CLADDING TECHNOLOGY SHANXI CO., LTDSurface Overlay Welding Technology Application on Pinch Rolls
Literature Overview
This 2006 publication by Zhang Dongming and Wang Jiebing from Handan Iron and Steel Group and the 718th Research Institute of China Shipbuilding Industry Corporation, published in Welding, addresses the application of surface overlay welding technology on pinch rolls used in continuous casting and hot rolling operations. Pinch rolls are critical components in the metallurgical industry that grip and control the movement of steel slabs and billets during production. Their surface condition directly affects product quality, production efficiency, and maintenance costs.
The paper represents a significant contribution to the practical application of overlay welding in heavy industry, combining metallurgical expertise with welding engineering knowledge to develop effective solutions for roll surface hardening and repair.
Technical Background and Requirements
Pinch rolls in continuous casting machines and hot strip mills operate under severe conditions characterized by high contact pressures, sliding friction, thermal cycling, and potential chemical attack from scale and lubricants. The service life of pinch rolls is primarily limited by surface wear, which manifests as material loss from the roll surface, increased roughness, and eventual loss of dimensional accuracy.
The base material of pinch rolls is typically a medium-carbon steel or low-alloy steel such as 45# steel, 40Cr, or 35CrMo. These materials provide adequate structural strength but insufficient surface hardness and wear resistance for prolonged service. The surface hardness of as-rolled or machined pinch rolls is typically 200 to 250 HB, which is inadequate for the demanding service conditions.
| Parameter | Base Material | Overlay Requirement |
|---|---|---|
| Surface hardness | 200-250 HB | 45-55 HRC |
| Wear resistance | Low | High |
| Toughness | Adequate | Must be maintained |
| Thermal stability | Limited | Must withstand 600-800 deg C |
| Service life | 3-6 months | Target: 12-24 months |
Overlay Welding Process Design
The overlay welding process described in the paper involves the deposition of a hardfacing alloy layer on the pinch roll surface to achieve the required hardness and wear resistance. The selection of overlay material is critical and depends on the specific service conditions.
For pinch rolls in continuous casting applications, where the primary wear mechanism is abrasive wear from scale and oxide particles, a high-carbon martensitic alloy such as a chrome-carbon type hardfacing is typically selected. These alloys can achieve hardness values of 55 to 60 HRC in the as-welded condition.
For pinch rolls in hot rolling applications, where thermal fatigue and adhesive wear are also significant, a multi-layer approach may be employed. The first layer serves as a transition layer to reduce dilution and improve bonding, while subsequent layers provide the required surface hardness.
The welding process parameters are carefully controlled to achieve the desired metallurgical properties:
| Parameter | Value | Rationale |
|---|---|---|
| Electrode type | Low-hydrogen, high-alloy | Reduce porosity, improve toughness |
| Current | 150-250 A | Adequate penetration without excessive dilution |
| Arc voltage | 22-28 V | Stable arc, good deposition |
| Travel speed | 50-80 mm/min | Control heat input |
| Preheat | 150-250 deg C | Reduce thermal gradient |
| Interpass temperature | 250-350 deg C | Control cooling rate |
| Number of layers | 2-4 | Achieve required thickness and hardness |
Defect Prevention and Quality Control
The primary defects encountered in overlay welding of pinch rolls include:
| Defect | Cause | Prevention |
|---|---|---|
| Cracking | High carbon equivalent, hydrogen | Low-hydrogen electrodes, proper preheat, post-weld heat treatment |
| Porosity | Flux contamination, moisture | Flux baking, electrode storage control |
| Lack of fusion | Surface contamination, low heat input | Thorough cleaning, optimize welding parameters |
| Excessive dilution | Too few layers, large electrode | Increase layers, reduce electrode diameter |
| Roll distortion | Uneven heat input | Symmetric welding sequence, post-weld machining |
The authors emphasize the importance of post-weld heat treatment to reduce residual stresses and improve the toughness of the overlay layer. A tempering treatment at 550 to 600 degrees Celsius for 2 to 4 hours can reduce hardness by 5 to 10 HRC while significantly improving toughness and reducing the risk of cracking during service.
Engineering Practice and Performance Results
The paper documents practical results from the application of overlay welding on pinch rolls at Handan Iron and Steel Group. The key performance improvements include:
- Service life extension from 3 to 6 months to 12 to 24 months, representing a 2 to 4 times improvement.
- Reduction in maintenance frequency and associated downtime costs.
- Improved surface finish of rolled products due to reduced roll surface roughness.
- Cost savings from reduced roll replacement frequency.
The successful implementation required careful attention to several practical aspects. First, the roll surface must be thoroughly prepared by machining to remove any damaged material and achieve a smooth, clean surface. Second, the welding sequence must be planned to distribute heat input evenly around the roll circumference, preventing localized overheating and distortion. Third, post-weld machining is required to restore the roll to its precise dimensional specifications.
Study Insights
This work demonstrates the significant economic and operational benefits that can be achieved through the proper application of overlay welding technology. The extension of pinch roll service life from months to years represents a substantial improvement in production efficiency and cost reduction.
A key insight from this paper is the importance of tailoring the overlay welding process to the specific service conditions. Different wear mechanisms require different overlay materials and process parameters. A one-size-fits-all approach is not appropriate, and careful analysis of the service environment is essential for optimal results.
The paper also highlights the importance of quality control and non-destructive testing. Regular inspection of overlay layers for defects such as cracking, porosity, and lack of fusion is essential to ensure reliable performance. Engineers should establish comprehensive inspection procedures that include visual examination, penetrant testing, and hardness verification.
Summary
The 2006 paper by Zhang Dongming and Wang Jiebing provides valuable engineering guidance for the application of surface overlay welding on pinch rolls in metallurgical applications. The documented process parameters, defect prevention strategies, and performance results offer a practical roadmap for engineers seeking to extend the service life of critical rolling mill components. The systematic approach to material selection, process design, and quality control described in this paper represents best practices that should be adopted in similar applications across the metallurgical industry.