Highly anticorrosive martensitic stainless steel, and manufacturing method therefor

Abstract

Disclosed is a highly anticorrosive martensitic stainless steel having uniformly distributed fine chromium carbide so as to have improved corrosion resistance and being applicable as tableware with suitable hardness when strengthened by heat treatment, and a manufacturing metho therefor.The highly anticorrosive martensitic stainless steel according to an embodiment of the present disclosure includes, in percent by weight (wt%), 0.14 to 0.21% of C, 0.05 to 0.11% of N, 0.1 to 0.6% of Si, 0.4 to 1.2% of Mn, 14.0 to 17.0% of Cr, 0.2 to 0.32% of C+N, and the balance of Fe and inevitable impurities, has a PREN value, represented by Formula (1), of 16 or more, and has a precipitation temperature of chromium carbide of 950° C. or lower.

1 . A hot-rolled, annealed highly anticorrosive martensitic stainless steel sheet comprising, in percent by weight (wt%), 0.14 to 0.21% of C, 0.05 to 0.11% of N, 0.1 to 0.6% of Si, 0.4 to 1.2% of Mn, 14.0 to 17.0% of Cr, 0.2 to 0.32% of C+N, and the balance of Fe and inevitable impurities,
 wherein chromium carbide or chromium nitride is distributed in a microstructure at a density of 25 particles/100 µm 2 ,   a precipitation temperature of chromium carbide is 950° C. or lower, and   a PREN value, represented by Formula (1) below, is 16 or more:           Cr+3   .3       Mo       +       16       N            (wherein Cr, Mo, and N represent contents (wt%) of each alloying element).   
     
     
         2 . The hot-rolled, annealed highly anticorrosive martensitic stainless steel sheet according to  claim 1 , wherein an elongation is 20% or more. 
     
     
         3 . A Highly anticorrosive martensitic stainless steel comprising, in percent by weight (wt%), 0.14 to 0.21% of C, 0.05 to 0.11% of N, 0.1 to 0.6% of Si, 0.4 to 1.2% of Mn, 14.0 to 17.0% of Cr, 0.2 to 0.32% of C+N, and the balance of Fe and inevitable impurities,
 wherein a PREN value, represented by Formula (1) below, is 16 or more,   a value, represented by Formula (2) below, is 950 or less:           Cr       +       3   .3       Mo       +       16       N                   674       +       569       C       -       4.14       Si       +       0   .46       Mn       +       10   .3       Cr       +       193       N            (wherein Cr, Mo, N, C, Si, and Mn represent contents (wt%) of each alloying element).   
     
     
         4 . The highly anticorrosive martensitic stainless steel according to  claim 3 , wherein a Rockwell hardness is in a range of 47 to 53 HRC. 
     
     
         5 . The highly anticorrosive martensitic stainless steel according to  claim 3 , wherein a pitting potential is 180 mV or more in a 3.5% NaCl aqueous solution at 25° C. 
     
     
         6 . A method for manufacturing a highly anticorrosive martensitic stainless steel, the method comprising:
 hot rolling a slab comprising, in percent by weight (wt%), 0.14 to 0.21% of C, 0.05 to 0.11% of N, 0.1 to 0.6% of Si, 0.4 to 1.2% of Mn, 14.0 to 17.0% of Cr, 0.2 to 0.32% of C+N, and the balance of Fe and inevitable impurities;   batch annealing the hot-rolled steel material; and   hardening heat-treating the hot-rolled, annealed steel material,   wherein the batch annealing comprises a first cracking process performed in a temperature range of 720 to 900° C. for 5 to 25 hours and a second cracking process performed in a temperature range of 500 to 700° C. for 5 to 15 hours, and   the hot-rolled, annealed steel material comprises ferrite as a matrix in which chromium carbide or chromium nitride is distributed at a density of 25 particles/100 µm 2  or more.   
     
     
         7 . The method according to  claim 6 , wherein the batch annealing further comprises a pre-cracking process performed in a temperature range of 400 to 600° C. for 5 to 10 hours before the first cracking process. 
     
     
         8 . The method according to  claim 7 , wherein the temperature is raised at a rate of 40 to 200° C./h after the pre-cracking process until the first cracking process. 
     
     
         9 . The method according to  claim 6 , wherein the temperature is lowered at a rate of 10° C./h or more after the first cracking process until the second cracking process. 
     
     
         10 .  The method according to  claim 6 , wherein the hardening heat-treating comprises an austenitizing treatment process performed at a temperature of 1,000° C. or higher for 1 minute or more, and a quenching process to room temperature at a rate of 0.15° C./s or more. 
     
     
         11 . The method according to  claim 10 , wherein the hardening heat-treating further comprises a deep freezing process performed in a temperature range of -150 to -50° C. for 10 seconds to 5 minutes and a tempering process performed in a temperature range of 400 to 600° C. for 30 minutes to 2 hours, after the quenching process.