Method for producing a zinc-magnesium-galvannealed hot-dip coating and flat steel product provided with such a coating

Abstract

A process may be utilized to produce a galvannealed Zn—Mg hot dip coating that provides improved corrosion protection on a steel substrate, and to a flat steel product having such characteristics. To this end, a steel substrate may be subjected to hot dip coating in an Fe-saturated melt bath heated to 350-650° C., wherein the melt bath comprises in percent by weight 0.1-0.16% Al, 0.1-0.6% Mg, and also <2% Si, <1% each of Ni or Cu, <0.3% Co, <0.0001% Mn, <0.5% Sr, <0.1% each of Pb, B, Bi or Cd, <0.2% each of REM, Ti or Cr, or <0.5% Sn, with the balance being zinc and unavoidable impurities. Further, a galvannealing treatment may be conducted in which the steel substrate is kept at 450-800° C. for 10-25 seconds to produce a galvannealed Zn—Mg hot dip coating on the steel substrate. The coating may comprise Zn, unavoidable impurities, and in percent by weight 0.10-0.5% Al, 5.0-15.0% Fe, 0.10-0.8% Mg and <2 % Si, <1% each of Ni, Cu, <0.3% Co, <0.0001% Mn, <0.5% Sr, <0.1% each of B, Bi, Cd, Pb, <0.2% each of Cr, Ti, REM, <0.01% Sn.”

1 .- 12 . (canceled) 
     
     
         13 . A process for producing a galvannealed zinc-magnesium hot dip coating on a steel substrate, the process comprising:
 providing a steel substrate;   hot dip coating the steel substrate in an Fe-saturated melt bath heated to a bath temperature of 350° C.-650° C., wherein the Fe-saturated melt bath comprises 0.1%-0.16% by weight Al, 0.1%-0.6% by weight Mg, zinc, and unavoidable impurities; and   performing a galvannealing treatment in which the steel substrate that has been hot dip-coated is kept at a galvannealing temperature of 450° C.-800° C. over a galvannealing time of 10-25 seconds to produce a galvannealed zinc-magnesium hot dip coating on the steel substrate, wherein the galvannealed zinc-magnesium hot dip coating comprises zinc, unavoidable impurities, and 0.10%-0.5% by weight Al, 5.0%-15.0% by weight Fe, 0.10%-0.8% by weight Mg.   
     
     
         14 . The process of  claim 13  wherein
 the Fe-saturated melt bath further comprises at least one of <2% by weight Si, <0.1% by weight Pb, <0.2% by weight Ti, <1% by weight Ni, <1% by weight Cu, <0.3% by weight Co, <0.0001% by weight Mn, <0.2% by weight Cr, <0.5% by weight Sr, <0.1% by weight B, <0.1% by weight Bi, <0.1% by weight Cd, <0.2% by weight REM, or <0.5% by weight Sn, and 
 the galvannealed zinc-magnesium hot dip coating further comprises at least one of <2% by weight Si, <0.1% by weight Pb, <0.2% by weight Ti, <1% by weight Ni, <1% by weight Cu, <0.3% by weight Co, <0.0001% by weight Mn, <0.2% by weight Cr, <0.5% by weight Sr, <0.1% by weight B, <0.1% by weight Bi, <0.1% by weight Cd, <0.2% by weight REM, or <0.01% by weight Sn. 
 
     
     
         15 . The process of  claim 13  wherein the Fe-saturated melt bath comprises 0.1%-0.15% by weight Al. 
     
     
         16 . The process of  claim 13  wherein the Fe-saturated melt bath comprises 0.01%-0.5% by weight Fe. 
     
     
         17 . The process of  claim 13  wherein the Fe-saturated melt bath comprises 0.1%-0.4% by weight Mg. 
     
     
         18 . The process of  claim 13  wherein the bath temperature of the Fe-saturated melt bath is 430° C.-490° C. 
     
     
         19 . The process of  claim 13  wherein the galvannealing temperature at which the steel substrate is kept during the galvannealing treatment is 540° C.-720° C. 
     
     
         20 . The process of  claim 13  wherein the galvannealing time is 12-24 seconds. 
     
     
         21 . The process of  claim 13  wherein the steel substrate is a flat steel product. 
     
     
         22 . The process of  claim 13  wherein the steel substrate comprises an IF steel. 
     
     
         23 . A flat steel product having a galvannealed zinc-magnesium hot dip coating that comprises:
 zinc;   unavoidable impurities;   0.10%-0.5% by weight Al;   5.0-15.0% by weight Fe; and   0.10-0.8% by weight Mg.   
     
     
         24 . The flat steel product of  claim 23  further comprising at least one of:
 <2% by weight Si; 
 <0.1% by weight Pb; 
 <0.2% by weight Ti; 
 <1% by weight Ni; 
 <1% by weight Cu; 
 <0.3% by weight Co; 
 <0.0001% by weight Mn; 
 <0.2% by weight Cr; 
 <0.5% by weight Sr; 
 <0.1% by weight B; 
 <0.1% by weight Bi; 
 <0.1% by weight Cd; 
 <0.2% by weight REM; or 
 <0.01% by weight Sn. 
 
     
     
         25 . The flat steel product of  claim 23  comprising an IF steel. 
     
     
         26 . The flat steel product of  claim 23  wherein the galvannealed zinc-magnesium hot dip coating is free of zeta phase.