GB/T 4334.1-2000 — Method of 10 Per Cent Oxalic Acid Etch Test for Stainless Steels

This is the English translation of the Chinese National Standard GB/T 4334.1-2000. The original Chinese PDF is also embedded at the bottom of this page for reference.

---

GB/T 4334.1-2000

Method of 10 Per Cent Oxalic Acid Etch Test for Stainless Steels

ICS: 77.040.99   |   Issued: 2000-10-25   |   Implemented: 2001-09-01

Published by: General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China

---

Foreword

This standard is technically equivalent to Japanese Industrial Standard JIS G 0571-1980 Method of 10 Per Cent Oxalic Acid Etch Test for Stainless Steels. It is substantially identical to the Japanese standard in scope, specimen preparation, test solution, test equipment, test conditions and procedures, and test results evaluation. Additional requirements for specimen sampling and sensitization treatment of welded specimens have been added.

This revision made the following modifications:

• Added Chapter 2 (Normative References) and Chapter 8 (Test Report)
• Added Clause 3.1.3 requirements for sampling of welded pipes
• Adjusted the content of original Clause 1.1.6 (now 3.1.6)
• Cancelled original Clause 1.2.3
• Specified the accuracy class of the ammeter in original Clause 2.1 (now 5.1)
• Added Clause 6.3 in original Chapter 3 (now Chapter 6)
• Added grade 1Cr18Ni9Ti to Table 4
• Moved the content from original Appendix A into the main text after adjustment

The GB/T 4334 series includes the following parts:

• GB/T 4334.1 — Method of 10 Per Cent Oxalic Acid Etch Test for Stainless Steels
• GB/T 4334.2 — Sulphuric Acid-Ferric Sulphate Corrosion Test Method for Stainless Steels
• GB/T 4334.3 — 65 Per Cent Nitric Acid Corrosion Test Method for Stainless Steels
• GB/T 4334.4 — Nitric-Hydrofluoric Acid Corrosion Test Method for Stainless Steels
• GB/T 4334.5 — Sulphuric Acid-Copper Sulphate Corrosion Test Method for Stainless Steels

This standard replaces GB/T 4334.1-1984 from its date of implementation.

---

1 Scope

This standard specifies the specimen, test solution, test equipment, test conditions and procedures, evaluation of test results, and test report for the 10% oxalic acid etch test method for stainless steels.

This standard is applicable as a screening test method for intergranular corrosion of austenitic stainless steels. After electrolytic etching in a 10% oxalic acid solution, the metallographic structure of the etched surface is examined under a microscope to determine whether further prolonged hot-acid tests (sulphuric acid-ferric sulphate, 65% nitric acid, nitric-hydrofluoric acid, or sulphuric acid-copper sulphate) are required.

It may also be used as an independent intergranular corrosion test method where destruction of the component or equipment under test is not permitted.

---

2 Normative References

The following standards constitute provisions of this standard through reference in this text:

• GB/T 655-1994 — Chemical reagents — Ammonium persulphate
• GB/T 2100-1980 — Technical conditions for stainless and acid-resistant steel castings
• GB/T 9854-1988 — Chemical reagents — Oxalic acid

---

3 Specimens

3.1 Sampling and Preparation

3.1.1 Specimens from pressure-worked steel products shall be taken from the same heat number, same heat treatment batch, and same specification.

3.1.2 Casting specimens shall be taken from test blocks poured from the same heat number of molten steel, in accordance with GB/T 2100. For grades containing the stabilizing element titanium, samples shall be taken from the last-poured block of that heat.

3.1.3 Welded pipe specimens shall be taken from the same heat number, same heat treatment batch, and same specification of welded pipe.

3.1.4 Welded test specimens shall be taken from test blocks made of the same steel and using the same welding procedure as the product.

3.1.5 The surface to be examined shall be the service surface. For welded joint specimens, this shall include the parent metal, heat-affected zone, and weld metal surfaces. Cross-sections must be examined when evaluating pit structure.

3.1.6 Specimens shall ideally be cut by shearing. If shearing is used, the affected zone shall be removed by machining or grinding.

3.1.7 The surface to be examined shall be polished to facilitate etching and metallographic examination.

3.2 Sensitization Treatment

3.2.1 Before sensitization and testing, specimens shall be degreased with an appropriate solvent or detergent (non-chlorinated) and dried.

3.2.2 Sensitization treatment is performed before polishing. For extra-low-carbon steels (carbon content ≤ 0.03%) and stabilized grades (containing titanium or niobium), the sensitization schedule is: 650 °C, held for 2 hours for pressure-worked specimens or 1 hour for castings, then air-cooled.

3.2.3 Welded specimens shall be tested in the as-welded condition. For welded components that undergo thermal processing above 350 °C after welding, the specimens shall additionally receive sensitization treatment. The sensitization schedule shall be specified by agreement.

---

4 Test Solution

4.1 Dissolve 100 g of super-pure grade oxalic acid (conforming to GB/T 9854) in 900 mL of distilled or deionized water to prepare a 10% oxalic acid solution.

4.2 For molybdenum-bearing steels where a step structure is difficult to develop, an alternative solution of 10% ammonium persulphate may be used, prepared by dissolving 100 g of analytical-grade ammonium persulphate (conforming to GB/T 655) in 900 mL of distilled or deionized water.

