The time required for carbon diffusion from martensite to enrich surrounding austenite from 0.27 to 1.04% C during the formation of low-carbon matensite is 10~(-7)s in order of magnitude as calculated. It does prove that the diffusion of carbon atoms can keep pace with the formation of lath martensite. From thermodynamical calculation, it is reasonable to recognize that the precipitation of carbon from martensite results the enrichment of austenite. TEM observation revealed that the quenched structure in a 0.12C-low Ni-Cr steel mainly contains lath martensite and interlath retained austenite, and also twin martensite. The existence of the latter further confirms the occurrence of carbon diffusion to enrich austenite during the martensite formation, and twin martensite forms at the parent phase where carbon enrichment is not very high. The interface of austenite and martensite is somewhat straight. The typical upper bainite (B_Ⅱ), B_Ⅲ type bainite and carbide-free bainite (B_1) can aU appear in the ame steel and there exists superledges at the interface of austenite and bainitie ferrite which is quite different to that of austenite and martensite. In addition, from the kinetics point of view. the growth rate of low-carbon martensite is 3 to 4 order of magnitude greater than that of upper bainite. It is more likely to conclude that the mechanism of the formation of lath martensite is not identical with that of bainite.

A study was made of the correlation between the mechanical properties and the microstructure variation of an Fe-Ni-Cr base superalloy on prolonged heat exposure. It was found that the notch sensitivity of the alloy is closely related to TiC film precipitated along grain boundaries. With raising temperature and prolonging time of aging treatment, the TiC films coarsen gradually into block so that the notch sensitivity vanished from the alloy. Because of the minute block-shaped σ-phase is distributed along the grain boundaries, the high temperature tensile elongation and the rupture toughness of the alloy as well as its notch sensitivity ilimination could be improved. However, its room temperature tensile elongation and impact ductility are reduced, yet no great harm was influenced upon them as compared with the same contents of TiC and boride.

The phase and structure transformation of bainite during tempering after isothermal quenching were studied on steel 3Cr3Mo3VNb. It was shown that the secondary hardening of bainite is similar to martensite, mainly formed by precipitation of fine dispersed carbides such as Mo_2C, V_4C_3, NbC, etc. The slow dissolution of coarse cemetite in bainite retards the precipitation rate of carbides during tempering. The decomposition and transformation of the retained austenite in bainite differ from that in martensite. The lower dislocation density in bainite is unfavourable for the aggregation and coarsening of carbides. As a result of the coaction of abovementioned factors, the bainite has superior secondary hardening effect, thermal strength and structural stability to martensite formed by straight tempering.

SEM and EMPA observations were carried out on specimens of high purity Al-12.5%Si eutectic alloy in which certain amount of Na was added. The results indicated that the Al-Si eutectie itself forms cellular and dendritic eutectic colony with the increase of Na added in the Al-Si euteetic alloy.

The process of flake formation in steel was investigated by means of SEM, TEM EPMA and AES as well as acoustic emission technique. The results show whatever size of a flake may be, an "unwelded" smooth micropore was observed on its surface. The comparative experiment was made on the fracture surface of the dehydrogenated specimen, the "unwelded" micropores of identical type were also observed. It may be ascertained that the micropores are interdendritic voids and/ or hydrogen bubbles remaining in the solidified steel ingot, and not internal crack after hot-rolling. These voids and bubbles are unable to weld closely by hotrolling and form the nuclei of flakes in steel. These flakes grow gradually up during air cooling. Their growth will be continued and sometimes stopped till 20—30 days. The acoustic emission detected only signals for flakes growing, no one for sudden cracking, i. e. no incubation time for nucleation occurred. Three principal features of the micromorphology of flake fracture are trasgranular quasicleavage, intergranular wave-like stripes and elongated smooth "unwelded" micropores. The abovementioned mechanism of the flake formation may also illustrate the process of "bright-flakes" formation in Al alloy forgings.

An Auger electron spectroscopical study was made of the correlation between the temper brittleness and the grain boundary segregation of P together with alloying elements as Ni, Cr and Mn in steels 35CrMnSi and 35CrNi3 containing 450 ppm P. It was shown that the steels tested attributed substantially their temper brittleness to the P segregation along the prior austenite grain boundaries. Although in so called "ductile state", namely oil quenched at 1200℃, tempered at 625℃ for 1h and water quenched, a lot of P segregated already along the grain boundary, thus, the steels embrittled markedly. After embrittlement treatment by step cooling, intergranular P concentration increased sharply. During this treatment, the increasing rate of P segregation along grain boundary in Ni-Cr steel is greater than that in Cr-Mn-Si steel. The FATT of the steels tested is directly proportional to the intergranular P content. The intergranular segregation of Ni in Ni-Cr steel is related linearly to that of P. To the steels, the addition of La may improve their temper embrittlement owing to decrease of intergranular P concentration under similar state.

