Microstructure and Performance Analysis of Wear-Resistant Weld Overlay on Q235 Carbon Steel Plates
1. Definition and Fundamental Principles
Wear-resistant weld overlay on Q235 carbon steel plates refers to the metallurgical bonding of a high-hardness, abrasion-resistant alloy layer onto the surface of low-carbon structural steel (Q235, equivalent to ASTM A36/EN S235JR) through controlled arc welding processes. The objective is to create a composite structure that retains the toughness and formability of the base metal substrate while providing a surface layer capable of withstanding severe abrasive, erosive, and adhesive wear conditions.
The fundamental metallurgical principles governing this technology include:
- Dilution Control: The degree of base metal dilution into the overlay layer directly determines the final hardness and microstructure. Q235 steel, containing approximately 0.14–0.22% carbon, introduces soft ferrite and pearlite into the melt pool, which must be minimized through multi-pass strategies.
- Microstructural Engineering: The wear resistance of the overlay is governed by the formation of hard phases such as martensite (B' or B''), ledeburite (Fe₃C + austenite), chromium carbides (Cr₇C₃, Cr₂₃C₆), and boron carbides (B₄C, B₆C), depending on the alloy system selected.
- Thermal Cycling Effects: Each subsequent pass acts as a tempering cycle for the previous pass. This must be accounted for in multi-pass overlay designs to achieve the target hardness in the final surface layer.
- Residual Stress Management: The coefficient of thermal expansion mismatch between the overlay and Q235 substrate generates significant residual stresses that can lead to cracking, delamination, or premature failure.
2. Category and Business Positioning
Within the operational framework of Cladding Technology Shanxi Co., Ltd., this capability falls squarely under the TIG/MIG Weld Overlay Technology Route, specifically addressing surface hardening and wear protection applications. The study of Q235 steel plate wear overlay microstructure and performance serves as a foundational qualification and process development activity that underpins the company's ability to deliver certified, repeatable weld overlay solutions.
The business positioning of this capability encompasses:
- Process Qualification Base: Establishing documented microstructure-property relationships enables the company to develop and qualify Welding Procedure Specifications (WPS) that meet customer and regulatory requirements.
- Product Value Enhancement: Converting inexpensive Q235 structural steel into wear-resistant components extends service life by 3–10× compared to bare carbon steel, delivering significant cost savings to end users in mining, cement, power generation, and material handling industries.
- Technical Differentiation: Demonstrated expertise in overlay metallurgy, particularly dilution control and microstructure optimization, positions the company as a specialist provider rather than a commodity welder.
3. Technical Purpose and Value
3.1 Primary Technical Objectives
The research and application of wear-resistant weld overlay on Q235 steel plates aims to achieve the following measurable objectives:
- Achieve surface hardness of ≥500 HV (typically 500–700 HV depending on alloy system) in the final overlay pass
- Maintain interfacial bonding strength exceeding 400 MPa (tensile test per ASTM A253 or equivalent)
- Ensure crack-free overlay with acceptable dilution levels (<15% for high-alloy systems, <30% for medium-alloy systems)
- Produce overlay layers with uniform microstructure and hardness distribution across the full deposition width
3.2 Value Chain Contribution
From a customer value perspective, this capability enables:
- Extended Equipment Life: Components such as chutes, hoppers, screens, and wear plates fabricated from Q235 steel with wear overlay can last 3–10 times longer than uncladded equivalents
- Reduced Maintenance Downtime: Longer service intervals between component replacement reduce unplanned shutdowns
- Lower Total Cost of Ownership: Despite higher initial fabrication cost, the lifecycle cost is significantly reduced due to fewer replacements
- Design Flexibility: Engineers can use readily available, low-cost Q235 steel for structural requirements and apply wear protection only where needed, avoiding expensive all-alloy designs
4. Key Process and Implementation Points
4.1 Alloy System Selection
The choice of overlay alloy system is critical and depends on the wear mechanism and service conditions:
| Alloy System | Typical Hardness (HV) | Key Hard Phases | Wear Mechanism Resistance | Representative Standards |
|---|---|---|---|---|
| High Carbon Martensite (HRC 50–55) | 480–620 | Tempered martensite + carbides | Sliding/abrasive wear | GB/T 12469, ASTM A220 |
| High Carbon High Chromium (HRC 55–60) | 600–750 | Cr₇C₃, Cr₂₃C₆ + martensite | Abrasive + corrosive wear | GB/T 12469, AWS A5.29 |
| Leadedurite (High Carbon + Chromium) | 550–700 | Ledeburite + austenite | Severe impact + abrasion | GB/T 12469, ISO 12170 |
