U.S. patent application number 12/067756 was filed with the patent office on 2008-12-11 for process for manufacturing cold-formed precision steel pipes.
This patent application is currently assigned to MHP MANNESMANN PRAZISROHR GMBH. Invention is credited to Sven Herzing, Wolfgang Mussmann, Lothar See, Josef Siekmeyer.
Application Number | 20080302452 12/067756 |
Document ID | / |
Family ID | 37420849 |
Filed Date | 2008-12-11 |
United States Patent
Application |
20080302452 |
Kind Code |
A1 |
Siekmeyer; Josef ; et
al. |
December 11, 2008 |
Process for Manufacturing Cold-Formed Precision Steel Pipes
Abstract
The invention relates to a process for manufacturing
cold-formed, in particular cold-drawn, precision steel pipes for
application in particular as pressure-operated cylinder pipes with
optimum addition of one or several alloying elements as well as
impurities caused by melting. A seamless, hot-formed pipe blank or
welded pipe blank made from a hot strip with defined starting
condition is hereby drawn in one pass or in several passes into a
finished pipe, and the pipe undergoes a heat treatment before the
finishing pass.
Inventors: |
Siekmeyer; Josef; (Ratingen,
DE) ; Mussmann; Wolfgang; (Remscheid, DE) ;
See; Lothar; (Dusseldorf, DE) ; Herzing; Sven;
(Iserlohn, DE) |
Correspondence
Address: |
HENRY M FEIEREISEN, LLC;HENRY M FEIEREISEN
708 THIRD AVENUE, SUITE 1501
NEW YORK
NY
10017
US
|
Assignee: |
MHP MANNESMANN PRAZISROHR
GMBH
59067 HAMM
DE
|
Family ID: |
37420849 |
Appl. No.: |
12/067756 |
Filed: |
August 18, 2006 |
PCT Filed: |
August 18, 2006 |
PCT NO: |
PCT/DE2006/001457 |
371 Date: |
July 9, 2008 |
Current U.S.
Class: |
148/519 |
Current CPC
Class: |
C22C 38/02 20130101;
C22C 38/04 20130101 |
Class at
Publication: |
148/519 |
International
Class: |
C21D 9/08 20060101
C21D009/08 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 21, 2005 |
DE |
10 2005 046 459.9 |
Claims
1-10. (canceled)
11. A process for manufacturing a precision steel pipe having the
following chemical composition (in weight-%): TABLE-US-00003 C =
0.05-0.25 Si = 0.15-1.0 Mn = 1.0-3.5 Al = 0.020-0.060 V max. 0.20 N
max 0.150 S max 0.030
and impurities caused by melting, said process comprising the steps
of: drawing a pipe blank with defined starting condition in at
least one pass; subjecting the pipe blank to a heat treatment; and
subjecting the pipe blank to a finishing drawing step to produce a
finished pipe.
12. The process of claim 11, wherein the pipe blank is a seamless,
hot-formed pipe blank.
13. The process of claim 11, wherein the pipe blank is welded pipe
blank made from a hot strip.
14. The process of claim 11, further comprising the step of adding
at least one alloying element selected from the group consisting of
Cr, Mo, Ni, W, Ti, and Nb.
15. The process of claim 11, further comprising the step of adding
alloying elements in a following composition (in weight-%):
TABLE-US-00004 Cr max. 0.80 Mo max. 0.65 Ni max. 0.90 W max. 0.90
Ti max. 0.20 Nb max. 0.20
16. The process of claim 11, wherein the heat treatment comprises
the step of heating the pipe blank to a temperature of in a range
of 910-940.degree. C., cooling the pipe blank, and exposing the
pipe blank to a tempering treatment.
17. The process of claim 16, wherein the cooling step comprises
accelerated cooling.
18. The process of claim 17, wherein the accelerated cooling step
comprises quenching.
19. The process of claim 11, wherein the quenching step is
implemented by means of a water shower.
