High strength seamless tubes and hollow sections for

High strength seamless tubes and
hollow sections for cranes and machine
building applications
PRODUCTION AND PROPERTIES – REPRINT FROM „STAHLBAU”, ISSUE 9, 2015
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24.05.2016 08:44:08
Topics
Thomas Müller
Boris Straetmans
DOI: 10.1002/stab.201510310
High strength seamless tubes and hollow sections
for cranes and machine building applications
Production and Properties
High strength tubes and hollow sections for cranes and machine
building applications are used with increasing utilization of the
designs to cover continuously growing requirements. For many
applications limiting construction weight is a necessity. Either
regulatory inputs, like axle load limitation of mobile cranes, or
other application-specific requirements such as load capacity of
crawler cranes are covered. Additionally high strength steels allow wall thickness reductions and thereby give opportunity to reduce the effort of welding. For design and execution beside yield
strength and static properties mostly ductility, impact properties
and preferable easy processing through uniform properties of
the used steel grade are key interests. This article will provide
an overview of requirements, manufacturing and properties of
high strength seamless tubes and hollow sections.
Hochfeste nahtlose Rohre und Stahlbauhohlprofile für Krane und
den Maschinenbau – Herstellung und Eigenschaften. Hochfeste
1 Introduction
Over decades, materials with higher
yield-strengths have been developed
for the production of seamless hot
rolled tubes and hollow sections. Today, quenched and tempered highstrength tubes and hollow sections
are available with yield strengths of
up to 960 MPa. These are used, for
example, in crane construction, hydraulic cylinders, and in other frame
constructions in machine engineering
which are subject to static or dynamic
loads, for instance in agriculture machinery (Fig. 1).
Rohre und eckige Stahlbauhohlprofile für Krane sowie für den
Maschinenbau werden eingesetzt, um bei zunehmender Auslas
tung den stetig wachsenden Anforderungen an die Konstruktion
gerecht zu werden. In vielen Anwendungen besteht die Notwen
digkeit, Konstruktionsmassen zu begrenzen. Damit werden ent
weder regulatorische Vorgaben, wie beispielsweise Achslastbe
schränkungen bei Mobilkranen, oder andere anwendungsspezi
fische Erfordernisse erfüllt, wie die Steigerung der Hakenlast bei
Gittermastkranen. Zudem bietet sich die Möglichkeit, Wanddi
cken zu reduzieren und damit den Verarbeitungsaufwand beim
Schweißen zu reduzieren. Für Bemessung und Ausführung sind
neben der Streckgrenze und den statischen Eigenschaften meist
die Duktilität, die Kerbschlagzähigkeit sowie eine möglichst einfa
che Verarbeitung durch gleichmäßige Eigenschaften der einge
setzten Werkstoffe von zentralem Interesse. Dieser Beitrag bietet
einen Überblick über Anforderungen, Herstellung und Eigen
schaften hochfester nahtloser Rohre und Stahlbauhohlprofile.
ments derived from engineering
standards, guidelines, and laws led to
a primary focus on developing highstrength materials. Several research
projects were promoted to meet structural requirements in terms of mate-
rial properties and processing techniques ([1], [2], [3]).
Increased automation changes
the boundary conditions in manufacturing facilities. The consequence is a
need for higher precision in cuttings,
2 Requirements
The development of high-strength materials has been motivated by the need
to handle higher static, dynamic, and
lifting loads, and larger dimensions, as
well as by a desire to extend service
life, and by other factors that influence the production. These require-
Fig. 1. Applications for improved and high-strength steel tubes and structural hollow sections from left to right lattice crawler crane Liebherr LR13000 (Liebherr), hydraulic cylinder (iStock.com/pic4you), agricultural machinery (iStock.com/pic4you)
Bild 1. Anwendungsbereiche für höher- und hochfeste Stahlrohre und Stahlbauhohlprofile, v. l. n. r. Gittermastraupenkran LR13000 (Fa. Liebherr); Hydraulikzy
linder (iStock.com/pic4you), Landmaschinen (iStock.com/pic4you)
© Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin · Stahlbau 84 (2015), Heft 9, S. 650–654
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T. Müller/B. Straetmans · High strength seamless tubes and steel hollow sections for cranes and machine building applications
After piercing, all metalworking
processes continue with the first essential forming, and stretching respectively, according to the rolling procedure relevant for the specific dimension. As the temperature of the hollow
block drops during the forming process, the steel must be reheated to rolling temperature in a reheating furnace
before it can be rolled to the final dimensions in a sizing or stretch-reducing mill. The roll stands of these mills
facilitate the production of round
tubes and square/rectangular sections.
