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)
• Electrolytic Etching Method

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.

Electrolytic Etching Method

• 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.