Weld Overlay and Hot-Rolled High Chromium Iron / Low Carbon Steel Wear-Resistant Composite Plate: Performance Study and Process Analysis
1. Definition and Fundamental Principles
The technology described in this study refers to a hybrid composite plate fabrication method that combines weld overlay (surfacing) deposition of high chromium cast iron (HCCI) onto a low carbon steel substrate, followed by hot rolling to consolidate the interface, refine the microstructure, and achieve a homogeneous, metallurgically bonded wear-resistant composite plate. The resulting product integrates the excellent abrasion resistance of high chromium iron (typically 25–40 wt% Cr) with the formability, weldability, and structural toughness of low carbon steel base plates.
1.1 Metallurgical Mechanism
The process operates on two complementary metallurgical principles:
- Weld Overlay Deposition: A high chromium iron alloy is deposited onto the low carbon steel base plate through a welding process (typically submerged arc welding, gas-shielded arc welding, or electroslag welding). The overlay creates a dilution-controlled transition zone between the base and the wear layer, typically achieving a dilution ratio of 15–30%.
- Hot Rolling Consolidation: After overlay, the composite blank is reheated to a temperature between 850°C and 1050°C and hot rolled to the final thickness. This step homogenizes the microstructure, eliminates residual stresses from the welding process, refines grain size at the interface, and ensures full metallurgical bonding across the entire interface area.
1.2 Microstructural Evolution
The performance of the composite plate is governed by the microstructural characteristics of each zone:
- Wear Layer (High Chromium Iron): Characterized by a matrix of pearlite or martensite with dispersed Cr7C3 and Cr23C6 carbides, providing hardness in the range of HRC 58–65.
- Transition/Dilution Zone: A gradient zone where carbon and chromium content decrease from the wear layer toward the base, typically 0.5–2.0 mm thick. This zone must be carefully controlled to avoid brittle phases or excessive hardness mismatch.
- Base Layer (Low Carbon Steel): Maintains its original ferrite-pearlite microstructure after hot rolling, providing ductility (elongation ≥ 20%) and impact toughness (CVN ≥ 47 J at 20°C).
2. Category and Business Positioning
2.1 Technology Classification
This process falls within the company's Weld Overlay Technology route (TIG/MIG weld overlay category), with an additional hot rolling consolidation step that differentiates it from conventional single-pass or multi-pass surfacing. It represents an advanced variant where the welding process serves as the initial bonding method, and hot rolling serves as the final consolidation and dimensional accuracy step.
2.2 Positioning Within the Company's Product Portfolio
| Dimension | Positioning |
|---|---|
| Technology Route | Weld Overlay (Surfacing-Welding) + Hot Rolling Hybrid |
| Product Category | Wear-Resistant Composite Plate (Hardfacing Composite) |
| Target Market | Heavy industry — mining, cement, power generation, aggregate processing, mining equipment |
| Competitive Advantage | Superior interface integrity vs. explosion welding; lower cost vs. fully cast composite; customizable wear layer composition |
| Value Proposition | Extends service life of wear components by 3–8× compared to monolithic carbon steel; reduces total cost of ownership |
3. Technical Purpose and Value
3.1 Primary Technical Objectives
- Achieve a metallurgically bonded interface with no delamination under cyclic or impact loading
- Control dilution in the transition zone to optimize the hardness-ductility balance
- Produce plates with uniform hardness distribution across the wear layer (±3 HRC variation)
- Ensure the base plate retains adequate formability for downstream bending, machining, and welding operations
- Achieve dimensional accuracy suitable for direct fabrication into components (flatness ≤ 1.5 mm/m)
3.2 Quantified Performance Targets
| Property | Wear Layer (HCCI) | Base Layer (Low Carbon Steel) | Interface Bond Strength |
|---|---|---|---|
| Hardness | HRC 58–65 (HBW 650–700) | HBW 120–160 | — |
| Tensile Strength | — | ≥ 420 MPa | — |
| Impact Energy (20°C) | — | ≥ 47 J (Charpy V-notch) | — |
| Abrasion Resistance | 3–8× that of Q235/Q345 steel | Baseline | — |
| Interface Peel Strength | — | — | ≥ 15 MPa (ASTM A780) |
| Wear Layer Thickness | 3–15 mm (typical) | 6–50 mm | — |
3.3 Contribution to Qualification Building
This research study directly supports the company's qualification development in the following areas:
- WPS/PQR Qualification: Establishes validated welding procedure specifications for HCCI overlay on low carbon steel substrates, providing data for qualification under NB/T 47014, ASME IX, or AWS D10.9.
