• 소성∙가공
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• 제12권4호
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• pp.364-369
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• 2003

Non-heat treated steels are attractive in the steel-wire industry since the spheroidization and quenching-tempering treatment are not involved during the processing. However, non-heat treated steels should satisfy high strength and good formability without performing heat treatment. Therefore, it is important to investigate optimum materials showing a good combination of strength and formability after the drawing process. In this study, three different steels such as dual phase steel, low-Si steel, and ultra low carbon bainitic steel were used to study their mechanical properties and the cold formability. The cold formability of three steels was investigated by estimating the deformation resistance and the forming limit. The deformation resistance was estimated by calculating the deformation energy, and the forming limit was evaluated by measuring the critical strain revealing crack initiation at the notch tip of the specimens. The results showed that deformation resistance was the lowest in the low-Si steel, and the forming limit strains of ultra low carbon bainitic steel and low-Si steel were higher than that of commercial SWRCH45F steel.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2003년도 춘계학술대회논문집
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• pp.307-310
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• 2003

Non-heat treated steels are attractive in the steel-wire industry since the spheroidization and quenching-tempering treatment are not involved during the processing. In this study, three different steels such as dual phase steel, low-Si steel, and ultra low carbon bainitic steel were used to investigate their deformation resistance and forming limit. Deformation resistance was estimated by calculating the deformation energy and the forming limit was evaluated by measuring the critical strain revealing crack initiation at the notch tip of the specimens. The results showed that deformation resistance was the lowest in the low-Si steel, and the forming limit strain was the highest in the ultra low carbon bainitic steel.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.157-158
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• 2002

A surface hardenable low alloy carbon steel was implanted with medium energy (20 - 50KeV) $N_2^+$ ions to produced a modified hardened surface. The implantation conditions were varied and are given in several doses. The surface hardness of treated and untreated steels were measured using depth sensing ultra micro indentation system (UMIS). It is shown that the hardness of nitrogen ion implanted steels varied from 20 to 50GPa depending on the implantation conditions and the doses of implantation. The structure of the modified surfaces was examined by X-ray photoelectron spectroscopy (XPS). It was found that the high hardness on the implanted surfaces was as a result of formation of non-equilibrium nitrides. High-resolution XPS studies indicated that the nitride formers were essentially C and Si from the alloy steel. The result suggests that the ion implantation provided the conditions for a preferential formation of C and Si nitrides. The combination of evidences from nano-indentation and XPS, provided a strong evidence for the existence of $sp^3$ type of bonding in a suspected $(C,Si)_xN_y$ stoichiometry. The formation of ultra hard surface from relatively cheap low alloy steel has significant implication for wear resistance implanted low alloy steels.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2008년도 International Meeting on Information Display
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• pp.247-249
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• 2008

Low Temperature a-Si:H TFT on stainless steel substrate has been developed for the flexible electrophoretic display. Stability of low temperature a-Si:H TFT is more important point than its initial device characteristics. Thus, we have studied device characteristics of low temperature a-Si:H TFT in terms of stability for driving electrophoretic display.

• 한국재료학회지
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• 제11권6호
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• pp.512-518
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• 2001

6.5wt%Si강판을 낮은 철손실, 고투자율 그리고 자왜가 거의 0으로 우수한 자성재료로 잘 알려져 있다. 본 실험에서는 화학기상증착 (Chemical Vapor Deposition)으로 6.5wt%Si 강판을 만들었다 이 과정은 튜브 노내에서 실리콘의 함량이 낮은 Si강판에 SiCl$_4$가스를 반응시킨다. 이때 SiCl$_4$가스에서 분해된 Si의 원자들은 모재인 강판 표면에 증착되어 표면층에 Si가 풍부한 층을 형성한다. 마지막으로 고온에서 확산과정을 통하여 모재 내부로부터 실리콘의 함량이 균일한 강판을 얻을 수 있다. 0.5mm두께를 갖은 6.5wt%Si 강판의 철손실은 고주파수에서 약 8.92W/kg를 나타냈으며 투자율은 53,300으로 일반 실리콘강판, 즉 2.5wt%Si강판의 투자율 37,100보다 약 두배 가량 증가하였다. 또한 기계적인 특성을 평가하기 위해서 일반 0.5wt%Si강판과 773K의 온도에서 수시간 열처리한 강판을 인장실험 하였다. 따라서 수 시간 열처리한 시편에서 연신율이 증가함을 알 수 있었으며 파단면을 관찰한 결과 입 계파단면이 현저히 감소했음을 알았다

• 한국재료학회지
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• 제14권12호
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• pp.863-869
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• 2004

The purpose of this research is to investigate the mechanical property and ductile-brittle transition temperature of Ti-Nb-P added extra low carbon interstitial free steel having a tensile strength of 440 MPa. The mechanical property and transition temperature of hot rolled steel sheets were more influenced by the coiling temperature rather than by the small amount of alloying element. Further, at the same composition, the property of the specimen coiled at low temperature was superior to that obtained at higher coiling temperature. The fracture surface of 0.005C-0.2Si-1.43Mn steel coiled at $630^{\circ}C$ showed a ductile fracture mode at $-100^{\circ}C$, but coiling at $670^{\circ}C$ showed a transgranular brittle fracture mode at $-90^{\circ}C$. The galvannealed 0.006C-0.07Si-1.33Mn steel sheet annealed at $810^{\circ}C$ has tensile strength and elongation of 442.8 MPa and $36.6\%$, respectively. The transition temperature of galvannealed 0.006C-0.07Si-1.33Mn steel sheet was increased with a drawing ratio, and the transition temperature of the galvannealed 0.006C-0.07Si-1.33Mn steel was $-60^{\circ}C$ at a drawing ratio of 1.8

