Overlay Welding Repair of Rolling Mill Guide Plate Heads

Literature Overview

This 1994 paper by Wan Weiguo from the Steel Research Institute of Maanshan Iron and Steel Company, published in "Welding" (Issue 4, pp. 22–23), addresses the overlay welding repair of guide plate heads used in wire rod rolling mills. The paper provides a detailed analysis of the wear problem and the development of an effective overlay welding solution that significantly extends component life.

Service Background and Problem Statement

The case study involves the second wire rod rolling mill line at Maanshan Steel's Third Rolling Mill, which produces 200,000 tons of wire rod annually. The imported guide plates (K15 type) experience significant consumption, with the guide plate head being the primary wear component.

Guide Plate Construction

The K15 guide plate consists of two parts:

• Guide plate body — The structural component that holds the guide plate head
• Guide plate head — The wear-prone component that directly contacts the wire rod

Material Comparison and Performance

The original specification used 45 steel guide plate heads, which provided adequate toughness but insufficient wear resistance. The average service life was only half a shift (approximately 4 hours), with the failure mode being the formation of deep wear grooves on the guiding surface.

Overlay Welding Solution Development

The paper describes the development of an overlay welding process to improve the wear resistance of the 45 steel guide plate heads while maintaining their adequate toughness.

Design Philosophy

The overlay welding approach addresses the fundamental trade-off between hardness and toughness:

• The 45 steel base provides excellent fracture toughness and resistance to impact loading
• The overlay layer provides high hardness and wear resistance for the contact surface
• The combination achieves superior performance to either material used alone

Process Development

The overlay welding process for guide plate head repair involves several critical steps:

1. Surface preparation

• Machining of the wear surface to remove damaged material
• Creation of a chamfered groove for mechanical interlock
• Thorough cleaning to ensure good adhesion
• Preheating to 200–300°C to reduce thermal cracking risk

1. Overlay welding parameters

• Welding process: SMAW (Shielded Metal Arc Welding)
• Electrode type: Hard facing electrode with appropriate hard phase composition
• Current: 120–180 A (depending on electrode diameter)
• Travel speed: 60–100 mm/min
• Number of layers: 1–2 layers
• Layer thickness: 3–5 mm per layer

1. Post-weld treatment

• Controlled cooling (air cooling or furnace cooling)
• Stress relief if required
• Precision grinding to final dimensions

Consumable Selection

The selection of the overlay welding consumable is critical to the success of this repair. The ideal consumable for this application should provide:

• Hardness of HV 600–900 in the as-deposited condition
• Adequate fracture toughness to resist impact from wire rod contact
• Good weldability with 45 steel substrate
• Acceptable porosity levels
• Reasonable cost

Common consumable types suitable for this application include:

• Type I hard facing electrodes — Iron-based with Cr-C-Cr₂C₃ hard phases
• Type II hard facing electrodes — Nickel-based with Co-Cr-C hard phases
• Type III hard facing electrodes — Nickel-copper alloys with hard particles

Performance Results

The overlay welded guide plate heads demonstrated significant improvement in service life compared to the original 45 steel specification:

The overlay welded solution achieved service life comparable to or exceeding the expensive high chromium-nickel alloy while maintaining better toughness characteristics and at significantly lower cost.

Engineering Practice Considerations

Several practical considerations emerged from this case study:

1. Wear pattern analysis — Understanding the specific wear pattern (groove formation) helped in designing the overlay geometry to provide maximum material in the critical wear zone.
2. Production impact — The extended service life directly reduced production interruptions due to guide plate head replacement, improving overall mill availability.
3. Cost-benefit analysis — The overlay welding process cost was a fraction of the cost of high alloy replacement parts, while providing comparable or superior performance.
4. Standardization — The successful process was documented and standardized for consistent application across all guide plate head repairs in the mill.
5. Operator training — Proper execution of the overlay welding process requires skilled welders familiar with hard facing techniques and the specific requirements of this application.

Key Technical Insights

This paper demonstrates the effectiveness of overlay welding as a solution to the hardness-toughness trade-off problem in wear-prone components. The guide plate head application is particularly instructive because it illustrates how a simple, cost-effective approach (overlay welding on a conventional steel base) can outperform expensive specialized alloys when properly executed.

The technical success of this approach depends on several factors:

• Proper consumable selection matched to the specific wear mechanism
• Careful control of welding parameters to minimize dilution while maintaining good metallurgical bond
• Adequate surface preparation to ensure overlay adhesion
• Post-weld machining to achieve required geometric accuracy

The economic benefits are substantial when considering the annual production volume of 200,000 tons of wire rod. Each guide plate head that lasts 8–12 times longer than the original specification translates to significant savings in both material costs and production downtime.