| Boron Carbide Reinforced | 800–1200 | B₄C, B₆C particles | Highly abrasive materials | GB/T 12469 |
| Tungsten Carbide Reinforced | 1000–1500 | WC particles in matrix | Severe abrasion + impact | GB/T 12469, AWS A5.29 |
4.2 Welding Process Parameters
For TIG (GTAW) weld overlay on Q235 plates, the following parameter ranges are typical for achieving optimal microstructure and bonding:
| Parameter | Transition Pass | Overlay Pass 1 | Overlay Pass 2 (Final) |
|---|---|---|---|
| Process | TIG (GTAW) | TIG (GTAW) | TIG (GTAW) |
| Current (A) | 120–160 | 140–180 | 130–170 |
| Voltage (V) | 10–13 | 11–14 | 11–14 |
| Travel Speed (mm/min) | 150–250 | 180–300 | 150–250 |
| Shielding Gas | Argon (99.99%) | Argon (99.99%) | Argon (99.99%) |
| Filler Wire Ø (mm) | 2.0–2.5 | 2.0–2.5 | 2.0–2.5 |
| Interpass Temperature (°C) | ≤150 | ≤150 | ≤150 |
| Preheat (°C) | 100–150 | — | — |
4.3 Multi-Pass Overlay Strategy
The multi-pass approach is essential for managing dilution and achieving target hardness:
- Preparation: Surface preparation per GB/T 8923.1 Sa 2.5 (near-white metal blast cleaning); edge beveling at 30°–45° to ensure full penetration and metallurgical bond
- Preheating: Apply uniform preheat of 100–150°C to Q235 substrate to reduce thermal gradient and minimize cracking risk; maintain throughout welding
- Transition Pass: Deposit a compatible filler (e.g., E309L or E310L per AWS A5.4) to create a dilution buffer between Q235 and the final overlay alloy. This pass typically has 30–50% dilution, which is acceptable as it serves as a bonding layer.
- Overlay Passes: Deposit 2–3 passes of the selected wear-resistant alloy. The first overlay pass may have 10–20% dilution; subsequent passes progressively reduce dilution as the previous pass becomes the substrate. The final pass should exhibit <10% dilution for high-alloy systems.
- Post-Weld Heat Treatment (PWHT): For high-carbon martensitic systems, apply tempering at 400–550°C for 2 hours to reduce residual stress and improve toughness without significantly reducing hardness. For ledeburitic systems, solution treatment at 1050–1150°C followed by controlled cooling may be required.
- Peening/Stress Relief: Mechanical peening of the final overlay surface can introduce compressive residual stresses that improve fatigue and wear resistance.
4.4 Microstructure Control Factors
The resulting microstructure of the wear-resistant overlay is governed by the following factors that must be controlled during fabrication:
- Cooling Rate: Controlled by travel speed, heat input, and interpass temperature. Faster cooling promotes martensitic transformation; slower cooling allows carbide precipitation and spheroidization.
- Carbon Equivalency of Dilution: Q235 dilution introduces low-carbon ferrite, reducing overall carbon content in the overlay. This must be compensated through alloy selection or additional overlay passes.
- Cr/C Ratio: Determines whether carbides form as chromium-rich (Cr₇C₃, Cr₂₃C₆) or iron-rich (Fe₃C) phases, significantly affecting hardness and fracture toughness.
- Grain Size: Fine grain microstructure (achieved through rapid cooling or grain refiners) enhances both hardness and toughness simultaneously.
5. Applicable Standards and Acceptance Criteria
5.1 Welding Procedure and Qualification Standards
| Standard | Scope | Relevance to Q235 Wear Overlay |
|---|---|---|
| GB/T 985.1 | Welding procedure qualification test methods | WPS qualification testing methodology |
| GB/T 985.2 | Welding procedure qualification requirements | Qualification requirements for overlay welding |
| GB/T 986.1 | Welder qualification test methods | Welder performance qualification |
| NB/T 47014 | Welding procedure qualification (pressure vessels) | Required for pressure vessel overlay applications |
| ASME Section IX | Welding, Brazing, and Fusing Qualifications | WPS/PQR qualification per QW-400 series for overlay |
| ISO 15614-1 | Welding procedure qualification for fusion welding | International procedure qualification |
| ISO 9606-1 | Welder qualification test for arc welding | Welder certification requirements |
5.2 Material and Performance Standards
| Standard | Scope | Key Requirements |
|---|---|---|
| GB/T 12469 | Welding consumables for hardfacing | Filler metal classification and performance requirements |
| GB/T 700-2006 | Hot rolled steel plates for general use | Q235 base material specification |
| ASTM A220 | Castings, carbon and alloy steel for pressure parts | Reference for overlay alloy chemistry |
| AWS A5.29/A5.29M | Specification for hard-facing electrodes and rods | US standard for hardfacing consumables |
| ISO 12170 | Welding consumables – Hardfacing deposits | International hardfacing consumable specification |
| NACE MR0175/ISO 15156 | Materials for H₂S-containing environments | Applicable when overlay is in sour service |
5.3 Acceptance Criteria
- Visual Inspection (VT): No cracks, porosity >0.5 mm, undercut >1 mm, or excessive spatter. Conformity to GB/T 3323 or ISO 17637.
