| In order to improve efficiency of power generation,steam parameters of thermal power generating units are continuously improved.It puts forward more severe tests on the performance of heat-resistant steel.In this paper,Al and Ni is added into the existing mature T/P92 ferritic heat-resistant steel heat-resistant steel.Better high-temperature performance is expected to be obtained by adjusting and optimizing alloy composition.According to the contents of Al and Ni,the four kinds of steels studied in this paper were respectively denoted as A#(0.89 Al,3.64Ni),B#(1Al,1.39Ni),C#(2.93 Al,7.09Ni)and D#(2.86 Al,3.67Ni).After smelting,forging and solution heat treatment,the steel ingots were obtained.Hot-rolled plates of 2mm and 4mm thick and cold-rolled plates of 1mm thick plates were obtained by hot rolling and cold rolling.It was analyzed the evolution of microstructure of the tested steels during hot working process.Compared with the microstructure and performance of four kinds of test steels,the high-temperature mechanical properties were tested.Its mechanism of strengthening was discussed.The main conclusions are as follows.(1)After solution heat treatment,the microstructure of A# is a mixture of mainly martensite and a small amount of ferrite;there are only martensite lath in B#;the microstructure of C# and D# are mainly ferrite and pearlite.In the subsequent hot working process,the microstructure of each group of samples remain unchanged,only change in morphology and quantity.(2)During the hot-working processing,the microhardness of steels are increased accordingly.The order of hardness of rolled steel plates from high to low is B#>C#>D#> A#.The microhardness of B# 1mm cold-rolled sheet reachs the highest value of 550HV;that of C# 1mm cold-rolled plate is second only to B# to 527 HV.(3)The variation law of high-temperature tensile strength and hardness of hot-rolled steel plates is consistent.The strength and plasticity of A# and B# in three groups of 1mm cold-rolled sheets are similar to that of 2mm hot-rolled plates.But because C# has the outstanding second phase strengthening effect,the strength of C# is increased by 68 MPa to 507 MPa compared with its 2mm hot-rolled sheet,which is the highest among the rolled samples.The fracture mode of all rolled specimens in high temperature tensile test is ductile fracture.From what has been discussed above,C# has the most excellent comprehensive properties.Because the cementite of C# has the highest amount of precipitation on ferrite matrix and grain boundary,and the second phase strengthening effect is dominant;Ni also improves its plasticity.These ensure that the strength and plasticity of the three rolling treatments are excellent.The microstructure of A# is martensite and ferrite,which are both weak in strength and plasticity.The microstructure of B# is lath martensite with the best strength but the worst plasticity.The microstructure of D# is ferrite and a small amount of cementite with the poor strength but the best plasticity. |
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