Bimetallic wear-resistant plate armor testing verifies the chemical composition, hardness, bond integrity, and abrasion performance of hardfaced composite plates used in mining, cement, and power generation equipment. This guide explains the sampling requirements, key test items, and internationally recognized methods—including ASTM G65 abrasion testing, hardness measurement, and ultrasonic bond examination—applied by accredited third-party laboratories to confirm quality, compliance, and service life.
Technical Overview
Bimetallic wear-resistant plate armor is a composite engineering material consisting of a hard, carbide-rich wear layer metallurgically bonded to a tough, weldable substrate. The wear layer is typically produced by submerged arc welding or open-arc hardfacing using high-chromium, chromium-niobium, or tungsten carbide tubular wires, while the base plate is usually low-carbon structural steel such as Q235 or Q345. This combination delivers surface hardness of 55–65 HRC or higher while retaining the impact tolerance, formability, and weldability required for severe bulk-material handling service.
Testing is essential because the properties that determine service life are invisible to visual inspection: overlay chemistry, dilution at the bonded interface, carbide volume fraction, bond integrity, and the hardness gradient through the overlay. Accredited third-party laboratories evaluate these parameters against recognized ASTM, ISO, EN, and GB standards to verify incoming plates, fabricated liners, and repair welds against design requirements.
- Verify overlay alloy chemistry and carbide-forming element content
- Confirm surface hardness and hardness distribution through the overlay
- Evaluate metallurgical bond strength and interface integrity
- Quantify abrasion resistance relative to reference materials
- Check overlay thickness, dimensional tolerances, and surface quality
Testing Samples
Production Plate Coupons
Full-thickness rectangular coupons, typically 150–300 mm square, are cut from the head, tail, and mid-length of each production plate or batch. These coupons provide material for hardness, metallographic, bond, and abrasion specimens while representing the full range of welding parameters used across the plate.
Interface and Cross-Section Specimens
Cross-section blanks are extracted perpendicular and parallel to the welding direction to expose the overlay, fusion line, and heat-affected zone. These specimens are used for macro-etch examination, microhardness traverses, carbide structure evaluation, dilution measurement, and crack-depth assessment.
Hardfacing Consumable Samples
Samples of the tubular wire or electrode, together with undiluted weld pads deposited under controlled parameters, are analyzed to confirm the alloy classification of the consumable in accordance with EN 14700 and the manufacturer's declared chemistry.
Fabricated Armor Components
Finished or installed components—chute liners, hopper plates, curved segments, fan blade shrouds, and repair-welded zones—can be sampled using portable instruments or localized coupon extraction during prefabrication and maintenance outages.
Testing Items
A typical inspection program for bimetallic wear plate armor covers the following items, selected according to the purchase specification and service environment.
- Chemical composition of the overlay and base plate (C, Cr, Nb, Mo, W, V, Mn, Si, P, S)
- Surface macro-hardness (HRC) and micro-hardness (HV) of carbides and matrix
- Bond shear strength and tensile properties across the interface
- Interface bond integrity and disbond mapping by ultrasonic testing
- Dry sand rubber wheel abrasion mass loss per ASTM G65
- Overlay thickness, base thickness, total thickness, and flatness tolerances
- Macro- and micro-structure: carbide morphology and volume fraction, dilution rate, crack depth and distribution
- Bend adhesion testing of the overlay layer
- Charpy impact toughness of the base plate for low-temperature or high-impact service
- Optional items: neutral salt spray corrosion resistance, elevated-temperature hardness retention
Testing Methods
Chemical Composition Analysis
The base plate is analyzed by spark optical emission spectrometry per ASTM E415 or GB/T 4336. The overlay is analyzed by X-ray fluorescence per ASTM E572 or by OES on a flat, ground weld bead, with carbon and sulfur determined by infrared combustion absorption per ASTM E1019. Results are compared against the declared alloy system and the EN 14700 classification.
Hardness Testing
Surface Rockwell C hardness is measured on a ground overlay surface at multiple locations per ASTM E18, GB/T 230.1, and ISO 6508-1. Vickers micro-hardness per ASTM E384, GB/T 4340.1, and ISO 6507-1 is performed on a polished cross-section to profile carbide hardness (commonly 1200–1800 HV0.1) and matrix hardness as a function of depth, revealing excessive dilution at the fusion line.
