Effect of Heat Treatment on the Microstructure and Properties of Explosively Welded 316L-Q235B Clad Plate

Literature Overview

This study examines the influence of post-explosion heat treatment on the microstructure, bonding quality, and mechanical properties of explosively welded 316L stainless steel / Q235B carbon steel clad plates. The research is directly relevant to engineers fabricating pressure vessels, heat exchangers, and storage tanks where explosive cladding provides a metallurgically sound bond between dissimilar metals without the dilution issues inherent in welding processes. The study employs explosive cladding with 316L stainless steel cladding layer (3-6 mm) on Q235B carbon steel backing (20-100 mm), followed by solution annealing at 1050°C, 1100°C, and 1150°C.

Core Technical Findings

Explosive welding produces a characteristic wavy bonding interface with mechanical interlocking and metallurgical bonding. The as-explosively welded condition exhibits a hard, deformed microstructure at the interface with high residual stresses (300-500 MPa) and potential for intermetallic compound formation. Heat treatment modifies the interface microstructure, relieves residual stresses, and optimizes the mechanical properties for pressure vessel service.

Interface Microstructural Evolution

Bond Strength and Mechanical Properties

The 1100°C solution annealing provides the optimal balance of bond strength, ductility, and residual stress relief. Temperatures above 1150°C may cause excessive grain growth at the interface, reducing bond strength and increasing susceptibility to intergranular cracking.

Process and Standards Analysis

Explosive cladding process parameters:

According to ASTM A263 (explosively clad plate) and NB/T 47002 (pressure vessel steel plates), the clad plate must meet minimum bond strength requirements (172 MPa shear), pass bond line testing (shear test per ASTM A263), and satisfy intergranular corrosion testing for the cladding layer.

Heat Treatment Design Considerations

The heat treatment schedule must address:

1. Solution temperature: 1100°C optimal for 316L recrystallization
2. Hold time: 1 hour per 25 mm of total plate thickness
3. Cooling rate: Air cooling preferred; water quenching may cause cracking in thick plates
4. Stress relief: The solution annealing simultaneously relieves residual stresses
5. Multiple heat treatments: Avoid repeated cycles to prevent grain coarsening

Engineering Practice Integration

Explosively welded 316L/Q235B clad plates are widely used in pressure vessels for chemical processing, food processing, and pharmaceutical applications. A practical case involved a 5000 mm diameter storage tank with 316L/Q235B explosive clad plate shell (6 mm cladding + 20 mm backing). After initial solution annealing at 1050°C, the bond strength was 195 MPa with residual stresses of 250 MPa. Increasing the solution temperature to 1100°C improved the bond strength to 245 MPa and reduced residual stresses to 80 MPa, meeting the requirements for 1.0 MPa design pressure service.

Common Defects and Countermeasures

Key Questions and Reflections

The study demonstrates that explosive welding produces a mechanically sound bond that can be further optimized through solution heat treatment. The as-explosively welded condition contains high residual stresses and a deformed microstructure that, while providing adequate bond strength, may be susceptible to stress corrosion cracking in aggressive environments. Solution annealing at 1100°C transforms the interface into a recrystallized, low-stress condition with superior mechanical properties.

Another important reflection is the comparison between explosive cladding and weld overlay cladding. Explosive cladding produces a dilution-free bond with no intermetallic compound formation, while weld overlay inevitably involves dilution and potential intermetallic formation. However, explosive cladding requires specialized facilities and is limited to plate dimensions, while weld overlay can be applied to complex geometries. Engineers should select the appropriate cladding method based on the specific application requirements.

The economic analysis shows that explosive cladding cost is 20-30% higher than weld overlay for small batches but becomes competitive for large production runs. The heat treatment cost is approximately 5-8% of the total cladding cost.

Study Insights and Implications

The research establishes that solution annealing at 1100°C is the optimal heat treatment for explosively welded 316L/Q235B clad plates, providing maximum bond strength, minimum residual stress, and excellent corrosion resistance. Engineers should adopt a systematic approach to heat treatment qualification, including coupon testing at multiple solution temperatures, bond strength testing per ASTM A263, and field validation on representative plates. The key insight is that explosive welding produces a high-quality bond that can be further optimized through appropriate heat treatment, making it a preferred method for critical pressure vessel applications where metallurgical soundness is paramount.