Application of Lincoln Electric Welding Consumables in Composite Weld Overlay of Slab Continuous Casting Rolls
1. Definition and Technical Principles
The application of Lincoln Electric welding consumables in composite weld overlay of slab continuous casting rolls represents a specialized surface engineering process in which a high-performance overlay alloy is deposited onto a base roll substrate to provide enhanced wear resistance, thermal shock resistance, and corrosion resistance. Slab continuous casting rolls—particularly strand guides, oscillating rolls, and secondary cooling zone rolls—are subjected to extreme thermal cycling, abrasive contact with hot steel slabs, and corrosive cooling environments. The composite weld overlay process creates a functionally graded interface between the structural base material and the overlay layer, combining the toughness of the substrate with the hardness and durability of the overlay alloy.
Lincoln Electric, a globally recognized manufacturer of welding consumables and equipment, produces a wide range of solid wires and flux-cored wires specifically designed for overlay applications. Their consumable product lines include hard-facing wires (such as Lincoln LAC-6, Lincoln LAC-7, Lincoln LAC-9), stainless steel overlay wires (Lincoln L-65, Lincoln L-68), and nickel-based overlay wires (Lincoln L-19, Lincoln L-32) that are widely specified for heavy-duty industrial applications including continuous casting roll repair and refurbishment.
The fundamental metallurgical principle governing this application involves the controlled dilution between the base metal and the overlay layer. In slab continuous casting rolls, the base material is typically a high-strength cast iron (such as ASTM A532 Class 1 or Class 2) or a forged steel (ASTM A396/A397). The dilution ratio—typically maintained between 20% and 40% for optimal performance—directly influences the final microstructure, hardness profile, and service life of the overlay. Lincoln Electric's consumables are formulated with specific alloy compositions (high chromium, tungsten, cobalt, or molybdenum content) that maintain their functional properties even under these dilution conditions.
2. Category and Business Positioning
This technology falls squarely within the company's TIG/MIG weld overlay technology route, specifically addressing the industrial and energy sector segment. Within the broader portfolio of Cladding Technology Shanxi Co., Ltd., this entry serves as a critical knowledge asset that bridges consumable selection expertise with process qualification capability. The "learning experience" (学习心得) nature of this document indicates a systematic approach to technology absorption and internal capability development—transforming supplier-specific product knowledge into qualified, repeatable manufacturing processes.
In terms of business positioning, this capability addresses a high-value repair and refurbishment market segment. Slab continuous casting rolls in steel mills require periodic overlay repair (typically every 6–18 months depending on operating conditions), creating a recurring revenue stream. The ability to specify, qualify, and apply premium American-brand consumables such as Lincoln Electric wires differentiates the company from competitors who rely solely on domestically produced alternatives, particularly for critical applications where end-users (steel mills) have strict consumable specifications.
3. Technical Purpose and Value
3.1 Primary Technical Objectives
- Surface Hardness Enhancement: Achieve overlay hardness of 45–55 HRC (for chromium-cobalt alloys) or 35–45 HRC (for tungsten carbide-cobalt alloys) to resist abrasive wear from hot steel slab contact
- Thermal Fatigue Resistance: Create a crack-resistant overlay that withstands repeated thermal cycling between ambient temperature and 600–1200°C contact temperatures
- Corrosion Resistance: Provide protection against acidic scaling compounds and cooling water corrosion in secondary cooling zones
- Service Life Extension: Increase roll service intervals by 2–5 times compared to uncladded or conventionally repaired rolls
3.2 Value to Customer and Company
The use of Lincoln Electric consumables in slab continuous casting roll overlay delivers measurable economic value to steel mill customers through reduced unplanned downtime, extended roll life, and improved slab surface quality. For the company, this entry contributes to:
