Additional elements such as vanadium, silicon, nickel, boron, niobium and titanium also influence hardenability and weldability. Steels of increased hardenability tend to form brittle microstructures in the heat affected zone, which may result in cracking. Steels featuring reduced weldability are commonly referred to as ‘problem steels’ as a result of the problem areas that are directly caused by shrinkage stresses, rapid cooling rates and the presence of hydrogen.
Electrodes for welding problem steels are chromium nickel austenitic types containing delta ferrite in the range of 10–80%. The weld metal is insensitive to hot cracking above 1 200°C. At ambient temperatures, the weld metal is strong and tough and is capable of withstanding heavy impact and shock loading in service.
Problem steels fall into two categories, i.e. ferritic types which require preheat and austenitic steels such as 11–14% manganese steels, which require minimum heat input.
When hardenable ferritic steel types are to be welded, reference should be made to the section on mild and medium tensile steels for the calculation of the carbon equivalent and preheat temperatures.
Problem steel electrodes are suitable for welding combinations of dissimilar steels such as chromium, molybdenum, creep resistant steels and stainless steels to mild and low alloy steels. Care should be taken when welding such combinations to ensure that excessive dilution between the base and weld metal does not occur.