• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2006년도 춘계학술대회 논문집
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• pp.172-175
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• 2006

Effects of deformation at austenite non-recrystallization region and cooling rate on the microstructure and mechanical properties of low carbon (0.06 wt. %) high strength low alloy steels have been investigated. Average grain size decreased and polygonal ferrite transformation promoted with increasing deformation amount due to increase of ferrite nucleation site. As cooling rate increased, the major microstructure changed from polygonal ferrite to acicular ferrite and the fraction of M/A constituents gradually increased. Discontinuous yielding occurred in highly deformed specimen due to the formation of polygonal ferrite. However, small grain size of highly deformed specimen caused lower ductile-to-brittle transition temperature than slightly deformed specimen.

• Journal of Biosystems Engineering
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• 제23권2호
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• pp.187-194
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• 1998

This study was carried out to investigate mechanical properties o major part for agricultural machinery in Korea. The results are as follows ; 1. The mechanical Properties for heat resisting steel bars, alumium alloy castings, carbon steel for machine structural use, chromium molybdenum steels, high strength brass castings and carbon tool steels are proper for Korean standard. 2. The mechanical properties fir spring steels used to mould board, share of plow and blade of rotary are not suitable to Korean standard. Ⅰ think that a counterplan for quality rising is necessary such as supply of good quality materials and improvement of new materials in Korean agricultural machinery.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2005년도 추계학술대회 논문집
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• pp.456-459
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• 2005

Continuous cooling transformation behaviors were studied fur low carbon HSLA steels containing three different level $(1\~3\;wt\%)$ of Ni addition. Thermo-mechanical processing (TMP) simulations to construct continuous cooling (CCT) diagram were conducted by using Gleeble system. As cooling rate increased, pearlite, granular bainite, acicular ferrite, bainitic ferrite and lath martensite were transformed from deformed austenite. Fully bainitic microstructure were developed at all cooling rate condition in high Ni containing steel due to hardenability increasing effects of Ni. Ni also influenced the transformation kinetics. At the slowest cooling rate of $0.3^{\circ}C/s$, transformation delayed with decreasing Ni contents because of the diffusion of substitutional alloy elements. However, cooling rate slightly increased to $1^{\circ}C/s$, transformation kinetics accelerated with decreasing Ni contents because nucleation of bainite was sluggish due to hardening of residual austenite.

• 한국분말야금학회:학술대회논문집
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• 한국분말야금학회 2006년도 Extended Abstracts of 2006 POWDER METALLURGY World Congress Part2
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• pp.933-934
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• 2006

The present study examines the sintering behaviour and effect of manganese addition both mechanically-blended and mechanically alloyed on Cr-Mo low alloyed steels to enhance the mechanical properties. Mn sublimation during sintering provides some specific phenomena which facilitate the sintering of alloying elements with high oxygen affinity. First step is the optimization of milling time to attain a master alloy with 50% of Mn which is diluted in Fe-1.5Cr-0.2Mo water atomized prealloyed powder by normal mixing. These mixtures are pressed to a green density of $7.1g/cm^3$ and sintered at $1120^{\circ}C$ in $90N_2-10H_2$ atmosphere.

• Corrosion Science and Technology
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• 제9권2호
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• pp.67-73
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• 2010

Niobium microalloying is effective in hot-rolled and cold-rolled steels by providing a fine-grained microstructure resulting in increased strength. To optimize the strengthening effect, alloy design and hot-rolling conditions have to be adapted. As a key issue the dissolution and precipitation characteristics of Nb are discussed in particular with regard to the run-out table conditions. It is then considered how the hot-rolled microstructure and the solute state of Nb interact with the hot-dip galvanizing cycle. The adjusted conditions allow controlling the morphology and distribution of phases in the cold-rolled annealed material. Additional precipitation hardening can be achieved as well. The derived options can be readily applied to produce conventional HSLA and IF high strength steels as well as to modern multiphase steels. It will be explained how important application properties such as strength, elongation, bendability, weldability and delayed cracking resistance can be influenced in a controlled and favorable way. Examples of practical relevance and experience are given.

• International Journal of Ocean Engineering and Technology Speciallssue:Selected Papers
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• 제3권1호
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• pp.40-48
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• 2000

The term "deep holes" is used to describe the machining of holes with a relatively large length to diameter ratio. The main feature of BTA deep hole drilling is the stabilization of cutting force necessary for the self guidance of the drill head. An additional feature is the cutting tool edges that are unsymmetrically placed on the drill head. There is an increasing necessity to predict the hole geometry and other dynamic stability behavior of deep hole drilling guidance. In this study, the effects of BTA deep hole drilling conditions on the hole profile machined piece are analyzed using domain analysis technique. The profile of deep hole drilled work piece is related to cutting speed, feed rate, chip flow, tool wear, and so on. This study deals with the experimental results obtained during the BTA drilling on SM45C, SM55C carbon steels and SCM440 steels under various cutting conditions, and these results are compared with analytical evaluations.aluations.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2007년도 춘계학술발표회 초록집
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• pp.114-115
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• 2007

The corrosion characteristics of Cr steels were investigated to protect Cr steels from the SO2-gas corrosion in the coal-fired power plant. The samples tested were low alloy ferritic steel (ASTM T22, 23), martensitic steel (ASTM T91, 92, 122), and austenitic stainless steel (ASTM 347HFG). The corrosion tests were performed between 600oC and 1000oC in Ar + (0.2, 1)%SO2 gas for 100 hr. Chromium was quite beneficial to corrosion resistance, while iron was not. The corrosion resistance increased in the order of T22, T23, T91, T92, T122, and 347HFG.

• 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.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 춘계학술대회 논문집
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• pp.395-399
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• 2004

Four microalloyed steels containing B were investigated in terms of hardenability, mechanical properties and microstructure depending upon the cooling rates in order to develop the steel grade for the cold forged fasners. The alloy with the largest DI value among 4 alloys, which contains $0.12\%\;C,\;1.54\%\;Mn,\;0.65\%\;Cr,\;0.11\%V,\;0.040\%Ti\;and\;0.0033\%B$, showed the larest shift to the right hand side in the TTT diagram, implying the wide allowable cooling rate range subsequent to hot rolling in long bar processing, Mechanical tests indicated that yield strength are dependent upon the DI value in water quenched specimens but other properties showed almost the same values. In the same grade of steel, the increase in cooling rates causes the decrease in elongation but the increase in strength, reduction of area and Charpy impact values. Microstructural examination in steel grade with the larest DI values revealed martensitic structure In the water quenched state, a mixture of martensite and bainite in the oil quenched, and ferrite + pearlite in the air cooled and the forced air cooled but the latter showed finer microstructure.

• Advances in materials Research
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• 제7권3호
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• pp.195-201
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• 2018

High Strength low alloy steels containing various levels of C, Nb and Mn were used and for each of which, a simulated double thermal cycle was applied with the same first peak temperature and different second peak temperatures to produce HAZ microstructure corresponding to multi-pass weld. Effect of double cycle second temperature on the microstructure was observed and compared with single cycle results obtained from previous works, it was found that the percentage of martensite austenite constituent (MA) increases by Nb addition for all steels with the same Mn content and the increase in Mn content at the same Nb content shows an increase in MA area fraction as well. MA area fraction obtained for the double cycle is larger than that obtained for the single cycle for all steels used which imply that MA will have great role in the brittle fracture initiation for double cycle and the inter-pass temperature should be controlled for medium and high-carbon Mn steel to avoid large area fraction of MA. The beneficial effects of Niobium obtained in single pass weld were not observed for the double cycle or multi pass welds.