• 한국주조공학회지
• /
• 제2권2호
• /
• pp.10-17
• /
• 1982

This study has been carried out to determine the change of mechanical properties and microstructures by the heattreatment to relieve the residual stresses for gray cast irons. The results have been obtained from the experiment as follows; 1) The annealing above $600^{\circ}C$ for the stress relieving of gray cast iron decrease the tensile strength and hardness 2) The decrease reates of tensile strength and hardness of gray cast iron after annealing above $600^{\circ}C$ are increased with increasing the holding time. 3) The gray cast iron containing the elements of Mn, Cr has increased the heating temperature for the decrease of tensile strength and hardness. 4) The decrease of mechanical properties by annealing are assumed that the formation of ferrite takes placed from the decomposition of eutectoid cementite in the matrix.

• 한국주조공학회지
• /
• 제31권2호
• /
• pp.66-70
• /
• 2011

Hot dip aluminizing (HDA) is widely used in industry for improving corrosion resistance of material. The formation of intermetallic compound layers during the contact between dissimilar materials at high temperature is common phenomenon. Generally, intermetallic compound layers of $Fe_2Al_5$ and $FeAl_3$ are formed at the Al alloy and Fe substrate interface. In case of cast iron, high contact angle of graphite existed in the matrix inhibits the formation of intermetallic compound layer, which carry with it the disadvantage of a reduced reaction area and mechanical properties. In present work, the process for the removal of graphite existed on the surface of specimen has been investigated. And also HDA was proceeded at $800^{\circ}C$ for 3 minutes in aluminum alloy melt. The efficiency of graphite removal was increased with the reduction of particle size in sanding process. Graphite appears to be present both in the region of melting followed by re-solidification and in the intermetallic compound layer, which could be attributed to the fact that the surface of cast iron is melted down by the formation of low melting point phase with the diffusion of Al and Si to the cast iron. Intermetallic compound layer consisted of $Fe(Al,Si)_3$ and $Fe_2Al_5Si$, the layer formed at cast iron side contained lower amount of Si.

• 한국주조공학회지
• /
• 제4권4호
• /
• pp.20-29
• /
• 1984

It is very important to obtain gray and ductile cast irons with completely pearlitic structure by addition more economical alloying elements. In this study, 9 melts of gray iron and 5 melts of Mg-treated ductile cast iron were made according to Sb content (0-0.08% Sb). Each melt were casted to ${\phi}20mm$ test bars in sand mold under the same condition and inspected microstructure, mechanical and thermal properties. The results obtained from this study are as follows: 1. It is confirmed that Sb should be an economical, simple and useful additive for avoiding ferrite in gray and even in ductile cast irons. 2. For gray cast iron, the recommended ladle addition of metallic Sb amounts to 0.05%. At these levels, Sb has no detrimental influence on the mechanical properties of gray cast irons, which are normally modified according to their pearlite content without increasing the chilling tendency. 3. Despite its adverse influence on graphite shape in ductile iron, Sb can be used as a pearlite stabilizing alloying element even in the case of Mg - treated iron. The quantity to be added does not exceed 0.04% in the case of thinwalled castings. 4. The nodule count is increased very much and the shape of graphite particles become remarkably spheroidal. The matrix may be fully pearlitized, except for thin - walled castings, because the high nodule count results inevitably in some ferrite. 5. The $Ac_1$ and pearlite decomposition temperature are rised in accordance with increasing of additive Sb amount.

