Zhuojin Pipe Fitting Co., LtdResearch on Overlay Welding of Mechanical Rolling Rolls
Literature Overview
This paper by Ji Hairong, Li Xianghai, and Wang Huaiyu from the Technical Department of the Fifth Division of China Railway 13th Bureau, published in Western Exploration Engineering (2002, Vol. 14, No. 5, pp. 130–132), addresses the problem of small-scale damage and wear in mechanical rolling rolls during service and proposes a solution using specially designed alloy powder for overlay welding. The authors describe the development and application of a high-chromium steel alloy powder for overlay welding, which improves roll life and reduces losses, enabling rapid return to production.
Background and Problem Statement
Mechanical rolling rolls are critical components in various industrial processes, including mining, construction, and manufacturing. These rolls are subjected to severe abrasive and adhesive wear during operation, and even minor damage (such as surface spalling, chipping, or localized wear) can significantly affect roll performance and product quality. Traditional repair methods (such as grinding or replacement) are often insufficient for addressing small-scale damage, and the cost of replacing entire rolls is prohibitive.
The authors identify the following key challenges in rolling roll repair:
- Rapid wear progression: Small-scale damage can rapidly progress to severe wear if not addressed promptly, leading to production downtime.
- Material compatibility: The repair material must be compatible with the base roll material to ensure adequate bonding and avoid cracking.
- Cost and time constraints: The repair process must be quick and economical to minimize production downtime and repair costs.
- Surface quality requirements: The repaired surface must meet the dimensional and surface finish requirements for the intended application.
Alloy Powder Development
The authors developed a special high-chromium steel alloy powder for overlay welding of rolling rolls. The key characteristics of the alloy powder are summarized in the following table:
| Parameter | Specification | Purpose |
|---|---|---|
| Chromium content | 20–30% | Provides wear resistance through chromium carbide formation |
| Carbon content | 2–4% | Promotes carbide formation and increases hardness |
| Molybdenum content | 2–5% | Improves hot hardness and wear resistance |
| Nickel content | 3–5% | Stabilizes austenite and improves toughness |
| Powder particle size | 75–150 μm | Ensures good flowability and melting characteristics |
| Target overlay hardness | 50–60 HRC | Provides high wear resistance |
| Overlay thickness | 3–5 mm | Provides sufficient wear allowance |
The high-chromium steel alloy powder is designed to form a hard carbide matrix (primarily Cr7C3 and Cr23C6) in a tough austenitic or martensitic binder phase. This composite microstructure provides a combination of high hardness (for wear resistance) and adequate toughness (to resist impact and spalling). The molybdenum addition improves the hot hardness of the overlay deposit, which is critical for applications where the rolls are exposed to elevated temperatures. The nickel addition stabilizes austenite in the microstructure, improving toughness and reducing the risk of cracking.
Overlay Welding Process
The overlay welding process used by the authors involves the following steps:
- Surface preparation: The damaged area of the roll is ground to remove loose material and expose fresh metal. The surface is cleaned to remove oil, grease, and contaminants.
- Preheating: The roll is preheated to 200–300°C to reduce the cooling rate and prevent cracking.
- Overlay welding: The alloy powder is applied to the surface using a powder-fed welding process (such as GTAW with powder feeding or plasma arc welding with powder injection). The welding parameters are optimized to ensure complete fusion and minimize dilution.
- Post-weld heat treatment: The overlay deposit is heat treated to relieve residual stresses and achieve the target hardness. The heat treatment parameters (temperature, time, cooling rate) are optimized for the specific alloy powder composition.
- Machining and finishing: The overlay surface is machined to the required dimensions and surface finish.
The following table summarizes the welding parameters used in the process:
| Parameter | Value |
|---|---|
| Welding process | GTAW with powder feeding |
| Shielding gas | Argon (99.99% purity) |
| Current | 150–250 A |
| Voltage | 18–25 V |
| Travel speed | 100–200 mm/min |
| Powder feed rate | 50–100 g/min |
| Preheat temperature | 200–300°C |
| Interpass temperature | ≤ 250°C |
Performance Evaluation
The authors report that the overlay-welded rolls have demonstrated excellent performance in service. The key performance indicators are summarized in the following table:
| Performance Indicator | Before Overlay | After Overlay | Improvement |
|---|---|---|---|
| Surface hardness | 25–30 HRC | 50–60 HRC | 2–2.4x |
| Wear life | 500–1000 hours | 2000–4000 hours | 2–4x |
| Repair time | 8–16 hours | 2–4 hours | 2–4x faster |
| Repair cost | High (full replacement) | Low (overlay only) | 50–70% reduction |
The significant improvement in wear life and the reduction in repair time and cost demonstrate the economic viability of the overlay welding approach. The authors also report that the overlay-welded rolls have been successfully used in various applications, including mining, construction, and manufacturing, with consistent performance and reliability.
Quality Control and Inspection
The quality of the overlay weld deposit is critical to the performance and reliability of the repaired roll. The authors emphasize the importance of comprehensive quality control, including:
- Visual inspection: The overlay surface should be free of cracks, porosity, undercut, and excessive reinforcement.
- Magnetic particle testing (MT): The overlay weld deposit should be inspected using MT to detect surface and near-surface cracks.
- Hardness testing: The hardness of the overlay deposit should be verified at multiple locations across the surface.
- Dimensional inspection: The diameter and surface finish of the repaired roll should be verified to ensure that it meets the requirements for the intended application.
Key Questions and Reflections
The paper raises several important questions for further investigation:
- How does the alloy powder composition affect the dilution ratio and the final properties of the overlay deposit?
- Can the overlay welding process be automated for high-volume repair applications?
- What is the effect of thermal cycling on the long-term performance of the overlay deposit?
- How does the overlay layer affect the rolling force and product quality?
Study Insights and Implications
This paper provides a practical and economical solution to the problem of small-scale damage and wear in mechanical rolling rolls. The authors' development of a special high-chromium steel alloy powder and their systematic approach to process optimization and quality control are exemplary. The significant improvements in wear life, repair time, and repair cost demonstrate the economic viability of the overlay welding approach. For engineers in the mining, construction, and manufacturing industries, this paper serves as a valuable reference for developing overlay welding solutions to extend the service life of critical rolling components.