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There is a tendency to generalize that the fatigue strength at 10＾7-10＾8 cycles in high cycle fatigue increases linearly with tensile strength, but it is not known in low cycle fatigue. This study was down to investigate the relationship between the static strength and the fatigue strength in low cycle range depending on the behavior of fatigue crack growth. In this experiment, it was shown that the fatigue strength in low cycle range also varies directly with static strength on SM45C steel.

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The effect of pre-annealing heat treatment on annealing texture if studied in solution heat-treated extra low carbon steels with Ti or Nb additions. The development of {111} texture is more evident in Ti-Nb added steel than in Ti-added steel or Nb-added steels.

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The fatigue crack growth behaviors of the base metal, the heat affected zone and the weld metal in AISI 304 stainless steel weldment were studied. The effects of the rolling direction, the content of δ-ferrite, sensitization and solution heat treatment were also investigated. The fatigue crack growth rates in the weld increased in the order of the weld metal, the base metal and the heat affected zone. But was found independent of the rolling direction. Sensitized specimens showed low fatigue crack growth rate in low ΔK region, however, intergranular facets were observed on the fatigue fracture surface. The fatigue crack growth rates of the base metal, the heat affected zone and the we1d metal were decreased with the solution heat treatment. The content of δ-ferrite up to 10.1% did not influence the fatigue crack growth rate with an exception of the specimens with 7.8% which showed a decreased crack growth rate.

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In order to investigate behaviour if simultaneous dephosphorization and desulfurization three kinds of 5㎏ lots of molten pig iron samples were prepared under Ar atmosphere as follows : a) primarily, pig iron of α_0=f_0[%O] =1.5×10^(-4), and [Si]=0.84%, b) second samples of [Si]=0.05% and α_0= 2.1 ×10^(-4) by addition of ferric oxide to the first sample as much as 12g/㎏-H.M. and holding for 30 min, c) sample of [Si] =0.03% and α_0=2.4×10^(-4) by charging a double quantity of ferric oxide to the first sample. As much as 10 and 20g of soda ash was charged from the top of the respective melt and the change in the composition of the each melt was traced as a function of time. The experimental results are summarized as follows. 1. The rate of dephosphorization at slag/metal interface is proportional to the difference between [P] and [Si] : (수식) 2. The oxygen activity of the melt decreased rapidly and exhibited minimum values, the level of which lowered as the silicon content of the melt was greater. 3. In case if [Si]=0.084%, the desulfurization presumably proceeded according to the reaction, (Na₂O)+[C]+[S]=(Na₂S)+CO ; and [S] reached to a level of 0.001% after holding 30min. on addition of soda ash.

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Behavior of the reduction of iron oxide in ilmenite and titanium slags by various solid carbons was investigated in the temperature range of 1000℃ l150℃. A laboratory scale rotary kiln for the prereduction was employed to study the effects of reduction time and temperature, using various carbons as reducing agents of the prereduction process. Maximum metallization (95%) of FeO in ilmenite was achieved at about 1100℃. The reduction process of ilmenite including newly confirmed phase (pseudorutile) could be expressed in four elementary reduction stages, and also the phase transformation of ilmenite and titanium slags during the reduction process was investigated with the aid of X-ray diffraction analysis and electronmicroscopy.

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The effects of sintering temperature, sintering atmosphere and sintering time on dimensional changes, microstructures and mechanical properties of Al-4.3wt.% Cu powder compacts have been investigated. The compact sintered at 560℃ shows a considerable expansion, while the swelling is followed by a rapid contraction at higher temperature. Dimensional changes are also affected by sintering atmosphere, with sintering in H₂atomsphere resulting in greater expansion. The compacts sintered at above 600℃ have been homogenized within 10 minutes and the prolonged sintering time have promoted the grain growth of sintered compact. The optimum mechanical properties are obtained by sintering at 600℃ for 30 minutes in N₂atmosphere. The model experiment used spherical coarse Cu powder haute been performed to observe the formation and behaviour of the liquid phase during sintering of Al-Cu powder compacts.

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The effects of hold time in tensile strain on the behavior of high temperature low cycle fatigue in AISI 304L stainless steal at 865k were investigated in Ar atmosphere under the axial strain control at a strain rate of 4×10^(-3)/s. Under triangular continuous cycling, fracture was occurred by the transgranular propagation of fatigue crack initiated at the specimen surface. In the fatigue test with 30 min. hold time at the peak tensile strain, the fatigue crack is observed to be propagated by transgranular mode only and no grain boundary creep cavities are observed. But when the critical fatigue life under hold time is compared with that of continuous test, it decreased significantly with decreasing plastic strain amplitude. From the experimental results, decrease in the fatigue life with tensile hold time compared to continuous cycling could be explained as follows ; reduction of the number of cycles to the crack initiation is considered to he the easier formation of the persistent slip band during tensile hold time. And decrease in the number of cycles to the crack propagation is considered to be the increased crack growth rate caused by increase of the crack tip opening displacement under tensile hold time.

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Deoxidation of Cu by injection of butane as reducing gas instead of conventional green wood was studied through small scaled hot model experiment together with KOH-CO₂water mode1 experiment. Deoxidationin by butane was compared with green wood deoxidation and the rate of deoxidation of Cu was interpreted on the basis of gas absorption theory. According to hot model experiments, the effect of butane on deoxidation was excellent and the deoxidation of Cu was a very rapid reaction. It was found that the rate of overall reaction increased with increasing gas flow rate. The effects of various injection methods of gas on liquid-phase mass transfer were investigated through water model experiments based on the gas absorption theory to obtain basic information on reactor design in Cu refining. According to the results obtained in this study, cylindrical vessel and bottom blowing were effective in batch operation. Injection by single nozzle was more effective than that by multiple nozzles, and small size nozzle and increased flow rate also increased reaction rate.

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Interface migration was observed during the CAP process of the T-15 high speed steel with addition of boron or boric acid. The reason of the interface migration was an alyzed by EDAX analysis and model experiments. The main cause of this phenomenon was attributed to the occurrence of coherence strain by the composition change of tungsten atoms during cooling.

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The continuous refining process which enables to refine the molten iron in stream lined flow was studied the slag metal counter current operating method in runner type reactor. The simultaneous desiliconization and dephosphorization proceeded over 60% in spite of high Si content, while the decarburization was supressed. The simulation model based on the mass transfer in reaction zones with and without O₂ blowing expressed fairly the actual reaction in the reactor. The contributions of the slag/metal reaction zone with out O₂blowing were estimated to be 26-32% for desiliconization and 47-53% for dephosphorization. From the results obtained here, the continuous process for pre-treatment of molten pig iron was conformed to be possible technically.

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