COMPOSITE COMPOSITION STEEL FOR HIGH STRENGTH AND HIGH PERCENTAGE OF BOLT HAVING GOOD DELAYED FRACTURE RESISTANCE AND PREPARATION METHOD THEREOF

摘要

Purpose: providing the organized steel of a synthetic for bolt and preparation method thereof, provides bolt, has high intensity, the high percentage of elongation and good delayed fracture resistance. Construction: the composite parts steel for bolt includes: the 0. of (i) carbon4-0.The 2. of 60 wt%, silicone0-4.The 0. of 0 wt%, manganese2-0.8 wt% ; 0.- the 0. of 25 chromium8 wt%, less than the 0. of sulphur01 wt%, less than the 0. of phosphorus01 wt%, the 0. of nitrogen005-0.01 wt% and less than the 0. of oxygen005 wt% ; (ii) at least one, is selected from the 0. of vanadium05-0.The 0. of 2 wt%, niobium05-0.The 0. of 2 wt%, nickel3-2.The 0. of 0 wt%, boron001-0.The 0. of 003 wt%, molybdenum01-0.The 0. of 5 wt%, titanium01-0.The 0. of 2 wt%, tungsten01-0.The 0. of 5 wt%, copper01-0.The 0. of 2 wt% and cobalt01-0.5 wt% ; (iii), the holding of Fe and inevitable impurity, wherein fine composition has the composite parts of the martensite of ferrite and adjusting, and ferritic phase ratio is 8-20%. The method includes: step: (i) control ferritic phase ratio in the phase ratio of 8-20% and austenite in 80-92% by heating composite parts tempering from Ac3-(Ac3-Ac1)/1.3 to Ac3-(Ac3-Ac1)/5.It's 20 minutes past 5 wide-ultras; (ii) it is tempered step (i), by being rapidly allowed to cool in a cooling velocity of 70& degree; In the C/ second of a temperature of 300 600& degree; C more than 20 minutes.