유동상 침탄시 저탄소 합금강의 침탄능에 미치는 Ni 함량 및 분위기 가스압력의 영향

노용식,김영희,이상윤 ( Y . S . Roh,Y . H . Kim,S . Y . Lee ) 한국열처리공학회 1990 熱處理工學會誌 Vol.3 No.3

This study has been conducted to establish the carburizing characteristics of low carbon alloy steels with varying amount of Ni element gas-carburized for 2hours at 930℃ in an atmosphere of 94% N₂-6% C₃H_8 gas mixture with some changes in gas pressure passing throgh the diffusion plate in the fluidized-bed furnace. The results obtained from the experiment are as followes : (l) Optical micrograph has shown that the carburized layer consists of retained austenite and plate martensite and that retained austenite increases as the pressure of gas mixture passing through the diffusion plate as well as Ni content increase. (2) Chemical analysis has shown that carbon potential increases and carburizability is also improved due to a less degree of fluidization as the pressures of gas mixtures passing through the diffusion plate increase, resulting in, however, a severe formation of soot, and the gas pressure is necessarily regulated. (3) It has been revealed that carbon concentration hardness values at a given distance measured from the surface within the carburized case. Increase with increasing the pressure of gas mixtures passing through the diffusion plate and decrease with increasing Ni content. (4) The effective case depth has been shown to almost linearly increase as the pressure of gas mixtures passing through the diffusion plate is increased and to decrease with increasing Ni content.

질소-프로판-공기분위기에서 저탄소 합금강의 침탄시 내부산화 특성에 미치는 가스조성의 영향

노용식,김성만,김영희,김한군,이상윤 ( Y . S . Roh,S . M . Kim,Y . H . Kim,H . K . Kim,S . Y . Lee ) 한국열처리공학회 1991 熱處理工學會誌 Vol.4 No.4

This study has been performed to investigate into the internal oxidation characteristics of low carbon steel with respect to the added amount of air in nitrogen-propane atmosphere after gas carburizing for various times at 930℃. The results obtained from the experiment are as follows ; (1) Optical micrographs have shown that the internal oxidation is unlikely to occur in the gas atmosphere without air and that oxidized zone in the outer surface layer is formed in the gas atmosphere with air revealing that the depth of oxidized zone increases with increasing the added amount of air. (2) The formation of internally oxidized zone in the outer surface layer has been found to be inhibited as Ni content increases, i, e, the amount of alloying element increases. (3) The depth of oxidation has been measured to increase with almost parabolically gas carburizing time of up to 6 hours.

저 탄소강의 오스테나이트 질화 시 암모니아 가스첨가 조건변화가 표면층 조직 및 기공변화에 미치는 영향

이제원 ( Jewon Lee ),노용식 ( Y. S. Roh ),성장현 ( J. H. Sung ),임수근 ( S. G. Lim ) 한국열처리공학회 2019 熱處理工學會誌 Vol.32 No.5

Low carbon steel (S20C steel) and SPCC steel sheet have been austenitic nitrided at 700℃ in a closed pit type furnace by changing the flow rate of ammonia gas and heat treating time. When the flow rate of ammonia gas was low, the concentration of residual ammonia appeared low and the hardness value of transformed surface layer was high. The depth of the surface layer, however, was shallow. With increasing the concentration of residual ammonia by raising up the ammonia gas flow, both the depth of the surface layer and the pore depth increased, while the maximum hardness of the surface layer decreased. By introducing a large amount of ammonia gas in a short time, a deep surface layer with minimal pores on the outermost surface was obtained. In this experiment, while maintaining 10~12% of residual ammonia, the flow rate of inlet ammonia gas, 7 liter/min, was introduced at 700℃ for 1 hour. In this condition, the thickness of the surface layer without pores appeared about 60 μm in S20C steel and 30 μm in SPCC steel plate. Injecting additional methane gas (carburizing gas) to this condition played a deteriorating effect due to promoting the formation of vertical pores in the surface layer. For 1^st transformed surface layer for S20C steel, maintaining 10~12% residual ammonia condition via austenitic nitriding process resulted in ε phase with relatively high nitrogen concentration (just below 4.23 wt.%N) among the mixed phases of ε+γ. The ε phase was formed a specific orientation perpendicular to the surface. For 2^nd transformed layer for S20C steel, γ phase was rather dominant (just above 2.63 wt.%N). For SPCC steel sheet, there appeared three phases, γ, α(M) and weak ε phase. The nitrogen concentration would be approximately 2.6 wt.% in these phases condition.

