High-Strength Wear-Resistant Alloy Weld Overlay for Sintering Machine Tail Scraper
1. Definition and Technical Principles
The application of high-strength wear-resistant alloy weld overlay on sintering machine tail scrapers represents a critical surface engineering solution in the metallurgical and iron-ore processing industry. A sintering machine tail scraper is a structural component located at the discharge end of the sintering machine belt system, responsible for scraping off the sintered ore cake from the belt surface. This component is subjected to extreme abrasive wear, impact loading, and thermal cycling, making conventional carbon steel or low-alloy steel base materials insufficient for service life requirements.
The fundamental principle of weld overlay in this application involves the deposition of a metallurgically distinct, wear-resistant alloy layer onto the working surfaces of the scraper through arc welding processes. The overlay alloy—typically a martensitic or austenitic high-chromium alloy—creates a composite structure where the base material retains its toughness and structural integrity while the surface layer provides exceptional hardness (typically 45–60 HRC), abrasion resistance, and impact tolerance. The metallurgical bond between the overlay and substrate is achieved through controlled dilution management, preheating, and interpass temperature control, ensuring a coherent interface free of cracking and delamination.
The key metallurgical mechanisms that provide wear resistance in these overlay alloys include:
- Hard carbide precipitation — Chromium carbides (Cr₇C₃, Cr₃C) and iron carbides (Fe₃C) dispersed within a hardened matrix
- Martensitic transformation — Rapid cooling from the solid solution state produces a hard, fine martensitic microstructure
- Grain refinement — Low dilution welding parameters produce fine-grained overlay deposits with superior mechanical properties
- Thermal stability — Alloying elements such as Cr, Mo, and V maintain hardness at elevated operating temperatures encountered in sintering environments
2. Category and Business Positioning
This capability falls within the TIG/MIG Weld Overlay technology route of Cladding Technology Shanxi Co., Ltd. It is classified as a hardfacing and wear-resistant overlay service, distinct from corrosion-resistant cladding applications. In the company's service portfolio, this application serves the mining, iron ore processing, and heavy industrial equipment maintenance sectors.
The business positioning of this capability is threefold:
- Aftermarket service provider — Repair and refurbishment of worn scraper components for existing sintering plants
- OEM partner — Supply of pre-overlay-processed scraper components to sintering machine manufacturers
- Technical consulting — Selection of appropriate overlay alloys, process design, and qualification support for customer-specific applications
This entry demonstrates the company's applied engineering competence in translating metallurgical principles into field-proven solutions for demanding industrial wear environments. It is a representative case study that validates the company's process know-how, operator skill level, and quality management system maturity.
3. Technical Purpose and Value
3.1 Primary Technical Objectives
The deployment of high-strength wear-resistant alloy weld overlay on sintering machine tail scrapers is driven by the following engineering objectives:
- Extended service life — Increasing component life from 3–6 months (bare steel) to 18–36 months or longer, depending on operating conditions
- Reduced unplanned downtime — Minimizing production interruptions caused by scraper failure and emergency replacement
- Lower total cost of ownership — Reducing replacement frequency, material consumption, and labor costs associated with maintenance
- Maintenance of process quality — Ensuring consistent scraper geometry and belt contact to maintain uniform sinter cake discharge
3.2 Quantitative Value Assessment
| Parameter | Conventional Steel Scraper | Overlay-Enhanced Scraper | Improvement Factor |
|---|---|---|---|
| Surface Hardness (HRC) | 20–25 | 45–60 | 2.0–2.5× |
| Abrasion Resistance Index | 1.0 (baseline) | 4.0–8.0 | 4–8× |
| Service Life | 3–6 months | 18–36 months | 3–6× |
| Annual Replacement Count | 2–4 units | 0.5–1 unit | 50–75% reduction |
| Unplanned Downtime Events/Year | 4–8 | 0–2 | 75–100% reduction |
3.3 Customer Value Proposition
For iron ore sintering plant operators, the adoption of overlay-enhanced tail scrapers delivers measurable economic benefits including reduced maintenance budgets, improved production continuity, and elimination of emergency procurement cycles. The technical practice documented in this capability entry provides a validated reference for customer confidence in the company's overlay service quality.
