钢中马氏体在回火转变中所引起的内耗峰

用扭摆测量淬硬碳钢的内耗,当测量温度由室温渐渐升高时,在130℃附近有一个内耗峰出现。当温度达到170℃后再降温测量,这个内耗峰完全消逝不见。上述的现象在含碳0.29％到1.4％的几种淬硬碳钢和淬硬滚珠钢中都曾经看到。由内耗峰的出现可以认为马氏体在第一个回火阶段中的转变产物(ε-碳化铁)与母体具有共格性,由于共格界面的应力感生运动而引起内耗。曾用具有马氏体组织的0.25％碳钢试样作实验,没有观测到上述的内耗峰。但是当回火温度达到280-300℃以后,在降温或升温测量中都观测到一个内耗峰(在150℃附近)。这表示低碳马氏体在第三个回火阶段中的转变产物与母体具有共格性。但是由于这个内耗峰的表现与上述高碳试样的内耗峰不同,所以我们认为这转变产物并不是ε-碳化铁。

INTERNAL FRICTION PEAKS ASSOCIATED WITH THE TEMPERING OF MARTENSITE IN STEELS

Internal friction in hardened carbon steels was measured with a torsion pendulum and an internal friction peak was observed around 130℃ when measurements were taken from room temperature upwards. This peak disappeared completely after the temperature of the specimen reached 170℃. This phenomenon was observed in carbon steels containing carbon ranging from 0.29% to 1.4%, and also in an alloy steel. The appearance of this internal friction peak seems to indicate that the transformation product (ε-carbide) formed in the first-stage tempering of martensite is in coherence with its parent phase, and the origin of internal friction is the stress-induced movement of the plane of coherence.The above-mentioned internal friction peak was not observed in 0.25% carbon steel specimens having a martensite structure. However, after such a specimen has been tempered at a temperature around 300℃, an internal friction peak was observed around 150℃. This indicates that the transformation product formed in martensite containing 0.25% carbon in the third-stage tempering is in coherence with its parent phase. Since the internal friction peak associated with this transformation product behaves differently from that associated with this ε-carbide, so it may be concluded that this transformation product is not ε-carbide.