Austenitic stainless steel and manufacturing method thereof

Abstract

Disclosed are an austenitic stainless steel which may be utilized as various materials for an outer panel of a vehicle, a component for construction and the like and a manufacturing method thereof According to an embodiment, the austenitic stainless steel includes, in percent by weight (wt %), 0.005 to 0.03% of C, 0.1 to 1% of Si, 0.1 to 2% of Mn, 6 to 9% of Ni, 16 to 19% of Cr, 0.2% or less of N, and the remainder being Fe and unavoidable impurities. Assuming that a total thickness of the steel material is t, a value of an average grain size d in a thickness range of ¼t to ¾t is 5 μm or less, an ASP value represented by Formula (1) below is from 10 to 25, a value represented by Formula (2) below is 435 or more, and a value represented by Formula (3) below is 6000 or more. 551−462*([C]+[N])−9.2*[Si]−8.1*[Mn]−13.7*[Cr]−29*([Ni]+[Cu])−18.5*[Mo]−68*([Nb]+[V])  (1) (1600*[N])+(700/ )+(4*ASP)−(20*[Ni])+100  (2) YS*EL−500*([Ni]+[Cr])  (3) In Formulae (1), (2), and (3), [C], [N], [Si], [Mn], [Cr], [Ni], [Cu], [Mo], [Nb], and [V] represent weight percentages (wt %) of respective elements, YS represents yield strength (MPa), and EL represents elongation (%).

1 . An austenitic stainless steel comprising, in percent by weight (wt %), 0.005 to 0.03% of C, 0.1 to 1% of Si, 0.1 to 2% of Mn, 6 to 9% of Ni, 16 to 19% of Cr, 0.2% or less of N, and the remainder being Fe and unavoidable impurities,
 wherein assuming that a total thickness of the steel material is t, a value of an average grain size d in a thickness range of ¼t to ¾t is 5 μm or less, an ASP value represented by Formula (1) below is from 10 to 25, a value represented by Formula (2) below is 435 or more, and a value represented by Formula (3) below is 6000 or more:
   551−462*([C]+[N])−9.2*[Si]−8.1*[Mn]−13.7*[Cr]−29*([Ni]+[Cu])−18.5*[Mo]−68*([Nb]+[V])  (1)
 
   (1600*[N])+(700 /√{square root over (d)} )+(4*ASP)−(20*[Ni])+100  (2)
 
   YS*EL−500*([Ni]+[Cr])  (3)
 
   (wherein in Formulae (1), (2), and (3), [C], [N], [Si], [Mn], [Cr], [Ni], [Cu], [Mo], [Nb], and [V] represent weight percentages (wt %) of respective elements, YS represents a yield strength (MPa), and EL represents an elongation (%)).   
     
     
         2 . The austenitic stainless steel according to  claim 1 , wherein a value of Formula (4) below is 200 or more:
   Hv−([Ni]+[Cr])  (4)
   (wherein in Formula (4), Hv represents a Vickers hardness (Hv) and [Ni] and [Cr] represent weight percentages (wt %) of respective elements).   
     
     
         3 . The austenitic stainless steel according to  claim 1 , further comprising, in percent by weight (wt %), at least one of 0.4% or less of Cu, 0.2% or less of Mo, 0.25% or less of Nb, and 0.25% or less of V. 
     
     
         4 . The austenitic stainless steel according to  claim 1 , wherein the t is from 0.4 to 2.0 mm. 
     
     
         5 . The austenitic stainless steel according to  claim 1 , wherein a pitting potential, measured by dipping in a 3.5% NaCl solution at 30° C., is 250 mV or more. 
     
     
         6 . A method of manufacturing the austenitic stainless steel according to  claim 1 , the method comprising:
 hot rolling a slab comprising, in percent by weight (wt %), 0.005 to 0.03% of C, 0.1 to 1% of Si, 0.1 to 2% of Mn, 6 to 9% of Ni, 16 to 19% of Cr, 0.2% or less of N, and the remainder being Fe and unavoidable impurities, and cold rolling the hot-rolled steel material at room temperature with a reduction ratio of 40% or more; and   annealing the cold-rolled steel material at a temperature of 700 to 850° C.   
     
     
         7 . The method according to  claim 6 , wherein the slab is hot-rolled and then cold-rolled without being annealed. 
     
     
         8 . The method according to  claim 6 , further comprising skin pass rolling with a reduction ratio of 60% or more.