4. Key Process and Implementation Points
4.1 Overlay Alloy Selection
The selection of the appropriate hardfacing alloy is the most critical design decision in this application. The alloy must be matched to the specific wear mechanism, impact loading, and thermal environment experienced by the tail scraper.
| Alloy Type | Typical Composition | Hardness (HRC) | Impact Resistance | Recommended Application |
|---|---|---|---|---|
| High-Cr Martensitic | Cr 25–30%, C 2.5–3.5%, Mo 1–2% | 50–58 | Good | Pure abrasive wear, moderate impact |
| High-Cr High-V Martensitic | Cr 25–30%, C 2.5–3.5%, V 3–5%, Mo 1–2% | 55–62 | Excellent | Severe abrasion with high impact loading |
| Austenitic High-Alloy | Cr 20–25%, Ni 8–12%, C 2.0–3.0% | 40–48 | Outstanding | High impact + abrasion, thermal cycling |
| Medium-Cr Martensitic | Cr 10–15%, C 1.5–2.5%, Mo 0.5–1% | 45–55 | Fair | Moderate wear, lower cost requirement |
4.2 Substrate Preparation
Proper substrate preparation is essential for achieving sound metallurgical bonding and preventing overlay failure. The preparation sequence includes:
- Removal of existing coatings — Grinding or flame cutting to remove paint, rust, and previous weld deposits
- Geometry restoration — Machining or grinding worn areas to establish a uniform base profile for overlay deposition
- Surface cleaning — Mechanical cleaning to bare metal within 24 hours of welding to prevent re-oxidation
- Defect inspection — Visual and magnetic particle examination (MT) to identify cracks, porosity, or inclusions in the substrate
- Preheating assessment — Determination of required preheat temperature based on substrate carbon equivalent (CE) and section thickness
4.3 Welding Process Parameters
The welding process parameters must be carefully controlled to minimize dilution (target: <15–20%) while maintaining adequate penetration for sound bonding. The following table summarizes typical parameters for TIG and MIG overlay of high-Cr martensitic alloys:
| Parameter | TIG (GTAW) Overlay | MIG (GMAW) Overlay | Control Objective |
|---|---|---|---|
| Electrode/Wire | High-Cr hardfacing rod (e.g., Cr25Ni5) | High-Cr hardfacing wire (e.g., Cr25Ni5) | Composition control |
| Current | 80–150 A | 120–220 A | Adequate penetration, low dilution |
| Voltage | 14–18 V | 18–24 V | Stable arc, controlled bead profile |
| Travel Speed | 50–100 mm/min | 150–300 mm/min | Uniform bead width and height |
| Preheat Temperature | 150–250°C | 150–250°C | Prevent cold cracking in base metal |
| Interpass Temperature | ≤200°C | ≤250°C | Control grain growth, prevent softening |
| Shielding Gas | Ar (100%) | Ar (100%) or Ar + 5% CO₂ | Prevent oxidation, ensure clean deposit |
| Number of Passes | 2–4 passes | 1–3 passes | Achieve required overlay thickness |
| Target Overlay Thickness | 3–8 mm total | 3–8 mm total | Adequate wear allowance |
4.4 Multi-Layer Strategy
For thick overlay requirements or when dilution control is critical, a multi-layer approach is employed:
- Transition layer (if required) — A compatible alloy (e.g., 309L or medium-Cr) deposited first to reduce residual stress and prevent cracking at the base metal/overlay interface
- Build-up passes — Successive layers of the final hardfacing alloy deposited with controlled interpass temperature
- Final pass — Last layer deposited with optimized parameters to achieve flat, uniform surface finish
4.5 Post-Weld Treatment
- Controlled cooling — Allow natural cooling in still air; avoid water quenching or forced air cooling that could induce cracking
- Stress relief (if specified) — Low-temperature stress relief at 250–350°C for high-residual-stress applications
- Surface finishing — Grinding to achieve required dimensional accuracy and surface roughness (typically Ra 12.5–25 μm for scraper applications)
- Final hardness verification — Rockwell C hardness testing at specified locations on the overlay surface
5. Applicable Standards and Acceptance Criteria
5.1 Governing Standards
The design, execution, and acceptance of weld overlay on sintering machine tail scrapers shall comply with the following standards:
| Standard | Scope | Relevance |
|---|---|---|
| GB/T 985 | Welding symbols on engineering drawings | Overlay specification notation |
| GB/T 19866 | Welding procedure specification qualification | WPS qualification requirements |
| NB/T 47014 | Qualification of welding procedure specifications for pressure equipment | WPS qualification methodology |
| GB/T 223.01–223.13 | Chemical analysis methods for steel | Overlay composition verification |
| GB/T 231 | Brinell hardness test for metals | Hardness measurement (alternative to Rockwell) |
| GB/T 230.1 | Rockwell hardness test for metals | Surface hardness verification |
| GB/T 11345 | Ultrasonic testing of welds | Overlay internal defect detection |
