| In the 21st century, the high strength of Steel one of the research hotspots, how to improve the strength of the material has become an important research direction for lots of material workers. In this situation, ultra-high strength structural steel has come into being. Among many types of ultra-high strength structural steel, maraging steel is one of them with good overall performance. In overseas, maraging steel has already been widely applied in many advanced fields such as aviation, astronautics as well as the military and so on. However, in domestic the study on the steel is not mature, and the application of it is also relatively few, what is more, it was discovered that the strong plasticity matches of the steel is not very good which makes the application scope of the material to be restricted. To make maraging steel widely used in domestic and to circumvent the foreign standards, the development of new maraging steel becomes particularly important.In this paper, in order to improve the organization and properties of materials, the compositions of the steel was based on the basic 18Ni (250) steel, and an appropriate amount of Nb, B and V alloying element was added separately. Using vacuum induction furnace (VIM) and electro slag re-melt (ESR) double refined ways to reduce the impurity elements of the material. The phase transition temperature of new type of maraging steel of was measured by differential thermal analysis (DTA). Heat treatment on micro-structure and mechanical properties of the new maraging steel was studied. The re-crystallization temperature of austenite was determined by structure analyzing through optical microscopy (OM). Explored the influence ofα'?γcyclical phase transformation refine grain process on the structures properties of new maraging steel.The results showed that: c the mechanical properties of maraging steel with Nb element was superior to the maraging steel with B, V. A large number of banded structure was found in the forging process, such structure has seriously affected the properties of the material, such as anisotropy, lower plasticity, impact toughness and reduction of area. This paper focuses on the internal factors of the banded structure,Through integrated forging process (radial cross upsetting and rolling + axial upsetting and rolling) to enable the banded structure be basically fragmentized and through the appropriate heat treatment (1050℃×2h) made the banded structure of the material fragmentation and alimentation, uniformed the structure and compositions and effectively improved the mechanical properties of the material. addition of minor Nb element can refine grain, so that it made the grain size at solution state reach the ASTM 10.2 grade. After aging treatment, the intermetallic compounds are able to distribute homogeneously, so that the mechanical properties of 18Ni (M250) maraging steel have been improved greatly. The best heat treatment process for the new maraging steel is: 1050℃×2h +820℃×1h +480℃×5h. After this treatment the hardness of the material could be increased to 53.4 (HRC). Tensile strength (σb) = 2270MPa, yield strength (σ0.2)= 2070MPa, elongation (δ) =10%, area reduction ratio (ψ) = 40%.when solution at higher temperature the austenite transformed from martensite could occur recrystallization. The reverted austenite recrystallization temperature of the new maraging steel is about 900℃.α'-γCyclical phase transformation process under about 940℃could be used to refine the grain size from 100um to (10 ~ 20)um.Through analyzed the stucture and mechanical properties of sample showed that the melting process and heat treatment used in the experiment was reasonable, and could be able to meet the needs materials in actual production.
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