- Magnetic Particle Testing (MT): Per GB/T 26951 or ISO 17638; no linear indications >2 mm in the overlay or interface region.
- Hardness Testing: Vickers hardness per GB/T 4340.1 or ASTM E92; minimum hardness as specified in WPS (typically ≥500 HV for high-carbon systems); hardness uniformity within ±50 HV across the overlay surface.
- Microstructural Examination: Metallographic analysis per GB/T 13298 or ASTM E3; confirmation of expected hard phases; no excessive carbide network at grain boundaries (per ASTM E1264 intergranular carbide rating).
- Interface Bond Strength: Tensile test per ASTM A253 or GB/T 2651; minimum interface strength of 400 MPa or as specified in the applicable code.
- Impact Testing: Charpy V-notch per GB/T 229 or ASTM E23; minimum absorbed energy as specified (typically ≥27 J at service temperature for ductile overlay systems).
- Wear Testing: Pin-on-disc or dry sand rub test per GB/T 12444 or ASTM G99; wear rate compared to reference material.
- Chemical Analysis: Dilution measurement by optical emission spectroscopy (OES) or ICP; confirmation of dilution within acceptable limits per WPS.
6. Common Risks and Controls
| Risk | Cause | Detection Method | Control Measures |
|---|---|---|---|
| Cracking at Overlay/Substrate Interface | High carbon equivalent, excessive thermal stress, hydrogen embrittlement | MT, visual inspection, macro-etch | Preheat Q235 to 100–150°C; use low-hydrogen filler; control heat input; transition layer with austenitic filler |
| Overlay Cracking (Hot Cracks) | Liquid metal embrittlement, sulfur/phosphor segregation, excessive dilution | MT, macro-etch | Control dilution <15%; use high-Cr alloys with restricted solidification range; limit interpass temp |
| Insufficient Hardness | Excessive Q235 dilution, inadequate alloy content, improper cooling rate | Hardness testing | Multi-pass strategy; dedicated transition layer; verify filler chemistry; control heat input |
| Poor Adhesion/Delamination | Incomplete fusion, surface contamination, improper bevel preparation | Tensile test, ultrasonic testing | Sa 2.5 surface prep; full penetration welds; verify bevel geometry; adequate heat input for fusion |
| Excessive Residual Stress | High thermal gradient, constrained geometry | X-ray stress analysis, strain gauges | Preheat; controlled welding sequence; post-weld stress relief; peening |
| Porosity in Overlay | Contaminated filler, inadequate shielding, wet flux | RT, UT, visual | Dry storage of filler; proper gas flow; clean surfaces; pre-dry flux |
| Hardness Non-uniformity | Inconsistent heat input, varying dilution across width | Hardness traverse mapping | Stable welding parameters; consistent travel speed; automated welding where possible |
7. Application Scenarios Across Technology Routes
7.1 TIG/MIG Weld Overlay Route (Primary Application)
The Q235 wear overlay capability is the core technology under the TIG/MIG weld overlay route. Specific applications include:
- Mining Industry: Chutes, hoppers, and discharge pipes handling abrasive ore and tailings; wear plates for excavator buckets and conveyor rollers
- Cement Industry: Crusher hammers, mill liners, fan blades, and cyclone linings exposed to highly abrasive cement slurry
- Power Generation: Boiler burner components, ash handling chutes, and fan impellers subject to erosive fly ash
- Material Handling: Conveyor belt scrapers, transfer points, and structural wear plates in bulk material handling systems
- Marine Industry: Propeller blades, shafts, and hull components in high-corrosion/high-wear environments
For TIG overlay specifically, the lower heat input and precise control make it ideal for thin overlay layers (1–3 mm), repair applications on existing components, and situations requiring excellent microstructural control. MIG (GMAW) overlay is preferred for thicker deposits (3–10 mm) and higher production rates on large plate areas.
