GB/T 223.11-2025 Iron, steel and alloy—Determination of chromium content—Titrimetric method and spectrophotometric method English, Anglais, Englisch, Inglés, えいご
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Contents
Foreword
1 Scope
2 Normative References
3 Terms and Definitions
4 Method 1: Visual Titrimetric Method
5 Method 2: Potentiometric Titration Method
6 Method 3: Spectrophotometric Method (Sodium Carbonate Separation-Diphenylcarbazide Spectrophotometry)
7 test method
Iron,steel and alloy-Determination of chromium content-Titrimetric method and spectrophotometric method
WARNING – Personnel using this document shall have practical experience in laboratory work. This document does not address all potential safety issues. Users are responsible for implementing appropriate safety and health measures and ensuring compliance with national regulatory requirements.
1 Scope
This document specifies three methods for the determination of chromium content in pig iron, carbon steel, alloy steel, precision alloys, and high-temperature alloys:
Method 1: Visual titrimetric method (for chromium content of 0.1%–35% by mass in pig iron, carbon steel, alloy steel, high-temperature alloys, and precision alloys).
Method 2: Potentiometric titrimetric method (for chromium content of 0.25%–35% by mass in steel).
Method 3: Sodium carbonate separation-diphenylcarbazide spectrophotometric method (for chromium content of 0.005%–0.5% by mass in carbon steel, low-alloy steel, and precision alloys).
2 Normative References
The following referenced documents are indispensable for the application of this document. For dated references, only the cited version applies; for undated references, the latest version (including amendments) applies:
GB/T 223.13: Steel and alloys – Determination of vanadium content – Titrimetric and spectrophotometric methods (GB/T 223.13—2025, MOD ISO 4942:2016).
GB/T 223.76: Methods for chemical analysis of iron and steel – Flame atomic absorption spectrometric method for vanadium.
GB/T 6379.1: Accuracy (trueness and precision) of measurement methods and results – Part 1: General principles and definitions (IDT ISO 5725-1:1994).
GB/T 6379.2: Accuracy (trueness and precision) of measurement methods and results – Part 2: Basic method for the determination of repeatability and reproducibility of a standard measurement method (IDT ISO 5725-2:1994).
GB/T 6682: Specifications and test methods for water for analytical laboratory use (MOD ISO 3696:1987).
GB/T 7729: General rules for spectrophotometric methods in chemical analysis of metallurgical products.
GB/T 8170: Rules for rounding off numerical values and presentation of limiting values.
GB/T 12805: Laboratory glassware – Burettes (NEQ ISO 385:2005).
GB/T 12806: Laboratory glassware – Volumetric flasks (NEQ ISO 1042:1998).
GB/T 12808: Laboratory glassware – Pipettes.
GB/T 20066: Steel and iron – Sampling and sample preparation for chemical analysis (IDT ISO 14284:1996).
GB/T 20125: Low-alloy steel – Determination of multi-element contents – Inductively coupled plasma atomic emission spectrometry.
3 Terms and Definitions
No terms or definitions require clarification in this document.
4 Method 1: Visual Titrimetric Method
4.1 Principle
The test sample is dissolved in acid, and chromium is oxidized to chromium(VI) in sulfuric acid-phosphoric acid medium using ammonium persulfate with silver nitrate as a catalyst.
The chromium(VI) is then titrated with ammonium ferrous sulfate standard solution.
For samples containing vanadium:
Option 1: Use ferrous-o-phenanthroline solution as an indicator. Add an excess of ammonium ferrous sulfate standard solution and back-titrate with potassium permanganate solution.
Option 2: Measure vanadium using a national or international standard method and correct for its interference via theoretical calculation.
Interference from ≤2 mg of cerium in the test solution does not affect the determination.
4.2 Reagents and Materials
Unless otherwise specified, only analytically pure reagents and water of Grade 2 or equivalent purity (as per GB/T 6682) shall be used.
4.2.1 Sodium acetate anhydrous.
4.2.2 Hydrochloric acid: ρ ≈ 1.19 g/mL.
4.2.3 Hydrochloric acid (1+3): prepared by diluting hydrochloric acid (4.2.2).
4.2.4 Nitric acid: ρ ≈ 1.42 g/mL.
4.2.5 Phosphoric acid: ρ ≈ 1.69 g/mL.
4.2.6 Sulfuric acid (1+1): prepared by diluting sulfuric acid (ρ ≈ 1.84 g/mL).
4.2.7 Sulfuric acid (5+95): prepared by diluting sulfuric acid (ρ ≈ 1.84 g/mL).
4.2.8 Hydrofluoric acid: ρ ≈ 1.15 g/mL.
4.2.9 Sulfuric acid-phosphoric acid mixed acid: prepared by mixing 320 mL sulfuric acid (4.2.6), 80 mL phosphoric acid (4.2.5), and 600 mL water.
4.2.10 Silver nitrate solution (10 g/L): dissolve 1.0 g silver nitrate in 100 mL water, add a few drops of nitric acid (4.2.4), and store in a brown bottle.
4.2.11 Ammonium persulfate [(NH₄)₂S₂O₈] solution (300 g/L): prepare fresh before use.
4.2.12 Manganese sulfate [MnSO₄·H₂O] solution (40 g/L).
4.2.13 N-phenylanthranilic acid solution (2.0 g/L): dissolve 0.20 g reagent and 0.20 g anhydrous sodium carbonate in 20 mL water, then dilute to 100 mL with water.
4.2.14 Ferrous-o-phenanthroline solution: dissolve 1.49 g o-phenanthroline and 0.98 g ammonium ferrous sulfate in 50 mL water, then dilute to 100 mL.
4.2.15 Chromium standard solutions:
4.2.15.1 Chromium stock solution (2.000 mg/mL): dissolve 5.6578 g potassium dichromate (pre-dried at 150°C for 1 h) in water, dilute to 1000 mL.
4.2.15.2 Chromium standard solution A (1.000 mg/mL): dilute 50.00 mL stock solution (4.2.15.1) to 100 mL.
4.2.15.3 Chromium standard solution B (0.500 mg/mL): dilute 25.00 mL stock solution (4.2.15.1) to 100 mL.