| GB/T 26951 | Magnetic particle testing of welds | Surface and near-surface defect detection |
| ASTM A516 | Pressure vessel steel plates | Reference for substrate material properties (if applicable) |
| ASME Section IX | Welding, brazing, and fusing qualifications | WPS/PQR qualification framework |
| ISO 15614 | Qualification testing for welding of metallic materials | International WPS qualification standard |
| ISO 9712 | Qualification and certification of NDT personnel | NDT operator qualification |
| ISO 3834 | Quality requirements for fusion-welding of metallic materials | Quality management for welding operations |
| NACE MR0175 | Sulfide stress corrosion resistance (if H₂S environment) | Environmental resistance (if applicable) |
5.2 Acceptance Criteria
The following acceptance criteria shall be applied to overlay welds on tail scraper components:
- Visual inspection (VT) — 100% of overlay surface; no cracks, undercuts exceeding 0.5 mm, excessive spatter, or incomplete fusion visible
- Magnetic particle testing (MT) — 100% of overlay surface; no indications of cracks or linear defects; acceptance per GB/T 26951 Level I or II
- Ultrasonic testing (UT) — 100% of overlay thickness; no indications of laminations, delamination, or volumetric defects; acceptance per GB/T 11345 Level B
- Hardness testing — Minimum 5 test points per overlay area; all readings within specified range (typically 45–62 HRC for high-Cr martensitic alloys); no reading below 45 HRC
- Dilution testing (if required) — Metallographic examination at overlay/substrate interface; dilution shall not exceed 20% for full hardfacing properties
- Dimensional verification — Overlay thickness within ±1 mm of specified nominal thickness; surface flatness within 0.5 mm/m
6. Common Risks and Controls
6.1 Technical Risks
| Risk | Cause | Consequence | Control Measure |
|---|---|---|---|
| Cracking in overlay | High carbon equivalent, excessive restraint, inadequate preheat | Component failure, overlay spalling | Control preheat ≥200°C, limit interpass ≤250°C, select appropriate alloy with lower CE |
| Excessive dilution | High heat input, thin first pass, improper technique | Reduced hardness, loss of wear resistance | Reduce current, increase travel speed, use multi-pass with thinner first pass |
| Porosity | Contaminated substrate, inadequate shielding, wet electrode | Reduced bond strength, early failure | Thorough cleaning, proper gas flow rate, dry electrode storage |
| Delamination | Poor substrate preparation, insufficient penetration, hydrogen embrittlement | Overlay detachment from substrate | Grind to bare metal, verify first-pass penetration, control hydrogen with proper flux |
| Softening of overlay | Excessive interpass temperature, too many passes without cooling | Loss of hardness, accelerated wear | Enforce interpass temperature limits, allow cooling between passes |
| Undercut and irregular profile | Inconsistent technique, improper parameters | Stress concentration, reduced effective thickness | Operator training, parameter standardization, 100% visual inspection |
6.2 Quality Risks
- Non-qualified WPS — Mitigated by requiring qualified welding procedure specifications (WPS) validated through procedure qualification records (PQR) prior to production
- Unqualified welders — Mitigated by maintaining current welder qualification records per GB/T 19866 or ASME Section IX
- Inconsistent consumables — Mitigated by sourcing hardfacing electrodes/wire from approved suppliers with mill test certificates (MTC) and lot traceability
- NDT coverage gaps — Mitigated by documented NDT procedures with defined sampling plans and qualified Level II/III personnel per ISO 9712
6.3 Environmental and Safety Risks
- Fumes and UV radiation — Controlled through adequate ventilation, welding screens, and PPE compliance
- Hot work hazards — Controlled through hot work permits, fire watches, and proper material handling procedures
- Heavy metal exposure — Chromium and nickel fumes require respiratory protection and periodic medical surveillance
7. Application Across Technology Routes
7.1 TIG/MIG Weld Overlay (Primary Route)
This application is the primary domain of the TIG/MIG weld overlay route. The sintering machine tail scraper overlay is a representative case where:
- TIG welding is preferred for repair work, thin sections, and applications requiring precise heat input control and low dilution. It is ideal for on-site field repairs and small-batch component refurbishment.
- MIG welding is preferred for production overlay of new scraper components, thicker deposits, and higher throughput requirements. It offers superior deposition rates (3–5× TIG) while maintaining adequate dilution control.
- Hybrid approaches — TIG for transition layers and first passes, followed by MIG for build-up passes, combining precision with productivity.
