Martensite, iron-carbon alloys

M. Izaki and T. Omi, Structural Characterization of Martensitic Iron Carbon Alloy Eilms Electrodeposited from an Iron (II) Sulfate Solution, Metallurgical... 

Metallurgy was one of the first fields where material scientists worked toward developing new alloys for different applications. During the first years, a large number of studies were carried out on the austenite-martensite-cementite phases achieved during the phase transformations of the iron-carbon alloy, which is the foundation for steel production, later the development of stainless steel, and other important alloys for industry, construction, and other fields was produced. 

Koistinen, D.P. Marburger, R.E. (1959). A general equation prescribing the extent of the austenite-martensite transformation in pure iron-carbon alloys and plain carbon steels. Acta Metall., Vol. 7,59-60. 

The concept of a sohd solution was also discussed. One form of solid solution in an iron-carbon alloy, or steel (martensite), derives its high strength and hardness from the formation of an interstitial solid solution (carbon dissolved in iron). The following concept map represents this relationship ... 

Yet another microconstituent or phase called martensite is formed when austenitized iron-carbon alloys are rapidly cooled (or quenched) to a relatively low temperature (in the vicinity of the ambient). Martensite is a nonequilibrium single-phase structure that results from a diffusionless transformation of austenite. It may be thought of as a transformation product that is competitive with pearlite and bainite. The martensitic transformation occurs when the quenching rate is rapid enough to prevent carbon diffusion. Any diffusion whatsoever results in the formation of ferrite and cementite phases. 

The martensitic transformation is not, however, unique to iron-carbon alloys. It is found in other systems and is characterized, in part, by the diffusionless transformation. 

The alloy that is the subject of Figure 10.21 is not an iron-carbon alloy of eutectoid composition furthermore, its 100% martensite transformation temperature hes below room temperature. Because the photomicrograph was taken at room temperature, some austenite (i.e., the retained austenite) is present, having not transformed to martensite. 

Figure 10.22 The complete isothermal transformation diagram for an iron-carbon alloy of eutectoid composition A, austenite B, bainite M, martensite P, pearlite.

With regard to the representation of the martensitic transformation, the M(start), M(50%), and M(90%) lines occur at identical temperatures for both isothermal and continuous-cooling transformation diagrams. This may be verified for an iron-carbon alloy of eutectoid composition by comparison of Figures 10.22 and 10.25. 

We now discuss the mechanical behavior of iron-carbon alloys having the microstructures discussed heretofore—namely, fine and coarse pearlite, spheroidite, bainite, and martensite. For all but martensite, two phases are present (ferrite and cementite), and so an opportunity is provided to explore several mechanical property-microstructure relationships that exist for these alloys. 

For iron-carbon alloys, in addition to discussions of the heat treatments that produce the several microconstituents (fine/coarse pearlite, bainite, martensite, etc.) and their mechanical properties, correlations were made between mechanical properties and structural elements of these microconstituents. These correlations are indicated in the following concept map ... 

Mechanical Behavior of Iron-Carbon Alloys Tempered Martensite... 

FE On the basis of the accompanying isothermal O transformation diagram for a 0.45 wt% C iron-carbon alloy, which heat treatment could be used to isothermally convert a microstructm-e that consists of proeutectoid ferrite and fine pearlite into one that is composed of proeutectoid ferrite and martensite ... 

An important item in this array of matenals is the class known as maraging steels. This group of high nickel martensitic steels contain so Htde carbon that they are often referred to as carbon-free iron—nickel martensites (54). Carbon-free iron—nickel martensite with certain alloying elements is relatively soft and ductile and becomes hard, strong, and tough when subjected to an aging treatment at around 480°C. 

Unalloyed White Iron Low-Alloy White Iron Martensitic White Iron (Ni-hard) High-Carbon, High-Chromium, White Iron... 

The martensitic stainless steels are iron-chromium alloys with greater than 10.5% chromium which can be hardened by suitable cooling to room temperature following a high-temperature heat treatment. Because of the low chromium content and high carbon content the corrosion resistance of martensitic stainless steels is limited compared with other stainless steels. On the other hand martensitic stainless steels are hardenable and exhibit high strength and hardness. These steels are relatively low-cost alloys. 

