Abstract
The ductility of cobalt-free maraging steel is unsatisfactory because of the high content of Ti. Traditional heat treatment can not effectively improve the ductility of this kind steel. In this contribution, high-energy electro-pulsing is adopted in a T250 steel to solve this problem efficiently. It is found that the EPS treatment (electro-pulsing treatment under water-cooling condition) can accelerate the formation of retained austenite and nano stacking faults. Meanwhile, the microstructure is also refined by EPS treatment. Then, taking the EPS sample as the initial state, nano-reverted austenite combined with finer η-Ni3Ti precipitates are formed during EPA treatment (electro-pulsing treatment under air-cooling condition), compared with TA (traditional aging) treatment. The results of mechanical properties indicate that the strength and elongation are both enhanced by electro-pulsing treatment. Consequently, the electro-pulsing treatment can be a promising technology to devise cobalt-free maraging steel with better properties.
Highlights
Since the 1960s, maraging steels have become irreplaceable materials in navigation and aviation fields by virtue of their excellent strength, toughness, and corrosion resistance [1,2,3]
As for the electro-pulsing treatment (EPS) sample, the corresponding microstructure is mainly comprised of lath-like martensite
The above mentioned results indicate that the martensitic laths and prior austenitic grains of T250 steel are refined by electro-pulsing treatment, and the refined martensite is a consequence of the refined prior austenitic grains [31]
Summary
Since the 1960s, maraging steels have become irreplaceable materials in navigation and aviation fields by virtue of their excellent strength, toughness, and corrosion resistance [1,2,3]. The soft matrix is only the foundation of the advanced mechanical properties of maraging steels and appropriate aging regime must be taken into force to guarantee a huge increment in strength. Some inter-metallic compounds, such as Ni3 Ti and Ni3 Mo with hexagonal crystal structure will be formed, which will lead to the increment in strength [5]. In order to further enhance the strengthening effect, the element cobalt is added to maraging steel for the dynamic interaction between cobalt and molybdenum elements, i.e., the prior positions of molybdenum atoms will be occupied by cobalt atoms so that the precipitation of Ni3 Mo compounds will be promoted [6]
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