Steel strip, sheet or blank for producing a hot formed part, part, and method for hot forming a blank into a part

Abstract

A hot formed part produced from such a steel strip, sheet or blank, to the use of such a hot formed part, and to a method for forming such a steel blank or a preformed part made from such a blank, into a part.

1 . The steel strip, sheet or blank for producing hot formed parts having the following composition in weight %:
 C: 0.03-0.17,   Mn: 0.65-2.50,   Cr: 0.2-2.0,   Ti: 0.01-0.10,   Nb: 0.01-0.10,   B: 0.0005-0.005,   N: ≤0.01,   wherein Ti/N≥3.42,   and optionally one or more of the elements selected from:   Si: ≤0.1,   Mo: ≤0.1,   Al: ≤0.1,   Cu: ≤0.1,   P: ≤0.03,   S: ≤0.025,   O: ≤0.01,   V: ≤0.15,   Ni: ≤0.15   Ca: ≤0.15   the remainder being iron and unavoidable impurities.   
     
     
         2 . The steel strip, sheet or blank according to  claim 1 , wherein:
 C: 0.05-0.17, and/or   Mn: 1.00-2.10, and/or   Cr: 0.5-1.7, and/or   Ti: 0.015-0.07, and/or   Nb: 0.02-0.08, and/or   B: 0.0005-0.004, and/or   N: 0.001-0.008,   Ca: ≤0.01.   
     
     
         3 . The steel strip, sheet or blank according to  claim 1 , wherein the sum of the amount of Mn and Cr is less than 2.7. 
     
     
         4 . The steel strip, sheet or blank according to  claim 1 , wherein Mn, Cr and B are used in such amounts that (B×1000)/(Mn+Cr) is in the range of from 0.185-2.5. 
     
     
         5 . The steel strip, sheet or blank according to  claim 1 , provided with a zinc based coating or an aluminium based coating or an organic based coating. 
     
     
         6 . The steel strip, sheet or blank according to  claim 5 , wherein the zinc based coating is a coating containing 0.2-5.0 wt % Al, 0.2-5.0 wt % Mg, optionally at most 0.3 wt % of one or more additional elements, the balance being zinc and unavoidable impurities. 
     
     
         7 . A hot formed part produced from a steel strip, sheet or blank according to  claim 1 , the hot formed part having a tensile strength of at least 750 MPa. 
     
     
         8 . The hot formed part according to  claim 7 , having a total elongation (TE) of at least 5% and/or a bending angle (BA) at 1.0 mm thickness of at least 100°. 
     
     
         9 . The hot formed part according to  claim 7 , the hot formed part having a microstructure comprising at most 60% bainite, the remainder being martensite. 
     
     
         10 . A method of use of a hot formed part according to  claim 7 , comprising forming the hot formed part into a structural part in a body-in-white of a vehicle. 
     
     
         11 . A method for hot-forming a steel blank or a pre-formed part into a part comprising the steps of:
 a. heating the blank, or a pre-formed part produced from the blank, wherein the blank or the blank from which the pre-formed part is produced is according to  claim 1 , to a temperature T 1  and holding the heated blank at T 1  during a time period t 1 , wherein T 1  is higher than the Ac 3  temperature of the steel, and wherein t 1  is at most 10 minutes;   b. transferring the heated blank or pre-formed part to a hot-forming tool during a transport time t 2  during which the temperature of the heated blank or preformed part decreases from temperature T 1  to a temperature T 2 , wherein the transport time t 2  is at most 20 seconds;   c. hot forming the heated blank or preformed part into a part; and   d. cooling the part in the hot-forming tool to a temperature below the Mf temperature of the steel with a cooling rate of at least 30° C./s.   
     
     
         12 . The method according to  claim 11 , wherein the temperature T 1  in step (a) is 50-100° C. higher than the Ac 3  and/or the temperature T 2  is above Ar 3 . 
     
     
         13 . The method according to  claim 11 , wherein the time period t 1  in step (a) is at least 1 minute and at most 7 minutes and/or the time period t 2  in step (b) is at most 12 seconds. 
     
     
         14 . The method according to  claim 11 , wherein the part is cooled in step (d) with a cooling rate in the range of 30-150° C./s. 
     
     
         15 . A vehicle comprising at least one hot formed part according to  claim 7 . 
     
     
         16 . A vehicle comprising at least one hot formed part produced according to  claim 11 . 
     
     
         17 . The steel strip, sheet or blank according to  claim 1 , wherein:
 C: 0.07-0.15,   Mn: 1.20-1.80,   Cr: 0.8-1.5,   Ti: 0.025-0.05,   Nb: 0.03-0.07,   B: 0.001-0.003,   N: 0.002-0.005, and   Ca: ≤0.01.   
     
     
         18 . The steel strip, sheet or blank according to  claim 1 , wherein the sum of the amount of Mn and Cr is between 0.5 and 2.5. 
     
     
         19 . The steel strip, sheet or blank according to  claim 1 , wherein Mn, Cr and B are used in such amounts that (B×1000)/(Mn+Cr) is in the range of from 0.5-1.5. 
     
     
         20 . The hot formed part produced from a steel strip, sheet or blank according to  claim 1 , the part having a tensile strength of at most 1400 MPa. 
     
     
         21 . The hot formed part according to  claim 7  having a total elongation (TE) of at least 7% and/or a bending angle (BA) at 1.0 mm thickness of at least 140°. 
     
     
         22 . The hot formed part according to  claim 7 , the part having a microstructure comprising at most 40% bainite, the remainder being martensite. 
     
     
         23 . The method according to  claim 11 , wherein the time period t 1  in step (a) is at least 1 minute and at most 7 minutes and/or the time period t 2  is between 2 and 10 seconds. 
     
     
         24 . The method according to  claim 11 , wherein the part is cooled in step (d) with a cooling rate of 30-100° C./s.