Propriétés à haute température de l'acier inoxydable

Stainless steel have good strength and good resistance to corrosion and oxydation at elevated temperatures. Stainless steel are used at temperatures up to 1700° F for 304 and 316 and up to 2000 F for the high temperature stainless grade 309(S) and up to 2100° F for 310(S). Stainless steel is used extensively in échangeur de chaleur, super-heaters, chaudière, feed water heaters, valves and main steam lines as well as aircraft and aerospace applications.

Figure 1 gives a broad concept of the hot strength advantages of stainless steel in comparison to low carbon unalloyed steel. Table 1 shows the short term résistance à la traction et limite d'élasticité vs temperature. Table 2 shows the generally accepted temperatures for both intermittent and continuous service.

With time and temperature, changes in metallurgical structure can be expected with any metal. In stainless steel, the changes can be softening, carbide précipitations, or embrittlement. Softening or loss of strength occurs in the 300 series (304, 316, etc.) stainless steel at about 1000° F and at about 900° F for the hardenable 400 (410<, 420, 440) series and 800° F for the non-hardenable 400 (409, 430) series (refer to Table 1).

Précipitation du carbure can occur in the 300 series in the temperature range 800 – 1600° F. It can be deterred by choosing a grade designed to prevent carbide precipitation i.e., 347 (Cb added) or 321 (Titane added). If carbide precipitation does occur, it can be removed by heating above 1900° and cooling quickly.

Hardenable 400 series with greater than 12% chromium as well as the non-hardenable 400 series and the acier inoxydable duplex are subject to embrittlement when exposed to temperature of 700 – 950° F over an extended period of time. This is sometimes call 885F embrittlement because this is the temperature at which the embrittlement is the most rapid. 885F embrittlement results in low ductility and increased dureté et résistance à la traction at room temperature, but retains its desirable propriétés mécaniques at operating temperatures.

Table 1 Short Term Résistance à la traction vs Température (à l'état recuit sauf pour 410)

* traité thermiquement by oil quenching from 1800° F and tempering at 1200° F

Table 2 Generally Accepted Service Températures

It may seem to be illogical that the “continuous” service temperature would be higher than the “intermittent” service temperature for the 300 series grades. The answer is that intermittent service involves “thermal cycling”, which can cause the high temperature scale formed to crack and spall. This occurs because of the difference in the coefficient of expansion between the stainless steel and the scale. As a result of this scaling and cracking, there is a greater deterioration of the surface than will occur if the temperature is continuous. Therefore the suggested intermittent service temperatures are lower. This is not the case for the 400 series (both ferritic and martensitic grades). The reason for this is not known.

Références connexes :
Utilisation de l'acier inoxydable dans des conditions de haute température (voir tableau)
Tube en acier inoxydable résistant à la corrosion
Résistance à la corrosion des tubes en acier inoxydable
Effets de la température sur la résistance des métaux
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Tube ondulé en acier inoxydable sans soudure
DIN 2391 Tubes d'acier de précision sans soudure
EN 10305-1 E215 E235 E355 Tube en acier de précision sans soudure Tubes
Tube en acier inoxydable non résistant aux acides
Recuit brillant Tubes en acier inoxydable
Normes sur les tubes et tuyaux à haute température
Propriétés techniques de l'acier inoxydable à haute température
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