GB/T 38933-2020 in English
VALIDCold rolled steel sheet for automobile-Test method of phosphate conversion coatings
- Issued on:2020-06-02
- Implemented on:2020-12-01
- File Format:PDF
- Delivery:Via email within 1~3 business days
$117.00
《GB/T 38933-2020汽车用冷轧钢板 磷酸盐转化膜试验方法》由TC183（全国钢标准化技术委员会）归口，TC183SC6（全国钢标准化技术委员会钢板钢带分会）执行，主管部门为中国钢铁工业协会。
Introduction
Analysis of the core content of the standard
| Test items | Technical indicators | Detection methods | Equipment requirements |
|---|---|---|---|
| Crystal size | μm-level measurement | SEM scanning electron microscopy method | Scanning electron microscope(1000x) |
| Membrane weight | g/m² unit | GB/T9792 weight method | Analytical balance (precision 0.1mg) |
| P ratio | Hopeite/Phosphophyllite intensity ratio | X-ray diffraction method | X-ray diffractometer(Co target) |
Detailed explanation of key test methods
5.1 Appearance inspection specification
The standard clearly distinguishes between allowable defects and unallowable defects:
- Allowable defects include 3 types of situations such as slight water marks and color difference in welding areas
- Unallowable defects involve 5 serious problems such as rust and local lack of film
Automobile door panel phosphating case
When a certain automobile enterprise applied the standard, it was discovered that there was uneven crystallization at the bend of the door panel. It was determined that this was a processing state difference allowed by the standard and would not affect the subsequent painting quality.
Technology Evolution Analysis
Compared with the old version of the standard, the main upgrades of the 2020 version are:
- Added requirements for zinc-manganese-nickel phosphate film detection
- Clarified the field of view selection specifications for SEM detection
- Refined the temperature control accuracy of the salt spray test (±1℃)
Implementation Suggestions
Laboratory Configuration Plan
| Equipment Type | Key Parameters | Calibration Period |
|---|---|---|
| Salt Spray Test Chamber | In compliance with GB/T10125 | 3 months |
| X-ray diffractometer | Co target 40kV/35mA | 6 months |
Troubleshooting
When P ratio abnormality occurs, it is recommended to follow the following process to troubleshoot:
- Check the metal ion ratio of the phosphating solution
- Verify the purity of the X-ray diffractometer target
- Recalibrate the diffraction intensity benchmark
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