- Process Capability Documentation: Generates the technical evidence required for customer audits and supplier qualification programs in mining and heavy industry.
- Standard Development Input: Provides experimental data that can contribute to industry standards for weld-overlay composite plates.
4. Key Process and Implementation Points
4.1 Process Flow Overview
- Base Plate Preparation: Cut low carbon steel plate (Q235, Q345, or equivalent) to required dimensions; surface preparation to SA 2.5 minimum (GB/T 8923.1) or equivalent grit-blasted finish.
- Pre-heat Application: Apply localized or full pre-heat at 150–250°C to reduce thermal gradient and minimize cracking risk at the interface.
- Weld Overlay Deposition: Deposit HCCI alloy using submerged arc welding (SAW), gas metal arc welding (GMAW/MIG), or electroslag welding (ESW). Multi-pass deposition is used for thicknesses > 5 mm.
- Post-Weld Heat Treatment (PWHT): Stress relief at 550–650°C for 2 hours per 25 mm of thickness to reduce residual stresses and temper the overlay microstructure.
- Hot Rolling Consolidation: Reheat the composite blank to 900–1050°C; roll to final thickness in 2–4 passes with controlled reduction per pass (≤ 25%).
- Final Inspection and Testing: Dimensional verification, hardness profiling, NDT, and mechanical testing per applicable standards.
4.2 Critical Process Parameters
| Process Step | Parameter | Recommended Range | Critical Control |
|---|---|---|---|
| Base Plate Pre-heat | Temperature | 150–250°C | Prevents cracking in high-carbon overlay |
| Weld Overlay (SAW) | Current / Voltage | 500–800 A / 28–36 V | Controls penetration and dilution |
| Weld Overlay (SAW) | Travel Speed | 150–300 mm/min | Affects bead profile and dilution ratio |
| Weld Overlay (SAW) | Flux Composition | Basic or agglomerated flux | Controls slag properties and gas shielding |
| Weld Overlay (MIG) | Wire Feed Speed | 6–12 m/min | Controls deposition rate |
| Weld Overlay (MIG) | Shielding Gas | Ar 98% + CO₂ 2% or Ar 95% + CO₂ 5% | Prevents oxidation and porosity |
| PWHT | Temperature / Hold Time | 550–650°C / 2 h per 25 mm | Reduces residual stress to < 50 MPa |
| Hot Rolling | Reheat Temperature | 900–1050°C | Austenitization for grain refinement |
| Hot Rolling | Reduction per Pass | ≤ 25% | Prevents folding and segregation |
| Hot Rolling | Coil/Final Temperature | 600–750°C | Controls final microstructure |
4.3 Dilution Control Strategy
Dilution is the single most critical parameter governing composite plate performance. The following strategies are employed:
- Multi-Pass Deposition: The first pass (root pass) typically achieves 30–40% dilution; subsequent passes reduce cumulative dilution to 15–25%.
- Reduced Penetration Parameters: Using lower current density, higher travel speed, or narrower groove geometry to minimize base metal melting.
- Backing Strip: Use of a consumable or reusable backing to limit root penetration.
