| With the rapid development of cutting-edge technologies, there are new requirements for high-performance equipment and machinery. Then it is necessary to produce higher strength, better toughness parts materials. Therefore, the production of ultra-high strength steel becomes a major hot spot of the scientific development of the material. Maraging steel as a super-fine steel is widely used in the important components of rocket engine shells, missiles and aircraft weapons. The 18NiNb maraging steel in this paper not only has good thermal processing, cold working properties and weldability, but its heat treatment process is also simple.In this paper, using double smelting process of vacuum induction melting (VIM) and electroslag remelting (ESR) to reduce the content of gas, inclusions and harmful elements in maraging steel, improve the organizational structure and uniformity of the steel, enhance its strong toughness. And in order to improve the organization and properties of materials, Nb element was added and the composition ratio of each element of steel was optimized. In the dual-melting process, process parameters suitable for such steel were selected. Two kinds of slag system CaF2: Al2O3: TiO2 = 50:25:25 and slag system CaF2: Al2O3: CaO: TiO2 = 65:20:10:5 were used in electroslag remelting process.The steel composition analysis showed that: the aluminum element had a certain burning in vacuum induction melting; while the Al and Ti had a large degree of burnout in the ESR process. In this paper, the qualitative and rating of non-metallic inclusion in improved 18NiNb maraging steel produced by vacuum induction melting and metallographic method. Results indicated that removing of the larger size of the sulfide and single-particle inclusions in steel by ESR was efficient and the inclusions in steel produced by ESR were mainly small oxide inclusions, of which number decreased significantly, of which distribution were diffuse, and the 18NiNb alloy steel ingot quality was further enhanced.Based on the test and analysis of structure and properties of steel with the ESR and VIM+ESR, as well as that of steel remelted with two kinds of ESR slag, the results showed that: the inclusions and harmful gas are effectively reduced, the density of steel greatly increased, and the grains are refined in the steel after electroslag remelting. Hardness and strength of steel have increased. The hardness and strength of quaternary slag steel is superior to ternary slag steel at the same aging temperature. This is because aluminum, titanium element of the quaternary slag steel burned less and has more precipitations of aging strengthening phase (eg, Ni3Ti, Ni3Mo) than that of ternary slag steel. Therefore, the intensity is higher. |
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