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

About the Journal

  Current Issue
    , Volume 18 Issue 1 Previous Issue    Next Issue
    For Selected: View Abstracts
    THE NON-EQUILIBRIUM SEGREGATION OF BORON TO AUSTENITE GRAIN BOUNDARIES
    He Xinlai; Chu Youyi; Ke Jun (T. Ko) (Beijing University of Iron and Steel Technology; Beijing)
    Acta Metall Sin, 1982, 18 (1): 1-10. 
    Abstract   PDF (838KB) ( 751 )
    By means of high resolution particle-tracking autoradiography the regularity of boron segregation to austenite grain boundaries has been studied, and the boron concentration profiles across segregated grain boundaries and characteristic parameters for non-equilibrium grain boundary segregation (width of boron-depleted zone, degree and width of boron-segregated band) have been measured. It has been shown that this kind of grain boundary segregation has following features:There exists boron-depleted zone adjacent to segregated grain boundary, which is responsible for supplying of boron to grain boundary during cooling. This kind ofl segregation during cooling is very sensitive to cooling rate. Rapid cooling can inhibit it, and the segregation state would progressively develop from continuous band to discontinuous aggregation and even apparent precipitation as cooling rate decreases. The width of boron-depleted zone is inversely proportional to the square root of cooling rate. The temperature relationship of segregation opposites to the expectation of equilibrium grain boundary segregation. The higher the quenching temperature, the more incremental are the segregated degree and the width of boron depleted zone.The test has been demonstrated that the boron segregation at austenite grain boundaries in quenched steel is a non-equilibrium grain boundary segregation phenomena occurred during cooling.
    References | Related Articles | Metrics
    THE MECHANISM OF NON-EQUILIBRIUM SEGREGATION OF BORON TO AUSTENITE GRAIN BOUNDARIES
    He Xinlai; Chu Youyi; Ke Jun (T. Ko) (Beijing University of Iron and Steel Technology; Beijing)
    Acta Metall Sin, 1982, 18 (1): 11-118. 
    Abstract   PDF (8827KB) ( 667 )
    It has been demonstrated that the boron segregation at austenite grain boundaries in quenched steel is a non-equilibrium grain boundary segregation phenomena occurred during cooling. In this paper, by way of resolving nonisothermal diffusion equation, a theoretical formula for non-equilibrium grain boundary segregation has been derived, and the relationship among width of boron depleted zone, quenching temperature, cooling rate, activation energy and diffusion constant of non-equilibrium grain boundary segregation has been established. The theoretical prospects agreed with experimental results satisfactorily.From experimental results and theoretical analysis, an atomic model for nonequilibrium grain boundary segregation has been suggested, based on the moving of boron atoms along with supersaturationies vacancies or divacancies to grain boundaries (sink of vacancy) during cooling. In light of this new idea of nonequilibrium grain boundary segregation, the complicated effects of boron on hardenability of steel can be explained unambiguously.
    References | Related Articles | Metrics
    INTERNAL FRICTION ASSOCIATED WITH THE MARTENSITIC TRANSFORMATION OF AuCd ALLOYS
    Yang Zhaojin; Zou Yifeng; Zhang Zhifang; Wang Yening (Dep't of Physics; Nanjing University; Nanjing)
    Acta Metall Sin, 1982, 18 (1): 21-29. 
    Abstract   PDF (8917KB) ( 584 )
    The height of the Q~(-1) peak due to martensitic transformation in AuCd alloy increased significantly in successive measuring runs. It was found to be related to the increase of interfaces of parent-martensite according to metallographic examinaětion. The authors put forward a model based on the hysteresis loss mechanism associated with stress-induced motion of the interface dislocations. A new Q~(-1) peak above M_s was observed. It was confirmed to be a relaxation peak due to a certain thermal activation process. For AuCd(46.1 at.-% Cd)alloy, normal bcc(?)orthorhombic transition changed to bcc(?)hexagonal transition after 1—2 measuring runs. It is suggested that defects play a central role in the change.