7.2 Hydraulic Explosive Bonding
While hydraulic explosive bonding is primarily employed for corrosion-resistant cladding of large structural components (pipes, plates, vessels), it has limited direct application to tail scraper overlay. However, the technology route contributes indirectly by:
- Providing cladded base plates (e.g., Cr-Ni austenitic over carbon steel) that serve as substrate materials for subsequent hardfacing overlay
- Offering a complementary solution for scraper components where both corrosion resistance (at the base) and wear resistance (at the surface) are required
- Demonstrating the company's capability in multi-step surface engineering solutions that combine bonding and overlay technologies
7.3 Explosion Welding
Explosion welding is not typically applied to tail scraper components due to the small size and complex geometry of these parts. However, the technology route is relevant in the following contexts:
- Manufacturing of explosion-welded clad plate from which scraper blanks are fabricated prior to hardfacing overlay
- Providing high-integrity base materials with guaranteed metallurgical bond quality for subsequent overlay operations
- Enabling the production of multi-layer clad substrates (e.g., austenitic/carbon steel) that offer enhanced toughness at the interface for subsequent hardfacing
7.4 Integrated Technology Approach
The optimal solution for sintering machine tail scrapers may combine multiple technology routes in a sequential workflow:
- Step 1: Explosion welding or hydraulic bonding to produce a clad substrate plate with corrosion-resistant inner layer
- Step 2: Machining of clad plate to scraper geometry
- Step 3: TIG/MIG hardfacing overlay of wear-resistant alloy on working surfaces
- Step 4: Final machining and quality verification
This integrated approach maximizes component performance by addressing both wear and corrosion simultaneously, while leveraging the strengths of each technology route.
8. Contribution to Qualification Building, Product Delivery, and Customer Value
8.1 Qualification Building
The documented practice of high-strength wear-resistant alloy weld overlay on sintering machine tail scrapers contributes to the company's qualification portfolio in the following ways:
- WPS/PQR library expansion — Each application generates qualified welding procedure specifications that can be referenced for similar future projects, reducing qualification lead times
- Welder qualification maintenance — Production work on diverse alloys and geometries maintains and expands welder qualification records across multiple positions and processes
- NDT capability validation — Complex overlay inspection requirements validate and develop NDT capabilities for challenging surface engineering applications
- Customer qualification — Successful delivery and field performance documentation establishes the company as a qualified supplier within customer approved vendor lists (AVL)
- Standard compliance demonstration — Systematic adherence to GB/T, NB/T, ASME, and ISO standards demonstrates quality management system maturity to prospective customers and certification bodies
8.2 Product Delivery Enhancement
This capability directly supports product delivery through:
- Accelerated turnaround — In-house overlay capability eliminates outsourcing delays and enables rapid response to customer repair requests
- Customization flexibility — Ability to select from multiple alloy systems and adjust overlay thickness/geometry to specific customer requirements
- Batch and single-piece capability — TIG for single repair pieces, MIG for batch production, providing flexibility in order fulfillment
- On-site and shop-based service — Capability to perform overlay in the workshop or at customer facilities, minimizing logistics costs and downtime
- Traceability and documentation — Complete delivery documentation including MTC, WPS/PQR references, welder IDs, NDT reports, and hardness test certificates
8.3 Customer Value Creation
The technical practice documented in this entry creates measurable customer value:
Case Study Value: A typical iron ore sintering plant operating 2–3 sintering machines with continuous production schedules faces significant economic impact from scraper failures. Each unplanned scraper replacement event results in 8–24 hours of production loss, with associated costs including lost production value (approximately ¥50,000–150,000 per hour depending on plant capacity), emergency logistics, and additional labor. The overlay-enhanced scraper solution reduces replacement frequency by 50–75%, translating to annual savings of ¥300,000–1,200,000 per machine. This represents a return on investment (ROI) exceeding 500% within the first year of adoption.
- Risk reduction — Customers gain confidence in component reliability, reducing operational risk exposure
- Technical partnership — The company positions itself not merely as a processor but as a technical partner providing alloy selection guidance, process optimization, and performance monitoring
- Knowledge transfer — Documentation of practical experience enables customers to make informed decisions about maintenance strategies and component specifications
- Competitive differentiation — Demonstrated field-proven capability distinguishes the company from generic welding service providers in the competitive surface engineering market
9. Conclusion and Forward Outlook
The practice of applying high-strength wear-resistant alloy weld overlay to sintering machine tail scrapers exemplifies the company's core competence in applied surface engineering. This capability, grounded in rigorous metallurgical understanding, disciplined process control, and systematic quality management, delivers substantial economic value to customers in the iron ore processing industry.
Looking forward, the company can leverage this proven practice to expand into adjacent applications including:
- Conveyor roller and idler overlay for mineral processing
- Crusher jaw plate and cone liner hardfacing
- Grinding mill liner overlay
- Slurry pump component refurbishment
- Excavator bucket tooth and cutting edge hardfacing
Each new application builds upon the metallurgical fundamentals, process know-how, and quality infrastructure established through the sintering machine tail scraper practice, creating a compounding qualification and capability advantage that strengthens the company's market position in the industrial wear protection sector.