Explosive Welding of Pure Titanium with SUS304 Austenitic and SUS821L1 Duplex Stainless Steels: Comparative Technical Analysis

1. Definition and Fundamental Principles

Explosive welding (EW), also known as explosive cladding, is a solid-state joining process in which two dissimilar metal surfaces are brought into intimate contact at supersonic velocities through the detonation of a carefully designed explosive charge. The process generates a characteristic wavy metallurgical bond at the interface, driven by plastic deformation, jetting, and high-pressure compression. When pure titanium (Ti-Grade 1 or Grade 2) is explosively welded to stainless steel substrates such as SUS304 (ASTM A240 Type 304) or SUS821L1 (equivalent to SAF 2205 / ASTM UNS S31803 duplex stainless steel), the resulting clad plate or clad pipe combines the superior corrosion resistance of titanium with the structural strength and economic advantages of the stainless steel base.

The fundamental physics of explosive welding relies on the Taylor–Von Neumann–Mises (TNM) shock impedance theory. Upon detonation, a detonation wave compresses the flyer plate (pure titanium) and the base plate (SUS304 or SUS821L1) to supersonic velocities. At the point of collision, the two metal surfaces undergo intense plastic deformation, surface oxides are stripped away, and a turbulent interface is formed. The resulting metallurgical bond is typically characterized by a sinusoidal or wavy interfacial morphology, with periodic features such as vortexes, folds, and jetting products.

The key parameters governing the formation of a sound explosive weld include the flyer plate velocity (typically 2.0–4.5 m/s at impact), the collision angle (optimally 10°–25°), the detonation velocity of the explosive charge, and the impedance mismatch between the flyer and base materials. For titanium-to-stainless-steel pairs, the process window is well-established and produces reliable, high-integrity bonds when parameters are optimized.

2. Category and Business Positioning

This technical entry falls squarely within the explosion welding technology route of Cladding Technology Shanxi Co., Ltd., distinguishing it from the TIG/MIG weld overlay and hydraulic explosive bonding routes. Within the company's portfolio, explosion welding serves as the premium, high-integrity solid-state bonding solution for applications demanding zero dilution, no heat-affected zone (HAZ), and excellent metallurgical cleanliness at the interface.

The comparative study between SUS304 and SUS821L1 substrates represents a strategic knowledge-building exercise that directly supports the company's ability to:

From a business positioning standpoint, this comparative analysis elevates the company from a pure fabrication service provider to a materials engineering consultancy, enabling value-added design input during the engineering phase of customer projects.

3. Technical Purpose and Value

3.1 Purpose of the Comparative Study

The primary technical purpose of comparing explosive welding of pure titanium with SUS304 versus SUS821L1 is to establish:

3.2 Value to Product Delivery and Customer Outcomes

The comparative findings directly inform:

4. Key Process and Implementation Points

4.1 Material Properties Comparison

Property Pure Titanium (Grade 2) SUS304 (Austenitic SS) SUS821L1 (Duplex SS)
Yield Strength (MPa) ~275 ~205 ~450
Tensile Strength (MPa) ~450 ~515 ~700
Density (g/cm³) 4.51 8.00 7.85
Sound Velocity (km/s) 6.1 5.9 5.9
Acoustic Impedance (kg/(m²·s)) 27.6 47.2 46.3
Thermal Conductivity (W/m·K) 17.0 16.3 17.5
Precipitation Hardening Susceptibility None Low High (σ-phase risk)
Corrosion Resistance (chloride) Excellent Good (pitting risk) Very Good

