V-ti-n High-strength Weathering Profile Development,

Anti-atmosphere steel is also called atmospheric corrosion resisting steel. It is an important kind of metal materials. When compared with stainless steel, anti-atmosphere steel is more economical and is extensively used in steel structures such as civil work, vehicles, tower frame, container etc. Starting from Cor-Ten steel, which is a kind of low alloy steel containing Cu successfully developed by an American company called U. S. Steel in 1930s, anti-atmosphere steel has been under constant development. Eighty years of research and practice proves that anti-atmosphere steel itself does not resist atmospheric corrosion, it is the compact rust layer initially developed on the steel that has the power to resist atmospheric corrosion. Recently, the focus of research of anti-atmosphere steel has been shifted to how to improve the mechanical properties of anti-atmosphere steel. All steel makers are bent on researching how to produce higher strength anti-atmosphere steel so as to widen the use of this kind of steel.Since there is always a lack of high strength products in section steels, this paper puts forward a test proposal to produce high strength anti-atmosphere steel by appropriately increasing the amount of Mn in the series of Cr-Ni-Cu steels with low P, making the full use of Mn's reinforcement ability in solidification, meanwhile adding micro alloys of V, Ti, N to comprehensively improve the formation of fine grain. To probe the effects of Mn, V, Ti, N etc. in improving the strength, first, 150kg of anti-atmosphere steel is smelted in middle-frequency induction furnace in lab, then poured in three times into ingots, adding Fe-Mn alloys before each pouring. Ingots is then forged into 0 20mm round bars so as to study Mn's effects on anti-atmosphere steel; Second, anti-atmosphere steel is smelted again in middle-frequency induction furnace with V added after Mn has been increased by 1.4%, then poured into 50kg ingots and then forged into 0 20mm round bars too; Finally it comes the time for industrial test in which Pangang's smelting process is adopted to produce continuously-cast anti-atmosphere steel blooms which are subsequently surface-dressed, reheated and then rolled into 310 Z shaped steel through two-stage transversely arranged rolling mill. Normal mechanical property tests, atmospheric corrosion resisting test, weldability test and time validity test are then conducted.Test results and analysis show: for the series of Cr-Ni-Cu steels with low P, if Mn is increased by 0.80%, the yield strength (R_el) of these anti-atmosphere steels can be improved by 80Mpa or so. However, excessive Mn has adverse effects on low temperature impact toughness and weldability. The increase of Mn is only helpful for producing anti-atmosphere steels whose yield strengths are lower than 400Mpa. Adding V without increasing N in steels can only produce high strength anti-atmosphere steels whose yield strengths are between 400～450Mpa. However, adding V and minor Ti with N controlled between 0.010%～0.018% in steels can only produce high strength anti-atmosphere steels whose yield strengths are more than 450Mpa. When alloys of V, Ti, N are added in anti-atmosphere steels, N exists in steels in compound form rather than in dissociated form, and this would not influence the time validity of steels. The great amount of V (CN) or produced in V-Ti-N anti-atmosphere steels is the base for fine grain formation. VN attaches to tiny MnS inclusions, forming the core of ferrite. This improves the formation of ferrite inside grains, giving the grains of anti-atmosphere steel chances to be fully fine-grained. Fine grain level can be up to 10 class or more, and average grain diameter is around 8um.The critical cooling velocity of V-Ti-N anti-atmosphere steels with Mn content around 1.4% is 0.83°C/S. In the process of rolling, only natural air cooling shall be adopted, for wind cooling may possibly result in bainite. Anti-atmosphere steel not only has an atmospheric corrosion resisting abilityequivalent to that of Cor TenA, but also can pass beveled Y-slope welding crack test, exhibiting excellent weldability and a good atmospheric corrosion resisting ability.