• 분석과학
• /
• 제13권2호
• /
• pp.200-207
• /
• 2000

구상흑연 주철과 고압처리된 Ni-C 합금에서 SEM, HRTEM, EELS 등을 이용하여 구상흑연 입자의 성장 기구를 연구하였다. 두 시료로부터 추출된 각각의 구상흑연입자의 내부 미세조직 및 격자상이 서로 비교되었으며 EELS를 이용하여 각 구상흑연 입자 내부에서 흑연결합을 하는 $sp^2$와 다이아몬드 결합을 하는 $sp^3$의 비가 측정되었다. 구상흑연 주철에서의 구상흑연 입자는 뚜렷한 결정립계면 및 조대한 결함을 갖고 있었다. 반면에 고압처리된 Ni-C 합금 내부에 생성된 구상흑연 입자는 구상흑연 주철의 것에 비해 미세조직 내부의 결함이 현저히 적었으며 안정한 다이아몬드 결합을 하는 $sp^3$ 결합을 다량 함유하고 있었다. 본 실험에서의 구상흑연 입자 내부의 미세조직 및 결합 특성상의 차이는 고압처리된 Ni-C 합금에서의 구상흑연 입자가 구상흑연 주철에서의 구상흑연 입자와는 다른 기구에 의하여 성장하였다는 것을 보여주는 증거이다.

• 소성∙가공
• /
• 제27권6호
• /
• pp.339-346
• /
• 2018

This study investigated the microstructure and wear properties of extruded hyper-eutectic Al-Si (15wt.%) alloy in an engine oil environment. The wear mechanism of the material was also analyzed and compared to conventional gray cast iron. In microstructural observation results of Al-15wt.%Si alloy, primary Si phase ($45.3{\mu}m$) and eutectic Si phase ($3.1{\mu}m$) were found in the matrix, and the precipitations of $Mg_2Si({\beta}^{\prime})$, $Al_2Cu({\theta}^{\prime})$ and $Al_6(Mn,Fe)$ were also detected. In the case of gray cast iron, ferrite and pearlite were observed. It was also observed that flake graphite ($20-130{\mu}m$) were randomly distributed. Wear rates were lower in the Al-Si alloy as compared to those of gray cast iron in all load conditions, confirming the outstanding wear resistance of Al-15wt.%Si alloy in engine oil environment. In the $4kg_f$ condition, the wear rate of gray cast iron was $6.0{\times}10^{-5}$ and that of Al-Si measured $0.8{\times}10^{-5}$. The microstructures after wear of the two materials were analyzed using scanning electron microscope (SEM) and electron backscatter diffraction (EBSD). The primary Si and eutectic Si of Al-Si alloy effectively mitigated the abrasive wear, and the Al matrix effectively endured to accept a significant amount of plastic deformation caused by wear.

• 열처리공학회지
• /
• 제13권4호
• /
• pp.231-238
• /
• 2000

Flake graphite cast irons with the high damping capacity have been used for the control of vibration and noise occurring in the members of various mechanical structures under vibrating conditions. However, the damping capacity which is morphological characteristics of graphite is one of the important factors in reducing the vibration and noise, but hardly any work has deal with this problem. Therefore, the authors have examined the damping capacity of various cast irons with alloying elements and studied the influences of the matrix structures, mechanical properties and morphological characteristics of graphite. The main results obtained are as follows: Effects of pouring temperature on the damping capacities and mechanical properties were investigated in 3.6%C cast iron. At $1400^{\circ}C$, specific damping capacity showed the maximum value, and decreased with increase pouring temperature. Mechanical properties showed opposite trend with the damping capacity. And then, effects of Ni on the damping capacities and mechanical properties have been investigated in 3.6%C gray cast iron. At 0.2%Ni content, specific damping capacity showed the maximum value, and decreased with further increase in Ni content. Graphite length also showed same behavior. This indicates that the specific damping capacity has a close relation with graphite length. In case of Mo addition in 3.6%C-0.2%Ni cast iron, specific damping capacity and tensile strength was 27% and $20kgf/mm^2$ at 3.6%C-0.2%Ni-0.3%Mo cast iron respectively.

