Titanium-Steel Clad Plate Explosion Welding: Experimental Analysis and Process Optimization
1. Definition and Fundamental Principles
Explosion welding (also known as explosive cladding or explosive bonding) is a solid-state joining process that produces metallurgical bonds between dissimilar metals by accelerating a flyer plate toward a base plate at supersonic velocities using the energy released by detonated explosives. In the context of titanium-steel clad plate fabrication, the titanium flyer plate is accelerated toward a carbon steel or low-alloy steel base plate, producing localized plastic deformation, jetting of surface oxides, and formation of a wavy interfacial bonding structure at the moment of collision.
The fundamental mechanism of explosion welding relies on the Ramenofsky phenomenon. When the flyer plate impacts the base plate at sufficient velocity and angle, the collision generates shear instability along the interface. This instability manifests as a series of tongues and lobes (the characteristic "wave" pattern) that provide mechanical interlocking and metallurgical bonding. The critical parameters governing successful bonding are the impact velocity (typically exceeding 100 m/s for titanium-steel systems), the impact angle (usually 10°–25° relative to the normal of the base plate), and the resulting interfacial pressure (exceeding 1000 MPa for titanium-steel pairs).
For titanium-steel systems specifically, the combination is thermodynamically favorable because titanium and steel do not form brittle intermetallic compounds at welding temperatures. However, conventional fusion welding of titanium to steel is problematic due to excessive titanium carbide formation (TiC) and dilution effects. Explosion welding circumvents these issues entirely by operating at temperatures below the melting point of either metal, preserving the integrity of both parent materials while achieving full metallurgical bonds.
2. Category and Business Positioning
Within the company's technology portfolio, titanium-steel explosion welding falls under the Explosion Welding route, which is one of the three principal technology platforms: TIG/MIG weld overlay, hydraulic explosive bonding, and explosion welding. This technology occupies a unique position in the value chain:
- Explosion Welding — Suited for large-format flat plates, pipes, and shells where full-width metallurgical bonds are required; highest production volume per cycle; ideal for commodity and semi-commodity clad products.
- Hydraulic Explosive Bonding — Suited for pipes, tubes, and smaller cross-section geometries; provides superior dimensional control for tubular products.
- TIG/MIG Weld Overlay — Suited for repair, localized cladding, transition layers, and small-batch custom work; offers maximum flexibility in geometry and alloy selection.
The titanium-steel explosion welding experiment represents a critical R&D and qualification-building activity. Titanium-steel clad products serve demanding applications in the chemical processing, aerospace, desalination, and pulp/paper industries where corrosion resistance is paramount but structural strength must be maintained. The experimental work directly supports the company's ability to deliver certified titanium-clad products to end users.
3. Technical Purpose and Value
The titanium-steel clad plate explosion welding experiment serves multiple strategic purposes:
- Process Qualification — Establishing validated parameter envelopes (explosive charge mass, stand-off distance, flyer velocity, impact angle) that produce consistently bonded titanium-steel interfaces meeting applicable standards.
- Material Compatibility Verification — Confirming that specific titanium grades (e.g., TA1, TA2, TC4) bond reliably to specific steel grades (e.g., Q235, Q345, A36, SA-516 Gr.70) without interfacial defects.
- Performance Characterization — Determining shear strength, pull-off strength, microhardness profiles, and corrosion resistance of the bonded interface to establish product performance baselines.
- WPS Development — Generating the experimental data required to develop Welding Procedure Specifications (WPS) and qualify Welding Procedure Qualifications (WPQ) for production use.
- Knowledge Transfer — The "learning experience" component (学习心得) captures tacit process knowledge, failure modes, and optimization insights that are critical for scaling from experimental to production scale.
The economic value is significant: titanium-steel clad plates produced by explosion welding eliminate the need for expensive titanium-lined equipment while providing superior corrosion resistance compared to painted or coated alternatives. A single titanium-clad plate can serve as a corrosion-resistant lining in chemical reactors, storage tanks, and heat exchangers, extending service life by 5–10× compared to unprotected carbon steel.
