Classification of Stainless Steels

Following a classification introduced by Zapffe and later modernized to accommodate new grades, stainless steels can be divided into five distinct classes (see Table 2.20). Each class is identified by the alloying elements that affect their microstructure and for which each is named. These classes are as follows  

In practice, empirical parameters called nickel and chromium equivalents can be utilized to assess the relative stability of austenite and ferrite, respectively. These equivalents are defined as follows  

---

Classification of stainless steels by alloy content and microstructure... 

The use of iron-base metallic sutures started as early as 1666. The most commonly used metallic suture now is stainless steel, which is an alloy of mainly iron, chromium and nickel. However, due to the wide range of possible alloy compositions, the incorporation of trace elements, and fabrications, there are many different grades of stainless steels (Sutow, 1990). The three-digit classification of stainless steel is based upon the main composition in the alloy stipulated by the American Iron and Steel Institute (AISI) ... 

One of the most widely used classifications of stainless steels is based on the Schaeffler diagram. Fig. 1-6 (Schaeffler, 1949). The figure shows the dependence of the structure of high-alloy steels on the chrome- and nickel-equivalent. It is obvious that the chrome-equivalent includes all the ferrite-stabilizing elements and the nickel-equivalent all the austenite-stabilizing elements. For example a high-alloy stainless steel with 25% Ni and 20% Cr has a fully austenitic structure whereas a stainless steel with 18% Cr has a mainly ferritic structure. 

Salt, sodium chloride classification compound. Stainless steel, mix of iron and carbon classification mixture. Tap water, dihydrogen oxide plus impurities classification mixture. Sugar, chemical name sucrose classification compound. Vanilla extract, natural product classification mixture. Butter, natural product classification mixture. Maple syrup, natural product classification mixture. Aluminum, metal classification in pure form—element (sold commercially as a mixture of mostly aluminum with trace metals, such as magnesium). Ice, dihydrogen oxide classification in pure form—compound when made from impure tap water—mixture. Milk, natural product classification mixture. Cherry-flavored cough drops, pharmaceutical classification mixture. 

Table 4.1 Classification of stainless and heat resistant steels...

There are three general classification systems used to identify stainless steels. The first relates to metallurgical structure and places a particular stainless steel into a family of stainless steels. The other two, namely, the AlSl... 

When a block is inside, the entrance panel is closed and the inspection is ready to start. The inside of the stainless steel X-ray tubehead housing is clad in lead with an on/ofT shutter in front of a thin plastic X-ray window. The thin window is to ensure the IP 65 classification. The window is of plastic that is not affected by the cleaning agents. The on/off shutter is interlocked with the entrance and exit panels so X-rays can be kept on at all times without risk of radiation leakage or exposure of the frozen fish blocks prior to the actual inspection. 

Production and Shipment. Estimated adiponitrile production capacities in the U.S. in 1992 were about 625 thousand metric tons and worldwide capacity was in excess of lO metric tons. The DOT/IMO classification for adiponitrile is class 6.1 hazard, UN No. 2205. It requires a POISON label on all containers and is in packing group III. Approved materials of constmction for shipping, storage, and associated transportation equipment are carbon steel and type 316 stainless steel. Either centrifugal or positive displacement pumps may be used. Carbon dioxide or chemical-foam fire extinguishers should be used. There are no specifications for commercial adiponitrile. The typical composition is 99.5 wt % adiponitrile. Impurities that may be present depend on the method of manufacture, and thus, vary depending on the source. 

Units are available in stainless steel or protected mild steel, often prefabricated, up to 12.5 m in diameter, capable of processing >5 m /s depending on the separation efficiency required. When the separator is used for classification of granular soflds, smaller-diameter (<4 m) units are used, separating nearly all particles coarser than - 150 fim. 

The uses of steel are too diverse to be Hsted completely or to serve as a basis of classification. Inasmuch as grades of steel are produced by more than one process, classification by method of manufacture is not advantageous. The most useful classification is by chemical composition into the large groups of carbon steels, alloy steels, and stainless steels. Within these groups are many subdivisions based on chemical composition, physical or mechanical properties, or uses. 

Table 3.11. AISI Classifications of Wrought Stainless and Heat-Resisting Steels (based on AlSl type numbers) [19]...

The corrosivity of soils also depends upon the oxidation-reduction potential as classified by Booth et al.15 The classification scheme of the corrosivity of soils is given in Table 4.4b. Macrogalvanic cells are formed in underground pipelines due to foreign structure the combination of new and old pipe dissimilar metals (stainless steel and carbon steel) differential aeration dissimilar soils and stray currents. All these lead to localized corrosion of underground pipelines. 

---