Effect Of Cu On Microstructure Evolution And Properties Of Double-Stabilized Ferritic Heat-Resistant Stainless Steel

Nb and Ti double-stabilized ferritic heat-resistant stainless steel has the advantages of good heat resistance,excellent corrosion resistance,low coefficient of linear expansion,as well as low cost,and is widely used in automotive exhaust systems,power station boilers and solid oxide batteries.However,in recent years,the strict constraints of energy saving and consumption reduction in the industrial field have continued to put forward higher requirements for the performance of ferritic heat-resistant stainless steel.In this context,the development of high-performance ferritic heat-resistant stainless steel is particularly urgent.In this paper,we use 0Cu and 1.5Cu niobium-titanium dual-stabilized ferritic stainless steel as the object,using light microscopy,scanning electron microscopy,transmission electron microscopy,tensile experiments and thermal fatigue experiments,etc.,to study the effect of Cu addition on the precipitation behavior,room temperature and high temperature mechanical properties of ferritic heat-resistant stainless steel under different aging treatment conditions,to reveal the mechanism of Cu in ferritic heat-resistant stainless steel,in order to provide a certain experimental basis for the development of high performance ferritic heat-resistant stainless steel.stainless steel development to provide some experimental basis.The specific findings of the study are as follows.The 0Cu experimental steel precipitates Fe₂Nb(Laves)phase and niobium-titanium carbides mainly during aging above 700°C.After Cu alloying,the Cu-rich phase precipitates preferentially in the steel in the temperature range of 600 to 800°C,and the Cu-rich phase promotes the formation and refines the size of the Nb-containing phase.The nano-scale Cu-rich phase can be obtained at lower aging temperatures or shorter aging times.The precipitation of Cu-rich phase can significantly improve the hardness of the experimental steel.1.5Cu experimental steel achieves the best age-hardening effect after holding at 600°C for 60 min,with a hardness value of 271 HV,which is 37%higher compared to the solid solution state.At the same time,the 1.5Cu experimental steel also showed good strengthening effect,with tensile strength of 787 MPa,yield strength of 623MPa,and elongation up to 22.1%.The fracture morphology analysis showed that with the increase of aging temperature,the fracture transverse cracks of 0Cu experimental steel increased,the size of tough nests decreased,the tearing characteristics weakened,and the brittleness tendency both increased.the Cu addition intensified the fracture brittleness tendency of experimental steel,promoted the fracture by along the crystal,and reduced the toughness of experimental steel.The high-temperature tensile strength of 0Cu and 1.5Cu experimental steels decreased with increasing temperature,but the elongation increased.In the 600?800°C interval,Cu addition significantly improved the high-temperature strength of the experimental steels.However,the strengthening effect of Cu-rich phase precipitation diminished with increasing temperature.The high-temperature fracture mode of both experimental steels was ductile fracture,but Cu addition reduced the metal mobility.The precipitated phase or nitride is the main source of cracking,but the deleterious effect of these defects diminishes with increasing temperature.the mode of thermal fatigue crack extension of 0Cu and1.5Cu experimental steels changes with increasing upper limit temperature.At 25?700°C thermal cycling,severe intergranular oxidation is present in both experimental steels,and crack extension along grain boundaries increases with increasing cycle cycles.In this temperature range,the Cu element promoted the grain boundary oxidation in the experimental steels,which made the cracks more likely to extend.In the thermal cycling from 25?1000?,the thermal fatigue cracks in both experimental steels appeared to extend through the grain and the intergranular oxidation phenomenon disappeared.The crack width increased significantly with the increase of cycling cycles.The Nb-rich phase precipitation and local oxidation are the main reasons for the thermal fatigue crack extension,and the addition of Cu aggravates the oxide shedding at the crack and reduces the thermal fatigue performance.