Explosion-Rolling TA1/Q345R Composite Plate: Microstructure, Properties, and Process Technology
1. Introduction and Technical Overview
The explosion-rolling composite process represents a hybrid manufacturing technology that combines explosive welding with subsequent hot or warm rolling to produce bimetallic clad plates with enhanced bonding quality, improved metallurgical compatibility, and superior mechanical properties. This entry specifically addresses the microstructural evolution and mechanical performance of TA1 (Grade 1 Titanium) and Q345R (Chinese standard carbon steel) composite plates produced through this combined process. The study provides critical insight into how the secondary rolling operation modifies the interface microstructure, eliminates porosity and waviness defects inherent to pure explosion welding, and enhances the overall integrity of the clad laminate.
TA1/Q345R composite plates serve a demanding niche in the chemical, petrochemical, and nuclear industries where the combination of titanium's exceptional corrosion resistance and carbon steel's structural strength and cost-effectiveness is required. This technical review consolidates process knowledge essential for qualification building, product specification development, and customer-facing engineering support.
2. Definition and Fundamental Principles
2.1 Explosion Welding Mechanism
Explosion welding is a solid-state bonding process in which a flyer plate (in this case, TA1 titanium) is accelerated to high velocity (typically 200–800 m/s) by the detonation of an explosive charge (e.g., TNT, ammonium nitrate, or composite explosives) and impacts a base plate (Q345R carbon steel) at an oblique angle (typically 5°–15°). The collision generates sufficient kinetic energy to produce a high-strain-rate, high-temperature interaction that drives a hydrodynamic jet from the leading edge, cleans oxide layers from both surfaces, and produces intimate atomic contact. The resulting interface exhibits a characteristic wavy (sinusoidal) morphology with periodic bonding zones and unbonded regions.
2.2 Rolling Enhancement Mechanism
The subsequent rolling step—performed either hot (at temperatures above the recrystallization temperature of both materials) or warm—serves several critical functions:
- Interface flattening: Reduces or eliminates the sinusoidal waviness pattern, producing a straighter, more uniform bond line with increased bonded area fraction.
- Defect closure: Compacts porosity, micro-voids, and unbonded regions that may exist in the as-welded interface.
- Grain refinement: Promotes dynamic recrystallization at the interface, producing a finer, more equiaxed grain structure that improves ductility and fatigue resistance.
- Thickness reduction: Enables production of thinner clad plates (down to 0.5–1.0 mm cladding thickness) by starting with thicker explosion-welded stock and rolling to final gauge.
- Property homogenization: Reduces gradient in mechanical properties through the clad thickness, producing more predictable performance under service loading.
3. Material System Characterization
3.1 TA1 Titanium Alloy (Cladding Layer)
| Property | Typical Specification |
|---|---|
| Composition (Ti balance) | Fe ≤ 0.20%, C ≤ 0.10%, O ≤ 0.20%, N ≤ 0.05% |
| Tensile Strength | ≥ 275 MPa (per ASTM B265 / GB/T 13640) |
| Yield Strength (0.2% offset) | ≥ 170 MPa |
| Elongation | ≥ 24% |
| Crystal Structure | HCP (α-phase) |
| Corrosion Resistance | Excellent in chlorides, seawater, sulfuric acid, hydrofluoric acid |
3.2 Q345R Carbon Steel (Base Layer)
| Property | Typical Specification |
|---|---|
| Composition | C ≤ 0.20%, Mn ≤ 1.6%, Si ≤ 0.35%, P ≤ 0.030%, S ≤ 0.030% |
| Tensile Strength | 470–630 MPa (per GB/T 713) |
| Yield Strength | ≥ 345 MPa |
| Elongation | ≥ 21% (for thickness ≤ 16 mm) |
| Impact Energy | ≥ 34 J at 0°C (Charpy V-notch, per GB/T 713) |
| Application | Pressure vessels, heat exchangers, nuclear-grade components |
4. Microstructure Analysis of the Bond Interface
4.1 As-Welded Interface (Explosion Welding Only)
The as-explosion-welded interface between TA1 and Q345R exhibits a classic wavy pattern with the following characteristics:
- Wave amplitude: Typically 0.1–0.5 mm, depending on impact velocity and angle
- Wave period: 0.5–3.0 mm
- Bonded area fraction: 70–95% (varies with process parameters)
- Intermetallic compounds: Minimal to moderate formation; thin Ti-Fe intermetallic layers (TiFe, Ti₂Fe, TiFe₂) may appear at high-temperature bonding zones, typically 1–10 μm thick
- Oxide inclusions: Titanium oxides (TiO₂) and iron oxides are entrapped at unbonded wave crests and troughs
