Stainless martensitic-ferritic

Hydrogen embrittlement in single-phase austenitic stainless steels has been primarily correlated with two metallurgical variables alloy composition and the presence of second phases, such as ferrite and martensite. Ferrite can be present in austenitic stainless steels as a result of material processing, while martensite can be induced by mechanical straining. Both ferrite and strain-induced martensite render austenitic stainless steels more vulnerable to hydrogen embrittlement. The ferrite... 

Stainless steels are the most widely used alloys for heat and corrosion resistance and low temperature toughness. Wrought stainless steels are named for their metallurgical structure martensitic, ferritic, austenitic, duplex, and precipitation hardening. Cast stainless steels groups are heat resistant and corrosion resistant. 

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

H. Spaehn, Stress corrosion cracking and corrosion fatigue of martensitic, ferritic, and ferritic-austenitic (duplex) stainless steel, in P. Marcus, J. Oudar (Eds.), Corrosions Mechanisms in Theory and Practice, Marcel Dekker, Inc., New York, 1995, pp. 449-487... 

Selection of material. As dealt with in previous sections, conventional stainless steels, with martensitic, ferritic, austenitic or ferritic-austenitic (duplex) structure, are sensitive to crevice corrosion (Table 7.4). Newer high-alloy steels with high Mo content show by far better crevice corrosion properties in seawater and other Cl-containing environments (see Section 10.1). 

Stainless steel contains at least 10.5 % chromium and a maximum of 1.2 % carbon and is therefore per definition high alloyed. Based on their microstructure, stainless steels can be subdivided into ferritic, martensitic, ferritic-austenitic, and austenitic steels. According to their usage properties, stainless steels can be categorized into corrosion-resistant steels, heat-resistant steels, and high-temperature steels (Klocke 2010). 

The five main classes of stainless steels are martensitic, ferritic, austenitic, precipitation-hardenable, and duplex. 

Ferritic stainless steel alloys (i.e., AISI 400 series) exhibit a chromium content ranging from 17 to 30 wt.% Cr but have a lower carbon level, usually less than 0.2 wt.% C, than martensitic stainless steels. Ferritic stainless steels exhibit the following common characteristics ... 

Section 6.7 is dedicated to the recent improvements concerning the knowledge of the long-term fatigue and creep behavior in conventional austenitic stainless steels, stiU in relationship with the specihc in-service conditions of interest for the out-of-core components. The properties of tempered martensite-ferritic steels and conventional austenitic stainless steels can then be compared. The creep resistance of advanced austenitic stainless steels and Incolloy 800 is also discussed in this section. Finally, Section 6.8 sums up the main results of interest and highlights further research works which are required for the design of components of Generation IV reactors. 

Experimental creep failure stress—lifetime curves of the steel 316L(N) are plotted for tests carried out at temperatures between 525 and 700°C (Fig. 6.3). The extrapolation of these curves based on high-stress data leads to overestimated lifetimes. For example, the extrapolation of a curve at 700° C differs by a factor of 10 at low stress with respect to available experimental data. Therefore, long-term creep lifetimes cannot be predicted by the extrapolations based on short-term data. Similar conclusions have been drawn for ferritic-martensitic steels. But it should be highlighted that this transition occurs much earlier in austenitic stainless steels. The comparison of Figs. 6.23 and 6.24 shows that the transition time is about 4 years in austenitic stainless steels but reaches at least 10 years in tempered martensite-ferritic steels. 

In spite of their differences in chemical composition, precipitates, microstructures, etc., similarities in the creep behavior of austenitic stainless steels and tempered martensite-ferritic steels should be noticed such as ... 

The design of thermal power plants and new-generation nuclear reactors has been the reason for carrying out many smdies on the behavior of tempered martensitic steels and austenitic stainless steels subjected to fatigue and/or creep at high temperature (450—650°C). This chapter reviews firstly the numerous recent experimental and simulation works concerning tempered martensite-ferritic steels. Then, creep and fatigue properties of the two steel families are compared on both micro- and macroscales. Finally, recommended further works are mentioned. 

Because their as-received condition microstructure differs strongly from that of tempered martensite-ferritic steels, the stress-strain behavior of austenitic stainless steels differs strongly from that of martensitic steels. During creep and cychc deformation with and without hold time, dislocation production and microstructure are observed, which lead to hardening instead of softening. As creep strain rates in martensitic steels are usually higher than in austenitic stainless steels, necking is... 

Such predictions may provide inputs for fatigue-relaxation damage modeling, which should he based on the synergy between oxidation and oxide layer fracture in tempered martensite-ferritic steels but creep cavitation in austenitic stainless steels. 

Stainless steels, as the name implies, are much more corrosion resistant than ordinary steels. Their primary alloying ingredient is Cr, although they may also contain Ni and Mo. They may be classified into three categories ferritic, austenitic, and martensitic. Ferritic stainless steels (400 series) consist of a-iron with a bcc structure and are magnetic because of the bcc Fe. Heat-treated 440 stainless is one of the hardest stainless steeb and is used for fine cutlery. 

The enhanced strength and corrosion properties of duplex stainless steels depend on maintaining equal amounts of the austenite and ferrite phases. The welding thermal cycle can dismpt this balance therefore, proper weld-parameter and filler metal selection is essential. Precipitation-hardened stainless steels derive their additional strength from alloy precipitates in an austenitic or martensitic stainless steel matrix. To obtain weld properties neat those of the base metal, these steels are heat treated after welding. 

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. 

There are three groups of stainless alloys (I) martensitic, (2) ferritic, and (3) austenitic. 

Times to failure for various stainless steels tested in MgClj have been shown to increase with increasing proportions of martensite present Perhaps the role of martensite under anodic dissolution conditions is comparable to that of ferrite in duplex stainless steels where the enhanced dissolution of one phase prevents crack initiation in the other. There is, of course, another aspect of martensitic transformation that should be mentioned, i.e. the transformation of austenite to martensite either in the bulk material or at a growing crack tip that can give increased susceptibility to... 

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