The variation of several typical domain patterns in 3%Si-Fe sheets with tension was studied by colloid technique. The characteristics and trends of their changing were described. The mechanism of domain refining was revealed. The antimagnetizing nuclei will be grown and become new 180° domain under tension. A formula describing the change of domain with tension was derived. The maximum of core loss reducing corresponding to the tilt angle φ=2° has been described in the light of domain structure change.

The stress corrosion cracking (SCC) susceptibility of steel 34CrNi3Mo with different yield strength grades in 30% NaOH aqueous solution at 80℃ has been examined by the measurement of their K_(ISCC) either at open circuit potential (-1050mV) or cathodically polarized at-1400mV (SCE). It is shown that the SCC under the open circuit potential condition is of a strain generated active path corrosion (SGAPC) type, and under the cathodically polarized condition is of a hydrogen embrittlement (HE) type. With the increasing of the yield strength of the steel, the K_(ISCC) is increased under the open circuit condition, and sharply decreased under the cathodically polarized condition. For HE type, the reducing the strength of steel may effectively decrease the SCC susceptibility; while, for SGAPC type, it may increase the SCC susceptibility. Thus, the usual understanding of the effect of the strength on SCC susceptibility arrived from the tests of high strength steels in aqueous solution seems not to be suitable to those SCC of SGAPC type.

Observations were demonstrated of 3 different types of the fatigue crack propagation of pearlitic structure: type A——the crack intersects the multiple ferrites and cementites simultaneously; type B——the crack cuts the ferrite and cementite one after another and type C——the crack propagates only through ferrite plate or along interface of ferrite and cementite. The fractographic examination indicated that the 3 fracture types in the process of fatigue crack propagation appear as different feature and proportion. In the slow stage of the fatigue crack propagation, it is the type A with partly type C or B; in the stable stage, mainly type A and B as well as marked fatigue striation; while in fast speed stage, the cleavage or dimple with partly striation predominantly.

Fracture toughness was determined for various thickness, B=20—120mm, of compact tension specimens of a cast Mg alloy ZM5 according to ASTM E399—78. A proposal could be thus made to the relaxation of P_(max)/P_Q from≤1.1 to ≤1.6 for this alloy.

For the first time the optical constants of different sulphides were measuredusing interference layer microscopy to enable them to be utilized for quantitativemetallography. In addition to the measurement of the refractive index and absorp-tion coefficient it was also possible to give the conditions that enable the maximumpossible light-dark contrast as well as a good colour contrast to be achieved in thepolished specimen. The layer materials that almost completely extinguish thereflectivity of the different phases are reported together with the exact colouraccording to DIN 6164. A method of presentation was found for all phases, notonly the sulphides, that enabled the refractive index at which the amplitudecondition was fulfilled to be exactly determined. There is a mathematical relation-ship that can be simply derived for all phases between the reflectivity at theinterference minimum of a phase and the refractive index of the layer providingnon-absorbent layer materials are used.The sulphides represent a very complicated phase group for the metallographer as the amplitude condition can be over- or under- fulfilled by coating with the layer materials under discussion e.g. ZnS or ZnSe. One of the aims of this work was to provide the necessary data.

Ground control problems in subievel caving become evident as the rock pressure increases with depth. Recently, a finite element analysis of the stability problems of the sublevel caving method was completed by the authors. This paper summarizes the results of stress analysis in sublevel extraction drifts under different stress field conditions by using linear elastic and nonlinear elasto-plastic finite element modeling techniques. A critical stress concentration will occur in the uppermost sublevel drifts beneath the caved area or blasted ore area. During the blasting and drawing cycle, a tensile and shear failure condition could develop in the central extraction drift when it would be mined last. Under a high horizontal stress field condition, almost all tensile stress in the back of the extraction drifts will be eliminated and only slight yield can be seen in the floor of the extraction drifts. Compared to the cases under the gravitational stress field condition, the total yielding zone will be grtly reduced because of the increase of horizontal confining stress with depth. However, it is predicted that the centre of each ore column side will experience excessive shear stress that probably will result in ore failure.The two major conclusions drawn from this study to improve the overall stability of sublevel caving are: (1) the width of extraction drifts must be carefully controlled and an appropriate stoping sequence selected; and (2) the sublevel caving method can be used in deep mining if the pillar width is increased correspondingly with mining depth.

