GB/T 4334.1-2000: Method of 10% Oxalic Acid Etch Test for Stainless Steels

National Standard of the People’s Republic of China

ICS 77.040.99
Released: 2000-10-25
Implemented: 2001-09-01
Issued by: State Bureau of Quality and Technical Supervision

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 inspecting intergranular corrosion of austenitic stainless steels. After electrolytic etching of the specimen in 10% oxalic acid solution, the metallographic structure of the etched surface is observed under a microscope to determine whether long-term hot acid tests such as sulfuric acid-ferric sulfate, 65% nitric acid, nitric acid-hydrofluoric acid, and sulfuric acid-copper sulfate are required.

2. Normative References

• GB/T 655-1994: Chemical Reagent – Ammonium Persulfate
• GB/T 2100-1980: Technical Requirements for Stainless Acid-Resistant Steel Castings
• GB/T 9854-1988: Chemical Reagent – Oxalic Acid

3. Specimen Sampling

• 3.1.1 Wrought steel: same heat number, heat treatment batch, and specification
• 3.1.2 Castings: per GB/T 2100, same heat number
• 3.1.3 Welded pipes: same heat number, heat treatment batch, specification
• 3.1.4 Welding specimens: same product steel and welding process
• 3.1.5 Inspection surface shall be the service surface. Welded joint specimens shall include base metal, heat-affected zone, and weld metal

4. Sensitization Treatment

For ultra-low carbon steels (carbon content ≤ 0.03%) and stabilized steel grades (with titanium or niobium added), sensitization treatment regime is 650°C, holding for 2 hours for wrought specimens and 1 hour for castings, followed by air cooling.

5. Test Solution

Dissolve 100g of premium pure oxalic acid in 900 mL of distilled water or deionized water to prepare 10% oxalic acid solution.

6. Test Conditions

• Current density: 1 A/cm²
• Etching time: 90 seconds
• Solution temperature: 20°C to 50°C
• Microscope magnification: 200x to 500x

7. Structure Classification

Category	Name	Characteristics
Class I	Step Structure	No corrosion grooves at grain boundaries
Class II	Mixed Structure	Corrosion grooves, no grains surrounded
Class III	Ditch Structure	Grains surrounded by corrosion grooves
Class IV	Free Ferrite Structure	No grooves, ferrite revealed
Class V	Continuous Ditch Structure	Deep, continuous corrosion grooves
Class VI	Pit Structure I	Many shallow pits, few deep pits
Class VII	Pit Structure II	Few shallow pits, many deep pits

8. Test Report Requirements

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

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Original PDF Document

Download Original PDF: GBT_4334-2008_金属和合金的腐蚀_不锈钢晶间腐蚀试验方法—45a97cc1-a0e6-49ee-8f34-d0ea11ca169f.pdf

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This standard replaces GB/T 4334.1-1984. Released 2000-10-25, implemented 2001-09-01.