- Hot Rolling Effect: The subsequent hot rolling step further homogenizes the dilution zone, reducing the effective dilution zone thickness from 2–3 mm to 0.5–1.5 mm through plastic deformation and recrystallization.
4.4 Material Selection for Overlay
| HCCI Grade | Cr Content (wt%) | C Content (wt%) | Hardness (HRC) | Application |
|---|---|---|---|---|
| High Chromium Iron Type I | 25–30 | 2.5–3.5 | 58–62 | General abrasion (mining, cement) |
| High Chromium Iron Type II | 30–35 | 2.5–3.5 | 62–65 | Severe abrasion + moderate impact |
| High Chromium Iron Type III | 35–40 | 2.0–3.0 | 63–66 | Extreme abrasion + corrosion resistance |
5. Applicable Standards and Acceptance Criteria
5.1 Manufacturing and Material Standards
- GB/T 8490 — Wear-resistant cast iron (reference for HCCI composition)
- GB/T 1591 — Low carbon steel base plate (Q345 series)
- GB/T 3274 — Carbon structural steel (Q235 series)
- ASTM A105 / ASTM A36 — Carbon steel equivalents for export markets
- ASTM A780 — Standard for clad plate (interface bond testing methodology)
- ASTM A516 / ASTM A515 — Pressure vessel steel equivalents
- ISO 3369 — Billet and plate for pressure vessels (reference)
5.2 Welding Procedure and Qualification Standards
- NB/T 47014 — Qualification of welding procedures for pressure equipment (China)
- ASME Section IX — Qualification rules for welding, brazing, and fusion bonding (USA)
- AWS D10.9 — Specification for welding procedure and performance qualification for wear-resistant surfacing
- ISO 15614-1 — Qualification testing of welding procedures for metallic materials (arc welding)
- ISO 14732 — Arc welding — Welding procedure qualification
- GB/T 19866 — Welding procedure qualification for steel
5.3 Non-Destructive Testing Standards
- GB/T 11345 — Ultrasonic testing of welds (equivalent to ISO 17635)
- GB/T 3323 — Radiographic testing of welds (equivalent to ISO 17636-1)
- GB/T 15055 — Magnetic particle testing (equivalent to ISO 9934)
- ASTM E165 — Magnetic particle examination
- ASTM E2312 — Eddy current examination
- ASTM A780 — Peel test for interface bond strength verification
5.4 Mechanical Testing and Acceptance Criteria
| Test | Standard | Acceptance Criteria |
|---|---|---|
| Hardness (Wear Layer) | ASTM E18 / GB/T 231.1 | HRC 58–65, uniformity ±3 HRC |
| Hardness (Base Layer) | ASTM E18 / GB/T 231.1 | HBW 120–160 (Q235) or HBW 140–200 (Q345) |
| Tensile Test (Base) | ASTM A370 / GB/T 228.1 | UTS ≥ 420 MPa (Q345), ≥ 375 MPa (Q235) |
| Charpy Impact (Base) | ASTM E23 / GB/T 229 | ≥ 47 J at 20°C, ≥ 34 J at -20°C |
| Peel Test (Interface) | ASTM A780 / GB/T 13143 | ≥ 15 MPa peel strength |
| Hardness Gradient | ASTM A780 | No abrupt transition; gradient zone ≤ 2 mm |
| Flatness | GB/T 3260 / ASTM A6 | ≤ 1.5 mm per meter length |
| UT Inspection | GB/T 11345 / ISO 17635 | No indications exceeding Level II per acceptance level B |
6. Common Risks and Controls
6.1 Technical Risks
| Risk | Cause | Consequence | Control Measure |
|---|---|---|---|
| Cracking in Overlay | High carbon + high Cr; rapid cooling; hydrogen embrittlement | Loss of wear layer integrity; product rejection | Pre-heat 150–250°C; post-weld heat treatment; low-hydrogen flux/wire; limit interpass temperature |
| Excessive Dilution | High current; low travel speed; deep penetration | Reduced hardness in wear layer; loss of abrasion resistance | Multi-pass strategy; reduced penetration parameters; backing strip; monitor dilution via hardness profiling |
| Interface Delamination | Incomplete melting at interface; oxide inclusions; residual stress | Peel failure; catastrophic in service | Adequate pre-heat; clean surface preparation; hot rolling consolidation; PWHT stress relief |
| Porosity in Overlay | Absorbed gas (H₂, N₂, O₂); flux moisture; poor shielding | Reduced density; stress concentration | Dry flux storage; adequate gas shielding; proper wire feed parameters |
