GB/T 1954-2008: Methods of Measurement for Ferrite Content in Austenitic Cr-Ni Stainless Steel Weld Metals

GB/T 1954-2008 — Methods of Measurement for Ferrite Content in Austenitic Cr-Ni Stainless Steel Weld Metals

Standard Number: GB/T 1954-2008
Replaces: GB/T 1954-1980
Ngày đăng: 2008-06-26  |  Effective: 2009-01-01
Modified adoption of: ISO 8249:2000 (MOD)
ICS: 25.160.20  |  Classification: J33

Issuing Body: Standardization Administration of the People’s Republic of China

📄 Original Standard PDF (Chinese)

Download Original GB/T 1954-2008 PDF (Chinese)

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Table of Contents

1. Scope
2. Normative References
3. Terms and Definitions
4. Magnetic Method
5. Metallographic Method
6. Test Report

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1 Scope

This standard specifies the methods for measuring ferrite content. It applies to austenitic and austenitic-ferritic (duplex) Cr-Ni stainless steel weld metals. The magnetic method specified in this standard does not apply to austenitic stainless steel castings and forgings.

2 Normative References

The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies.

• GB/T 20878 — Stainless and Heat-Resisting Steels: Designations and Chemical Compositions

3 Terms and Definitions

3.1 Primary Ferrite (δ-Ferrite)

High-temperature ferrite that forms directly from solidification of the liquid metal and is retained at room temperature.

3.2 Ferrite Number (FN)

An arbitrary, dimensionless quantity derived from magnetic measurements, used to express ferrite content in austenitic and duplex stainless steel weld metals.

3.3 Primary Standard

A reference standard with a precisely defined non-magnetic coating (copper with a hard chromium plating, polished) on a carbon steel base (carbon content below 0.18%). Each standard is marked with an internationally recognized FN value corresponding to a specific weld metal. Applicable for Magnegauge instruments.

3.4 Secondary Standard

A weld metal specimen produced according to standard procedures. Each specimen’s FN value is determined using a Magnegauge calibrated against a primary standard. Used for periodic calibration of magnetic ferrite measuring instruments.

4 Magnetic Method

4.1 General Principles

Ferrite measuring instruments based on magnetic attraction force or magnetic permeability principles shall be used. The ferrite content in austenitic and austenitic-ferritic stainless steel weld metals shall be expressed as the Ferrite Number (FN).

4.2 Measurement of Shielded Metal Arc Weld (SMAW) Deposited Metal

4.2.1 Specimen Preparation

a) Prepare test specimens by surfacing on a substrate with the electrode under test, using the shape and dimensions shown in Figure 1. Two parallel copper plates may be placed on the substrate during surfacing.

b) Minimum deposited metal height H0 ≥ 13 mm. For electrodes with diameter ≤ 4.0 mm, each deposited layer shall consist of a single weld bead. For electrodes with diameter > 4.0 mm, the bead width shall not exceed 3 times the core wire diameter. Each deposited layer shall consist of two or more weld beads. During welding, the arc shall not contact the copper plates.

c) Welding current shall comply with Table 1. Arc striking and extinguishing shall be performed at the beginning and end of each weld layer. The welding direction shall be alternated after completing each weld bead. After each weld bead is completed, cool with water; interpass temperature shall not exceed 100°C. The final layer shall be air-cooled to 425°C before water cooling.

d) Each weld bead shall be cleaned before depositing the next bead.

e) The final layer shall consist of a single weld bead with a width not exceeding 3 times the core wire diameter.

f) For austenitic stainless steel (FN ≤ 30), the deposited surface shall be machined with a coarse file, parallel to the weld bead direction, not across the weld bead. Mechanical cold working shall not be used.

g) For duplex stainless steel (FN > 30), grinding with an abrasive wheel is permitted, finishing with abrasive paper up to 600 grit. Care shall be taken to avoid excessive force causing overheating.

Note: Mechanical cold working can produce martensite, whose magnetic permeability can affect ferrite measurements.

The ground surface shall be flat and smooth, free of welding ripples, continuous along the weld bead length, and not less than 5 mm in width.

4.2.2 Measurement

At least 8 readings shall be taken at different positions along the weld bead length on the ground surface. During measurement, vibration shall be avoided. The probe shall be in contact with the test surface and perpendicular to it. For deposited metal with FN ≤ 20, the average of 5 readings at each position shall be taken as the test result; for FN > 20, the maximum of 5 readings at each position shall be used. The average of at least 6 measurement positions shall be the result for the specimen.

4.3 Preparation and Measurement of Other Weld Metal Specimens

Preparation and measurement of other weld metal specimens shall reference the SMAW provisions above. For submerged arc welding, flux-cored wire surfacing, and similar processes, specimen length and width shall be increased. For any other welding process, the specimen shall have at least 6 weld layers with the final layer being a single bead. Measurement shall be performed along the centerline of the weld bead.

4.4 Measurement of Production Welds

4.4.1 Test specimens from production welds and deposited metal may be taken from test plates provided for inspection, or measurements may be taken directly on the production weld or deposited layer.

4.4.2 Measurement positions shall be as specified by product technical conditions or agreed upon by both parties. The measured surface shall normally be ground flat.

4.4.3 For long welds and large-area deposited metal, sampling measurement shall be conducted at specified proportions agreed upon by both parties. When welding operators are changed, welding parameters are altered, plate thickness changes, or cooling conditions change, timely re-measurement shall be performed.

4.4.4 When measuring transition layers is required by technical conditions, the overlap zone of the two outermost weld beads shall be used as the measurement position.

4.4.5 If non-uniform ferrite distribution is discovered during measurement, the average, maximum, and minimum values and their positions shall be reported separately.

