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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.
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.
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.
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
Welding manganese steel involves anyone of the following cases
  • Joining manganese steel to itself or to unalloyed, low alloy steel
  • Rebuilding worn out surfaces
For joining manganese steels and manganese steels to carbon steels, austenitic stainless consumables have to be used to obtain a tough and strong joint.
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.
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
Steels of unknown composition are also treated as having limited weldability so that the weld does not fail in any respect.
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.
Tool steels have a higher carbon content along with chromium, nickel, molybdenum, vanadium and are generally heat-treated to achieve certain specific properties.
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.
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
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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