| Hot Rolling Folding | Excessive reduction per pass; low rolling temperature | Internal defects; thickness non-uniformity | Limit reduction ≤ 25% per pass; maintain rolling temperature > 850°C |
| Hardness Non-Uniformity | Uneven cooling; compositional segregation; rolling inhomogeneity | Variable wear performance across plate | Controlled cooling rate; uniform overlay thickness; verify via grid hardness mapping |
6.2 Quality Control Measures
- In-Process Monitoring: Real-time monitoring of welding parameters (current, voltage, travel speed, wire feed speed) with automated data logging.
- Interpass Inspection: Visual and magnetic particle inspection of each weld pass before continuing deposition.
- Hardness Mapping: Grid-pattern hardness testing (minimum 10 points per 1000 mm²) across the wear layer and transition zone.
- Sectional Metallography: Periodic cross-sectional examination to verify interface integrity, dilution zone thickness, and absence of defects.
- Hot Rolling Parameter Control: Continuous temperature monitoring with thermocouples; automated roll force feedback to detect anomalies.
7. Application Scenarios Across the Company's Technology Routes
7.1 TIG/MIG Weld Overlay Route
The weld overlay-hot rolling process studied here represents the core technology of the company's weld overlay route. Specific application scenarios include:
- Mining Equipment Liners: Chute linings, conveyor troughs, and hopper walls where high chromium iron overlay provides 3–5× life extension over plain carbon steel.
- Cement Industry: Mill liners, cyclone liners, and transfer chutes subject to abrasive slurry wear.
- Aggregate Processing: Crusher hammers, screens, and conveyor belts where impact-abrasion is dominant.
- Custom Fabricated Components: Where plate thickness, geometry, or size exceeds the range available through explosion welding or hydraulic bonding.
Advantage of Weld Overlay Route: Unlimited plate size and thickness; fully customizable overlay composition; ability to produce complex geometries through post-fabrication welding and machining.
7.2 Hydraulic Explosive Bonding Route
While the studied process uses weld overlay as the primary bonding method, the company's hydraulic explosive bonding route offers complementary capabilities:
- Complementary Application: Hydraulic explosive bonding is preferred for very large plates (> 3000 mm × 1500 mm) where weld overlay would be time-prohibitive and residual stress management becomes challenging.
- Material Compatibility: Hydraulic bonding achieves a cold-welded interface with zero dilution, which is advantageous when the base material must maintain its full mechanical properties without any heat-affected zone.
- Process Selection Criteria: Weld overlay + hot rolling is preferred for HCCI/carbon steel combinations due to the excellent metallurgical compatibility and the ability to customize the dilution zone for optimal performance.
7.3 Explosion Welding Route
The explosion welding route provides additional capability for the company's composite plate portfolio:
- High Dilution Sensitivity Applications: When zero dilution is required (e.g., nickel-based or cobalt-based overlay layers), explosion welding provides a dilution-free interface.
- Large Format Production: Explosion welding can produce plates up to 6000 mm × 2500 mm in single shots, suitable for bulk production of standard wear plate sizes.
- Performance Comparison: The weld overlay + hot rolling process studied here offers superior interface toughness (due to the metallurgical bond through the dilution zone) compared to the mechanical interlocking bond of explosion welding, making it more suitable for applications involving cyclic loading and thermal cycling.