4.4.6 Strong magnetic materials near the instrument (such as low carbon steel and cast iron) shall be kept away. For Magnegauge instruments, ferromagnetic materials shall be kept at least 18 mm away from the probe.

Caution: When measuring stainless steel welds on clad plates and thin deposited layers (thickness ≤ 5 mm), the probe sensitivity depth should be understood to avoid affecting measurement accuracy.

4.5 Calibration of Measuring Instruments

Ferrite measuring instruments and their built-in calibration blocks shall be calibrated periodically (normally not exceeding one year) using a Magnegauge or secondary standard. Each measurement range shall have one calibration point.

Table 2 — Maximum Permissible Calibration Error

Range	Maximum Permissible Error
0 < FN ≤ 4	±0.25
4 < FN ≤ 10	±0.5
10 < FN ≤ 20	±0.8
20 < FN ≤ 40	±5% of standard value FN
FN > 40	±8% of standard value FN

Table 1 — Welding Parameters and Surfacing Dimensions

Electrode Diameter (mm)	Welding Current (A)	Width (mm)	Length (mm)
1.6	—	12.5	30
2.0	55	12.5	30
2.5	65–75	12.5	40
3.2	90–100	12.5	40
4.0	120–140	12.5	40
5.0	165–180	15	40
6.3	240–260	18	40

5 Metallographic Method

5.1 Specimen Preparation

5.1.1 At least 8 metallographic specimens shall be taken from test plates supplied with the product.

5.1.2 For deposited metal, surfacing shall be performed in the flat position on a steel plate 12 mm–16 mm thick, with at least 5 layers. Each weld bead width shall not exceed 4 times the core wire diameter. The top surface shall be not less than 20 mm × 100 mm. Interpass temperature shall not exceed 100°C.

5.1.3 Metallographic specimens of 10 mm–20 mm shall be cut from the middle section perpendicular to the welding direction. The cross-section is the observation surface.

5.1.4 The observation surface shall be ground and polished per standard metallographic procedures. Mechanical polishing shall produce a smooth mirror surface. Electrolytic polishing shall produce a surface free of scratches.

5.1.5 After polishing, the specimen surface may be chemically or electrolytically etched to reveal ferrite.

Table 3 — Recommended Electrolytic Polishing Solutions

No.	Composition	Temp (°C)	Current Density (A/cm²)	Remarks
1	NaOH 400 g/L	Room	—	Steel cathode; area ratio ≥ 5
2	HClO₄ (70–72%) 300 mL + Glacial acetic acid 900 mL	20–30	0.2–0.8	Steel cathode; area ratio ≥ 5
3	HClO₄ 20% + Ethanol 80% (volume)	< 20	—	Steel cathode

Table 4 — Recommended Etching Solutions

No.	Composition	Time	Remarks
1	FeCl₃ 5 g + HCl 50 mL + H₂O 100 mL	1–3 min	Wipe method
2	CuSO₄ 20 mL + HCl 20 mL + H₂O 100 mL	—	Wipe; reveals ferrite preferentially
3	NaOH 10 g + H₂O 100 mL (electrolytic)	—	Specimen as cathode
4	NaOH 10 g + H₂O 100 mL (electrolytic)	—	Specimen as anode
5	HCl 10 mL + H₂O 100 mL (electrolytic)	—	Specimen as anode

5.2 Measurement

5.2.1 The ferrite volume percentage is measured using the metallographic line intercept method. At a microscope magnification of not less than 500×, use a micrometer eyepiece with 100 divisions. The relative amount (number of divisions intersected out of 100) gives the ferrite content in that field. Typically no fewer than 10 representative fields are measured.

Formula:

ψ̄ = (Σ gᵢ / n) × 100%

Where: ψ̄ = average ferrite content, n = number of measured fields, gᵢ = divisions intersected by ferrite in the i-th field.

5.2.2 For single-sided welds, the measurement position is the transverse cross-section at the center of the outermost weld bead on the major face. For double-sided welds, both major faces.

5.2.3 For deposited metal, the measurement position is the cross-section at the center of the outermost layer.

5.2.4 In general, three metallographic specimens are taken; each specimen measured in 10+ representative fields; average of three specimens is the final result.

5.2.5 For double-sided welds, the average of both major faces is the result.

5.2.6 When agreed to measure a specific layer or position, the average of 10+ representative fields is the result.

5.2.7 If particularly non-uniform distribution is found, report average, maximum, and minimum with notes.

5.3 Metallographic Standard Reference Charts

5.3.1 Metallographic standard reference charts provide approximate ferrite content ranges. This standard includes two sets of charts (SMAW weld at 500× and 1000× magnification) for comparative screening and semi-quantitative tests.

5.3.2 When using these charts, specimen preparation and measurement follow the line intercept method provisions.

6 Test Report

The test report shall include (format reference in Appendix A):

1. Measurement method
2. Welding material designation
3. Welding material specification
4. Quantity [FN or ferrite percentage (ψ)]
5. Measured values

Appendix A (Informative) — Reference Format for Test Data

A reference format for weld ferrite test data reporting is provided, including specimen identification, measurement positions, FN values, test data (10 points per specimen), averages, instrument information, and signatures.

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This is an English translation of the Chinese National Standard GB/T 1954-2008. The original Chinese standard was published by the Standardization Administration of the People’s Republic of China.

Original drafting organizations: Harbin Welding Institute, Tianjin Bridge Welding Materials Group Co., Ltd., Tianjin Jinqiao Welding Materials Group Co., Ltd., Advanced Technology & Materials Co., Ltd.

Main drafters: Sun Shaofan, Song Zuying, Hou Laichang, Di Dafu