Use of a Steel for an Additive Manufacturing Process, Method for Producing a Steel Component and Steel Component

Abstract

The production of steel components in an additive process using a steel powder having a mean grain diameter of 5-150 μm, and comprising (in wt % ) 0.08-0.35% C, up to 0.80% Si, 0.20-2.00% Mn, up to 4.00% Cr, 0.3-3.0% Mo, 0.004-0.020% N, 0.004-0.050% Al, up to 0.0025% B, up to 0.20% Nb, up to 0.02% Ti, up 0.40% V, up to 1.5% Ni, up to 0.3% Cu, up to 2.0% Co, at least one of Nb, Ti, V, and S, wherein Nb is 0.003-0.20%, Ti is 0.001-0.02%, V is 0.02-0.40% and/or S is 0.001-0.4%, and the remainder being iron and unavoidable impurities, where % Al/27+% Nb/45+% Ti/48+% V/25>% N/3.5. The steel component has a structure including at least 80 vol % of bainite, with the remainder being retained austenite, ferrite, perlite and/or martensite. and after shaping and before an optional heat treatment, has a tensile strength of ≥900 MPa, a yield strength of ≥560 MPa and an elongation at break A5.65 of ≥8%.

1 . A steel powder for the production of steel components by an additive manufacturing process which comprises (in wt %):
 C: 0.08-0.35%,   Si: 0-0.80%,   Mn: 0.20-2.00%,   Cr: 0-4.00%,   Mo: 0.3-3.0%,   N: 0.004-0.020%,   Al: 0.004-0.050%,   B: 0-0.0025%,   Cu: 0-0.3%,   Co: 0-2.0%,   at least one element from the group consisting of Nb, Ti, V, and S, wherein   the Nb content is 0.003-0.20 wt %,   the Ti content is 0.001-0.02 wt %,   the V content is 0.02-0.40 wt %   and/or   the S content is 0.001-0.4 wt %,   with the remainder being iron and unavoidable impurities,   wherein the Al content % Al, the Nb content % Nb, the Ti content % Ti, the V content % V and the N content % N of the steel satisfy the following condition:
   %Al/27+%Nb/45+%Ti/48+%V/25>%N/3.5, 
   and wherein the grains of the steel powder have an average diameter of 5-150 μm.   
     
     
         2 . The steel powder according to  claim 1 , wherein the steel powder has a C content of at least 0.09 wt %. 
     
     
         3 . The steel powder according to  claim 1 , wherein the steel powder has a Cr content of at least 0.5 wt %. 
     
     
         4 . The steel powder according to  claim 1 , wherein the S content of the steel powder is at least 0.003 wt %. 
     
     
         5 . The steel powder according to  claim 1 , wherein the S content of the steel powder is at most 0.1 wt %. 
     
     
         6 . The steel powder according to  claim 1 , wherein the steel powder has a B content of at least 0.0005 wt %. 
     
     
         7 . The steel powder according to  claim 1 , wherein the steel powder has an N content of at least 0.006 wt %. 
     
     
         8 . The steel powder according to  claim 1 , wherein the steel powder has a Cu content of less than 0.3 wt %. 
     
     
         9 . The steel powder according to  claim 1 , wherein the steel powder has an Mo content of less than 0.7 wt %. 
     
     
         10 . A method for producing a steel component, comprising:
 a) melting a steel which comprises (in wt %):
 C: 0.08-0.35%, 
 Si: 0-0.80%, 
 Mn: 0.20-2.00%, 
 Cr: 0-4.00%, 
 Mo: 0.3-3.0%, 
 N: 0.004-0.020%, 
 Al: 0.004-0.050%, 
 B: 0-0.0025%, 
 Cu: 0-0.3%, 
 Co: 0-2.0%, 
 at least one element from the group consisting of Nb, Ti, V, and S, wherein 
 the Nb content is 0.003-0.20 wt %, 
 the Ti content is 0.001-0.02 wt %, 
 the V content is 0.02-0.40 wt % 
 and/or 
 the S content is 0.001-0.4 wt %, 
 with the remainder being iron and unavoidable impurities, 
 wherein the Al content % Al, the Nb content % Nb, the Ti content % Ti, the V content % V and the N content % N of the steel satisfy the following condition:
   %Al/27+%Nb/45+%Ti/48+%V/25>%N/3.5; 
 
   b) producing a steel powder from the steel melted in step a), wherein the grains of the steel powder have an average diameter of 5-150 μm;   c) producing the component by using an additive manufacturing process, wherein
 c.1) at least one portion of the steel powder by volume is exposed to a temporary heat input with subsequent cooling, so that the steel powder particles, which are present in the heated volume portion and respectively adjoin each other, enter into a firmly-bonded connection and are solidified after cooling to form at least one volume portion of the component to be produced; and 
 c.2) optionally, re-applying a further portion of the steel powder to the volume portion solidified in step c.1) and repeating step c.1) with the further portion of the steel powder, wherein steps c.1) and c.2) are repeated until the component to be produced is completely finished. 
   
     
     
         11 . A steel component produced according to the method of  claim 10 . 
     
     
         12 . The steel component according to  claim 11 , wherein a structure of the steel component comprises at least 80 vol % bainite and the remainder of the structure comprises retained austenite, ferrite, perlite and/or martensite. 
     
     
         13 . The steel component according to  claim 11 , wherein before the optional step e), the steel component has a tensile strength of at least 900 MPa, a yield strength of at least 560 MPa and an elongation at break A5.65 of at least 8%. 
     
     
         14 . The steel component according to  claim 11 , wherein after the optional step e), the steel component has a tensile strength of at least 1050 MPa, a yield strength of at least 615 MPa and an elongation at break A5.65 is at least 8%. 
     
     
         15 . The method according to  claim 11 , further comprising machining the produced component to shape. 
     
     
         16 . The method according to  claim 11 , further comprising final heat treating the resulting produced component to form strength increasing precipitates in the structure of the component. 
     
     
         17 . The method according to  claim 16 , wherein the heat treating is an ageing process in which the component is held at a temperature of 450-600° C. over a period of 0.5-6 hours.