    References | Related Articles | Metrics
    FORMATION OF μ-PHASE AND ITS EFFECT ON MECHANICAL PROPERTIES OF CAST NICKEL-BASE SUPERALLOYS
    Cai Yulin; Zheng Yunrong (Institute of Aeronautical Materials; Beijing)
    Acta Metall Sin, 1982, 18 (1): 30-122. 
    Abstract   PDF (8043KB) ( 695 )
    Studies were made of the formation and chemical composition of precipitated plate like μ-phase as well as its effect on the TTT curve, fracture feature and mechanical properties of cast nickel base superalloy. It was found that the temperature of formation of plate like μ-phase is within wide range from 800 to 1140℃. Its baseplane is parallel to the hexagonal plane {0001}. It precipitates from plane {111} of γ-matrix. The cleavage fracture feature under impact, tensile and stress tests below 760℃ appears along baseplane {0001} of μ-phasc. For the superalloy containing 1—1.5 wt-% μ-phase, the impact value at 20℃, the stress rupture life and the tensile ductility at 20℃ and 760℃ decrease obviously, but the stress rupture ductility increases distinctly, especially under elevated temperatures. The (?)_v value seems to be not the only factor to control the μ-phase formed, and yet to relate to both (Mo+W) at.-% and Mo/(Mo+W). Besides, the boron content may also be effective to retard its formation.
    References | Related Articles | Metrics
    EFFECT OF THE MODE OF OVERLOAD ON THE BEHAVIOUR OF FATIGUE CRACK PROPAGATION
    Ouyang Jie; Yan Minggao (Institute of Aeronautical Materials; Beijing)
    Acta Metall Sin, 1982, 18 (1): 38-125. 
    Abstract   PDF (2999KB) ( 528 )
    The effects of different modes of overload, including tensile, compressive, tensile-compressive and compressive-tensile, on the behaviour of fatigue crack propagation in LY12 A1 alloy were investigated. From a study of the changes in micro-morphology, the plastic zone size and strain distribution around the crack tip and the fracture analysis before and after various overloading, it is suggested that various modes of overload produce different influences on FCP, and the retardation behaviour of FCP after tensile overloading may be described as a combination effect of several factors acting on the crack tip and its surrounding region. A general mechanism of the effect of tensile overload on FCP behaviour is proposed.
    References | Related Articles | Metrics
    MECHANISM OF HYDROGEN INDUCED DELAYED PLASTICITY
    Chu Wuyang; Xiao Jimei (Hsiao Chi-mei); Li Shiqiong; Ju Shuyan (Beijing University of Iron and Steel Technology; Beijing)
    Acta Metall Sin, 1982, 18 (1): 47-57. 
    Abstract   PDF (1337KB) ( 587 )
    For various carbon and low-alloy steels with a wide range of the tensile strength, the effect of hydrogen on the apparent yield stress, which is a necessary exterior stress to produce the local macroscopi c plasti c deformation, was investigated with smooth tensile, bending, pre-cracked type Ⅰ-, type Ⅲ- and combined type Ⅰ+Ⅲ specimens. The results show that the effect of hydrogen on the yield strength of a smooth tensile specimen is insignificant, the difference between the charged and uncharged specimens is less than 10%. However, for the smooth bending or pre-cracked Ⅰ-type specimen with a. tensile stress gradient, hydrogen can decrease the apparent yield stress considerably if the strength of steel and the amount of hydrogen entering into the specimen exceed their critical values. This is the cause of hydrogen induced delayed plastic deformation and hydrogen induced delayed cracking.The effect of hydrogen on the apparent yield stress increases with increasing strength of the steel and average hydrogen concentration in the specimen. The reduction of the apparent yield stress of charged pre-cracked specimens is more evident than that of smooth bending ones. The hydrogen induced apparent yield stress reduction is a phenomenon controlled by hydrogen diffusion, it depends markedly on the strain rate and test temperature.For type Ⅲ- cracked specimens, in which there is no hydrostatic stress the apparent torsional yield stress of the charged specimens does not decrease and K_(ⅢH)=K_(ⅢC). But hydrogen induced delayed plasticity and cracking can occur on the specific plane inclined at an angle of —45° to the original crack plane, For combined type Ⅰ+Ⅲ specimens, the apparent torsional yield stress can be decreased only when K_1 is so large that hydrogen induced delayed plasticity can occur under the action of K_1 itself.