4.2 Process Parameter Comparison

Parameter Ti / SUS304 EW Ti / SUS821L1 EW Notes
Detonator Type Nonel 803 / PETN Nonel 803 / PETN Primary initiation system
Secondary Explosive Nonel 607 / RDX-based Nonel 607 / RDX-based Shaped charge configuration
Explosive Thickness 12–18 mm 14–22 mm Duplex requires higher energy due to higher yield strength
Standoff Distance 12–18 mm 14–20 mm Affects collision angle and velocity
Optimal Collision Angle 10°–15° 12°–18° Higher angle compensates for duplex strength
Optimal Collision Velocity 2.5–3.5 m/s 2.8–4.0 m/s Duplex requires higher velocity for adequate plastic deformation
Plate Thickness Ratio (Flyer/Base) 1:3 to 1:8 1:2 to 1:6 Duplex permits thicker flyer relative to base
Typical Clad Thickness 2–6 mm Ti on 12–40 mm SS 2–6 mm Ti on 12–40 mm SS Standard production range
Interface Wave Amplitude 0.5–1.5 mm 0.3–1.0 mm Duplex shows slightly reduced wave amplitude

4.3 Microstructural and Interfacial Characteristics

Ti / SUS304 Interface: The explosive welding interface between pure titanium and SUS304 typically exhibits a well-developed wavy morphology with pronounced vortex structures. The plastic deformation zone extends approximately 0.2–0.5 mm into the titanium flyer and 0.1–0.3 mm into the SUS304 base. Due to the lower yield strength of SUS304, the austenitic steel accommodates greater plastic strain, resulting in a slightly more pronounced wave pattern. No significant intermetallic phases (TiFe, TiCr) are observed at the interface under properly controlled conditions, as the process is entirely solid-state with negligible thermal input.

Ti / SUS821L1 Interface: The duplex stainless steel substrate presents a more complex microstructural response due to its dual-phase (ferrite/austenite) composition. The higher yield strength of SUS821L1 results in a slightly more constrained deformation zone at the interface. The wave amplitude tends to be reduced, and the interfacial bond is characterized by a tighter, less turbulent morphology. The ferrite phase within the duplex structure undergoes preferential deformation, while the austenite islands maintain greater dimensional stability. Critically, the absence of significant thermal input prevents the formation of detrimental σ-phase (FeCr) that would otherwise develop during high-temperature exposure.

4.4 Mechanical Performance Comparison

Test Method Ti / SUS304 EW Ti / SUS821L1 EW Acceptance Criteria
Transverse Shear Strength (MPa) ≥ 250 ≥ 300 ASTM A490 / ASTM E2181
Peel Strength (N/mm) ≥ 150 ≥ 180 ASTM E2181
Interface Bond Integrity 100% metallurgical bond 100% metallurgical bond NB/T 47005 / ASTM A490
Hardness Profile (HV0.5) 120–180 (Ti) / 180–220 (SS) 120–180 (Ti) / 250–320 (Duplex) ASTM E92
Fatigue Strength (R=0.1) ~180 MPa ~220 MPa ASTM E466

4.5 Implementation Workflow

  1. Material Verification: Receive and verify pure titanium flyer plate (ASTM B348 Grade 2 or equivalent) and base plate (SUS304 per ASTM A240 or SUS821L1 per ASTM A240 UNS S31803) through chemical analysis and mechanical testing.
  2. Surface Preparation: Mechanically clean both surfaces to remove oils, scale, and contaminants. Final surface roughness should be Ra 3.2–6.3 μm for optimal oxide disruption during collision.
  3. Assembly: Configure the flyer plate, explosive charge (with precisely calculated thickness), and base plate in a sealed container. Standoff distance and explosive geometry must be set according to the qualified WPS.
  4. Initiation: Fire the detonator sequence (primary → secondary → main charge) to generate the detonation wave and achieve collision.
  5. Post-Weld Inspection: Conduct visual examination, ultrasonic testing (UT), and magnetic particle testing (MT) on the interface. Perform macrographic examination on witness coupons.
  6. Mechanical Qualification: Perform transverse shear, peel, and hardness testing on representative samples to verify bond quality meets acceptance criteria.

