Application of Overlay Welding Technology on Hot Rolling Guide Rolls

Literature Overview

This paper by Ge Baowen, published in Baosteel Technology (2004, Issue 1, pp. 14-16), reports on the successful application of Cr-Mo series welding materials for overlay welding on hot rolling guide rolls at Baosteel. The author is affiliated with Baosteel Engineering Technology Co., Ltd. The study addresses a significant operational challenge in hot strip mills: the limited service life of guide rolls, which are subjected to extreme conditions including high temperatures, mechanical contact with hot steel strips, and corrosive scale attack.

Background and Service Conditions

Hot rolling guide rolls play a critical role in the hot strip mill by guiding the steel strip between rolling stands and ensuring proper alignment. Their service conditions are exceptionally demanding:

• Temperature exposure — Contact with steel strips at temperatures ranging from 800°C to 1100°C
• Mechanical loading — Contact pressure from the steel strip and occasional strip misalignment events
• Scale adhesion — Iron oxide scale from the hot strip adheres to the roll surface, creating abrasive particles
• Thermal cycling — Repeated heating and cooling during rolling operations
• Cooling water impingement — Direct water spray for roll cooling creates thermal shock conditions

The base material of guide rolls is typically a medium carbon steel or low-alloy steel, which lacks the necessary surface hardness and wear resistance for prolonged service under these conditions. Overlay welding provides an effective means of enhancing surface properties without replacing the entire roll.

Welding Material Selection

The selection of Cr-Mo series welding materials is based on several metallurgical considerations:

Material Properties

Metallurgical Rationale

Chromium in the overlay material serves multiple functions:

• Forms hard chromium carbides (Cr7C3, Cr23C6) that provide wear resistance
• Improves oxidation resistance at elevated temperatures
• Enhances scale spalling resistance, reducing abrasive wear from adhered scale

Molybdenum contributes:

• Solid solution strengthening at elevated temperatures
• Improved thermal stability of the microstructure
• Enhanced resistance to thermal fatigue cracking

Overlay Process Considerations

Pre-Welding Preparation

• Surface cleaning to remove scale, rust, and contaminants
• Edge preparation to ensure good fusion between overlay and base material
• Pre-heating to reduce thermal stress and minimize cracking risk (typically 150–250°C for medium carbon steels)

Welding Parameters

The specific welding process is not detailed in the abstract, but for guide roll overlay applications, the following processes are commonly employed:

• Submerged arc welding (SAW) — High deposition rate, good for thick overlays
• Flux-cored arc welding (FCAW) — Good versatility, moderate deposition rate
• Metal arc air gouging for removal — For multi-pass overlay buildup

Post-Weld Treatment

• Controlled cooling to minimize residual stress
• Possible stress relief heat treatment depending on overlay thickness and base material
• Surface finishing to achieve required surface roughness for strip guidance

Performance Results

The paper reports that the Cr-Mo overlay material was successfully applied to Baosteel hot rolling guide rolls and demonstrated:

• Effective improvement in roll quality — Surface properties met operational requirements
• Extended service life — Significant increase in roll life compared to uncladded or conventionally clad rolls
• Production application success — The material was validated in actual production conditions

Engineering Practice Integration

For hot rolling mill operators and maintenance engineers, this study provides valuable guidance:

1. Material selection criteria — The Cr-Mo system offers an optimal balance of hardness, wear resistance, thermal stability, and cost-effectiveness for guide roll applications.
2. Overlay thickness optimization — The overlay thickness must be sufficient to provide wear protection but not so thick as to cause excessive thermal mass or stress concentration at the interface.
3. Periodic inspection — Overlay layers degrade over time and require periodic inspection and re-cladding to maintain operational performance.
4. Welding procedure qualification — Proper welding procedure qualification (WPQ) is essential to ensure consistent overlay quality and avoid defects such as cracking, porosity, or poor fusion.

Defect Prevention and Quality Control

Study Insights and Reflections

This paper, while brief, captures an important aspect of industrial welding practice: the practical application of overlay technology to extend component life in demanding service conditions. The selection of Cr-Mo series materials reflects sound metallurgical reasoning—chromium for carbide formation and oxidation resistance, molybdenum for thermal stability and solid solution strengthening. The success of this application at Baosteel, one of China's largest steel producers, provides strong validation of the approach. For engineers working in rolling mill maintenance, this study underscores the importance of material selection matched to specific service conditions, and the value of overlay welding as a cost-effective alternative to complete component replacement. The relatively early publication date (2004) also suggests that this technology has been in industrial use for well over a decade, confirming its reliability and practical merit.