Martensitic stainless steel is commonly used in the medical implant instrument. The alloy has drawbacks in terms of strength and wear properties when applied to instruments with sharp parts. 440C STS alloy, with improved durability, is an alternative to replace 420 J2 STS. In the present study, the carbide precipitation, and mechanical and corrosion properties of STS 440C alloy are studied as a function of different heat treatments. The STS 440C alloy is first austenitized at different temperatures; this is immediately followed by oil quenching and sub-zero treatment. After sub-zero treatment, the alloy is tempered at low temperatures. The microstructures of the heat treated STS 440C alloy consist of martensite and retained austenite and carbides. Using EDX and SADP with a TEM, the precipitated carbides are identified as a Cr23C6 carbide with a size of 1 to 2 μm. The hardness of STS 440C alloy is improved by austenitization at 1,100 oC with sub-zero treatment and tempering at 200 oC. The values of Ecorr and Icorr for STS 440C increase with austenitization temperature. Results can be explained by the dissolution of Cr-carbide and the increase in the retained austenite. Sub-zero treatment followed by tempering shows a little difference in the properties of potentiodynamic polarizations.

Abstract
1. 서 론
2. 실험방법
    2.1 STS 440C 시편
    2.2 STS 440C의 열처리 공정
    2.3 미세조직 및 결정구조 분석
    2.4 경도 측정
    2.5 동전위 분극 시험
3. 결과 및 고찰
    3.1 미세 조직 특성
    3.2 기계적 특성
    3.3 부식 거동
4. 결 론
References

• 김민구(전남대학교 공과대학 신소재공학부) | Mingu Kim (School of Materials Science and Engineering School, Chonnam National University)
• 이광민(전남대학교 공과대학 신소재공학부) | Kwangmin Lee (School of Materials Science and Engineering School, Chonnam National University) Corresponding author