On the basis of the related isothermal sections of ternary systems and the liquid or solid zones of quaternary systems at 1600℃, the attack resistance of MgO-CaO refractories has been examined with certain oxides, conventional steelmaking slags and P_2O_5-containing slags. It seems that the converter lining made of MgO-CaO refractories with a certain amount of CaO contained got the better than the MgO refractory alone to resist the attack of either conventional or P_2O_5-containing steelmaking slags.

Thermal analytical study of the liquidus of Al-Al_2Cu-Ag_2Al corner in the phase diagram of Al-Cu-Ag system was made if possible to ascertain a suitable fillet metal in Al brazing at medium temperature range. The system belongs to a eutectic type. The composition of the eutectic point is: Al 40.0%, Cu 19.3%, Ag 40.7% and its temperature 500℃. A phase diagram has been figured.

The distribution of vorticity, velocity and temperature of the melt puddle were obtained by the viscous hydrodynamic equations. It is found that the thickness of thermal gradient layer, ΔR_T, and viscous shear layer, ΔR_v, of the alloy Fe_(40)Ni_(40)P_(14)B_6 are 140 and 11μm respectively. The quench rate on the ribbon at the ribbon-melt interface is (4.6—2.3)×10~6℃/s, and the solidification time is (0.8—1.6)×10~(-4)s. The empirical equations of thickness, h, and width, b, of the amorphous wide ribbons are in accord with the experimental data in the range of 3—5%. The observed relations among h, b and wheel velocity, ν_r, are well described by the model of nearly ideal cooling. The Prandtl number, Pr=7.8×10~(-2) indicating the thermal gradient layer was 13 times thicker than the viscous shear layer, and the Nusselt number, Nu=1—2 indicated intermediate cooling condition at the ribbon-wheel interface.

The remelting of consumable electrode and the Mg distribution in various zones at electrode tip during VAR process of a Ni-base superalloy Ni-10Cr-15Co-6W-6Mo-4Al-2Ti were studied. It was found that a remelted metal ring sticks to the electrode surface near tip. The Mg distributes in the metal ring rather homogeneously, but in remelted metal layer or in the liquid-solid binary phase zone heterogenously. The thickness of the remelted metal layer is varied with its position from electrode tip and averaged 1—1.5mm. The Mg content increased gradually with the increase of distance from the metal film/atmosphere interface via liquid/ solid binary phase zone to the unmelted electrode. The Mg concentra-tion either in the remelted metal ring, [Mg]_r, or in the outer layer of remelted liquid metal was less than that in the remelted ingot, [Mg]_i. Under present experimental conditions, [Mg]_(0.15)=0.18[Mg]_e=[Mg]_r; [Mg]_(0.40)=0.30[Mg]_e =[Mg]_i, where [Mg]_(0.15) and [Mg]_(0.40)=Mg concentration in the outer layer of remelted liquid metal at 0.15 and 0.40mm respectively; [Mg]_e and [Mg]_i=Mg concentration in electrode and in ingot respectively. It seems that the Mg is mainly evaporized in the droplet forming period during VAR process. The liquid metal flows round the surface of electrode tip and is unable to expose fully under vacuum. The process of Mg evaporation may be controlled by the transfer rate of Mg atoms from unmelted electrode into the liquid metal film/atmosphere interface. The coefficient of mass transfer K_(12)=0.107 cm·s~(-1). The Mg content in remelted ingot, [Mg]_i=[Mg]_e exp(-K_(12)Aγw~(-1). Thus, the optimum [Mg]_i can be realized by controlling [Mg]_e and the remelting rate w.

A calculational formulation for v.-%, f, of γ′-phase in the precipitation hardening Ni-base superalloys was proposed as:where C denotes each wt-% of its own alloying element. It is available from the data obtained by chemical analysis. The abovementioned formulation was verified by about 20 commercial superalloys.

The plastic zone of crack tip of wedge opening loading specimens were studied by positron annihilation technique. The line-shape parameters of Doppler broadening of annihilating radiation were measured. The value of S parameters was calibrated by specimens with known amount of strain. Then the distribution of the plastic strain in the plastic zone as a measure of the density of defects was determined. Experimental results indicate:1. The dimension of plastic zone is exactly the same as that determined by fracture mechanics.2. The distribution of strain in the plastic zone is not homogeneous.3. There is a high strain area at the very tip of the crack.4. The strain in the plastic zone is increased after electrochemical hydrogenation. Iso-strain curves are expanded preferentially in the direction of greatest shear stress. It is concluded that hydrogen facilitates the propagation of dislocations or the sliding of movable dislocations and vacancies can generate at the same time.