    References | Related Articles | Metrics
    AN IN S ITU STUDY OF CRACK NUCLEATION AND PROPAGATION IN PEARLITE DURING DEFORMATION
    Xu Yongbo; Liu Minzhi (Institute of Metal Research; Academia Sinica; Shenyang)
    Acta Metall Sin, 1982, 18 (1): 58-128. 
    Abstract   PDF (4240KB) ( 973 )
    The microprocess of deformation and fracture of structural steels containing 0.15, 0.45 and 0.79% C respectively have been examined by tensile testing on SEM. For the specimens of steels 15 and 45, it was observed that the deformation is mainly undergone in proeutectoid ferrite, as well as shear, multipe-slip and colony rotation exhibited in pearlite. The crack is almost entirely nucleated at the interface of the inclusion/matrix or pearlite/ferrite. The fracture mode is ductile. In specimens of eutectoid steel T8, the cementite lamellae may be plastically deformed to some extent, and its tendency increases with the decrease of interlamellar spacing. When the microstructure contains fine pearlite, a uniform strain distribution, a wider strain range as well as slip and bending phenomena of cementite lamellae have been observed. Fracture is of ductile characteristic. On the contrary, coarse pearlite deformed more inhomogeneously with localized strain in intense shear bands. The crack nucleation is initiated by cracking of cementite lamellae along shear bands. The fracture is brittle. The cracking phenomenon along shear deformation bands in eementite lamellae has been discussed by the authors referring to the model of pile-up of dislocations.
    References | Related Articles | Metrics
    THE EFFECT OF Zr ON THE GRAIN GROWTH BEHAVIOUR AND PROPERTIES OF Fe-Ni-Co-Cu TYPE ALLOYS
    Ma Jusheng (Tsinghua University; Beijing)
    Acta Metall Sin, 1982, 18 (1): 64-131. 
    Abstract   PDF (4808KB) ( 568 )
    In order to control the quality induced by the grain growth during high temperature annealing of Fe-Ni-Co-Cu type alloys, Zr modification can effectively control the grain size to ASTM grade 5 to 6 during annealing at 1050℃.The form of existence of Zr in the alloys is investigated to search for the mechanism of grain growth retarded by Zr.The effect of the structure and size of particles formed by Zr on retarding the grain boundary mobility is analyzed and the factors influencing the effect of Zr retarding grain growth are discussed.It is shown that the addition of Zr in these alloys has improved the properties concerned with grain refinement, such as the characteristics of the grain boundary penetration by brazing alloys, workability, chemical stability, anti-SCC ability etc., and had little effect on its thermal expansion, mechanical properties and weldability by of TIG welding. These alloys modified by proper amount of Zr showed good performance during application to instruments and apparatus.
    References | Related Articles | Metrics
    A STUDY ON DUAL-PHASE STEEL 20
    Lei Tingquan; Shen Xianpu (Harbin Institute of Technology; Harbin)
    Acta Metall Sin, 1982, 18 (1): 75-133. 
    Abstract   PDF (3751KB) ( 690 )
    A study was made on the microstrueture, properties and deformation behaviour of intercritically quenched ferrite-martensite dual-phase steel 20 under coldrolling. The results indicate that both structure and properties of martensite and ferrite phases are quite different from those of single-phase ones. The conventional mixture law, which is commonly used to evaluate the strength of the fibre-reinforced composite materials seems to be not applicable. The model of deformation of the dual phase steel 20 in the process of cold rolling may be proposed by a gradual transition from stress-equal model at the starting to strain-ratio-equal model on the later stage. Its work-hardening may be attributed to a change from nonequal strengthening state to strength-ratio-equal state A summarized plot for its deformation behaviour during cold-rolling is also given to understand rather easily the relative variation of the structure and properties of each phase in the whole process.
