CLADDING TECHNOLOGY SHANXI CO., LTDResearch on Cladding of Rolling Mill Rolls
Literature Overview
This paper, published in Western Exploration Engineering in 2002 by Ji Hairong, Li Xianghai, and Wang Huaiyu from the Technical Section of China Railway 13th Bureau Fifth Division, presents a focused investigation into the weld overlay cladding technology applied to rolling mill rolls. Rolling mill rolls are subjected to extreme combined loading conditions including cyclic contact pressure, high-temperature friction, and abrasive wear from the workpiece. The study addresses the selection of cladding materials, process parameter optimization, and quality control measures specific to roll application.
Technical Background and Requirements
Rolling mill rolls operate under conditions that are uniquely demanding for surface engineering:
| Parameter | Typical Range | Critical Requirement |
|---|---|---|
| Contact pressure | 100-300 MPa | Subsurface fatigue resistance |
| Surface temperature | 200-800°C | Thermal stability of overlay |
| Sliding velocity | 0.5-5 m/s | Coefficient of friction control |
| Cycle frequency | 10-50 cycles/min | Fatigue life |
| Required overlay thickness | 2-8 mm | Sufficient wear reserve |
| Surface roughness (Ra) | 0.2-0.8 μm | Dimensional accuracy |
The primary failure modes addressed include surface cracking, spalling, delamination of the overlay layer, and excessive wear leading to dimensional deviation. Each failure mode requires a distinct mitigation strategy in the cladding design.
Cladding Process Selection and Optimization
The authors evaluated multiple cladding processes for roll application and concluded that submerged arc welding (SAW) with flux-cored wire offered the best combination of deposition rate, layer quality, and cost-effectiveness for large-diameter rolls. The process parameters were optimized through systematic experimentation.
Process Parameters for SAW Cladding of Rolls
- Shielding flux: HJ431 or modified ceramic-type flux
- Filler wire: H08CrMoSiA or equivalent chromium-molybdenum alloy wire
- Current: 500-700 A (DC, electrode negative)
- Voltage: 32-38 V
- Travel speed: 400-600 mm/min
- Wire feed rate: 4-6 m/min
- Preheating temperature: 200-300°C
- Inter-pass temperature: 250-350°C
- Number of layers: 2-4 depending on required thickness
The authors emphasized the importance of the welding sequence on cylindrical rolls. A spiral welding pattern was recommended over circumferential passes to minimize residual stress concentration at the overlay-to-base interface. The spiral pitch was optimized to be approximately 1.5 times the wire diameter, ensuring adequate overlap without excessive local heat input.
Microstructural Considerations
Metallographic analysis of the cladding interface revealed a critical diffusion zone 50-150 micrometers wide where carbon and alloy elements had migrated from the base roll steel into the overlay. This diffusion zone exhibited reduced hardness (dropping to 28-32 HRC from the overlay hardness of 45-50 HRC) and represented the weakest link in the cladding system. The authors proposed a countermeasure involving the application of a transition layer with composition intermediate between the base steel and the final overlay, effectively grading the hardness profile and eliminating the sharp hardness discontinuity at the interface.
Quality Control and Defect Prevention
The study incorporated a comprehensive quality control framework addressing each stage of the cladding operation:
| Stage | Inspection Method | Acceptance Criteria |
|---|---|---|
| Base preparation | Visual + MT | No surface defects > 0.5 mm |
| Post-cladding | UT (contact method) | No lack of fusion or cracks |
| Surface finish | Profile measurement | Deviation < 0.05 mm |
| Hardness | Rockwell C | Uniform within ±3 HRC |
| Bond strength | Peel test (if applicable) | > 400 MPa |
| Post-heat treatment | Dimensional check | Distortion < 0.1 mm |
A particularly important finding concerned the effect of post-weld heat treatment on the overlay properties. Tempering at 600°C for 2 hours reduced the overlay hardness by approximately 5 HRC but significantly improved toughness and eliminated residual stresses that could lead to delayed cracking during service. This tempering was identified as essential for hot rolling applications where the roll surface temperature exceeded 400°C.
Study Insights and Reflections
This paper provides valuable practical guidance on roll cladding that remains highly relevant to current industrial practice. The authors' systematic approach to process parameter optimization, combined with their attention to the often-neglected interface diffusion zone, demonstrates engineering maturity. The recommendation for spiral welding patterns on cylindrical components is particularly noteworthy, as it addresses a fundamental metallurgical concern (residual stress directionality) that many practitioners overlook.
The transition layer concept, while not novel in principle, is presented here with specific compositional guidance that makes it directly implementable. The emphasis on post-weld tempering as a non-negotiable step for hot-service rolls reflects a deep understanding of the metallurgical consequences of weld overlay on heavily alloyed components.