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Methods of Sampling Steel for Chemical Analysis (SAE J408-1999)
Understanding Ladle Analysis and Check Analysis
Ladle analysis (or heat analysis) is the chemical composition reported to the purchaser, determined from one or more test samples taken during the pouring of the steel. In common practice, multiple samples are taken representing the first, middle, and last portions of the heat to survey uniformity and for control purposes. This is known as ladle sampling.
Check analysis, as defined in SAE J408-1999, is an analysis of the metal after it has been rolled or forged into semifinished or finished forms. It serves to verify the average composition of a heat or lot as represented by the ladle analysis, or to determine variations in composition within a heat or lot. It is not a duplicate determination to confirm a previous result. Results from check analysis can differ from each other and from the ladle analysis due to segregation.
⚠️ Check Analysis Limitations: Check analysis should not be used as a simple duplicate check. It is intended for verification of average composition or to identify variations. For highly segregating elements or specific steel types, check analysis may not be representative without clear evidence of misapplication.
Sampling Procedures and Minimum Requirements
For check analysis, each heat in a lot or shipment is considered separately. To indicate adequately the representative composition, samples are selected from a minimum number of pieces as shown below.
| Lot Size (tons) | Minimum Number of Pieces to Sample |
|---|---|
| Up to 15 tons (13.6 metric tons) inclusive | 4 pieces |
| Over 15 tons (13.6 metric tons) | 6 pieces |
If the number of pieces in a melt is less than the specified number, one sample shall be taken from each piece.
Sample Preparation: Steel samples for check analysis should be in the as-received condition from the steel producer, as subsequent heating operations may affect analytical results. Drillings or chips are taken without applied water, oil, or other lubricants, and must be free from scale, grease, dirt, or foreign substances. For carbon analysis, steel drills are used, not carbide-tipped drills. The surface metal should be discarded before sampling to ensure freedom from scale, decarburization, etc. Chips must be well mixed; those too coarse to pass a No. 10 (2000 µm) sieve or too fine to remain on a No. 30 (590 µm) sieve are not suitable. For pieces with cross-sectional area up to 16 in² (100 cm²) inclusive, the drill diameter is approximately 1/2 in (13 mm).
🛠️ Sampling Best Practice: Always discard surface metal before sampling, use sharp steel drills without lubricants, and mix chips thoroughly. Sieve analysis to appropriate size ensures reliable results.
Key Considerations for Representative Sampling
Segregation is the natural phenomenon in steel solidification where components with the lowest freezing points concentrate in parts of the ingot that solidify last. This results in a non-uniform distribution of elements. The degree of segregation depends on steel type and composition, casting temperature, ingot shape and size, and the inherent segregating characteristics of the elements.
Due to segregation, check analysis is not considered appropriate for rimmed or capped steels, especially for carbon, phosphorus, and sulfur, unless misapplication is clearly indicated. Similarly, check analysis for phosphorus and sulfur in rephosphorized or resulfurized steels is generally inappropriate without clear evidence of misapplication. The effect of segregation makes the ladle analysis more representative of the average composition of a melt than the analysis of a single sample from the finished material. However, check analysis of properly located samples from a sufficient number of pieces can afford a reasonable comparison with the ladle analysis.
Engineering Design Insight: When relying on composition for material performance, engineers should recognize that segregation can cause significant variation in check analysis results, particularly in certain steel grades. Proper sampling location and multiple samples are essential to obtain a fair average. In critical applications, it is advisable to rely on ladle analysis rather than a single check analysis from a finished piece. Understanding the segregating behavior of elements and the limitations of check analysis helps avoid incorrect material rejections or acceptance.
Frequently Asked Questions
What is the difference between ladle analysis and check analysis?
Ladle analysis is determined from samples taken during pouring of the heat and reported as the official composition. Check analysis is performed on the rolled or forged product to verify the average composition or detect variations. It is not a duplicate determination and is subject to segregation effects.
How many samples are required for check analysis?
For lots up to 15 tons, a minimum of four pieces should be sampled; for lots over 15 tons, six pieces. If the lot has fewer pieces than the required number, sample each piece.
Why is check analysis not recommended for rimmed or capped steels?
These steels have significant composition non-uniformity, especially for carbon, phosphorus, and sulfur, due to segregation. Check analysis for these elements is only considered appropriate if misapplication is clearly indicated.
What factors influence segregation in steel?
Segregation is affected by steel type and composition, casting temperature, ingot shape and size, and the inherent segregating characteristics of the elements. The degree of segregation varies across different steel types and ingot geometries.