    References | Related Articles | Metrics
    INFLUENCE OF Cr ON "SOFTENING EFFECT" OF 30CrNiSMoV STEEL
    Lu Zaojun; Wu Baorong; Wu Peizhi; Li Guiyen; Wang Qi; Lu Hongxiu; Li Xueyuan; Jin Qingqian; Wang Degen (Central Iron and Steel Research Institute; Ministry of Metallurgical Industry; Beijing)
    Acta Metall Sin, 1982, 18 (1): 85-134. 
    Abstract   PDF (1472KB) ( 501 )
    The influence of Cr contents on the softening effect of steel 30CrNi5MoV was investigated by using optical microscopy, TEM and phase analysis. The conditional proportion limit, σ_p_(50), of the steel falls sharply as the increasing of Cr contents in the range 0.22—1.61% under same other experimental conditions. It was deduced that its falling rate is expressed as: σ_p_(50)=1352—245×Cr%. The softening effect may be substantially resulted from that Cr changes the solubility of solute in α-ferrite, coarsens the martensitic substructure and reduces the ratio of the grain size of carbides to their interparticle spacings.
    References | Related Articles | Metrics
    MICROSTRUCTURAL STABILITY AND ITS INFLUENCE ON EMBRITTLEMENT OF FERRITIC-AUSTENITIC STAINLESS STEEL 00Cr18NiSMo3Si2
    Wu Jiu; Chen Rongxian; Li Xueyuan; Lu Jinsheng; Ji Shaohua; Huo Shuyun; Li Diankun (Central Iron and Steel Researeh Institute; Ministry of Metallurgical Industry; Beijing)
    Acta Metall Sin, 1982, 18 (1): 95-137. 
    Abstract   PDF (4037KB) ( 770 )
    The influence of the microstructural stability on the embrittlement in ferriticaustenitic stainless steel, 00Crl8Ni5Mo3Si2, was investigated. After solution treated at 980℃ and subsequently aged between 450—900℃, the steel has undergone two types of transformations, namely α→γ'+χ(σ) and α→α'+precipitates of intermetallic phases. During aging in temperature range of 450—750℃, the lamellar intermetallic phases Fe_3Cr_3Mo_2Si_2 precipitates preferentially along grain boundaries and a topological close packed phase Fe_(2.4)Cr_(1.3)MoSi (R phase) appears in the ferrite grains, while in 750—900℃ the χ phase is merely a metastable one which changes easily to σ phase. A study was also made of the kinetic curve of isothermal decompcsition of α-ferrite. The results indicated that the fracture feature of the steel between 550—650℃ is quite different from that between 800—900℃. In the range of 550—650℃, the intergranular brittle fracture is caused substantially by the precipitation of the lamellari ntermetallic phase Fe_3Cr_3Mo_2Si_2 arranged regularly along grain boundaries, but in 800—900℃, thequasicleavage fracture is connected with the lumpy precipitates of σ and χ phases.
    References | Related Articles | Metrics
    EFFECT OF VOLUME FRACTION AND SIZE OF FINE γ' ON CREEP STRENGTH OF A DS NICKEL-BASE SUPERALLOY
    Lin Donglian (T. L. Lin); Yao Deliang (Shanghai Jiaotong University); Ltn Xianjin (Shanghai Institute of Iron and Steel); Sun Chuanqi (Beijing Institute of Aeronautical Materials)
    Acta Metall Sin, 1982, 18 (1): 104-140. 