---

5 Test Equipment

5.1 DC power supply and variable resistor for etching; an ammeter of appropriate range with accuracy class 0.5.

5.2 The cathode shall be a steel cup made of austenitic stainless steel or a stainless steel sheet of sufficient surface area. The anode is the specimen. If a steel sheet is used as the cathode, an appropriate fixture shall be employed to hold the specimen in the test solution. The etching circuit is shown in Figure 1.

Figure 1 — Electrolytic Etching Apparatus
1 — Stainless steel container; 2 — Specimen; 3 — DC power supply; 4 — Variable resistor; 5 — Ammeter; 6 — Switch

---

6 Test Conditions and Procedures

6.1 Place the etching specimen as the anode, pour in 10% oxalic acid solution, use a stainless steel cup or sheet as the cathode, and switch on the current.

Parámetro	Oxalic Acid Solution	Ammonium Persulphate Solution
Current density	1 A/cm2	1 A/cm2
Etching time	90 s	5 – 10 min
Solution temperature	20 – 50 °C	—

6.2 After etching, rinse the specimen with running water and dry it. Examine the entire etched surface under a metallurgical microscope at a magnification of 200–500 times. Classify the structure according to Tables 1, 2 and Figures 2–8.

6.3 A fresh solution shall be used for each test.

---

7 Classification of Etched Structures

Table 1 — Grain Boundary Morphology Classification

Clase	Name	Structural Characteristics
Class I	Step structure	Corrosion grooves at grain boundaries; grains exhibit a stepped appearance. See Figure 2.
Class II	Mixed structure	Corrosion grooves at grain boundaries, but no individual grain is completely surrounded by grooves. See Figure 3.
Class III	Groove structure	Corrosion grooves at grain boundaries; individual or all grains completely surrounded by grooves. See Figure 4.
Class IV	Free ferrite structure	For castings and welded joints: no corrosion grooves at grain boundaries, ferrite is revealed. See Figure 5.
Class V	Continuous groove structure	For castings and welded joints: deep groove structures forming continuous groove patterns. See Figure 6.

Table 2 — Pit Morphology Classification

Clase	Name	Structural Characteristics
Class VI	Pit structure I	Predominantly shallow pits, few deep pits. See Figure 7.
Class VII	Pit structure II	Few shallow pits, predominantly deep pits. See Figure 8.

Table 3 — Relationship Between Screening Test and Other Test Methods

Structure Class	Pressure-worked specimens				Castings and welded specimens
	H2SO4-Fe2(SO4)3	65% HNO3	HNO3-HF	H2SO4-CuSO4	65% HNO3	H2SO4-Fe2(SO4)3	HNO3-HF	H2SO4-CuSO4
Class I	×	×	×	×	—	—	—	—
Class II	×	×	×	○	—	—	—	—
Class III	□	—	—	○	—	—	—	—
Class IV	—	—	—	—	×	×	×	×
Class V	—	—	—	—	□	□	○	—
Class VI	×	×	×	—	×	×	×	—
Class VII	×	○	×	—	×	○	×	—

Legend: × = no further testing required; ○ = additional testing required; — = not applicable; □ = one of the listed methods shall be selected.

Table 4 — Relationship Between 10% Oxalic Acid Etch Test and Hot-Acid Tests by Steel Grade

Hot-Acid Test	Stainless Steel Grades	Purpose
65% Nitric Acid Test	00Cr19Ni9, 00Cr19Ni10, 0Cr17Ni12Mo2, 00Cr17Ni14Mo2, 00Cr18Ni12Mo2, 00Cr18Ni14Mo2Cu2, 0Cr19Ni13Mo3, 00Cr19Ni13Mo3, 0Cr18Ni12Mo2Cu2, 00Cr18Ni14Mo2Cu2	Chromium carbides and σ-phase
65% Nitric Acid Test	0Cr18Ni9, 00Cr19Ni10, 0Cr18Ni9Ti	Chromium carbides
HNO3-HF Test	00Cr18Ni12Mo2Cu2, 00Cr18Ni14Mo2Cu2, 00Cr17Ni14Mo2, 0Cr17Ni12Mo2, 00Cr19Ni13Mo3, 0Cr18Ni10Ti, 0Cr18Ni11Nb	Chromium carbides and σ-phase
HNO3-HF Test	00Cr17Ni12Mo2, 00Cr17Ni14Mo2, 0Cr18Ni12Mo2Cu2, 00Cr18Ni14Mo2Cu2, 00Cr19Ni13Mo3	Chromium carbides
H2SO4-CuSO4 Test	00Cr18Ni9, 00Cr19Ni10, 0Cr17Ni12Mo2, 0Cr17Ni14Mo2, 0Cr18Ni12Mo2Cu2, 00Cr18Ni14Mo2Cu2, 0Cr19Ni13Mo3, 00Cr19Ni13Mo3, 0Cr18Ni10Ti, 00Cr18Ni11Nb, 1Cr18Ni9Ti	Chromium carbides

---

8 Test Report

The test report shall include the following information:

1. Specimen name and test area dimensions
2. Current density
3. Etching time and temperature
4. Metallographic photographs after etching
5. Classification result

---

Download Original Chinese Standard (PDF)

📄️ Download Original PDF (GB/T 4334.1-2000)

Embedded PDF Document

WhatsApp: +86-18658777855
Correo electrónico: 1007788887@qq.com