以不含Cu (0Cu)和含1.4%Cu (1.4Cu)的HSLA钢为研究对象，利用OM、SEM、EBSD等技术手段研究了Cu对HSLA合金钢显微组织的影响，利用APT表征了纳米富Cu团簇的析出特征，并通过拉伸和冲击实验测定了合金钢的力学性能。结果表明，淬火态Cu固溶在基体中，经回火后则以富Cu团簇的形式在基体和界面处析出。Cu对回火态HSLA合金钢的原始奥氏体晶粒尺寸、显微组织及有效晶粒尺寸均无明显影响，但对其强度和冲击功影响较大。1.4Cu钢经过450 ℃回火处理后获得最佳强化效果，其屈服强度比0Cu钢提升了143 MPa，此时1.4Cu钢的室温冲击功仅为24 J，断口以河流花样为主，其断裂方式为准解理脆性断裂；而0Cu钢的室温冲击功高达127 J，其断裂方式为韧窝的韧性断裂。APT实验结果表明，2种回火态合金钢的板条界面处均存在C、Cr、Ni、Mn元素的富集。与0Cu钢相比，1.4Cu钢的板条界面处存在大量富Cu团簇，从而导致较大的应力集中，有利于裂纹的萌生，并且板条界面处析出的富Cu团簇会排斥Mo元素，抑制了Mo元素在板条界处的偏聚，相对降低了板条界面处的结合强度，有利于裂纹沿板条界扩展。此外，富Cu团簇在强化基体的同时，也会降低基体的韧性，加快裂纹在基体内的扩展。因而，1.4Cu钢在获得最佳强化效果时其冲击性能较差。

The Cu bearing high strength low alloy (HSLA) steels exhibit high-strength, high toughness and good weldability, which have been widely used in shipbuilding, offshore structures etc. Due to the extremely poor impact energy when attained peak strength, the Cu bearing HSLA steels are usually used at overaged state, which have a good combination of impact energy and strength. In order to clarify the effect of Cu on mechanical properties especially on the impact energy for HSLA steels at peak ageing state, two HSLA steels without Cu (0Cu) and with 1.4%Cu (1.4Cu), were prepared by vacuum induction melting in this study. The influence of Cu on the microstructure of HSLA steel was investigated by OM, SEM and EBSD. Meanwhile, the Cu-riched clusters were characterized by APT and the mechanical properties were measured by tensile test and impact test. The results show that the Cu is completely solid-solutioned into the matrix after quenching, and there are a great number of Cu-riched clusters precipitated in the matrix and boundaries after tempering. Cu element has no obvious effect on the prior austenite grain size, microstructure and effective grain size of tempered HSLA steel, but has significant influence on the strength and impact energy for tempered HSLA steel. After tempered at 450 ℃, the 1.4Cu steel attained the maximum yield strength (1053 MPa), higher than that of 0Cu steel. It is worth noting that the impact energy of 1.4Cu steel tempered at 450 ℃ is only 24 J at room temperature and the impact fracture is a quasi-cleavage brittle fracture mode dominated by river patterns. However, 0Cu steel exhibits a completely ductile fracture mode dominated by dimples at room temperature and the impact energy is 127 J. The APT results show that both 0Cu and 1.4Cu tempered steels have the segregation of C, Cr, Ni, Mn elements at the lath boundary. Compared with 0Cu steel, there precipitate a great number of Cu-riched clusters at the lath boundary for 1.4Cu steel, which will result in the stress concentration and then promote the crack initiation at the lath boundary. In addition, the Cu-rich clusters precipitated at the lath boundary could prevent the Mo segregated at the lath boundary, which will decrease the bonding energy and then promote the crack propagation along the lath boundary. Besides, the negative effect of strengthening due to the Cu-riched clusters at matrix will also accelerate the crack propagation in the matrix, which will decrease the impact energy of 1.4Cu steel. Therefore, the impact energy of 1.4Cu steel is much lower than that of 0Cu steel at room temperature.