- Deformation bands: Severe plastic deformation on the titanium side produces elongated grains parallel to the interface
4.2 Post-Rolling Interface
The rolling operation fundamentally transforms the interface microstructure:
- Waviness reduction: Amplitude decreases by 50–90%; in some cases, a near-planar interface is achieved
- Bonded area improvement: Increases to 95–99%+ through compaction of previously unbonded regions
- Grain refinement: Dynamic recrystallization produces equiaxed grains (10–30 μm) in the titanium near-interface zone; ferrite-pearlite microstructure in Q345R is refined near the bond line
- Intermetallic layer control: Rolling at controlled temperatures can either increase or decrease intermetallic thickness depending on temperature and time; optimal rolling temperatures (700–850°C) minimize brittle intermetallic growth while promoting recrystallization
- Residual stress relief: Partial annealing during hot rolling reduces the high residual stresses generated during explosion welding
- Texture development: Rolling introduces preferred crystallographic orientation in both layers, affecting anisotropy of mechanical properties
4.3 Intermetallic Compound Formation
The TA1/Q345R system is particularly sensitive to intermetallic compound formation at the interface. The following Ti-Fe intermetallic phases may develop:
| Phase | Composition | Crystal Structure | Hardness | Effect on Bond Strength |
|---|---|---|---|---|
| TiFe | ~45 wt% Ti | Orthorhombic | ~1000 HV | Brittle; detrimental if thick |
| Ti₂Fe | ~73 wt% Ti | Hexagonal | ~800 HV | Moderately brittle |
| TiFe₂ | ~29 wt% Ti | Hexagonal | ~900 HV | Brittle; detrimental |
| Ti₃Fe | ~82 wt% Ti | Hexagonal | ~700 HV | Less brittle; acceptable in thin layers |
Critical control principle: The total intermetallic layer thickness should be maintained below 5–10 μm to ensure acceptable shear strength and fracture toughness at the bond interface. Excessive intermetallic growth (above 20 μm) leads to brittle interfacial fracture and significant reduction in peel/shear strength.
5. Mechanical Properties and Performance Evaluation
5.1 Bond Strength Testing
| Test Method | Standard | Typical Acceptance Criteria | Notes |
|---|---|---|---|
| Shear Strength (transverse) | GB/T 15249 / ASTM A493 | ≥ 200 MPa (or ≥ 0.7 × base metal shear strength) | Standard qualification test for clad plates |
| Shear Strength (longitudinal) | GB/T 15249 / ASTM A493 | ≥ 150 MPa | Lower than transverse due to interface orientation |
| Peel Strength (90°) | ASTM A493 | ≥ 10 kN/m (varies by specification) | Direct measure of interface adhesion |
| Tensile Strength (clad coupon) | GB/T 15249 | ≥ 0.8 × base metal tensile strength | Ensures cladding does not weaken overall plate |
5.2 Effect of Rolling on Mechanical Properties
Post-rolling typically improves the following:
- Shear strength: Increases by 15–40% compared to as-welded condition due to improved bonded area and refined interface microstructure
- Fracture toughness: Improved through reduction of stress-concentrating wave peaks and voids
- Impact resistance: Enhanced by residual stress relief and grain refinement
- Uniformity: Reduced scatter in bond strength across the plate area
5.3 Corrosion Performance
The corrosion resistance of the composite plate is governed by the TA1 cladding layer, provided the bond is fully intact without defects that could allow corrosive media to penetrate to the steel substrate. Key considerations include:
- Galvanic compatibility: TA1 and Q345R have a significant potential difference (~0.8 V in chloride solutions); any bond defect creates a galvanic cell that accelerates under-clad corrosion of the steel
- Seam integrity: Edge sealing (by welding, roll-bending, or mechanical fastening) is critical to prevent crevice corrosion at plate edges
- Potential testing: Potential mapping per ASTM G57 or NACE TM0169 can detect bond defects by identifying localized potential shifts
6. Process Parameters and Implementation
6.1 Explosion Welding Parameters
| Parameter | Typical Range | Effect on Bond Quality |
|---|---|---|
| Impact velocity | 300–600 m/s | Higher velocity → more energy → better bonding but increased intermetallic formation |
| Impact angle | 5°–15° | Optimal for TA1/Q345R: 8°–12° |
| Explosive charge mass ratio | 1.0–3.0 (charge mass / flyer mass) | Higher ratio → higher velocity; must balance with cost and safety |
| Standoff distance | 20–50 mm | Affects flyer acceleration and impact velocity |
| Plate thickness ratio | Flyer:Base = 1:3 to 1:10 | Affects strain distribution and bonding efficiency |
| Surface preparation | Grinding to Ra ≤ 3.2 μm, or shot blasting | Critical for oxide removal; roughness must be controlled |
