• Journal of Welding and Joining
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• 제32권5호
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• pp.7-12
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• 2014

In this study, API-X100 steel pipes were welded with various kinds of welding wires in the laser-arc hybrid welding process. 10kW fiber laser source was combined to MIG arc welding process. API X-100 steel of base metal was of 16.9mm thickness, and butt welding applied. After welding, full penetration weld was acquired by 1-pass welding. A root porosity and the lack of fusion was observed in some welding conditions. By the mixing the melted wire, acicular ferrite, polygonal ferrite, pro-eutectoid, aligned side plate, and bainite structures were observed at the weld metal. From the observation of hybrid weld, unmixed zone had more Ni and Cr. The unmixed zone was a 1/3 area of the weld metal. As the mechanical test of the hybrid welding, tensile test and impact test applied. From the tensile test, all of the welding except SM70S was fractured at the base metal. The result of the impact test at -30 degree C led 60J~320J of the absorbed energy. The result of the low-absorbed energy might be from the coarse equiaxed structures of the weld metal.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집A
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• pp.501-506
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• 2001

The creep crack growth properties in 3.5NiCrMoV steel were investigated at $550^{\circ}C$ by using CT specimen under constant $C_t$ condition that was held during crack growth of 1mm distance. $C_t$ lely on load line displacement rate and $C^*$ usually increase with crack length though load is reduced in order to maintain constant $C_t$ value as crack growth. Fully coalesced area(FCA) ahead of crack tip tend to increase as $C_t$ increase to the critical value, and after that value FCA decrease. For the tertiary creep stage of crack growth test, the most of displacement is due to the steady state creep, except only small part due to the primary creep and other effects. Therefore, tests were mainly interrupted in the tertiary stage to obtain high value of $C_t$. At constant load and $C_t$ region, crack growth slope was 0.900 and 0.844 each, on the other hand $C^*$ slope was 0.480.

• 한국정밀공학회지
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• 제18권5호
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• pp.105-111
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• 2001

The creep crack growth properties in 3.3NiCrMoV steel were investigated at 55$0^{\circ}C$ by using CT specimen under constant load and constant Ct condition that was held during crack growth of Imm distance. Ct lelied on load line displacement rate, C＊usually increased with crack length though load is reduced in order to maintain constant Ct value as crack growth and appeared scatter band. At constant load and Ct region, crack growth slope was 0.900 and 0.844 each, on the other hand C＊ slope was 0.480. Fully coalesced area(FCA) ahead of crack tip increased as Ct increase to the critical value, and after that value FCA decreased. For the tertiary creep stage of crack growth test, the most of displacement was due to the steady state creep, except only small part due to the primary creep and other effects. Therefore, tests were mainly interrupted in the tertiary stage to obtain high value of Ct.

• Applied Microscopy
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• 제7권1호
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• pp.45-49
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• 1977

용탕의 온도는 탄소의 비율을 높이기 위하여 $1500^{\circ}C$ 이하로 해야 하며, 주입온도는 $1460^{\circ}C$ 내외가 적당하다. 주조상태에서 소지의 침상석출물은 orthorhombic $(Fe,\;Mn)_3C$로 판명되었다. 냉간압연비는 클수록 결정이 미세화되고 또한 경도도 증가하였다. 표면탈탄이 얼어 나면 표면층에 martensite가 형성되어 성형하기가 어려우므로 argon 분위기를 쓰는 것이 좋았다. 두께 1 mm 판재의 경우 수인처리 온도가 $950^{\circ}C$ 이하일 때 탄화물 stringer 가 나타났고, $1020^{\circ}C$ 에서 30 분간 가열했을 때 탄화물이 의 소지에 고용되었다. C 함량이 클수록 인장강도와 연신률이 증가하였다. Ni, Cr 및 V 을 미량 첨가했을 때 인장강도 및 연신률이 커졌으며 또한 굽힘성도 좋았다.

• 대한의용생체공학회:학술대회논문집
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• 대한의용생체공학회 1996년도 춘계학술대회
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• pp.133-136
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• 1996

We investigated how hydroxyapatite (HA) coating onto a porous super stainless steel (S.S.S, 22Cr-20Ni-6Mo-0.25N) affects bone ingrowth in a dog transcortical femoral model. Implants were histologically evaluated after 4 and 48 weeks of implantation, and the bone bonding strength at the bone/implant interface was examined by employing the pull-out test. The direct osseous tissue bonding onto the HA-coated S.S.S was observed, but the uncoated stainless steels had thin fibrous tissue layers. The mean interface strength of the HA-coated S.S.S was 1.5 and 2.5 times greater than those of the S.S.S and the 316L SS after one year of implantation, respectively. In preliminary studies, no toxic responce was observed from a cytotoxicity test of the S.S.S, having similar corrosion resistance to titanium. Our results suggest that early osteoconductive nature of HA coating may induce long term osteointegration for a bioinert substrate.

