铸态Z3CN20-09M双相不锈钢经1200 ℃热锻后,采用400 ℃热老化100、1000、3000 h处理。利用SEM和EBSD分析了铸态及锻态Z3CN20-09M双相不锈钢的显微组织和热老化1000、3000 h的冲击断口,采用纳米力学探针和冲击试验机测试了铸态及锻态Z3CN20-09M双相不锈钢热老化0、100、1000、3000 h微区力学性能和冲击性能。研究表明,经热加工后铁素体晶粒的取向呈现无序态,奥氏体晶粒由粗大的柱状晶经再结晶后变成细小的等轴晶。随热老化时间延长,铸态和锻态材料的冲击功都呈现下降趋势。热老化1000 h,铸态和锻态材料均呈现微孔聚集型断裂,断口出现大量韧窝花样。热老化3000 h,铸态和锻态材料均呈现韧窝/解理混合型断裂特征,铁素体发生脆性解理断裂, 奥氏体以撕裂或呈微孔聚集型断裂。铁素体区域内取向不同导致锻态材料冲击断口解理特征明显少于铸态材料。
Duplex stainless steels are widely used in nuclear industry for their excellent mechanical behavior, good weldability and superior ressistance to corrosion, the fracture toughness of which will be deteriorated with ageing time, as they are exposed to a certain temperature (204~538 ℃). In the present work, hot forging will be employed to induce the change of ferrite grain orientation and refinement of austenite grains; it is expected to improve the impact toughness after long-term thermal ageing. The microstructure and impact surface morphology of Z3CN20-09M duplex stainless steel were investigated by using SEM and EBSD. The micro-mechanical properties and impact properties of Z3CN20-09M duplex stainless steel at different thermal ageing time were tested by a nano-indenter and an instrumented impact tester. The results show that the crystal orientation of ferrite changes obviously and the austenite is changed from the original coarse columnar grains to the fine equiaxed grains after hot working. The im pact toughness of cast materials and forged materials decreases greatly with ageing time. The charpy impact energy of both aged and unaged forged-materials is higher than that of cast material. Cast material and forged material exhibit microvoid coalescence fracture in the early of thermal ageing; after 3000 h thermal ageing, the impact fracture features changes from ductile dimples to brittle cleavages in ferrites and tearings or dimples in austenites. However, cleavage features in forged material are significantly less than those in cast material due to the difference in ferrite crystal orientation.
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