temperature is affecting on the mechanical properties such as strength
Thank you for all ,
please , open attach file from (J.A.Pope" metal fatigue " ,london , Chapman )
It is known that as the temperature increases, the strength of the steel decreases at the expense of increasing plasticity. Excretion does only in the range of up to 100 ° C, where the strength of some steels (doped) increases. This is due to the different thermal expansion of the chemical elements in the steel. The greater the amount of impurities this effect is more pronounced.
I believe that two points need to be clarified in order for your question to be better addressed to:
- Which steel are you referring to?
- When you you say strength, which one is more meaningful to you, yield or tensile strength?
Nevertheless, in the case of you are working with a carbon steel, it is possible that your material is undergoing dynamic strain aging (DSA), which you could perhaps confirm by observing a jerky behavior in the 100°C stress-strain curve. The strength decrease observed on temperatures above 300°C would be related to the decline of DSA and no jerky flow would be observed. In general terms, a thermally activated phenomena might be occurring and increasing your strength at 100°C, and ceases to be active at higher temperatures, thus resulting in the usual decrease of strength.
If you are indeed working with a carbon steel, perhaps this paper could assist you with your doubts:
Li, C-C., and W. C. Leslie. "Effects of dynamic strain aging on the subsequent mechanical properties of carbon steels." Metallurgical Transactions A 9.12 (1978): 1765-1775.
Could you check the results again ? Usually the trend seen is just opposite to what you got. Strength decreases as the temperature increases. Around 300 -500 Blue brittleness prevails which increases the strength, further increase in temp will decrease the strength again.
Dear followers
If we take the diffusion of carbon and/or nitrogen atoms from the solid solution side to dislocations side is responsible mechanism for strength increase on aging up to 250C. Now above this temperature is the process is reversible.
Best regards
Thank you for all ,
please , open attach file from (J.A.Pope" metal fatigue " ,london , Chapman )
This behavior is a well-known phenomenon and is referred to as dynamic strain aging (DSA). It has nothing to do with the mismatch between the thermal expansion of chemical elements in steel, and can occur in high-purity steels, as well. Of course, it highly depends on the type of steel too.
In general, Interstitial atoms (C and N) are mainly the elements that give rise to strain aging. Diffusion of these elements to active dislocations forms a locking atmosphere that hinders further motion of the dislocation. To proceed with plastic deformation, a higher stress level must be achieved in order to free the dislocation from such locking atmosphere. The whole mechanism is diffusion-controlled and is thus a thermally activated process. In the temperature range you mentioned, mobility of interstitial atoms is high enough so they can surpass the dislocation motion. However, at sufficiently high strain rates, dislocation velocity will be higher than the mobility of interstitial atoms so dislocations can escape the locking atmosphere. In other words, DSA is not merely a temperature-dependent phenomenon, but is controlled by a combination of strain rate and temperature.
This was a short and very elementary description of DSA mechanism. The actual process is more complicated than that and there are other contributing factors, as well (e.g. the effect of other elements, intermetallics, etc.). As mentioned by others, you can look for keywords such as ‘strain aging’, ‘dynamic strain aging’, ‘blue brittleness’ and ‘Portevin–Le Chatelier effect’ in steels to get more information about the mechanisms.
Dear Michael Rethmeier ,
can you give more information about what do you mean
Metal has more than one crystal structures, and it will change from one structure to other
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