- Building consumable qualification databases that support WPS (Welding Procedure Specification) development
- Establishing technical credibility with international-standard consumable suppliers
- Creating a knowledge base that enables rapid deployment to similar applications (tubular casting rolls, billet casting rolls)
- Supporting certification requirements for ASME Section IX or AWS D10.9 qualification procedures
4. Key Process and Implementation Points
4.1 Consumable Selection Matrix
| Application Zone | Recommended Lincoln Consumable | Wire Type | Typical Hardness (HRC) | Key Alloying Elements | Welding Process |
|---|---|---|---|---|---|
| Strand Guide (High Wear) | Lincoln LAC-7 | Stick Electrode | 45-55 | Cr-Co-C (Chromium-Cobalt-Carburide) | SMAW / GMAW |
| Oscillating Roll (Thermal Shock) | Lincoln LAC-6 | Stick Electrode | 45-55 | Cr-Co (High Chromium-Cobalt) | SMAW |
| Secondary Cooling Roll | Lincoln L-65 | Stick Electrode | 28-38 | Cr-Ni (Stainless 309-type) | GMAW / FCAW |
| Transition Layer | Lincoln L-68 | Stick Electrode | 25-32 | Cr-Ni-Mo (Duplex-type) | GMAW |
| High-Temperature Zone | Lincoln L-19 | Stick Electrode | 35-42 | Ni-Cr (Stellite-type) | SMAW / GMAW |
4.2 Typical Process Parameters for GMAW (MIG) Overlay
| Parameter | Range / Value | Notes |
|---|---|---|
| Shielding Gas | Argon (100%) or Ar/CO₂ (98/2) | Pure argon for Ni-based; Ar/CO₂ for Fe-based overlays |
| Wire Diameter | 1.0 mm – 1.6 mm | 1.0 mm for transition layers; 1.2-1.6 mm for build-up layers |
| Deposition Rate | 0.8 – 2.5 kg/h | Higher for build-up; lower for transition/control layers |
| Travel Speed | 80 – 200 mm/min | Adjusted for bead width and penetration control |
| Heat Input | 0.8 – 1.8 kJ/mm | Critical for dilution control and microstructure |
| Preheat Temperature | 150 – 300°C | Depends on base material carbon equivalent |
| Interpass Temperature | ≤ 250°C (Fe-based); ≤ 150°C (Ni-based) | Strict control to prevent cracking in Ni-base overlays |
| Layer Thickness per Pass | 3 – 5 mm | Multiple passes for total overlay thickness of 6-12 mm |
4.3 Multi-Layer Overlay Strategy
- Surface Preparation: Machining the roll surface to remove existing damaged layers, achieving a clean, smooth substrate with Ra ≤ 12.5 μm. Edge preparation with 30°-45° chamfers for proper fusion at boundaries.
- Transition Layer (Pass 1): Application of a compatible transition alloy (e.g., Lincoln L-68 or Lincoln L-65) to reduce dilution and provide metallurgical compatibility between the high-carbon base material and the overlay. This layer is typically 2-3 mm thick with controlled low heat input.
- Build-up Layer (Passes 2-3): Application of the functional overlay alloy (e.g., Lincoln LAC-7) in 2-3 passes to achieve the required total thickness. Each pass maintains interpass temperature control and proper bead overlap (70-80% overlap ratio).
- Post-Weld Heat Treatment (PWHT): Stress relief annealing at 500-650°C for 2-4 hours (depending on overlay thickness) to relieve residual stresses and improve microstructural homogeneity.
- Final Machining: Precision grinding of the overlay surface to achieve specified geometry tolerances (typically ±0.05 mm dimensional tolerance, surface finish Ra ≤ 3.2 μm for strand guides).
4.4 Critical Implementation Considerations
- Dilution Control: The transition layer composition and thickness must be optimized for each base material. Cast iron bases (high carbon, graphite phases) require more aggressive transition strategies than low-carbon steel bases.
- Crack Prevention: Nickel-based overlays (Lincoln L-19, L-32) are susceptible to hydrogen cracking and solidification cracking. Strict consumable baking (200°C for 2 hours), low hydrogen flux-cored alternatives, and controlled cooling rates are essential.
- Roll Geometry: Cylindrical rolls require either robotic or manual circumferential welding with careful attention to bead continuity and overlap at the start/stop points. Spiral patterns are commonly used for uniform coverage.
- Thermal Distortion: Continuous casting rolls have tight geometric tolerances (runout ≤ 0.02 mm). Thermal management through symmetric welding sequences, preheating, and post-weld stress relief is mandatory.
