Critical lower temperature of furnace tube
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What is the critical lower temperature limit of the furnace tube? What’s the use?
At room temperature, the microstructure of carbon steel and chrome-molybdenum steel is 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 – but it seems that’s what you mean based on your description. The normal temperature for an iron-carbon alloy is 727 degrees. The temperature changes after adding alloying elements, usually rising; an accurate value requires measurement, though empirical formulas are generally used for calculation.