GB/T 226-2015 Test Method for Macrostructure and Defect of Steel by Etching

Standard Information

• Standard Number: GB/T 226-2015
• Replaces: GB/T 226-1991
• Release Date: September 11, 2015
• Implementation Date: June 1, 2016
• Proposed by: China Iron and Steel Association
• Managed by: National Steel Standardization Technical Committee (SAC/TC 183)

Scope

This standard specifies three test methods for examining macrostructure and defects in steel:

• Hot Acid Etching Method
• Cold Acid Etching Method (including dendrite etching)
• Método de grabado electrolítico

This standard applies to acid etching inspection of steel macrostructure and defects. Other materials may be tested by reference to this standard.

Key Technical Requirements

Sample Preparation

• Sample thickness: Generally 20-30 mm
• Longitudinal sample length: Generally 1.5 times the side length or diameter
• Minimum distance from cutting surface:
  • Hot saw cutting: ≥20 mm
  • Cold saw cutting: ≥10 mm
  • Flame cutting: ≥25 mm
• Surface roughness (Ra) requirements:
  • Hot acid etching: ≤1.6 μm
  • Cold acid etching: ≤0.8 μm (dendrite etching: ≤0.025 μm after polishing)
  • Electrolytic etching: ≤1.6 μm

Hot Acid Etching Method (Recommended for Arbitration)

Recommended etching solutions vary by steel type:

• Carbon/Alloy structural steel, tool steel, stainless steel: 1:1 hydrochloric acid solution, 70-80°C, 5-40 min
• Austenitic stainless steel/heat-resistant steel: HCl 10 parts + HNO₃ 1 part + water 10 parts, 70-80°C
• High-speed tool steel: HCl 38 parts + H₂SO₄ 12 parts + water 50 parts, 60-80°C

Cold Acid Etching Method

13 types of cold etching solutions are specified for different steel types including carbon steel, alloy steel, stainless steel, nickel-based alloys, and precision alloys.

Método de grabado electrolítico

• AC Electrolytic: 15-30% HCl solution, voltage ≤36V, current ≤400A, 5-30 min
• DC Electrolytic: Sample as anode, HCl solution with optional boric acid, current density varies by sample area

Result Documentation

• Hot/Cold/Electrolytic etching results: Optical photography or digital imaging
• Dendrite etching results: Scanning imaging (resolution >1000 dpi)

Sample Preservation Methods

• Neutralization: Soak in 10% ammonia alcohol solution, rinse with hot water, dry
• Passivation: Immerse in concentrated nitric acid (~5 seconds), rinse, dry
• Coating protection: Apply varnish or plastic film

Environmental Safety

Waste acid must be treated according to GB 8978-1996 Class II pollutant discharge regulations.

Test Report Requirements

The inspection report shall include:

1. Client unit
2. Steel grade
3. Melting (batch) number
4. Sample number
5. Sample cutting direction
6. Test method
7. Test results
8. Inspector and report date

Download Original Standard

📄 Download Original PDF (GB/T 226-2015 Chinese Standard)

Note: This is an English translation summary of GB/T 226-2015. For official purposes, please refer to the original Chinese standard document.

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