Tube shell for manufacturing a seamless steel pipe and a method for its manufacture
View Patent ↗A pierced shell of an austenitic stainless steel having a good inner surface condition is provided, and a means is established which can perform mass production on an industrial scale of a good quality seamless steel pipe of stainless steel. An austenitic stainless steel billet with a P content of at most 0.040% and an S content of at most 0.020% is pierced under conditions such that the pipe expansion ratio H (outer diameter of shell/diameter of billet to be worked) satisfies the following equation to obtain a tube shell of an austenitic stainless steel. {P(%)/(0.025×H−0.01)} 2 +{S(%)/(0.015×H−0.01)} 2 ≦1. When manufacturing a seamless steel pipe of an austenitic stainless steel, the above-described shell is rolled to form a pipe.
1. A tube shell for manufacturing a seamless steel pipe of austenitic stainless steel, characterized in that the P content of the steel constituting the shell is at most 0.040 mass % and the S content is at most 0.020 mass %, and the shell is pierced with skewed rolls under conditions that the pipe expansion ratio H satisfies the following equation.
[
P
0.025
×
H
-
0.01
]
2
+
[
S
0.015
×
H
-
0.01
]
2
≤
1
[
Equation
1
]
wherein
H=outer diameter of shell (mm)/diameter of billet (mm)
P: P content of shell (mass %)
S: S content of shell (mass %).
2. A tube shell as claimed in claim 1 wherein the austenitic stainless steel contains a total of at least 10 mass % of at least one of Al, Cr, Cu, Mn, Mo, Ni, Nb, Si, Ti, W, V, and Zr.
3. A tube shell as claimed in claim 1 wherein the pipe expansion ratio is at least 1.15.
4. A tube shell as claimed in claim 1 wherein the P content of the steel is at most 0.020 mass % and the S content is at most 0.005 mass %.
5. A tube shell as claimed in claim 1 wherein the ratio of t/d is at most 7% in which “t” is the wall thickness of the shell after piercing and “d” is the outer diameter of the shell after piercing.
6. A method of manufacturing a seamless steel pipe of a high alloy steel, characterized by performing piercing of a tube shell for manufacturing a seamless steel pipe as claimed in claim 1 and then performing sizing.
7. A tube shell as claimed in claim 2 wherein the pipe expansion ratio is at least 1.15.
8. A tube shell as claimed in claim 2 wherein the P content of the steel is at most 0.020 mass % and the S content is at most 0.005 mass %.
9. A tube shell as claimed in claim 3 wherein the P content of the steel is at most 0.020 mass % and the S content is at most 0.005 mass %.
10. A tube shell as claimed in claim 2 wherein the ratio of t/d is at most 7% in which “t” is the wall thickness of the shell after piercing and “d” is the outer diameter of the shell after piercing.
11. A tube shell as claimed in claim 3 wherein the ratio of t/d is at most 7% in which “t” is the wall thickness of the shell after piercing and “d” is the outer diameter of the shell after piercing.
12. A tube shell as claimed in claim 4 wherein the ratio of t/d is at most 7% in which “t” is the wall thickness of the shell after piercing and “d” is the outer diameter of the shell after piercing.
13. A tube shell as claimed in claim 1 , wherein the tube shell is pierced with skewed rolls from a billet which has been heated to at least 1200° C.
14. A method of manufacturing a tube shell for manufacturing a seamless steel pipe of an austenitic stainless steel, characterized by performing piercing with skewed rolls on a steel billet having a P content of at most 0.040 mass % and an S content of at most 0.020 mass % under conditions in which the pipe expansion ratio satisfies the following equation:
[
P
0.025
×
H
-
0.01
]
2
+
[
S
0.015
×
H
-
0.01
]
2
≤
1
[
Equation
2
]
wherein
H=outer diameter of shell (mm)/diameter of billet (mm)
P: P content of shell (mass %)
S: S content of shell (mass %).
15. A manufacturing method for a tube shell as claimed in claim 14 wherein the austenitic stainless steel contains a total of at least 10 mass % of at least one of Al, Cr, Cu, Mn, Mo, Ni, Nb, Si, Ti, W, V, and Zr.
16. A manufacturing method for a tube shell as claimed in claim 14 wherein the pipe expansion ratio is at least 1.15.
17. A manufacturing method for a tube shell as claimed in claim 14 wherein the piercing with skewed rolls is performed under conditions in which the heating temperature of the billet is at least 1200° C. and the ratio t/d after piercing (t is the wall thickness of the shell after piercing and d is the outer diameter of the shell) is at most 7%.
18. A manufacturing method for a tube shell as claimed in claim 14 wherein when piercing with skewed rolls is performed, if the diameter of the billet is d b (mm), the roll diameter at the roll gorge portion is D r (mm), and the roll rotational speed is N (rpm), then the peripheral speed of the skewed rolls is in the following range:
300≦( D r ×N )/ d b ≦500.
19. A method of manufacturing a seamless steel pipe of a high alloy steel, characterized by manufacturing a tube shell for manufacturing a seamless steel pipe by the manufacturing method claimed in claim 6 , then performing pipe rolling of the resulting shell, and then performing sizing.
20. A manufacturing method for a tube shell as claimed in claim 15 wherein the pipe expansion ratio is at least 1.15.
21. A manufacturing method for a tube shell as claimed in claim 15 wherein the piercing with skewed rolls is performed under conditions in which the heating temperature of the billet is at least 1200° C. and the ratio t/d after piercing (t is the wall thickness of the shell after piercing and d is the outer diameter of the shell) is at most 7%.
22. A manufacturing method for a tube shell as claimed in claim 15 wherein when piercing with skewed rolls is performed, if the diameter of the billet is d b (mm), the roll diameter at the roll gorge portion is D r (mm), and the roll rotational speed is N (rpm), then the peripheral speed of the skewed rolls is in the following range:
300≦( D r ×N )/ d b ≦500.
23. A manufacturing method for a tube shell as claimed in claim 16 wherein when piercing with skewed rolls is performed, if the diameter of the billet is d b (mm), the roll diameter at the roll gorge portion is D r (mm), and the roll rotational speed is N (rpm), then the peripheral speed of the skewed rolls is in the following range:
300≦( D r ×N )/ d b ≦500.
24. A manufacturing method for a tube shell as claimed in claim 17 wherein when piercing with skewed rolls is performed, if the diameter of the billet is d b (mm), the roll diameter at the roll gorge portion is D r (mm), and the roll rotational speed is N (rpm), then the peripheral speed of the skewed rolls is in the following range:
300≦( D r ×N )/ d b ≦500.
25. A manufacturing method for a tube shell as claimed in claim 14 , wherein the piercing with skewed rolls is performed under conditions in which the heating temperature of the billet is at least 1200° C.