Ferritic stainless steel excellent in corrosion resistance and impact resistance

Abstract

Provided is a ferritic stainless steel having improved impact resistance and corrosion resistance at high temperatures by suppressing formation of a sigma phase in the steel. The ferritic stainless steel composition may include an amount of about 0.015% or less (excluding 0%) of carbon (C), an amount of about 0.17% or less (excluding 0%) of silicon (Si), an amount of about 1.35% or less (excluding 0%) of manganese (Mn), an amount of about 17 to 20% of chromium (Cr), an amount of about 0.1 to 0.5% of titanium (Ti), an amount of about 3 to 5% of aluminum (Al), and iron (Fe) constituting the remaining balance of the steel composition. In particular, the steel composition satisfies [Equation 1] below. (20Si+Mn)/Al<0.7  [Equation 1], where Si, Mn, and Al denote the content (%) of each component.

What is claimed is: 
     
         1 . A ferritic stainless steel comprising:
 an amount of about 0.015 wt % or less (excluding 0 wt %) of carbon (C),   an amount of about 0.17 wt % or less (excluding 0 wt %) of silicon (Si),   an amount of about 1.35 wt % or less (excluding 0 wt %) of manganese (Mn),   an amount of about 17 to 20 wt % of chromium (Cr),   an amount of about 0.5 wt % or less (excluding 0 wt %) of titanium (Ti),   an amount of about 3 to 5 wt % of aluminum (Al), and   iron (Fe) constituting the remaining balance of the ferritic stainless steel,   all the wt % based on the total weight of the ferritic stainless steel,   wherein contents of Si, Mn, and Al satisfy [Equation 1],
   (20Si+Mn)/Al<0.7  [Equation 1]
 
   wherein Si, Mn, and Al in Equation 1 represent the content (wt %) of each component.   
     
     
         2 . The ferritic stainless steel of  claim 1 , wherein
 the stainless steel comprises an amount of about 0.1 to 0.5 wt % of Ti based on the total weight of the ferritic stainless steel.   
     
     
         3 . The ferritic stainless steel of  claim 1 , further comprising:
 zirconium (Zr), calcium (Ca), and magnesium (Mg),   wherein contents of Zr, Ca and Mg satisfy [Equation 2],
   0.001≤Zr+Ca+Mg≤0.01  [Equation 2]
 
   
       wherein Zr, Ca, and Mg in Equation 2 represent the content (wt %) of each component. 
     
     
         4 . The ferritic stainless steel of  claim 1 , further comprising:
 an amount less than 0.001 wt % of oxygen (O) and an amount of about less than 0.02 wt % of nitrogen (N) based on the total weight of the ferritic stainless steel.   
     
     
         5 . The ferritic stainless steel of  claim 1 , wherein a volume fraction of a sigma phase formed in a temperature range of about 300 to 900° C. is less than 5%. 
     
     
         6 . The ferritic stainless steel of  claim 5 , wherein the volume fraction of the sigma phase formed in the temperature range of about 300 to 900° C. is about 0.5% or less or is not precipitated. 
     
     
         7 . The ferritic stainless steel of  claim 6 , wherein the volume fraction of the sigma phase formed in the temperature range of about 300 to 900° C. is not precipitated. 
     
     
         8 . The ferritic stainless steel of  claim 1 , wherein a volume fraction of Cr 3 Si formed in the temperature range of about 300 to 900° C. is about 0.5% or less. 
     
     
         9 . The ferritic stainless steel of  claim 1 , wherein a volume fraction of each of AlN and Al 2 O 3  formed in the temperature range of about 300 to 900° C. is about 0.0001% or less. 
     
     
         10 . The ferritic stainless steel of  claim 1 , wherein a volume fraction of M 23 C 6  formed in the temperature range of about 300 to 900° C. is less than about 0.2%. 
     
     
         11 . The ferritic stainless steel of  claim 1 , wherein a volume fraction of a laves phase formed in the temperature range of about 300 to 900° C. is about 0.2% or less. 
     
     
         12 . The ferritic stainless steel of  claim 1 , wherein a pitting potential (Ept) of the ferritic stainless steel in about 3.5% of sodium chloride (NaCl) at a temperature of about 25° C. is about 300 mV SCE  or greater. 
     
     
         13 . The ferritic stainless steel of  claim 1 , wherein a time required for forming rust in a condition of about 5% of sodium chloride (NaCl) after 3% of a salt water is sprayed is about 250 days or greater. 
     
     
         14 . The ferritic stainless steel of  claim 1 , wherein
 impact resistance strength of the ferritic stainless steel measured by a Charpy keyhole-notch impact test is about 55 J or greater.   
     
     
         15 . A ferritic stainless steel consisting of:
 an amount of about 0.015 wt % or less (excluding 0 wt %) of carbon (C),   an amount of about 0.17 wt % or less (excluding 0 wt %) of silicon (Si),   an amount of about 1.35 wt % or less (excluding 0 wt %) of manganese (Mn),   an amount of about 17 to 20 wt % of chromium (Cr),   an amount of about 0.5 wt % or less (excluding 0 wt %) of titanium (Ti),   an amount of about 3 to 5 wt % of aluminum (Al), and   iron (Fe) constituting the remaining balance of the ferritic stainless steel,   all the wt % based on the total weight of the ferritic stainless steel,   wherein contents of Si, Mn, and Al satisfy [Equation 1],
   (20Si+Mn)/Al<0.7  [Equation 1]
 
   wherein Si, Mn, and Al in Equation 1 represent the content (wt %) of each component.   
     
     
         16 . The ferritic stainless steel of  claim 15 , wherein
 the stainless steel comprises an amount of about 0.1 to 0.5 wt % of Ti based on the total weight of the ferritic stainless steel.   
     
     
         17 . The ferritic stainless steel of  claim 15 , further comprising:
 zirconium (Zr), calcium (Ca), and magnesium (Mg),   wherein contents of Zr, Ca and Mg satisfy [Equation 2],
   0.001≤Zr+Ca+Mg≤0.01  [Equation 2]
 
   
       wherein Zr, Ca, and Mg in Equation 2 represent the content (wt %) of each component. 
     
     
         18 . The ferritic stainless steel of  claim 15 , further comprising:
 an amount less than 0.001 wt % of oxygen (O) and an amount of about less than 0.02 wt % of nitrogen (N) based on the total weight of the terrific stainless steel.   
     
     
         19 . An exhaust system component comprising a ferritic stainless steel of  claim 1 . 
     
     
         20 . A vehicle comprising an exhaust system component of  claim 19 .