Wear-Resistant Cladding Repair Process for Cold-Rolled Rolls

Literature Overview

The study note focuses on the weld-overlay repair technology applied to cold-rolled work rolls that have suffered severe wear during long-term service in steel mill rolling mills. Cold-rolled rolls are subjected to extreme contact pressure, sliding friction, and chemical attack from the metal being rolled, which leads to progressive surface degradation. When the roll diameter falls below the minimum service limit, traditional grinding and re-diametering can no longer restore geometry, and cladding repair becomes the economically viable alternative. The literature reviewed presents a systematic approach to selecting cladding materials, process parameters, and post-weld treatments specifically tailored for cold-rolled roll restoration.

Core Technical Content

Material Selection and Design Considerations

The selection of cladding material for cold-rolled rolls must balance hardness, toughness, and thermal stability. The most commonly employed materials include high-carbon chrome alloys such as Stellite 6 (Co-Cr-W), high-chromium white iron, and martensitic stainless steels with carbon content above 0.8 wt%. A typical design approach involves applying a graded layer structure, where the first layer (transition layer) is composed of a material with good metallurgical compatibility to the roll substrate, while the second and third layers provide the desired wear-resistant properties.

Process Parameters and Welding Sequence

The cladding repair of cold-rolled rolls is typically performed using submerged arc welding (SAW) or gas metal arc welding (GMAW) with a multi-pass sequence. Preheating is critical to prevent cold cracking in the high-carbon substrate. The recommended preheat temperature ranges from 250°C to 350°C, depending on the carbon equivalent of the base material. Interpass temperature must be maintained between 250°C and 300°C throughout the welding operation.

The welding sequence follows a spiral pattern along the roll circumference to ensure uniform heat input distribution. Each pass must be ground flush before the next layer is applied, and the grinding direction should alternate between axial and circumferential to prevent groove formation that could become stress concentrators.

Common Defects and Countermeasures

Based on the literature and practical experience, the following defects are most frequently encountered during cladding repair of cold-rolled rolls.

Engineering Practice Integration

In practice, the repair of a cold-rolled work roll typically requires the following procedural steps. First, the worn roll is removed from the mill and inspected using magnetic particle testing (MT) to identify any pre-existing surface cracks or subsurface defects. Any detected cracks must be ground out and re-inspected before cladding begins. The roll surface is then cleaned by grinding to expose sound metal, removing any decarburized layer or oxide scale.

A critical aspect of the repair process is the dimensional control. After cladding, the roll must be turned back to its original diameter with a tolerance of ±0.02 mm. This requires precise calculation of the cladding build-up height, typically 3-5 mm beyond the target diameter to allow for final machining. The hardness profile after heat treatment should be verified at multiple radial positions to confirm uniformity, with target hardness typically in the range of 55-62 HRC for the working layer.

The post-weld heat treatment is performed in a controlled atmosphere furnace to prevent oxidation. The temperature is held at 550-650°C for a duration of 2 hours per 25 mm of roll thickness, followed by furnace cooling. This tempering treatment relieves residual stresses and ensures the desired hardness level is achieved without inducing new residual stresses that could cause roll failure during service.

Key Questions and Reflections

One significant challenge identified in the literature is the trade-off between hardness and toughness in the cladding layer. While higher hardness improves wear resistance, it reduces the ability of the cladding to absorb impact loads and resist spalling. The literature suggests that a multi-layer approach with gradually increasing hardness from the substrate outward is the optimal solution. Another important consideration is the effect of thermal cycling during rolling service on the long-term stability of the cladding layer. Repeated heating and cooling can cause thermal fatigue cracking, particularly at the fusion line between layers.

The economic analysis presented in the literature indicates that cladding repair can extend roll life by 2-3 times compared to the original condition, with a cost savings of approximately 60-70% compared to roll replacement. This makes the technology highly attractive for mills with frequent roll change schedules.

Study Insights and Implications

The study of cold-rolled roll cladding repair technology highlights several important engineering principles. First, material compatibility at the fusion line is paramount, and the use of transition layers with austenitic composition is essential for preventing cracking. Second, process control, particularly of preheat and interpass temperatures, has a direct impact on the metallurgical quality of the repair. Third, the spiral welding sequence and uniform pass thickness are critical for achieving dimensional accuracy and hardness uniformity. These insights are directly transferable to other cladding applications in the steel industry, such as hot-rolled roll repair and work roll restoration in continuous casting machines. The systematic approach of material selection, process parameter optimization, and quality verification provides a robust framework that can be adapted to different cladding scenarios with appropriate adjustments to material specifications and thermal cycle control.