Submerged arc welding consumables. Part 2 - specifications

Part 1
Part 3

Of all the arc welding processes, only submerged arc welding uses two completely separate components, both of which may have a major effect on the mechanical properties of the weld deposit. This makes the specifying of consumables somewhat complicated. It will not be possible therefore to cover all the alloy types in this brief article which will cover the carbon, carbon-manganese and low alloy structural steels only.

BS EN 756 is the specification for wires and wire/flux combinations in non-alloy and fine grain steels with a minimum yield strength of up to 500N/mm ² . The specification covers the classification of the wire chemical composition and the wire/flux combination. It also specifies the mechanical properties of all weld metal deposits in the as-welded condition.

The classification is divided into five parts:

• a symbol indicating the process - in the case of submerged arc welding this is 'S'.
• two digits indicating either the tensile properties of a multi-run deposit or the tensile properties of the parent metal to be welded using a two run technique - see Tables 1 and 2.

Table 1. Symbols for tensile properties - multi-run technique

Table 2. Symbols for tensile properties - two-run technique

Note that the two-run technique has two tensile results specified; one for the minimum yield strength of the parent metal, one for the tensile strength of the welded joint.

Table 3 gives the temperature at which the average Charpy-V impact value of 47J may be achieved for both multi-run and two-pass techniques. A standard set of conditions is given in Table 6 for multi-run welding. The welding parameters for the test piece produced using a two run technique must be within a range specified by the manufacturer.

Table 3. Symbol for Charpy-V impact properties

Table 4 of the specification gives the symbols for the type of flux. There are 10 fluxes listed, identified by an abbreviation of the main constituents as below.

Table 4. Flux type symbol

Table 5 contains a listing of the chemical composition of 22 wires and is too lengthy to include in full in this article. The wires all contain a maximum carbon content of 0.15% and range from plain carbon, through C-Mn, C-Mo, Mn-Mo to Ni and Ni-Mo. All are prefixed 'S' followed by a number from 1 to 4 denoting from 0.5% Mn (1) to 2% Mn (4). The addition of nickel and/or molybdenum is denoted by the chemical symbol of the alloy addition being included. Thus an S3 wire contains 1.5% Mn, an S2Ni1Mo 1% Mn,1% Ni and 0.5% Mo.

Table 5 Metallurgical behaviour - pick-up or loss of Si and Mn

The designation for a flux/wire combination designed to provide a multi-run weld metal with a minimum yield strength of 500N/mm ² , a minimum Charpy-V impact value of 47J at -40°C using a Mn-Mo wire with an aluminate-basic flux would be BS EN 756 S 50 4 AB S4Mo.

In addition to BS EN 756 which specifies the mechanical properties expected from a particular flux/wire combination, there is an additional specification, BS EN 760, that specifies the fluxes in greater detail, including the application for which a flux may be used. The specification uses a total of seven symbols, four being compulsory and three optional. The first symbol,'S', identifies the flux as being intended for submerged arc welding and the second the method of manufacture. This may be 'F', a fused flux; 'A', an agglomerated flux and 'M', a mixture of fused and agglomerated. The third part gives an indication of the chemical constituents and uses the same notation as in Table 4 above. In addition BS EN 760 gives a range of percentages for each of the constituents in Table 1.

The fourth part gives a symbol for the application(s), Class 1 being intended for the welding of carbon and low alloy steels, including high strength structural and creep resistant steels. There is no alloying from this class of flux. Class 2 fluxes are for the welding of, and the surfacing with, stainless and heat resisting steels and nickel alloys. Class 3 is for use with hard surfacing weld metals, the flux providing such elements as carbon, chromium and molybdenum to the weld deposit.

The remaining three symbols are not compulsory and comprise, firstly, a number or chemical element symbol that defines what is termed in the specification as the 'metallurgical behaviour' of the three classes of flux mentioned above. Two digits then specify the pick-up or loss of silicon and manganese (in this order) to be expected when welding carbon or low alloy steels using flux Class 1, as shown in Table 5 below. Flux Classes 2 and 3 may be characterised by the use of a chemical symbol to identify the alloying element being added via the flux, eg Cr, if the flux is chromium compensating.

The current type is indicated by the addition of DC or AC to the symbols and finally an 'H', followed by a number, gives the weld metal hydrogen level expected from a correctly dried or baked flux eg H5.

A designation for a flux supplied in accordance with BS EN 760 may therefore be S A AF 1 55 DC H5 for an agglomerated alumina-calcium fluoride basic flux intended for the welding of carbon or low alloy steels, no pick-up or loss of silicon or manganese, used with DC welding current and with a hydrogen content of less than 5mls/100gms weld metal.

It must be remembered that the properties given by these designations are obtained from as welded, all weld metal specimens deposited using standard welding parameters of current, voltage and travel speed.

The properties achieved in a production weld may be entirely different due to the effects of dilution from the parent metal, higher or lower heat input, different wire diameters, preheat and interpass temperatures and post weld heat treatment. It is essential, therefore, that the suitability of a flux/wire combination is confirmed by procedure qualification testing.

Note also that flux/wire combinations supplied to the same specification designation by different manufacturers may not necessarily provide similar mechanical properties or weld cleanliness.

This article was written by Gene Mathers.