Scientia Sinica

No. 1 KE, MA: INTERNAL FRICTION ASSOCIATED WITH TEMPERING OF MARTENSITE 25

brine, the 130°C peak was observed as shown by curve I of Fig. 4. If it was quenched into mineral oil from the same temperature, the 130°C peak was not observed as:shown by curve III. It is to be noticed that in the latter case an internal friction peak was observed around 40°C, a peak known to be associated with the stress-induced micro-diffusion of carbon in @-tron. The appearance of this 40°C peak shows that the specimen contains ferrite. Curve Il of Fig. 4 was observed when the specimen was quenched into 10% brine from 700°C. The curve has no 130°C peak, and the 40°C peak is higher, indicating that the ferrite in the specimen dissolves more carbon in solid solution.

In experiments with 0.25% carbon specimen vacuum-treated at 950°C and quenched into water, a troostite structure was obtained and the internal

Temperature (°C)

Internal Friction (Q-!)

250 200 150 100 75 50 25 0.005 0.004 0.003 0.002 0.001 0 1.9 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 1000/T —>

Fig. 5. Internal friction in 0.25% C specimen (with a troostite structure).

friction curve observed is shown in Fig. 5. The shape of the curve is similar to that of curve II of Fig. 4. Further experiments on 0.25% carbon specimen

will be described in § IV. 3. Experiments on alloy-steel.

A IIXI5 specimen (0.96% C) was oil-quenched from 1100°C and internal friction measured starting at room temperature. Curve I of Fig. 6 was obtained with a frequency of vibration of 1.5 cycles per second. This curve appears to be broadened around 130°C. Another similarly heat-treated specimen was refrigerated at -78°C immediately after the quenching in order to allow the retained austenite in the specimen to transform partly into martensite. The 130°C peak is much more pronounced for this specimen as is shown by curve II of Fig. 6. After the temperature reached somewhere around 170°C, measurements were taken by lowering the temperature. The 130°C peak completely disappeared.