A study was made of the development of a cheaper and more satisfactory non-magnetic steel 30Mn20Al3 after consideration of the stable austenitie structure for Fe-Mn-A1 series. The effects of A1 and C contents on the stability of Fe-20Mn austenite and the mechanical properties of the alloy have been investigated. Results show that an addition of A1 to Fe-Mn alloy may restrain the transformation of γ→ε and γ→ε→α', and reduce the martensitic transition temperature. The action of C on austenite stabilization may be more obvious, As compared with the wellknown austenitie stainless steel 1Cr18Ni9Ti, the steel 30Mn20A13 exhibited superior strength, plasticity, austenite stability, magnetic permeability and resistivity, as well as more satisfactory low temperature properties. Based upon the abovementioned, it is recommended that the steel 30Mn20A13 seems to be available for nonmagnetic and cryogenic uses even down to -196℃. In additional, its production costs may be reduced to such extent about 1/3 of that for 1Cr18Ni9Ti.

An attempt was made to develop an austcnitic cryogenic and non-magnetic steel 30Mn23Al4Cr5 with desirable combination of superior properties. Results of experiments indicated that the steel 30Mn23A14Cr5 is possessed of satisfactory strength and excellent toughness from room temperature to -269℃, i. c. V-notched impact toughness equal to 2048 kJ/m~2 at -269℃. Its low temperature austenite is quite stable, no α'-or ε-martensite was observed under tensile test at -269℃. after 10 or 50％ deformed respectively.Furthermore, other properties were also determined as: low magnetic permeability about 1.005, high resistivity up to 1.08, lower cold constraction and higher resistance to atmospheric corrosion than ferrite 9％Ni steel, and less aging embrittlement than conventional Cr-Ni austcnitic steels. Thus, the proposal can be made that the steel 30Mn23Al4Cr5 is indeed applicable to such uses as a cryogenic steel from -150 to -269℃ and a non-magnetic steel from 600 to -269℃.

The martensite morphology and the shape memory effect of the Cu-10.10％ A1-4.51％Zn-3.76％Mn-0.39％Ni aUoy have been studied. It was shown that the martensite formed on cooling is of the spear type of self-accommodating configuration, but the stress-induced martensite is of the sheet type. These two morphologies are thermoelastic martensites having good shape memory effect. Experimental results indicate that the air-cooled and hot-rolled specimens have the best shape memory property with the maximum recovery ratio greater than 95％. Martensite obtained by rapid quenching has a slightly lower shape memory effect and a higher recovery temperature. Burst-type martensite occasionally appears when the specimen is cooled directly into liquid nitrogen. Preliminary energy dispersive spectrum analysis has shown that the Mn content of the burst type martensite is slightly lower than that of other morphologies.

The cyclic creep and stress rupture behaviour of two representative particle strengthcncd alloys, an oxide dispersion strengthened nickel-base alloy and a nickel-base supcralloy strengthened by γ' precipitates, has been studied. It was found that the minimum creep rate decreases with increasing frcquency and the rupture life generally increases with increasing frequency in the load cycled and the frequency range of 0.05-6 cycles/h at 760℃. For the supcraIloy strengthened by γ' precipitates, however, the rupture lives decreased at the highest frequencies used, apparently due to frequency induced increase in degree of planar slip.An analysis was made of the plastic and anelastic strains that occur during the on-load and off-load periods, and of dislocation structures during cyclic creep. The observed behaviour and thc apparent material strengthening during cyclic loading was found not to bc attributable to a cyclic strain hardening effect but rather to the effects of anclastic strain that is accumulated during the on-load period and recovered during the off-load period. Using a phenomenological model based on the anelastic mechanism, a cyclic creep deceleration or creep/fatigue deceleration factor was derived. It shows reasonable agreement with the expcrimentally observed behaviour.

The true stress-strain curves of certain typical metals have been measured precisely with a diametrical extensometer improved by authors. According to the theoretical relationship which the ultimate uniform strain ε_B corresponds to the intersection of the flow stress curve and the rate of strain hardening curve, the effect of matrix and second phase on these two curves, i. e., on the ε_B has been investigated. Preliminary results have demonstrated that the dσ/dε νs e curve mainly depends on the matrix while the σ νs e curve is sensitive to the second phase.The strain hardening curve of a material obeying power hardening relation can be divided into three stages in a lg-lg plot except yielding stage. Thus, there are 3 strain hardening exponents n_1, n_2, n_3 and two knee strains ε_1, ε_2. It shows that n_1 is sensitive to the matrix state while n_2 is sensitive to the second phase. The existance of n_3 is a problem to be worth notice. Since there are several stages on the strain hardening curve the relation n=ε_B can not be established. It has shown that only those metals with high stacking fault energy can nearly suit with the relation n_2=ε_B under the condition ε_1<ε_B.