6.2 Rolling Parameters
| Parameter | Typical Range | Notes |
|---|---|---|
| Rolling temperature (titanium side) | 700–900°C | Above recrystallization temperature of TA1 (~600°C) |
| Rolling temperature (steel side) | 700–900°C (simultaneous heating) | Must be coordinated to avoid differential thermal expansion issues |
| Reduction ratio (per pass) | 10–25% | Total reduction can be 30–70% across multiple passes |
| Number of passes | 3–10 | Depends on initial and final thickness |
| Cooling rate | Controlled air cooling or furnace cooling | Fast cooling may increase residual stress; slow cooling may promote intermetallic growth |
| Final thickness | 1.5–50 mm (total plate) | Cladding thickness: 0.5–5.0 mm typical |
7. Applicable Standards and Acceptance Criteria
7.1 Product Standards
- GB/T 15249 — Composite steel plates for pressure vessels (Chinese standard covering qualification and testing)
- GB/T 19079 — Composite steel plates for chemical industry
- NB/T 47015 — Technical requirements for composite steel pressure vessels (Chinese nuclear/pressure vessel standard)
- ASTM A403 — Standard specification for corrosion-resistant steel-clad steel plates
- ASTM A493 — Standard specification for corrosion-resistant steel-clad steel plates, sheets, and strips
- ASTM A240/A240M — Chromium and chromium-nickel stainless steel plate (reference for cladding material properties)
- GB/T 13640 — Titanium and titanium alloy plates, sheets, and strips (TA1 material specification)
- GB/T 713 — Steel plates for pressure vessels (Q345R base material specification)
7.2 Process and Qualification Standards
- ASME Section VIII, Division 1, Appendix 4 — Qualification requirements for clad pressure vessels
- ASME Section IX — Welding and brazing qualifications (for any subsequent welding operations)
- GB/T 15249 — Includes qualification procedures for explosion-welded clad plates
- ASTM A493 — Qualification testing requirements (shear, peel, tensile tests)
7.3 Non-Destructive Testing Standards
- ASTM E164 — Ultrasonic testing of clad plates (through-transmission method)
- ASTM E2630 — Electromagnetic testing of clad plates (eddy current method)
- GB/T 15249 — Specifies NDT requirements for composite plates (ultrasonic or electromagnetic)
- NB/T 47013 — NDT methods for pressure vessel components (Chinese standard)
7.4 Acceptance Criteria Summary
| Requirement | Acceptance Criterion | Test Method |
|---|---|---|
| Bond strength (shear) | ≥ 200 MPa transverse; ≥ 150 MPa longitudinal | GB/T 15249 / ASTM A493 |
| Bond strength (peel) | ≥ 10 kN/m (90° peel) | ASTM A493 |
| NDT - Ultrasonic | No unbonded areas > 20 mm diameter; total unbonded area < 5% of test area | ASTM E164 |
| NDT - Electromagnetic | No unbonded areas > specified limit; no through-thickness defects | ASTM E2630 |
| Visual inspection | No surface defects, cracks, or excessive waviness on cladding surface | Visual per GB/T 15249 |
| Microstructure | No excessive intermetallic (>10 μm); no unbonded regions at interface | Optical microscopy / SEM |
8. Common Risks and Controls
8.1 Process Risks
| Risk | Cause | Effect | Control Measure |
|---|---|---|---|
| Unbonded areas | Insufficient impact energy; surface contamination; excessive oxide | Reduced bond strength; potential for under-clad corrosion | Optimize impact parameters; rigorous surface preparation; post-weld rolling |
| Excessive intermetallic | High impact velocity; prolonged rolling at high temperature | Brittle interface; reduced shear strength | Control impact velocity; limit rolling temperature and time |
| Cracking in titanium layer | Excessive rolling reduction; low rolling temperature (below recrystallization) | Plate rejection; reduced ductility | Control reduction per pass; ensure adequate rolling temperature |
| Thickness variation | Non-uniform rolling; misaligned plates | Non-conformance to thickness specification | Use precision rolling mills; monitor thickness continuously |
| Edge defects | Rolling edge effects; explosion welding edge wave irregularities | Stress concentration; potential crack initiation | Trim edges after rolling; edge sealing in final product |
| Hydrogen embrittlement (titanium) | Moisture contamination during explosion; high rolling temperature in humid environment | Reduced ductility; delayed cracking | Dry environment control; post-rolling annealing if needed |
8.2 Material Risks
- Titanium contamination: TA1 titanium is highly reactive with oxygen, nitrogen, and hydrogen at elevated temperatures. Rolling must be conducted in a controlled atmosphere (vacuum, argon, or nitrogen-free environment) to prevent contamination and property degradation.
