Actually in all of the chemical compositions, the most impact of contribution for corrosion resistance is not Ni, but Cr, which make sure the ferric stainless steel. It usually contains 11% ~50%. But if the Cr is over 50% that will broke the heat and cold processing properties. So as usually it contains between 11% ~35%.
Except Cr, Mo can improve corrosion resistance property in the second position. Adding the mass fraction of Mo can improve enhance the partial corrosion-resistant properties like pitting corrosion and crevice corrosion. The Mo ratio is not less than 0.1% which can improve corrosion resisting property and crinkle resisting property. Upper range of peak concentration can not be more than 5%, if it does be more than that can’t help improvement the above properties, on the contrary, it will decrease the properties of corrosion resistance and processing. Therefore, the mass fraction ratio should be controlled within 1.0% approximately that make sure the mechanical properties and corrosion resisting properties. The index of pitting-resistance property of ferritc stainless steel is PRE=(approximate) w(Cr)+3.3w(Mo).
Ag and Cu in ferritic stainless steel can play an antiseptic role in there. Niobium and titanium can stabilize the alloy. Because they can combine the carbon and nitrogen to be carbide and nitride which can refine grain and restrain it from forming chromium’s carbide and chromium’s nitride. Therefore, it can enhance the intergranular corrosion-resistance.
How about Ti ? Let about Ti. With developments, experts find Ti ratio should be w(Ti)=0.08+8[w(c)+w(N)], or Ti% should be more than total of N%+C%. To enhance the quality of plate slab then decrease repairing when slab are being repaired. So composite micro-alloying Nb+Ti can save the cost.
Post time: Sep-08-2017