• International Journal of Safety
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• 제8권1호
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• pp.6-9
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• 2009

The crack in a J85 engine V.G. actuator arm shaft for a bell crank on the engine compressor was investigated. The crack was observed in twenty two shafts during the inspection of 238 shafts. The failure analysis of shaft cracks was performed by chemical composition analysis using ICP(Inductively Coupled Plasma) and by fracture surface and microstructure analysis using FE-SEM and optical microscope. The crack initiated from the top and bottom and propagated to the center along the grain boundaries. From the chemical composition analysis, the fractography of the fracture surface and the microstructure, it was found that the failure mechanism of the shafts is the inclusion-related intergranular decohesion crack. The inclusion was found out from MnS particle by EDS(Energy Dispersive Spectroscopy). The crack initiated MnS inclusion in the grain boundary and propagated with the increase of applied shear stress during long operation. In order to prevent the fracture, NDI(Nondestructive inspection) is needed periodically as recommended.

• 대한기계학회논문집A
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• 제20권12호
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• pp.3899-3908
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• 1996

In order to clarify the effects of nonmetallic inclusion contents insteels (SM45C & SCM440) on the tool life, cutting experiment was performed under various cutting conditions. Tool life, cutting force, roughness of machined surface and cutting mechanism are examined on these two kinds of steel. The following conclusions were obtained from the analysis (1) Cutting force of the steels was not affected by chemical component and nonmetallic inclusion. (2) If the rate of amount, Ca/S has a value grater than about 0.2 and addition of less amount of Al, Mn, tool wear of tips decreasesinturning. (3) It is also proved that higher contents of nonmetallic inclusion improve roughness of the surface. (4) Less amount of Ca, higher amount of S, Mn and Al improve the chip breakability.

• Metals and materials international
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• 제24권6호
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• pp.1432-1437
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• 2018

This work investigated edge-cracking behavior of equiatomic CoCrFeMnNi high-entropy alloy during hot rolling at rolling temperatures $500{\leq}T_R{\leq}1000^{\circ}C$. Edge cracks did not form in the material rolled at $500^{\circ}C$, but widened and deepened into the inside of plate as $T_R$ increased from $500^{\circ}C$. Edge cracks were most severe in the material rolled at $1000^{\circ}C$. Mn-Cr-O type non-metallic inclusion and oxidation were identified as major factors that caused edge cracking. The inclusions near edge region acted as preferential sites for crack formation. Connection between inclusion cracks and surface cracks induced edge cracking. Rolling at $T_R{\geq}600^{\circ}C$ generated distinct inclusion cracks whereas they were not serious at $T_R=500^{\circ}C$, so noticeable edge cracks formed at $T_R{\geq}600^{\circ}C$. At $T_R=1000^{\circ}C$, significant oxidation occurred at the crack surface. This accelerated edge crack penetration by embrittling the crack tip, so severe edge cracking occurred at $T_R=1000^{\circ}C$.

• Journal of Welding and Joining
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• 제3권1호
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• pp.3-10
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• 1985

Lamellar tearing susceptibility and through-thickness tensile ductility have been investigated in $40kg/mm^2 and 50kg/mm^2$ class tensile strength steel plates in terms of cleanliness of non-metallic inclusion and welding condition. The plate which had 0.01% cleanliness of A-type inclusion (MnS) had 61% of the reduction of area in the through-thickness direction and did not show lamellar tearing. Lamellar tearing susceptibility decreased with increasing the preheat and interpass temperature. The plate which had 0.04% cleanliness of A-type inclusion did not show lamellar tearing under the condition of 75.deg. C of preheat and interpass temperature.

• 소성∙가공
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• 제19권5호
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• pp.311-319
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• 2010

Rare earth metal Ce has a relatively low melting point and high specific gravity. Because of its significantly high affinity to oxygen, nitrogen and sulfur, it is highly usable as a steel refining agent. However, because Ce compound has relatively high specific gravity, it is difficult to be separated from molten steel through floatation, and it degrades the purity of molten steel, or may clog the nozzle in continuous casting. Such problem may be solved by using an appropriate deoxidation agent together with Ce and settling molten steel sufficiently after refining. Thus a fundamental study in the formation behavior of non-metallic inclusion in Ce added Hyper Duplex STS melts was investigated. The addition amount of Ce, melt temperature were considered as experimental variables. A main non-metallic inclusion in mother alloy is 51(wt%MnO) - 27.6(wt%SiO$_2$)- 10.9(wt%$Cr_2O_3$). Non-metallic inclusion was dramatically decreased and the particle size was fined as the amount of Ce increased. Moreover (%MnO) and (%SiO$_2$) of non-metallic inclusion were decreased. But (%$Al_2O_3$)were relatively increased. The number of non-metallic inclusion were decreased and the large particle size were increased by increasing the temperature of molten steel.

