Welcome to our technical questions page. Here are five technical questions and answers provided by my colleague and friend Mr Stuart Thomas IEng/Inc/EWE, Technical Services Manager Bohler Welding UK Ltd. He has donated them to help you kick start any enquires you may have. Please click on the + sign to open the answer, Also use the form below to ask your questions. If we cannot provide you with what you need, we may know some one who you could contact.



Q: What is the preferred welding consumable for joining mild steel to stainless steel?

A: Consumable selection should be based on the base metal chemistry and the percentage dilution levels. The consumable chosen should produce a weld deposit with a microstructure that is not crack sensitive. We do not want to form martensite but we want a ferrite level of >5% in the weld metal. The typical grade of filler material chosen is a 309L type.

Q:Why do we need a preheat when welding steels like EN 8 or EN24?

A:Steels such as EN8 and EN24 have high Carbon contents plus they are alloyed with Cr, Ni and Mo. This makes them highly hardenable steels which influences the rate at which they produce crack sensitive microstructures after welding. Preheating the steel prior to welding slows the cooling rate in the weld area. This may be necessary to avoid cracking of the weld metal or heat affected zone. The need for preheat increases with steel thickness, weld restraint, the carbon/alloy content of the steel, and the diffusible hydrogen of the weld metal.

Q:What shielding gas should I be using with Stainless Steel Flux cored wires?

A:The recommended shielding gas is Argon + 18%Co2 (Standard states Argon + 15-25%CO2). 100CO2 can also be used but mechanical properties are reduced and weld finish is inferior

Q:Why do I suffer with porosity when welding Aluminium?

A:The root cause of this problem is due to the fact that Aluminium has a high affinity for Hydrogen. Hydrogen is absorbed into weld pool which forms pores in the solidifying weld metal. The most common sources of hydrogen are hydrocarbons and moisture from contaminants on the parent material and filler wire surfaces. To minimise the risk (but not guarantee pore free welds), rigorous cleaning of base material surface and filler wire should be carried out. Avoidance of water vapour is critical.

Q: What filler material should I select for welding H13 tool steel?

A:. You should be able to answer what condition the tool is in prior to welding and also what hardness is required from the welded deposit before you start? The typical product range used is UTP 73 G2/UTP 73 G3 or UTP 73 G4 dependant on the final hardness required. Welding procedure is then defined by the condition of the base material.