US2021115527A1PendingUtilityA1

Method for manufacturing a hot-formed article, and obtained article

Assignee: TATA STEEL IJMUIDEN BVPriority: Nov 29, 2016Filed: Nov 24, 2017Published: Apr 22, 2021

Est. expiryNov 29, 2036(~10.3 yrs left)· nominal 20-yr term from priority

Inventors:Shangping Chen Christiaan Theodorus Wilhelmus Lahaye Radhakanta Rana Guido Cornelis Hensen

C21D 2211/002C21D 9/0068C21D 1/19C22C 38/06C22C 38/22C21D 2211/005C22C 38/28C22C 38/34C23C 2/06C22C 38/26C21D 2211/001C21D 2211/008C22C 38/24C22C 38/38C22C 38/32

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References

Claims

Abstract

A method for hot-forming a steel blank into an article including the steps of: a. heating a steel blank to a temperature T 1 and holding the heated blank at T 1 during a time period t 1 , wherein T 1 is in the range of Ac 1 to Ac 3 +200° C. and wherein t 1 is at most 12 minutes, b. transferring the heated blank to a hot-forming tool during a transport time t 2 during which the temperature of the heated blank decreases from temperature T 1 to a temperature T 2 , wherein T 2 is above Ar 1 and wherein the transport time t 2 is at most 12 seconds, c. forming the blank in the hot-forming tool into an article and quenching it in the hot-forming tool from a temperature T 2 to a temperature T 3 at a cooling velocity V 2 of 25° C./s or more, d. isothermal holding the article at a temperature T 4 for a time period t 4, e. wherein temperature T 3 and/or temperature T 4 is between Ms and Mf and wherein t 4 is more than 10 seconds and less than 10 minutes, f. cooling the article from temperature T 4 to room temperature at a cooling velocity V 4. The invention also relates to a hot-formed article obtained by the method.

Claims

exact text as granted — not AI-modified

1 . A method for hot-forming a steel blank into an article comprising the steps of:
 a. heating a steel blank to a temperature T 1  and holding the heated blank at T 1  during a time period t 1 , wherein T 1  is in the range of Ac 1  to Ac 3 +200° C. and wherein t 1  is at most 12 minutes,   b. transferring the heated blank to a hot-forming tool during a transport time t 2  during which the temperature of the heated blank decreases from temperature T 1  to a temperature T 2 , wherein T 2  is above Ar 1  and wherein the transport time t 2  is at most 12 seconds,   c. forming the blank in the hot-forming tool into an article and quenching it in the hot-forming tool from temperature T 2  to a temperature T 3  at a cooling velocity V 2  of 25° C./s or more,   d. isothermal holding the article at a temperature T 4  for a time period t 4 ,   e. wherein temperature T 3  and/or temperature T 4  is between Ms and Mf and wherein t 4  is more than 10 seconds and less than 10 minutes,   f. cooling the article from temperature T 4  to room temperature at a cooling velocity V 4 , wherein
 1. T 3  is between Ms and Mf and wherein T 4  is between Bs and Ms, or 
 2. T 3  is between Bs and Ms and wherein T 4  is between Ms and Mf, or 
 3. both T 3  and T 4  are between Ms and Mf, 
   and wherein the microstructure of the hot-formed article is a complex phase microstructure consisting of, by volume fraction (vol. %) (sum up to 100)
 at least 80 vol. % bainite and tempered martensite, wherein the tempered martensite is less than 50 vol. %, and 
 at most 20 vol. % ferrite and/or martensite, and/or retained austenite. 
   
     
     
         2 . The method according to  claim 1 , wherein the article is held at temperature T 3  during a holding time  3  of 1 to 180 seconds. 
     
     
         3 . The method according to  claim 1 , wherein the article is heated from temperature T 3  to temperature T 4  at a velocity V 3  of at least 15° C./s. 
     
     
         4 . The method according to  claim 1 , wherein the article is cooled from temperature T 3  to temperature T 4  at a velocity t 3  of at most 15° C./s. 
     
     
         5 . The method according to  claim 1 , wherein the article is cooled from temperature T 4  to room temperature at a cooling velocity V 4 , in the range of 0.1-20° C./s. 
     
     
         6 . The method according to  claim 1 , wherein T 1  is in the range of Ac 1  to Ac 3 +150, and wherein the steel blank is heated with a heating velocity V 1  in the range of 10-25° C./s. 
     
     
         7 . The method according to  claim 1 , wherein the steel blank comprises in wt %:
 C: 0.10-0.50,   Mn: 0.50-4.00,   Si: &lt;2.0,   Al: &lt;2.0,   Cr: &lt;1.5,   Ti: &lt;0.10,   B: &lt;0.008,   Nb: &lt;0.10,   and optionally one or more of the elements selected from   V: &lt;0.2,   Ca: &lt;0.003,   N: &lt;0.005,   P: &lt;0.015,   S: &lt;0.03,   Mo: &lt;0.5,   Cu: &lt;1.0,   Ni: &lt;1.0,   the remainder being Fe and unavoidable impurities.   
     
     
         8 . The method according to  claim 1 , wherein the blank, is provided with a zinc based coating or an aluminium based coating or an organic based coating or any other coating designed to reduce oxidation and/or decarburisation during the hot forming process. 
     
