Steel for hot forming

Abstract

A steel for hot forming. The steel for hot forming has the following composition in weight%: C: 0.10-0.25, Mn: 1.4-2.6, Si:<0.4, Cr:<1.0, Al:<1.5, P:<0.02, S:<0.005, N:<0.03, B:<0.0004, 0:<0.008 and optionally: Ti:<0.3, Mo:<0.5, Nb:<0.3, V:<0.5, Ca:<0.05, the remainder being iron and unavoidable impurities. Also disclosed is a strip, sheet or blank produced with such a steel, a method for producing a hot formed product, such a product and the use thereof

1 . A steel for hot forming having the following composition in weight %:
 C: 0.10-0.25,   Mn: 1.4-2.6,   Si: ≦0.4,   Cr: ≦1.0,   Al: ≦1.5,   P: ≦0.02,   S: ≦0.005,   N: ≦0.03,   B: ≦0.0004,   O: ≦0.008   and optionally:   Ti: ≦0.3,   Mo: ≦0.5,   Nb: ≦0.3,   V: ≦0.5,   Ca: ≦0.05,   
       the remainder being iron and unavoidable impurities. 
     
     
         2 . The steel according to  claim 1 , wherein the composition has at least one elemental range selected from the group consisting of:
 C: 0.12-0.23   Mn: 1.6-2.5   Si: ≦0.3   Cr: ≦0.8   Al: ≦0.5 and   O: ≦0.005   N: ≦0.01   B: ≦0.0003 and/or   Ti: ≦0.1   Mo: ≦0.2   Nb: ≦0.1   V: ≦0.2 and   Ca: ≦0.01.   
     
     
         3 . The steel according to  claim 1 , wherein the composition has at least one elemental range selected from the group consisting of:
 C: 0.15-0.21   Mn: 1.8-2.4   Si: ≦0.2   Cr: ≦0.7,   Al: ≦0.05   N: ≦0.006   Ti: ≦0.02   Mo: ≦0.08   Nb: ≦0.02   V: ≦0.02 and   B: ≦0.0001.   
     
     
         4 . The steel according to  claim 1 , wherein Mn+Cr≧2.5 weight %. 
     
     
         5 . A strip, sheet, blank, or tube produced with the steel according to  claim 1 . 
     
     
         6 . The strip, sheet, blank or tube according to  claim 5 , pre-coated with a layer of aluminium or an aluminium based alloy, or pre-coated with a layer of zinc or a zinc based alloy. 
     
     
         7 . The strip, sheet, blank or tube according to  claim 6 , wherein the pre-coating comprises 5 to 13 wt % silicon and/or less than 5 wt % iron, the remainder of the pre-coating being aluminium. 
     
     
         8 . The strip, sheet, blank or tube according to  claim 7 , wherein the pre-coating comprises 8 to 12 wt % silicon and/or 2 to 5 wt % iron, the remainder of the pre-coating being aluminium. 
     
     
         9 . The strip, sheet, blank or tube according to  claim 6 , wherein the pre-coating is an iron-zinc diffusion coating obtained by heat treating a zinc layer, the zinc layer comprising Al<0.18 wt % and Fe<15 wt %, the remainder of the zinc layer being zinc and traces of other elements. 
     
     
         10 . The strip, sheet, blank or tube according to  claim 6 , wherein the pre-coating comprises 0.5 to 4 wt % Al and 0.5 to 3.2 wt % Mg, the remainder of the pre-coating being zinc and traces of other elements. 
     
     
         11 . A method for producing a hot formed product using the strip, sheet, blank or tube according to  claim 6 , comprising the following steps:
 providing the blank from the strip or sheet, or providing the tube   heating the blank or tube to a temperature above Ac1 temperature of the steel, to a temperature of at most 1000° C.   transporting the heated blank or tube into a hot forming press   forming the blank or tube into a product in the press   quenching the product to provide it with desired mechanical properties.   
     
     
         12 . The method according to  claim 11 , wherein the blank or tube is at least partially heated to a temperature higher than Ac1, but lower than 950° C. 
     
     
         13 . The method according to  claim 11 , wherein the heated blank or tube is forcibly cooled before putting it in the hot forming press. 
     
     
         14 . A product produced by the method according to  claim 11 . 
     
     
         15 . A motor vehicle comprising the product according to  claim 14 . 
     
     
         16 . The steel according to  claim 1 , wherein the steel comprises Al≦0.1 wt %, B≦0.00009 wt %, Cr 0.2-0.7 wt %, and Mn+Cr≧2.6 wt %. 
     
     
         17 . The strip, sheet, blank or tube according to  claim 7 , wherein the pre-coating has a thickness between 10 and 40 μm per side. 
     
     
         18 . The strip, sheet, blank or tube according to  claim 9 , wherein the pre-coating has a thickness between 5 and 15 μm per side. 
     
     
         19 . The strip, sheet, blank or tube according to  claim 10 , wherein the pre-coating has a thickness between 5 and 15 μm per side. 
     
     
         20 . The method according to  claim 11 , wherein the blank or tube is at least partially heated to a temperature higher than Ac3, but lower than 900° C., and wherein the product is quenched with an average cooling rate between the furnace and M s  temperature above the critical quenching rate (CQR) to obtain the mechanical properties of R m >1500 MPa but lower than the critical cooling rate (CCR) which is the minimal cooling rate at which 100% martensite is formed.