• Metals and materials international
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• 제24권6호
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• pp.1333-1345
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• 2018

The effect of manganese sulfide (MnS) inclusions on the machinability of free-cutting steel is based on their morphology, size and distribution. Furthermore, the plasticity of MnS is high during the hot working caused different characterization of MnS. In this study, the deformation behavior of MnS in 1215MS steel after a thermomechanical process was investigated at 1323 K. The microstructures of MnS inclusions were characterized by optical microscopy, scanning electron microscopy, energy-dispersive spectrometry, and electron backscattering diffraction (EBSD). As the thickness reduction of the inclusions increased from 10 to 70%, their average aspect ratio increased from 1.20 to 2.39. In addition, the deformability of MnS inclusions was lower than that of the matrix. The possible slip systems of A, B, C, and D plane traces were (${\bar{1}}0{\bar{1}}$)[${\bar{1}}01$], ($10{\bar{1}}$)[101], (011)[$01{\bar{1}}$], and (110)[$1{\bar{1}}0$]. Furthermore, the EBSD measurements suggested that slip planes in MnS inclusions occur on {110} planes.

• 보존과학회지
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• 제28권4호
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• pp.367-376
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• 2012

철기 생산 기술은 당시 사회 발전을 가늠하는 척도로서 과거의 제철 방법을 이해하기 위한 철기 유물의 미세조직과 개재물에 대한 다양한 연구가 진행되고 있다. 본 연구에서는 고려시대로 추정되는 고양 벽제 제철 유구에서 일괄로 수습된 철제 유물의 시편을 채취하여 광학현미경과 미세경도시험기, SEM-EDS를 이용하여 미세 조직의 성분분석을 통해 제철과 제련 기술을 추론하여 보았다. 연구결과 철괴는 주철괴와 탄소강 철괴로 분류되었다. 주철괴의 경우 백주철 조직과 인(P)의 함량이 높은 회주철 조직으로 분류되었으며 회주철 내 높은 P의 함량은 석회질 등의 융제가 첨가되며 혼입된 것으로 판단된다. 따라서 주철 조직의 철괴 및 고탄소강 철괴는 제련공정을 거치지 않은 선철들로 추정된다. 또한 철기 제작에는 크게 두가지 방법이 사용된 것으로 판단된다. 첫번째는 주물에 주철을 부어 제작하는 주철괴 제작 방법이며, 두번째는 선철의 제련 공정을 통하여 생산되는 탄소강을 제작하는 방법이다. 특히 탄소강의 고른 강 조직과 적은 양의 MnS 개재물은 현대 제철 조직과 매우 유사한 특징을 지니나 고양 벽제 제철유구에서 수습된 탄소강 내 Mn의 함유에 대하여 판단하기에는 좀 더 많은 연구가 이루어져야 할 것이며, 주철의 제강공정을 통한 고탄소강의 생산 가능성도 염두에 두어야 할 것으로 사료된다.

• Metals and materials international
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• 제24권6호
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• pp.1394-1402
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• 2018

This study investigates the mechanism of MnS precipitation on $Al_2O_3-SiO_2$ inclusions during the solidification of non-oriented silicon steel, especially the influence of the phase structures and sizes of the oxides on the MnS precipitation, by scanning electron microscopy and transmission electron microscopy coupled with energy dispersive spectrometry. The investigation results show that MnS tends to nucleate on submicron-sized $Al_2O_3-SiO_2$ inclusions formed by interdendritic segregation and that it covers the oxides completely. In addition, MnS can precipitate on micron-sized oxides and its precipitation behavior is governed by the phase structure of the oxides. The MnS embryo formed in a MnO-containing oxide can act as a substrate for MnS precipitation, thus permitting further growth via diffusion of solute atoms from the matrix. MnS also precipitates in a MnO-free oxide by the heterogeneous nucleation mechanism. Furthermore, MnS is less prone to precipitation in the $Al_2O_3$-rich regions of the $Al_2O_3-SiO_2$ inclusions; this can be explained by the high lattice disregistry between MnS and $Al_2O_3$.

• 한국신뢰성학회지:신뢰성응용연구
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• 제15권3호
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• pp.197-206
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• 2015

Failure analysis of pre-insulated pipe (SPPS 380, 400A) transporting high temperature water ($95{\sim}110^{\circ}C$) for a plant was carried out. The damaged area (${\Phi}5mm$) of pre-insulated pipe was found only on welds. The chemical composition of damaged pipe meets specification of carbon steel pipes for pressure service (KS D 3562). As results of microstructure analysis, crack propagated from outer to inside after pitting corrosion occurred on the outside surface. The non-metallic inclusion existed on the end of crack. And the non-metallic inclusion continuously and linearly formed along with the bond line of welds. Based on SEM-EDS analysis, the nonmetallic inclusions have higher Manganese (Mn) and Oxygen (O) content but sulfur (S) was not detected. As results of water quality analysis, hydrogen ion concentration and minerals like Fe, Mg, Si were in low level. But the content of dissolved oxygen (11.2 ppm) was slightly higher than that of standard. It seems that the cause of damaged pipe is grooving corrosion due to MnO inclusion formed on bond line and corrosion took place nearby welds.

• Journal of Welding and Joining
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• 제22권5호
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• pp.58-64
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• 2004

Although leakage at a low carbon steel pipe made by electrical resistance welding (ERW) was reported due to grooving corrosion, the cause for the corrosion has not yet been cleared. In order to clarify the main cause, failure analysis on the leaked pipe was carried out, followed by metallographic investigation and corrosion test for the various ERW pipe made with different welding heat input. The microstructure, particularly inclusion content, of the weldment is dependant on the welding heat input applied. For an improper low heat input, the amount of inclusion at the weld was high. High inclusion content accelerated grooving corrosion at the weld. It is therefore that welding heat input should be controlled based on the carbon content of the pipe in order to improve the corrosion resistance of the ERW pipe.