• Journal of the Korean Society for Heat Treatment
• /
• v.30 no.1
• /
• pp.6-12
• /
• 2017

In this study tensile and impact properties of three hypo-eutectoid steels containing different micro-alloying elements were investigated in terms of microstructural factors such as pro-eutectoid ferrite grain size, pearlite fraction, interlamellar spacing, and cementite thickness. Yield point phenomenon appeared in all the steel specimens during tensile testing, and ultimate tensile stress was mainly dependent on pearlite fraction. On the other hand, the refinement of austenite grain size caused by the addition of micro-alloying elements resulted in the increment of ferrite volume fraction and carbon contents in pearlite because of the refinement of pro-eutectoid ferrite grain size. As a result, cementite thickness in pearlite increased and had an effect on deteriorating the low temperature impact toughness.

• Transactions of Materials Processing
• /
• v.15 no.8 s.89
• /
• pp.609-614
• /
• 2006

Micro-alloyed steels(MA steels) for cold forging was developed to replace the usual quenched and tempered steel. MA steels have several advantages over the conventional quenched and tempered carbon steels. First of all, energy consumption could be lowered due to the elimination of spherodizing annealing and quenching/tempering heat treatment. Also, bending during quenching could be avoided when MA steels are applied for manufacturing of long fastener parts. However, larger amount of load is exerted on the dies compared than in the case of conventional mild steels, which might lead to the earlier fracture of dies, when MA forging steels are applied in forging practice. Therefore, die lift could be a critical factor to determine whether HA forging steels could be widely applied in cold forging practice. In the present study, authors have investigated the forging characteristics of non-heat treated micro-alloyed steel by using a series of experimental and numerical analyses. Firstly, microstructural features and its effect on the deformation behavior have been studied. Numerical analysis has been done on the forging of guide rod pin to investigate for the optimization of forging process and die stress prediction.

• Proceedings of the KWS Conference
• /
• 2009.11a
• /
• pp.110-110
• /
• 2009

본 연구에서는 전산유체역학적 방법을 이용하여 레이저-GMA 하이브리드 용접에서 용융풀 거동에 대한 3차원 과도해석을 수행하였다. 철강재의 주요 합금원소 중 하나인 크롬의 용융풀에서의 거동을 구현하기 위해 크롬에 대해 추가적인 보전 방정식을 도입하였다. 이를 이용하여 합금원소 분포에 대한 용접 변수별 영향을 해석적으로 분석하였으며 이를 EPMA(Electron Probe Micro Analyzer)를 통해 분석한 시험결과와도 비교하였다. 결과적으로 용접변수 중 선행 조건이 합금원소 분포에 구별할만한 영향을 미침을 알 수 있었고 이는 용융풀의 거동을 지배하는 주요 유동 패턴의 상이함에 기인한 것으로 보여진다.

• Corrosion Science and Technology
• /
• v.3 no.3
• /
• pp.112-117
• /
• 2004

This work investigated the material properties of Ni-P-B alloy electrodeposits obtained from a Ni sulfamate bath as a function of the contents of the P and B sources($H_3PO_3$ and dimethyl amine borane complex(DMAB), respectively) with/without additives. Chemical composition, residual stress, microstructure and micro hardness were investigated using ICP(inductively coupled plasma) mass spectrometer, flexible strip, XRD, TEM and micro Vickers hardness tester, respectively. From the results of the compositional analysis, it was observed that P and B are incorporated competitively during the electrodeposition and the sulfur from the additive is codeposited into the electrodeposit. The measured residual stress value increased in the order of Ni, Ni-P, Ni-B and Ni-P-B electrodeposits indicating that boron affects the residual tensile stress greater than phosphorus. As the contents of the alloying element sources of P and B increased, crystallinity and the grain size of the electrodeposit decreased. The effect of boron on crystallinity and grain size was also relatively larger than the phosphorus. It can be explained that the boron with a smaller atomic radius contributes to the increase of residual stress in the tensile direction and the larger restraining force against the grain growth more significantly than the phosphorus with a larger atomic radius. Introduction of an additive into the bath retarded crystallization and grain growth, which may be attributed to the change of the grain growth kinetics induced by the additive adsorbed on the substrate and electrodeposit surfaces during electrodeposition.