• 열처리공학회지
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• 제25권6호
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• pp.283-291
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• 2012

In order to increase the anti-oxidation property during the tailor welding blanked hot press forming process for a high strength boron steel sheet, we performed a different coating method on the boron-steel sheet such as 87% Al - 13% Si and Fe - 8.87 Zn dipping plating procedure. However, during laser welding process, the Al-Si coated steel sheet has showed a low tensile strength and about half value of elongation than the original boron-steel sheet. Aluminum and silicon, elements of coating layer were diffused into the boron-steel matrix and have shown a low strength result than non-coated specimen. On the other hand, Zinc-coated boron-steel has expectedly showed a excellent tensile strength and micro-harness value in the welded area like original boron-steel.

• 대한금속재료학회지
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• 제49권4호
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• pp.281-290
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• 2011

In order to gain better understanding of the selective surface oxidation and its influence on the galvanizability of a transformation-induced plasticity (TRIP) assisted steel containing 1.5 wt.% Si and 1.6 wt.% Mn, a model experiment has been carried out by depositing Si and Mn (each with a nominal thickness of 10 nm) in either monolayers or bilayers on a low-alloy interstitial-free (IF) steel sheet. After intercritical annealing at $800^{\circ}C$ in a $N_2$ ambient with a dew point of $-40^{\circ}C$, the surface scale formed on 590 MPa TRIP steel exhibited a microstructure similar to that of the scale formed on the Mn/Si bilayer-coated IF steel, consisting of $Mn_{2}SiO_{4}$ particles embedded in an amorphous $SiO_{2}$ film. The present study results indicated that, during the intercritical annealing process of 590 MPa TRIP steel, surface segregation of Si occurs first to form an amorphous $SiO_{2}$ film, which in turn accelerates the out-diffusion of Mn to form more stable Mn-Si oxide particles on the steel surface. During hot-dip galvanizing, particulate $Fe_{3}O_{4}$, MnO, and Si-Mn oxides were reduced more readily by Al in a Zn bath than the amorphous $SiO_{2}$ film. Therefore, in order to improve the galvanizability of 590 TRIP steel, it is most desirable to minimize the surface segregation of Si during the intercritical annealing process.

• 대한금속재료학회지
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• 제50권4호
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• pp.300-309
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• 2012

Low-carbon steels and a stainless steel were oxidized isothermally and cyclically between $1050^{\circ}C$ and $1200^{\circ}C$ for up to 100 min in air to find the effect of alloying elements of Si, Mn, Ni, and Cr on their oxidation. The most active alloying element of Si was scattered inside the oxide scale, at the scale-alloy interface and as internal oxide precipitates beneath the oxide scale. Manganese, which could not effectively improve the oxidation resistance, was rather uniformly distributed in the oxide scale. Nickel and chromium tended to present at the lower part of the oxide scale. Excessively thick porous scales formed on the low-carbon steels, whereas thin but non-adherent scales containing $Cr_2O_3$ formed on the stainless steel.

• 한국진공학회지
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• 제7권1호
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• pp.59-65
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• 1998

13.56MHz를 사용하는 r.f.PACVD(Plasma assisted chemical vapor deposition)방법 으로 다층 다이아몬드상 카본(DLC)필름을 Si wafer기판 위에 합성하였다. 다층 DLC필름은 2.5$\mu$m두께의 순수한 DLC필름과 0.2$\mu$m두께의 Si이 함유된 Si-DLC필름으로 구성되었으 며, ball on disk type의 tribometer를 이용하여 대기 중에서 다층 DLC필름의 마모거동을 고 찰하였다. 표면층으로 합성된 Si-DLC필름내의 Si함량이 증가함에 따라 다층 DLC필름과 AISI52100 steel ball 사이에 0.1 이하의 낮은 마찰계수를 유지하는 기간이 증가하였다. 44,000cycle과 158,400cycle의 마모실험 후 측정된 다층 DLC필름의 마모율은 각각 $2.5\times10^{-8}\sim1.8\times10^{-7}\textrm{mm}^3$/rev.과 $7.1\times10^{-9}\sim1.8\times10^{-8}\textrm{mm}^3$/rev.로 나타났다. 158,400cycle의 마모실험 후 측정된 마모율은 내마모 특성이 우수한 DLC필름보다도 2배 정도 우수한 것으로 나타났 다. 마모시험에 의해 형성된 debris의 조성을 분석한 결과, 이런 낮은 마찰계수와 우수한 내 마모 특성은 steel ball의 wear 표면을 덮고 있는 Si oxide debris층의 형성에 따른 결과로 판단되었다. 또한, 이러한 steel ball의 wear scar표면에 형성된 debris층을 제거하여도, 새로 운 Si oxide debris층이 wear scar표면에 다시 생성되어 낮은 마찰계수를 유지하고 있었다.