Page 132 - SSAB Welding Handbook Edition 2

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23.0 The influence of the alloys and contaminants on the Weldox and Hardox grades Welding handbook

23.3 Chromium (Cr) and molybdenum The effect from boron can best be achieved if it
(Mo) does not react with nitrogen or oxygen in the steel.
Before boron is added, a thorough refinement of
Chromium and molybdenum enhance the yield oxygen is made in the molten steel and then titanium
strength, tensile strength and hardness of the parent or aluminum is added in order to react with the
metal. nitrogen and create nitrides. These nitrides will not
react with the boron.
These elements support the formation of martensite
in the Hardox and Strenx grades. In addition,
both chromium and molybdenum contribute to 23.6 Niobium (Nb), titanium (Ti),
substitutional solution hardening of the parent vanadium (V) and aluminum (Al)
metal. Molybdenum has a stronger overall influence
on the increased yield strength, tensile strength and Niobium, titanium, vanadium and aluminum are
hardness of the parent metal compared to chromium added in small amounts. The content is normally
for martensitic steels that are tempered at high hundredths of a percent for each element. Each
temperatures. For these steels, both molybdenum of these alloys – except aluminum – can react with
and chromium can form carbides that have a either carbon and/or nitrogen and then form carbides,
precipitation hardening effect on the parent metal. nitrides or carbon nitrides. However, aluminum can
only form aluminum nitrides. These substances
can achieve grain refinement and precipitation
23.4 Nickel (Ni) ©SSAB
hardening. The precipitates that cause precipitation
hardening are smaller than those that counteract
The most important function of nickel is its ability grain growth.
to increase the toughness of the parent metal. There
are different theories behind this fact but there is The result of alloying the steel with these substances
not a complete explanation as to why. One possible is an increased yield strength, tensile strength and
reason is that nickel promotes grain refinement. hardness of the parent metal.

Nickel can also increase the yield strength and tensile However, their influence can have an opposite effect
strength of the parent metal since it contributes to on the toughness of the parent metal. The ability
substitutional solution hardening and, to some extent, to promote grain refinement supports an increased
it supports the establishment of martensite in the toughness in the parent metal while the precipitation
parent metal. hardening effects support a decreased toughness.

23.5 Boron (B)

Boron is primarily added to steel because it supports
the formation of martensite in the parent metal.
This effect is achieved with very low fractions of
the element. The level of boron is less than 50 ppm
(parts per million) in the Hardox and Strenx grades.

132 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.