The chemical analysis methods for iron, steel and alloys are well‑established and are generally carried out in accordance with the national standard GB/T 223 series (Methods for chemical analysis of iron, steel and alloys). This standard series includes dozens of specific analytical procedures, with different determination methods for various elements such as carbon, sulfur, manganese, silicon, phosphorus, chromium, nickel, molybdenum, etc. The following is a systematic classification and interpretation of the core content of chemical analysis methods for iron, steel and alloys:
I. Main Classification of Analytical Methods
Based on different measurement principles, they are mainly divided into two categories: wet chemical analysis and instrumental analysis.
1. Wet Chemical Analysis
This is a traditional and classical method that determines element content through chemical reactions.
- TitrationThe sample is dissolved and titrated with a standard solution.Applications: carbon (non-aqueous titration), manganese (potentiometric titration), chromium (ammonium ferrous sulfate titration).
- Spectrophotometry / ColorimetryElements react with specific reagents to form colored compounds; the content is determined by the color intensity (absorbance).Applications: silicon (molybdenum blue method), phosphorus (molybdenum blue method), titanium, copper, vanadium, etc.
- GravimetryElements are converted into precipitates, and the content is calculated by weighing the mass of the precipitate.Applications: silicon (perchloric acid dehydration gravimetry), tungsten.
2. Instrumental Analysis
Analysis based on physical or physicochemical properties of substances, featuring high speed and high precision.
- Spectroscopic Analysis
- Optical Emission Spectrometry (OES): The preferred method for rapid on‑site analysis in steelmaking, capable of simultaneously determining dozens of elements including C, Si, Mn, P, S, etc.
- X‑ray Fluorescence Spectrometry (XRF): Used for multi‑element analysis of solid bulk samples without dissolution.
- Atomic Absorption Spectrometry (AAS): Used for determining trace metallic elements such as lead, cadmium and zinc.
- Inductively Coupled Plasma Optical Emission Spectrometry (ICP‑OES): Commonly used in modern laboratories, enabling simultaneous determination of multiple trace and major elements.
- Carbon‑Sulfur Analyzer (CS Analyzer): Specifically used for rapid determination of carbon and sulfur content by high‑frequency combustion infrared absorption method.
II. General Procedure for Chemical Analysis
A complete chemical analysis in the laboratory typically includes the following steps:
- Sampling
- Representativeness: Sampling must be performed at specified positions of steel products (e.g., head, end, edge) in accordance with standards such as GB/T 20066.
- Sample preparation: The steel sample is processed into drillings or bulk form, free of oil, grease and scale.
- Sample DecompositionThe metallic sample is dissolved into a homogeneous solution using acids (hydrochloric acid, nitric acid, sulfuric acid, phosphoric acid) or alkalis. This is a critical step requiring complete dissolution.
- Separation & EnrichmentExtraction, precipitation or ion exchange is performed if matrix elements interfere with determination or the analyte content is extremely low.
- DeterminationMeasurement is carried out using an appropriate method: titration, colorimetry or instrumental detection.
- Data Processing & ReportingResults are derived from calibration curves or standard formulas, and a material test certificate is issued.
III. Standard Systems and Application Scenarios
- National Standard GB/T 223: The most widely used standard for chemical analysis of iron and steel in China.
- International Standards ISO 4940 / 4941: Corresponding internationally recognized methods for iron and steel analysis.
- ASTM E Series: Standards of the American Society for Testing and Materials, commonly applied for export products or foreign‑funded enterprises.
Typical Application Examples
- Pressure vessel manufacturing: During incoming inspection of raw materials, random testing of key elements (C, Si, Mn, P, S, Cr, Ni, etc.) must be conducted in accordance with GB/T 223 to ensure materials meet the requirements of GB 150 or the purchase contract.
- On‑site furnace analysis: To control the steelmaking process, steel plants use optical emission spectrometers to measure molten steel composition within minutes for formula adjustment.