• Corrosion Science and Technology
• /
• v.16 no.5
• /
• pp.257-264
• /
• 2017

Film of new Ti-15Zr-5Nb alloy formed during galvanic anodizing in orthophosphoric acid solution was characterized by optical microscope, scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and Raman micro-spectroscopy. Its anticorrosive properties were determined by electrochemical techniques. The film had a layer with nanotube-like porosity with diameters in 500-1000 nm range. The nano layer contained significant amounts of P and O as well as alloying element. Additionally, Raman micro-spectroscopy identified oxygen as oxygen ion in $TiO_2$ anatase and phosphorous as $P_2O_7{^{4-}}$ ion in phosphotitanate compound. All potentiodynamic polarization curves in artificial Carter-Brugirard saliva with pH values (pH= 3.96, 7.84, and 9.11) depending on the addition of 0.05M NaF revealed nobler behavior of anodized alloy and higher polarization resistance indicating the film is thicker and more compact nanolayer. Lower corrosion rates of the anodized alloy reduced toxicity due to less released ions into saliva. Bigger curvature radii in Nyquist plot and higher phase angle in Bode plot for the anodized alloy ascertain a thicker, more protective, insulating nanolayer existing on the anodized alloy. Additionally, ESI results indicate anodized film consists of an inner, compact, barrier, layer and an outer, less protective, porous layer.

• Journal of Technologic Dentistry
• /
• v.23 no.1
• /
• pp.31-43
• /
• 2001

This study was performed to observe the micro-structure change of surface, behavior of oxide change of element, the component transformation of the alloy and the bonding strength between the porcelain interface in order to investigate effects of indium, tin on interfacial properties of porcelain fused to low gold alloy. Hardness of castings was measured with a micro-Vicker's hardness tester. The compositional change of the surface of heat-treated specimen was analyzed with an EDS and an EPMA. The interfacial shear bonding strength between alloy specimen and fused porcelain was measured with a mechanical testing system(MTS 858.20). The results were as follows: 1) The hardness value of alloy increased as increasing amount of indium addition. 2) The formation of oxidation increased as increasing indium and tin contents after heat treatment. 3) Diffusion of indium and tin elements increased as increasing indium and tin contents in metal-porcelain surface after porcelain fused to metal firing. 4) The most interfacial shear bonding strength was increased as increasing a composition of adding elements, and a heat-treatment time, and an oxygen partial pressure. From the results of this study it was found that the addition of alloying elements such as indium and tin increase hardness of as-cast alloy, produce surface oxide layer of adding elements by heat-treatment which may improve interfacial bonding strength between alloy and porcelain.

• Journal of Advanced Marine Engineering and Technology
• /
• v.38 no.9
• /
• pp.1087-1093
• /
• 2014

Stainless steels stabilized with Ti or Nb are largely used in offshore and shipbuilding industries due to its excellent corrosion resistance. In this study, carbide stabilizers, Ti and Nb, were added to stainless steel 304 specimens with different concentrations(Ti: 0.26%, 0.71%, Nb: 0.29%, 0.46%, 0.71%), and their mechanical and electrochemical characteristics were evaluated. Micro-Vickers hardness testing was employed to characterize the mechanical characteristics with alloying elements. Electrochemical evaluation techniques including Tafel analysis, cyclic polarization experiment, galvanostatic experiment were utilized to compare the corrosion characteristics of the specimens. The result of hardness tests revealed that Nb containing specimens showed increasing hardness with increasing alloying contents while adding Ti had little effect on increase in hardness. In the case of electrochemical measurements, the electrochemical characteristics of the specimens were enhanced with increasing Nb contents while they were deteriorated with increasing Ti contents. As a result, different stabilizers and their contents may produce significant differences in electrochemical characteristics, and there such effect must be taken account of in development of stainless steels for marine environment.

