Ferritic stainless steel for hot-water tank with welded structure, and hot-water tank

Abstract

Disclosed is a ferritic stainless steel for hot-water tanks with welded structure, comprising, in terms of % by mass, at most 0.02% of C, from 0.01 to 0.30% of Si, at most 1% of Mn, at most 0.04% of P, at most 0.03% of S, from more than 21 to 26% of Cr, at most 2% of Mo, from 0.05 to 0.6% of Nb, from 0.05 to 0.4% of Ti, at most 0.025% of N, and from 0.02 to 0.3% of Al, and optionally containing at least one of at most 2%, preferably from 0.1 to 2% of Ni and at most 1%, preferably from 0.1 to 1% of Cu, with a balance of Fe and inevitable impurities.

1 . A ferritic stainless steel for hot-water tanks with welded structure, comprising, in terms of % by mass,
 at most 0.02% of C,   from 0.01 to 0.30% of Si,   at most 1% of Mn,   at most 0.04% of P,   at most 0.03% of S,   from more than 21 to 26% of Cr,   at most 2% of Mo,   from 0.05 to 0.6% of Nb,   from 0.05 to 0.3% of Ti,   at most 0.025% of N,   from 0.02 to 0.3% of Al,   with a balance of Fe and inevitable impurities.   
   
   
       2 . A ferritic stainless steel for hot-water tanks with welded structure, comprising, in terms of % by mass,
 at most 0.02% of C,   from 0.01 to 0.30% of Si,   at most 1% of Mn,   at most 0.04% of P,   at most 0.03% of S,   from more than 21 to 26% of Cr,   at most 2% of Mo,   from 0.05 to 0.6% of Nb,   from 0.05 to 0.3% of Ti,   at most 0.025% of N,   from 0.02 to 0.3% of Al,   and further containing at least one of at most 2% of Ni and at most 0.1% of Cu,   with a balance of Fe and inevitable impurities.   
   
   
       3 . A ferritic stainless steel for hot-water tanks with welded structure, comprising, in terms of % by mass,
 at most 0.02% of C,   from 0.01 to 0.30% of Si,   at most 1% of Mn,   at most 0.04% of P,   at most 0.03% of S,   from more than 21 to 26% of Cr,   at most 2% of Mo,   from 0.05 to 0.6% of Nb,   from 0.05 to 0.3% of Ti,   at most 0.025% of N,   from 0.02 to 0.3% of Al,   and further containing at least one of from 0.1 to 2% of Ni and from 0.1 to 1% of Cu,   with a balance of Fe and inevitable impurities.   
   
   
       4 . A ferritic stainless steel for hot-water tanks with welded structure, comprising, in terms of % by mass,
 at most 0.02% of C,   from 0.01 to 0.30% of Si,   at most 1% of Mn,   at most 0.04% of P,   at most 0.03% of S,   from more than 21 to 26% of Cr,   at most 2% of Mo,   from 0.05 to 0.6% of Nb,   from 0.05 to 0.4% of Ti,   at most 0.025% of N,   from 0.02 to 0.3% of Al,   with a balance of Fe and inevitable impurities.   
   
   
       5 . A ferritic stainless steel for hot-water tanks with welded structure, comprising, in terms of % by mass,
 at most 0.02% of C,   from 0.01 to 0.30% of Si,   at most 1% of Mn,   at most 0.04% of P,   at most 0.03% of S,   from more than 21 to 26% of Cr,   at most 2% of Mo,   from 0.05 to 0.6% of Nb,   from 0.05 to 0.4% of Ti,   at most 0.025% of N,   from 0.02 to 0.3% of Al,   and further containing at least one of at most 2% of Ni and at most 1% of Cu,   with a balance of Fe and inevitable impurities.   
   
   
       6 . A ferritic stainless steel for hot-water tanks with welded structure, comprising, in terms of % by mass,
 at most 0.02% of C,   from 0.01 to 0.30% of Si,   at most 1% of Mn,   at most 0.04% of P,   at most 0.03% of S,   from more than 21 to 26% of Cr,   at most 2% of Mo,   from 0.05 to 0.6% of Nb,   from 0.05 to 0.4% of Ti,   at most 0.025% of N,   from 0.02 to 0.3% of Al,   and further containing at least one of from 0.1 to 2% of Ni and from 0.1 to 1% of Cu,   with a balance of Fe and inevitable impurities.   
   
   
       7 . The terrific stainless steel for hot-water tanks with welded structure as claimed in  claim 1 , wherein the corrosion resistance level of the steel is such that, when the steel is worked into a cold-rolled, annealed and acid-washed steel sheet, then the steel sheet is TIG-welded with no back gas sealing, and the test piece having the welded part directly as it is untreated is tested in a dipping test where the test piece is dipped in an aqueous solution with 2000 ppm of Cl −  at 80° C. for 30 days (using a Pt assistant cathode), and after the test, the corrosion depth is at most 0.1 mm. 
   
   
       8 . A hot-water tank with welded structure, which has a welded part formed by TIG-welding with no back gas sealing of a steel material comprising the stainless steel of  claim 1 , and which is used in such a manner that the TIG-welded part on the back bead side thereof is, directly as it is with no treatment given thereto, exposed to hot water.