Wear Resistance of Hard Alloy Weld Overlay Deposits After Post-Weld Heat Treatment

1. Definition and Fundamental Principles

Hard alloy weld overlay refers to the deposition of ceramic-metallic composite materials—typically tungsten carbide (WC), chromium carbide (Cr₃C), titanium carbide (TiC), or silicon carbide (SiC) particles embedded in a metallic binder matrix—onto a base substrate through arc welding processes. The post-weld heat treatment (PWHT) of these overlay deposits is a critical metallurgical operation designed to relieve residual stresses, modify carbide morphology, reduce porosity, and optimize the hardness-wear-resistance relationship of the deposited layer.

The wear resistance of hard alloy overlay deposits is governed by several interdependent mechanisms:

Carbide hardness and volume fraction: The intrinsic Vickers hardness of discrete carbide particles (e.g., WC at ~2300 HV, Cr₃C at ~1300 HV) combined with their volumetric distribution determines abrasive resistance.
Binder matrix properties: The toughness and ductility of the metallic binder (commonly martensitic, austenitic, or precipitation-hardened) govern resistance to impact and fatigue wear.
Carbide morphology and distribution: Post-weld heat treatment can coarsen or refine carbide particles, dissolve and re-precipitate carbides, and modify the WC-to-η-phase (Fe₂W₄C) transformation ratio, which directly influences wear performance.
Residual stress state: Compressive residual stresses introduced or modified by heat treatment improve fatigue life and spalling resistance.
Interface bonding quality: The metallurgical bond between the overlay deposit and the transition/base metal is critical for load transfer and delamination resistance.

2. Category and Business Positioning

This technical capability falls within the TIG/MIG weld overlay route of Cladding Technology Shanxi Co., Ltd., specifically addressing the metallurgical qualification and process optimization of hardfacing overlay systems. The research into wear resistance after heat treatment bridges the gap between welding process execution and final product performance verification.

Within the company's three primary technology routes:

TIG/MIG Weld Overlay: This entry directly supports the development and qualification of hard alloy overlay WPS (Welding Procedure Specifications) where post-weld heat treatment is a mandatory or recommended step. It informs the selection of PWHT cycles, soak temperatures, and cooling rates that maximize wear performance while maintaining deposit integrity.
Hydraulic Explosive Bonding: While not directly applicable to explosive bonding interfaces, the metallurgical knowledge gained from studying heat-treated hard alloy overlays informs the design of hybrid clad plates where explosively bonded substrates receive subsequent weld overlay hardfacing with PWHT.
Explosion Welding: Similarly, the wear resistance data and heat treatment protocols derived from this research support the development of composite wear parts where explosively bonded components are subsequently hardfaced and heat treated as a multi-step manufacturing sequence.

3. Technical Purpose and Value

The primary purpose of studying the wear resistance of hard alloy weld overlay deposits after heat treatment is to establish a scientifically validated relationship between PWHT parameters and tribological performance. This enables the following value contributions:

Process qualification: Establishing documented PWHT cycles that produce repeatable, qualified wear resistance levels for specific hard alloy systems (e.g., WC-Co, Cr₃C-NiCr, TiC-NiCr).
Product specification: Providing quantifiable wear resistance data (abrasion volume loss in mm³/N·m, or cycles in pin-on-disk tests) that can be specified in customer purchase orders and acceptance criteria.
Risk mitigation: Identifying the detrimental effects of improper heat treatment—such as WC decomposition into η-phase at excessive temperatures, carbide coarsening, or cracking—allowing proactive process controls.
Competitive differentiation: Demonstrating technical depth in metallurgical optimization beyond simple welding execution, positioning the company as a full-service cladding and overlay provider capable of delivering performance-qualified products.

4. Key Process and Implementation Points

4.1 Hard Alloy Overlay Deposition

Hard alloy overlay deposits are typically applied using submerged arc welding (SAW), gas-shielded metal arc welding (GMAW/MIG), or gas tungsten arc welding (GTAW/TIG), depending on the required layer thickness and geometry. The hard alloy powder is either fed as a consumable (SAW) or pre-placed as a powder layer on the substrate prior to welding (MIG/TIG with powder pre-placing).

