Hot Rolling Support Roll Cladding Technology Study Note

Literature Overview and Technical Background

Hot rolling support rolls (backup rolls) are critical components in steel strip and plate mills, subjected to extreme combinations of contact pressure, thermal cycling, and mechanical loading. The outer surface of support rolls must possess high hardness (typically HV 400–500), excellent wear resistance, and adequate impact toughness to resist spalling and fatigue failure. This study investigates advanced cladding (weld overlay) technologies for manufacturing and repairing hot rolling support rolls, focusing on process optimization, microstructure control, and service performance evaluation.

Core Technical Content

Cladding Process Selection for Support Rolls

The study evaluates multiple cladding processes for support roll manufacturing:

Process	Typical Application	Hardness (HV)	Layer Thickness (mm)	Throughput
ESW (Electroslag Welding)	Thick overlay on large rolls	380–480	10–40	High
SAW (Submerged Arc Welding)	Medium-thickness overlay	400–520	5–20	Medium-High
PTA (Plasma Transferred Arc)	Precision overlay	450–580	2–8	Low-Medium
Laser Cladding	Thin high-quality overlay	500–650	1–5	Low
GMAW (MIG)	Field repair	350–450	3–10	Variable

Microstructure and Property Optimization

The cladding layer microstructure is primarily bainitic or martensitic, depending on the filler composition and cooling rate. The study identifies the following optimization strategies:

Filler material design: High-carbon low-alloy compositions (C: 0.8–1.2%, Cr: 8–12%, Mo: 1–3%) produce hard bainitic microstructures with excellent wear resistance. For applications requiring higher toughness, reduced carbon content (C: 0.4–0.6%) with retained austenite stabilization (Ni: 3–5%) is recommended.
Heat treatment integration: Post-weld tempering at 500–550°C for 2–4 hours transforms the as-welded martensite to tempered martensite with improved toughness while maintaining hardness above HV 400.
Layer-by-layer composition control: A graded approach using a transition layer (medium carbon, 0.5% C) between the base roll material and the high-carbon overlay reduces residual stress and improves interfacial bonding.

Critical Quality Considerations

Roll surface quality: After cladding, the roll surface must be ground to Ra ≤ 0.4 μm for strip mills. The overlay layer must be free from porosity, inclusions, and surface defects that could transfer to the rolled product.
Thermal stability: The overlay must maintain hardness under repeated thermal cycling (ambient to 800°C). The study demonstrates that Mo and V additions improve thermal stability by stabilizing carbides.
Bond strength: The interface between the overlay and substrate must withstand contact pressures exceeding 3 GPa. Shear bond strength testing per ASTM A263/A264 is essential.

Engineering Practice and Defect Analysis

Based on extensive experience with support roll cladding, the following defect modes are commonly encountered:

Defect Type	Root Cause	Detection Method	Countermeasure
Cracking at interface	Excessive heat input, poor preheat	RT, MT	Reduce heat input, increase preheat to 200–300°C
Roll spalling in service	Insufficient core toughness, thermal fatigue	Visual, UT	Improve base material toughness, optimize tempering
Surface porosity	Flux contamination, inadequate gas shielding	PT, RT	Improve flux quality, enhance shielding gas flow
Hardness variation	Inconsistent cooling rate, composition variation	Hardness testing	Control interpass temperature, verify filler composition
Delamination	Poor wetting, residual stress	UT, ring test	Optimize preheat, apply graded layers

FMEA Analysis for Critical Operations

Applying FMEA methodology to the cladding process:

Preheat operation: Severity 8, Occurrence 4, Detection 5 → RPN 160. Action: Implement automated preheat monitoring with temperature logging.
Welding parameter control: Severity 9, Occurrence 3, Detection 4 → RPN 108. Action: Use CNC-controlled welding with real-time parameter monitoring.
Post-weld inspection: Severity 7, Occurrence 5, Detection 3 → RPN 105. Action: Combine UT and MT inspection with 100% coverage.

Study Insights and Implications

The most significant finding from this study is the demonstration that ESW cladding can produce overlay layers with mechanical properties comparable to cast-iron or forged roll materials, while offering superior flexibility in component design and significantly lower material costs. The study shows that with proper process control, ESW-cladded support rolls achieve service lives of 6–10 million tons of steel processed, comparable to conventionally manufactured rolls.

A particularly valuable insight is the relationship between interpass temperature control and final overlay properties. Maintaining interpass temperature between 150–250°C during multi-pass ESW deposition produces a more uniform microstructure with reduced hardness variation across the layer thickness. This is often overlooked in practice but is critical for consistent roll performance throughout their service life. The study also emphasizes that the transition from manufacturing to repair applications requires additional consideration of the existing surface condition, including work-hardened zones and residual stress states from previous grinding operations.