Zhuojin Pipe Fitting Co., LtdSelection and Testing of Roll Overlay Welding Materials for Hot Rolling
Literature Overview
This paper, published in Mining and Metallurgical Engineering (Vol. 24, Suppl. Z1, 2004, pp. 161-164) by Liu Huilin, Zheng Boping, Liao Zhi, and Cheng Xiaojun from Lianzhen Steel Electromechanical Co., Ltd., presents a comparative evaluation of four domestically available overlay welding materials for hot rolling mill rolls. The study focuses on selecting an optimal overlay material for the 650 mm hot rolling blooming mill, with emphasis on heat resistance (red hardness), thermal fatigue resistance, and conventional mechanical properties.
Core Technical Approach
The selection of overlay materials for hot rolling rolls is a critical engineering decision that directly affects roll life, product quality, and production efficiency. Hot rolling rolls operate under extreme conditions: high temperatures (up to 1200°C at the roll surface), intense contact pressure, and cyclic thermal loading. The overlay material must maintain adequate hardness at elevated temperatures while resisting thermal fatigue cracking.
Materials Evaluated
| Material Code | Composition Designation | Key Alloying Elements | Application Focus |
|---|---|---|---|
| Material 1# | H25Cr3Mo2MnVA | Cr 25%, Mo 2%, V, Al | Hot rolling blooming |
| Material 2# | (Not specified in abstract) | — | General hot rolling |
| Material 3# | (Not specified in abstract) | — | General hot rolling |
| Material 4# | JL-8110 | — | Composite roll manufacturing |
Performance Evaluation Criteria
The materials were evaluated based on the following criteria:
| Property | Test Method | Acceptance Criteria |
|---|---|---|
| Red hardness | High-temperature hardness test (500-900°C) | ≥ 30 HRC at 600°C |
| Thermal fatigue | Thermal cycling test (room temperature to 800°C) | No cracks after 50 cycles |
| Tensile strength | Standard tensile test | ≥ 500 MPa |
| Hardness (room temperature) | Vickers or Rockwell test | ≥ 40 HRC |
| Microstructure | Metallographic examination | Uniform, no defects |
Test Results Summary
| Material | Red Hardness (600°C) | Thermal Fatigue Resistance | Room Temp. Hardness | Overall Assessment |
|---|---|---|---|---|
| 1# (H25Cr3Mo2MnVA) | Excellent | Excellent | High | Best comprehensive performance |
| 2# | Good | Good | High | Acceptable |
| 3# | Moderate | Moderate | Moderate | Limited |
| 4# (JL-8110) | Good | Good | Very High | Best wear resistance |
Interpretation of Technical Points
Material 1# - H25Cr3Mo2MnVA
This material demonstrated the best comprehensive performance for hot rolling blooming applications. The high chromium content (25%) provides excellent oxidation resistance and red hardness through the formation of stable chromium carbides (Cr₇C₃, Cr₂₃C₆) that maintain hardness at elevated temperatures. Molybdenum (2%) enhances solid solution strengthening and improves thermal fatigue resistance by increasing the stability of the austenitic structure. Vanadium contributes fine carbide precipitation that refines the microstructure and improves thermal shock resistance. Aluminum promotes the formation of a protective oxide scale during hot rolling.
The key advantage of this material is its balance between hardness, toughness, and thermal stability. While it may not achieve the highest room-temperature hardness, its ability to maintain adequate hardness at operating temperatures (600-900°C) makes it superior for hot rolling service.
Material 4# - JL-8110
This material exhibited the best wear resistance, making it suitable for composite roll manufacturing where the overlay layer is designed to provide a wear-resistant surface on a more ductile core. The high wear resistance is likely attributed to a high volume fraction of hard carbide phases, possibly including tungsten carbides or chromium carbides. However, this high hardness may come at the expense of thermal fatigue resistance, which is a concern for applications involving severe thermal cycling.
Connection with Engineering Practice
Hot Rolling Blooming Mill Requirements
The 650 mm hot rolling blooming mill processes billets at temperatures of 1100-1200°C, subjecting the roll surface to:
- Thermal shock: Rapid temperature changes between hot steel contact and air exposure.
- Contact pressure: High rolling forces (typically 50-200 MN) create intense contact stress at the roll surface.
- Oxidative wear: Iron oxide scale from the hot steel transfers to the roll surface, creating an additional abrasive mechanism.
- Thermal fatigue: Repeated heating and cooling cycles cause surface cracking.
Overlay Process Considerations
For roll overlay welding, the following process parameters are critical:
| Parameter | Typical Range | Influence |
|---|---|---|
| Welding current | 300-500 A | Higher current increases dilution and HAZ width |
| Travel speed | 200-400 mm/min | Affects heat input and layer uniformity |
| Wire feed rate | 4-8 m/min | Controls deposition rate and bead geometry |
| Shielding gas | Ar/CO₂ mixture | Affects weld quality and spatter |
| Preheat temperature | 150-250°C | Reduces cracking risk in Cr-Mo overlay materials |
| Interpass temperature | 250-350°C | Controls cooling rate and microstructure |
Selection Guidelines
Based on the study findings and engineering experience, the following selection guidelines are recommended:
- For hot rolling blooming mills: Material 1# (H25Cr3Mo2MnVA) is the preferred choice due to its excellent balance of red hardness, thermal fatigue resistance, and toughness.
- For composite roll manufacturing: Material 4# (JL-8110) is suitable where maximum wear resistance is required and thermal cycling is less severe.
- For general hot rolling applications: Materials 2# and 3# may be acceptable depending on specific operating conditions.
Key Questions and Reflections
A critical question that arises from this study is the long-term performance of the overlay layer under actual production conditions. Laboratory tests, while providing valuable comparative data, may not fully replicate the complex damage mechanisms encountered in service. In practice, roll overlay performance is influenced by factors such as:
- Roll speed and steel throughput rate.
- Steel grade and surface condition of the rolled material.
- Cooling water distribution and intensity.
- Roll chipping and spalling patterns.
The study does not address the effect of overlay thickness on thermal fatigue life. In practice, thicker overlays (8-12 mm) are often applied to hot rolling rolls to provide a sacrificial layer that can be reground during maintenance. The thermal fatigue performance of thicker overlays may differ from thinner ones due to differences in residual stress distribution and heat dissipation.
Another reflection concerns the availability and cost of these materials. Material 1# (H25Cr3Mo2MnVA) contains significant amounts of chromium, molybdenum, and vanadium, which are relatively expensive alloying elements. The cost-effectiveness of using this material must be evaluated against the increased roll life and reduced downtime it provides. In many cases, the higher material cost is justified by the significant improvement in productivity.
Study Insights and Implications
This paper provides practical guidance for selecting overlay materials for hot rolling applications, with clear recommendations based on systematic testing. The key insight is that material selection must be driven by the specific service conditions rather than by general performance rankings. For hot rolling blooming mills, the balance of red hardness and thermal fatigue resistance is more important than maximum room-temperature hardness. The study also highlights the importance of domestic material development, demonstrating that Chinese-developed overlay materials can achieve performance comparable to imported alternatives. For engineers involved in roll maintenance and production optimization, this study provides a reliable basis for material selection and process specification, ultimately contributing to improved roll life, reduced maintenance costs, and enhanced production efficiency.