| The purpose of this paper is to obtain a kind of martensitic stainless steel with high strength,high toughness,high hardness,wear resistance and corrosion resistance,which can be applied to 350 o C corrosion environment.In this paper,on the basis of1Cr15Ni3Mo2Cu2W1 VN martensitic stainless steel,by removing molybdenum,tungsten and vanadium elements,adding a small amount of niobium,to improve its performance,a new type of niobium containing high strength and high toughness martensitic stainless steel was developed.Compared with 1Cr16Ni4Cu2 N steel,the influence of Nb on the microstructure,mechanical properties and hot workability of high strength and high toughness martensitic stainless steel were studied by the thermodynamic calculation,quenching,cold treatment,tempering,microstructure observation,chemical phase analysis,mechanical property test and hot compression.Thermodynamic calculation and experimental results showed as following.In equilibrium,the Nb containing steel is only one Z phase more than the Nb free steel,and 0.27% Nb has a slight influence on the ?-ferrite in test steel.Nb has a significant effect on the microstructure refinement of martensitic stainless steel.After quenching and cryogenic treatmen,the amount of retained austenite in the steel is greatly reduced.The tempering temperature has obvious influence on the martensite lath shape of the test steel,when the tempering temperature is high,there are some rod carbides in none Nb steel;there are more dispersed second phase particles in theNb-bearing steel and the boundary of the strip becomes blurred.There is still a small amount of retained austenite in none Nb steel with tempering temperature at 400-470?for 3 hours,when the tempering temperature is 500?,the M23C6 phase appeared in the two kinds of testing steels.With the increasing of tempering temperature,the NbC phase increased in the Nb-bearing steel and the residual austenite content of the two kinds of testing steels were reduced significantly.The room temperature tensile properties of Nb-bearing steel higher than no Nb test steel with tempering temperature at 400-600?.Tensile strength and yield strength of testing steel all increased with tempering temperature at 400-470?.The tensile strength of the two kinds of testing steels were significantly decreased at the tempering temperature more than 470?,the yield strength is decreased rapidly at 470-500?,and it decreases slowly over 500?.The yield strength of Nb-bearing steel containing test and none Nb test steel highest values were 1377 MPa and 1254.5MPa,a difference of122.5MPa.The plasticity and toughness of Nb-bearing steel are higher than that of none Nb steel.The tensile fractures of the two kinds of testing steels at room temperature are belongs to ductile fracture.After tempering at different temperatures,the tensile properties of Nb-bearing steel at 350? were higher than those of none Nb steel,the trend is similar to that of room temperature tensile properties.The yield strength of Nb-bearing steel containing test and none Nb test steel highest values were 1155 MPa and 1030 MPa,a difference of115 MPa.The impact energy at room temperature of the two kinds of testing steels decreases firstly and then increases with the increasing of tempering temperature.However,the hardness value increases firstly and then decreases,when the tempering temperature is 500?,the lowest value appears,the lowest values of Nb-bearing steel and none Nb steel were 24 J and 10 J respectively,and the difference between them was14 J.When the maximumhardness value of the testing steel appeared at 450?,the hardness of the testing steel was reduced linearly with the increasing of tempering temperature,and the hardness of the Nb-bearing steel was higher than that of none Nb steel.Nb bearing steel and none Nb steel the highest hardness values were 49.05 HRC and 46.1HRC,a difference of 2.95 HRC.Hot compression deformation at temperature range from 1000 to 1100 oC,the teststeel is basically in the recovery and partial dynamic recrystallization stage.Under the deformation conditions of 1130-1180 C,70% reduction and 10s-1 strain rate,two kinds of test steel both are in the state of completely dynamic recrystallization.Under the conditions of 1000-1180,10s-1 and 70%,the two kinds of test steels both have good thermal processing properties. |
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