Low alloy steels contain a few percent (typically between 1 and 7%) of elements such as Cr, Ni, Mo and V. This category includes chromium steels (containing up to 5% Cr and 1% Mo) and nickel steels (containing up to 5% Ni).
Low alloy steels are generally weldable (see What is weldability?), but it is important to know the service, joint configuration and the subgroup of the material type. Low alloy steels can be welded by most processes, as long as adequate precautions are taken to avoid defects. It is important to know the composition of the material, either from a mill sheet or a dedicated chemical analysis, as composition influences weldability significantly.
With increasing carbon or alloy content, low alloy steels generally become more difficult to weld as the heat affected zone hardness increases. The need for postweld heat treatment (PWHT) of these joints also increases. The composition is also important in identifying high, but allowable, levels of residual elements such as sulphur or phosphorus, which can lead to problems with liquation cracking or temper embrittlement during PWHT.
To avoid fabrication hydrogen cracking, it is important to use low hydrogen processes and consumables, particularly as increasing the carbon and alloy content, and increasing the section thickness, increases the risk of hydrogen cracking. A post-heattreatment may be required to reduce the levels of hydrogen in the weld region.
Weldability of materials (carbon-manganese and low alloy steels)
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