Hot forming or hot working of metals are very common manufacturing and shaping practices in the metallurgy industry. To establish successful metal forming applications, you need to understand the physics behind the flow of metal in deformation processes.
The physics behind the metal deformation processes quite different in cold and hot working processes. The flow characteristics of cold metal in cold metalworking processes are already explained. Here we explain the general parameters affecting the flow of metal in hot metalworking processes. This parameter is called strain rate sensitivity.
With the increasing temperature of metals, the strain hardening effect decreases and one may expect metal will behave like plastic materials. But in high temperatures, there is another phenomenon called strain rate is dominating factor in the deformation capability of the heated metal.
Strain rate is generally expressed as the velocity of deformation of the metal. In most applications, the strain rate seems to be the same as the tool which deforms the heated metal.
We generally know that, with the increasing temperatures, the flow stress decreases. This is why the metals are heated to elevated temperatures in hot working processes.
But at the elevated temperatures, there is another dominating factor on flow stress, which is the strain rate that we explained above. With the increased strain rate of metal, resistance to deformation increases, also the required stress to deform metal increases.
The effect of strain rate on deformation changes metals to metals. So, the effect of strain rate on deformation which is also called strain rate sensitivity changes for different metals. The general equation for each metal can be like this;
At this equation, ‘C’ is the strength constant which can be similar to the strength coefficient in flow stress, but not. ‘m’ is the strain rate, sensitivity exponent. You can find the required stress value to apply to metal at elevated temperatures, due to the strain rate. These coefficients also change with the changing temperature.
This can be a summary of information about the effect of strain rate on the flowability of metals at elevated temperatures.
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