13th International Conference on Fracture June 16–21, 2013, Beijing, China -2- Table 1. Chemical composition (mass%) Grade C Si Mn Ni Mo Co Ti Al Fe 300G 0.005 0.05 0.01 18.47 5.14 9.09 0.89 0.11 Bal. 350G 0.001 0.01 0.01 17.89 4.27 12.36 1.3 0.08 Bal. Table 2. Mechanical properties Steel Aging condition Vickers hardness HV 0.2% proof stress σ0.2 (MPa) Tensile strength σB (MPa) Reverted austenite γ(%) A (300G) 753K,2.8ks 550 1730 1833 0 B (300G) 813K,150ks 550 1634 1798 10 C (350G) 753K,150ks 705 2300 2370 0 Figure 1 shows the aging curves of maraging steels. Aging conditions were determined in such a way that the 300-grade steel was either under-aged or over-aged so that it had nearly the same hardness of 550HV but different structures, while the 350-grade steel was peak-aged and had a hardness of 705HV. The above mentioned ageing conditions are indicated by circles in Fig. 1, respectively. X-ray diffraction detected that only the structure of over-aged steel featured with 10% of reverted austenite. Therefore, the effects of the hardness and the reverted austenite can be examined separately. The under-aged, over-aged and peak-aged 18%Ni maraging steels will be denoted hereafter as Steel A, Steel B and Steel C, respectively. Figure 1. Aging curves of maraging steels 0.1 1 10 100 1000 450 500 550 600 650 700 750 Steel A : 753K,2.8ks Steel B : 813K,150ks Steel C : 753K,150ks Hardness, HV Aging time, t ks
RkJQdWJsaXNoZXIy MjM0NDE=