5. Applicable Standards and Acceptance Criteria
5.1 Governing Standards
| Standard | Scope of Application |
|---|---|
| ASTM A532 | Cast Irons for Engineering Purposes (base material specification) |
| ASTM A396/A397 | Carbon Steel Forgings for Boilers and Pressure Vessels (forged roll blanks) |
| ASME Section IX | Qualification of Welding Procedures and Welders (WPS/PQR qualification) |
| AWS D10.9 | Specification for Qualification of Welding Procedures for PTA Weld Overlay Cladding |
| AWS A5.23 | Specification for Carbon Steel Electrodes for Shielded Metal Arc Welding (Lincoln LAC series) |
| AWS A5.9 | Specification for Stainless Steel Electrodes for Shielded Metal Arc Welding (Lincoln L-65, L-68) |
| GB/T 11345 | Ultrasonic Testing of Welds (NDT acceptance) |
| GB/T 3975 | Non-destructive Testing—Ultrasonic Testing of Welds (Chinese standard) |
| ASTM E165 | Standard Practice for Magnetic Particle Examination |
| ASTM B557 | Standard Specification for Nickel-Cobalt-Chromium Alloys (Stellite-type overlays) |
| NACE MR0175/ISO 15156 | Sour Service Requirements (if applicable to corrosive environments) |
5.2 Acceptance Criteria
- Visual Inspection (VT): No cracks, porosity, undercuts, or excessive spatter. Bead width uniformity within ±10% of nominal. Surface smoothness Ra ≤ 3.2 μm after machining.
- Penetrant Testing (PT): ASTM E709 compliance. No linear indications exceeding 3 mm in length. No cluster indications exceeding 10 mm.
- Magnetic Particle Testing (MT): ASTM E165 compliance. No surface cracks or linear indications. Background pattern only acceptable.
- Ultrasonic Testing (UT): GB/T 11345 Level 2 minimum. No defects exceeding acceptance criteria for the overlay thickness. Full-bond verification (no delamination between overlay and base).
- Hardness Testing: Overlay hardness within specified range (e.g., 45-55 HRC for LAC-7). Hardness gradient from overlay to base must be gradual (no abrupt transition exceeding 10 HRC/mm).
- Macrograph Examination: Cross-section reveals full fusion at overlay-base interface, no unmelted inclusions, proper dilution profile, and absence of macro-segregation.
- Dimensional Verification: Roll diameter tolerance ±0.05 mm. Runout ≤ 0.02 mm. Overlay thickness uniformity within ±0.5 mm circumferentially.
6. Common Risks and Controls
| Risk Category | Description | Control Measures |
|---|---|---|
| Hot Cracking | Solidification cracking in Ni-base overlays due to low melting point eutectics at grain boundaries | Use of proper transition layer; interpass temperature ≤150°C; low hydrogen consumables; controlled cooling rate |
| Hydrogen-Induced Cracking (HIC) | Delayed cracking in high-strength base material or Ni-base overlay | Consumable baking per manufacturer specs; preheat ≥200°C; post-weld bake at 200-250°C for 4 hours |
| Excessive Dilution | Carbon and impurity pickup from base material degrades overlay properties | Multi-pass with transition layer; controlled heat input; proper base material preparation |
| Thermal Distortion | Roll geometry deviation exceeding tolerance due to asymmetric heat input | Symmetric welding sequence; fixture clamping; post-weld stress relief; in-process geometric monitoring |
| Delamination | Loss of bond between overlay and base due to poor fusion or residual stress | Adequate preheat; proper base preparation (grinding to bare metal); UT verification; controlled cooling |
| Consumable Contamination | Moisture absorption or oxidation of Lincoln consumables during storage/transport | Strict storage conditions (dry, temperature-controlled); first-in-first-out inventory; baking before use; sealed packaging verification |
| Spatter and Surface Defects | Poor surface quality requiring excessive post-machining | Optimized shielding gas flow; proper gun angle (10-15° trailing); appropriate wire feed speed; clean base surface |
7. Application Across Company Technology Routes
7.1 TIG/MIG Weld Overlay (Primary Application Route)
This technology entry directly contributes to the company's core TIG/MIG weld overlay capability. The Lincoln Electric consumable knowledge base enables:
- WPS Development: Qualified welding procedures using Lincoln consumables that meet ASME Section IX and AWS D10.9 requirements, expanding the company's qualification portfolio
- Process Flexibility: Ability to switch between SMAW (stick welding with Lincoln LAC series) and GMAW (MIG with Lincoln solid or flux-cored wires) based on roll geometry and accessibility
- Robotic Integration: Lincoln consumables are compatible with automated orbital and circumferential welding systems for consistent, repeatable overlay on cylindrical rolls
