Explosive Welding Preparation of Hastelloy C276 Q345R Clad Plate and Heat Treatment Study

Literature Overview and Industrial Significance

This literature examines the fabrication of Hastelloy C276 on Q345R clad plates through explosive welding, with particular attention to the effects of post-weld heat treatment on the microstructure, mechanical properties, and corrosion resistance of the composite. Hastelloy C276 is a nickel-molybdenum-chromium alloy renowned for its exceptional resistance to reducing acids, hydrochloric acid, and a wide range of corrosive media, making it indispensable in chemical processing, pharmaceutical manufacturing, and environmental remediation equipment. Q345R, a Chinese standard low-alloy structural steel with a minimum yield strength of 345 MPa, serves as an economical base material for pressure vessels and heat exchangers.

The combination of C276 and Q345R through explosive welding offers a cost-effective alternative to monolithic C276 construction, reducing material costs by 60–70% while maintaining the corrosion resistance of the cladding layer. However, the dissimilar metal nature of this combination introduces challenges related to thermal expansion mismatch, potential intermetallic formation, and residual stress management, all of which must be addressed through careful process design and appropriate heat treatment.

Core Technical Analysis of the Explosive Welding Process

The explosive welding of C276 on Q345R requires careful optimization of process parameters to achieve a metallurgically sound bond without introducing defects. The following table summarizes the key process parameters and their effects:

The collision velocity for this material combination typically ranges from 2.0 to 3.5 km/s, which is slightly lower than for lighter metal combinations due to the high density of both C276 and Q345R. The interface morphology exhibits the characteristic wavy pattern, with wave amplitudes of 0.15–0.35 mm and wavelengths of 1.5–3.0 mm. The diffusion layer thickness at the as-welded interface is typically 3–10 μm, containing a mixture of Fe-Ni, Fe-Mo, and Cr-Ni intermetallic compounds.

Microstructural Evolution at the Interface

The as-welded interface of C276-Q345R exhibits a complex microstructure characterized by severe plastic deformation on both sides of the interface, a thin diffusion zone, and a distribution of intermetallic compounds. The Q345R side shows elongated ferrite grains with pearlite colonies aligned in the direction of detonation, indicating significant plastic flow during the collision. The C276 side exhibits a recrystallized microstructure with fine grains near the interface, resulting from the rapid heating and cooling during the welding process.

Intermetallic compounds at the interface include Fe₂Mo, FeMo₃, Ni₃Fe, and Cr₂Ni, which form preferentially at the wave peaks where contact pressure is highest. The volume fraction of these intermetallics in the as-welded condition is typically 3–6%, which is within acceptable limits. However, the nature and distribution of these compounds change significantly after heat treatment, which is the central focus of this study.

Heat Treatment Effects on Microstructure and Properties

The study investigates the effects of various heat treatment cycles on the C276-Q345R clad plate, including solution treatment, aging, and stress relief annealing. The results demonstrate that heat treatment can significantly improve the mechanical properties and corrosion resistance of the composite while managing the intermetallic compound distribution.

Solution treatment at 1050°C for 1 hour followed by water quenching effectively dissolves most of the intermetallic compounds at the interface, resulting in a cleaner, more ductile bond. However, this treatment introduces significant residual stresses due to the thermal expansion mismatch between C276 and Q345R during cooling. The coefficient of thermal expansion for C276 is approximately 14.5 × 10⁻⁶/°C, while for Q345R it is approximately 12.0 × 10⁻⁶/°C, resulting in a differential strain of about 2.5 × 10⁻⁴ per degree Celsius during cooling from 1050°C to room temperature.

Subsequent aging at 750°C for 4 hours allows for the precipitation of beneficial phases within the C276 matrix, including the γ' (Ni₃(Al,Ti)) strengthening phase, which improves the overall mechanical properties of the cladding layer. This aging treatment also partially relieves the residual stresses introduced during solution treatment, resulting in a more stable microstructure.

Corrosion Performance After Heat Treatment

Corrosion testing was conducted through potentiodynamic polarization in 1 M HCl, 0.5 M H₂SO₄, and 3.5% NaCl solutions, as well as through long-term immersion testing. The results demonstrate that the combined solution-aging heat treatment cycle provides the best balance between mechanical properties and corrosion resistance.

The improvement in corrosion resistance after heat treatment is attributed to the dissolution of intermetallic compounds at the interface, which eliminates potential sites for galvanic corrosion initiation. Additionally, the precipitation of γ' phase during aging improves the homogeneity of the C276 microstructure, reducing local variations in corrosion potential.

Engineering Practice and Quality Control Considerations

The fabrication of C276-Q345R clad plates through explosive welding followed by heat treatment presents several practical challenges that must be addressed in industrial production. First, the dimensional accuracy of the clad plate after heat treatment must be maintained within acceptable tolerances, typically ±0.5 mm for width and ±0.3 mm for thickness. The thermal expansion mismatch during heat treatment can cause slight warping, which must be corrected through post-heat-treatment machining or mechanical flattening.

Second, the quality of the explosion weld interface must be verified through non-destructive testing before heat treatment. Ultrasonic testing using contact probes at frequencies of 2.5–5 MHz can detect lack of bonding and delamination defects. The acceptance criteria for UT inspection should require 100% of the interface to show continuous bonding, with no indications of lack of fusion exceeding 2 mm in length.

From a process control perspective, the study recommends implementing a PDCA (Plan-Do-Check-Act) cycle for each production batch. The Plan phase involves selecting optimal process parameters based on material specifications and previous experience. The Do phase involves executing the explosive welding and heat treatment according to the approved procedure. The Check phase involves comprehensive inspection through UT, macroscopic examination, and mechanical testing. The Act phase involves documenting results and making adjustments to the process parameters for subsequent batches.

The study concludes that explosive welding followed by a combined solution-aging heat treatment cycle is an effective method for producing high-quality C276-Q345R clad plates suitable for chemical processing and environmental remediation applications. The resulting composite combines the corrosion resistance of Hastelloy C276 with the structural strength and economic viability of Q345R, offering a compelling alternative to monolithic alloy construction. Future work should focus on extending the service life assessment through accelerated aging tests and evaluating the performance under actual process conditions, including cyclic temperature and pressure variations.