발간논문

Home > KJMM 논문 > 발간논문

keyword :

A thorough examination has been carried out on the change of microstructure and hardness of cold-worked modified Hadfield steel by isothermal heating, from which the following conclusions could be drawn. 1) Precipitation of the carbide and pearlitic constituents was promoted considerably by cold-working. 2) Carbide precipitation occurred, when cold-worked modified Hadfield steel was reheated, in the temperature range between 270 and 940℃. This precipitation took place most rapidly between 500 and 850℃. Formation of pearlitic constituents was restricted to the temperature range 380-760℃, and was the most rapid in the vicinity of 650℃. 3) Formation of the carbide was preferentially preceded on the slip line in the lower temperature range, but with the increase in temperature and heating time, it was found both on the grain boundary, and slip line. On further increase in temperature, the carbide was spheroidized. 4) Increased amounts of transformation products led to higher hardness with a maximum of about Hv 470 obtained on heating at 550℃ for 100 hours. A more effective hardner contributing to the maximum hardness appeared to be acicular carbide rather than pearlitic constituents.

keyword :

A1-4.5% Cu alloy without grain refiner and degassing agent was allowed to solidify in a cylindrical die with 200℃ under high hydrostatic pressure ranging from 0 ㎏/㎠ to 2,000㎏/㎠ at 750℃ pouring temperature. Castings solidified, under pressure showed the following characteristics; (1) Suppression of shrinkage cavity and porosity (2) Columnar crystal change to equiaxed crystal by increasing the applied pressure (3) Refinement of grain size (4) Improvement in mechanical properties to 1,000㎏/㎠

keyword :

Sintering of wire was performed to define the material transport path in nickel activated sintering of tungsten. After sintering at the temperature range of 1000℃ to 1200℃ in a hydrogen atmosphere the neck growth was measured and the inverse slope of log (r/a) vs. log t plot was turned out to be approximately 7.7, where r, a and t are the neck radius, and wire radius, and sintering time respectively. The activation energy for the sintering was estimated to be about 40 ㎉/mole which is considerably less than that for sintering of pure tungsten. The present results seem to support grain boundary diffusion mechanism in nickel activated sintering.

keyword :

The effect of Al in molten borax on the electroboronizing and on the wear resistance has been studied. Wear test using the lubricant was made as a function of frictional rate and frictional distance. The boronized depth and microhardness were increased with increasing Al content, electrolysis time and electrolysis temperature. The molten electrolyte of 10-30g Al/200g Na₂B₄O_7 was considered as the optimum composition for wear resistance, and when the eletrolysis time was 4hr and electrolysis temperature was 800℃, the best result of wear resistance was obtained. The wear resistance was raised in case of tempering the pre-quenched specimen at 250℃ for 2hrs. The high temperature wear test showed that at elevated temperature the wear volume of boronized specimen was decreased than at room temperature.

keyword :

Using the Ferrovac E iron specimens cathodically charged with hydrogen, investigations of the mechanism of hydrogen entry into the alpha-iron were carried out. According to the experimental results, the delaying time due to the formation of hydrogen concentration at the metal surface was investigated in terms of the amount of amorphous arsenic electrodeposited on the cathode surface.

keyword :

An attempt has been made to extract the cell grade alumina from domestic shale bearing chiastolite, The process adopted was the soda ash sintering process with sodium carbonate and lime as additives. The effects of the shale particle size, the sintering temperature, and the amounts of the additives on the extraction of alumina have been investigated. The results are summerized as follows; (1) The optimum sintering temperature and the particle size range were found to be 1,000℃ and 150 to 200 meshes, respectively. (2) The weight ratio of Na₂CO₃as a additive to Al₂O₃, in shale 1 to 1.5 showed much better result than 1 to 1.

keyword :

This work was carried out for some observations on crystal growth under pressure in an ammonium chloride/water analogue system, with a view to explore possible similarities with the mode of solidification in metals. An ammonium chloride solution having 37% wt. composition was used, and crystallisation phenomena were observed in this solution frozen at atmosphere and under pressure, depending on the pouring temperatures. Crystallisation phenomena under pressure greatly differed from the ones at atmosphere; they were as follows; (i) Cooling rate was much faster under pressure than that at atmosphere, stimulating dendrite fragmentation. (ii) Growth rate of columnar and/or equiaxed grains was increased under pressure. (iii) A sweeping effect ahead of the advancing interfaces was much more effective under pressure. (iv) A recess of columnar or equiaxed zone near the mold wall by applying pressure stimulated the formation of new crystals, but this was not in atmosphere. (v) Equiaxed zones were formed mainly by simultaneous nucleation at the lower pouring temperature, and at the higher ones mainly by convection. These effects were more effective under pressure.

keyword :

keyword :

keyword :