• Journal of Powder Materials
• /
• v.27 no.4
• /
• pp.311-317
• /
• 2020

In this study, the effects of Co content on the microstructure and Charpy impact properties of Fe-Cr-W ferritic/martensitic oxide dispersion strengthened (F/M ODS) steels are investigated. F/M ODS steels with 0-5 wt% Co are fabricated by mechanical alloying, followed by hot isostatic pressing, hot-rolling, and normalizing/tempering heat treatment. All the steels commonly exhibit two-phase microstructures consisting of ferrite and tempered martensite. The volume fraction of ferrite increases with the increase in the Co content, since the Co element considerably lowers the hardenability of the F/M ODS steel. Despite the lowest volume fraction of tempered martensite, the F/M ODS steel with 5 wt% Co shows the highest micro-Vickers hardness, owing to the solid solution-hardening effect of the alloyed Co. The high hardness of the steel improves the resistance to fracture initiation, thereby resulting in the enhanced fracture initiation energy in a Charpy impact test at - 40℃. Furthermore, the addition of Co suppresses the formation of coarse oxide inclusions in the F/M ODS steel, while simultaneously providing a high resistance to fracture propagation. Owing to these combined effects of Co, the Charpy impact energy of the F/M ODS steel increases gradually with the increase in the Co content.

• Proceedings of the Korean Institute of Surface Engineering Conference
• /
• 2016.11a
• /
• pp.197-197
• /
• 2016

Commercially pure titanium (CP Ti) and Ti-6Al-4V alloys have been widely used for biomedical applications. However, the use of the Ti-6Al-4V alloy in biomaterial is then a subject of controversy because aluminum ions and vanadium oxide have potential detrimental influence on the human body due to vanadium and aluminum. Hence, recent works showed that the synthesis of new Ti-based alloys for implant application involves more biocompatible metallic alloying element, such as, Nb, Hf, Zr and Mo. In particular, Nb and Hf are one of the most effective Ti ${\beta}-stabilizer$ and reducing the elastic modulus. Plasma electrolyte oxidation (PEO) is known as excellent method in the biocompatibility of biomaterial due to quickly coating time and controlled coating condition. The anodized oxide layer and diameter modulation of Ti alloys can be obtained function of improvement of cell adhesion. Manganese(Mn) plays very important roles in essential for normal growth and metabolism of skeletal tissue in vertebrates and can be detected as minor constituents in teeth and bone. Radio frequency(RF) magnetron sputtering in the various PVD methods has high deposition rates, high-purity films, extremely high adhesion of films, and excellent uniform layers for depositing a wide range of materials, including metals, alloys and ceramics like a hydroxyapatite. The aim of this study is to research the Mn coatings on the micro-pore formed Ti-29Nb-xHf alloys by RF-magnetron sputtering for dental applications. Ti-29Nb-xHf (x= 0, 3, 7 and 15wt%, mass fraction) alloys were prepared Ti-29Nb-xHf alloys of containing Hf up from 0 wt% to 15 wt% were melted by using a vacuum furnace. Ti-29Nb-xHf alloys were homogenized for 2 hr at $1050^{\circ}C$. Each alloy was anodized in solution containing typically 0.15 M calcium acetate monohydrate + 0.02 M calcium glycerophosphate at room temperature. A direct current power source was used for the process of anodization. Anodized alloys was prepared using 270V~300V anodization voltage at room. Mn coatings was produced by RF-magnetron sputtering system. RF power of 100W was applied to the target for 1h at room temperature. The microstructure, phase and composition of Mn coated oxide surface of Ti-29Nb-xHf alloys were examined by FE-SEM, EDS, and XRD.