Weld Overlay Technology Application on Hot Rolling Delivery Roll Cladding

Literature Overview

This 2004 study by Ge Baowen of Baosteel Engineering Technology Co., Ltd. addresses the practical application of weld overlay technology on hot rolling delivery rolls, a critical component in the continuous casting and hot rolling production line. The research originates from the demanding industrial environment of Baosteel, where delivery rolls must withstand extreme thermal cycling, abrasive contact with red-hot steel slabs, and repeated mechanical loading. The study reflects the engineering challenge of extending roll service life through surface engineering techniques, specifically weld overlay cladding, to reduce production downtime and maintenance costs.

Core Technical Content

The primary objective of cladding hot rolling delivery rolls is to create a hard, wear-resistant, and thermally stable surface layer on a tough carbon steel or low-alloy steel base. The overlay layer must resist both adhesive and abrasive wear from the moving slab, while also maintaining sufficient toughness to avoid spalling under thermal shock. The study examines the selection of overlay materials, welding process parameters, and the resulting microstructural and mechanical properties of the cladding layer.

Overlay Material Selection and Composition

The selection of overlay consumables is governed by the tribological conditions at the roll surface. For hot rolling delivery rolls, the overlay material must exhibit high hardness at elevated temperatures (typically 800–1100 °C operating range), good thermal fatigue resistance, and adequate bond strength to the substrate. Common overlay consumables include hardfacing alloys based on Cr-C-Mo systems, Ni-based alloys with carbide-forming elements, and Co-based alloys for higher temperature service.

Parameter	Typical Range	Requirement
Operating temperature	800–1100 °C	Thermal stability of overlay
Overlay hardness (as-welded)	45–60 HRC	Wear resistance
Overlay hardness (after heat treatment)	50–62 HRC	Enhanced wear life
Bond strength to substrate	≥ 20 MPa	Structural integrity
Overlay thickness	3–8 mm	Adequate wear life
Number of weld passes	2–4	Uniform composition and properties

Welding Process Parameters

The welding process employed for delivery roll cladding typically involves submerged arc welding (SAW) or gas metal arc welding (GMAW) for the build-up passes, followed by hardfacing passes. Process control is critical to avoid dilution of the overlay composition with the base metal and to prevent cracking due to high carbon and alloy content in the hardfacing material.

Process Parameter	Typical Value	Effect
Welding current (SAW)	400–600 A	Penetration and dilution control
Welding voltage (SAW)	28–35 V	Arc stability and bead shape
Travel speed	300–500 mm/min	Heat input and cooling rate
Preheat temperature	150–250 °C	Crack prevention
Interpass temperature	150–250 °C	Residual stress control
Post-weld stress relief	550–650 °C × 2 h	Residual stress reduction

The dilution rate between the base metal and overlay layer is a critical parameter. For hardfacing applications, dilution should be controlled below 10–15% to maintain the intended hardening mechanisms such as carbide precipitation and martensitic transformation. Excessive dilution leads to softening of the overlay and premature wear failure.

Defect Analysis and Countermeasures

Common defects encountered during delivery roll cladding include surface cracks, undercut, porosity, and delamination at the overlay-substrate interface. A systematic FMEA approach reveals the following defect modes:

Defect Type	Root Cause	Countermeasure
Surface cracking	High carbon content, rapid cooling	Increase preheat, reduce travel speed, use low-hydrogen flux
Undercut	Excessive travel speed, improper gun angle	Reduce travel speed, adjust torch angle to 10–15°
Porosity	Moisture in flux, contamination	Dry flux storage, clean substrate surface
Delamination	Inadequate bond, hydrogen embrittlement	Increase preheat, apply post-weld heat treatment
Spalling in service	Thermal fatigue, high residual stress	Stress relief treatment, optimize overlay thickness

Engineering Practice Insights

In the Baosteel production environment, the cladding operation must be integrated with the roll manufacturing schedule to minimize production interruption. The roll is typically removed from service after 3–5 rolling campaigns, when surface wear depth reaches 2–3 mm. The cladding process involves grinding the worn surface flush, applying the overlay layer in multiple passes, and performing post-weld heat treatment. The total cycle time for re-cladding a delivery roll is approximately 24–48 hours, depending on the number of passes and heat treatment requirements.

The study highlights that the economic benefit of cladding delivery rolls is substantial: a single cladding operation can extend roll life by 2–3 times compared to bare rolls, reducing the annual roll consumption by approximately 40–50%. However, the quality of the overlay is paramount, as any defect in the cladding layer can lead to catastrophic roll failure during hot rolling, resulting in significant production losses and safety hazards.

Study Insights and Implications

This early-2000s study from Baosteel represents a mature industrial application of weld overlay technology in heavy steel production. The key takeaway is that successful cladding of hot rolling delivery rolls requires not only appropriate material selection but also rigorous process control, thorough defect prevention, and integration with the production maintenance schedule. The study underscores the principle that surface engineering is not merely a material selection exercise but a holistic engineering discipline encompassing metallurgy, welding technology, thermomechanical processing, and production logistics. Future improvements in this area may involve advanced monitoring of overlay integrity during service and the development of multi-layer overlay systems with tailored property gradients.