Parameter	WC-Co System	Cr₃C-NiCr System	TiC-NiCr System
Typical Deposit Hardness (as-welded)	HRC 65–72	HRC 60–68	HRC 58–65
Carbide Volume Fraction	50–70%	55–75%	50–65%
Maximum PWHT Temperature	950°C (limit for WC stability)	1050–1150°C	1000–1100°C
Recommended Soak Time	1–2 hours per 25 mm thickness	2–4 hours per 25 mm thickness	2–3 hours per 25 mm thickness
Cooling Method	Furnace cool to 500°C, then air cool	Furnace cool to 600°C, then air cool	Furnace cool to 550°C, then air cool
Post-Treatment Hardness	HRC 70–78 (surface)	HRC 65–72	HRC 62–68

4.2 Post-Weld Heat Treatment Cycles

The PWHT cycle is the critical variable that distinguishes a qualified hard alloy overlay from a merely deposited layer. Key considerations include:

Preheating: Base metal preheat at 200–400°C to reduce thermal gradient and minimize cracking risk during subsequent PWHT.
Heating rate control: Maximum 150°C/hour for the first 200°C above ambient; 100°C/hour thereafter to prevent thermal shock and cracking in the brittle hard alloy deposit.
Soak temperature selection: Must be below the decomposition temperature of the primary carbide. For WC-based overlays, temperatures above 950°C promote the exothermic decomposition reaction: 4WC + Fe → Fe₂W₄C + C, which reduces hardness and wear resistance.
Soak duration: Calculated based on deposit thickness, typically 1 hour per 25 mm, ensuring complete stress relief and carbide homogenization throughout the deposit cross-section.
Cooling rate: Controlled furnace cooling to below the martensite start temperature (typically 500–600°C) followed by air cooling. Rapid cooling may introduce high residual stresses and cracking in the brittle carbide-rich microstructure.
Post-cooling stress relief: A final low-temperature stress relief at 300–400°C for 2–4 hours may be applied to further reduce residual stresses without affecting carbide stability.

4.3 Wear Testing Methodologies

Wear resistance characterization following PWHT employs standardized tribological testing methods:

Test Method	Standard	Wear Mechanism Evaluated	Typical Result Reporting
Abrasive wear (two-body)	ASTM G65 (Dry Sand Rubber Wheel)	Sliding abrasion by hard particles	Volume loss (mg or mm³)
Abrasive wear (three-body)	ASTM G99 (Pin-on-Disk)	Rolling/sliding abrasion	Mass loss (mg) or wear rate (mm³/N·m)
Erosion wear	ASTM G74 (Eroding Impact)	Particle impingement	Mass loss vs. impact angle
Impact-abrasion wear	ASTM G80 (Cemented Carbide Impact)	Combined impact and sliding	Volume loss (mm³)
Adhesive wear	ASTM G99 (Pin-on-Disk, dry)	Surface adhesion and transfer	Friction coefficient and wear scar area

5. Applicable Standards and Acceptance Criteria

5.1 Welding Procedure and Qualification Standards

ASME Section IX: Governs welding procedure qualification and performance qualification for overlay welding, including hardfacing processes.
ASME Section II Part D: Specifications for welding consumables, including hard alloy powder electrodes and wires.
ASTM A514 / ASTM A743: Base material specifications where hard alloy overlay is applied.
NB/T 47014.2: Chinese standard for welding procedure qualification of pressure vessels (weld overlay).
GB/T 19804: Chinese standard for welding procedure qualification.
ISO 15614-1 / ISO 15614-2: Qualification testing of welding procedures for steels and non-ferrous metals.
ISO 9606-1 / ISO 9606-2: Qualification testing of welders for steels and non-ferrous metals.

5.2 Heat Treatment Standards

ASME Section VIII Div. 1, UG-116: Post-weld heat treatment requirements for pressure vessels.
ASME Section IX, QW-408: Post-weld heat treatment qualification and acceptance.
ASTM A388: Standard specification for post-weld heat treatment of carbon and low-alloy steel parts.
GB/T 3077: Chinese standard for post-weld heat treatment of steel parts.
NB/T 47015: Chinese standard for welding procedure qualification for pressure vessels.

5.3 Wear Resistance and Hardness Acceptance

ASTM E384: Rockwell hardness testing of metallic materials (for overlay surface hardness verification).
ASTM E92: Vickers microhardness testing (for carbide and binder matrix characterization).
ASTM G65 / ASTM G99: Wear resistance testing as described above.
ISO 3374: Wear testing by abrasion (rubber wheel method).
ISO 4406: Wear testing by dry sliding.

