Scientia Sinica

No. 1 KE, MA: INTERNAL FRICTION ASSOCIATED WITH TEMPERING OF MARTENSITE 23

Specimens of low-carbon steel were carburized to have a carbon content of 1.3%, 1.2%, 1.1%, 0.72%, 0.52% and 0.29%. Internal friction measurements with these specimens showed that an internal friction peak was observed around 130°C when the specimen contained martensite, and no 130°C peak was observed when the specimen contained no martensite or when a martensitecontaining specimen was tempered at a temperature above 170°C.

Temperature (°C)

200 180 160 140 120 100 80 60 0.009

0.008 0.007 0.006 0.005

0.004

Internal Friction (Q-!)

0.003

0.002 »

0.001 2 22) 2) 24 25) 26 27) 21829) 7330) 3 1000/1 —>

Fig. 2. Internal friction peak associated with the first-stage tempering of the quenchhardened steel containing 0.72% C (quenched from 910°C). Peak disappeared completely when measurements taken with lowering temperature from 170180°C. (1) 0.72% C—A specimen containing 0.72% carbon was quenched into cold water from 910°C. Metallographic examinations showed that the specimen has a martensitic structure. The internal friction curve for this specimen is shown in Fig. 2, in which a pronounced peak occurs at 130140°C. As measurements were taken up to 170-180°C and then the temperature was lowered, the internal friction peak disappeared completely as shown in the same figure.

(2) 052% C—When a specimen containing 0.52% C was quenched from 910°C so as to have a martensitic structure, the internal friction peak observed was shown by curve I in Fig. 3. The peak is seen to increase again at higher temperatures. When a similar specimen was furnace-cooled from 910°C so as to have a pearlitic structure, curve III was observed without the 130°C peak. This curve remains flat up to 240°C.