HOT WATER TANK AND METHOD FOR PRODUCING THE SAME
A hot water tank having, on the inner surface thereof, a back bead formed by TIG-welding with no back gas sealing of steel members to each other having a composition comprising, % by mass, C: at most 0.025%, Si: at most 1%, Mn: at most 1%, P: at most 0.045%, S: at most 0.01%, Ni: from 0.1 to 1%, Cr: from more than 21 to 25%, Mo: from 0.1 to 2%, Al: from 0.02 to 0.3%, N: at most 0.025%, and Cu: from 0 to 1%, and containing at least one of Ti: from 0.05 to 0.4% and Nb: from 0.05 to 0.5%, with the balance of Fe and inevitable impurities, wherein the Cr concentration in the steel basis material in the area having oxide scale soluble in an aqueous chloride solution, as formed therein in the heat-affected zone on the welded back side thereof, is at least 16% by mass in the depth region of at least 10 nm from the steel basis material/oxide scale interface.
1 . A hot water tank having, on the inner surface thereof, a back bead formed by TIG-welding of steel members having a Cr content of from more than 21 to 25% by mass to each other with no back gas sealing, wherein the Cr concentration in the steel basis material in the area having oxide scale soluble in an aqueous chloride solution, as formed therein in the heat-affected zone on the TIG-welded back side thereof, is at least 16% by mass in the depth region of at least 10 nm from the steel basis material/oxide scale interface.
2 . A hot water tank having, on the inner surface thereof, a back bead formed by TIG-welding with no back gas sealing of steel members to each other having a composition comprising, % by mass, C: at most 0.025%, Si: at most 1%, Mn: at most 1%, P: at most 0.045%, S: at most 0.01%, Ni: from 0.1 to 1%, Cr: from more than 21 to 25%, Mo: from 0.1 to 2%, Al: from 0.02 to 0.3%, N: at most 0.025%, and containing at least one of Ti: from 0.05 to 0.4% and Nb: from 0.05 to 0.5%, with the balance of Fe and inevitable impurities.
3 . The hot water tank as claimed in claim 2 , wherein the steel material further contains Cu: at most 1%.
4 . The hot water tank as claimed in claim 2 , wherein the Cr concentration in the steel basis material in the area where oxide scale soluble in an aqueous chloride solution is formed in the heat-affected zone on the TIG-welded back side thereof is at least 16% by mass in the depth region of at least 10 nm from the steel basis material/oxide scale interface.
5 . The hot water tank as claimed in claim 1 , which has oxide scale having a Cr concentration of at least 30% by mass on the steel material surface near the back bead.
6 . The hot water tank of claim 1 , which has a structure so designed as not to have a flange not for a watercourse for water (including hot water) and not for an insert port for electric communication members.
7 . A method for producing a hot water tank, comprising a step of TIG-welding of steel members having a composition comprising, % by mass, C: at most 0.025%, Si: at most 1%, Mn: at most 1%, P: at most 0.045%, S: at most 0.01%, Ni: from 0.1 to 1%, Cr: from more than 21 to 25%, Mo: from 0.1 to 2%, Al: from 0.02 to 0.3%, N: at most 0.025%, and containing at least one of Ti: from 0.05 to 0.4% and Nb: from 0.05 to 0.5%, with the balance of Fe and inevitable impurities, to each other with no back gas sealing, thereby to form a back bead on the inner surface of the tank.
8 . The method for producing a hot water tank as claimed in claim 7 , wherein the steel material further contains Cu: at most 1%.
9 . The hot water tank as claimed in claim 3 , wherein the Cr concentration in the steel basis material in the area where oxide scale soluble in an aqueous chloride solution is formed in the heat-affected zone on the TIG-welded back side thereof is at least 16% by mass in the depth region of at least 10 nm from the steel basis material/oxide scale interface.
10 . The hot water tank as claimed in claim 2 , which has oxide scale having a Cr concentration of at least 30% by mass on the steel material surface near the back bead.
11 . The hot water tank as claimed in claim 3 , which has oxide scale having a Cr concentration of at least 30% by mass on the steel material surface near the back bead.
12 . The hot water tank as claimed in claim 4 , which has oxide scale having a Cr concentration of at least 30% by mass on the steel material surface near the back bead.
13 . The hot water tank of claim 2 , which has a structure so designed as not to have a flange not for a watercourse for water (including hot water) and not for an insert port for electric communication members.
14 . The hot water tank of claim 3 , which has a structure so designed as not to have a flange not for a watercourse for water (including hot water) and not for an insert port for electric communication members.
15 . The hot water tank of claim 4 , which has a structure so designed as not to have a flange not for a watercourse for water (including hot water) and not for an insert port for electric communication members.
16 . The hot water tank of claim 5 , which has a structure so designed as not to have a flange not for a watercourse for water (including hot water) and not for an insert port for electric communication members.