Page 66 - SSAB Welding Handbook Edition 2

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11.0 Cutting of Weldox and Hardox Welding handbook

Reduced cutting speed Oxy-fuel cutting has the highest thermal impact
followed by plasma cutting and laser cutting. Fig.
Reduced cutting speed is a convenient method to 11.10 illustrates the HAZ for Strenx 1100 – Strenx
reduce the risk for cracks during oxy-fuel cutting. 1300 and the Hardox grades except Hardox HiTuf
When cutting speed is reduced, the material heats up and Hardox HiTemp.
around the cut front and the heat affected zone will
be wider. This affects the residual stresses in such
a way that the risk of cut edge cracking is reduced.
One should though bear in mind that reduced cutting
speed is not as reliable as preheating or postheating
and should only be used as a substitute if, for instance,
the workshop does not have appropriate pre/postheat- Hardness
ing equipment. Oxy-fuel
Oxy-fuel under water
If reduced cutting speed is used it is important that Plasma
the cutting speed don’t exceeds the one listed in in Laser
table 11.6, otherwise the risk for cutting cracks won’t
be reduced at all. Distance from the cut edge

Fig. 11.10: Hardness profiles in HAZ after thermal cutting of Hardox
Reduced cutting speed is not applicable for plasma or and Strenx with different cutting methods.
laser cutting. ©SSAB
Reducing the risk of softening
Slow cooling The resistance of the steel to softening depends on
Regardless of whether or not preheating of the cut its chemistry, microstructure and the way in which
parts are employed, a slow cooling rate will reduce it has been processed. The smaller the part that
the risk of cut edge cracking. Slow cooling can be is thermally cut, the greater the risk of the whole
achieved if the parts are stacked together while still component being softened. If the temperature of the
warm from the cutting process, and are covered steel gets too high, the hardness of the steel will be
with an insulating blanket. Allow the parts to slowly reduced, according to fig. 11.11 (check maximum
cool down to room temperature. This measure is allowable temperature in table 11.4-11.5).
valid for oxy-fuel, plasma and laser cutting.

650
11.5 Hardness properties in the HAZ 600 Hardox 600
The properties of the HAZ depend on: 550 Hardox 500
500
4 Whether or not the steel was tempered during Hardness HBW 450
manufacturing, and if so, how it was carried out 400 Hardox 400
4 The chemical composition of the steel 350
4 The impact of the thermal treatment from the 300
cutting process
100 150 200 250 300 350400 450
The width of the HAZ increases with increasing Tempering temperature (°C)
thermal impact from the cutting process. For
instance, cutting with the same power and reduction Fig. 11.11: Hardness profiles in HAZ after thermal cutting of Hardox
and Strenx with different cutting methods.
of the cutting speed leads to a wider HAZ. Different
thermal cutting processes have different thermal
impact, resulting in wider or narrower HAZ.
66 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.