CLADDING TECHNOLOGY SHANXI CO., LTDHardfacing Technology for 1450 Hot Strip Mill Rolls
Literature Overview and Background
The 1450 mm hot strip mill is a workhorse of modern steel production, with work rolls and backup rolls experiencing severe wear and damage during operation. The work rolls, in particular, are subjected to temperatures exceeding 900 °C, high contact stresses, and continuous thermal cycling. This literature presents a comprehensive hardfacing technology for 1450 mill rolls, covering material selection, process development, quality assurance, and field performance data. The study is based on extensive industrial trials conducted at multiple steel mills.
Core Technical Content
The hardfacing technology is differentiated by roll type. Work rolls receive a high-temperature wear-resistant overlay designed to resist adhesive wear and scale adherence, while backup rolls receive a combination of a tough transition layer and a hardfacing layer to resist surface indentation and fatigue cracking.
| Roll Type | Base Material | Hardfacing Alloy | Target Hardness (HRC) | Overlay Thickness |
|---|---|---|---|---|
| Work roll | 38CrMoAlA or similar | High-Cr high-V martensitic iron | 50–58 | 4–8 mm |
| Backup roll | 42CrMo or similar | Medium-Cr high-toughness alloy | 40–48 | 3–5 mm |
| Transition layer | Same as base | Ni-base or Ni-Cr alloy | 35–42 | 1–2 mm |
The welding process for work rolls employs submerged arc welding (SAW) for the transition layer and manual metal arc welding (MMAW) with specialized hardfacing electrodes for the overlay. The SAW parameters are: current 550–750 A, arc voltage 32–38 V, flux coverage 5–8 mm, and travel speed 250–400 mm/min. The MMAW parameters are: current 180–240 A, arc voltage 24–28 V, and travel speed 150–250 mm/min.
Process Development and Quality Assurance
The process development follows a systematic approach:
- Base metal characterization and weldability assessment
- Consumable selection and qualification per NB/T 47014 or equivalent
- Weld procedure specification (WPS) development and qualification
- Pilot trials on representative roll sections
- Field trials and performance monitoring
- Process optimization based on field feedback
Quality assurance includes ultrasonic testing (UT) of the base metal welds, magnetic particle testing (MT) of surface defects, hardness profile measurement across the overlay thickness, and metallographic examination of the microstructure. The acceptance criteria require no cracks, no delamination, and hardness variation within ±5 HRC across the overlay surface.
| Inspection Method | Coverage | Acceptance Criterion |
|---|---|---|
| UT (A-scan) | 100% of base metal welds | No indications above acceptance threshold |
| MT | 100% of surface | No linear indications > 2 mm |
| Hardness test | Grid pattern (50 mm spacing) | Within specified range ±5 HRC |
| Metallography | 3 samples per roll | No cracks; sound microstructure |
| Dimensional check | Full length profile | Within tolerance ±0.5 mm |
Field Performance and Economic Analysis
Field trials demonstrated that hardfaced work rolls achieved a service life of 8000–12000 tons of strip production, compared to 5000–7000 tons for standard cast rolls. Backup rolls showed a service life improvement of 40–60%. The economic analysis indicates that the hardfacing cost per ton of production is approximately 60% lower than the cost of replacing with new cast rolls.
However, the literature also identifies challenges: work roll overlay spalling can occur when the thermal cycling rate exceeds the design limit, and backup roll overlay delamination can occur at the roll neck region due to excessive bending stress. The recommended countermeasures include optimizing the transition layer composition for improved toughness and limiting the overlay thickness near the roll neck.
Study Insights and Implications
This literature provides a well-documented, field-validated hardfacing technology for 1450 mill rolls. The key insight is that the transition layer design is critical — it must bridge the mechanical property gap between the base metal and the hardfacing alloy while maintaining sufficient toughness to resist fatigue cracking. For engineers developing hardfacing procedures for similar mill rolls, the literature emphasizes the importance of matching the overlay alloy to the specific wear mechanism and operating conditions of each roll type. The systematic quality assurance approach, combining multiple NDT methods, provides a reliable framework for ensuring overlay integrity before returning rolls to service.