Explosive welding, also known as explosive cladding, is a solid-state welding process. It uses a controlled detonation to propel the cladding metal at high velocity against the backing metal, facilitating an atomic-level bond at the interface. The theory emerged in the 1940s, with American engineer Philipchuk achieving the first successful explosion weld between aluminum and steel .
The process generates extreme pressure gradients (up to 10 GPa) and detonation velocities of 2400-3600 m/s. The angled collision front creates a high-speed plasma jet that cleans the surfaces, enabling a clean bond. The high pressure causes metal near the collision front to behave like a viscous fluid, resulting in the characteristic wavy interface .
Precise control of explosive energy is crucial. Excessive energy can fracture the wavy interface or cause localized melting, forming brittle intermetallic compounds; insufficient energy prevents proper bonding. Explosive quantity depends on the metal's strength and thickness, and the environment is a key factor. The main steps include material preparation, surface treatment, assembly, explosion, finishing, and testing. Common cladding thicknesses are 3-25mm, as achieving adequate shear performance below 3mm is challenging .
Its core advantage is bonding dissimilar metal combinations (e.g., titanium, aluminum, copper, nickel to steel) often unachievable by conventional welding. It also allows large-area bonding in milliseconds while keeping the parent metals in solid state, preserving their properties. However, it's less suitable for complex shapes and requires expertise in explosion mechanics and strict safety regulations .
Weld overlaying was the earliest process for creating composite steel plates and is now often used for cladding components like heads, shells, and ring sections. The choice of method considers operational feasibility, position, chemical composition control of the overlay, and cost .
TIG and MIG are common methods. Balancing heat input is critical. High heat input increases deposition rate but can cause excessive dilution from the backing material, leading to off-spec cladding chemistry and requiring costly second layers. Low heat input reduces efficiency and may cause lack of fusion due to insufficient dilution. For large areas, submerged arc welding (SAW) and electroslag welding (ESW) are more economical. This process is suitable for components with wall thickness ≥25mm. If the heat-affected zone (HAZ) hardness in the backing steel exceeds limits after welding, post-weld heat treatment (PWHT), like tempering, is needed, considering its potential effect on the cladding material (e.g., avoiding sensitization temperatures for stainless steel cladding) .
Processing and Application of Composite Steel Plates
Plasma cutting is highly precise and yields clean cuts, making it ideal for composite plates. Cutting must always start from the cladding side. Thin plates can be sheared, also from the cladding side, to prevent edge tearing of the cladding metal .
Composite plates can be formed by cold processes like bending, rolling, forging, and stamping. Keeping the cladding surface and tooling clean is crucial. For cold deformation over 5%, stress relief annealing or intermediate annealing is usually required. During hot forming, heating temperature is critical: avoid the sensitization range for cladding like stainless steel, and ensure the temperature is within the austenitic single-phase zone for the backing steel, otherwise subsequent heat treatment is needed. After hot forming, the cladding surface must be cleaned to remove scale, annealing colors, tool marks, and corrosion to protect its special properties .
Welding composite plates requires ensuring the integrity of the cladding's special properties in the joint. Mutual dilution between the backing and cladding weld metals can be detrimental. Therefore, a transition layer weld is typically added between them to compensate for alloy element loss due to dilution from the backing metal; the transition layer filler metal should also have good plasticity and toughness. The common welding sequence for butt joints is: first the backing layer, then the transition layer, and finally the cladding layer. Qualified welding procedure specifications must be followed. Post-weld, slag, spatter, etc., should be removed. PWHT is often necessary for thick plates to relieve residual stresses .
Due to their combination of surface properties (e.g., corrosion resistance, hardness) and structural strength/toughness, composite plates are widely used in oil and gas, chemical, papermaking, pressure vessels, shipbuilding, offshore engineering, and water treatment .
Material Standards for Composite Steel Plates
Key standards include:
ASTM A263/SA263 (Stainless Steel Cr Clad)
ASTM A264/SA264 (Stainless Steel Cr-Ni Clad)
ASTM A265/SA265 (Nickel and Nickel Alloy Clad)
GB/T 8165 (Stainless Steel Clad Plates and Strips)
NB 47002.1 (Clad Plates for Pressure Vessels)