- Steel oxide scale: Q345R forms oxide scale during heating for rolling; this scale can interfere with the bond interface. Descaling (by mechanical or chemical methods) before final rolling is essential.
- Thermal expansion mismatch: Titanium and steel have different thermal expansion coefficients (α_Ti ≈ 8.6×10⁻⁶/K; α_Steel ≈ 12×10⁻⁶/K). Differential expansion during heating/cooling can introduce residual stresses that may compromise dimensional stability or promote cracking.
9. Application Across Company Technology Routes
9.1 Explosion Welding Route
The explosion-rolling process is a natural extension of the company's core explosion welding capability. The explosion welding route produces the initial bonded laminate, which is then refined by rolling. Key contributions include:
- Product range expansion: Enables production of thinner cladding layers (0.5–2.0 mm) that are difficult to achieve with explosion welding alone
- Quality enhancement: Rolling eliminates the primary limitation of explosion welding—residual waviness and variable bonded area—thereby improving product consistency
- Large-format capability: Explosion welding produces large plates (up to 6000×2000 mm); rolling can reduce these to final dimensions while maintaining bond quality
- Multi-layer configurations: Explosion welding can produce multi-layer laminates (e.g., TA1/steel/TA1 sandwich); rolling consolidates these into a uniform product
9.2 Hydraulic Explosive Bonding Route
The company's hydraulic explosive bonding technology offers an alternative to traditional explosive welding. The explosion-rolling knowledge base contributes to this route in the following ways:
- Process parameter correlation: Understanding of impact velocity, angle, and strain requirements from explosion welding directly informs hydraulic explosive bonding parameter selection
- Interface quality criteria: Microstructural acceptance criteria developed for explosion welding apply equally to hydraulic explosive bonding products
- Rolling integration: Hydraulic explosive bonding products can similarly benefit from post-bond rolling for waviness reduction and property enhancement
- Environmental advantage: Hydraulic explosive bonding eliminates explosive materials; combined with rolling, provides a safer, more controllable route to the same product quality
9.3 TIG/MIG Weld Overlay Route
While the explosion-rolling process is fundamentally different from weld overlay, the knowledge gained contributes to the company's weld overlay capabilities through:
- Microstructural understanding: Knowledge of Ti-Fe intermetallic formation at interfaces informs WPS development for TIG/MIG overlay of titanium or titanium-bearing alloys on carbon steel
- Corrosion performance data: Corrosion testing data from explosion-welded TA1/Q345R plates provides benchmark values for comparing weld overlay alternatives
- NDT methodology: Ultrasonic and electromagnetic testing techniques developed for explosion-welded interfaces are applicable to weld overlay bond quality verification
- Hybrid solutions: For applications requiring very thick cladding (>5 mm), a hybrid approach combining explosion welding (for base bond) and TIG/MIG overlay (for thickness build-up) may be specified; understanding both processes enables optimal design
10. Qualification Building and Customer Value
10.1 Qualification Support
This technical entry directly supports the company's qualification building program in several critical areas:
- WPS/PQR development: The process parameters documented (impact velocity, angle, rolling temperature, reduction) form the basis for Welding Procedure Specifications (WPS) and Procedure Qualification Records (PQR) under ASME Section IX or GB/T 15249
- Material qualification: Demonstrated microstructural and mechanical performance of TA1/Q345R composite plates validates the material combination for pressure vessel and chemical equipment applications
- NDT procedure qualification: Testing data supports the development and qualification of NDT procedures (ASTM E164 ultrasonic, ASTM E2630 electromagnetic) specific to this material combination and process
- Customer audits: Detailed technical documentation of microstructure, properties, and process control provides evidence for customer qualification audits and regulatory inspections
