Technology News
100
M
arch
2014
Cutting heavy ID scarf
GEBRÜDER Lennartz manufactures
and supplies carbide-tipped circular
saw blades for the ferrous and non-
ferrous industry.
The company’s new ECOmax Scarf
circular saw blade is customised for
cutting tubes and profiles with heavy ID
scarf on flying cut-off units. Previously,
conventional blades could be heavily
damaged after only a few cuts because
they cut the high strength weld bead
inside the bottom of the tube. The
service life of the blades was poor and
the cost per cut high.
Because of its special tooth form
and cutting geometry, and in combina-
tion with a new proprietary coating, the
ECOmax Scarf saw blade is suitable for
this application. The new design works
on single head machines as well as on
twin saws with the simultaneous opera-
tion of two saw blades. Successful
trials and on-going production usage,
together with target customers and
machine manufacturers, have shown the
ECOmax Scarf blades achieve up to 7m²
of material removal on welded tubes with
wall thickness up to 14mm. Further wear
life tests and enhancements are planned
to improve the blades’ performance.
Gebr Lennartz GmbH & Co KG
–
Germany
Fax: +49 2191 99 6060
Email:
Website:
Steel castings for tube mill rolls
with fatigue resistance
ROLLERS and rolling dies are subject
to cyclical pressure loads. In addition to
sufficiently high hardness and a good
resistance to wear, the tool materials
used must provide a sufficiently high
fatigue resistance against over-rolling,
according to Dörrenberg Edelstahl
GmbH.
In many cases, steel castings made
of carbide-rich cold worked steel
GX155CrVMo12-1 (M. no.1.2382)
are used. This material’s hardness
tempering behaviour is characterised
by a secondary hardness maximum
due to its alloy composition. The
setting of a working hardness of 58-
60 HRC can, therefore, take place at
tempering temperatures above 500°C,
with which the martensitic matrix of
its microstructure can decompress
considerably
and
increase
in
toughness.
In addition to this, 1.2382 steel
castings contain a carbide volume of
around 12 per cent, which has a positive
effect on the wear resistance. However,
the carbide is formed as a brittle
network, which means that cracks form
along the carbide network in the case
of mechanical overloading or fatigue,
and this can result in early failure due to
spalling (pitting) or fracture.
In this case, the special steel casting
material GP4M
®
represents a further
technical development. Its alloy
composition has been optimised so
that it shows a comparable hardness
tempering behaviour to standard
material 1.2382. GP4M, which is alloyed
with chromium, molybdenum and
vanadium, has a pronounced secondary
hardness maximum. Setting of a tough
martensitic microstructure matrix with
a hardness of 58-60 HRC can also be
achieved in this case through the use of
high tempering temperatures.
Unlike the case of the carbide-rich
standard material GX155CrVMo12-1,
the microstructure of the GP4M special
material stands out due to the lack of
the brittle carbide network.
The toughnessandductility is therefore
increased in comparison with standard
material. This can be noticed especially
during operational deployment, where
there is a surface fatigue hazard due
to continuous over-rolling of the tool.
The increased toughness can prevent
overload fracture during impact loading,
and can also prevent existing surface
cracks extending.
The low-carbide microstructure of
the GP4M material is also of benefit
during the manufacture of rollers. This
means that thermal internal stresses
between case and core occur in heat
treatment during heating up and
cooling down, since the core lags in
terms of temperature depending on the
wall thickness.
During hardening the thermal internal
stresses are overlaid by additional
transformation internal stresses, so
that in the case of standard material
GX155CrVMo12-1 the crack risk is
extremely high, because it is not good
at accepting tensile internal stresses
due to its carbide network. The trans-
formation behaviour of GP4M cast steel
material is even slightly more beneficial
than in the case of standard material
GX155CrVMo12-1. This means that
quenching can take place more gently
during heat treatment without the material
having a reduced hardness level.
With the use of the GP4M material,
the realisation of more complex roller
geometries is easier than with previously
available standard materials. With a
settable working hardness of up to 60
HRC and a tougher microstructure, the
GP4M material also shows itself to have
a high resistance against surface fatigue
during operational deployment.
Dörrenberg Edelstahl GmbH
–
Germany
Fax: +49 2263 79 412
Email:
Website:
Shaping roller made of GP4M hardened to
58-60 HRC