업체탐방 : 선일열처리㈜

노용식 ( Y. S. Roh ) 한국열처리공학회 2005 熱處理工學會誌 Vol.18 No.5

복합열처리된 열간 가공용 금형공구강의 기계적 성질 및 열처리특성에 관한 연구

백성돈,노용식,최문성,최진원,이상윤 ( S . D . Beak,Y . S . Roh,M . S . Choi,J . W . Choi,S . Y .Lee ) 한국열처리공학회 1989 熱處理工學會誌 Vol.2 No.4

The effect of gas mixing ratios during gas nitrocarburizing treatment on the formation of compound layer and the mechanical properties has been studied for hot work tool steel by using a combined heat treating technique. The thickness of compound and diffusion layers has been shown to grow as a parabolic relation with increasing the amount of ammonia at a given flow quantity of CO₂gas. The compound layer consists mainly of ε-Fe₃(C, N) with small amounts of γ`-Fe₄N and α-Fe. The combined heat treated hot work tool steel has shown that the thickness of compound layer increases with increasing nitrocarburizing time, but the rate of growth slows down as gas nitrocarburizing time goes more than two hours. Tensile properties have given a remarkable improvement. In particular, the wear resistance of combined heat treated hot work tool steel has exhibited an improvement of about 165% greater than that obtained from conventional quenching and multi-tempering treatments.

플라즈마 질화처리된 중탄소합금강의 내마모특성에 관한 연구

조효석,노용식,신호강,이상윤 ( H . S . Cho,Y . S . Roh,H . K . Shin,S . Y . Lee ) 한국열처리공학회 1992 熱處理工學會誌 Vol.5 No.4

This study has been performed to investigate into some effects of temperature, gas mixing ratio and time on the optical microstructure, hardness and wear characteristics of medium carbon alloy steel treated by plasma nitriding. The results obtained from the experiment are summarized as follows : (1) Optical micrographs of AISI 4140 steel plasma-nitrided by the double stage technique have revealed that the nitrided layer is composed of the compound layer and the diffusion layer. The variation in temperature at the first stage gives effects, on the formation of compound layer and the growth rate is shown to be relatively fast at 460℃. (2) The thickness of compound layer has been found to increase with increasing nitrogen percentage in the gas mixture and the holding time. It is therefore recommended that a shorter holding time and a lower nitrogen percentage are more effective to produce a tougher compound layer and a diffusion layer only. (3) X-ray diffraction analysis for AISI 4140 steel has shown that the compound layer consist of γ`-Fe₄N and α-Fe and that tough compound layer diffustion layer only can be obtained by the double stage plasmanitriding process. (4) There is also a tendency that the total hardened layer depth increases with increasing temperature, time and nitrogen percentage in the first stage during the double stage plasma nitriding. (5) The wear resistance of plasma nitrided specimens has been found thobe considerably increased compared to the untreated specimens and the amount of increment has appeared to increase further with increasing nitriding temperature, holding time and notrogen percentage of gas mixture in the first stage treatment.

15-5PH 스테인리스강의 시효열처리 조건변화가 상변태 및 기계적 성질에 미치는 영향

김태수 ( T. S. Kim ),이제원 ( Jewon Lee ),노용식 ( Y. S. Roh ),성장현 ( J. H. Sung ),임수근 ( S. G. Lim ) 한국열처리공학회 2019 熱處理工學會誌 Vol.32 No.5

This study is to investigate the relationship between microstructural factors and tensile properties after aging heat treatment of the 15-5PH stainless steel at the temperature range of 450℃, 500℃ and 550℃ for various time. For the aging time of 2 hours, hardness showed maximum at 450℃ and then decreased with increasing aging temperature. While, hardness decreased gradually during aging 450℃, 500℃ and 550℃ from 1 hour to 5 hours but the hardness nearly unchanged until the 100 hours after 5 hours aging. When aging at 450℃, Cu atoms preferentially aggregated at the prior austenite grain boundaries and martensite lath boundaries, and Cu concentration at those boundaries was nearly unchanged even after aging for 100 hours. Therefore it was suggested that the coherency is still maintained after 100 hours aging at 450℃. Aging at 500℃ and 550℃ results in an increase in the concentration of Ni at the martensite lath boundaries and prior austenite grain boundaries, resulting in the formation of reversed austenite. Especially, when aged at 550℃ for 100 hours, the concentration of Ni remarkably increased at those boundaries, and thus the microstructure of herring bone shape was appeared. Considering the migration of Ni atom to the lath boundaries and prior austenite grain boundaries, Ni atoms contributed greatly to the formation of reversed austenite. On the other hand, it was found that Cu atoms hardly moving to those boundaries may not be contributed to the formation of reversed austenite. When aging at 450℃, the coarsening of the precipitated Cu atoms proceeded very slowly with increasing aging time, therefore the decrease in strengths were small but the reduction area was considerably increased due to the softening of the matrix. At the aging temperature of 500℃ and 550℃, the strengths decreased and the elongation and reduction area increased due to the appearance of the reversed austenite. Especially, the increase of reduction area was remarkable.