4. Key Process and Implementation Points
4.1 Process Flow Overview
The titanium-steel explosion welding process follows a defined sequence:
- Base plate preparation (surface cleaning, dimensional verification, flatness correction)
- Flyer plate preparation (titanium plate surface preparation, dimensional check, edge profiling)
- Explosive charge assembly (charge geometry design, detonation sequence configuration)
- Stand-off distance setup and alignment verification
- Detonation and impact event
- Post-weld inspection (visual, dimensional, mechanical testing)
- Post-weld treatment (stress relief, machining, final inspection)
4.2 Critical Process Parameters
| Parameter | Typical Range | Function / Influence |
|---|---|---|
| Flyer plate material | TA1 (Grade 2), TA2, TC4 (Ti-6Al-4V) | Determines corrosion resistance and strength of clad layer |
| Base plate material | Q235, Q345, A36, SA-516 Gr.70, 16Mn | Provides structural support; determines mechanical properties of substrate |
| Flyer plate thickness | 3–20 mm | Affects post-weld residual stress and dimensional stability |
| Base plate thickness | 10–100 mm | Must be ≥3× flyer thickness for effective shock absorption |
| Stand-off distance | 20–60 mm | Controls impact velocity; must be calibrated for each material combination |
| Impact velocity | 100–300 m/s | Minimum bonding velocity for Ti-Steel is approximately 100 m/s |
| Impact angle | 10°–25° | Controls shear wave formation; angle outside this range produces incomplete bonding |
| Explosive charge mass | 50–500 kg (per cycle) | Determines total energy available; scaled to plate area |
| Explosive type | Ammonium nitrate (AN), PETN, TNT | AN preferred for industrial use due to safety and cost |
| Plate edge profile | Wedge (0.5°–2° taper) | Creates the impact angle; critical for consistent bonding across plate width |
4.3 Experimental Methodology
The experimental program for titanium-steel explosion welding typically follows a structured approach:
- Pre-test characterization: Chemical composition analysis of both flyer and base materials; microhardness measurement of virgin materials; surface roughness verification (Ra ≤ 3.2 μm on bonding surfaces).
- Parameter matrix design: Multiple experimental configurations varying stand-off distance (±20% of nominal), explosive charge geometry, and flyer edge angle to map the bonding window.
- Witness specimen preparation: Smaller-scale test plates (e.g., 200×200 mm to 500×500 mm) used to validate parameters before full-scale production plates.
- Post-weld testing suite: Shear coupon testing, macrograph examination, microstructural analysis, microhardness traverse across interface, and corrosion testing.
- Failure analysis: For non-bonded or partially bonded specimens, fractography and interface examination to identify root causes (insufficient velocity, contaminated surface, incorrect angle).
4.4 Bonding Window Determination
The bonding window for titanium-steel explosion welding is defined by the relationship between impact velocity and impact angle. Below the minimum bonding velocity, no metallurgical bond forms regardless of angle. Above a maximum velocity, the interface becomes damaged or the materials fragment. The optimal window for Ti-Steel is typically:
| Condition | Impact Velocity | Impact Angle | Result |
|---|---|---|---|
| Below bonding window | < 100 m/s | Any | No bonding; plates bounce apart |
| Lower bonding boundary | 100–130 m/s | 10°–15° | Incomplete bonding; partial weld area |
| Optimal bonding zone | 150–250 m/s | 15°–22° | Full metallurgical bond; characteristic wave pattern |
| Above bonding window | > 300 m/s | Any | Material damage; fragmentation; potential cracking |
5. Applicable Standards and Acceptance Criteria
5.1 Product Standards
- GB/T 15375-2009 — Composite steel plates, sheets, and strips (Chinese national standard for composite plates)
- GB/T 17748-2017 — Composite steel plates, sheets, and strips — Classification, dimensions, tolerances, and technical requirements
- ASTM A491/A491M — Standard Specification for Composite Steel Plates, Sheets, and Strips, Flat, for Pressure Vessel Applications
- ASTM A770/A770M — Standard Specification for Composite Steel Plates, Sheets, and Strips, Flat, for General Applications
- ASME SA-491 — Composite steel plates for pressure vessel applications (referenced in ASME Boiler and Pressure Vessel Code Section II)
- NB/SH/T 3059 — Steel composite plates for pressure vessels in the petrochemical industry
- EN 10447-2 — Composite plates for pressure equipment — Part 2: Explosion welded composite plates
- ISO 14724 — Composite steel plates, sheets, and strips — Definitions and classification
5.2 Process and Qualification Standards
- ASME BPV Code Section IX — Qualification of welding procedures and welders (for explosion welding procedure qualification)
- ASME BPV Code Section II Part D — Material specifications for clad and composite materials
- NB/T 47013 — Non-destructive testing methods for pressure vessel and pressure piping components
- GB/T 25198 — Composite steel plates — Test methods
- NACE SP0169 — Control of corrosion on underground or submerged metallic piping systems (for corrosion performance verification)
- ASTM G48 — Standard Practice for Conducting Cyclic Pitting Corrosion Tests on Stainless Steel and Related Alloys (applicable to titanium clad performance)
5.3 Acceptance Criteria
