• 열처리공학회지
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• 제2권4호
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• pp.27-39
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• 1989

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 $CO_2$ gas. The compound layer consists mainly of ${\varepsilon}-Fe_3$(C, N) with small amounts of ${\gamma}^{\prime}-Fe_4N$ and ${\alpha}$-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.

• 한국재료학회지
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• 제12권7호
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• pp.568-572
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• 2002

Plasma sulfnitriding technology was employed to harden the surface of SKD61 steel. The plasma sulfnitriding was performed with 3 torr gas pressure at $580^{\circ}C$ for 20 hours. Plasma sulfnitriding resulted in the formation of very thin $2-3\mu\textrm{m}$ FeS sulfide layer on top of $15-20\mu\textrm{m}$ compound layer, which consisted of predominantly $\varepsilon$- $Fe{2-3}$ N and a second phase of $\Upsilon'-Fe_4$N. In comparision with plasma nitriding treatment, plasma sulfnitriding treatment showed better surface roughness and corrosion resistance due to the presence of the thin FeS layer. which coated microvoids and microcracks on top of the nitrided layer. It was also found that plasma sulfnitrided sample showed better wear resistance due to the presence of the thin FeS layer which acted as a solid lubricant.

• 한국재료학회지
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• 제16권12호
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• pp.766-770
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• 2006

The frictional behavior of oxide films on top of the plasma nitrocarburized compound layers was investigated in terms of post-oxidation treatment temperatures. The post-oxidation treatment at both temperatures($400^{\circ}C,\;500^{\circ}C$) produced magnetite($Fe_3O_4$) films which led to a significant enhancement in corrosion resistance. However, this process did not result in any improvement in frictional behavior of the nitrocarburized surface. The wear mechanisms were governed predominantly by the abrasive action of the slider on the surface irrespective of the counterface material(SiC and Bearing steel). When the specimen was sliding against a SiC counterface, the oxide films were destroyed during the early stage of the sliding process and the wear debris of the oxide film at the sliding track had a great influence on the friction coefficient. On the other hand, when sliding against a bearing steel counterface, the slider was mainly worn out due to the much higher hardness of the surface hardened layer. The fluctuation of the friction coefficient of $400^{\circ}C$-oxidized/ nitrocarburized specimen is much severer than that of $500^{\circ}C$ specimen, due to the less amount of wear debris.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2016년도 제50회 동계 정기학술대회 초록집
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• pp.171.1-171.1
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• 2016

재료의 표면 강화 방법 중의 하나인 질화공정을 이용하여 탄소강 S45C 소재의 질화 거동에 대하여 연구하였다. $520^{\circ}C$ 온도에서 질화 공정을 진행하여 공정시간에 따른 Kn값을 수소 센서로 측정하여 공정시간에 따른 N-potential의 변화와 그에 따른 화합물층 성장 및 화합물층의 상변화에 대해 관찰하였다. 화합물 층의 미세구조 변화는 광학현미경 및 주사전자현미경을 통해 관찰하였다. 가스 질화 처리 후 표면경도는 약 600Hv의 경도값이 측정되었고, 공정 시간이 늘어남에 따라 화합물층 및 경화깊이가 증가되고 표면 화합물이 성장하여 porous가 감소하는 것을 확인 할 수 있다. 경화깊이는 1440분 일 때 약 0.5mm 경화 깊이를 얻었고, 화합물층의 성장은 ${\varepsilon}$상(Fe2-3N)과 ${\gamma}$'상(Fe4N)으로 두 개의 상으로 형성되는 것을 관찰할 수 있었다. 시험 결과를 바탕으로 S45C 소재의 탄소 함량에 따른 lehrer diagram을 열역학 적으로 계산하고 화합물층의 형성 기구에 대해 비교 분석하였다.