CLADDING TECHNOLOGY SHANXI CO., LTDOptimization Analysis of Surfacing Process for Slab Mill Rolls
Literature Overview
This 2023 publication by Cao Limei, An Lirong, and Li Qiuhuo, affiliated with the School of Mechanical and Power Engineering at Yingkou Institute of Technology and Shigang Jingcheng Equipment Technology Co., Ltd., addresses the optimization of surfacing (cladding) processes for slab mill rolls. The collaboration between academia and industry represents a productive model for translating research into practical metallurgical improvements. Slab mill rolls operate under extreme conditions of thermal cycling, mechanical impact, and abrasive wear, making the selection and optimization of surfacing processes critical to operational reliability.
Technical Background
Slab mill rolls in steel mills experience severe service conditions including:
- Contact pressures exceeding 3000 MPa during rolling
- Surface temperatures reaching 800–1200°C from hot slab contact
- Abrasive wear from scale and oxide inclusion removal
- Thermal fatigue from repeated heating and cooling cycles
- Impact loading from slab feed irregularities
The base roll material is typically high-chromium cast iron (HCRI) or alloy steel, while the surfacing layer must provide enhanced wear resistance, thermal stability, and sufficient toughness to resist spalling.
Process Optimization Analysis
Surfacing Process Selection
| Process | Deposition Rate | Dilution | Heat Input | Applicability |
|---|---|---|---|---|
| Submerged Arc Welding (SAW) | High (5–10 kg/h) | Moderate (15–25%) | High | Thick overlay layers (>5 mm) |
| Electroslag Welding (ESW) | Very High (10–20 kg/h) | Low (5–15%) | Very High | Heavy-duty cladding |
| Flux-Cored Arc Welding (FCAW) | Moderate (3–6 kg/h) | Moderate (20–30%) | Moderate | Medium layers (3–8 mm) |
| Gas Metal Arc Welding (GMAW) | Moderate (2–5 kg/h) | High (25–35%) | Low-Moderate | Thin layers (<3 mm), complex geometries |
| Powder Flame Spraying | Low (1–3 kg/h) | Minimal | Low | Surface hardening only |
Optimized Process Parameters
The optimization study likely evaluates the following parameter combinations for achieving optimal metallurgical properties in the surfacing layer:
- Wire composition: High-carbon high-chromium (Cr8Mo2V, Cr15Mo, or similar) with controlled carbon content of 1.5–2.5% for martensitic structure
- Current density: 150–250 A/mm² for controlled penetration and dilution
- Travel speed: 80–200 mm/min depending on roll diameter and required layer thickness
- Wire angle: 10–15° from vertical for optimal arc stability and bead profile
- Shielding gas composition (for GMAW): 80% Ar + 20% CO₂ or 95% Ar + 5% CO₂ for stable arc and controlled oxidation
- Preheat temperature: 150–250°C to minimize thermal gradients in the heavy roll body
Microstructural Engineering
The optimization analysis should address the following microstructural considerations:
- Dilution control: The carbon and chromium content in the weld metal must be maintained above critical thresholds to ensure martensitic structure with adequate hardness (HRC 50–60). Excessive dilution from the base roll material reduces hardness below acceptable wear resistance levels.
- Microcrack resistance: High-carbon martensitic surfacing layers are inherently susceptible to microcracking. The optimization should consider:
- Post-weld heat treatment at 500–580°C to temper martensite and relieve residual stresses
- Multi-layer welding with controlled interpass temperature to allow stress relaxation
- Addition of microalloying elements (Ti, Nb, V) to pin crack propagation
- Bond strength: The interface between surfacing layer and base roll must withstand service loads without delamination. Critical factors include:
- Root pass full penetration into base material
- Absence of oxide inclusions at the interface
- Compatibility of thermal expansion coefficients between layers
Quality Control and Defect Prevention
| Defect Type | Root Cause | Prevention Strategy |
|---|---|---|
| Surface microcracks | High carbon, insufficient tempering | PWHT at 520±20°C for 2h; control C content <2.0% |
| Spalling | Excessive residual stress, poor toughness | Multi-pass with stress-relieving interpass holds |
| Incomplete bonding | Surface contamination, insufficient root heat | Acid pickling + grinding before surfacing; verify root pass |
| Excessive porosity | Flux moisture, contamination | Flux drying at 300°C for 2h; clean wire and base |
| Hardness non-uniformity | Inconsistent dilution, cooling rate variation | Parameter stability monitoring; hardness mapping |
Engineering Practice Integration
The practical value of this optimization study extends to the entire roll refurbishment lifecycle. In modern steel mills, roll surfacing is performed during planned maintenance intervals, typically every 50,000–100,000 tons of rolled product. The optimization parameters developed should be documented in a weld procedure specification (WPS) conforming to NB/T 47014 or ASME IX, with corresponding welder qualification per the same standards.
The economic impact of optimized surfacing parameters is substantial. A single slab mill roll weighing 5–15 tons can cost USD 80,000–200,000 to manufacture. Extending roll life through optimized surfacing from 50,000 to 80,000 tons of throughput represents a significant reduction in cost per ton of steel produced.
Study Insights
The 2023 publication timing reflects current industry priorities in reducing maintenance costs and improving operational efficiency. The systematic optimization approach described is consistent with modern continuous improvement methodologies and provides a framework that can be adapted to other heavy-duty surfacing applications including ingot mold rolls, finishing mill rolls, and wear plate fabrication.