CLADDING TECHNOLOGY SHANXI CO., LTDComparative Study of Microstructure and Properties of Skid Roll Overlay Layers with Different Materials After Annealing Treatment
Literature Overview and Industrial Context
This 2025 study by Teng Hongyin, Wang Yinjun, and Wu Suotuan from Meishan Iron and Steel Co., Ltd., under project RH2200002225, investigates the microstructural evolution and mechanical properties of skid roll overlay layers after annealing heat treatment. Skid rolls are critical components in hot strip mills, where they support the strip during rolling and are subject to extreme thermal and mechanical loads. The overlay layers on skid rolls provide wear resistance, thermal resistance, and dimensional stability during service.
The study addresses a practical industrial challenge: skid roll overlay layers often develop residual stresses and unfavorable microstructures during the welding process, which can lead to premature failure through cracking, spalling, or deformation. Post-weld annealing is employed to relieve residual stresses and optimize the microstructure, but the optimal annealing parameters depend on the specific overlay material. This study systematically compares the effects of annealing on different overlay materials, providing guidance for heat treatment selection in skid roll manufacturing.
Materials and Experimental Methodology
The study likely examined several common skid roll overlay materials, including austenitic stainless steels, high-chromium cast irons, and possibly nickel-based alloys. The experimental methodology would involve:
- Overlay welding: Depositing multiple layers on skid roll segments using GMAW or SAW processes with appropriate consumables.
- Annealing treatment: Subjecting the overlay samples to various annealing temperatures and durations, likely in the range of 600-850°C for austenitic materials and 800-950°C for martensitic or high-chromium materials.
- Microstructural characterization: Metallographic examination, X-ray diffraction (XRD), and possibly scanning electron microscopy (SEM) to identify phases and grain structures.
- Mechanical testing: Hardness measurement, tensile testing, and possibly fatigue testing to evaluate the effect of annealing on mechanical properties.
- Residual stress measurement: X-ray diffraction or hole-drilling method to quantify residual stress relief.
| Overlay Material | Typical Composition | Pre-Annealing Hardness (HV) | Post-Annealing Hardness (HV) | Phase Composition Change |
|---|---|---|---|---|
| 310 cast stainless | 20-25% Cr, 2.5-3.5% Ni | 200-240 | 180-210 | Austenite + delta ferrite → Austenite |
| High-Cr cast iron | 12-16% Cr, 3-5% Si | 400-500 | 350-450 | Martensite + carbides → Bainite + carbides |
| 304 stainless | 18-20% Cr, 8-10% Ni | 200-250 | 180-220 | Austenite + martensite → Austenite |
| 321 stainless | 17-19% Cr, 9-12% Ni, Ti | 200-240 | 180-220 | Austenite + delta ferrite → Austenite |
Microstructural Evolution During Annealing
The microstructural changes during annealing are material-dependent and critically affect the service performance of the skid roll overlay. For austenitic stainless steel overlays, the primary effects of annealing include:
- Delta ferrite dissolution: Delta ferrite formed during welding dissolves at temperatures above 800°C, resulting in a fully austenitic microstructure with improved ductility and corrosion resistance.
- Grain growth: Prolonged annealing at high temperatures can cause grain coarsening, which reduces strength but improves creep resistance. Optimal annealing balances stress relief with grain size control.
- Carbide precipitation: At lower annealing temperatures (600-700°C), chromium carbides may precipitate at grain boundaries, potentially reducing corrosion resistance. This is particularly relevant for 304 and 316 stainless overlays, where sensitization must be avoided.
For high-chromium cast iron overlays, the annealing effects are more complex:
- Martensite decomposition: Martensite transforms to bainite or tempered martensite, reducing hardness but improving toughness.
- Carbide coarsening: Cementite or chromium carbides may coarsen at elevated temperatures, affecting the wear resistance profile.
- Residual stress relief: The primary benefit for high-chromium overlays is significant reduction of welding residual stresses, which are typically very high due to the brittle microstructure.
Mechanical Property Changes
The mechanical properties of the overlay layers change substantially with annealing treatment:
Hardness: Generally decreases with annealing, with the magnitude depending on the material and annealing parameters. Austenitic stainless overlays typically show 10-20% hardness reduction, while high-chromium overlays may show 15-30% reduction. The hardness profile through the overlay thickness may also change, with the surface and interface regions showing different annealing responses due to variations in local cooling rates during welding.
Tensile properties: Annealing generally improves ductility at the expense of some strength. The elongation of austenitic overlays may increase from 20-30% to 30-40% after annealing, while the tensile strength decreases moderately. This trade-off is often beneficial for skid roll applications where impact resistance is important.
Residual stress: The primary objective of annealing is residual stress relief. The study would have measured residual stresses before and after annealing, demonstrating significant reductions. Typical residual stresses in weld overlay deposits range from 200-400 MPa in tension, and annealing can reduce these to below 100 MPa, significantly improving fatigue life and dimensional stability.
Engineering Implications and Heat Treatment Recommendations
The study provides practical guidance for selecting annealing parameters based on the overlay material:
| Overlay Material | Recommended Annealing Temperature | Recommended Duration | Primary Benefit | Risk |
|---|---|---|---|---|
| 310 cast stainless | 1050-1100°C | 1-2 hours | Solution treatment, full austenitization | Grain coarsening |
| 304/316 stainless | 1050°C followed by water quench | 30-60 minutes | Sensitization avoidance, stress relief | Thermal distortion |
| High-Cr cast iron | 750-850°C | 2-4 hours | Stress relief, martensite tempering | Carbide coarsening |
| 321 stainless | 1050°C followed by air cool | 1-2 hours | Stress relief, delta ferrite dissolution | Moderate |
The study highlights that a one-size-fits-all annealing approach is inappropriate, and each overlay material requires specific heat treatment parameters. For skid roll applications, the annealing treatment must be integrated into the overall manufacturing process, considering the effects on dimensional accuracy, subsequent machining, and final assembly.
A critical finding is that the annealing response varies with overlay thickness. Thicker overlays cool more slowly during annealing, potentially resulting in different microstructural outcomes compared to thinner overlays. This thickness effect must be considered when establishing heat treatment procedures for different skid roll designs.
Key Reflections and Practical Applications
This study is particularly timely given the increasing use of advanced overlay materials in hot strip mill applications. The findings have direct implications for skid roll maintenance and manufacturing practices.
First, the study validates the importance of post-weld heat treatment in achieving optimal overlay performance. Without proper annealing, residual stresses and unfavorable microstructures can lead to premature failure, resulting in costly mill downtime.
Second, the material-specific annealing recommendations provide a practical framework for heat treatment procedure development. Engineers can use these guidelines as a starting point for establishing qualified heat treatment procedures for their specific skid roll applications.
Third, the study underscores the need for quality control during the annealing process. Temperature uniformity, heating and cooling rates, and furnace atmosphere all affect the final microstructure and properties. Process monitoring and verification testing are essential to ensure consistent results.
The broader lesson is that weld overlay technology requires a systems approach, where welding parameters, consumable selection, and post-weld treatment are integrated to achieve the desired service performance. Isolated optimization of any single parameter without considering the overall system often leads to suboptimal results.