COMPARISON OF THERMOPLASTICITY BETWEEN Mn-S AND Mn-V-S MICROALLOYED MEDIUM CARBON STEEL
The hot ductility of Mn-S and Mn-V-S microalloyed medium carbon steel under different high temperature conditions was measured by Gleeble-3800 thermal simulation test machine,and the fracture failure mechanism of the two steels in different temperature ranges was analyzed.The results show that the tensile strength of the two kinds of steel decreases the least in the temperature range of 800～850 ℃.The main reason is that the temperature range of 800～850 ℃ is in the partial recrystallization zone,the recrystallization degree increases with the increase of temperature,the grain is further refined and the strength is supplemented.In the temperature range of 850～1 200 ℃,the average tensile strength of Mn-S steel decreases by 53.9 MPa for every 100 ℃ increase.The change of tensile strength of Mn-V-S steel is generally uniform,and the average tensile strength decreases by 53.9 MPa every 100 ℃.In Mn-V-S steel,the second phase particles of vanadium are precipitated below 950℃,which reduces the content of C in solid solution,and the tensile strength is lower than that of Mn-S steel,and the re-dissolution of V occurs above 950 ℃,and the strength of the two tends to be similar.The change of section shrinkage of the two non-tempered steels can be divided into two parts:linear rise and plateau period.Taking 1 000 ℃ as the dividing line,the section shrinkage of Mn-S steel increases slightly with the increase of temperature in the temperature range of 750～850 ℃,while the plasticity increases significantly in the temperature range of 850～950 ℃.The shrinkage rate of steel section is more than 90％in the range of 900～1 200 ℃.The section shrinkage of Mn-V-S steel in the temperature range of 750～1 000 ℃ increases with the temperature more evenly,and the section shrinkage rate is above 90％at 900 ℃,and reaches the highest at 1 200 ℃,with the highest value of 99.4％.The section shrinkage rate of the two steels in the temperature range of 750～850 ℃ is lower than 80％,mainly because the proeutectoid ferrite is distributed in a network along the grain boundary,resulting in stress concentration during stretching.It is recommended to avoid deformation in this temperature range in actual production.
microalloyed medium carbon steelthermoplasticityrecrystallization zonefracture failureproeutectoid ferritedeformation temperature
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