Materials Science and Engineering A 527 (2010) 3057–3063 Contents lists available at ScienceDirect Materials Science and Engineering A journal homepage: www.elsevier.com/locate/msea Study on fatigue property of a new 2.8 GPa grade maraging steel Wei Wang a,c , Wei Yan a , Qiqiang Duan b , Yiyin Shan a , Zhefeng Zhang b , Ke Yang a,∗ a Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China b Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China c Graduate University of Chinese Academy of Sciences, Beijing 10049, China article info Article history: Received 31 August 2009 Received in revised form 9 December 2009 Accepted 1 February 2010 Keywords: Maraging steel Fatigue property S–N curve Fatigue crack abstract A new 2.8 GPa grade maraging steel was developed in the present work and the tension–tension fatigue property of the steel was studied after peak-aging treatment. The results showed that the steel could reach an ultimate tensile strength of 2760 MPa, a fracture toughness of 31.6 MPa m 1/2 , and a fatigue limit of 1150 MPa at stress ratio of 0.1. It was revealed that the fatigue crack initiation of the steel mainly originated from the surface at high stress level but from the interior inclusions at low stress level. From the observations by transmission electron microscope (TEM) and fatigue crack propagation curves, it was proposed that the cyclic softening occurred, which was induced by the resolution as well as the growth of precipitates, and the poor fatigue crack growth resistance and high fatigue crack propagation rate might be the main reason for the relatively low fatigue limit of the steel. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Maraging steels exhibit unique combinations of ultra-high strength and excellent fracture toughness, and are taken as impor- tant material candidates for critical applications such as rocket engine cases, submarine hulls and cryogenic missiles [1–4]. The automobile manufacturers and corresponding component suppli- ers of all over the world have been looking for ultra-high-strength materials for weight reduction or other reasons, in which maraging steel with super-high strength can be considered as a new choice. Except for the high tensile strength, the fatigue property becomes another critical issue to be focused because most of the components often serve under cyclic loading condition. However, regarding to the ultra-high strength of maraging steels, their fatigue strength is found to be far below the expected value which is usually empir- ically predicted by taking half of the ultimate tensile strength of steels. In order to improve the fatigue strength of the maraging steels and hence extend their applications, an effective way is to reduce the content of those elements harmful to the fatigue prop- erty and the relevant fatigue fracture mechanism needs to be deeply investigated [5–7]. In the present work, based on progresses of the previous studies [3,6–8], a new maraging steel with high Ni, Ti and low Mo contents, possessing an ultimate tensile strength up to 2.8 GPa and fracture toughness above 30 MPa m 1/2 , was developed to study its fatigue ∗ Corresponding author. Tel.: +86 24 23971628; fax: +86 24 23971517. E-mail address: [email protected] (K. Yang). behavior after the peak-aging treatment. Additionally, the fatigue fracture mechanism of this maraging steel was also discussed. 2. Experimental procedure The experimental steel was melted in a 300 kg vacuum induction melting furnace at first, and then was remelted in a vacuum arc melting furnace. After homogenization at 1250 ◦ C for 24 h, the ingot was rolled to a cross-section dimension of 55 mm × 55 mm, which was finally forged into rods with 22 mm in diameter followed by air-cooling. The final chemical composition of the steel is listed in Table 1. The specimens for tests were cut from the middle part of the forged rods, and those for tensile and fatigue tests were cut with the load direction in accord with the rolling direction. Specimens were solution treated at 820 ◦ C for 1 h followed by a cryogenic treatment in liquid nitrogen for 1 h to remove the retained austenite, and then were aged at different temperatures and times. Tensile test was carried out with an MTS810 testing machine at a crosshead speed of 2 mm/min, and each result was taken from an average of three tests. For the fatigue test, the frequency was 104 Hz with a sine wave, and the stress ratio was 0.1. The dimension of fatigue specimen is shown in Fig. 1a. The plane strain fracture toughness (K IC ) was measured using three-point bending method in accordance with ASTM E399 specification and the value of K IC was taken from an average of three tests. The dimension of specimen for K IC measurement is shown in Fig. 1b. All the tests were conducted at room temperature in air. Specimens after aging treatment were mechanically ground and polished for microhardness test with load of 500 g and loading 0921-5093/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.msea.2010.02.002
Study on fatigue property of a new 2.8 GPa grade maraging steel
Apr 28, 2023
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