the rate of dissolution is limited by the cathodic reaction,the transfer of oxygen is a controlling factor. On the contrary, when the processis limited by the anodic reaction, the reaction will be controlled by the rate ofammonium ion diffusion as well as by the chemical reaction rate with ammo-nia. Criteria for the rate of dissolution of copper will rise or fall with timehave been found. Conditions for the autocatalytic reaction to take place havealso been investigated.
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    CHANGES OF CRACK GROWTH MORPHOLOGY IN STEEL UNDER CORROSION FATIGUE CONDITION
    Zheng Wenlong Shanghai Institute of Material Research
    Acta Metall Sin, 1980, 16 (4): 454-500. 
    Abstract   PDF (3630KB) ( 784 )
    Through the analysis of parts failed in service by electronfractography andfracture mechanics, and by corrosion fatigue (CF) and stress corrosion cracking(SCC) experiments, it was shown that under the condition of CF,the crackingmorphology of steel is not merely governed by a single mechanism. It dependsupon the critical stress intensity factor of the steel K_(IC), CF maximum stress in-tensity factor K_(Imax), threshold SCC intensity factor range △K, frequency f, stressratio R, etc. In case of (dK/da)>0, three basic fracture morphologies wereobserved: (a) when K_(Imax) References | Related Articles | Metrics
    FRACTURE MECHANICS ANALYSIS OF THE NITRIDED CASE ON NODULAR CAST IRON
    Hu Yixiang Dalian Locomotive Works
    Acta Metall Sin, 1980, 16 (4): 463-469. 
    Abstract   PDF (440KB) ( 554 )
    A method for clarifying the effect of nitrided case on the fracture of anodular cast iron has been proposed. Assuming that the effect of the nitrided caseis a linear superimposure of the strengthening of matrix in the case and theresidual stress, quantitative expressions of the fracture toughness as well as thethreshold of fracture toughness are achieved. Results obtained from the nodularcast iron appear to be in reasonable agreement with the experimental data.
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    THE DISTRIBUTION OF DEFORMATION IN TUBE ROUNDS DURING MANNESMANN PIERCING
    Lu Yuqiu;Wang Xianjin Beijing Institute of Iron and Steel Technology
    Acta Metall Sin, 1980, 16 (4): 470-479. 
    Abstract   PDF (1526KB) ( 622 )
    The distribution of deformation in the section of tube rounds during Man-nesmann piercing has been experimentally studied with a view to establishing itsmechanism. It was shown: 1. The distribution of the intensity of strain across the diameter of a tuberound is inhomogeneous with W-shaped. The intensity of strain on the sur-face layer and centre layer is stronger than that on the intermediate layer. 2. Its inhomogeneity increases during the process. 3. Distinct deformation at the centre of the tube rounds has taken place be-fore the cavity occurs, so that the fracture is tough. 4. It is proved that the results obtained by adopting three experimental meth-ods are very alike.
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    MICROSCOPIC STUDY ON SLAGGED HIGH-ALUMINA ARC FURNACE ROOF BRICKS
    Gao Zhenxin Luoyang Institute of Refractory Research
    Acta Metall Sin, 1980, 16 (4): 480-504. 
    Abstract   PDF (4135KB) ( 746 )
    An aspect is summarized of microscopic studies on certain slagged high-alumina bricks dismantled after arc furnace roof service with various steel smelt-ing operations in the past years since 1957. The bricks were attacked mainly byMgO, CaO and iron oxides. The MgO had its sources by evaporation and infiltra-tion from either magnesite fettling material or basic furnace wall under highertemperatures. It was identified by X-ray powder pattern and by microscopic ob-servation that the periclase grains or/and needles occur in the slagged zone ofbricks. The iron oxides, if presence, accumulated themself mostly on the surfacelayer of slagged zone, formed an assemblage of reaction products and convertedinto two systems of ferro-spinels as (MF')A and (F'M)F. However, only MAspinel was formed with less iron oxides content. Other equilibrium phases contain-ing CaO may be monticellite and anorthite. The reaction products observed seemto be calcium- hexaluminate and gehlenite in the inner layer of slagged zone,and a certain amount of glass is also present.
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    AN IN SITU OBSERVATION OF DEFORMATION AND FRACTURE PROCESS IN METAL PART I THE DEFORMATION AND FRACTURE IN PEARLITIC STRUCTURE
    Xu Yongbo;Liu Mingzhi;Zhu Guiqiu;Yu Zhang Institute of Metal Research; Academia Sinica
    Acta Metall Sin, 1980, 16 (4): 485-506. 
    Abstract   PDF (2708KB) ( 605 )
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