5.4 Acceptance Criteria Summary

Acceptance Parameter	Typical Requirement	Test Method
Surface hardness (after PWHT)	HRC ≥ 65 (WC system); HRC ≥ 60 (Cr₃C system)	ASTM E14 (Rockwell C)
Carbide retention (WC system)	WC volume fraction ≥ 50% after PWHT	SEM/EDS metallographic analysis
Abrasion wear rate	≤ 0.1 mm³/N·m (WC system); ≤ 0.3 mm³/N·m (Cr₃C system)	ASTM G99
Crack-free deposit	No cracks ≥ 0.5 mm in any 100 mm length	Visual + penetrant (ASTM E165)
Deposit thickness	Per WPS specification (typically 3–15 mm)	Ultrasonic thickness (ASTM E797)
Interface bonding	Full metallurgical bond, no delamination	Metallographic cross-section examination

6. Common Risks and Controls

6.1 WC Decomposition During Heat Treatment

Risk: Exceeding the decomposition temperature of WC (~950°C in iron-rich environments) causes the formation of soft η-phase (Fe₂W₄C, ~1200 HV) and graphite carbon, reducing surface hardness from HRC 75+ to HRC 55–60 and dramatically decreasing wear resistance.

Control: Strict furnace temperature control with calibrated thermocouples; maximum soak temperature limited to 900–950°C for WC-based overlays; use of temperature-indicating labels on workpieces.

6.2 Carbide Coarsening and Agglomeration

Risk: Prolonged soak times or excessive temperatures cause carbide particle coarsening (Ostwald ripening), reducing the number of hard particles per unit area and creating soft binder-rich regions between enlarged carbides.

Control: Optimize soak time based on deposit thickness; avoid unnecessary extended holds; consider solution treatment followed by controlled aging for precipitation-hardened binder systems.

6.3 Cracking During Heat Treatment

Risk: Thermal stresses during heating and cooling of the brittle, high-carbide-fraction overlay deposit can cause transverse or longitudinal cracking, compromising both wear resistance and structural integrity.

Control: Limit heating and cooling rates (≤150°C/hour); ensure adequate preheat; consider intermediate stress relief cycles; use furnace cooling rather than air cooling for thick deposits.

6.4 Incomplete Stress Relief

Risk: Insufficient PWHT leaves high tensile residual stresses in the overlay deposit, promoting spalling, delamination, and premature failure under service loading.

Control: Verify PWHT cycle adequacy through residual stress measurement (X-ray diffraction or hole-drilling method per ASTM E837); ensure soak temperature is above 600°C for stress relief of low-alloy steels.

6.5 Interface Dilution and Soft Zone

Risk: Excessive base metal dilution at the overlay-substrate interface creates a soft zone (HRC 30–45) that serves as a wear initiation site and weak link in the composite structure.

Control: Use a transition layer (e.g., 309L or 310 stainless steel) between base metal and hard alloy overlay; limit dilution to ≤20% by controlling welding parameters and pre-heat conditions.

7. Application Scenarios Across Company Technology Routes

7.1 TIG/MIG Weld Overlay Applications

This research directly supports the following TIG/MIG weld overlay applications:

Mineral processing equipment: Hard alloy overlay on ball mill liners, grinding rods, and crusher jaws where PWHT-optimized wear resistance extends service life by 3–5× compared to untreated deposits.
Oil and gas industry: WC-based overlay on drill collars, stabilizers, and wellhead components where controlled heat treatment ensures carbide retention and impact-abrasion resistance.
Cement and power generation: Cr₃C-based overlay on fan blades, cyclone liners, and mill internals where high-temperature stability of the heat-treated deposit is critical.
Mining equipment: TiC or WC overlay on excavator buckets, shovels, and dragline components where combined impact and abrasion resistance is required.

7.2 Hydraulic Explosive Bonding Integration

While hydraulic explosive bonding produces metallurgically bonded interfaces without melting, the subsequent application of hard alloy weld overlay with optimized PWHT creates hybrid composite structures:

Stainless/Carbon steel clad plates with hardfaced surfaces: Explosively bonded 304/316 stainless steel on carbon steel substrate, followed by WC-Co hardfacing on the stainless surface with PWHT-optimized wear resistance.
Pressure vessel components: Explosively bonded corrosion-resistant cladding on vessel shells, with hard alloy overlay applied to wear-prone areas (nozzles, manways) and subsequently heat treated per ASME Section VIII requirements.

