Composition analysis is the technique of qualitatively and quantitatively determining the elemental composition of a metal sample by scientific analytical methods. By purpose it falls into two types: melting analysis, used in smelting to control product quality in real time, and product analysis, used for finished product quality control or material identification.

Metal composition analysis is essentially the analysis of element content, and there are many techniques: chemical analysis, atomic and ICP spectroscopy, X-ray energy dispersive spectroscopy (EDX), electron spectroscopy, X-ray diffraction (XRD), mass spectrometry (MS), spectrophotometry, spark optical emission spectrometry and gas analysis. This article focuses on the recommended methods for finished metal materials.

Part 1. Single element wet methods

These methods are represented by the GB/T 223 series for steel, GB/T 20975 for aluminium alloys and GB/T 5121 for copper alloys, using atomic absorption spectrometry, spectrophotometry, titration (potentiometric, coulometric, neutralisation), gravimetry and gas analysis to determine each element one at a time. They are highly targeted and are often used as arbitration methods for metal analysis. Their disadvantage is obvious: efficiency is low, since a metal sample usually requires analysis of more than ten elements, which means more than ten complete tests, and the demands on operator skill are very high.

Part 2. Spark optical emission spectrometry

These methods are represented by GB/T 4336 for carbon and low alloy steel, GB/T 11170 for stainless steel, GB/T 13748.21 for magnesium alloys and GB/T 7999 for aluminium alloys. The high temperature of an arc or spark vaporises elements directly from the solid sample and excites them to emit their characteristic wavelengths, and the percentage of each element is measured by spectral analysis. Accuracy is high, multiple elements can be analysed simultaneously, operation is simple and fast, no chemical reagents or special consumables are needed, and the method is more environmentally friendly. Solid samples can be measured directly. The drawbacks are that sample shape and size requirements apply, since a flat surface of a certain size and thickness is needed, and the method depends on reference standards: the closer the composition of the reference standard to the sample, the more accurate the result.

Part 3. Inductively coupled plasma optical emission spectrometry (ICP-OES) and gas analysis

These methods are represented by GB/T 20125 for low alloy steel, GB/T 20975.25 for aluminium alloys, GB/T 5121.27 for copper alloys, GB/T 20123 for carbon and sulphur in steel and GB/T 20124 for nitrogen in steel. The elements in the metal are divided into two groups: those analysed by ICP-OES, and those that ICP-OES cannot measure, which are measured with carbon sulphur analysers and oxygen nitrogen hydrogen analysers. Together they cover all elements. Convenience lies between the first two approaches: chemical reagents are needed for sample preparation and operators need some skill, but the method is more flexible and not limited by reference standards.

Part 4. Capability summary

Part 5. NTEK and its metal laboratory

Metal mechanical properties. Tensile strength, yield strength, elongation, Brinell hardness, Vickers hardness, Rockwell hardness.

Metal composition analysis. Metal grade analysis, metal purity analysis.

Metallographic analysis. Metallographic microstructure, non-metallic inclusions, grain size, weld quality.

Metal coatings. Coating thickness, micro pores and micro cracks, coating potential difference, coating adhesion.