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本文通过板坯连铸、钢板控轧控冷(TMCP)、固溶淬火回火(QT)工业生产流程,开发低C含Cu高强韧NV-F690特厚(厚度t为80 mm)船体和海洋平台用钢板.使用SEM,EBSD和TEM分别研究了淬火(Q)态和QT态钢板的精细组织,测试了距离钢板表面t/4处(高冷却速率)和芯部t/2处(低冷却速率)的室温硬度和拉伸性能,在-60和-80℃下进行了Charpy冲击(Charpy V notch,CVN)示波实验.结果表明,淬火速率较大有利于板条组织形成和提高大角度晶界比例,t/4处的组织为板条状贝氏体(LB),板条间存在细小片状马氏体/奥氏体(M/A)组元,晶粒间大角度晶界(>15°)体积分数为67.5%;t/2处的组织为粒状贝氏体(GB)+LB,大角度晶界体积分数为63.0%;Q态下的LB具有高位错密度,但晶粒内不存在Cu析出相.经过650℃回火150 min,钢板的强韧性匹配优良,低温下呈韧性断裂,大量含Cu弥散沉淀相在基体组织内析出.t/2处的M/A组元分解为Cr-Mo碳化物,贝氏体板条宽度为0.4μm,大角度晶界分数为62.5%;t/4处的LB板条回复,板条内存在与基体取向差较大的亚晶,大角度晶界分数提高到71.7%,板条平均宽度为0.2μm.在-80℃下,NV-F690钢板t/4处的韧性高于t/2处的韧性.随着纤维断裂位移的增大,韧窝断裂区比例和韧窝尺寸逐渐增大,NV-F690钢低温Charpy冲击能量逐渐提高.
In this paper, we developed a low-C, high-toughness NV-F690 hull and sea with a thickness of 80 mm through slab continuous casting, TMCP and QT industrial processes. The microstructure of the plate for the plate was studied by means of SEM, EBSD and TEM.The microstructures of quenched (Q) and QT steel were investigated respectively at t / 4 (high cooling rate) and t / 2 (Room temperature) and tensile properties at room temperature, and Charpy V notch (CVN) experiments were carried out at -60 and -80 ℃ .The results show that the larger quenching rate is conducive to the formation of lath and increase the large angle The grain boundary ratio, the tissue at t / 4 is lath-like bainite (LB), and the lamellar martensite / austenite (M / A) (> 15 °) was 67.5%. The microstructure was grained bainite (GB) + LB at t / 2, and the volume fraction of the large-angle grain boundaries was 63.0%. LB in Q state had high dislocation density, There was no precipitation phase of Cu in the grains.After 650 ℃ tempering for 150 min, the strength and toughness of the steel plate matched well, ductile fracture occurred at low temperature, and a large amount of Cu-precipitated phase precipitated in the matrix.M / A group The metathesis is Cr-Mo carbide , The width of bainite lath is 0.4μm and the large-angle grain boundary fraction is 62.5%. The LB lath at t / 4 reverts with the presence of subgrains with large difference in orientation between the laths and the high-angle grain boundaries To 71.7%, and the average width of slats is 0.2μm.The toughness at t / 4 of NV-F690 steel is higher than that at t / 2 at -80 ℃ .With the increase of fiber fracture displacement, dimple fracture zone The proportion and dimple size gradually increased, and the Charpy impact energy of NV-F690 steel gradually increased.