Shaped sheet metal part with improved processing properties

Abstract

The invention relates to a process for producing a shaped sheet metal part having at least one first and one second zone having different material properties, and to such a shaped sheet metal part.

1 .- 16 . (canceled) 
     
     
         17 . A process for producing a shaped sheet metal part having at least one first zone and one second zone having different material properties, comprising following steps:
 (a) providing a sheet metal blank made from a flat steel product comprising a steel substrate composed of steel comprising iron, unavoidable impurities, and in % by weight:
 C: 0.27-0.5%, 
 Si: 0.05-0.6%, 
 Mn: 0.4-3.0%, 
 Al: 0.10-1.0%, 
 Nb: 0.001-0.2%, 
 Ti: 0.001-0.10%, 
 B: 0.0005-0.01%, 
 P: ≤0.03%, 
 S: ≤0.02%, 
 N: ≤0.02%, 
 Sn: ≤0.03%, and 
 As: ≤0.01%; 
   (b) heating the sheet metal blank such that an Ac3 temperature of the sheet metal blank is at least partly exceeded and a temperature T ins  of the sheet metal blank on insertion into a forming tool provided for a hot press forming operation in step (c) is at least partly at a temperature above Ms+100° C. where Ms is a martensite start temperature;   (c) inserting the heated sheet metal blank into a forming tool, where the forming tool has a temperature control device for closed-loop control of temperature of at least one of its sections that comes into contact with the sheet metal blank during the hot press forming, and where a transfer time t trans  required for removing from a heating device and the inserting of the heated sheet metal blank is not more than 20 s, preferably not more than 15 s;   (d) hot press forming the sheet metal blank to the shaped sheet metal part, where the sheet metal blank, in the course of hot press forming, is cooled down to a first target temperature in the first zone and a second target temperature in the second zone, where the second target temperature is greater than the first target temperature, in order to establish a different microstructure in the first and second zones; and   (e) removing the cooled shaped sheet metal part from the tool.   
     
     
         18 . The process of  claim 17 , wherein the steel substrate composed of the steel further comprises one or more of elements Cr, Cu, Mo, Ni, V, Ca, and W in following contents:
 Cr: 0.01-1.0%,   Cu: 0.01-0.2%,   Mo: 0.002-0.3%,   Ni: 0.01-0.5%,   V: 0.001-0.3%,   Ca: 0.0005-0.005%, and   W: 0.001-1.0%.   
     
     
         19 . The process as claimed in  claim 17 , characterized in that the sections that come into contact with the sheet metal blank during the hot press forming include at least one first section and one second section, where the first section comes into contact with the first zone during the hot press forming and the second section comes into contact with the second zone during the hot press forming, and where the first section is heated to a first tool temperature and the second section is heated to a second tool temperature, where the first tool temperature is lower than the second tool temperature. 
     
     
         20 . The process as claimed in  claim 19 , characterized in that the first tool temperature is not more than 200° C. and/or the second tool temperature is at least 200° C. 
     
     
         21 . The process as claimed in  claim 19 , characterized in that the first target temperature is not more than 250 K above the first tool temperature and/or the second target temperature is not more than 100 K above the second tool temperature. 
     
     
         22 . The process as claimed in  claim 17 , characterized in that cooling characteristics of the sheet metal blank in step (d) are established at least partly via contact pressures applied in the forming tool. 
     
     
         23 . The process as claimed  claim 17 , characterized in that a forming rate in the hot press forming operation in step (d) is controlled with reference to a duration for which the section of the forming tool which is under closed-loop control in respect of its temperature comes into contact with the sheet metal blank during the hot press forming. 
     
     
         24 . The process as claimed in  claim 17 , characterized in that the sheet metal blank has regions of different thickness. 
     
     
         25 . The process as claimed in  claim 17 , characterized in that the forming tool has a die and a ram adjustable for forming in a recess of the die. 
     
     
         26 . The process as claimed in  claim 17 , characterized in that the temperature control device is designed in a form of a cooling device and/or in a form of the heating device. 
     
     
         27 . The process as claimed in  claim 17 , characterized in that the sections that come into contact with the sheet metal blank during the hot press forming include at least one first section and one second section, where the first section comes into contact with the first zone during the hot press forming and the second section comes into contact with the second zone during the hot press forming, where the first section is heated to the first tool temperature by means of the temperature control device configured as a cooling device and the second section is heated to the second tool temperature by means of a temperature control device configured as a heating device. 
     