7.2 Hydraulic Explosive Bonding Route (Complementary Application)
While hydraulic explosive bonding (hydroforming with explosive cladding) is primarily used for through-thickness cladding where a continuous metallurgical bond across the full plate thickness is required, the Q235 wear overlay research provides valuable input in the following ways:
- Hybrid Cladding Design: In applications requiring both corrosion resistance (through-thickness cladding) and surface wear resistance (overlay), hydraulic explosive bonding can be used to clad Q235 with a corrosion-resistant alloy (e.g., 304L, 316L), followed by TIG wear overlay on the cladding surface. The microstructure research informs the transition layer design between the explosive-bonded layer and the final wear overlay.
- Substrate Qualification: Understanding Q235 behavior under welding thermal cycles is essential when applying weld overlay to previously explosively bonded components, ensuring the interface integrity is maintained.
- Repair and Maintenance: Components initially fabricated with explosive bonding may require localized wear repair through TIG overlay during maintenance. The research supports the development of qualified repair procedures.
7.3 Explosion Welding Route (Supporting Application)
Explosion welding produces through-thickness clad plates through high-velocity impact bonding. The relationship to Q235 wear overlay research includes:
- Post-Explosion Welding Overlay: Explosion-welded clad plates (e.g., 304L/Q235 or 316L/Q235) may subsequently receive a wear-resistant TIG overlay on the cladding surface for applications requiring both corrosion and wear resistance. The Q235 overlay research provides the metallurgical foundation for designing these multi-layer composite structures.
- WPS Development for Exp-Welded Substrates: The microstructure-property relationships established through Q235 overlay research directly inform the development of welding procedures for overlaying onto explosion-welded substrates, where the interface microstructure and residual stress state differ from virgin Q235.
- Qualification Transferability: Understanding the dilution behavior and microstructural evolution of Q235 under welding thermal cycles supports the qualification of overlay procedures on explosion-welded substrates, as the base metal behavior is well-characterized.
8. Contribution to Qualification Building and Product Delivery
8.1 Qualification Building
The systematic study of Q235 wear overlay microstructure and performance directly contributes to the company's qualification portfolio in the following ways:
- WPS/PQR Database: Each qualified overlay procedure on Q235 adds to the company's library of qualified procedures, reducing future qualification costs and accelerating project timelines.
- Material Coverage: Q235 is the most widely used structural steel in Chinese manufacturing. Having qualified overlay procedures on this material maximizes the applicability of the company's capabilities across customer industries.
- Performance Documentation: Documented hardness profiles, microstructural data, dilution measurements, and mechanical test results provide the technical evidence required for customer audits and project qualification submissions.
- Welder Qualification: The research supports the development of welder performance qualification procedures that demonstrate the company's workforce capability.
8.2 Product Delivery Enhancement
- Repeatable Quality: Understanding the microstructure-property relationships enables the company to predict and control overlay performance, ensuring consistent product quality across production batches.
- Optimized Process Parameters: Research findings translate directly into optimized welding parameters that balance productivity, quality, and consumable cost.
- Reduced Rework: Knowledge of failure modes (cracking, porosity, insufficient hardness) enables proactive prevention through process controls, reducing scrap and rework rates.
- Customer Confidence: Detailed metallurgical documentation and test reports demonstrate technical competence and provide customers with the data needed for their own design and qualification activities.
8.3 Customer Value Proposition
"By combining the structural economy of Q235 carbon steel with expertly engineered wear-resistant overlay layers, Cladding Technology Shanxi delivers composite components that achieve 3–10× the service life of bare carbon steel at a fraction of the cost of all-alloy alternatives. Our documented microstructural expertise ensures that every overlay delivers predictable, verified performance in the most demanding abrasive service environments."
9. Conclusion
The systematic investigation of wear-resistant weld overlay microstructure and performance on Q235 carbon steel plates represents a fundamental technical capability that underpins the company's TIG/MIG weld overlay business. This research-driven approach to overlay metallurgy enables the company to:
- Develop and qualify welding procedures that meet the requirements of GB, NB, ASME, ISO, and AWS standards
- Deliver consistently high-quality wear-resistant components with documented performance
- Provide technical support and metallurgical expertise that differentiates the company from commodity welding service providers
- Integrate overlay capabilities with hydraulic explosive bonding and explosion welding routes for comprehensive cladding solutions
The investment in fundamental metallurgical understanding of Q235 wear overlay translates directly into accelerated project delivery, reduced technical risk, and enhanced customer confidence—key competitive advantages in the industrial cladding and surface engineering market.