• 한국주조공학회지
• /
• 제20권2호
• /
• pp.122-128
• /
• 2000

Strip casting process is a new technology that makes a near net shape thin strip directly from molten metal. With this process, a large amount of energy and casting cost could be decreased from the abbreviation of reheating and/or hot rolling process. Ductile cast iron which has spheroidal graphite in the matrix is the most commercial and industrial material, because of its supreme strength, toughness, and wear resistance etc. But it cannot be produced to the thin strip owing to difficulty in rolling of ductile cast iron. In this study, ductile cast iron strips are produced by the twin roll strip caster, with different chemical compositions of C, Si, and Mn contents. And then heat-treated, microstructures and mechanical properties are examined. The microstructures of as-cast strip are that of white cast iron which consists of the mixture of cementite and pearlite, but the equiaxed crystal zone of the pearlite or segregation zone of cementite exists in the center region of the strip thickness, which cannot be observed in the rapidly solidified metallic mold cast specimens. This structure is supposed to be formed from the thermal distribution of strip and the rolling force. Comparing with the structures of each strips after heat treatment, increasing Si content makes smaller spheroidal graphite and more compact in the matrix, furthermore the less of Mn content makes the ferrite matrix be obtained clearer and easier. As a result of the tensile test of graphitization heat-treated strips, the yield strengths are about 250 MPa, the tensile strengths are about $430{\sim}500$ MPa, and the elongations are about $10{\sim}13%$. In the case of the strip which has the smaller and more compact spheroidal graphite in the ferrite matrix, the higher tensile strength and better drawability could be obtained.

• 대한기계학회논문집A
• /
• 제39권8호
• /
• pp.765-772
• /
• 2015

주철은 산업현장에서 중장비나 철도차량 등과 같은 다양한 기계장치의 주재료로 널리 사용된다. 이러한 기계장치의 운전 성능은 접촉 특성에 따라 크게 좌우되며 이를 개선시키기 위한 연구들이 진행되고 있다. 본 연구에서는 모래와 알루미나 입자가 주철의 마찰/마모 특성에 미치는 영향에 대해 다양한 조건에서의 미끄럼 실험을 통해 규명하였다. 입자의 크기 및 시편 온도 등을 변수로 하여 스틸 볼이 pin 으로 장착된 pin-on-reciprocator 방식의 트라이보테스터를 사용하여 실험을 진행하였다. 주사전자현미경(Scanning Electron Microscope), confocal microscope 와 3d profiler 를 이용해서 주철 시편과 스틸 볼의 마모 표면을 관찰하고 마모량을 정량적으로 측정하여 마모 특성을 파악하였다. 실험 결과 주철의 마찰/마모 특성은 입자 주입에 의해 크게 달라짐을 알 수 있었다. 또한, 주철 시편에 가해준 온도에 따라 마찰/마모 특성이 크게 달라지는 것을 확인하였다. 이 연구의 결과는 산업에서 주철 재료의 트라이볼로지 특성을 이해하는데 도움이 될 것이다.

• Journal of Welding and Joining
• /
• 제20권4호
• /
• pp.551-556
• /
• 2002

Solid particle erosion wear characteristics of high Cr white iron hardfacing were investigated using the erosion wear test method according with the ASTM G76-95. Wear experiments, where the blast angle, blast distance and blast pressure were selected as test variables, were planned and analyzed by response surface method (RSM to evaluate the wear loss statistically and quantitatively. The measured wear losses well coincided with the calculated ones by the experimental equation. The wear loss of high Cr cast iron hardfacing was increased with blasting pressure, but affected in a complicated way by the blasting angle and distance. Erosion wear of high Cr cast iron hardfacing could be well predicted by RSM analysis of wear variables.

• 한국주조공학회지
• /
• 제8권3호
• /
• pp.296-309
• /
• 1988

In this study the mechanical properties of ferritic ductile cast iron in as-cast are discussed by metallographic considering the effect of phosphorus content(about 0 - 0.8wt.%). In ferritic S.G. cast iron containing about 4.2wt.% Si, 0.5wt.% Ni, 0.02wt.%B, these samples are investigated for castability, microstructure, machinability, wear resistance, mechanical and thermal properties. The main results are summarized as follows. 1) The chill depth increased greatly with P addition up to about 0.6wt.% but the tensile strength and the elongation are decreased smoothly. 2) The size of S.G. and the amount of steadite increase with increasing P content. This means the tendency of increasing the number of S.G. 3) The maximum value of wear by mechanical fracture was appeared at the abrasion speed of 1.14m/sec and the plastic Flow layers are stretched longly on the wear surface with decreasing P content. 4) Although the coefficient of thermal expansion increased with P addition, the cast iron growth was slowing down extremely at 0.6w.% P or more.