GB/T 39077-2020 in English

Interpretation of the core content of the standard

This standard designs three types of harmful phase detection methods for economical austenite-ferrite duplex stainless steel:

Analysis of key technical points

1. Microstructure inspection method

The distribution of harmful phases was observed under a 500-1000x microscope using the electrolytic etching technology (oxalic acid/sodium hydroxide solution). Note:

• Deduct the influence of twin boundaries
• The arbitration adopts the average value of five fields of view
• The weldment needs to select the rating chart according to the weld PREN value

2. Charpy impact test method

The sample preparation strictly follows GB/T229, with special attention:

• Full-size samples are preferred, and small sizes need to be negotiated
• The notch position of the weldment is implemented in accordance with GB/T2650
• Re-inspection rules: The single value can be 70% lower than the limit, but the average value must meet the standard

3. Ferric chloride corrosion test method

Key control points:

• The sample surface Ra≥0.8μm and pickling is prohibited
• Solution ratio: 5%FeCl3+1%NaNO3
• The temperature is strictly controlled at 25℃±1℃

Implementation suggestions

Analysis of Standard Evolution

This standard innovatively:

• Established a testing system for economical dual-phase steel for the first time
• Introduced a quantitative indicator of the percentage of phase boundary content P
• Associated the PREN value grouping with the testing method

Compared with ISO/ASTM standards, it adds differentiated requirements for 20Cr type A/B group, which is more in line with the actual application of materials in China.