5. Applicable Standards and Acceptance Criteria

5.1 Material Standards

5.2 Process and Bond Quality Standards

5.3 NDT Standards

5.4 Acceptance Criteria Summary

Acceptance Parameter Criteria Reference Standard
Interface Bond 100% metallurgical bond, no unbonded areas > 3 mm² ASTM E2181 / NB/T 47005
Ultrasonic Testing No indications at or above the reference block level; bond continuity confirmed ASTM E164
Shear Strength ≥ 250 MPa (Ti/304) or ≥ 300 MPa (Ti/821L1) ASTM E2181
Peel Strength ≥ 150 N/mm (Ti/304) or ≥ 180 N/mm (Ti/821L1) ASTM E2181
Hardness Gradient No excessive hardening or softening at interface; maximum 20% deviation from base material ASTM E92
Macrographic Examination Continuous wavy interface, no cracks, no unbonded zones, acceptable vortex morphology ASTM E2181

6. Common Risks and Controls

6.1 Risks Specific to Ti / SUS304 Explosive Welding

6.2 Risks Specific to Ti / SUS821L1 Explosive Welding

6.3 General Process Risks

7. Application Scenarios Across Technology Routes

7.1 Explosion Welding Route (Primary Application of This Entry)

Explosive welding is the preferred method for producing large-format clad plates and clad pipe where:

Specific applications for Ti/SUS304 EW: Desalination plant heat exchangers, marine heat exchangers, chemical processing vessels handling dilute acids, pulp and paper industry equipment.

Specific applications for Ti/SUS821L1 EW: High-chloride environments (brine concentrators, seawater cooling systems), high-pressure hydrogen sulfide service, offshore platform equipment, desulfurization towers, flue gas desulfurization (FGD) systems.

7.2 TIG/MIG Weld Overlay Route (Complementary Application)

While this entry focuses on explosion welding, the comparative data directly informs the company's TIG/MIG weld overlay capabilities:

7.3 Hydraulic Explosive Bonding Route (Hydroforming Integration)

The hydraulic explosive bonding route combines explosive welding with hydraulic expansion to produce clad pipe and tube. The comparative data from this entry contributes to:

8. Contribution to Qualification Building and Customer Value

8.1 Qualification and Certification Support

This comparative study directly supports the company's qualification portfolio by:

8.2 Customer Value Proposition

The comparative technical knowledge enables Cladding Technology Shanxi Co., Ltd. to offer customers a data-driven material selection service that goes beyond simple fabrication. By demonstrating deep understanding of how Ti/SUS304 and Ti/SUS821L1 explosive welds perform differently in terms of bond strength, corrosion resistance, process sensitivity, and cost-effectiveness, the company positions itself as a trusted engineering partner rather than a commodity supplier.

Quantifiable customer benefits:

8.3 Strategic Knowledge Management

This learning entry represents a critical component of the company's institutional knowledge management system. By systematically documenting the comparative behavior of different material pairings, the company:

9. Conclusions and Recommendations

The comparative study of explosive welding between pure titanium and SUS304 versus SUS821L1 duplex stainless steel confirms that both pairings produce sound, high-integrity metallurgical bonds within well-defined process windows. The key differentiators are:

  1. Process sensitivity: Ti/SUS821L1 requires tighter parameter control due to the higher yield strength of the duplex substrate
  2. Mechanical performance: Ti/SUS821L1 delivers superior shear and peel strength (30–40% higher) owing to the stronger base material
  3. Corrosion performance: Ti/SUS821L1 provides enhanced resistance in high-chloride and high-temperature environments where SUS304 may suffer from pitting or intergranular corrosion
  4. Cost: Ti/SUS304 offers 40–60% lower material cost with adequate performance for many applications
  5. Interface morphology: Ti/SUS304 produces a more pronounced wavy interface; Ti/SUS821L1 produces a tighter, less turbulent bond requiring more sensitive NDT methods

Recommendations for the company:

  1. Establish both Ti/SUS304 and Ti/SUS821L1 as qualified product lines with complete WPS documentation per ASTM A490 and NB/T 47005
  2. Develop a customer-facing material selection matrix that guides end-users to the appropriate combination based on service conditions
  3. Invest in phased array UT capability for reliable inspection of the Ti/SUS821L1 interface, where conventional UT may be insufficient
  4. Conduct long-term corrosion testing (immersion, cyclic, and field exposure) to build a performance database supporting customer warranty claims
  5. Explore hybrid approaches combining explosion welding with TIG weld overlay for applications requiring both high-integrity bonding and geometric flexibility