     
         28 . The process as claimed in  claim 17 , characterized in that the flat steel product comprises an aluminum-based anticorrosion coating, where the anticorrosion coating especially comprises an alloy layer and an Al base layer. 
     
     
         29 . The process as claimed in  claim 17 , wherein the shaped sheet metal part is held at the first target temperature in the first zone before it is removed from the tool. 
     
     
         30 . A shaped sheet metal part formed from a flat steel product comprising a steel substrate made of steel comprising iron, unavoidable impurities, and in % by weight:
 C: 0.27-0.5%,   Si: 0.05-0.6%,   Mn: 0.4-3.0%,   Al: 0.10-1.0%,   Nb: 0.001-0.2%,   Ti: 0.001-0.10%,   B: 0.0005-0.01%,   P: ≤0.03%,   S: ≤0.02%,   N: ≤0.02%,   Sn: ≤0.03%, and   As: ≤0.01%,   wherein the shaped sheet metal part comprises at least one first zone and one second zone,   wherein the shaped sheet metal part has a different microstructure in the first zone and in the second zone,   wherein the shaped sheet metal part has, in the first zone, one or more characteristics of:   a yield point of at least 1200 MPa, especially at least 1300 MPa;   a tensile strength of at least 1400 MPa, especially at least 1600 MPa;   an elongation at break A80 of at least 3.5%, especially at least 4%, especially at least 4.5%, preferably at least 5%;   a bending angle of at least 30°, especially at least 40°, preferably at least 45°;   a yield point ratio of at least 60% and at most 85%; and   Vickers hardness of at least 500 HV5, especially at least 540 HV5,   wherein the shaped sheet metal part has, in the second zone, one or more characteristics of:   a yield point of not more than 800 MPa, preferably of not more than 600 MPa, especially not more than 580 MPa;   a tensile strength of not more than 1000 MPa, especially of not more than 800 MPa;   an elongation at break A80 of at least 8%, especially at least 10%;   a bending angle of at least 80°, especially at least 90°, preferably at least 100°;   a yield point ratio of at least 60% and at most 85%; and   a Vickers hardness of not more than 320 HV5, especially of not more than 300 HV5, especially not more than 270 HV5.   
     
     
         31 . The shaped sheet metal part as claimed in  claim 30 , wherein the steel substrate made of the steel further comprises one or more of elements Cr, Cu, Mo, Ni, V, Ca, and W in following contents:
 Cr: 0.01-1.0%,   Cu: 0.01-0.2%,   Mo: 0.002-0.3%,   Ni: 0.01-0.5%,   V: 0.001-0.3%,   Ca: 0.0005-0.005%, and   W: 0.001-1.0%.   
     
     
         32 . The shaped sheet metal part as claimed in  claim 30 , characterized in that the shaped sheet metal part in the first zone has a microstructure with more than 95% martensite, especially more than 98%, and/or the shaped sheet metal part in the second zone has a microstructure with less than 95% annealed martensite and bainite and optionally up to 60% pearlite, where the residual austenite content is especially less than 3%, preferably less than 1%. 
     
     
         33 . The shaped sheet metal part as claimed in  claim 30 , where the Al/Nb ratio of Al content to Nb content is subject to following conditions: 
       
         
           
             
               
                 Al 
                 / 
                 Nb 
               
               ≤ 
               
                 20. 
                     
                 when 
                 ⁢ 
                     
                 Mn 
               
               ≤ 
               
                 1.6 
                 % 
                 ⁢ 
                     
                 by 
                 ⁢ 
                     
                 weight 
               
             
           
         
         
           
             and 
           
         
         
           
             
               
                 Al 
                 / 
                 Nb 
               
               ≤ 
               
                 30. 
                     
                 when 
                 ⁢ 
                     
                 Mn 
               
               ≥ 
               
                 1.7 
                 % 
                 ⁢ 
                     
                 by 
                 ⁢ 
                     
                 
                   weight 
                   . 
                 
               
             
           
         
       
     
     
         34 . The shaped sheet metal part as claimed in  claim 30 , characterized in that the shaped sheet metal part in the first zone has largely fine precipitates in the microstructure, especially in a form of niobium carbonitrides and/or titanium carbonitrides. 
     
     
         35 . The shaped sheet metal part as claimed in  claim 30 , comprising an aluminum-based anticorrosion coating, where the anticorrosion coating especially comprises an alloy layer and an Al base layer.