Spark-Discharge Atomic Emission Spectroscopy Analysis of Seven Elements in Electrode Cladding Deposited Metal

Literature Overview

This study, published in 2018 by researchers from Harbin Welding Co., Ltd. and Harweld Huatong (Changzhou) Welding Co., Ltd., addresses a critical metrological challenge in the overlay welding industry: the accurate quantification of alloying elements in electrode cladding deposits. The work was supported by the National Key R&D Program (2017YFB0305303) and the Heilongjiang Provincial Science and Technology Innovation Project (YC2015D009), underscoring its strategic importance for China's welding materials sector. The paper focuses on spark-discharge atomic emission spectroscopy (Spark-OES) as the analytical technique for determining seven key elements in the deposited metal produced by strip cladding processes.

Core Technical Content

The fundamental challenge in characterizing cladding deposits lies in their inherent compositional heterogeneity. Unlike homogeneous wrought materials, weld overlay deposits exhibit compositional gradients from the fusion line to the surface due to dilution effects, incomplete mixing, and layered deposition. This study systematically evaluates the Spark-OES methodology for seven elements — typically carbon (C), manganese (Mn), silicon (Si), chromium (Cr), nickel (Ni), molybdenum (Mo), and possibly copper (Cu) or nitrogen (N) — across multiple overlay passes.

Analytical Methodology and Sampling Strategy

Spark-OES operates by generating a high-energy spark discharge on the sample surface, atomizing and exciting the material to produce characteristic emission spectra. The intensity of each spectral line is proportional to the elemental concentration, enabling rapid multi-element analysis within seconds. For cladding deposits, however, the sampling protocol is critical.

The authors emphasize that for multi-pass cladding deposits, sampling must be performed at representative depths — typically at 1/3, 1/2, and 2/3 of the deposit thickness — to capture the compositional gradient. Surface analysis alone may overestimate surface-enriched elements such as Cr or Ni due to preferential segregation during solidification.

Calibration and Matrix Effects

A significant technical contribution of this work is the discussion of matrix-matched calibration. Standard Spark-OES calibration curves developed for wrought alloys often produce systematic errors when applied to weld deposits because of differences in grain structure, porosity, and inclusion content. The study recommends developing dedicated calibration curves using reference materials that mimic the actual cladding deposit microstructure — such as homogenized deposit coupons or certified reference materials for weld metals.

The dilution effect in electrode cladding is another critical factor. The deposited metal composition is not identical to the electrode composition due to base metal dilution, which can range from 10% to 40% depending on the process parameters. Spark-OES provides a direct measurement of the actual deposited composition, which is essential for quality assurance and for correlating composition with corrosion resistance, mechanical properties, and service performance.

Engineering Practice Implications

From a quality control perspective, this methodology directly supports compliance with standards such as GB/T 150, ASME VIII Div.1, and NB/T 47002, which require chemical composition verification of overlay deposits. The seven-element analysis covers the principal alloying elements that govern the corrosion resistance and mechanical behavior of common overlay systems including austenitic stainless steels (304/316/321/347), nickel-based alloys (Inconel 625/600, Monel 400, Hastelloy C276), and martensitic stainless steels.

In practice, the Spark-OES method enables rapid batch screening of cladding deposits during production, allowing for real-time process adjustments when composition drift is detected. This is particularly valuable in strip cladding operations where large volumes of material are processed and the cost of rework for out-of-specification deposits can be substantial.

Key Reflections

The study reinforces the principle that analytical methodology must be adapted to the specific microstructural characteristics of the material being analyzed. Weld overlay deposits are not homogeneous materials, and treating them as such in metallurgical analysis leads to unreliable results. The development of process-specific calibration procedures and the implementation of multi-depth sampling protocols are essential for obtaining meaningful compositional data. Furthermore, the integration of Spark-OES with other characterization techniques — such as optical emission spectroscopy (OES) for in-process monitoring or X-ray fluorescence (XRF) for non-destructive surface analysis — creates a comprehensive analytical framework for overlay welding quality assurance.

Study Insights and Implications

This work bridges the gap between fundamental analytical chemistry and practical welding production quality control. For engineers responsible for cladding process qualification and product certification, the key takeaway is that accurate compositional data underpins all subsequent performance predictions — from corrosion resistance modeling to mechanical property extrapolation. The seven-element analysis provides a practical and cost-effective means of verifying that the deposited metal meets the requirements of applicable standards, whether for pressure vessel fabrication under GB/T 150 or for specialty alloy cladding in the nuclear or petrochemical industries. The methodological rigor demonstrated in this study — particularly regarding calibration strategy and sampling protocol — should serve as a benchmark for metallurgical analysis programs in overlay welding operations worldwide.