발간논문

Home > KJMM 논문 > 발간논문

Austenitid Fe-31%Ni alloy was prepared by induction melting, and then effects of prior deformation degree on the susformed martensite were investigated. The results obtained in this study are as follows. 1. Although iron-nickel alloy contains little carbon content, the ausformed martensite of this alloy showed remarkable increase ih tensile strength. 2. The strengthening of ausformed martensite in this alloy was considered to be attributed to a direct transfer of lattice defects such as tangled and sessile dislocation formed in deformed austenite to martensite phase during martensitic transformation, and about 40 pct of work-hardening in prior austenite was introduced to the strength of martensite phase in susformed martensitic structure. 3. The elongation of austenite was decreased with increasing deformation degree. However the elongation of susformed martensite showed a nearly constant value, independent of austenite deformation degree.

keyword :

The continuous cooling phase transformations (CCT) in copper-aluminum alloys (11.1∼13.3 wt.% Al) have been studied. Five CCT diagrams have been constructed by dilatometry and thermal analysis. At higher cooling rates, the phase transformations are characterized by an ordering reaction and a martensite transformation. When the cooling rate is lowered, the ordering reaction of the matrix influences the subsequent transformations and thus a bainite transformation occurs. After proeutectoid precipitation, two ordering reactions and two martensite transformations are observed. On the other hand, at slow cooling an ordering reaction at about 270℃ is observed for all the studied alloys. This ordering corresponds to that of the α` or α`_p phase in which aluminum has been depleted. Eutectoid transformation at about 500℃ is observed at very slow cooling.

keyword :

Effects of Al contents on the microstructure and hardness of Ti-Al-4V alloys were investigated after solution anneal and aging treatment of the alloys containing 4. 5, 6, 9 and 12% Al, respectively. The titanium alloys exhibited different α+ β⇔ βtransformation temperatures, and their hardness after solution anneal was influenced by the formation and decomposition of α` transformed from β, whereas the hardness after aging treatment was affected by the decomposition of α`, agglomeration of βgrains and precipitation of α₂(Ti₃Al). It is believed that 4% V of the alloys kept fine α₂precipitates from growing and that the α₂, precipitates, in turn, retarded the agglomeration of β-grains. α₂precipitates of about 100Å were actually observed by transmission electron microscopy in Ti-9Al-4V and Ti-12Al-4V alloys after aging treatment whereas it was not possible to observe them in Ti-6Al-4V.

keyword :

The phase transformations during continuous cooling of β-Cu-Al alloys have been studied. When the aluminum content in the alloy is varied from 11.1 wt.% to 13.3 wt.%, the ordering and the martensite transformation temperatures change from 470℃ to 550℃ and from 405℃ to 145℃, respectively, at quenching. The process of the bainite transformation appearing at slower cooling rate is clearly explained by the formation of the ordered β₁-Cu₃Al phase and its stability. This ordered phase has transformed to martensite at about 300℃. The bainite plate of α` phase is ordered at about 270℃ and its structure is found to be identical to that of the β₁` martensite and its composition is about 10 wt.% in aluminum. At very slow cooling after the ordering reaction, a pseudopearlite lamellar phase, which is often visible in an ordered matrix, is formed due to eutectoid transformation. The microhardness of the alloys with 11.1 wt.%∼12.2 wt.% Al increases with the decrease of cooling rate until abundant precipitation of the ductile a phase appears. The maximum hardness corresponds to a composite microstructure of the martensite and the α` phase. As the aluminum content in the alloy decreases, the maximum hardness increases and is obtained at high cooling rate.

keyword :

An advanced Ni-base superalloy, MA6000E, combining both gamma prime and oxide dispersion strengthening has been developed by using mechanical alloying process at INCO. The nominal composition of the alloy is Ni-15Cr-2Mo-4W-4.5Al-2.5Ti-2Ta-0.15Zr-0.05C-0.01B-1.1Y₂O₃. The 100 hours rupture strength at 1093℃ of the alloy (165 MPa) is about three times higher than that of the best conventional superalloy. Creep stress exponent at 1093℃ is about 40, and the apparent creep activation energy is about 160 ㎉/mole at intermediate temperature. Stress-rupture properties are not degraded significantly after thermal cycling.

keyword :

To formulate the sulfur partitioning between basic steelmaking stags and metal in terms of the ionic treatments, the thermodynamic relation between equilibrium quotients and cationic concentrations proposed by Flood et al have been applied to the measured values. The results obtained are as follows. 1. Sulfur equilibrium is expressed by following equations. Stag/metal ; log {(N_o^(2-)/N_s^(2-) ·([a_s]/[a_o])} = -1.47N`_(ca)^(2+) - 1.92N`_(Fe)^(2+) - 3.15N`_(Mg)^(2+) Gas/slag ; log {{(N_o^(2-)/N_s^(2-) ·(P_s₂/P_o²)^½} = 2.35N`_(ca)^(2+) + 2.79N`_(Fe)^(2+) + 4.03N`_(Mg)^(2+) N_(A-) and N`_(M^+) are ionic Fraction and electrically equivalent fraction in the stags respectively. 2. The distribution ratio of sulfur between slags and metal is expressed by following equation. log {N_s^(2-)/[a_s]} = (-936/T + 1.375) + log C`_s - log [a_o] or, = (5214/T - 1.228) + log C`_s - log a_Fe_tO log C`_s { = N_s^(2-)·(P_o₂/P_s₂)^½} = - (2.35 N`_(ca)^(2+) + 4.03 N`_(Mg)^(2+)) + log(1 - N_(sio)₄- ) 3. The values of log { N_s^(2-)/[a_s] } are in good agreement with the measured values in the composition range of (CaO+MgO)/SiO₂> 1.7 for Fe_tO-SiO₂- CaO - MgO(sat) slags.

keyword :

The paper describes factors influencing the choice of the unit, problems encountered during the commissioning and the present smelter operation.

keyword :

keyword :

keyword :