The Effect of Heat Treatment on the Creep Rupture Strength of Low Carbon 21/4 Cr-1Mo Steel
1973 Volume 59 Issue 8 Pages 1113-1123
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1973 Volume 59 Issue 8 Pages 1113-1123
The creep rupture strength of a 21/4Cr-1Mo steel was studied in relation to preheat treatment and microstructure. Results were summarized as follows:
(1) Creep rupture strength did not always proportional to the strength at room temperature. In the short time range, the creep strength was decreased in the order of the OQ (15mm ∅; bar was quenched into still still oil), the WQ (15 mm ∅; bar was quenched into stirring water), and the FC (furnace cool in 30°C/hr) steel, while in the long time range the order was the FC, the OQ, and the WQ steel.
(2) The greatest creep strength of the OQ steel, in the short time range, was attributable to the following two points;
(i) it contained much more finely dispersed carbides than the FC steel, and (ii) the ratio of needle-like carbides to total number of carbides was higher and the ferrite grains were more stable than in the WQ steel.
(3) The superior creep resistance of the FC steel could be due to the stability of the ferrite grains and the sluggish precipitation of M2C carbides during creep.
(4) The creep stress influenced on the formation of rod-like carbide, the acceleration of softening in quenched steels and the acceleration of spheroidization of pearlite.
From these results, it was concluded that carbides, e3pecially the mode of precipitation of carbides during creep test, played an important role in the creep strength, and the shape of ferrite grains was also important to ensure the microstructural stability at high temperatures, though this effect was in a less degree.
