Research On The Thermal Plasticity And Thermal Softening Resistance Of Secondary Hardened Steel M54

The secondary hardening ultra-high strength M4 steel has a great potential in the high-end equipment manufacturing industries attributing to its excellent strength and toughness matching,outstanding stress corrosion resistance,and low cost.However,problem such as cracking after forging has yet to be resolved,and its application can be further extended.This thesis systematically studies the above-mentioned two problems of M54.Firstly,the influence of experimental temperature and strAln rate on M54's hot ductility(rate of reduction in area)was studied by means of Gleeble-1500 D thermal simulator.Secondly,the hot ductility of M54 after continuous forging was simulated through Gleeble-1500 D and the hot ductility was further utilized to evaluate the risk of cracking after forging.Finally,the thermal softening resistance of M54 was studied by high temperature tensile test,expecting to expand the application of M54.The mAln results are as follows:1.Both temperature and strAln rate significantly affect the hot ductility of M54 when the temperature lower than 1000?,.And in this temperature range,the decrease in strAln rate has a significant effect on the deterioration of hot ductility for M54.At a temperature range from 750 ? to 1000 ?,the hot ductility of M54 increases significantly with the rising of temperature;while at 600~750?,the hot ductility of M54 decreases with the increase of temperature.When the temperature is higher than1000 ?,temperature and strAln rate have relatively small influence on the hot ductility of M54.2.The ultimate strength of the M54 steel which has been subjected to secondary tension is mAlnly affected by the second tension,and first tension has a relatively small effect on ultimate strength of the M54 steel.Both first and second tension has an effect on the reduction in area of the secondary tension M54 steel.The higher the tensile temperature of the first tension,is more favorable for dynamic recrystallization to occur,there by increasing the reduction in area and improving the hot ductility.3.Both the strAln rate and the experimental temperature can affect the reduction in area by affecting the way of microcrack propagation,the degree of expansion and the degree of dynamic recrystallization.And reducing the strAln rate or lowering the experimental temperature induces the intergranular brittleness of the tensile specimen.4.If the starting forging temperature is 1100 ? and the final forging temperature is 800 ?,the reduction in area of the M54 forging after the whole continuous forging process is about 63%,which is very close to the brittle zone of steel,and it is prone to cracking after forging.In the continuous forging process,M54 should start at the highest possible temperature.The final forge should be in a high strAln rate to obtAln a better hot ductility,there by reducing the risk of cracking after fracture.5.The thermal softening resistance of M54 is better than the thermal softening resistance of AerMet100 in the temperature range from room temperature to 500 ?.At a temperature range from room temperature to 400 ?,the thermal softening resistance of M54 is slightly higher than that of AerMet100.In the temperature range from 400 ? to 500 ?,the thermal softening resistance of M54 has a significant advantage compared with the thermal softening resistance of AerMet100.