Ferritic stainless steel, with high and stable grain refining potency, and its production method

Abstract

A ferritic stainless steel comprising Cr: max 24 mass %, Ti: 200 to 1000 mass ppm, Zr: at least 200 mass ppm, whereby the Zr/Ti ratio is greater than 0.3, O: 10 to 150 mass ppm, N: at least 70 mass ppm, whereby the N/O ratio is greater than 1.5, C: max. 0.03 mass %, and balance Fe and residual elements.

1 . A ferritic stainless steel, wherein it comprises
 Cr: max 24 mass %,   Ti: 200 to 1000 mass ppm,   Zr: at least 200 mass ppm,   whereby the Zr/Ti ratio is greater than 0.3,   O: 10 to 150 mass ppm,   N: at least 70 mass ppm   whereby the N/O ratio is greater than 1.5,   C: max. 0.03 mass %, and   balance Fe and residual elements.   
     
     
         2 . A ferritic stainless steel according to  claim 1 , wherein it comprises Ti and/or Zr oxides/nitrides with a maximum diameter of 5 μm. 
     
     
         3 . A ferritic stainless steel according to  claim 1 , wherein it comprises a total number of more than 1×10 6  Ti and/or Zr oxides/nitrides per mm 3  of the steel. 
     
     
         4 . A method for producing of a ferritic stainless steel according to  claim 1 , wherein the method comprises the step of adding deoxidizers Si, Mn, Ti and Zr to a melt in the order of weak deoxidizer to strong deoxidizer, i.e. firstly Si and Mn, then Ti, and finally Zr. 
     
     
         5 . A method according to  claim 4 , wherein the method comprises the step of deoxidizing a melt with said deoxidizers in said order with an interval of 1 to 5 minutes between additions, holding the melt for at least one minute and casting the melt.