     
         9 . The method according to  claim 8 , wherein the zinc based coating is a coating containing 0.5-3.8 wt % Al, 0.5-3.0 wt % Mg, optionally at most 0.2 wt % of one or more additional elements, unavoidable impurities, the balance being zinc. 
     
     
         10 . The hot-formed steel article obtained by the method according to  claim 1 , wherein the steel comprises in wt %:
 C: 0.10-0.50,   Mn: 1.00-3.00   Si: ≤2.0;   Al: ≤2.0,   Cr: ≤1.5,   Ti: ≤0.10,   B: ≤0.008,   Nb: ≤0.10,   and optionally one or more of the elements selected from   V: ≤0.2,   Ca: ≤0.003,   N: ≤0.005,   P: ≤0.015,   S: ≤0.03,   Mo: ≤0.5,   Cu: ≤1.0,   Ni: ≤1.0,   the remainder being Fe and unavoidable impurities,   wherein the article has a YS of at least 600 MPa, and a UTS of at least 1000 MPa, and   wherein the article has a total elongation (TE) of at least 6% and a bending angle (BA) of at least 45°.   
     
     
         11 - 15 . (canceled) 
     
     
         16 . The method according to  claim 1 , wherein
 1. T 3  is between Ms and Mf and wherein T 4  is between Bs and Ms, or   2. T 3  is between Bs and Ms and wherein T 4  is between Ms and Mf, or   3. both T 3  and T 4  are between Ms and Mf, and T 3  and T 4  are the same,   and wherein the microstructure of the hot-formed article is a complex phase microstructure consisting of, by volume fraction (vol. %) (sum up to 100)
 at least 80 vol. % bainite and tempered martensite, wherein the tempered martensite is equal or less than 40 vol. %, and 
 at most 20 vol. % ferrite and/or martensite, and/or retained austenite. 
   
     
     
         17 . The method according to  claim 1 , wherein the microstructure of the hot-formed article is a complex phase microstructure consisting of, by volume fraction (vol. %) (sum up to 100)
 at least 80 vol. % bainite and tempered martensite, wherein the tempered martensite is equal or less than 30 vol. %, and   at most 20 vol. % ferrite and/or martensite, and/or retained austenite.   
     
     
         18 . The method according to  claim 3 , wherein the article is heated from temperature T 3  to temperature T 4  at a velocity V 3  of at least 20° C./s. 
     
     
         19 . The method according to  claim 3 , wherein the article is heated from temperature T 3  to temperature T 4  at a velocity V 3  of at least 30° C./s. 
     
     
         20 . The method according to  claim 4 , wherein the article is cooled from temperature T 3  to temperature T 4  at a velocity t 3  of at most 10° C./s. 
     
     
         21 . The method according to  claim 4 , wherein the article is cooled from temperature T 3  to temperature T 4  at a velocity  3  of at most 8° C./s. 
     
     
         22 . The method according to  claim 5 , wherein the article is cooled from temperature T 4  to room temperature at a cooling velocity V 4 , in the range of 1-15° C./s. 
     
     
         23 . The method according to  claim 5 , wherein the article is cooled from temperature T 4  to room temperature at a cooling velocity V 4 , in the range of 2-10° C./s. 
     
     
         24 . The method according to  claim 6 , wherein T 1  is in the range of Ac 1  to Ac 3 +100, and wherein t 1  is at most 10 minutes, and wherein the steel blank is heated with a heating velocity V 1  in the range of 10-25° C./s. 
     
     
         25 . The method according to  claim 6 , wherein T 1  is in the range of Ac 3 −50 to Ac 3 +50, and wherein t 1  is in the range of 2-8 min, and wherein the steel blank is heated with a heating velocity V 1  in the range of 10-25° C./s. 
     
     
         26 . The method according to  claim 7 , wherein the steel blank comprises in wt %:
 C: 0.15-0.40,   Mn: 1.00-3.00,   Si: 0.1-2.0,   Al: &lt;1.0,   Cr: &lt;1.2,   Ti: &lt;0.05,   B: &lt;0.005,   Nb: &lt;0.05,   and optionally one or more of the elements selected from   V: &lt;0.1   Ca: 0.0003-0.003,   N: &lt;0.003,   P: &lt;0.015,   S: &lt;0.01,   Mo: &lt;0.05,   Cu: &lt;1.0,   Ni: &lt;1.0,   the remainder being Fe and unavoidable impurities.   
     
     
         27 . The method according to  claim 1 , wherein the steel blank comprises in wt %:
 C: 0.15-0.35,   Mn: 1.00-2.50,   Si: 0.1-1.6,   Al: &lt;0.5,   Cr: 0.001-1.1,   Ti: &lt;0.04,   B: &lt;0.005,   Nb: 0.001-0.05,   and optionally one or more of the elements selected from   V: &lt;0.1   Ca: 0.0003-0.003,   N: &lt;0.003,   P: &lt;0.015,   S: &lt;0.01,   Mo: &lt;0.05,   Cu: &lt;1.0,   Ni: &lt;1.0,   the remainder being Fe and unavoidable impurities.

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