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Liu Z.-B.,Control Iron and Steel Research Institute, China | Yang Z.-Y.,Control Iron and Steel Research Institute, China | Liang J.-X.,Control Iron and Steel Research Institute, China | Zhang L.-N.,Fushun Special Steel Group | Zhang X.-L.,Fushun Special Steel Group
Cailiao Rechuli Xuebao/Transactions of Materials and Heat Treatment | Year: 2010

Precipitation behavior and transformation kinetics of reverted austenite in an ultra-high strength maraging stainless steel was investigated. Based on the characteristics of linear relationship between volume fraction of the reverted austenite and isothermal time during initial stage of aging process, the dynamic curves at the same transformation amount were obtained. The results show that no reverted austenite is observed in the steel when the aging temperature is lower than 450°C, and secondary martensitic transformation occurs when the aging temperature is above 650°C. With the increase of aging temperature, the time for reverted austenite precipitation is shortened. After aging at 540°C for 11.5 min, austenite begins to precipitate, and aging at 540°C for 4 h, 11.0% volume fraction of reverted austenite precipitates in the steel. The strength of the steel aged at 540°C for 4 h reaches up to 1940 MPa, and its fracture toughness (KIC) reaches up to 100 MPa ·m1/2. The thin reverted austenite precipitated at the boundaries of lath martensite and prior austenitic grains improves toughness and plasticity of the steel.

Liu Z.B.,Control Iron and Steel Research Institute, China | Liang J.X.,Control Iron and Steel Research Institute, China | Zhang X.L.,Fushun Special Steel Group | Yang Z.Y.,Control Iron and Steel Research Institute, China | Sun G.Q.,Control Iron and Steel Research Institute, China
Advanced Materials Research | Year: 2014

An alloy chemical composition of a new ultra-high strength stainless has been successfully designed through strengthening mechanisms of carbide and intermetallic compounds. The forging round bar with diameter of 200 mm has been manufactured by means of ultra-high purity smelting and the whole process technologies of micro-unit refinement and phase change control. It was revealed that the developed steel assumes tensile strength of 1960MPa, elongation of 13. 5%, fracture toughness KIC greater than 90MPa·m1/2, and KISCC greater 60MPa·m1/2. Based on the microstructural observation and phase identification, it was found that the M2C and the Laves phase were precipitated in the martensitic laths and a small amount of austenite phase was retained in between the Martensitic lath interfaces, which were related to the improved strength and toughness of the developed steel. Furthermore, it was indicated that the steel also presents high fatigue properties and good high-temperature mechanical properties. The corrosion resistance of the steel is equivalent to that of 15-5PH stainless steel but much better than that of the Aermet100 steel under the condition of the marine atmosphere and sea water immersion. This developed steel can be applied in marine corrosive environment without the surface protection and thus can save the expensive maintenance costs and avoid environmental pollution. Based on the promising properties, it was concluded that the developed steel has wide application prospects in the fields of aviation, aerospace, ships, advanced machinery, and advanced machinery manufacturing and other high-tech. © (2014) Trans Tech Publications, Switzerland.

Liu Z.-B.,Control Iron and Steel Research Institute, China | Liang J.-X.,Control Iron and Steel Research Institute, China | Yang Z.-Y.,Control Iron and Steel Research Institute, China | Gu L.-X.,Aerospace Research Institute of Materials And Processing Technology | And 2 more authors.
Hangkong Cailiao Xuebao/Journal of Aeronautical Materials | Year: 2011

There trial heats of 15-5PH stainless steel in different carbon contents melting by vacuum induction furnace were secured, and by using thermal simulation, best rolling temperature range of 900~1100°C has been gained. The effect of carbon content on transformation temperature and mechanical properties of the steel was studied, and the microstructure of aging were observed. The results showed that, the transformation temperature decreasing with the increasing of carbon content, after aging treatment, the strength of #1 steel was higher than the strength of #2 and #3 steel, and #1 steel also has better ductile plastic; Compare to #1 steel, the formation speed of reverted austenite is faster and amount is more in #2 and #3 steel with aging temperature increasing, this is main reason of the lower strength of #2 and #3 steel. After aging, the microstructure of 15-5PH steel is lath martensite and a few reverted austenite, with large amount of fine precipitates rich in copper, the Cu-rich precipitates are major enhancement patterns of the steel. So we recommend the chemical composition and technical parameters of #1 steel as engineering goal of 15-5PH steel, and provides some data for reference in the industrial production of the steel in the near future.

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