Bond Strength and Adhesion
Interface shear strength is determined per GB/T 6396 using dedicated shear specimens. Bend tests per GB/T 232 and ISO 7438, with the overlay in both tension and compression, reveal spallation or separation along the fusion line. Tensile testing of the base plate and composite section follows GB/T 228.1, ASTM E8/E8M, and ISO 6892-1, while Charpy impact testing follows ASTM E23, ISO 148-1, and GB/T 229 where specified.
Ultrasonic Bond Examination
Straight-beam ultrasonic examination per ASTM A578 or equivalent procedures detects lack of bonding, disbonds, and overlaid defects at the interface. The method also identifies transverse cracks that have propagated through the full overlay thickness to the fusion line, which are unacceptable.
Abrasion Wear Testing
The reference method is the dry sand rubber wheel abrasion test per ASTM G65 (Procedure A), reporting volume loss and relative wear resistance against a mild steel reference, typically a factor of 5–20 times depending on alloy and microstructure. For highly abrasive or wet conditions, supplementary methods such as ASTM B611 or ASTM G99 may be specified.
Metallographic Examination
Specimens are prepared per ASTM E3 and etched per ASTM E407 and GB/T 13298. Evaluation includes carbide type and volume fraction by image analysis, dilution rate (typically required not to exceed 15–25 percent), crack depth and spacing relative to overlay thickness, and fusion-line morphology. Macro-etched cross-sections per ASTM E381 are used to measure overlay thickness and check for porosity and slag.
Dimensional and Visual Inspection
Total thickness is measured by micrometer or ultrasonic thickness gauging, overlay thickness by calibrated cross-section or ultrasonic measurement, and flatness per EN 10029 or GB/T 709. Visual examination of weld bead appearance, crack pattern, and surface defects follows ISO 17637 requirements for welded joints.
Applications
Verified bimetallic wear plate armor is used across industries where abrasive and moderately impact-loaded surfaces must survive extended maintenance intervals.
- Mining and quarrying: chute liners, hopper linings, screen panels, and crusher wear plates
- Cement plants: grinding mill linings, separator cones, fan blades, and slide wear plates
- Power generation: coal chute armor, coal pipe elbows, induced draft fan liners, and ash hopper linings
- Steel and iron works: sinter machine screens, charging chutes, and slag handling channels
- Ports and dredging: shiploader chutes, transfer points, cutter suction dredger teeth, and pipeline liners
- Recycling and waste-to-energy: shredder linings, grates, and boiler tube armor
- Agricultural and construction machinery: bucket cutting edges, ripper points, and tillage components
FAQ
What surface hardness should bimetallic wear plate armor achieve?
Chromium carbide overlays typically measure 55–62 HRC, while complex chromium-niobium or tungsten carbide systems may exceed 60 HRC. Purchase specifications commonly require an average of at least 58 HRC with no single reading below 55 HRC, verified statistically across the plate surface.
Why do cracks appear on the overlay, and when are they unacceptable?
Regular transverse stress-relief cracks are an inherent feature of hard carbide overlays and accommodate weld shrinkage strain. They become unacceptable only when they penetrate through the overlay to the interface, cause spallation of wear-layer islands, or align continuously in the direction of material flow; metallographic crack-depth measurement and ultrasonic testing are used to make this determination.
What is dilution and why is it controlled?
Dilution is the proportion of melted base-plate metal mixed into the overlay, which lowers carbon and chromium content, reduces carbide volume fraction, and decreases hardness and wear life. It is controlled through welding heat input and travel speed, and verified by chemistry, hardness traverses, and microstructural estimation, with typical acceptance limits of 15–25 percent.
How frequently should bimetallic wear plates be tested?
Composition, hardness, and dimensional checks are normally performed on every production batch, while bond shear, metallographic, and ASTM G65 abrasion tests are carried out periodically by heat number or consumable lot, and in full during initial type approval or whenever the wire chemistry or welding process changes.
Can testing be performed on installed liners?
Yes. Portable hardness testers, ultrasonic thickness and bond probes, and surface replica metallography allow accredited third-party laboratories to conduct on-site condition assessment and remaining-life estimation; destructive coupon sampling is limited to locations where extraction does not compromise liner integrity.
