Fe-Ni-Mn Maraging Steels: Part Two

요약:

Maraging steels are a special class of low‐carbon ultra‐high‐strength steels which are produced by precisely controlling the amounts of nickel and manganese in the finished material.
The maraging response is highly dependent on the manganese content and at precise levels can produce profound hardness visible through classical age hardening curves as a function of aging temperature and time.

It is well known that Fe-Ni-Mn alloys show remarkable age-hardening behavior in the temperature range from 300 to 500°C. Although age hardening in these alloys has been studied extensively, the identity of precipitate particles in Fe-Ni-Mn alloys remains controversial. The f.c.t. θ-NiMn, b.c.c, β-NiMn, f.c.c. Ni3Mn and an ordered b.c.c. precipitate have been reported. These diversified opinions may be due to a variety of alloy compositions, various heat treatments or uncertainties of identification in electron diffraction analyses. The most common technique has been based on diffraction patterns from extracted precipitate particles. However, there are problems inherent in extraction methods in that lines from inclusions and oxides formed by the extraction solution may obscure the results. It should be noted that all reported results do not provide substantive experimental evidence for the specific precipitates.

In the study of Sung-Joon Kim and C. M. Wayman, the crystallography, the orientation relationship with the matrix and the shape of precipitates have been investigated using thin foil analytical electron microscopy and computer simulation of selected-area diffraction patterns (SADPs) for Fe-20wt.%Ni-Mn alloys.

The alloy compositions of the Fe-Ni-Mn studied are Fe-21.1wt.%Ni-1.27wt.%Mn (alloy A-0) and and Fe-20.8wt.%Ni-3.23wt.%Mn (alloy B-0); alloy A-0 has a lower manganese content than B-0 has.

The maraging response of the alloys investigated in this study was strongly dependent on the manganese content. The higher manganese alloys showed a similar precipitation behavior to that in low nickel Fe-Ni-Mn alloys with classical age hardening curves as a function of aging temperature and time. Fine spherical precipitates appeared first at 400°C aging, followed by the appearance of rod-shaped f.c.t. θ-NiMn and Widmanstätten austenite. Ordered f.c.t. θ-NiMn precipitates were identified using EDX analysis and confirmed by computer simulation of SADPs. The pronounced hardening is associated with the stress required for dislocations to cut through coherent zones or precipitates of spherical precipitates. The orientation relationship between metallic parent matrix and θ-NiMn precipitates is [011]M//[111]θ and (ĺ ĺ 1)M//(ĺ01)θ, whereas that between the martensite and Widmanstiitten austenite is the Kurdyumov-Sachs relation. The shapes of the θ-NiMn precipitates are dependent on the aging temperature. Rod-shaped θ-NiMn 16 precipitates become dominant at lower aging temperatures, while disc-shaped θ-NiMn appears at higher aging temperatures.

Floreen and Decker have shown that in 18 pct Ni maraging steels, the early stages of hardening may be represented by the empirical relationship:

Ht – H0 = ΔH = (Kt)n

where Ht = hardness at time t
H0 = initial hardness
K = constant
n = constant

During investigation of an Fe-12Ni-6Mn maraging alloy a similar behavior was found to occur (see Figure 1). This alloy consists of lath martensite in the air cooled condition and shows pronounced hardening on aging in the temperature range 350°C to 500°C (Figure 2). Hardening is due to precipitation of θ NiMn on dislocations (Figure 3).



Figure 1: Variation of initial hardness increase ΔH with aging time, t, in an Fe-12Ni-6Mn maraging alloy



Figure 2: Age-hardening curves for alloy



Figure 3: Thin foil electron micrograph of overaged alloy


References

1. S-J Kim, C. M. Wayman: Electron microscopy study of precipitates in Fe-Ni-Mn maraging alloys, Volume 136, 30 April 1991, p.121-129, Materials Science and Engineering A-Structure Materials Properties Microstructure and Processing, DOI :10.1016/0921-5093(91)90447-U;

2. D. R. Squires, E. A. Wilson: Kinetics of aging in an Fe-12Ni-6Mn maraging alloy, Metallurgical Transactions A, Vol.15A, October 1984, p.1947-1948.

기술 자료 검색

검색할 어구를 입력하십시오:

검색 범위

본문
키워드

머릿글
요약

Total Materia는 다양한 나라와 규격에 따른 금속학 이미지에 대한 정보를 포함하고 있습니다.

메뉴 표시줄에 특별히 디자인된 금속학 탭을 이용하여, 금속학 데이터가 포함된 관심 재질을 리스트에서 선택하실 수 있습니다.

또한 금속학 데이터는 표준 빠른 검색을 통해 찾을 수 있으며 규격 내 소그룹 페이지를 통해 이용 가능한 관련 자료들이 표시됩니다.

재질명을 '재질'창에 입력하신 후 규격을 알고 계신다면 규격을 선택하고 '검색' 버튼을 클릭합니다.


미세 구조에 대한 일반적인 정보가 관련 관심 재질의 화학 조성과 함께 출력됩니다.


구조의 세부 범위를 보여주는 여러 배율에서의 이미지가 가능하다면 제공됩니다.

다양한 조건을 선택할 수 있으며, '조건 선택' 메뉴를 사용하여 다양한 공정 및 열처리에 따른 금속학 이미지를 보여줍니다.



Total Materia 데이터베이스를 사용해 보실 수 있는 기회가 있습니다. 저희는 Total Materia 무료 체험을 통해 150,000명 이상의 사용자가 이용하고 있는 커뮤니티로 귀하를 초대합니다.