The effect of Co on the steady-state creep rate, apparent creep activation energy, stress-rupture time and microstructure of Udimet 500 type alloy with Co content up to 25 wt-％ has been investigated. The results show that the steadystate creep rate of alloy containing 10-15％ Co is the lowest under temperatures from 780 to 860℃ and the stress-rupture time for alloy containing 15％ Co is maximum. The creep activation energy for alloy without Co is of unique value, for ones containing Co is of duplicate values, and its transition temperature increases with the increase of Co content in the alloys. Co is substantially dissolved in the matrix. The quantity of γ'-phase in the alloys is nearly unchanged with variation of Co contents which can retard the growth of γ'-phase. Thus, it is proposed that Co content in Udimet 500 alloy may be reduced to 10-15％ without any detrimental effect on its strength and hot corrosion properties at elevated temperatures.

A study was made of the off-axis tensile properties of γ/γ'-a-Mo DS eutectic and of observation of the dynamic fracture process by SEM. If the loading direction deviates from the Mo fibre growth direction, the tensile strength and ductility decrease gradually. During the loading process, two types of cracking are observed: one is cracking of the fibre, and the other is delamination along the fibre-matrix interface. In plastic deformation, slip can pass through both the matrix and the fibre. As a rule, the thicker fibers are cracked earlier than the thinner ones, because they have less defects and better ductility. Delamination is the main source of final fracture.

Effects of a single overload on fatigue crack growth rate have been investigated at elevated temperatures in an Fe-Ni-base superalloy which has different levels of strength and ductility through different heat treatments. All the overload tests were conducted under the condition of constant load with CCT specimen. Crack length was monitored by using d. c. potential-drop technique. It is clear that the effect of overload represented by retardation cycles, N_D, is decreased at elevated temperatures but still of significance up to 700℃. The peak level of overload stress intensity factor, K_(o.p)., the overload ratio, r, the material yield stress, σ_y, and the crack length, a, at which an overload is applied have great influence on the post overload retardation, behaviour of fatigue crack growth. The retardation cycles, measured at 650℃, can be expressed by the following equation:N_D=N_0exp[m(r/aσ_y)~K_(o.p.)]Conditions of heat treatments have great influence on the effects of overloads. Alloy A with higher ductility and lower yield strength shows greater retardation effect than alloy W under the same overload conditions. The fracture surfaces of specimens subjected to overloading at elevated temperatures have been observed by using optical steromicroscope and SEM along with the measurements of the change of potential drops during the overload tests. Some explanations have been given.

Results of experiments indicated that the analysis of the cleavage fracture of silicon steel seems to be hard to solve by RKR model. The Weibull statistical theory was introduced to describe the volume effect of the cleavage fracture stress determined by smooth tensile and notched bend specimens. The temperature dependence of the cleavage fracture toughness and its scatter band of silicon steel is formulated by applying the HRR theory and the Rice-Johnson's stress analysis for the blunted crack tip zone, as well as by combining with the Weibull's statistical model. The experimental data are in agreement with the prediction.

The cleavage fracture stress of the dual phase steels has been evaluated with slow-bend test of blunt V-notched specimens. Their crack propagation path and fracture mode were indicated by the observations of the fracture morphology, the mieroeraek initiation and propagation of fracture surfaces under the cleavage temperature and the mierostrueture. According to the measurements of the cleavage fracture stress and the crack unit, the effective surface energy of the dual phase steels was also calculated by Griffith's equation. It was proposed that the cleavage fracture of the dual phase steels seems to be controlled by stress propagation and its regressive equation may be σ_f =0.33+19.33c~(-1/2) kgf/mm~2. Thus, the cleavage fracture stress may be increased by reducing the grain size of ferrite and martensite islands and by increasing the amount of evenly distributed lath martensite in the islands.

The low-temperature impact fracture of controlled-rolled and normalized steel 09MnNb has been investigated. Data on the load-flexibilty plot after impact test at various temperatures show that the steel either controlled-rolled or normalized offers higher resistance to tearing. The fracture occurred below the ductilebrittle transition temperature is by cleavage with dimpled rupture. The controlledrolled steel has a mixed α-grain structure which consists of equiaxial α-grains and "cold-worked" elongated grains with higher dislocation density, while the normalized steel has finer equiaxial α-grains with cell substructure of dislocation, of which the effective size of a-grain may be reduced. This microstructure of normalized steel makes the improved low-temperature impact property possible.