7.3 Explosion Welding Integration

Explosion welding produces high-energy interfaces that may require subsequent welding and heat treatment. The knowledge from this research supports:

Explosion-welded pipe with hardfaced internals: Copper-lined or stainless-lined pipes produced by explosion welding, with hard alloy overlay applied to high-wear sections and PWHT optimized for maximum abrasion resistance.
Composite wear parts: Multi-layer components where explosion welding provides the base clad structure and hard alloy weld overlay provides the surface wear protection, with integrated PWHT cycles addressing both the explosive bond interface and the overlay deposit.

8. Contribution to Qualification Building, Product Delivery, and Customer Value

8.1 Qualification Building

The systematic study of wear resistance after heat treatment directly contributes to the company's qualification infrastructure:

WPS qualification: Establishes documented PWHT cycles for each hard alloy system, enabling full WPS qualification per ASME Section IX or GB/T 19804.
Welder qualification: Defines the PWHT requirements that welders must understand and execute correctly, supporting ISO 9606-1 welder certification programs.
Quality system integration: Provides the technical basis for incorporating PWHT verification into the company's ISO 9001 quality management system, including documented procedures, training records, and traceability requirements.
Customer-specific qualification: Enables the company to perform customer-specific qualification tests (e.g., per API RP 5C1 for casing wear resistance or OEM-specific wear test protocols) with scientifically validated PWHT parameters.

8.2 Product Delivery

This research capability ensures reliable product delivery through:

Process repeatability: Documented PWHT cycles with controlled heating rates, soak temperatures, and cooling protocols ensure consistent wear performance across production batches.
Non-destructive verification: Integration of PWHT verification into the NDT program (ultrasonic thickness, penetrant testing, residual stress measurement) provides confidence in delivered product quality without destructive sampling.
Performance guarantee: Quantified wear resistance data enables the company to offer performance guarantees (e.g., "minimum 0.05 mm³/N·m wear rate per ASTM G99") backed by metallurgical evidence.
Traceability: Each production lot carries documented PWHT records (furnace charts, thermocouple calibrations, cycle parameters) enabling full traceability from raw material to delivered product.

8.3 Customer Value

The technical depth provided by this research translates directly into customer value:

Extended service life: Optimized PWHT can improve wear resistance by 40–80% compared to as-welded deposits, translating to 2–3× longer service intervals and reduced maintenance costs.
Reduced total cost of ownership (TCO): While PWHT adds processing time and cost, the dramatic improvement in wear life typically results in 30–60% reduction in TCO for critical wear components.
Reliability and safety: Crack-free, fully stress-relieved overlay deposits eliminate the risk of spalling and unexpected failure in safety-critical applications (pressure vessels, mining equipment, oil and gas well components).
Technical partnership: The ability to provide detailed metallurgical reports, wear test data, and PWHT documentation positions the company as a technical partner rather than a simple fabrication supplier, enabling long-term customer relationships and repeat business.
Customization capability: The understanding of PWHT-wear resistance relationships enables the company to tailor overlay and heat treatment solutions to specific customer wear environments (abrasive, adhesive, erosive, or combined mechanisms).

9. Summary and Recommendations

The study of wear resistance in hard alloy weld overlay deposits after post-weld heat treatment represents a critical metallurgical competency for Cladding Technology Shanxi Co., Ltd. It transforms the company from a welding execution provider into a performance-qualified overlay solutions provider. Key recommendations for continued development include:

Establish a dedicated wear testing laboratory with ASTM G65, G99, and G80 test rigs for in-house characterization of PWHT-optimized overlay deposits.
Develop a comprehensive database of PWHT cycles and corresponding wear performance data for all hard alloy systems in the company's product portfolio.
Integrate PWHT verification into the company's quality management system with documented procedures, training programs, and audit protocols.
Pursue customer-specific qualification programs (API, OEM, industry-specific) leveraging the PWHT-optimized wear resistance data.
Invest in advanced characterization capabilities (SEM, EBSD, XRD) to enable detailed microstructural analysis and further optimization of PWHT parameters.

By maintaining and expanding this technical capability, Cladding Technology Shanxi Co., Ltd. ensures that every hard alloy overlay product delivered to customers meets the highest standards of wear performance, reliability, and quality traceability.