7.4 Route Selection Decision Matrix
| Selection Criteria | Weld Overlay + Hot Rolling | Hydraulic Explosive Bonding | Explosion Welding |
|---|---|---|---|
| Maximum Plate Size | Unlimited (limited by welding setup) | 3000 × 1500 mm typical | 6000 × 2500 mm |
| Dilution Control | 15–30% (adjustable) | Zero | Zero |
| Interface Type | Metallurgical (diffusion bond) | Mechanical interlock + partial metallurgical | Mechanical interlock (jet pattern) |
| Overlay Thickness Range | 1–25 mm | 2–15 mm | 1–12 mm |
| Material Flexibility | High (any weldable overlay) | Medium (compatible material pairs) | Medium (compatible material pairs) |
| Production Speed | Slow (welding time dependent) | Fast (minutes per plate) | Fast (seconds per shot) |
| Cost (per m²) | Medium | Medium-High | Medium |
| Residual Stress | High (requires PWHT) | Moderate | Low-Moderate |
8. Contribution to Customer Value and Product Delivery
8.1 Quantified Customer Benefits
- Extended Service Life: 3–8× life extension over monolithic carbon steel in abrasive service environments, reducing replacement frequency and downtime.
- Weight Reduction: Composite plate allows thinner total section compared to solid wear-resistant material, reducing structural weight by 20–40%.
- Cost Savings: 30–50% reduction in total cost of ownership when considering material cost, fabrication time, and maintenance intervals.
- Customizability: Ability to tailor overlay composition (Cr%, C%, Mo%, Ni%) to specific wear mechanisms (abrasive, erosive, corrosive-abrasive).
8.2 Quality Assurance Framework
The research study provides the technical foundation for a comprehensive quality assurance framework:
- Material Certification: Full chemical analysis and mechanical testing of both base plate and overlay wire/rod per mill certificates and third-party verification.
- WPS/PQR Documentation: Qualified welding procedures with full parameter ranges, essential variables, and performance qualification test results.
- In-Process Quality Control: Parameter logging, interpass NDT, and hardness verification at defined intervals.
- Final Product Certification: Complete test report package including hardness map, mechanical test results, NDT reports, and dimensional inspection records.
- Traceability: Batch traceability from raw material through to finished product, enabling root cause analysis and quality improvement.
8.3 Standards Compliance for Market Access
- Domestic Market (China): Compliance with GB/T 13143 (clad plate), NB/T 47014 (welding qualification), and relevant industry specifications (MT/T for mining, JB/T for machinery).
- International Market: Compliance with ASTM A780, AWS D10.9, and ASME Section IX for welding qualification; EN 10133 for clad plate requirements in European markets.
- Pressure Vessel Applications: Additional compliance with ASME Section II-D material specifications and Section VIII fabrication requirements where composite plates are used in pressure-containing equipment.
9. Conclusion and Forward-Looking Development
The weld overlay combined with hot rolling process for high chromium iron / low carbon steel wear-resistant composite plate represents a mature, well-understood technology that bridges the gap between monolithic wear-resistant materials and explosion-welded composite plates. Its strengths lie in flexibility of production parameters, unlimited plate sizing, and the ability to engineer the interface through dilution control.
Key areas for continued development include:
- Automation of the welding overlay process to improve productivity and consistency
- Development of advanced HCCI compositions with improved impact resistance (addition of Mo, Ni, Nb)
- Integration of in-situ monitoring systems (thermal imaging, acoustic emission) for real-time defect detection
- Extension of the process to functionally graded materials with multiple overlay layers for multi-mechanism wear environments
- Digital twin development for process optimization and predictive quality assurance
This technology study provides the scientific foundation and process knowledge necessary for the company to deliver high-quality, certified wear-resistant composite plates that meet the demanding requirements of mining, cement, power generation, and heavy industry customers worldwide.