Research on Weld Overlay Repair Technology for Disc Shear Blades

Overview of the Study

This literature review focuses on the weld overlay repair technology applied to disc-type shear blades, which are critical cutting tools used extensively in metal processing, sheet steel slitting, and shearing operations. Disc shear blades are subjected to extreme mechanical and thermal loads during service, leading to edge wear, chipping, and dimensional degradation that compromise cutting quality and increase maintenance costs. The study examines how advanced weld overlay techniques can extend blade service life, restore geometric accuracy, and reduce overall operational expenses.

Core Technical Approach

The primary methodology involves surface preparation followed by multi-pass weld overlay deposition using hardfacing alloys. The process typically employs submerged arc welding (SAW) or gas metal arc welding (GMAW) for depositing wear-resistant layers on the cutting edge of the disc blade.

Surface Preparation and Preheat Parameters

Parameter	Specification	Rationale
Base material	45# or 50Cr steel	Typical shear blade material
Preheat temperature	200–300 °C	Reduce residual stress and prevent cracking
Surface cleaning	Grit blasting to Sa 2.5	Ensure metallurgical bond
Edge bevel angle	45°–60°	Facilitate multi-pass filling
Interpass temperature	≤ 250 °C	Control grain growth and HAZ hardness

Weld Overlay Alloy Selection

The selection of hardfacing alloys is critical to achieving the desired wear resistance while maintaining toughness to prevent brittle fracture during cutting operations.

Alloy Type	Typical Composition	Hardness (HV)	Application Scenario
Cr-based (Cr3C2)	25–30% Cr, 3–5% C, balance Fe	800–950	Slitting soft steel
Co-based	50–60% Co, 20–30% Cr, 5–10% W	600–700	Precision cutting, high-temp service
Ni-based	40–50% Ni, 15–25% Cr, 5–8% C	500–650	Tough service, thermal shock resistance
Fe-Cr-C	12–18% Cr, 4–6% C	700–850	General heavy-duty slitting

Process Development and Key Technical Points

Multi-Pass Deposition Strategy

The literature describes a three-stage approach: (1) a transition layer to mitigate dilution effects between the base steel and the hardfacing alloy, (2) intermediate passes with graded alloy composition, and (3) a final surfacing pass with the target hardfacing composition. This graded approach minimizes cracking susceptibility at the bond line, which is a well-documented challenge in Fe-based and Cr-based hardfacing systems.

Heat Input Control

Heat input is maintained in the range of 8–15 kJ/mm depending on the alloy system and pass number. Lower heat input (8–10 kJ/mm) is preferred for the final surfacing pass to preserve the fine carbide distribution and avoid excessive grain coarsening in the HAZ. The welding speed is typically 150–250 mm/min for SAW and 200–350 mm/min for GMAW.

Post-Weld Treatment

After cladding, the blades undergo stress relief annealing at 550–650 °C for 2 hours. This step is essential to reduce residual stresses that can lead to distortion and subsequent cracking during the first cutting cycle. Some implementations include a controlled cooling in furnace conditions to further minimize thermal gradient stresses.

Defect Analysis and Countermeasures

Defect Type	Root Cause	Detection Method	Countermeasure
Bond line cracking	Excessive carbon activity at interface	MT + UT	Introduce transition layer; reduce heat input
Porosity	Flux contamination, inadequate shielding	RT	Improve flux dryness; enhance gas flow
Excessive dilution	High heat input, inadequate edge preparation	Micro-hardness profiling	Multi-pass with graded composition
Surface cracking	Rapid cooling of hardfacing layer	PT	Increase interpass temperature; post-weld anneal
Distortion	Asymmetric heat distribution	Coordinate measurement	Symmetric welding sequence; clamping fixtures

Engineering Practice Integration

In practical implementation at sheet steel processing plants, the weld overlay repair approach has demonstrated a 3–5× extension in blade service life compared to conventional grinding-only restoration. A case study involving 1200 mm diameter slitting blades for 2 mm cold-rolled strip showed that blades repaired with Cr3C2-based hardfacing maintained acceptable edge geometry for 450–600 cutting hours, compared to 120–150 hours for ground-only blades.

The economic analysis revealed that the total cost per cutting hour decreased by approximately 40% when overlay repair was implemented, factoring in reduced blade replacement frequency, lower grinding consumable costs, and decreased downtime for blade changes.

Key Questions and Reflections

The study raises important questions about the long-term fatigue behavior of multi-pass overlay systems under cyclic loading conditions typical of continuous slitting operations. While the hardness and wear resistance are well-documented, the fatigue life of the overlay layer under repeated impact loading deserves further investigation. Additionally, the effect of different cutting speeds and strip hardness on overlay wear patterns warrants systematic study.

From a quality assurance perspective, implementing TOFD or PAUT for bond line integrity verification could provide more reliable assessment than conventional MT alone, particularly for thicker overlay layers where surface-breaking defect detection is less effective.

Study Insights and Implications

The literature confirms that systematic approach to weld overlay repair of shear blades — combining proper material selection, controlled heat input, graded composition deposition, and post-weld treatment — yields significant operational benefits. The key insight is that the transition layer strategy is not merely optional but essential for preventing bond line failures in high-carbon hardfacing systems deposited on medium-carbon steel substrates.

For future engineering practice, I recommend establishing a standardized repair protocol that includes documented preheat parameters, alloy selection criteria based on cutting application, in-process monitoring of heat input, and post-repair verification procedures. This systematic approach transforms blade repair from an ad-hoc maintenance activity into a controlled engineering process with predictable outcomes and traceable quality records.