Schaeffler diagram

Fig. 8.28 Schaeffler diagram (after Schaeffler and Schneider and Page )...

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. 

It should be mentioned that strictly speaking the Schaeffler diagram is only valid for the welded and non heat treated condition. But nevertheless the diagram is often used for a first orientation about the microstructure of an alloy. In connection with the welding or heat-treatment of stainless steels we must also consider the carbon content of the alloy. Stainless steels can fail because of... 

The relationship between alloying elements and alloy types illustrated in the Schaeffler diagram (Figure 9.1) is an important concept in understanding stainless steels. It has been established that certain elements, specifically chromium, molybdenum and silicon, are ferrite formers. Aluminum and niobium are also ferrite formers, although their effect is dependent on the alloy system. There are also elements that tend to promote the formation of austenite. The most often used are nickel, manganese, carbon, and nitrogen. 

Examination of the Schaeffler diagram offers insight into the reason for the composition of t) e 304, the cornerstone of the austenitic alloy family. After the corrosion resistance plateau of 18% chromium is reached, the addition of about 8% nickel is required to cause a transition from ferritic to austenitic. The primary benefit of this alloy addition is to achieve the austenitic structure that relative to the ferritics, is very tough, formable, and weldable. The added benefit, of course, is the improved corrosion resistance to mild corrodents. This includes adequate resistance to most foods, a wide range of organic chemicals, mild inorganic chemicals, and most natural environmental corrosion. 

Question by L. R. Lucas, University of California Radiation Laboratory Do you use the Schaeffler diagram to estimate... 

F. 3 Schaeffler diagram relationship between alloying element contents and the crystalhte structure of the resulting steel... 

Because the presence of 5 to 10% ferrite in the microstmcture is extremely beneficial, the choice of filler material composition is cmcial in suppressing the risk of cracking. An indication of the ferrite-austenite balance for different compositions is provided by the Schaeffler diagram. For example, when welding Type 304 stainless steel, a Type 308 filler material that has a slightly different alloy content is used. 

Answer by author The Constitution Diagram for Stainless Steel by A, I, Schaeffler provides an estimate of the phases present at room temperature, as determined by the chemical composition equivalents (Ni and Cr). There seems to be no direct corailary between the position of the stainless steel alloy on the Constitution Diagram and the alloys, stability at low temperatures,... 

The stainless steel casting must remain austenitic to be paramagnetic, and therefore the amount of ferrite and martensite, which are magnetic, must be very low. The Schaeffler constitution diagram for stainless steel [3], shown in Fig. 3, shows that the selected steel lies in the austenitic region. 

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