Materials such as metals, alloys, steels and plastics form the theme of the fourth chapter. The behavior and use of cast irons, low alloy carbon steels and their application in atmospheric corrosion, fresh waters, seawater and soils are presented. This is followed by a discussion of stainless steels, martensitic steels and duplex steels and their behavior in various media. Aluminum and its alloys and their corrosion behavior in acids, fresh water, seawater, outdoor atmospheres and soils, copper and its alloys and their corrosion resistance in various media, nickel and its alloys and their corrosion behavior in various industrial environments, titanium and its alloys and their performance in various chemical environments, cobalt alloys and their applications, corrosion behavior of lead and its alloys, magnesium and its alloys together with their corrosion behavior, zinc and its alloys, along with their corrosion behavior, zirconium, its alloys and their corrosion behavior, tin and tin plate with their applications in atmospheric corrosion are discussed. The final part of the chapter concerns refractories and ceramics and polymeric materials and their application in various corrosive media. 

Strong Attraction Steels carbon, alloy, tool Cast Irons gray, ductile, malleable Cobalt Nickel Stainless Steels ferritic, duplex, martensitic, martensitic precipitation hardening... 

Corrosion of Stainless Steels in Acids Stainless steels are iron-based alloys with chromium as the main alloying element. The most interesting alloys for technical applications are ferritic stainless steels, austentic stainless steels, and duplex stainless steels. The distinction between the stainless steels comes from their different crystallographic structures. Ferritic-martensitic stainless steels and martensitic stainless steels have less nickel and a higher carbon content and can be hardened by heat treatment. The corrosion behavior of these steels is mainly influenced by the formation of carbides, which generally increase the corrosion rate. 

Main crystalline constituents in carbon steels are ferrite, cementite, perlite, and, depending on heat treatment, bainite and martensite. Below approximately 723 °C, austenite in carbon steels is transformed into perlite and, according to the carbon content, ferrite or cementite. Thus, austenite is only present at room temperature in alloyed steels and not in carbon steels. The iron-carbon phase diagram shows the metallographic constitution for unalloyed carbon steels depending on the carbon content and the temperature. Fig. 2. 

Nik] Nikolin, B.I., Makogon, Yu.N., e -Martensite in Carbon-Free Iron Manganese Alloys with Copper (in Russian), Akad. Nauk Ukr. SSR, Metallofizika, 74, 103-105 (1978) (Electr. Prop., Crys. Structure, Experimental, 8)... 

Izo] Izotov, V.I., Khandarov, P.A., Structural Features of the Martensitic Transformation in Iron-Manganese-Carbon Alloys , Phys. Met. Metall., 32, 138-144 (1971) (Crys. Structure, Experimental, 16)... 

Ben] Benabder, A., Faivre, R, Influence of Formation and Decomposition of Low-Temperature Carbides on Graphitisation of Some Iron-Carbon-Silicon Alloys after a Martensitic-Type Quench (in French), Mem. Sci. Rev. Metall, 65(4), 309-315 (1968) (Experimental, Crys. Stmcture, Morphology, 15)... 

Physical metallurgy is a rather wide field of applications of Mossbauer spectroscopy and it is possible to enumerate only the main topics phase analysis, order-disorder alloys, surfaces, alloying, interstitial alloys, steel, ferromagnetic alloys, precipitation, diffusion, oxidation, lattice defects etc. Alloys are well represented by the iron-carbon system, the mechanism of martensite transformation, high-manganese and iron-aluminium alloys, iron-silicon and Fe-Ni-X alloys. 

Lys] Lysak, L.I., Drachinskaya, A.G., Storchak, N.A., Influenee of Austenite Ordering on the Martensitic Transformation in Iron-Alxuninixun-Carbon Alloys , Fiz. Met. Metalloved., 34(2), 107-114 (1972) (Crys. Structure, Experimental, 20)... 

The first iron—nickel martensitic alloys contained ca 0.01% carbon, 20 or 25% nickel, and 1.5—2.5% aluminum and titanium. Later an 18% nickel steel containing cobalt, molybdenum, and titanium was developed, and still more recentiy a senes of 12% nickel steels containing chromium and molybdenum came on the market. 

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