Study on Strength and Toughness of Secondary Hardening Alloy Steel for a New Generation of Needle-Valve Body
Diesel engine fuel injection system whose operating temperature and injection pressure both are higher needs to be provided with needle-valve body having even higher mechanical properties,corrosion resistance and reliability.The new generation of needle-valve body may be made of secondly hardening alloy steels that have high strength and good thermal stability.Two kinds of 5Cr-Mo-V secondary hardening steels with different chemical compositions were trial-produced by induction melting plus electroslag remelting(IM+ESR),and arc-furnace melting plus electroslag remelting(AFM+ESR),respectively,and were numbered A and B.The steels A and B were tested for hardness,impact toughness and microstructure after being quenched from 1 020 ℃ in gaseous nitrogen then tempered at 200,400,500 and 600 ℃.The results demonstrated that(a)after being quenched and tempered at 600 ℃,the hardness was 49.0 HRC for the steel A and 48.5 HRC for the steel B,the the tensile strength converted from the Rockwell hardness(HRC)was as high as 1 600 to 1 850 MPa,the impact absorption energy was about 400 J,and the microstructure consisted of tempered martensite and carbides for the steels A and B;and(b)an appropriate increase in molybdenum content in the 5Cr-Mo-V steel was enabled to suppress the decomposition of martensite during tempering at a left side temperature of the secondary hardening zone,that is,at 400 ℃,with the result that the tempering resistance of the steel was improved.
needle-valve bodyfuel injection systemsecondary hardeningalloy steelstrength and toughness
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