Scientia Sinica

26 SCIENTIA SINICA Vol, V

Temperature (°C)

450 400 350 300 250 200 . 150 100 75 50 25 0.015

0.010

0.005

Internal Friction (Q-!)

EERIG Tie a ae sp a ae ‘ 1000/1 —>

Fig. 6. Internal friction in IIX15 specimen after different heat treatments. Curve I, quenched into oil from 1100°C; curve Il, refrigerated at ~78°C immediately after the treatment in curve I.

These experiments show that the behaviour of the IIXI5 specimen is similar to that of the specimen containing 1.36% carbon. Accordingly, in this alloy steel as well as in carbon steels, the 130°C peak always appears when Martensite 1s present in the specimen and always disappears when the specimen consisting of martensite is tempered at a temperature corresponding to the first-stage tempering. These facts lead to the belief that the 130°C internal friction peak is associated with the transformation of martensite in the firststage tempering of hardened steels.

4. Some experiments on low-carbon martensite (0.25% C).

Ordinary welding-rods containing 0.25% C (determined by carbon analysis) were used as specimens in the experiment. The diameter of the rod is 2:mm. It was treated at 930°C for half an hour and then quenched into 10% brine. Metallographic examinations revealed a martensitic structure in the specimen. The internal friction for this specimen measured with a frequency of vibration of 2 cycles per second is shown by curve I of Fig. 7. The curve remains to be flat up to the temperature of 160°C. The occurrence of the 235°C peak indicates the existence of a state of stress in the specimen induced by quenching. The absence of the 40°C peak indicates the absence of ferrite («Fe) in the specimen.