Proprietăți la temperaturi ridicate Oțel inoxidabil

Stainless steel have good strength and good resistance to corrosion and oxidare 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 schimbător de căldură, super-heaters, cazan, 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 rezistență la tracțiune și rezistența la curgere 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 precipitații, 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).

Precipitarea carburii 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 (Titan 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 oțel inoxidabil 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 duritate și rezistență la tracțiune at room temperature, but retains its desirable proprietăți mecanice at operating temperatures.

Table 1 Short Term Rezistența la tracțiune vs Temperatura (in the annealed condition except for 410)

* tratat termic by oil quenching from 1800° F and tempering at 1200° F

Table 2 Generally Accepted Service Temperatures

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 suprafață 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.

Referințe conexe:
Utilizarea oțelului inoxidabil în condiții de temperatură ridicată consultați tabelul
Tub din oțel inoxidabil rezistent la coroziune
Rezistența la coroziune a tuburilor din oțel inoxidabil
Efectele temperaturii asupra rezistenței metalelor
Tuburi din oțel inoxidabil pentru temperaturi ridicate
Tuburi din oțel inoxidabil pentru temperaturi ridicate
Proprietate la temperaturi ridicate din oțel inoxidabil
Tuburi din oțel inoxidabil rezistente la căldură
Țevi sudate din oțel inoxidabil
Tuburi din oțel inoxidabil cu curbură în U
Tuburi de schimbător de căldură
Tuburi din oțel inoxidabil duplex
Tuburi pentru cazane, tuburi pentru condensator
Tuburi ondulate din oțel inoxidabil fără sudură
DIN 2391 Tuburi din oțel de precizie fără sudură
EN 10305-1 E215 E235 E355 Tuburi fără sudură din oțel de precizie Tuburi Tuburi
Tub din oțel inoxidabil nerezistent la acid
Tuburi din oțel inoxidabil cu recoacere strălucitoare
Standarde pentru tuburi și țevi pentru temperaturi înalte
Schimbarea la temperaturi ridicate Proprietăți mecanice din oțel inoxidabil
Oțeluri inoxidabile rezistente la căldură și oțeluri inoxidabile rezistente la coroziune - oțeluri pentru supape, superaliaje de fier Baes
Riscuri de producere a scânteilor în atmosfere de gaze explozive