GB/T 1954-2008Methods of measurement for ferrite content in austenitic Cr-Ni stainless steel weld metals (English PDF)

3.1 Ferrite

Ferrite refers to high-temperature ferrite which is formed directly through the

solidification and crystallization of liquid metal; it is retained to room temperature.

3.2 Ferrite Number (FN)

Ferrite number refers to standardized numerical value, which is artificially selected to

express ferrite content in Austenitic stainless steel, and ferritic-Austenitic stainless

steel weld metals.

3.3 Primary Standard

Primary standard refers to a layer of accurate non-magnetic coating standard sample

that is produced on carbon steel matrix with the carbon content of less than 0.18%.

The non-magnetic coating is made of copper; plated with hard chromium, and polished.

Each standard sample marks FN value of a certain equivalent magnetic weld metal

that is internationally universal. It is applicable to the calibration of measurement

instrument under standard magnetic attraction principle, for example, Mange-Gage.

3.4 Secondary Standard

Secondary standard refers to weld surfacing metal sample or sample with similar

surfacing metal structure that is produced in accordance with standard procedures.

Use Mange-Gage, which is calibrated through primary standard, to determine FN value

of each sample. It is applied to periodic calibration of ferrite measurement instrument

under magnetic method.

4.1 General Principles

Ferrite measurement instrument, which takes magnetic attraction or magnetic

permeability as the principle, shall be adopted for measurement. The measured ferrite

number (FN) shall be used to express ferrite content in Austenitic stainless steel,

Austenitic-ferritic stainless steel weld metals.

4.2 Measurement of Surfacing metal of Welding Rod Electric Arc Welding

4.2.1 Sample preparation

a) In accordance with the shape and dimensions shown in Figure 1, use test

welding rods to overlay a sample on the substrate. During the overlaying, two

copper plates may be parallelly placed on the substrate.

b) The overlaying layer's minimum height H is 13 mm (see NOTE b in Figure 1).

When the diameter of welding rod is >= 4.0 mm, each overlaying layer shall be

constituted of single weld bead. When the diameter of welding rod is < 4.0 mm,

the width of weld bead shall be not more than 3 times of the diameter of welding

core; each overlaying layer shall be constituted of two or more weld beads.

During the welding, electric arc is not allowed to contact the copper plates.

c) Welding current shall comply with the stipulations in Table 1; arc initiation and

arc extinction shall be on the head end and the tail end of the welding layer.

After the welding of a weld bead is completed, alter the welding direction.

d) 20 s after the welding of each weld bead is completed, use water-cooling; the

temperature between the beads shall be not more than 100 °C. Before water-

cooling, the top weld bead shall firstly be air-cooled to below 425 °C.

welding samples shall be as close to the stipulations in 4.2 as possible.

4.4 Measurement of Product Weld

4.4.1 In the measurement of product weld and weld metals, samples may be taken, or,

measurement may be directly conducted from the welding test piece provided for

product inspection. Or, measurement may be directly conducted on product weld or

overlaying layer. Measurement instrument shall comply with the stipulations in 4.5.

Measurement process shall comply with the stipulations in 4.2.

4.4.2 In the measurement of product weld and weld metals, the measuring parts shall

comply with the stipulations of product technical conditions, or, be determined by both

parties through negotiation. Generally speaking, the surface being measured shall be

polished. If the machining of the weld surface may trigger changes of anti-corrosion

property or other specific properties, and further affect product quality, then, in the

measurement of this type of welds (including overlaying metal), whether the surface

shall be polished shall be determined by both parties through negotiation. In the select

measurement location, in every 5 mm ~ 10 mm, take 1 measurement point. The

measurement shall comply with the stipulations in 4.2.2.

4.4.3 In terms of long weld and large-area of overlaying, conduct spot measurement

in accordance with a certain proportion. The proportion and part of spot measurement

shall be determined by both parties through negotiation. The part of spot measurement

shall be representative. Measurement points shall be uniformly distributed within the

range of the measurement part. When welding operators are replaced, welding

parameters are changed, plate thickness or cooling conditions are changed, re-

measurement shall be conducted in time.

4.4.4 When the transition layer is measured in accordance with the requirements of

technical conditions, the overlapped area of the two outermost weld beads shall be

considered as the measurement part.

4.4.5 During the measurement process, if ferrite distribution is found to be extremely

asymmetrical, the average value, the highest value, the lowest value and its part shall

be respectively provided in the measurement result.

4.4.6 During the measurement, it shall be guaranteed that the influence of strong

magnetic substance (for example, low carbon steel or cast iron, etc.) near the

instrument on the measurement result is eliminated. In terms of standard magnetic

instrument, during the measurement, the distance from surrounding ferromagnetic

substance to the measuring head shall be beyond 18 mm. Other types of probe-type

instruments shall be operated in accordance with the requested minimum distance

from ferromagnetic substance.

Please be cautious in the measurement of the stainless steel weld of composite board

and relatively thin stainless steel overlaying layer (layer thickness < 5 mm). The

5.2.3 In terms of surfacing metal, the central cross section of the outermost layer shall

be considered as the measurement part (as it is shown in Figure 5).

Figure 5 -- Surfacing Metal Measurement Part

When large-area overlaying has transition layer, the transition layer's ferrite content is

measured in accordance with the technical conditions, then, the junction of the two

outermost weld beads shall be considered as the measurement part.

If necessary, through the negotiation between both parties, measurement may be

conducted on a certain layer, a certain part, or layer-by-layer.

5.2.4 Under general circumstances, take 3 metallographic samples. In terms of each

sample, measure above 10 representative fields of view; take the average value as

the measurement result of the sample. Then, take the average value of the

measurement result of 3 samples as the final result.

5.2.5 In terms of double-sided weld, take the average value of two large surfaces as

the measurement result. If there are special demands, the average content of each

large surface may be listed.

5.2.6 When it is determined through an agreement between both parties that

measurement shall be conducted on a certain layer, a certain part or layer-by-layer,

the average value of above 10 representative fields of view shall be taken as the

measurement result.

5.2.7 If it is found during the measurement process that ferrite distribution is extremely

asymmetrical, then, the measurement result shall provide the average content, the

highest content and the lowest content, and add certain explanation.

5.3 Metallographic Standard Map

5.3.1 Metallographic standard map belongs to approximate or semi-quantitative

metallographic method, which can only provide a rough range of ferrite content. This

Standard attaches two groups of metallographic standard maps (respectively 500

times and 1,000 times of welding rod electric arc weld) for the purposes of comparative

screening test, intermediate approximate measurement and other semi-quantitative

tests (see Figure 6 and Figure 7).

Measurement Part

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