The effect of grain size on the tensile defomation behaviour of 1 and 3wt% Si-Fe alloys was studied over the temperature range from 25° to 800°C at strain rates of 10
-5 and 11/sec. The relations between the grain size and yield stress or flow stress at a given straln in both alloys were approximately represented by the Hall-Petch equation over the experimental range. The yield behaviour in both alloys was discussed to be separated into the following four temperature regions; (1) the low temperature deformation region below 300°C, (2) the athermal deformation region between 300° and 500°C, (3) the region of yielding phenomenon between 500° and 700°C, and (4) the high-temperature deformation region above 700°C.
The value of friction stress for yielding, σ
o, and its temperature and strain rate sensitivities in the region (3) increased with increasing Si content. For both alloys was also observed a new yielding phenomenon in the region (3). The apparent activation energy for this yielding was unchanged with Si content and about 93kcal/mol, and the activation area was changed with it, i. e. 170-200 bb
2 in 1% Si alloy and 70-100 bb
2 in 3% Si alloy.
The grain size dependnce of flow stress in the regions (3) and (4) was comlicated with the change of temperature and strain. This behaviour was explained qualitatively in terms of the modified work hardening model. The change in steady-state or maximum flow stress, σ
M, with Si content was almost the same to that of σ
o, and then the internal stress developed during defbrmation, σ
i (σ
M-σ
o) was considered to be nearly constant regardless of the Si content.
These results indicated that the high-tmeperature deformation mechanism in the two Si alloys was different from that of pure iron, and during the deformation the dislocation glide was considered to play an important role.
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