Strong evidences of tempered martensite-to-nitrogen-expanded austenite transformation in CA-6NM steel

Allenstein, A.N.; Cardoso, Rodrigo Perito; Machado, K.D.; Weber, S.; Pereira, K.M.P.; Santos, Celia Aparecida Lino dos; Panossian, Zehbour; Buschinelli, A.J.A.; Brunatto, Sílvio Francisco

doi:10.1016/j.msea.2012.05.075

Cited by 28 publications

(16 citation statements)

References 19 publications

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“…So the present work can open a new and promising field of R&D on heat and thermochemical treatments of high‐hardenability steels. Additionally, since the knowledge on paraequilibrium thermochemical treatments is far from being totally established, even if in technical literature different possibilities of treatments and paraequilibrium phase transformations have been studied—see, for example, studies by Scheuer et al, Allenstein et al, Wu et al, and Za et al [ 4,22–24 ] —the proposed treatment also opens up a new and wide field for scientific research on paraequilibrium phase formation/transformations.…”

Section: Figurementioning

confidence: 99%

A Novel Concept of Hybrid Treatment for High‐Hardenability Steels: Concomitant Hardening and Paraequilibrium Thermochemical Treatment to Produce Interstitially Hardened/Stabilized Austenite Surfaces

Toscano

Cardoso

Brunatto

2020

steel research int.

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Steel components' performance requirements are being strongly increased due to the technological evolution of machines. In most of the cases, surface and bulk material requirements are extremely different, so, an optimised component should present different surface and bulk properties. In such a context, the application of surface engineering processes becomes unavoidable and, to achieve the desired performance at acceptable cost, frequently, new materials and/or processing routes are necessary. The novel concept of hybrid treatment proposed here makes possible to obtain components with such characteristics in a single thermal cycle. So it should be a powerful tool helping to overcome the challenges imposed to the metallurgical industry to produce components that present simultaneously high strength and wear and corrosion resistances at lower costs. This process is the subject of a pending patent BR1020180150758 [1] and this communication has the objective of presenting the new hybrid treatment concept, proving its feasibility by means of a case study. The hybrid process, applicable to highhardenability steels, consists in carrying out a thermochemical treatment during the isothermal step of the martempering or austempering hardening treatment (see Figure 1), above the martensite start temperature and so in the metastable austenite field. Thus, this process combines a surface treatment and a substrate bulk treatment, in a same thermal cycle, probably leading to the reduction of the treatment costs as a whole (hardening plus thermochemical treatment). In addition, it enables to produce a hard interstitially hardened/stabilized austenite treated surface, supposedly presenting higher wear and corrosion resistances than the substrate bulk material. In this concept, depending on the steel hardenability and the chosen processing parameters, the bulk material can be either martensitic or bainitic. The stabilized austenite surface can be produced by paraequilibrium nitriding or carburizing thermochemical treatment. The new concept of hybrid treatment is schematically shown in Figure 1. The first step consists in heating a high-hardenability steel component until the austenitizing temperature, waiting for its complete transformation to stable austenite, and this is the "zero" time point in the Figure 1 scheme. In the sequence, the component/part is cooled down to a temperature that enables the paraequilibrium thermochemical treatment to be conducted, in the metastable austenite field, avoiding the martensitic transformation. The paraequilibrium thermochemical treatment step, in the present case nitriding, is successfully performed at temperatures usually below 420 C for austenitic steels. [2-4] As soon as the paraequilibrium thermochemical treatment step is concluded, the component/part can be cooled down to the room temperature. The last cooling step can produce different microstructure in the component bulk (see Figure 1): 1) for the process ending in "A", a martensitic bulk material will be produced;

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Section: Figurementioning

confidence: 99%

A Novel Concept of Hybrid Treatment for High‐Hardenability Steels: Concomitant Hardening and Paraequilibrium Thermochemical Treatment to Produce Interstitially Hardened/Stabilized Austenite Surfaces

Toscano

Cardoso

Brunatto

2020

steel research int.

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“…Among different surface modification processes, low-temperature plasma-assisted thermochemical treatments of martensitic stainless steels can be successfully employed to achieve this purpose. In this case, good results have been reported by applying plasma nitriding [2,[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21], carburizing [22][23][24], and also nitrocarburizing [6]. Likewise, very promising results were presented in refs.…”

Section: Introductionmentioning

confidence: 88%

Low-temperature plasma nitrocarburizing of the AISI 420 martensitic stainless steel: Microstructure and process kinetics

Anjos

Scheuer

Brunatto

et al. 2015

Surface and Coatings Technology

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“…In nitrided samples, the "diffusion layer" is fairly thin, while it is thicker when nitrocarburizing treatment is performed [78]. In martensitic and martensitic PH stainless steels which are subjected to low-temperature nitriding, expanded austenite can form both from the retained austenite and as a consequence of the transformation of martensite in austenite due to the austenite stabilizing effect of N [83,86,95].…”

Section: Characteristics Of the Modified Surface Layersmentioning

confidence: 99%

The “Expanded” Phases in the Low-Temperature Treated Stainless Steels: A Review

Borgioli

2022

Metals

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Low-temperature treatments have become a valuable method for improving the surface hardness of stainless steels, and thus their tribological properties, without impairing their corrosion resistance. By using treatment temperatures lower than those usually employed for nitriding or carburizing of low alloy steels or tool steels, it is possible to obtain a fairly fast (interstitial) diffusion of nitrogen and/or carbon atoms; on the contrary, the diffusion of substitutional atoms, as chromium atoms, has significantly slowed down, therefore the formation of chromium compounds is hindered, and corrosion resistance can be maintained. As a consequence, nitrogen and carbon atoms can be retained in solid solutions in an iron lattice well beyond their maximum solubility, and supersaturated solid solutions are produced. Depending on the iron lattice structure present in the stainless steel, the so-called “expanded austenite” or “S-phase”, “expanded ferrite”, and “expanded martensite” have been reported to be formed. This review summarizes the main studies on the characteristics and properties of these “expanded” phases and of the modified surface layers in which these phases form by using low-temperature treatments. A particular focus is on expanded martensite and expanded ferrite. Expanded austenite–S-phase is also discussed, with particular reference to the most recent studies.

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Strong evidences of tempered martensite-to-nitrogen-expanded austenite transformation in CA-6NM steel

Cited by 28 publications

References 19 publications

A Novel Concept of Hybrid Treatment for High‐Hardenability Steels: Concomitant Hardening and Paraequilibrium Thermochemical Treatment to Produce Interstitially Hardened/Stabilized Austenite Surfaces

A Novel Concept of Hybrid Treatment for High‐Hardenability Steels: Concomitant Hardening and Paraequilibrium Thermochemical Treatment to Produce Interstitially Hardened/Stabilized Austenite Surfaces

Low-temperature plasma nitrocarburizing of the AISI 420 martensitic stainless steel: Microstructure and process kinetics

The “Expanded” Phases in the Low-Temperature Treated Stainless Steels: A Review

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