Page 62 - SSAB Welding Handbook Edition 2

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11.0 Cutting of Weldox and Hardox Welding handbook

A common factor shared by the Hardox and Strenx enough for initiation of hydrogen cracks and therefore
grades is that the hardness, as well as the strength, sharp corners will increase the risk for cut edge crack-
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in this zone is higher than in other parts of the HAZ ing. This is true for all cutting methods both thermal
and unaffected parent metal. and cold cutting methods like AWJ cutting. If the fol-
lowing actions are considered the risk for cracks will
Zone II positioned between zone 1 and the decrease, see fig 11.5.
unaffected parent material is heated to temperatures
below 900°C during cutting. This temperature is not 1. If possible avoid sharp “inward facing” corners
high enough to transform the material to austenite. 2. If possible use smooth geometries
Since no austenite transformation occurs it is not 3. When sharp corners can’t be avoided, make a
possible to quench the material, instead it is being circular loops around “outward facing” corners
tempered by the heat from the cutting operation. when possible.
The hardness values in this zone vary, depending of 4. If the cutting operation is to be stopped (i.e. overnight)
the steel grade and the cutting procedure. make a clean cut to remove stress raisers.
During cooling, zone I strives to expand in the
thickness direction while zone II is unaffected or No Hardox and Strenx grades should be stored with
even shrinks. As a result, residual tensile stresses are sharp corners caused by cutting. The reason is to
created in the thickness direction in zone II. It is in avoid excessive residual stresses in these areas.
this zone with high tensile stresses where hydrogen
cracks can be initiated. The general tendency is that
these stress levels increases with larger plate Wear part
thicknesses.

Figure 11.4 illustrates the different zones of the Cutting geometri
HAZ in a thermal cut Hardox 450 plate.

Zone 1 Zone 2
Fig. 11.5: An appropriate procedure for cutting of corners. Take into
account that the cutting speed, is typically reduced at the cross
Unaffected parent metal section where the cutting path intersect in order to attain a stable
cutting operation.

Hardness Measures to avoid hydrogen cracking

To avoid cut edge cracking it is important to keep
both the hydrogen content and the tensile stresses in
the HAZ as low as possible.
Distance from the cut edge
During cutting performances the following actions
can be used in order to minimize the hydrogen con-
Fig. 11.4: Schematic hardness profile of the HAZ due to thermal
cutting of Hardox 450. tent as well as the residual stresses in the HAZ:

Tensile stresses due to global stress field 1. Preheating of the plate
2. Postheating of the plate
Quenching of plates also introduce residual stresses. 3. Applying reduced cutting speed at
During cutting of parts with sharp corners, the residual oxy-fuel cutting
stresses from the manufacturing are concentrated at 4. Combination of preheating, postheating and
such areas. These concentrated stresses might be high reduced cutting speed together with a prolonged
cooling process of the HAZ
62 This handbook contains general suggestions and information without any expressed or implied warranty of any kind. SSAB hereby expressly disclaims
all liability of any kind, including any damages, in connection with the use of the information and for their suitability for individual applications.
It is the responsibility of the user of this brochure to adapt the recommendations contained therein to the requirements of individual applications.