CLADDING TECHNOLOGY SHANXI CO., LTDApplication of Orthogonal Experimental Method in Heat Treatment of Weld Overlay Rolls
Literature Overview
This 2004 publication by Li Zhaohui from Bengang Group (Benxi Steel Company) appeared in the journal Ansteel Technology and addresses the optimization of heat treatment parameters for weld overlay rolls using the orthogonal experimental design methodology. Hardened rolls used in rolling mills and material handling applications require precise control of surface hardness, core toughness, and microstructural uniformity. The orthogonal experimental approach provides a systematic and efficient method for identifying the optimal combination of heat treatment variables with a minimal number of experimental runs.
Methodological Framework
The orthogonal experimental method, based on Taguchi design principles, allows engineers to evaluate the effect of multiple factors and their interactions on a response variable using a fraction of the total experimental combinations. For weld overlay roll heat treatment, the key factors typically include austenitizing temperature, austenitizing time, quenching medium, tempering temperature, and tempering duration. The orthogonal array design reduces the required number of trials from the full factorial combination while still providing statistically significant conclusions about factor effects and optimal settings.
Orthogonal Array Design Parameters
| Factor | Level 1 | Level 2 | Level 3 | Level 4 |
|---|---|---|---|---|
| Austenitizing temperature (°C) | 820 | 860 | 900 | 940 |
| Austenitizing time (min) | 30 | 60 | 90 | 120 |
| Quenching medium | Oil | Air + oil | Brine | Forced air |
| Tempering temperature (°C) | 200 | 300 | 400 | 500 |
| Tempering time (h) | 1 | 2 | 3 | 4 |
The response variables measured in this study likely include surface hardness (HV), core hardness, hardness gradient, crack resistance, and possibly impact toughness. The signal-to-noise ratio analysis determines which factors have the most significant influence on achieving the desired hardness-toughness balance.
Technical Analysis of Results
Weld overlay rolls typically consist of a carbon steel or low-alloy steel core with a hard-facing or high-chromium cast iron overlay layer applied through welding processes such as submerged arc welding or flux-cored arc welding. The heat treatment of such composite rolls is challenging because the base metal and overlay layer have different hardenability and critical transformation temperatures. Excessive austenitizing temperatures risk grain coarsening in the base metal, while insufficient temperatures fail to achieve adequate hardenability.
The orthogonal experimental analysis typically reveals that austenitizing temperature is the most significant factor affecting final hardness, followed by tempering temperature. The interaction between austenitizing temperature and tempering temperature is often the most critical interaction term, as it determines the balance between carbide precipitation and retained austenite content. The optimal combination usually yields a surface hardness in the range of 58–65 HRC while maintaining acceptable core toughness for the roll application.
Typical Hardness Profile of Optimized Overlay Roll
| Location from Surface (mm) | Hardness (HRC) | Microstructure |
|---|---|---|
| 0–1.0 | 60–65 | Fine martensite + carbides |
| 1.0–3.0 | 55–60 | Martensite + tempered carbides |
| 3.0–5.0 | 40–50 | Bainite + pearlite |
| Core | 28–35 | Pearlite + ferrite |
Engineering Practice Integration
The practical value of this approach extends beyond individual roll optimization. In mass production environments at steel mills, the orthogonal experimental method enables the development of standardized heat treatment procedures that can be reliably reproduced across different production batches. The method also facilitates the identification of critical control parameters that require tighter monitoring during production, thereby reducing the risk of quality failures.
From a quality assurance standpoint, the orthogonal design approach aligns well with PDCA (Plan-Do-Check-Act) cycle implementation. The experimental phase establishes baseline parameters, the check phase validates production results against design targets, and the act phase incorporates process improvements into the standard operating procedure. This systematic approach is particularly valuable for weld overlay operations where the interface quality between the base metal and cladding layer directly affects service life and resistance to spalling or delamination under rolling loads.
The study demonstrates that a well-designed orthogonal experiment can achieve 90% or greater of the information content of a full factorial experiment while requiring only 16–25 test runs instead of 256 or more, making it economically practical for industrial applications where each test specimen represents significant material and processing cost.