What are the critical lower temperature limits for carbon steel and chromium-molybdenum steel?
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I need help with what’s stated in the title: what are the critical lower temperature limits for carbon steel and chromium-molybdenum steel when it comes to the selection of furnace tube materials? And why is it said that austenitic steel has no critical lower temperature limit?
The last edit to this post was made by 15837357920 on 2015-11-17 at 10:54. At room temperature, the microstructure of carbon steel and chromium-molybdenum steel consists of ferrite + pearlite. When heating reaches the lower transformation temperature, the transformation of pearlite into austenite begins; this temperature is the critical lower limit temperature, which should normally be called the lower transformation temperature. However, it seems that this is what you mean based on your description. The normal temperature for an iron-carbon alloy is 727 degrees. The temperature changes after the addition of alloying elements; it generally increases. An accurate measurement is necessary, and in most cases empirical formulas are used for calculation. Austenitic steel remains in the austenite phase at room temperature; generally, the addition of Ni elements expands the austenite region, so it stays in the austenite phase even when heated, with no change occurring, and thus no lower transformation temperature exists.