Production Process Practice of 42CrMoM Steel for 12.9 Grade High Strength Wind Power Fasteners

As the national vigorously develops offshore wind power， the power of wind turbines is getting bigger and bigger， and the strength requirements for wind power fasteners are also increased， and high-strength fasteners have been more widely used.Steel grade 42CrMo is widely used in the manufacture of wind power fasteners with good mechanical properties after tempering， but it cannot meet the performance requirements of M64-M72 large size fasteners. For steel grade 42CrMoM with <inline-formula><alternatives><math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M2"><mi>ϕ</mi></math><graphic specific-use="big" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="alternativeImage/3E968021-2D75-4edd-B93A-2C8C4FCEE4B2-M001.jpg"><?fx-imagestate width="2.03200006" height="2.87866688"?></graphic><graphic specific-use="small" xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="alternativeImage/3E968021-2D75-4edd-B93A-2C8C4FCEE4B2-M001c.jpg"><?fx-imagestate width="2.03200006" height="2.87866688"?></graphic></alternatives></inline-formula>72 mm diameter， through "converter →LF refining →RH vacuum treatment → large square billet continuous casting → rolling → inspection， storage" production route， which generate the composition （mass fraction） design as /：0.41%C，0.27%Si，0.53%Mn，0.007%P，0.002%S，1.08%Cr，0.55%Mo，0.02%Cu，0.76%Ni，0.12%V，0.025%Nb，0.024%Al. By controlling tapping temperature at 1 600 ℃-1 680 ℃， continuous casting process adopts electromagnetic stirring and soft reduction technology， the rolling control and cooling control final rolling temperature is about 840 ℃. When the optimum process with quenching temperature 880 ℃+ tempering temperature 630 ℃ is chosen， the mechanical properties of tensile strength 1 282 MPa， yield strength 1 230 MPa， section shrinkage rate 57%， impact energy 62 J at -40 ℃ can be obtained， which meets the performance requirements of M72 12.9 wind power fasteners.