Metastable extension of solid solubility of transition metals, e.g. Fe, Co, Ni, Mn and Zr, in Ag under melt quenching was measured with lattice parameter method. Metastable solid solubility limit, C_(eq)~s, of these elements in Ag, under cooling rate about 10~5-10~6K/s, is 1.0, 1.5, 1.5, 3.0, 48 and 6.0 at.-％ respectively. Different mechanisms of the metastable extension was proposed. The metastable extension of 3 different kind of Ag alloy systems was discussed: eutectic system Ag-Zr; peritectic system of Ag with some simple metals and monotectic system of Ag with Fe, Co, Ni, Cr and Mn. Metastable extension of solid solubility of Zr in Ag is controlled by crystallizing rate of stable intermediate phase AgZr in liquid state. For A-A_mB_n, (or a(A)-A_mB_n) eutectic systems, the extension parameter C_(eq)s/C_(eu) is inversely proportional to the crystallizing rate of stable intermediate phase A_mB_n at eutectic composition C_(eu), and proportional to a parameter J=(C_m-C_(eu))/(C_(eu)-C_(eq)), where C_(eq) is equilibrium solid solubility, C_m is solute concentration of intermediate phase A_mB_n. For monotectic systems of Ag with transition metals Fe, Co, Ni, Cr and Mn, an immiscible gap exists in the liquid or undercooled melt, C_(eq)~s equals to the solute concentration corresponding to intersecting point of the boundary line of immiscible gap with solidus. C_(eq)~s as well as C_(eq)~1 are inversely proportional to parameter (n_(ws)~(1/3))_M/(n_(ws)~(1/3))_(Ag). For peritectic systems of Ag with simple metals, the electron compound with electron concentration e/a= 1.5 restrict further extension of solid solubility, this is the reason why the solid solubility of these systems extending up to the solute concentration with e/a=1.4.

The feature of deformation and fracture of a liquid phase sintered alloy 90W-7Ni-3Fe has been studied. It was found that the matrix of the alloy is the first to yield and to undergo plastic deformation. The cracks may be initiated along the W grain/matrix interfaces as the bonding force here is weak. While the bonding force is strengthened to a greater extent than the cleavage failure stress of W, the transgranular cleavage cracking of W grains and the plastic teaing of the matrix may happen simultaneously. Hydrogen is shown as one of the main sources of the inteffacial embrittlement of as-sintered specimen. The removal of the hydrogen both stored in the voids and dissolved in metals of the W grain/matrix interfaces is easily done by heat treatment under vacuum. Thereafter, the bonding force at interface as well as the tensile strength and plasticity of specimen can be modified.

The hydrogen storage behaviour of the Mg-rich rare earth alloys, La_2Mg_(17) and La_2Mg_(16)Ni, has been investigated. Two plateaus related to the reactions Mg2Ni+2H_2(?)Mg_2NiH_4 and Mg+H_2(?)MgH_2 respectively exhibit in the pressurecomposition isotherm of La_2Mg_(16)Ni alloy. Partial substitution of Mg by Ni in La_2Mg_(17) gives a two-phase mixture: the major is La_2Mg_(17) type phase and the minor, Mg_2Ni type one. Hydriding of the La_2Mg_(16)Ni alloy leads to the formation of MgH_2, La hydride and Mg_2NiH_4. An experiment was also carried out on the hydrogen absorption by the alloys under either normal temperature and lower pressure or normal pressure and elevated temperature. It was found that La_2Mg_(17) and La_2Mg_(16)Ni seem to be the considerable hydrogen storage materials.

The effect of trace S on the hot plasticity of high speed steels has been examined. It was shown that the S content in W14Cr4VMn steel decreased from 0.01％ down to a possible lowest limit of 0.002％ the number of cycles of the hot torsion test increases about 20％ under 950-1150℃. This indicates that the hot plasticity of the high speed steels may be deteriorated even if a trace S contained. AES was observed that the S segregation occurs along the austenite grain boundaries. The reason of the S segregation and its deterioration on the hot plasticity of the steels has also been discussed.

The segregation of the impurities, e. g. S, P, along grain boundaries of as-cast structure and of austenite in the high speed steels as well as the cleaning action of RE elements have been studied by AES. It was found that the more S and P the steels contain, the more their segregation occurs. The segregation becomes remarkably improved by the addition of RE elements, and the enrichment of S at grain boundary goes so far as to vanish when the RE added up to 0.05-0.08％. Some discussion on the segregation and the cleaning action have been also made.

Studies of the region≤50 at.-％ Er in the phase diagram of binary Er-Ge system were determined by X-ray diffraction analysis and DTA. Three compounds: ErGe_2, Er_2Ge_3 and ErGe were observed in this region. A eutectic reaction composed of 23 at.-％ Er occurs at 866℃. ErGe_2 and Er_2Ge_3 are formed by two peritectic reactions at 900 and 1043℃ respectively. DTA indicated that ErGe_2 undergoes a polymorphic transformation at 886℃. There is no detectable solubility of Er in Ge.

An improved method for the quantitative X-ray phase analysis is developed. The reference intensity ratio is first calculated theoretically, then modified by the analogue specimens with the true physical state and the testing conditions including microabsorption, preferred orientation, monochromator and automatic divergence slit. Thus, its accuracy can be much improved. Result of experiment showed that this modification is available for those samples which are hard to analyse by conventional method if their crystalline structure parameters associated with the phase are given. It may be also used to verify the accuracy of the reference intensity ratio measurement and to judge by what reason the error caused.

The distribution of boron and alloy elements in the boronized layer on Armco iron, steel 45, tool steel Cr12Mo, Cr26Mo or stainless steel Cr18Ni9Ti has been determined by a newly developed analytical method GDOS. Based on the contents of boron and alloy elements determined, the in-depth phase composition of borides in layer can be calculated. The results was verified by X-ray diffraction analysis with good agreement.