Hot bend pipe and a process for its manufacture
View Patent ↗A high-strength hot bend pipe which has a balance between an excellent strength of at least X70 grade and toughness and which has excellent tensile properties and a weld metal with excellent low temperature toughness is manufactured. A UOE steel pipe having a base metal with a composition of C: 0.03-0.12%, Si: 0.05-0.50%, Mn: 1.4-2.2%, S: at most 0.01%, Al: at most 0.06%, N: at most 0.008%, and a remainder of Fe and impurities, with the carbon equivalent (Ceq) being at most 0.36% and the weld cracking parameter (Pcm) being at most 0.22%, and having a weld metal with a weld cracking parameter (Pcm) of at most 0.28%, a B content of at most 5 ppm, and an O content of at most 280 ppm is heated to a temperature range of 900-1100° C. and subjected to bending, and then is immediately cooled to a temperature range of 300° C. or lower at a cooling rate of at least 3° C./sec, and then is tempered in a temperature range of 300-500° C.
1. A hot bend pipe for line pipe and having a strength of at least API X70 which is manufactured by carrying out bending of a welded steel pipe after heating to a temperature of at least 900° C. to at most 1100° C. and which has a quenched and tempered structure obtained by cooling after the bending at a cooling rate of at least 3° C. per second to a temperature range of 300° C. or lower followed by tempering in a temperature range of 300-500° C.,
characterized in that the base metal has a composition comprising, in mass percent, C: 0.03-0.12%, Si: 0.05-0.50%, Mn: 1.4-2.2%, S: at most 0.0050%, Al: at most 0.06%, N: at most 0.0070%, and a remainder of Fe and impurities, with the carbon equivalent (Ceq) defined by Equation (1) being at least 0.36% and the weld cracking parameter (Pcm) defined by Equation (2) being at most 0.22%, and
that the weld metal has a weld cracking parameter (Pcm) defined by Equation (2) of at most 0.30%, a B content of at most 5 ppm, and an oxygen content of at most 300 ppm:
Ceq
=
C
+
Mn
6
+
Cr
+
Mo
+
V
5
+
Cu
+
Ni
15
(
1
)
Pcm
=
C
+
Si
30
+
Mn
20
+
Cu
20
+
Ni
60
+
Cr
20
+
Mo
15
+
V
10
+
B
.
(
2
)
2. A hot bend pipe as set forth in claim 1 wherein the base metal further contains, in mass percent, at least one of Cu: at most 1.0%, Ni: at most 2.0%, Cr: at most 1.0%, Mo: at most 1.0%, Nb: at most 0.1%, V: at most 0.1%, and Ti: at most 0.03%.
3. A hot bend pipe as set forth in claim 1 wherein the base metal further contains at most 0.0030 mass percent of B.
4. A hot bend pipe as set forth in claim 1 , wherein the base metal further contains at most 0.005 mass percent of Ca.
5. A hot bend pipe as set forth in claim 2 wherein the base metal further contains at most 0.0030 mass percent of B.
6. A hot bend pipe as set forth in claim 2 , wherein the base metal further contains at most 0.005 mass percent of Ca.
7. A hot bend pipe as set forth in claim 3 , wherein the base metal further contains at most 0.005 mass percent of Ca.
8. A process for manufacturing a hot bend pipe characterized by heating a welded steel pipe having a base metal and a weld metal which satisfy the following conditions to a temperature range of 900-1100° C. and performing bending, then immediately cooling to a temperature range of 300° C. or lower at a cooling rate of at least 3° C./sec, and then performing tempering in a temperature range of 300-500° C.:
base metal: a composition, in mass percent of C: 0.03-0.12%, Si: 0.05-0.50%, Mn: 1.4-2.2%, S: at most 0.0050%, Al: at most 0.06%, N: at most 0.0070%, and a remainder of Fe and impurities, wherein the carbon equivalent (Ceq) defined by Equation (1) is at least 0.36% and the weld cracking parameter (Pcm) defined by Equation (2) is at most 0.22%, and
weld metal: the weld cracking parameter (Pcm) defined by Equation (2) is at most 0.30%, the B content is at most 5 ppm, and the oxygen content is at most 300 ppm:
Ceq
=
C
+
Mn
6
+
Cr
+
Mo
+
V
5
+
Cu
+
Ni
15
(
1
)
Pcm
=
C
+
Si
30
+
Mn
20
+
Cu
20
+
Ni
60
+
Cr
20
+
Mo
15
+
V
10
+
B
.
(
2
)
9. A process for manufacturing a hot bend pipe as set forth in claim 8 wherein the base metal further contains, in mass percent, at least one of Cu: at most 1.0%, Ni: at most 2.0%, Cr: at most 1.0%, Mo: at most 1.0%, Nb: at most 0.1%, V: at most 0.1%, and Ti: at most 0.03%.
10. A process for manufacturing a hot bend pipe as set forth in claim 8 wherein the base metal further contains at most 0.0030 mass percent of B.
11. A process for manufacturing a hot bend pipe as set forth in claim 8 wherein the base metal further contains at most 0.005 mass percent of Ca.
12. A process for manufacturing a hot bend pipe as set forth in claim 8 wherein the welded steel pipe is a UOE steel pipe or a weld pipe for roll bending.
13. A process for manufacturing a hot bend pipe as set forth in claim 9 wherein the base metal further contains at most 0.0030 mass percent of B.
14. A process for manufacturing a hot bend pipe as set forth in claim 9 wherein the base metal further contains at most 0.005 mass percent of Ca.
15. A process for manufacturing a hot bend pipe as set forth in claim 10 wherein the base metal further contains at most 0.005 mass percent of Ca.
16. A process for manufacturing a hot bend pipe as set forth in claim 9 wherein the welded steel pipe is a UOE steel pipe or a weld pipe for roll bending.
17. A process for manufacturing a hot bend pipe as set forth in claim 10 wherein the welded steel pipe is a UOE steel pipe or a weld pipe for roll bending.
18. A process for manufacturing a hot bend pipe as set forth in claim 11 wherein the welded steel pipe is a UOE steel pipe or a weld pipe for roll bending.