Surface Weld Overlay Fabrication of Side Press Modules Performance and Application

Literature Overview and Industrial Background

This study addresses the application of surface weld overlay technology to side press modules, which are critical components in rolling mill production lines where they are subjected to extreme mechanical loading, thermal cycling, and abrasive contact with hot metal surfaces. Side press modules typically experience combined wear mechanisms including adhesive wear from direct contact with heated steel slabs, erosive wear from scale and oxide debris, and thermal fatigue from repeated heating and cooling cycles during the rolling process. The literature examines the feasibility and effectiveness of applying hardfacing and wear-resistant overlay layers to extend the service life of these expensive components, which are often made from high-strength alloy steels or cast steels that are inherently expensive to replace.

Component Design and Material Selection

Side press modules in modern rolling mills are typically manufactured from materials such as 42CrMo, 34CrNiMo6, or equivalent high-strength alloy steels, with base hardness in the range of 25-35 HRC. The contact surfaces are exposed to temperatures of 800-1200°C during operation, with thermal cycling frequencies of several hundred cycles per day. The conventional approach of using through-hardened or case-hardened modules limits their service life to 3-6 months before replacement is required due to surface degradation.

The overlay approach investigated in this study involves applying 3-8 mm of weld overlay material to the contact surfaces of the modules, creating a sacrificial wear-resistant layer while retaining the base material for structural integrity. The overlay materials examined include:

Welding Process Selection and Parameters

The selection of welding process for side press module overlay is governed by several factors: the geometry of the component, the thickness of the overlay layer required, the base material weldability, and production throughput requirements. The study evaluates three primary processes:

Submerged Arc Welding (SAW) Overlay

SAW is well-suited for thick overlay layers (4-10 mm) on flat or slightly curved surfaces. The process provides deep penetration, high deposition rates (3-5 kg/h), and consistent microstructure. However, it requires pre-machined grooves on the module surface and is not suitable for complex geometries. Typical parameters include welding current of 500-700 A, arc voltage of 30-38 V, and travel speed of 150-300 mm/min.

Flux-Cored Arc Welding (FCAW) Overlay

FCAW offers greater flexibility for complex geometries and can be performed in various positions. The deposition rate is lower (1.5-3 kg/h) but the process is more versatile. Self-shielded flux-cored wires allow outdoor and field application without external shielding gas. The study found that FCAW overlay on side press modules provided good adhesion with dilution rates of 15-25% in the first pass and 8-15% in subsequent passes.

Gas Metal Arc Welding (GMAW) Overlay

GMAW provides the finest control over weld quality and is preferred for thin overlay layers (2-4 mm) where dimensional accuracy is critical. The process offers good visual appearance and minimal spatter. However, the lower deposition rate (1-2.5 kg/h) and higher consumable cost per unit area make it less economical for thick overlay applications.

Performance Evaluation Results

The study conducted comprehensive performance testing on overlay-treated side press modules, including hardness profiling, microstructural analysis, bond strength testing, and field trial evaluation.

Hardness Distribution

The hardness profile through the overlay layer thickness showed the expected gradient: highest hardness at the top surface (58-63 HRC for high-chromium alloys), gradually decreasing toward the interface due to dilution effects, with the base material hardness remaining at 28-32 HRC. The transition zone at the overlay-base interface typically spans 0.5-1.5 mm and represents the weakest region in terms of mechanical properties.

Bond Strength

Bond strength testing using the wedge tensile test method yielded values of 450-580 MPa for properly executed overlays, well above the minimum requirements of 400 MPa specified in relevant standards. The bond strength was found to be strongly dependent on surface preparation quality, with proper grinding to bare metal and removal of surface contaminants being essential for achieving reliable adhesion.

Field Trial Performance

In field trials at a hot rolling mill, overlay-treated side press modules demonstrated a service life extension of 2.5 to 4 times compared to conventional untreated modules. The overlay layers maintained their hardness even after 2-3 months of continuous operation at elevated temperatures, with only minor surface degradation observed. The primary failure mode was gradual wear through of the overlay layer, after which the base material was exposed and accelerated wear ensued. This observation underscores the importance of monitoring overlay thickness during maintenance intervals.

Defect Analysis and Countermeasures

The study identified several common defects in the overlay welding process and proposed countermeasures:

Engineering Practice Recommendations

Based on the findings of this study, the following recommendations are made for engineers involved in side press module overlay fabrication:

1. Surface preparation is paramount: all overlay surfaces must be ground to bare metal with a minimum Ra of 12.5 μm, followed by thorough cleaning to remove all oil, rust, and scale.
2. Multi-pass overlay is recommended for overlay thicknesses exceeding 3 mm to minimize dilution effects and ensure uniform microstructure throughout the layer.
3. A backing layer of low-carbon martensitic alloy should be applied as the first pass to reduce dilution and prevent cracking, followed by the final wear-resistant layer.
4. Post-weld heat treatment at 550-650°C for 2-4 hours is recommended to relieve residual stresses and improve toughness without significant hardness loss.
5. Regular thickness monitoring during operation should be implemented, with replacement or re-overlay scheduled when the overlay thickness falls below 1.5 mm.

Study Insights and Conclusions

This research demonstrates that surface weld overlay is a highly effective and economical approach for extending the service life of side press modules in rolling mill applications. The key to successful implementation lies in careful material selection matched to the specific wear environment, rigorous surface preparation, optimized welding parameters to control dilution and defect formation, and systematic post-weld treatment. The field trial results showing 2.5-4 times life extension provide compelling economic justification for adopting overlay technology, particularly when considering the high cost of module replacement and the associated downtime. Engineers should view weld overlay not merely as a surface treatment but as an integral part of the component design philosophy, where the overlay layer is designed to be sacrificial while protecting the expensive base material.