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| WELDING DISSIMILAR STEELS |
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| Joining Stainless Steel to Low Alloy or Carbon
Steel |
| The most common and important instance of dissimilar
metal joining is that of welding stainless steel to carbonmanganese
steel or to low alloy steel. The most common
application is attachments or transitions. |
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| The welding is almost always carried out with overalloyed
stainless consumables Le. having higher alloy
content than the base metal. Two different methods
are employed for this type of welding. The entire weld
groove can be filled up with the over-alloyed stainless
steel or any nickel based consumable. Otherwise, the
lower alloyed surface can be buttered with an overalloyed
stainless weld metal and then the groove can be
fi lled up with a consumable matching with the stainless
side. The welding can usually be performed without
preheating. However, if there is any recommendation
for that particular grade of steel, then that has to be
followed. |
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| WELDING MANGANESE STEELS |
| Manganese steel typically contains 11 - 14% manganese
and 1.0 - 1.4% carbon. Some other grades can have
other minor alloying elements. This steel has an ability
to work harden e.g. under high impact and/or high
surface pressure. These steels have to be reconditioned
by repairing cracks or breakages, rebuilding worn out
portions and hardfacing to extend service life. |
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| Weldability of manganese steel is governed by the fact
that it tends to become brittle when reheated and slowcooled.
Consequently, the interpass temperature should
not exceed 200°C. As a result, during welding of these
steels, the following matters should be noted |
- The heat input should be as low as possible
- Stringer beads should be used
- Simultaneous working with several components
should be done, as far as practicable
- The component can be cooled by putting it in cold
water
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| Welding manganese steel involves anyone of the following cases |
- Joining manganese steel to itself or to unalloyed, low
alloy steel
- Rebuilding worn out surfaces
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| For joining manganese steels and manganese steels to
carbon steels, austenitic stainless consumables have to
be used to obtain a tough and strong joint. |
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| Prior to surfacing also it is advisable to add a buffer
layer of austenitic stainless consumables. On top of
that regular 13% manganese type deposit is put as the
surfacing layer. |
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| WELDING “DIFFICULT TO WELD STEELS” |
| The following types of steel are regarded as 'diffi cult to
weld' for their high hardenability |
- High carbon steels
- High strength steels
- Spring steels
- Tool steels
- Wear-resistant steels
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| Steels of unknown composition are also treated as
having limited weldability so that the weld does not fail
in any respect. |
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| Welding theory says that all these steels can be welded
with matching ferritic consumables with proper preheating
and post-weld heat treatment (PWHT). But repair
welding, by nature, does not always allow preheating
or PWHT. Therefore, the safest way is to weld with
austenitic stainless or nickel-based consumables. The
risk of cracking due presence of hydrogen is neutralized
by the greater solubility of hydrogen in austenite and
also by the higher ductility of the weld metal. For welding
steels of unknown composition, the best choice is a
ferritic-austenitic duplex type of consumable. |
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| WELDING TOOL STEELS |
| Tool steels have a higher carbon content along with
chromium, nickel, molybdenum, vanadium and are
generally heat-treated to achieve certain specific
properties. |
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| The repair welding of tool steels without changing
their inherent properties is very difficult. This calls
for use of consumables producing a weld metal with
matching composition, microstructure and properties.
But practically, this is very difficult as it involves scaling
change of dimension and time. |
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| The welding is simplified by using specific consumables
developed for tool steels |
| Shock resistance, toughness,abrasion resistance |
Straight chrome martensitic deposit |
| Hot strength, abrasion resistance at high temperature |
Fine carbides in martensitic matrix |
| Edge retention at high temperature, impact toughness |
High speed steel deposit |
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| The welding is done by preheating the job to 200-500°C
(as per the type of steel) and maintaining it during the
course of the welding. The preheating and PWHT to be
followed can be found in different international standards
like SAE / AISI. |
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| More Info... |
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