20. The process of claim 16, wherein the cooling step comprises
exposure to static air.
21. The process of claim 16, wherein the tempering treatment is
carried out at a temperature range of 540 to 720.degree. C.
22. The process of claim 11, further comprising the step of
subjecting the finished pipe to a final annealing.
23. The process of claim 22, wherein the final annealing step is
carried out at a temperature range of 500 to 700.degree. C.
Description
[0001] The invention relates to a process for manufacturing
cold-formed, in particular cold-drawn, precision steel pipes
according to the preamble of claim 1.
[0002] Involved in particular in this context are precision steel
pipes according to DIN EN 10305, part 1 and 2, which are under high
internal pressure during operation and find application for example
as cylindrical pipes in the hydraulic or pneumatic fields.
[0003] The basic manufacturing process of seamless or welded,
cold-drawn precision steel pipes is described for example in the
Stahlrohr Handbuch [Steel Pipe Handbook], 12. ed. 1995, Vulkan
Verlag Essen.
[0004] Pipes manufactured in this way are characterized in
particular by narrow wall thicknesses and diameter tolerances.
[0005] Starting product may either be a seamlessly produced
hot-rolled pipe blank or a pipe blank made from a hot strip by
means of high frequency induction welding (HFI welding).
[0006] This pipe blank, labeled also as hollow, is drawn in the
following cold drawing process, which includes one or more passes,
to the required final size (diameter, wall thickness) for the
finished pipe.
[0007] Cold forming causes the material to solidify, i.e. yield
point and strength thereof increase while elongation and toughness
thereof become smaller at the same time.
[0008] This is a desired effect for many applications. As a
consequence of the reduced deformation capability, it is, however,
necessary to execute in some instances a recrystallizing heat
treatment before carrying out further forming processes, so that
the material can be cold formed again for the next drawing
process.
[0009] The properties of precision steel pipes made in this way are
described in DIN EN 10305 part 1 and 2.
[0010] Unalloyed quality steels up to E 355 as well as higher
strength grades up to StE 690 are used as steel grades.
[0011] In order to use such pipes under high pressure, e.g. as
hydraulic cylinder pipes, they have to meet high standards as far
as their toughness is concerned. Hydraulic cylinders control
movement patterns of many devices and machineries which are used,
i.a., also outdoors at great temperature fluctuations.
[0012] When exposed to temperature conditions of up to -20.degree.
C., risk of harm to persons and material cannot be absolutely ruled
out in view of the brittle fracture tendency of materials used to
date for cylinders or pipes under pressure.
[0013] Tests have shown that a notch impact energy of 27 J at
-20.degree. C., as typically demanded heretofore, is not sufficient
for standardized specimens to absolutely rule out structural
failure as a result of brittle fracture at this temperature.
[0014] Comparative systematic tests of ready-for-use cylinder
pipes, that include notch impact bending tests, drop weight tear
tests, and structure tests have shown that a substantially ductile
structural failure can be expected only when the notch impact
energy is at a minimum value commensurate with a shear fracture
area of 50% in the DWT test.
[0015] This means for example for a St52 that the values to be
attained in the notch impact bending test need to have a minimum
value of about 80 J at operating temperature to provide the
structural part with enough plastic deformation reserves to prevent
the risk of a brittle, multipart disintegration of the structural
part.
[0016] The notch impact energy determined in the notch impact
bending test for the finished pipe cannot be raised to the
necessary level by the currently employed manufacturing
process.
[0017] It is an object of the invention to provide a process for
manufacturing cold-formed, in particular cold-drawn precision steel
pipes for application in particular as pressure-operated cylinder
pipes, to positively ensure a substantially ductile failure of the
pipe in a simple and cost-efficient manner, even at operating
temperatures of up to -20.degree. C.
[0018] Based on the preamble, this object is attained in
combination with the characterizing features of claim 1.
