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Expert-Approved LIBS Analyzers for Carbon in Stainless Steels from Metal Analysis Group



This article delves into the analysis of carbon in various steel alloys, focusing on carbon steel, low alloy steel, and stainless steel, excluding tool steel from the discussion.

Carbon steel, a fundamental alloy comprising iron and carbon, forms the basis of many industrial applications. Low alloy steel incorporates carbon along with small additions of other alloying elements such as chromium, manganese, and molybdenum, typically up to a maximum of 5% total added alloying content. Meanwhile, stainless steel, renowned for its corrosion resistance, blends carbon with higher quantities of key elements like chromium, nickel, and molybdenum, offering a wide range of concentrations across numerous grades.

The significance of carbon in these steel types cannot be overstated. Carbon is added in varying levels ranging from 0.005% to 1.2%, depending on the desired properties for specific applications. While carbon steel primarily relies on carbon as the sole additive, low alloy and stainless steels incorporate additional elements to achieve diverse properties. Carbon influences a spectrum of characteristics such as weldability, hardness, corrosion resistance, tensile strength, and ductility. Incorrect carbon levels can lead to detrimental effects including alloy creep, stress rupture, weld decay, and various forms of corrosion.

In welding applications, carbon equivalent (CE) calculations serve to predict the heat-affected zone (HAZ) and determine the compatibility of materials being joined. Special precautions may be necessary during welding processes to mitigate risks associated with dissimilar components or elevated carbon equivalents.

Stainless steel, particularly the austenitic 300 series, represents a significant category known for its corrosion resistance. The low-carbon variants, denoted as "L" grades (e.g., 304L, 316L), mitigate intergranular corrosion by minimizing carbide precipitation along grain boundaries. Conversely, high carbon "H" grades, like 304H and 316H, offer enhanced strength at elevated temperatures but are susceptible to sensitization-induced corrosion in certain temperature ranges.

The distinction between "L" and "H" grades lies in their carbon content and application-specific properties. "L" grades are preferred for welding treatments or high-temperature applications, while "H" grades excel in strength, particularly at temperatures exceeding 500°C.

Analyzing carbon content is critical for ensuring the appropriate selection and performance of steel alloys in various applications. Historically, laboratory techniques and heavy field equipment were employed for this purpose. However, advancements in portable analytical technologies, such as handheld X-ray Fluorescence (XRF) spectroscopy and Laser Induced Breakdown Spectroscopy (LIBS), now facilitate on-site carbon analysis with greater speed and convenience. Handheld LIBS analyzers, in particular, have emerged as versatile tools for rapid and accurate determination of carbon content in steel alloys, transforming the landscape of field testing and verification.

In summary, carbon analysis plays a pivotal role in assessing the suitability and performance of steel alloys across diverse applications. Understanding the nuances of carbon content and its implications enables informed decision-making and ensures the integrity and safety of critical components in various industries