- Customer Specification Compliance: Many steel mills specify Lincoln or equivalent brand consumables in their repair specifications; this capability ensures contract compliance
7.2 Hydraulic Explosive Bonding (Complementary Route)
While hydraulic explosive bonding is not directly applicable to the weld overlay of continuous casting rolls, the consumable and metallurgical knowledge gained from Lincoln overlay applications informs:
- Base Material Selection: Understanding of how different base materials respond to thermal cycling informs the selection of base layers for explosively bonded clad plates used in continuous casting equipment housings and molds
- Interface Characterization: Techniques developed for overlay dilution analysis (macrography, hardness profiling) are transferable to explosive bond interface evaluation
- Post-Bonding Refurbishment: Explosively bonded roll assemblies may require weld overlay repair at damaged zones, where Lincoln consumable expertise is directly applicable
7.3 Explosion Welding (Complementary Route)
Explosion welding produces clad plates that can serve as base materials for subsequent weld overlay operations. The Lincoln consumable expertise is relevant in:
- Overlay on Explosion-Welded Clad Plates: When explosion-welded clad plates (e.g., stainless steel on carbon steel) are used in continuous casting equipment, additional overlay layers may be required for specific wear zones
- Repair of Explosion-Welded Assemblies: Any damage to the explosion weld bond line requires repair welding with compatible consumables—a direct application of the Lincoln consumable qualification
- Process Integration: The company can offer combined solutions—explosion welding for base cladding plus MIG/TIG overlay for localized high-wear zones—leveraging both technology routes
8. Qualification Building and Knowledge Transfer
8.1 WPS/PQR Qualification Framework
The learning experience documented in this entry forms the foundation for formal welding procedure qualification. The qualification process involves:
- WPS Development: Documenting all essential variables (process, consumable, diameter, polarity, gas, preheat, interpass temperature, travel speed, current, voltage) per ASME Section IX Part Q
- PQR Execution: Performing a qualification weld using the Lincoln consumable on a test coupon representative of the slab continuous casting roll base material
- Mechanical Testing: Transverse tensile tests, bend tests (face, root, side), hardness surveys, and macrograph examination per AWS D10.9
- WPS Approval: Issuing a qualified WPS based on PQR results, valid for the defined range of essential variables
- Welder Qualification: Qualifying individual welders on the approved WPS for production use
8.2 Knowledge Management Value
The "learning experience" format of this entry reflects a systematic approach to organizational knowledge capture. Its value includes:
- Accelerated Onboarding: New technicians can rapidly understand Lincoln consumable characteristics and application best practices without extensive trial-and-error
- Process Standardization: Converting experiential knowledge into documented procedures ensures consistent quality across multiple production shifts and operators
- Supplier Relationship Management: Demonstrating technical competence with Lincoln consumables strengthens the company's position as an authorized or preferred applicator, potentially qualifying for technical support and early access to new products
- IP Development: Unique process knowledge regarding consumable selection, parameter optimization, and multi-layer strategies can be developed into proprietary process know-how
9. Conclusion
The application of Lincoln Electric welding consumables in composite weld overlay of slab continuous casting rolls represents a mature, high-value technology that directly addresses critical maintenance needs in the steel industry. By systematically absorbing and qualifying this technology, Cladding Technology Shanxi Co., Ltd. strengthens its TIG/MIG weld overlay capability, expands its WPS qualification portfolio, and positions itself as a premium service provider capable of meeting the most demanding customer specifications. The documented learning experience serves as a critical knowledge asset that bridges consumable supplier expertise with the company's manufacturing execution capability, ultimately delivering extended equipment life, reduced downtime, and improved product quality to steel mill customers.