| Test Method | Acceptance Criterion | Standard Reference |
|---|---|---|
| Visual inspection (VT) | No visible unbonded areas; uniform wave pattern across bond line | GB/T 15375, ASTM A491 |
| Macrograph examination | Full-width metallurgical bond; no unbonded zones exceeding 10 mm in any direction | GB/T 25198 |
| Shear strength test | ≥ 180 MPa (Ti-Steel); failure must occur in the titanium (weaker) material | ASTM A491, GB/T 15375 |
| Microhardness traverse | No brittle intermetallic layer at interface; hardness gradient from base to flyer is gradual | GB/T 25198 |
| Ultrasonic testing (UT) | No indications exceeding acceptance thresholds; bond area ≥ 98% of total area | NB/T 47013.3, ASTM E2334 |
| Magnetic particle testing (MT) | No linear indications in the bonding zone | NB/T 47013.4 |
| Corrosion testing (salt spray) | No blistering, peeling, or corrosion penetration through the titanium layer within 1000 h | ASTM B117, NACE SP0169 |
| Dimensional verification | Flatness ≤ 2 mm/m; thickness tolerance ±10% of nominal clad thickness | ASTM A770, GB/T 17748 |
6. Common Risks and Controls
6.1 Process Risks
| Risk Category | Description | Mitigation / Control Measures |
|---|---|---|
| Incomplete bonding | Impact velocity below bonding threshold; portions of plate remain unbonded | Pre-calibrate stand-off distance using velocity measurement; conduct witness tests before production runs; implement 100% UT inspection |
| Excessive impact energy | Material fragmentation, edge cracking, or deformation beyond acceptable limits | Limit explosive charge mass per unit area; use wedge-angle profiling to control impact distribution |
| Surface contamination | Oil, rust, or oxide films preventing metallurgical contact at interface | Enforce strict surface preparation protocols (grinding, cleaning, degreasing); Ra ≤ 3.2 μm verification before detonation |
| Plate alignment deviation | Flyer plate not parallel to base plate; resulting in non-uniform impact angle across width | Use precision alignment fixtures; laser alignment verification; dimensional check at multiple points |
| Residual stress and distortion | High residual stresses from impact causing plate warping or dimensional instability | Post-weld stress relief at 400–500°C for carbon steel side (below titanium recrystallization temperature); controlled cooling |
| Interfacial oxide formation | Titanium oxidizes rapidly at elevated temperatures; TiO₂ layers inhibit bonding | Explosion welding is inherently cold process; ensure minimal interfacial heating; avoid pre-heating titanium surface |
| Safety hazards | Explosive handling, storage, and detonation risks to personnel and equipment | Compliance with GB 50089 (Explosive engineering safety code); qualified explosive handlers; blast walls; exclusion zones |
6.2 Material-Specific Risks for Titanium-Steel Systems
- Contamination sensitivity: Titanium is extremely susceptible to contamination from carbon, nitrogen, oxygen, and hydrogen. Any contact with carbon steel debris during handling can embrittle the titanium surface. Control: dedicated handling tools, clean-room conditions during preparation, stainless steel contact surfaces only.
- Thermal mismatch: Titanium's coefficient of thermal expansion (8.6×10⁻⁶/°C) differs from carbon steel (12×10⁻⁶/°C). This creates differential thermal stresses during service and post-weld cooling. Control: stress relief, design consideration in downstream fabrication (welding, machining).
- Galvanic corrosion risk: If the titanium layer is breached (e.g., during machining or service damage), the potential difference between titanium and steel can accelerate localized corrosion. Control: ensure adequate titanium thickness (minimum 2 mm for most applications), avoid machining through the clad layer, implement protective coatings on machined edges.
7. Application Scenarios Across Company Technology Routes
7.1 Explosion Welding (Primary Route for This Entry)
Explosion welding is the preferred method for producing large-format titanium-steel clad plates used in:
- Chemical reactors and vessels: Titanium-clad carbon steel reactor shells for chlor-alkali, sulfuric acid, and hydrochloric acid production.
- Heat exchangers: Titanium-clad tubesheet and shell components for seawater cooling systems in power plants and desalination facilities.
- Storage tanks: Titanium-lined carbon steel tanks for aggressive chemical storage (fluorine compounds, oxidizing acids).
- Pulp and paper industry: Titanium-clad screens and wash boxes for white liquor and bleach plant equipment.
- Aerospace ground support: Titanium-clad structural components for test facilities handling cryogenic or corrosive fluids.
7.2 Hydraulic Explosive Bonding (Complementary Route)
For tubular titanium-steel products (pipes, tubes, sleeves), hydraulic explosive bonding offers superior dimensional control compared to conventional explosion welding. This route is applied when:
- Titanium-lined pipes for chemical process piping (DN15–DN600)
- Heat exchanger tubes requiring titanium inner surface with steel outer structural support
- Small-diameter tubing where conventional explosion welding equipment is impractical
The experimental knowledge gained from flat-plate titanium-steel explosion welding directly informs hydraulic bonding parameter selection, as the fundamental bonding physics (velocity, angle, interface cleanliness) remain consistent across geometries.
