Analysis of Carbon and Sulfur in Cast Iron

It is well-known that carbon plays a key role in iron and steel fabrication. Properties, including ductility, brittleness, hardness and hardenability, for the most part, all depend on the content of carbon in the material.

That makes carbon the primary alloying element in cast iron, with levels typically greater than 2%. In the iron matrix, the presence of carbon can take on a variety of forms, e.g., bound to other elements as carbides, dissolved in the matrix or elementary as free graphite.

In contrast, sulfur is considered to be an undesirable contaminant element in cast iron. This is due to the fact it can prevent the graphite formation in cast iron and thus have a detrimental effect on the mechanical properties and its workability.

Quality- and process-control demand rapid and accurate analysis of the carbon and sulfur content in cast iron and other casted products. This article demonstrates the speed, simplicity and reliability of carbon and sulfur detection using the G4 ICARUS Series 2 equipped with a high-frequency (HF) induction furnace.

Measuring Principle

Combustion occurs within a sealed HF induction furnace under a flow of oxygen. While the sample, with the addition of a metallic accelerator, is heated by induction, combustion takes place at temperatures in excess of 2000 °C.

Sulfur compounds are then oxidized to SO2 and carbon to CO2. Subsequently, the total amount of carbon and sulfur elements are calculated in relation to the amount of these combustion gases, which are quantified using selective detection systems.

Analysis of Carbon and Sulfur in Cast Iron

Image Credit: Bruker AXS Inc.

Combustion Without Compromises: G4 ICARUS

With its robust HF-furnace equipped with ZoneProtect™, its novel vacuum-free automatic cleaning system, HighSense™ detectors and electronic flow- and pressure-control, the G4 ICARUS Series 2 is a smart decision for every industrial user who demands a reliable instrument, even in extreme conditions.

The G4 ICARUS Series 2 has the capacity to rapidly measure both carbon and sulfur in cast iron and related materials with excellent accuracy – usually in less than one minute.

Even in complex matrices like grey cast iron, where carbon is distributed unevenly in the form of graphite flakes, combustion analysis offers accurate results because it is a volumetric method, analyzing the whole mass of the sample.

Sample Preparation

It is recommended that users look at DIN EN ISO 14284 or ASTM E1806 for more information as they offer a comprehensive description of the standard practice for the appropriate sampling of cast iron, steel and iron.

Note: To prevent the risk of altering the distribution of metal and graphite, pig iron samples should not be washed with organic solvents due to ASTM E1806 samples taken during cast iron production.

Method Parameters

  • Analysis time 1: 25 seconds (power Level: 4)
  • Analysis time 2: 20 seconds (power level: 0)
  • Accelerators1:
    • Tungsten
    • High purity iron chips
  • Baseline check before analysis: 2 seconds
  •    Baseline check after analysis: 2 seconds
  • Crucible cool time: 10 seconds
  • Purge time: 5 seconds
  • Sample mass: ~0.2 - 0.3 g (weighed to 0.1 mg)
  • Start delay: 1 second 

Analysis of Carbon and Sulfur in Cast Iron

Image Credit: Bruker AXS Inc.

Calibration  

The calibration of the analyzer is conducted using cast iron reference material, e.g., EZRM B 481-1, EZRM B 483-1 or other appropriate reference material. 

Analysis of Carbon and Sulfur in Cast Iron

Image Credit: Bruker AXS Inc.

Procedure  

I. Determining the Blank Value  

Conduct at least three analysis runs of the blank value by introducing the described amount of accelerators into a preheated crucible and analyze.2 

II. Measuring Reference Materials  

  • Select CRMs for calibration and identify them in the analysis software with designation and the certified concentrations.
  • Weigh the necessary amount of reference material into a preheated2 crucible, and carry the exact mass into the analysis software. Cover the material with the desired amount of accelerator and analyze.
  • For each reference material used, repeat step 2 at least three times. Calibrate the analyzer with the blank values recorded under I. and the results acquired with reference materials II. (for further details, refer to the user manual).  

III. Sample Measurement  

  • Weigh a suitable amount of sample into a preheated crucible and carry the exact sample mass over to the analysis software.3 Add the desired amount of accelerator to the sample and analyze.
  • Repeat step 1 until a suitable amount of repetitions has been achieved. 

