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Abstract

The present invention discloses a steel for bolts, which comprises the following chemical elements in percentage by mass in addition to Fe and inevitable impurities: C: 0.37 to 0.45%; Si: 0.01 to 0.08%; Mn: 0.45 to 0.80%; Cr: 0.90 to 1.30%; Mo: 0.20 to 0.45%; Ni: 0.10 to 0.30%; V: 0.15 to 0.30%; and Al: 0.015 to 0.035%. The present invention further discloses a method for manufacturing the steel for bolts, which comprises the following steps: (1) smelting; (2) casting; (3) rough rolling; (4) high-speed wire rolling; (5) Stelmor controlled cooling; and (6) heat treatment, wherein the holding temperature of spheroidizing heat treatment is 760 to 790° C. and the holding time is 4 to 12 h, followed by a slow cooling process after the holding with a cooling speed of lower than 40° C./h. The drawing area reduction rate of a coil rod is controlled to 5 to 30%. The heating temperature of quenching and tempering heat treatment is 850 to 950° C. The tempering temperature is 500 to 600° C. The steel for bolts disclosed in the present invention has a uniform structure and performance, has low production costs, and has high strength and good delayed fracture resistance.

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First Claim