• Journal of Welding and Joining
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• 제7권4호
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• pp.30-37
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• 1989

Effect of heat treatment on mechanical properties of an overlay weldment was investigated. Over welding was carried out on the structural C-Mn mild steel substrate to take required test specimens. Shielded metal arc welding process with 13Cr-0.2Ni stick electrode was applied. The heat treatment temperatures and holding times were $450{\circ}C., 550{\circ}C., 650{\circ}C., 750{\circ}C., 850{\circ}C.$ and 0.5hr, 2hr, 10hr, respectively. Mechanical tests and microscopic inspection were also carried out to investigate welds soundness. Test results indicated that carbon migration was dominant near bonded zone. At temperature of around 650.deg. C, carburized layer and decarburized layer were formed remarkably along overlay welds region and C-Mn mild steel region, respectively. The wideth of these layers became wider with increasing heat treatment temperature and/or holding time at the elevated temperature, and this relationship agreed with Larson-Miller parameter. Side bending test results demonstrated that the crack free region of overlay welds could be deduced from the relationship between temperature and holding time.

• 플랜트 저널
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• 제4권2호
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• pp.60-65
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• 2008

As the operating conditions in a supercritical oxidation reactor are set in high temperature with high pressure causing a reactor suffering from the harsh circumstances. It means the reactor adopts itself with Fe-Cr alloy in acidic atmosphere with low pH value and Ni alloy in basic atmosphere with high pH value due to its superior corrosion resistance. The study, whose target waster water is pertinent to the latter part, has selected Ni alloy such as ostenite type stainless steel 304 and 316, superstainless steel AL6XN, Inconel 625, MAT 21, and titanium Gr. 5 in order to measure corrosion resistance against those samples under the same conditions of temperature and pressure applied for a supercritical oxidation reactor. The result shows the identifiable difference in corrosion resistance by observing the surface states through a scanning probe microscope as well as measuring the weight loss through making the samples above deposited in wastewater for two-week and four-week stay. The purpose of this corrosion experiment is to identify the most corrosion-resistant material among sample species pre-selected according to pH concentration of wastewater in pursue of applying for a reactor exposed to the extreme corrosion environment. It is because such a reactor made of a verified material enables to safeguard a stable operation under the supercritical wastewater processing facility.

• 한국자기학회:학술대회 개요집
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• 한국자기학회 1991년도 춘계연구발표회 논문개요집
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• pp.73-74
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• 1991

The films with ferromagnetic fine particles dispersed in nonmagnetic matrix, such as $Fe-Al_2O_3$ and Fe-Cu have been studied for use of magnetic recording medium, optically device and sensor. Their magnetic properties depend strongly on structural parameter such as size and volume fraction of ferromagnetic particles. Fe-Cr-Ni alloy sputtered films also have microstructure with ferromagnetic -- b.c.c phase and nonmagnetic f.c.c phase grains. Magnetic properties of these films depend strongly on such a unique structure. These are depend on the ratio in volume of ferromagnetic particles to nonmagnetic ones $V_F/V_N$, the saturation magnetization Ms increased with increase of $V_F/V_N$. The coercivity Hc of the as-deposited films took maximum value of about 200 Oe at adequate $V_F/V_N$ and then Ms and Squareness S were 500 emu/cc and 0.5, respectively.(omitted)

• 대한기계학회논문집A
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• 제22권1호
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• pp.44-51
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• 1998

In order to develop the evaluation methods of degradation for the Ni-Cr-Mo-V steel, which is in use for turbine rotor in nuclear power plant, the degraded materials were prepared by simulated degradation methods. The result of impact test and fatigue crack growth test shows that the FATT(Fracture Appearance Transition Temperature) and fatigue crack growth rate increased with the increase of degradation. And the result of new electrochemical polarization test method was suggested for the evaluating FATT, fatigue crack growth exponent and coefficient C values based on the results of relationship between corrosion current density(Icorr) & FATT, and the m & C and Icorr.

• 한국해양공학회지
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• 제5권1호
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• pp.88-96
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• 1991

Fatigue life and retardtion behavior after through-thickness were examined experimentally by using a CT specimen and surface-cracked specimen. The material used was 3% Ni-Cr-Mo steel. The fatigue crack shape before through-thickness is almost semicircular, and the measured aspect ratio is larger than the value obtained by calculation using the K value proposed by Newman-Raju. It is found that the crack growth behavior on the back side after through-ghickness is unique and can be divided into three stages a, b and c. A retardation parameter has been used successfully to predict the growth of cracks in specimen, and in this time, retardation factor is 4.3. By using the crack propagation rule considering on retardation state and the K value proposed by the authors, the remarkable crack growth behavior and the change in crack shape can be evaluated quantitatively.