Notes:  

1It is recommended to use one scoop (~1.5 g) of tungsten and one scoop (~0.7 g) of iron chip for general-purpose analysis of cast iron. Use two spoons (~3 g) of tungsten if sulfur contents fall below 50 ppm; this should be determined with the highest precision. For best accuracy, the accelerator should be weighed to the nearest 0.1 g, and the sample to accelerator ratio should remain constant. 

2For optimal precision, ceramic crucibles should be preheated in a muffle furnace at ≥1250 °C for at least 15 minutes or ≥1000 °C for a minimum of 2 hours. To prevent cross-contamination, crucibles should be handled with clean tongs and transferred to a desiccator for storage. 

3Mean = arithmetic average; STD = absolute standard deviation (1 sigma)  

Results  

The reproducibility of the G4 ICARUS Series 2 and the method described is evidenced by a sequence of repetitive measurements of reference materials and production samples.

Table 1. Source: Bruker AXS Inc.

EZRM B 481-1 certified values: C: 3.907 (± 0.009)%
S: 0.0040 (± 0.0004)%
Mass / g Carbon / % Sulfur / %
0.3033 3.901 0.039
0.3008 3.899 0.038
0.3059 3.911 0.042
0.3010 3.902 0.036
0.2993 3.912 0.041
Mean3) 3.900 0.0039
STD3) 0.006 0.0002

 

3) Mean = arithmetic average; STD = absolute standard deviation (1σ)

Table 2. Source: Bruker AXS Inc.

EZRM B 483-1 certified values: C: 2.463 (± 0.012)%
S: 0.103 (± 0.002)%
Mass / g Carbon / % Sulfur / %
0.2668 2.459 0.1032
0.3025 2.451 0.1030
0.3026 2.465 0.1039
0.3044 2.452 0.1039
0.2993 2.474 0.1053
Mean 2.461 0.104
STD 0.009 0.001

 

Analysis of Carbon and Sulfur in Cast Iron

Image Credit: Bruker AXS Inc.

Table 3. Source: Bruker AXS Inc.

Pig Iron (Ch11/3)
Mass / g Carbon / % Sulfur / %
0.2045 4.50 0.0317
0.2025 4.49 0.0319
0.1990 4.51 0.0321
0.2072 4.47 0.0318
0.2031 4.50 0.0318
Mean 4.49 0.0319
STD 0.02 0.0002

 

Table 4. Source: Bruker AXS Inc.

Cast Iron 1
Mass / g Carbon / % Sulfur / %
0.3028 1.369 0.0143
0.3055 1.368 0.0146
0.3093 1.372 0.0149
0.3014 1.380 0.0147
0.2967 1.372 0.0146
Mean 1.37 0.0146
STD < 0.01 0.0002

 

Table 5. Source: Bruker AXS Inc.

Cast Iron 2
Mass / g Carbon / % Sulfur / %
0.3067 4.42 0.0040
0.3042 4.44 0.0040
0.3029 4.40 0.0040
0.3073 4.40 0.0039
0.3046 4.41 0.0040
Mean 4.41 0.0040
STD < 0.02 < 0.0001

 

Table 6. Source: Bruker AXS Inc.

Cast Iron 3
Mass / g Carbon / % Sulfur / %
0.3023 2.75 0.141
0.3071 2.74 0.138
0.3090 2.75 0.141
0.3060 2.72 0.140
0.3027 2.71 0.140
Mean 2.73 0.140
STD < 0.02 < 0.002

 

Summary  

Combining HighSense™ detection systems with the G4 ICARUS Series 2’s precise electronic flow control offers outstanding, long-time stable analytical performance. 

The robust HF-furnace fitted with the industry-leading ZoneProtect™ and its novel automatic cleaner guarantees low cost of ownership, high availability with minimal maintenance and facilitates complete and clean combustion. 

The analytical performance, alongside the rapid speed of analysis and its simplicity, makes the G4 ICARUS Series 2 the optimal choice for the quality control of cast iron, pig iron and even other related foundry products such as mold powder.

Analysis of Carbon and Sulfur in Cast Iron

Image Credit: Bruker AXS Inc.

This information has been sourced, reviewed and adapted from materials provided by Bruker AXS Inc.

For more information on this source, please visit Bruker AXS Inc.

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