Cold rolled high strength low alloy steel

Abstract

A high strength low alloy steel. The high strength low alloy steel strip, sheet or blank, coated with zinc or a zinc alloy, has the following composition in weight %: C: 0.03-0.07, Mn: 0.70-1.60, Si: ≦0.2, Al: 0.005-0.1, Cr: ≦0.1, Cu: ≦0.2, N: ≦0.008, P: ≦0.03, S: ≦0.025, O: ≦0.01, Ti: 0.02-0.07, V: 0.04-0.15 Mo: ≦0.03, Nb: ≦0.03, Ca: ≦0.05, the remainder being iron and unavoidable impurities, wherein the steel strip, sheet or blank has a yield strength Rp0,2 of at least 420 MPa.

1 . A high strength low alloy steel strip, sheet or blank, coated with zinc or a zinc alloy, having the following composition in weight %:
 C: 0.03-0.07,   Mn: 0.70-1.60,   Si: 0.01-0.2,   Al: 0.005-0.1,   Cr: ≦0.1,   Cu: ≦0.2,   N: ≦0.008,   P: ≦0.03,   S: ≦0.025,   O: ≦0.01,   Ti: 0.02-0.07,   V: 0.04-0.15   Mo: ≦0.03,   Nb: ≦0.03,   Ca: ≦0.05,   
       the remainder being iron and unavoidable impurities, 
       wherein the steel strip, sheet or blank has a yield strength Rp0,2 of at least 420 MPa. 
     
     
         2 . The steel strip, sheet or blank according to  claim 1 , wherein:
 Mn: 0.80-1.40.   
     
     
         3 . The steel strip, sheet or blank according to  claim 1 , wherein the steel strip, sheet or blank has a yield strength Rp0,2 in longitudinal direction of at least 460 MPa. 
     
     
         4 . The steel strip, sheet or blank according to  claim 1 , wherein the steel strip, sheet or blank has an elongation A80 mm in longitudinal direction of at least 15%. 
     
     
         5 . The steel strip, sheet or blank according to  claim 1 , wherein the steel strip, sheet or blank has a tensile strength Rm in longitudinal direction of at least 480 MPa. 
     
     
         6 . The steel strip, sheet or blank according to  claim 1 , wherein the zinc or zinc alloy coating is a hot dip galvanized or hot dip galvannealed coating. 
     
     
         7 . The steel strip, sheet or blank according to  claim 1 , wherein the zinc alloy coating comprises 0.5 to 4 wt % Al and 0.5 to 3.2 wt % Mg, the remainder being zinc and traces of other elements, the coating having a thickness between 5 and 15 μpm per side. 
     
     
         8 . A method for producing a high strength low alloy steel strip comprising the following steps:
 producing a molten steel having the composition of  claim 1 ,   casting the molten steel in a casting apparatus,   hot rolling the casting with an end temperature of at least 880° C. into a strip,   coiling the hot rolled strip at a coiling temperature between 500° C. and 650° C.,   cold rolling the strip with an overall reduction of 50-75%,   continuous annealing the strip at an annealing temperature between 750° C. and 820° C.   
     
     
         9 . The method according to  claim 8 , wherein the annealed strip is hot dip coated with a zinc or zinc alloy coating. 
     
     
         10 . The method according to  claim 9 , wherein the coated strip is cold rolled in a temper mill with a reduction of 0.1-3.0%. 
     
     
         11 . The method according to  claim 8 , wherein the strip is cold rolled at a width of at least 1400 mm, with a gauge of 0.7-2.0 mm. 
     
     
         12 . The method according to  claim 8 , wherein the coiling temperature of the hot rolled strip is between 550° C. and 600° C. and/or the overall cold rolling reduction is 60-70% and/or the annealing temperature is between 760° C. and 800° C. 
     
     
         13 . The method according to  claim 8 , wherein the steel has Mn: 0.80-1.40. 
     
     
         14 . The method according to  claim 8 , wherein the produced steel strip has a yield strength Rp0,2 of at least 420 MPa. 
     
     
         15 . The method according to  claim 8 , wherein the produced steel strip has an elongation A80 mm of at least 15%. 
     
     
         16 . The steel strip, sheet or blank according to  claim 1 , wherein Mn: 0.80-1.30. 
     
     
         17 . The steel strip, sheet or blank according to  claim 1 , wherein the steel strip, sheet or blank has a yield strength Rp0,2 in a longitudinal direction of at most 580 MPa. 
     
     
         18 . The steel strip, sheet or blank according to  claim 1 , wherein the steel strip, sheet or blank has a tensile strength Rm of at least 520 MPa. 
     
     
         19 . The steel strip, sheet or blank according to  claim 1 , wherein the steel strip, sheet or blank has a tensile strength Rm in a longitudinal direction of at most 680 MPa. 
     
     
         20 . The steel strip, sheet or blank according to  claim 1 , wherein the zinc alloy coating comprises 0.5 to 4 wt % Al and 0.5 to 3.2 wt % Mg, the remainder being zinc and traces of other elements, the coating having a thickness between 6 and 13 μm per side. 
     
     
         21 . The method according to  claim 9 , wherein the coated strip is cold rolled in a temper mill with a reduction of 0.2-2.0%. 
     
     
         22 . The method according to  claim 8 , wherein the strip is cold rolled at a width of at least 1600 mm, with a gauge of 0.7-2.0 mm. 
     
     
         23 . The method according to  claim 8 , wherein the strip is cold rolled at a width of at a width of at least 1800 mm, with a gauge of 0.7-2.0 mm. 
     
     
         24 . The method according to  claim 8 , wherein the produced steel strip has a yield strength Rp0,2 of at least 460 MPa. 
     
     
         25 . The method according to  claim 8 , wherein the produced steel strip has a yield strength Rp0,2 of at most 580 MPa. 
     
     
         26 . The method according to  claim 1 , wherein the
 C: 0.04-0.06,   Mn: 0.80-1.30,   Si: ≦0.01-0.05,   Al: 0.015-0.0.55,   Cr: ≦0.05,   Cu: ≦0.05,   N: 0.002-0.008,   S: ≦0.025,   O: ≦0.005,   Ti: 0.02-0.06,   V: 0.05-0.15   Mo: ≦0.01,   Nb: ≦0.01, and   Ca: ≦0.01.