Accuracy of Carbon and Sulfur Analyzer in Measuring Sulfur in Steel by Combustion Iodometric Method

The combustion iodometric method for the determination of sulfur in iron and steel is affected by various factors such as furnace temperature, solvents, instruments and equipment. The combustion iodometric method for the determination of sulfur in iron and steel is the most widely used method for measuring sulfur in iron and steel due to its simple operation and rapid determination. Broad analysis methods. However, the method for determining sulfur is affected by various factors such as furnace temperature and flux. The sulfur recovery rate is low, generally less than 90%, sometimes only 60~70%. Therefore, it is important to master the analysis conditions. In order to improve the accuracy of sulfur determination by this method, the relevant information was consulted and the sulfur test was conducted on-site with a carbon-sulfur analyzer produced by our company.

Experiment: For the same standard sample (sulfur content of 0.033%) during the experiment, it is found that the titration rate is very critical, especially for high-sulfur samples. For this reason, experiments have been carried out, and the results show that not immediately titrating after oxy-fuel combustion will lead to low results. When titrating after waiting 30 seconds, the recovery rate will be reduced by nearly 30%, and the results of the titration immediately after the preset (preset a part of the iodine standard solution) 80% and the titration without preset are similar. Therefore, it is better to start the titration speed as quickly as possible, even if it is temporarily excessive, the result will not be affected.

1. The influence of sulfur recovery rate at combustion temperature

The form of sulfur in steel is relatively stable, and the combustion temperature needs to be increased to decompose and oxidize the sulfide. According to the data, the sulfur recovery rate can reach 90-96% when the furnace temperature is 1399℃, and about 98% when the furnace temperature is 1450~1510℃. The high-frequency furnace burning sulfur abroad has a higher recovery rate. When using a tube furnace to burn, the furnace temperature is difficult to reach 1350 ℃, but according to different materials, the furnace temperature should be increased as much as possible during combustion, general cast iron 1250 ℃, ordinary steel, low alloy 1300 ℃, high-speed steel, heat-resistant steel 1300-1350 ℃, in addition, a certain high temperature duration must be ensured to fully oxidize sulfur. Due to the large number of tube furnaces currently used in our country, in our tube furnace experiment, the combustion temperature of 1350℃ is about 5% higher than that of 1250℃.

2. The influence of oxygen flow rate on sulfur recovery

The oxygen flow rate during combustion is also not to be ignored. If the oxygen flow rate is small and the sample is not completely burned, the result will be low. If the oxygen flow rate is too large, part of the SO2 will continue to be oxidized to SO3, and the inability of SO3 to be titrated by the iodine standard solution will also make the result low. . Generally, the alloy steel is controlled at 1.5~3.0l/min, and the carbon steel is at 1.0~2.0l/min, and the recovery rate is higher. For convenience, it is generally appropriate to select an oxygen flow rate of 1.5~2.0l/min. In actual operation, the oxygen supply mode of "presence of large oxygen and rear control" should be adopted, which can effectively increase the burning speed and temperature of the sample. It is beneficial to the full oxidation of sulfur and the complete absorption of SO2, which is beneficial to the smooth progress of the titration reaction.

2 conclusion

The determination of sulfur in steel by combustion iodometry is affected by various factors such as furnace temperature, solvents, and equipment. The conversion rate of sulfur is often only a certain recovery rate under certain conditions. Therefore, as long as the analysis conditions are mastered, the standard steel sample and the unknown sample have the same combustion temperature as possible, the selected solvent is the same and the added amount is the same, the titration speed is preferred to be fast at the beginning, and the oxygen flow control is consistent. , The accuracy will be high, and the reproducibility will be good.