Chrome molybdenum steel tempering brittleness is refers to the long-term in 370 ℃ to 595 ℃ temperature range operation will produce the phenomenon of impact toughness drops.And our common hydrogen-forming equipment works in this temperature range for a long time.According to the experimental results, the annealing embrittlement tendency is the most serious in the commonly used chromal-aluminum steel of pressure vessel, which contains 2%-3% Cr.The influence of elements P, Sb, Sn, As, Si and Mn on the temper brittleness is relatively large.Embrittlement is reversible, severely brittle material that can be de-brittle with proper heat treatment.