Abstract: To address the insufficient detection accuracy in the ultra-low content range for carbon and sulfur elements in non-oriented silicon steel using the conventional infrared absorption method, this study systematically investigated the determination of ultra-low carbon and sulfur detection limits and the factors significantly affecting detection accuracy, and proposed a set of optimal configuration parameters. The method detection limits of carbon 0.6×10?? and sulfur 0.5×10?? were determined by the blank test standard deviation method (3σ criterion), extending the detection limit from the conventional 10×10?? to below 5×10??. Key influencing factors including crucible pretreatment, carrier gas, fluxing agent, sample preparation, and analysis power were optimized, with both carbon and sulfur dual-element data used as evaluation criteria throughout all optimization experiments. The optimal parameters were obtained: crucible pretreatment at 1100 ℃ for 30 min; in-plant pipeline oxygen (99.99% purity) with oxygen purifier; domestic W-Sn flux added before sample; no sample pretreatment needed; analysis power at 80%. Verification using reference materials with carbon 3.4×10?? and sulfur 4.4×10?? demonstrated accurate results and good precision, meeting the quality control requirements for high-grade non-oriented silicon steel production.

Key words: infrared carbon-sulfur analyzer; ultra-low carbon and sulfur; detection limit; accuracy; influencing factors