10.2 Product Delivery Enhancement
The explosion-rolling process knowledge enables the company to deliver:
- Higher quality products: Improved bond strength and reduced defect rates compared to explosion welding alone
- Broader specification range: Ability to meet tighter thickness tolerances and higher bond strength requirements
- Faster delivery: Rolling is a well-established, high-throughput process; the combined explosion-rolling route can be more efficient than explosion welding to final thickness alone
- Custom configurations: Flexibility to produce various cladding thicknesses, plate sizes, and multi-layer configurations from a single explosion-welded stock
10.3 Customer Value Proposition
"The explosion-rolling TA1/Q345R composite plate delivers superior corrosion resistance with enhanced mechanical integrity, combining the best attributes of titanium and carbon steel in a single, cost-effective component. Our expertise in this hybrid process ensures consistent quality, traceability, and compliance with the most demanding industry standards."
Key customer benefits include:
- Cost savings: Titanium cladding (0.5–3.0 mm) on carbon steel base reduces material cost by 60–80% compared to solid titanium construction
- Performance assurance: Documented bond strength, microstructural quality, and NDT verification provide confidence in long-term service performance
- Regulatory compliance: Full documentation package supports regulatory approval for pressure vessels, nuclear components, and chemical equipment
- Extended service life: Superior corrosion resistance of TA1 cladding extends equipment life in aggressive environments, reducing maintenance and replacement costs
11. Application Scenarios
| Industry | Application | Service Conditions | Key Requirement |
|---|---|---|---|
| Petrochemical | Heat exchanger tubesheets, reactor linings | High temperature, chloride-containing media | Corrosion resistance + structural strength |
| Nuclear Power | Containment components, cooling system parts | High purity water, radiation environment | NB/T 47015 qualification; radiation resistance |
| Chemical Processing | Storage tanks, pipe spools, reactor vessels | Acidic media (H₂SO₄, HCl, HF) | Full corrosion protection; NB/T 47015 / GB/T 19079 |
| Marine & Offshore | Sea water heat exchangers, desalination equipment | Seawater, high chloride concentration | Galvanic isolation; crevice corrosion prevention |
| Pharmaceutical | Reactor vessels, storage tanks | Aggressive cleaning chemicals, high purity requirements | Surface finish; biocompatibility; cleanability |
| Food Processing | Tanks, piping, heat exchangers | Food-grade chemicals, steam sterilization | Hygienic surface; corrosion resistance; food safety compliance |
12. Conclusion and Recommendations
The explosion-rolling TA1/Q345R composite plate technology represents a sophisticated manufacturing solution that leverages the company's core explosion welding expertise while adding the benefits of rolling refinement. The detailed microstructural understanding, mechanical property data, and process parameter knowledge documented in this technical entry provide a solid foundation for:
- Process optimization: Further refinement of impact parameters and rolling conditions to maximize bond quality and minimize intermetallic formation
- Standardization: Development of internal process specifications and quality standards based on the documented parameters and acceptance criteria
- Qualification expansion: Extension of the qualification database to additional material combinations (e.g., TA2/Q345R, TC4/Q345R, Hastelloy/Q345R) using the same methodological framework
- Customer engagement: Use of technical data to support engineering proposals, design reviews, and qualification audits with major end-users and regulatory bodies
- Continuous improvement: Integration of post-market performance data and failure analysis findings back into process development for ongoing quality enhancement
This technical capability positions Cladding Technology Shanxi Co., Ltd. as a qualified supplier of high-integrity bimetallic composite products for the most demanding industrial applications, with documented expertise spanning the full chain from raw material selection through explosion welding, rolling, NDT, and final product qualification.