    Abstract   PDF (4272KB) ( 632 )
    The effect of volume fraction and size of fine γ' on creep strength of a directionally solidified nickel-base superalloy——DSK3 at 760℃ has been examined. DSK3 was solution heat treated at 1100—1270℃ to homogenize the alloy and dissolve coarse γ' and eutectic γ—γ' constituents which subsequently reprecipitated in the form of a uniform fine γ' dispersion with various volume fractions (0.25—0.63) and different sizes (0.1—0.3μm) upon cooling and aging. The size and amount of fine γ' increased with the increase of solid solution temperature. The creep rupture life increased and the secondary creep rate decreased as the solution temperature increased and the relationship t_f and e at 760℃ can be expressed as:(?)~αt_f=c where a=1 and c≈5.5. The improvement of creep rupture life was found to be due to a decrease of secondary creep rate and an extension of secondary stage of creep. The secondary creep rate (?) is strongly dependent on size a, interparticle spacing λ and volume fraction v_f of fine γ', and it takes the form:(?)∝α/v_f~(2/3)(1-v_f~(1/3)) or (?)∝λ~2/αThe dislocations structure and morphology of γ' of the alloy produced by creep to primary, secondary and tertiary stage at 760℃ under 73.8 kgf/mm~2 and 78 kgf/mm~2, and at 950℃ under 25 kgf/mm~2 was examined in TEM. During the primary stage of creep at 760℃ under 73.8 kgf/mm~2 or 78 kgf/mm~2 dislocations are moving between the γ' cuboids shearing the γ matrix. Two sets of dislocations intersecting or reacting each other in the γ matrix are visible, but no dislocation is ever observed inside the γ' cuboids. A dense 3-dimensional dislocation network has formed in the γ matrix of the alloy during secondary creep. A few superlattice dislocation pairs were found in the γ' at 760℃ under 78 kgf/mm~2, but still no dislocation in the γ' under 73.8 kgf/mm~2 is observed in secondary stage of creep.The morphology and size of γ' are changing during creep at 950℃ under 25 kgf/mm~2, especially at the end of secondary stage of creep and during tertiary stage of creep. In the early primary stage of creep dislocation structure is similar to that at 760℃ but two sets of α/2<110> dislocations can react more easily and form a 2-dimensional dislocation networks covering the γ—γ' interface in the later primary stage of creep. γ' particles start to coarsen and become a plate shape by lateral merging of cubes without noticeable thickening of the plates from secondary stage of creep.Direct observation of dislocation structure and γ' morphology in relation with secondary creep rate suggests a high temperature creep model for the nickel-base superalloy in the range of temperature and applied stress where shearing of the γ' phase does not control the straining process. During secondary creep, strain is mainly the result of climb rate of dense 2- or 3-dimensional dislocation networks and the free path of dislocation glide in γ. Secondary creep rate (?) can be described as:(?)=NAbR where N is the density of dislocation sources; A the sweeping area of a dislocation, b the magnitude of the Burgers vector of the dislocation and R the climb rate of the dislocation over γ' particle or the number of critical link length of dislocation network can be developed to operate in a unit time, i. e., the number of operating sources of the dislocation in a unit time.The volmne fraction v_f and size of γ' will play an important role in secondary creep rate (?) by changing the configuration and density of the dislocation and influencing the process of the dislocation climb (recovery) in γ matrix. Applying the following equation relating the applied stress and dislocation density ρ to creep process:σ= σ_0+αGbρ~(1/2) where G is the shear modulus, α the strengthening proportional constant by the interaction of dislocations and σ_0 flow stress due to all causes other than dislocation-dislocation interaction, and combining climb model given by Anscll and Weertman the equation for secondary creep rate (?) can be derived as:(?)=K/G~3T λ~2/α(σ-σ_0)~n exp(-Q_s/RT) or (?)=K/G~3T α/v_f~(2/3)(1-v_f~(1/3))~2(σ-σ_0)~n exp (-Q_3/RT) where K is a constant, Q_s the activation energy for self-diffusion, and n=4—5. The expression relating λ, α, v_f and (?) predicted by the theory agrees satisfactorily with experimental results.
    References | Related Articles | Metrics