Weldable steel building component and method for making same
The invention concerns weldable steel building components whereof the chemical composition comprises, by weight: 0.10%≦C≦0.22%, 0.50%≦Si≦1.50%, AI≦0.9%, 0%≦Mn≦3%, 0%≦Ni≦5%, 0%≦Cr≦4%, 0%≦Cu≦1%, 0%≦Mo+W/2≦1.5%, 0.0005%≦B<0.010%, N≦0.025%, optionally at least one element selected among V, Nb, Ta, S et Ca, in contents less than 0.3%, and/or among Ti and Zr in contents not more than 0.5%, the rest being iron and impurities resulting from preparation, the aluminium, boron, titanium and nitrogen contents, expressed in thousandths of %, of said composition further satisfying the following relationship: B≦⅓×K+0.5, (1) with K=Min (I*; J*), I*=Max (0; I) and J*=Max (0; J), I=Min (N; N−0.29(Ti−5)), J=Min {N; 0.5 (N 0.52 AI+√j(N 0.52 AI) 2 +283)}, the silicon and aluminium contents of the composition additionally verifying the following conditions: if C>0.145, then Si+AI<0.95 and whereof the structure is bainitic, martensitic or martensitic/bainitic and further comprises 3 to 20% of residual austenite.
1. Weldable component of structural steel, wherein the chemical composition comprises, by weight:
0.10%≦C≦0.22%
0.50%≦Si≦1.50%
0%<Al≦0.9%
0%≦Mn≦3%
0%≦Ni≦5%
0%≦Cr≦4%
0%≦Cu≦1%
0%≦Mo+W/2≦1.5%
0.0005%≦B≦0.010%
0%<N≦0.025%
optionally at least one element selected from V, Nb, Ta, S and Ca, at contents of less than 0.3%, and/or from Ti and Zr at contents of less than or equal to 0.5%, the remainder being iron and impurities resulting from the production operation,
the contents of aluminium, boron, titanium and nitrogen, expressed in thousandths of %, of the composition also satisfying the following relationship:
B
≥
1
3
×
K
+
0.5
,
(
1
)
with K=Min (I*; J*)
I*=Max (0; I) and J*=Max (0; J)
I=Min (N; N−0.29(Ti−5))
J=Min (N; 0.5(N−0.52 Al+√{square root over ((N−0.52 Al) 2 ÷283)})),
the contents of silicon and aluminium of the composition also complying with the following conditions:
if C>0.145, then Si+Al<0.95;
whose structure is bainitic, martensitic or martensitic-bainitic and also comprises from 3 to 20% of residual austenite; and
the chemical composition also satisfies the following relationship:
% Cr+3(% Mo+% W/2)≧1.8.
2. Steel component according to claim 1 , wherein chemical composition also satisfies the following relationship:
1.1% Mn+0.7% Ni+0.6% Cr+1.5(% Mo+% W/2)≧1 (2).
3. Steel component according to claim 2 , wherein the chemical composition satisfies the following relationship:
1.1% Mn+0.7% Ni+0.6% Cr+1.5(% Mo+% W/2)≧2 (2).
4. Steel component according to claim 1 , wherein chemical composition also satisfies the following relationship:
% Cr+3(% Mo+% W/2)≧2.0.
5. Method for manufacturing a weldable steel component according to claim 1 , comprising
austentizing the component by heating at a temperature of from Ac 3 to 1000° C., and it is then cooled to a temperature of less than or equal to 200° C., in such a manner that, at the core of the component, the rate of cooling between 800° C. and 500° C. is greater than the critical bainitic velocity, and
optionally, tempering at a temperature of less than or equal to Ac 1 .
6. Method according to claim 5 , wherein, at the core of the component, the cooling rate between 500° C. and a temperature of less than or equal to 200° C. is from 0.07° C./s to 5° C./s.
7. Method according to claim 5 or 6 , wherein, after cooling tempering is effected at a temperature of less than 300° C. for a period of time of less than 10 hours.
8. Method according to claim 5 or 6 , wherein no tempering is carried out.
9. Method for manufacturing a weldable steel plate comprising the steel component according claim 1 , wherein the thickness of the steel plate is from 3 mm to 150 mm, comprising quenching the plate, wherein the cooling rate V R at the core of the component between 800° C. and 500° C. and the composition of the steel being such that:
1.1% Mn+0.7% Ni+0.6% Cr+1.5(% Mo+% W/2)+log V R ≧5.5
wherein V R being in ° C./hour.
10. Method for manufacturing a weldable steel plate according to claim 9 , the cooling rate V R at the core of the component between 800° C. and 500° C. and the composition of the steel being such that:
1.1% Mn+0.7% Ni+0.6% Cr+1.5(% Mo+% W/2)+log V R ≧6
wherein V R being in ° C./hour.
11. Method according to claim 5 , wherein the chemical composition of the steel satisfies the following relationship:
1.1% Mn+0.7% Ni+0.6% Cr+1.5(% Mo+% W/2)≧1 (2).
12. Method according to claim 11 , wherein the chemical composition of the steel satisfies the following relationship:
1.1% Mn+0.7% Ni+0.6% Cr+1.5(% Mo+% W/2)≧2 (2).
13. Method according to claim 5 , wherein the chemical composition of the steel satisfies the following relationship:
% Cr+3(% Mo+% W/2)≧2.0.
14. Method according to claim 9 , wherein the chemical composition of the steel satisfies the following relationship:
1.1% Mn+0.7% Ni+0.6% Cr+1.5(% Mo+% W/2)≧1 (2).
15. Method according to claim 14 , wherein the chemical composition of the steel satisfies the following relationship:
1.1% Mn+0.7% Ni+0.6% Cr+1.5(% Mo+% W/2)≧2 (2).
16. Method according to claim 9 , wherein the chemical composition of the steel satisfies the following relationship:
% Cr+3(% Mo+% W/2)≧2.0.