Advantageous improvements are the subject matter of subclaims.
[0019] According to the teaching of the invention, a process is
applied in which the pipe blank is finish-drawn in one or more
passes, wherein the pipe undergoes a heat treatment before
finish-drawing, and the steel pipe has the following chemical
composition (in %):
TABLE-US-00001 C = 0.05-0.25 Si = 0.15-1.0 Mn = 1.0-3.5 Al =
0.020-0.060 V max. 0.20 N max 0.150 S max 0.030,
with optional addition of one or more alloying elements such as Cr,
Mo, Ni, W, Ti, or Nb as well as impurities caused by melting.
[0020] The optional addition of the alloying elements is dependent
on the required property profile, i.e. according to the desired
mechanical properties, and have advantageously the following
contents (in weight-%):
TABLE-US-00002 Cr max. 0.80 Mo max. 0.65 Ni max. 0.90 W max. 0.90
Ti max. 0.20 Nb max. 0.20.
[0021] The heat treatment itself includes a classical hardening
with subsequent tempering of the pipes. Austenitizing is carried
out at temperatures of about 910-940.degree. C. depending on the
respective material, followed by a quenching process to form a
hardening structure. Quenching may be executed using various
quenching media, typically quenching is implemented by means of
water using a water shower. When using air-hardening materials,
cooling may be realized through exposure to static air.
[0022] Tempering treatment follows hardening and is carried out at
temperatures of about 540-720.degree. C. depending on the
material.
[0023] The advantage of the proposed process is the realization of
a very even homogenous microstructure with superior toughness by
providing a heat treating step before the finishing pass, which
microstructure is substantially maintained even after the finishing
pass of the pipe. Tests have shown that the values for the notch
impact energy at -20.degree. C. and 50% shear fracture area in the
DWT test lie for transverse test specimen at a superior 80 J and
for longitudinal test specimen at 100 J.
[0024] A possible demand by customers for a final annealing in the
form of a stress-free annealing after the finishing pass leads to
an additional improvement of the notch impact energy values and
thus toughness of the structural part.
[0025] The final annealing is carried out advantageously at a
temperature range of 600-700.degree. C. in dependence on the
material, whereby care should be taken that the temperature should
be precisely set in dependence on the material properties to be
attained, like e.g. strength, elongation at fracture, and notch
impact energy.
[0026] Test of pipes made in accordance with the process according
to the invention have shown the elimination of the otherwise
typically encountered ferritic-pearlitic microstructure of the
construction steels with pronounced variations in the notch impact
energy level in transverse as well as longitudinal test specimens
in materials produced by the process according to the
invention.
[0027] This is clearly shown by the test results for notch impact
energy values on cylinder pipes of StE 460 mod., as illustrated in
FIG. 1. An almost identical notch impact energy level of up to
about 180 J is reached in longitudinal as well as transverse
direction.
[0028] As illustrated in FIG. 2, the structural parts made from the
steel pipe StE 460 mod. in accordance with the invention have,
compared to the steel pipe produced in a conventional manner, a
sufficiently high proportion of ductile fracture behavior at
temperatures of up to -20.degree. C., and thus have sufficient
plastic deformation reserves to positively prevent the risk of a
disintegration of the structural part into several parts.
[0029] The material concept according to the invention thus allows
the operation of hydraulic cylinders even at the temperature range
of up to -20.degree. C.
[0030] In certain steel grades, there is the positive side effect
of a significant increase of the strength values. This allows
advantageously a reduction in wall thickness of the cylinder pipes
by about up to 30% and thus a reduction in weight, satisfying the
demands of lightweight construction.
[0031] In summary, it should be noted that the process in
accordance with the invention for manufacturing cylinder pipes
subject to pressure positively prevents a multipart structural
failure even at operating temperatures of up to -20.degree. C. and
moreover permits a reduction in wall thickness of the cylinder wall
of up to 30%.
* * * * *