Stainless steel martensitic type

Fig. 5. Metastable Fe—Ni—Cr "temary"-pliase diagram where C content is 0.1 wt % and for alloys cooled rapidly from 1000°C showing the locations of austenitic, duplex, ferritic, and martensitic stainless steels with respect to the metastable-phase boundaries. For carbon contents higher than 0.1 wt %, martensite lines occur at lower ahoy contents (43). A is duplex stainless steel, eg. Type 329, 327 B, ferritic stainless steels, eg. Type 446 C, 5 ferrite + martensite D, martensitic stainless steels, eg. Type 410 E, ferrite + martensite F, ferrite + pearlite G, high nickel ahoys, eg, ahoy 800 H,...

Martensitic Stainless Steels. The martensitic stainless steels have somewhat higher carbon contents than the ferritic grades for the equivalent chromium level and are therefore subject to the austenite—martensite transformation on heating and quenching. These steels can be hardened significantly. The higher carbon martensitic types, eg, 420 and 440, are typical cutiery compositions, whereas the lower carbon grades are used for special tools, dies, and machine parts and equipment subject to combined abrasion and mild corrosion. 

The martensitic alloys contain 12 to 20 percent chromium with controlled amounts of carbon and other additives. Type 410 is a typical member of this group. These alloys can be hardened by heat treatment, which can increase tensile strength from 550 to 1380 MPa (80,000 to 200,000 Ibf/in ). Corrosion resistance is inferior to that of austenitic stainless steels, and martensitic steels are generally used in mildly corrosive environments (atmospheric, freshwater, and organic exposures). In the hardened condition, these materials are very susceptible to hydrogen embrittlement. 

The four stainless steel types are austenitic ferritic duplex and martensitic. The discovery of stainless steel (12.8% Cr, Fe alloy) is due to the work22 of H. Brearly in 1912. The approximate composition of austenitic and ferritic stainless steels is listed in Table 4.5. 

Allegheny Ludlum Technical Data Blue Sheet Martensitic Stainless Steel Types, 410, 420, 425 Mod and 440A, Allegheny Ludlum Corporation, 1998. 

If the total amount of other metals present in iron exceeds about 5%, the alloy is sometimes called a high-alloy steel. Most stainless steels are in this category because the chromium content is between 10% and 25%, and some types also contain 4% to 20% nickel. Stainless steels, so-called because of their resistance to corrosion, are of several types. The form of iron having the fee structure is known as y-Fe or austenite. Therefore, one type of stainless steel (that also contains nickel) is known as austenitic stainless steel because it has the austenite (fee) structure. Martensitic stainless steels have a structure that contains a body-centered... 

A preliminary approach to the selection of the stainless steel for a specific application is to classify the various types according to the alloy content, microstructure, and major characteristic. Table 3 outlines the information according to the classes of stainless steels-austenitic, martensitic, and ferritic. Table 4 presents characteristics and typical applications of various types of stainless steel while Table 5 indicates resistance of stainless steels to oxidation in air. 

Figure 3 shows the change in the saturation magnetization with strain in Type (A) specimens. It is clear that the saturation magnetization increases with increasing deformation (strain). This is because that the paramagnetic phase in austenitic stainless steels transforms into ferromagnetic a martensite phase by the plastic deformation. It is also found that the saturation... 

Ferrite is essentially pure iron with a body-centered cubic crystal stracture. Ferrite forms from austenite at about 1675°F (915°C), as the austenite cools from a normalizing heat treatment. Because ferrite does not contain enough carbon to permit the formation of martensite, it is not hardenable by heat treatment. The most common truly ferritic steel is Type 405 SS, a ferritic stainless steel. The generic term ferritic steel often refers to carbon or low-alloy steels that contain other phases in addition to ferrite. Such steels are usually hardenable by heat treatment. Ferritic steels become brittle at low temperatures. This phenomenon is reversible, that is, the steels regain their former toughness after being warmed up. Ferritic steels are also susceptible to hydrogen embrittlement. 

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