超高强度马氏体时效钢的力学行为与微观组织演化的关系

Relationship Between Mechanical Behavior and Microstructure for an Ultra-high Strength Maraging Steel

用高分辨透射电镜(HRTEM)和原子探针层析技术(APT)等手段研究了2.4 GPa级超高强度马氏体时效钢在时效过程中析出相的演化规律及其与材料力学性能的关系。对组织观察的结果表明,马氏体时效钢在时效过程中析出相的演化规律分为三个阶段:时效初期富Ni和富Ti团簇的形成、峰时效期金属间化合物Ni3Ti及其界面处富Mo相的形成、过时效阶段Ni3Ti的粗化和富Mo相过渡为Ni3Mo。力学性能的实验结果表明,随着时效时间的延长抗拉强度呈现先提高后降低的趋势,时效时间为4 h时抗拉强度达到最大值2560 MPa。断裂韧性呈现与抗拉强度相反的变化趋势,时效时间为4 h时的断裂韧性值最低,仅为20 MPa·m1/2。根据不同时效阶段材料中析出相的演化规律,探讨了马氏体时效钢的力学行为与析出相的关系。

Precipitate evolution during aging process as well as its effect on mechanical properties of a 2.4 GPa grade ultra-high strength maraging steel was investigated by means of high resolution transmission electron microscope(HRTEM)and atom probe tomography(APT).It was found that at the initial stage of aging Ni and Ti atoms segregated rapidly and Ni-Ti clusters formed in the matrix.At the peak-aging time the Ni-Ti clusters transformed into Ni3 Ti,and the Mo-rich phase appeared at the Ni3 Ti/matrix interface.With extension of the aging time Ni3 Ti phase started to coarsen and the Mo-rich phase transformed into Ni3 Mo.Mechanical property tests show that the ultimate tensile strength increased firstly and then started to decrease after peak-aging time.A mutually exclusive relation between the ultimate tensile strength and fracture toughness was found,especially,when the aging time was 4 h the ultimate tensile strength reached to the maximum value of 2560 MPa,however the fracture toughness decreased down to the minimum value of 20 MPa·m1/2.Finally,the effect of the morphology of the precipitates on both the strength and fracture toughness is discussed based on the results of the precipitates evolution during aging process.