Production method of hot rolled steel sheet and production method of hot-dip galvanized steel sheet

Abstract

A method for producing a hot rolled steel sheet includes a slab heating step of heating a steel slab in a slab heating furnace, a step of hot-rolling the heated steel slab in a rough rolling mill to form a strip and a finish rolling mill, and a coiling step of coiling the strip around a coiler. The atmosphere in steps from the slab heating step to the coiling step is a non-oxidizing atmosphere. The slab steel contains C: 0.01-0.15%, Si: 0.1-1.8%, Mn: 1.0-2.7%, Al: 0.01-1.5%, P: 0.005-0.025%, and S: 0.01% or less, by mass. A hot-dip galvanized steel sheet is produced by pickling the hot rolled steel sheet to remove mill scale, or by pickling the sheet and further cold-rolling the sheet, and subsequently by subjecting the resultant to hot-dip galvanizing.

1 . A method for producing a hot rolled steel sheet, comprising:
 heating a steel slab in a slab heating furnace,   hot-rolling the heated steel slab in a rough rolling mill and a finish rolling mill to form a strip,   and   coiling the strip in a coiler,   wherein the steps from heating the steel slab to coiling the strip are performed in a non-oxidizing atmosphere.   
     
     
         2 . The method for producing a hot rolled steel sheet according to  claim 1 ,
 wherein the non-oxidizing atmosphere is a N 2  atmosphere.   
     
     
         3 . The method for producing a hot rolled steel sheet according to  claim 2 , wherein the non-oxidizing atmosphere is the N 2  atmosphere containing H 2  in an amount of 1 to 10% by volume, and further has a dew point of −40° C. to +20° C. 
     
     
         4 . The method for producing a hot rolled steel sheet according to  claim 1 , wherein the steel slab contains: C, 0.01-0.15%, Si: 0.1-1.8%, Mn: 1.0-2.7%, Al: 0.01-1.5%, P: 0.005-0.025%, and S: 0.01% or less, by mass. 
     
     
         5 . The method for producing a hot rolled steel sheet according to  claim 4 , wherein the steel slab further contains at least one element selected from the group consisting of Cr: 0.05-1.0%, Mo: 0.05-1.0%, Nb: 0.005-0.05%, Ti: 0.005-0.05%, Cu: 0.05-1.0%, Ni: 0.05-1.0%, and B: 0.001-0.005%, by mass. 
     
     
         6 . A method for producing a hot-dip galvanized steel sheet, comprising:
 removing mill scale by pickling the hot rolled steel sheet produced by the method according to  claim 4 ,   or   removing mill scale by pickling the hot rolled steel sheet and further cold-rolling the hot rolled steel sheet; and subsequently   hot-dip galvanizing the hot rolled steel sheet.   
     
     
         7 . A method for producing a hot-dip galvanized steel sheet, further comprising: subjecting an alloying treatment to the hot-dip galvanized steel sheet produced by the method according to  claim 6 .