Elliptical dimensions are also feasible. The last steps of production are
straightening, non-destructive tests,
cutting, marking, and if necessary,
bundling [4].
Fig. 2. Scheme of processes for seamless tube production
Bild 2. Schematische Übersicht der Nahtloswarmwalzverfahren
compensation of material tolerances,
and the application of sophisticated
separating processes which have little
or almost no influence on the material.
This is the basis to successfully process
high-strength steel with homogeneous
properties, even at the welding seams.
3 Production of seamless tubes
and hollow sections
The basic material for seamless tube
production is usually continuous casting. Regardless of the subsequent
seamless tube rolling process, the basic material is cropped to the required
4 Material properties of high-strength
seamless tubes and hollow sections
length. In a rotary hearth furnace the
steel is then heated up to rolling temperature, before a cross rolling process forms it into a hollow block. This
ingenious invention was made by the
Mannesmann brothers at the end of
the 19th century. To this day it is the
basis for almost all seamless tube rolling processes. In order to produce
tubes with large dimensions and
heavy weights per meter, some rolling
processes require the use of ingot casting. After heating, the ingot goes
through a piercing press where it is
pre-pierced and transformed into a
hollow block (Fig. 2).
The development of fine-grained steels
has already begun in the 1950ies. Today it includes higher-strength mate
rials up to approx. 500 MPa yield
strength, and high-strength heat
treated materials up to 960 MPa. Progress in metallurgical engineering,
such as the development of materials
with low phosphorus and sulphur
contents, and substantially improved
purity paved the way for these steels
with high yield strength and increased
ductility [5].
Higher-strength fine-grained steel
with a minimum yield strength of up
Table 1. Essential mechanical properties of some fine grain steel grades (extract) out of EN 10210-1 [6] and FineXcell®material data sheets in comparison to a standard grade S355J2H
Tabelle 1. Wesentliche mechanische Eigenschaften einiger Feinkornstahlsorten (Auszug) der EN 10210-1 [6]
und FineXcell®-Werkstoffdatenblätter im Vergleich zu einer Standardgüte S355J2H
Strength
category
normalstrength
Grade
Heat treatment
S355J2H
rolled
S355NH
normalized
Tensile test
Notch impact test
Reh, and Rp0,2
min
in MPa
in MPa
A
min.
in %
355
470 to 630
22
Rm
S355NLH
higherstrength
S460NH
high-strength
S690QL
S460NLH
S690QL1
hardened and
tempered
S770QL
S890Q
S890QL1
S960QL
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460
540 to 720
17
690
770 to 960
16
770
820 to 1 000
15
890
960 to 1 110
14
960
980 to 1 150
10
Test temperature
in °C
KV
min
in J
–20
27
–20
40
–50
27
–20
40
–50
27
–40
45
–60
40
–40
45
–40
45
–60
30
–40
27
T. Müller/B. Straetmans · High strength seamless tubes and steel hollow sections for cranes and machine building applications
5 Processing and application
Fig. 3. Heat treatment process
Bild 3. Vergütungsprozess
to 500 MPa, and high requirements
on toughness, as for example 40 J at
–20 °C or 27 J at –50 °C, are normalized. But they can also be made in a
normalizing rolling process with re
gulated temperature control. Highstrength fine-grained steels with minimum yield strengths of 500 MPa to
960 MPa are hardened and tempered
in a separate process, after hot rolling.
For this purpose they are heated up
to austenitizing temperature, water
quenched, and then tempered at defined temperatures and retention
times (Fig. 3).
The heat treatment process
(Fig. 3) thus guarantees a yield
strength that usually starts at minimum 690 MPa. This marks a significant difference to higher-strength
materials. The guaranteed minimum
ductility is subject to steel grades, and
can be up to 16 %. The notch impact
strength is guaranteed between 27 J to
50 J, and temperatures from –40 °C,
–50 °C or –60 °C.
After the heat treatment, the micro structure and the chemical composition of high-strength tubes and
structural steel sections lead to fundamentally different mechanical prop
erties, compared to higher-strength
steels and simple mild steels (e.g.
S355J2H according to EN 10210 [6])
in as-rolled state (Fig. 4).
