The mass effect and the hardenability of ADI, using a specially designed apparatus for end-quench test in austempering, were studied. Two types of cone shape specimens were applied for austempering treatment. The changes of Vickers hardness, microstructure, morphology of bainite and retained austenite with distance from quench end at given temperature were investigated with first type of cone shape specimen. The shape of bainite changes and hardness of bainite lowers on the border of pearlite because of increase of transformation temperature.
  Hardenability of iron alloyed with Mo and/or Cu was evaluated with second type of cone shape specimen. A multiple linear regression analysis using the pearlite free half-cooling time data was performed to quantify the effects of Cu and/or Mo on suppression of the pearlite transformation. Half-cooling time is defined as the time required to cool from the austenitizing temperature to the temperature which is midway between the austenitizing temperature and austempering temperature.
  Moreover predicting the micro-structure and hardness of ADI was tried by the heat flow analysis with personal computer. Basing on predetermined end-quench data, the prediction in the way of simulating temperature distribution at pearlite free or 50 % pearlite plus ferrite half-cooling time after dipping into austempering bath by SOLDIA-EX was well coincident with practical ADI.

抄録全体を表示

The apparent viscosity of fusible alloys suspended with copper powder was determined to be larger when the suspending solid particles were finer in size and complex in shape like that of the dendrite. On the basis of these results, the growth features of primary crystals in various cast irons were studied by means of measuring the apparent viscosity in the early stages of solidification.
The results are summarized as follows.
In the case of hypoeutectic cast irons :
(1) When the iron is held in the liquid state, the primary dendrite becomes finer with increasing holding time.
(2) Inoculation facilitates the primary crystallisation and the formation of fine dendrites with many arm branchings. In the iron held for, 30 min after inoculation, however, coarser dendrites than those in the original iron are found.
(3) In the process of holding the iron at a fixed temperature during solidification, dendrite arms are enlarged or extinguished violently and thus the coarsening of the whole dendrite grains proceeds gradually. This phenomenon is different from the coarsening process of the dendrite in hypoeutectic Al-Si alloys.
In the case of hypereutectic cast irons :
(4) No change in size of the primary flake graphite is found in irons held in the liquid state.
(5) Inoculation to the hypereutectic cast iron facilitates the crystallisation of primary flake graphites and changes their shape.

抄録全体を表示

  Apparent viscosity of solidifying Cu-Sn alloys was measured from the liquid state successively by the torsional oscillation method. The apparent viscosity increases gradually in the initial stage of solidification and abruptly at completion of the dendrite skelton. The apparent viscosity in the initial stage shows practical viscosity of bulk solidliquid phase. While, that after abrupt increase is a parameter showing resistance of the rigid dendrite skelton to the microscopic flow of residual liquid. A concept “hydraulic radius“ showing an interskelton spacing is introduced in the latter stage. A closed correlation between hydraulic radius and fraction solid at a moment of abrupt increase in apparent viscosity shows a critical condition to transfer from bulky flow of the solid-liquid phase to interskelton one. The shape of solidifying primary solids governs the apparent viscosity of solid-liquid mixture and easiness of dendrite skelton forming. Preferred growth of dendrites in the arm direction leads to high apparent viscosity and abrupt increase in viscosity at lower fraction of solid.

抄録全体を表示

Measurement was made on viscosities of partially solidified binary alloys Fe-C (3 and 4%C), Sn-Pb (1.0, 1.5, 5, 15, 25, and 45%Pb), and Al-Cu (4.5 and 10%Cu), and iron-base alloys (Fe-2%Cr-1.5%C, Fe-25%Cr-20%Ni-0.4%C, and Fe-28%Cr-0.4%C). A rotating coaxial cylinder viscometer was used. Solid fraction was calculated for the observed temperatures with the aid of the equation proposed by Scheil. The viscosities were found to depend on the solid fraction, the cooling rate, and the shear rate, as has been reported by FLEMINGS.
When the calculated value of solid fraction was more than 0.6 at the eutectic temperature, the relation between the viscosity and the solid fraction was similar to that for dispersed systems; that is, the viscosity increased remarkably in the range of solid fraction over about 0.5. When the calculated solid fraction at the eutectic temperature was less than 0.6, the viscosity rapidly increased after the temperature of alloy reached the eutectic one.
The viscosity of the iron-base alloys was found to be affected more intensively by the cooling rate than by the shear rate.

抄録全体を表示

鋳鉄の硬度等の機械的特性の向上を目標として、鋳鉄の摩擦攪拌処理を行った。この際、機械的特性に及ぼすツールの傾斜角度の影響を調べ、接合条件を最適化した。

抄録全体を表示

Apparent viscosity of partially solidified alloys is expected to be extremely influenced by the size and morphology of crystals. An Al-5%Cu alloy was stirred during solidification with a paddle or a columnar rotor, and factors affecting the apparent viscosity and structure of the alloy slurry were investigated.
The apparent viscosity (μ/Pa·s) of the slurry was approximated by the following equation as a function of the rotation speed (n/s⁻¹) between rotor and crucible, the cooling rate (V_c/K·s⁻¹) and the fraction solid (f_s).
(This article is not displayable. Please see full text pdf.)
\ oindentwhere A=1.8 (paddle) and 0.9 (columnar rotor).
Primary crystals were broken into fine quasi-spherical particles by the stirring, while some of them coalesced into complicated particles in the slurry.
A relationship was observed between the apparent viscosity and the particle coupling ratio R_n, that is, the ratio of the number (mm⁻²) of fine quasi-spherical primary particles to the number (mm⁻²) of complicated particles.

