Steel sheet for galvanizing with excellent workability, and method for manufacturing the same

Abstract

A high strength ductile steel sheet for extra deep drawing mainly used for interior or exterior plates of automobile bodies, and a method for manufacturing the same are disclosed. The steel sheet comprises, by weight %, C: 0.010% or less, Si: 0.1% or less, Mn: 0.06˜1.5%, P: 0.15% or less, S: 0.020% or less, Sol. Al: 0.10˜0.40%, N: 0.010% or less, Ti: 0.003˜0.010%, Nb: 0.003˜0.040%, B: 0.0002˜0.0020%, Mo: 0.05% or less, one or both of Sb: 0.005˜0.05% and Sn: 0.005˜0.05%, a total amount of Sb and Sn being in the range of 0.005˜0.1% when both of Sb and Sn are added to the steel sheet, and the balance of Fe and other unavoidable impurities. The steel sheet has surface agglomerates having an average diameter of 1 μm or less, and a tensile strength of 28˜50 kgf/mm 2 .

1 . A steel sheet for galvanizing with excellent workability, comprising, by weight %:
 C: 0.010% or less, Si: 0.1% or less, Mn: 0.06˜1.5%, P: 0.15% or less, S: 0.020% or less, Sol. Al: 0.10˜0.40%, N: 0.010% or less, Ti: 0.003˜0.010%, Nb: 0.003˜0.040%, B: 0.0002˜0.0020%, Mo: 0.05% or less, one or both of Sb: 0.005˜0.05% and Sn: 0.005˜0.05%, a total amount of Sb and Sn being in the range of 0.005˜0.1% when both of Sb and Sn are added to the steel sheet, and the balance of Fe and other unavoidable impurities,   wherein the steel sheet has surface agglomerates having an average diameter of 1 μm or less, and a tensile strength of 28˜50 kgf/mm 2 .   
     
     
         2 . The steel sheet according to  claim 1 , wherein the average diameter of the surface agglomerates is suppressed in growth by 10% or less for an increase in annealing temperature of 10° C. 
     
     
         3 . The steel sheet according to  claim 1 , wherein the surface agglomerates comprise singular or composite oxides of Si, Al, Mn and Ti. 
     
     
         4 . A method for manufacturing a steel sheet for galvanizing with excellent workability, comprising:
 reheating a steel slab comprising by weight %: C: 0.010% or less, Si: 0.1% or less, Mn: 0.06˜1.5%, P: 0.15% or less, S: 0.020% or less, Sol. Al: 0.10˜0.40%, N: 0.010% or less, Ti: 0.003˜0.010%, Nb: 0.003˜0.040%, B: 0.0002˜0.0020%, Mo: 0.05% or less, one or both of Sb: 0.005˜0.05% and Sn: 0.005˜0.05%, a total amount of Sb and Sn being in the range of 0.005˜0.1% when both of Sb and Sn are added to the steel sheet, and the balance of Fe and other unavoidable impurities;   hot rolling the reheated steel slab with finish rolling at a finish rolling temperature of a single phase austenite region to form a steel sheet, followed by coiling the hot rolled steel sheet;   cold rolling the hot rolled steel sheet; and   continuously annealing the cold rolled steel sheet at a temperature of 700° C. or more.   
     
     
         5 . The method according to  claim 4 , wherein reheating is performed at a temperature in the range of 1,100˜1,300° C., the finish rolling is performed at a temperature in the range of 830˜920° C., the coiling is performed at a temperature in the range of 500˜700° C., the cold rolling is performed at a reduction ratio of 65% or more, and the annealing is performed at a temperature in the range of 780˜860° C. 
     
     
         6 . The method according to  claim 4 , further comprising: air cooling or water cooling after coiling the hot rolled steel sheet. 
     
     
         7 . The method according to  claim 4 , wherein coarsening of surface agglomerates is suppressed by 10% or less for an increase in annealing temperature of 10° C. in the annealing temperature range. 
     
     
         8 . The method according to  claim 6 , wherein coarsening of surface agglomerates is suppressed by 10% or less for an increase in annealing temperature of 10° C. in the annealing temperature range. 
     
     
         9 . The steel sheet according to  claim 2 , wherein the surface agglomerates comprise singular or composite oxides of Si, Al, Mn and Ti. 
     
     
         10 . The method according to  claim 5 , further comprising: air cooling or water cooling after coiling the hot rolled steel sheet. 
     
     
         11 . The method according to  claim 5 , wherein coarsening of surface agglomerates is suppressed by 10% or less for an increase in annealing temperature of 10° C. in the annealing temperature range.