Low-alloy fine-grained steels
have a carbon content of below
0.20 %. Whilst the properties of higher-strength fine-grained steels are
mainly achieved through normalizing
heat treatment in combination with
grain refining V microalloying. To
achieve quenched and tempered highstrength fine-grained steels it is necessary to use solid solution elements,
like Cr, Mo, Ni and W, in order to
achieve basis strengths. These are additionally combined with V, Nb and
All standard welding methods can be
applied to weld high-strength tubes
and hollow sections. To achieve similar properties in the welding seams, as
well as in the base material, the mechanical and technological properties
of the filler metals should match those
of the base material. High-strength
fine-grained steels require particular
attention to the properties in the
heat-affected zone (HAZ), as well as
to the cold cracking behaviour. Aside
Ti as grain-refining elements. Prefera- from the choice of material and weld
bly, V is used in combination with N metal this property change is also set
in a defined stoichiometry to form ho- by a process parameter: the coolmogeneously distributed carbon-ni- down time t8/5.
With increasing material strength
tride precipitates, which inhibit the
grain growth and increase the recrys- it becomes more important to meet
tallisation stopping temperature over the defined processing specifications.
the final rolling temperature. This pro- Optimised heat conduction whilst obcedure induces an increased strength serving the specified t8/5 time is therethrough deformation solidification [5]. fore of particular importance for the
It is generally accepted that grain- processing of high-strength materials
boundary strengthening according to ([7], [8]). Trained and experienced
the Hall–Petch relation has a benefi- welding operators can easily meet the
cial effect on ductility, and increases t8/5 time by adhering to the pre-heating and interpass temperature, and by
the yield strength (Fig. 5).
Fig. 4. Microstructure state
Bild 4. Gefügezustände
Fig. 5. Schematic about influence of grain size to impact behavior
Bild 5. Schematische Darstellung des Einflusses der Korngröße auf die Kerbschlagzähigkeit
Sonderdruck aus: Stahlbau 84 (2015), Heft 9
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T. Müller/B. Straetmans · High strength seamless tubes and steel hollow sections for cranes and machine building applications
Fig. 6. Fabrication of steelconstruction
hollow section node
Bild 6. Herstellung eines Stahlbauhohlprofilknotens
considering sheet thickness, welding
velocity, and welding beads (Fig. 6).
At the same wall thickness, highstrength fine-grained steels allow a
greater load on the construction,
compared to S355J2H steels; at a reduced wall thickness they have the
same effect, provided that admissible
strain is not exceeded. Under the
given set of boundary conditions the
characteristics of the material, including the connections, guarantee good
material behaviour in terms of distortion and high ductility.
The influence of material fatigue
is of growing importance in machine
engineering, but also in other fields,
such as bridge engineering. The number of cycles-to-failure that need to be
withstood to bear stress without damages, range from a few thousand (Low
Cycle Fatigue) to a fatigue strength of
2 · 106. The stress range of bearable
cycles-to-failure (fatigue strength) is
primarily influenced by stress increases that occur at the notches.
Welded joints constitute geometric
and metallurgic notches. Hence, they
are of special interest in the fatigue
load analysis of high-strength materials. Various post-treatments on the
welding seam (high frequency impact treatment), such as hammering,
grinding etc. help to increase fatigue
strength and to achieve a higher notch
impact class.
This treatment also inhibits
crack-growth of already formed
cracks. Failure induced by breakage
occur thus only at a high number of
cycles-to-failure.
Particularly in regards to shortterm strength, components made of
high-strength steels benefit from
higher nominal yield strengths. This
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phenomenon allows for wider stress
ranges. Furthermore, these can bear
higher stress levels (medium stress).
An updated version of EN 13001-3-1
[11] based on new research results has
been drafted over recent years, taking
into account existing rules and standards (e.g. EN 1993-1-9 [9] and FKM-
guideline [10]).
Aside from applying highstrength tubes, the use of structural
steel sections of up to 960 MPa yield
strength has lately been established.
As with the production of tubes, the
seamless hot-forming process benefits
from manufacturing conditions, i.e.
the homogeneous micro structure
without metallurgic notches (welding
seam). Additionally, low residual
stress in the entire cross section reduces the risk of distortion. This characteristic also provides excellent
workability, especially at the profile
corners.
Small corner radii allow for the
positioning of bore-holes and welding
seams close to the corners. This creates larger connection faces. Recent
developments facilitate the optimisation of the already small corner radii
of hot-formed hollow sections. Consequently, this allows for the design of
corner radii with the maximum size of
a single nominal wall thickness.
In comparison to tubes, structural steel sections feature simpler
cutting-patterns and clear connection
geometry with sections of straight
welding joints. The advantage over
cold-formed hollow sections is a
clearly reduced welding seam volume
(Fig. 7), and a more efficient construction.