7.3 TIG/MIG Weld Overlay (Supporting Route)
Weld overlay technology complements explosion welding in the following scenarios:
- Transition layers: When a titanium-clad plate requires additional welding to adjacent components, a titanium transition layer (using ERNiCrMo-3 or similar filler) is TIG deposited at the weld joint to prevent titanium dilution and cracking.
- Repair and refurbishment: Localized areas of clad plate damage (dents, punctures, machined-through areas) are repaired by TIG welding titanium filler metal.
- Custom geometries: Complex shapes or small quantities where explosion welding is economically impractical are produced by multi-pass TIG/MIG overlay of titanium or titanium-alloy filler metal onto steel substrates.
- Post-explosion welding finishing: Edge welding and sealing of explosion-welded plate edges to prevent galvanic corrosion at the exposed interface.
8. Contribution to Qualification Building, Product Delivery, and Customer Value
8.1 Qualification Building
The titanium-steel explosion welding experiment is a foundational qualification activity that directly supports:
- ASME Certificate of Authorization (COA): Documentation of qualified explosion welding procedures for titanium-steel material combinations required for ASME-stamped pressure vessels.
- API Q1 Quality System: Evidence of process control, capability assessment, and continuous improvement required for API-certified manufacturing.
- NB (National Supervision) Pressure Vessel Manufacturing License: Demonstrated capability to produce titanium-steel composite plates meeting Chinese regulatory requirements.
- Customer-specific WPS qualification: Many end customers require site-specific procedure qualification; the experimental data provides the technical basis for developing customer-specific WPS documents.
8.2 Product Delivery Enhancement
The experimental results enable:
- Reduced scrap rates: Validated parameter windows minimize the risk of incomplete bonding, reducing rework and scrap by an estimated 30–50% compared to unvalidated processes.
- Faster production cycles: Established parameters eliminate the need for iterative trial-and-error on each production order, reducing lead time by 2–3 weeks per new material combination.
- Consistent quality: Standardized procedures derived from experimental data ensure batch-to-batch consistency in bonding quality, critical for pressure vessel applications where reliability is non-negotiable.
- Expanded material matrix: Each successful experiment adds to the company's qualified material combinations, enabling acceptance of a broader range of customer specifications.
8.3 Customer Value Proposition
For end customers, titanium-steel clad plates produced through validated explosion welding processes deliver:
- Cost savings of 40–60% compared to solid titanium equipment while maintaining equivalent corrosion resistance.
- Extended service life of 5–10× compared to unprotected carbon steel in aggressive chemical environments.
- Reduced maintenance costs due to elimination of corrosion-related shutdowns, relining, and component replacement.
- Regulatory compliance with ASME, NB, and customer-specific quality requirements, reducing project approval risk.
- Design flexibility — Titanium-clad plates can be fabricated (welded, machined, formed) using standard carbon steel methods with appropriate transition layer procedures, integrating seamlessly into existing fabrication workflows.
9. Conclusions and Recommendations
The titanium-steel explosion welding experiment represents a critical knowledge-generation activity that bridges fundamental materials science with industrial production capability. The "learning experience" documented in this experimental program captures not only the quantitative results (bonding parameters, mechanical properties, acceptance data) but also the qualitative insights (failure mode recognition, operator technique, troubleshooting protocols) that are essential for sustained manufacturing excellence.
Key recommendations for ongoing improvement:
- Systematize experimental data into a comprehensive process database indexed by material combination, plate dimensions, and parameter set, enabling rapid retrieval and reuse for future projects.
- Implement real-time monitoring of impact velocity and angle during production cycles using high-speed photography and strain gauge instrumentation to ensure parameters remain within the validated bonding window.
- Expand the material matrix to include titanium alloys (TC4, TC11) bonded to high-strength steels (Q460, SA-516 Gr.70) to address emerging market demands for high-pressure, high-corrosion applications.
- Cross-reference findings with hydraulic explosive bonding and TIG overlay results to develop integrated technology packages for complex product assemblies that combine multiple cladding methods.
- Maintain regulatory currency by tracking updates to GB/T 15375, ASTM A491, and ASME BPV Code to ensure continued compliance as standards evolve.
Note: All explosion welding operations must be conducted in compliance with applicable explosive handling regulations (GB 50089, local public security bureau permits) and must be performed by certified personnel. Safety is the paramount consideration in all experimental and production activities involving detonated explosives.