抄録全体を表示

  A method of approximation was proposed for explicit finite difference thermal calculations of casting solidification where a larger than normal time step is employed so as to reduce the total computing time up to the end of solidification. This was made possible by noting the fact that the maximum permissible time step during solidification is much larger than the ones before and after solidification. By including the superheat into the apparent heat of solidification, calculation of the process of superheat dissipation, for which a small time step is needed, was made unnecessary. The calculation of the process after the end of solidification posed a problem, because, then, a small time step was again necessary.
  An approach was made to solve the problem by switching the time step from large to small at a certain time. Results of numerical experiments indicated that, depending on the combination of the thermal properties of casting and mold materials, the method is relatively successful in some cases and not in others. It was found that the proposed method is most successful in aluminum sand castings and a reduction of computing time to about one tenth is possible with a relatively small sacrifice in precision.

抄録全体を表示

  The influence of solid fraction on thixotropic behavior of partially solidified alloy slurry was investigated by using hypoeutectic Al-Cu alloy. Speeds of viscosity shift caused by shear rate change were used to estimate the thixotropy. The shear rate increased abruptly, then elapsed time dependencies of viscosity decrease were measured for slurries had various solid fraction. Slurries in the solid fraction range between 50 % and 70 % showed most immediate fluidity recovery. This fraction range agreed with the fraction range derived by an assumption. That is, the aggregation of solid particles lowered the effective liquid fraction at lower shear rate by liquid phase entrapping. From these results and observation of microstructure of slurries, it was found that the apparent solid fraction change was responsible for the thixotropy of this alloy.

抄録全体を表示

A semi-solid slurry of a hypereutectic Al-Si alloy containing fine primary silicon crystals is producible by "slurry-melt mixing (SMM)" process. In the SMM process, a melt of a phosphorus-added hypereutectic Al-Si alloy (second-alloy melt) is mixed with a semi-solid slurry of a hypoeutectic Al-Si alloy (first-alloy slurry) which has been solidified with stirring in a furnace-cooled vessel. In this study, the change in apparent viscosity of the stirred slurry, whose silicon content changed from 8 to 20mass% by mixing of molten Al-32mass%Si alloy, was measured continuously during the SMM process. Immediately after the mixing of the second-alloy melt, the apparent viscosity decreases drastically from 7 to about 0 Pa•s. This abrupt change is attributed to the following facts: (1) The primary alpha-phase which has been crystallized in the first alloy remelts rapidly in the mixed alloy. (2) The fraction of the primary silicon in the mixed alloy is lower than that of the primary alpha-phase in the first alloy, though there is a strong driving force of crystallization of the primary silicon in the mixed alloy in comparison with the conventionally solidified Al-20mass%Si alloy. (3) The apparent viscosity of the hypereutectic alloy is similar in order of magnitude to that of the hypoeutectic alloy of the same fraction solid.

抄録全体を表示

  Fluidity of Cu-8%Sn base ternary alloys containing Si, Al or Fe was measured with spiral shell mold. The alloys showed the minimum fluidity at a dilute concentration of Si, Al or Fe and high fluidity at higher concentration. The metal flows in two different states : complete liquid state and liquid-solid coexisting state. Flow length in the complete liquid state decreases with Si or Al content. It decreases first and then increases with increasing Fe content. When the alloy contains Si or Al, slender dendrites grow and the fraction solid at the flow stop is low at dilute concentration of Si or Al, while it increases at concentration higher than 1 percent, because of rupture of dendrites. When the alloy contains Fe, shorter and rounded dendrites grow and the fraction solid at flow stop increases remarkably. Flow length in the liquid-solid coexisting state depends on the fraction solid at flow stop. Fluidity of the alloys is represented by the sum of the lengths of the above two states.

抄録全体を表示

  In recent years, there has been an increase in the amount of manganese (Mn) contained in cast iron due to changes in raw materials. It is thought that the increase of Mn contents has a bad influence on the mechanical properties of cast iron. This study aims to investigate the effects of Mn content and post inoculation for mechanical properties and structural changes of FCD450-10 with different thicknesses. In this study, spheroidal graphite cast iron was used as specimens with a Mn concentration of 0.3%, 0.6%, 0.9%. The rates of the cooling of specimens to the eutectic temperature were 0.22K/s, 0.12K/s and 0.08K/s, respectively, for different thickness of specimens. It was observed that thick wall specimens with a cooling rate of 0.12K/s or less had large graphite and grain diameters. In addition, when the Mn content was 0.9% or more, coarse cementite occurred in the last region to solidify (intercellular structure) with the segregation of Mn to the cell boundary. On the other hands, for the specimens with post inoculation, graphite nodule count and cell count increased, and the pearlite area decreased. Course cementite also disappeared in the specimens. Mn segregating to cell was concentrated in the pearlite. Mechanical properties decreased with decreasing cooling rate and increasing amount of post inoculant. This is due to chunky graphite formed.

抄録全体を表示