Zhuojin Pipe Fitting Co., LtdResearch on Overlay Welding of Steel Rolls
Literature Overview
This paper by Tan Zheng from the Bar and Wire Rod Plant of Tangshan Iron and Steel Co., Ltd., published in China Metallurgy (2005, Vol. 15, No. 8, pp. 32-36), presents a comprehensive study on the overlay welding technology for steel rolling mill rolls. The work covers the development status of roll overlay welding technology, automatic submerged arc surfacing processes, and detailed experimental investigations of four different overlay welding materials: 27Cr3Mo2MnVWTi, 3Cr13, 35MnSi, and 3Cr2W8V. This industrial research provides practical guidance for roll repair and performance enhancement in steel production environments.
Overlay Materials and Process Parameters
The study evaluates four overlay welding materials with distinct compositions and intended applications:
| Material Designation | Key Alloying Elements | Typical Application | Expected Hardness Range |
|---|---|---|---|
| 27Cr3Mo2MnVWTi | Cr, Mo, Mn, V, W, Ti | Hot working rolls | Medium-high |
| 3Cr13 | Cr (martensitic) | Hot working rolls | Medium |
| 35MnSi | Mn, Si (low alloy) | General purpose rolls | Low-medium |
| 3Cr2W8V | Cr, W, V (high alloy) | Hot working rolls | High |
The automatic submerged arc surfacing (SAS) process was selected as the primary welding method for this study, which is appropriate for the large surface areas of rolling mill rolls and provides good process repeatability. Submerged arc welding offers several advantages for roll overlay applications, including high deposition rates, deep penetration, low spatter, and the ability to use large diameter flux-cored wires for efficient buildup.
Microstructural and Performance Analysis
The study investigated the post-weld heat treatment regimes and their effects on the microstructure and mechanical properties of each overlay material. Key findings include:
- Dilution behavior: The dilution rate between the overlay deposit and the roll substrate was analyzed for each material. Dilution is a critical parameter in roll overlay welding because it affects the final composition and properties of the overlay layer. Higher dilution rates generally reduce the hardness and wear resistance of the overlay but may improve toughness and reduce cracking susceptibility.
- Chemical composition: The actual chemical composition of the overlay deposits after welding was measured and compared with the nominal filler wire composition. The differences between nominal and actual compositions provide quantitative dilution data that are essential for process control.
- Microstructure evolution: Each overlay material develops a distinct microstructure upon solidification and subsequent heat treatment. The martensitic materials (3Cr13, 3Cr2W8V) develop carbide-rich structures, while the lower-alloy materials (35MnSi) develop more ferritic-bainitic structures.
- Hardness profiles: The hardness of each overlay deposit was measured across the depth of the overlay layer, revealing hardness gradients that reflect the dilution profile and microstructural variations.
- Wear resistance: Abrasion testing was performed to quantify the wear resistance of each overlay material, providing direct comparison of service performance potential.
- Mechanical properties: Tensile strength, elongation, and impact toughness were evaluated to assess the overall mechanical integrity of the overlay deposits.
Post-Weld Heat Treatment Considerations
Post-weld heat treatment is essential for optimizing the properties of overlay weld deposits on rolling mill rolls. The treatment parameters must be carefully selected based on the overlay material composition:
- Tempering for martensitic overlays: Materials such as 3Cr13 and 3Cr2W8V require tempering after welding to reduce residual stresses and achieve the desired balance of hardness and toughness. Temper temperatures typically range from 400°C to 600°C depending on the required hardness level.
- Normalizing for low-alloy overlays: Materials such as 35MnSi may benefit from normalizing treatment to refine the grain structure and improve uniformity of properties.
- Stress relief for all overlays: Regardless of the specific overlay material, stress relief treatment is recommended to reduce welding residual stresses that can lead to overlay cracking or delamination during service.
Material Selection Guidance
Based on the experimental results, the author proposes the following material applicability recommendations:
| Service Condition | Recommended Material | Rationale |
|---|---|---|
| High temperature, moderate abrasion | 3Cr13 | Good hot hardness and moderate wear resistance |
| High temperature, severe abrasion | 3Cr2W8V | Highest hot hardness and wear resistance |
| General purpose, moderate conditions | 27Cr3Mo2MnVWTi | Balanced properties with multiple alloying elements |
| Low temperature, light service | 35MnSi | Adequate properties at lower cost |
Engineering Practice Implications
For steel mills considering roll overlay welding as a repair and enhancement strategy, several practical considerations emerge from this study:
- Substrate preparation: The roll surface must be thoroughly cleaned and prepared before overlay welding to ensure proper metallurgical bonding. Surface oxidation, scale, and contamination must be removed through grinding or machining.
- Welding sequence planning: For large roll surfaces, the welding sequence should be planned to minimize distortion and residual stress accumulation. Symmetrical welding patterns and back-step welding techniques can help control distortion.
- Interpass temperature control: Maintaining appropriate interpass temperatures is critical to prevent excessive grain growth and to ensure uniform microstructure development in multi-pass overlay welds.
- Quality inspection: Post-weld inspection should include hardness mapping, visual examination for surface defects, and potentially non-destructive testing (magnetic particle testing or ultrasonic testing) to detect subsurface defects.
- Service monitoring: After installation, the overlay welds should be monitored for early signs of failure, including cracking, spalling, or excessive wear, to enable timely intervention before catastrophic roll failure.
Key Questions and Reflections
This industrial research paper provides practical data but leaves several questions open for further investigation. The long-term durability of overlay welds under repeated thermal cycling in hot rolling conditions is not extensively addressed. Thermal fatigue cracking at the overlay-substrate interface is a known failure mode that should be evaluated through thermal cycling tests. Additionally, the cost-effectiveness analysis comparing overlay welding repair versus complete roll replacement would provide valuable economic justification for adopting this technology.
The study also does not extensively discuss the effect of overlay welding on roll dimensional accuracy and surface finish, which are critical parameters for product quality in rolling operations. Post-weld grinding and machining to achieve required dimensional tolerances add to the overall process cost and time.
In summary, this paper by Tan Zheng provides valuable industrial experience and experimental data on overlay welding of steel rolling mill rolls using four different filler materials. The systematic evaluation of dilution behavior, microstructure, hardness, and wear resistance offers practical guidance for material selection and process optimization. Steel mills seeking to extend roll life and reduce maintenance costs should consider this research as a foundation for developing their own overlay welding programs, with attention to material selection, process parameter control, and post-weld heat treatment optimization.