6 Summary
Higher and high-strength tubes and
hollow sections combine high yield
strengths with excellent strain behaviour and good notch impact properties. They are therefore suitable for
applications that have to meet high
technical demands and standards.
The continuous homogeneous properties of hot-formed materials, tight geometric tolerances, and the welding-related processing have leveraged
this class of materials over recent
years. The applied research on these
applications has promoted their popularity and made significant contributions to enhance the processing quality. In this respect, high-strength materials usefully complement existing
processes, to meet future challenges
in construction and manufacturing
technology.
Bibliography
[1] Ummenhofer, T., Herion, S., Hrabowski, J., Feldmann, M., Eichler, B., Bucak, Ö., Lorenz, J., Boos, B., Eiwan, C.,
Stötzel, J.: Bemessung von ermüdungs
beanspruchten Bauteilen aus hoch und
ultrahochfesten Feinkornbaustählen
im Kranund Anlagenbau. Forschungsbericht P778. Forschungsvereinigung
Stahlanwendung e.V., Düsseldorf: Verlag und Vertriebsgesellschaft mbH 2013.
[2] Ummenhofer, T., Veselcic, M., Dietrich, R., Nussbaumer, A., Zamiri, F.:
Optimaler Einsatz von Hohlprofilen
und Gussknoten im Brückenbau aus
Stahl S355 bis S690. Düsseldorf: Verlag
und Vertriesgesellschaft mbH 2014.
[3] Puthli, R., Herion, S., Bergers, J., Sedlacek, G., Müller, C., Stötzel, J., Höh-
Fig. 7. Connection using different corner radii
Bild 7. Anschluss bei unterschiedlichen Kantenradien
T. Müller/B. Straetmans · High strength seamless tubes and steel hollow sections for cranes and machine building applications
ler, S., Bucak, Ö., Lorenz, J.: Beurteilung
des Ermüdungsverhaltens von Kran
konstruktionen bei Einsatz hoch- und
ultrahochfester Stähle. Forschungs
bericht P 512. Forschungsvereinigung
Stahlanwendung e.V., Düsseldorf: Verlag und Vertriebsgesellschaft mbH 2006.
[4] Kümmerling, R.: Das Schrägwalzen
von Rohren. Stahl und Eisen 109 (1993),
H. 9, S. 503–511.
[5] Bruns, C., Müller, T., Liedke, M.,
Scheller, W.: Schweißen hochfester
Nahtlos-Rohre für den Kranbau. DVS
Berichte Band 267 , S. 440–446, 2010.
[6] EN 10210: Warmgefertigte Hohlprofile für den Stahlbau aus unlegierten
Baustählen und aus Feinkornbaustäh
len – Teil 1: Technische Lieferbedingungen, Teil 2: Grenzabmaße, Maße
und statische Werte, CEN, 2006.
[7] Bruns, C., Müller, T., Liedke, M., Scheller, W.: Schweißen im Kranbau – Nahteigenschaften hochfester Rohre. DVS
Berichte Band 275, S. 399–405, 2011.
[8] SEW 088 Schweißgeeignete Feinkorn
baustähle. Richtlinien für die Verarbeitung, besonders für das Schmelzschweißen. Düsseldorf: Verlag Stahleisen
mbH 1993.
[9] DIN EN 1993-1-9: Eurocode 3: Be
messung und Konstruktion von Stahlbauten – Teil 1-9: Ermüdung. Deutsche
Fassung EN 1993-1-9:2005 + AC:2009,
2010-12.
[10] FKM-Richtlinie – Rechnerischer Festigkeitsnachweis für Maschinenbauteile. VDMA-Verlag, 2012.
[11] DIN EN 13001-3-1: Krane – Kons
truktion allgemein – Teil 3-1: Grenzzustände und Sicherheitsnachweis von
Stahltragwerken, CEN, 2013-12.
Authors of this article:
Dr.-Ing. Thomas Müller,
[email protected],
Dipl.-Ing. Boris Straetmans,
[email protected],
Vallourec Deutschland GmbH,
Theodorstraße 109,
40472 Düsseldorf
Sonderdruck aus: Stahlbau 84 (2015), Heft 9
7
www.vallourec.com
www.vallourec.com
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V D02B0017B-16GB
Vallourec Deutschland GmbH
Industry Division
Theodorstraße 109
40472 Düsseldorf, Germany
Phone +49 (211) 9 60 35 80
[email protected]
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