Dynamic Stress and Residual Stress Analysis During the Cladding Process of Large Frame Structures

Literature Overview

This 2010 study by Zhong Zhiyong and colleagues from Baosteel Equipment Maintenance Co., Ltd. (Baosteel Machinery Factory) addresses the dynamic stress and residual stress behavior during the cladding process of large frame structures. Published in the Journal of Welding, this work tackles a practically significant problem in heavy industrial equipment manufacturing, where large steel frame structures require protective cladding layers for corrosion or wear resistance.

Core Technical Content

Large frame structures—such as those used in rolling mill equipment, bridge cranes, and heavy machinery bases—present unique challenges during cladding operations due to their size, complexity, and the significant thermal and mechanical distortions that can occur during welding. The study employs both experimental measurement and numerical simulation approaches to characterize the stress state during and after the cladding process.

Stress Development Mechanism

The welding cladding process on large frame structures involves complex stress development driven by:

1. Thermal expansion and contraction: Localized heating creates differential thermal expansion between the weld zone and the surrounding cooler base metal, generating compressive stresses in the heat-affected zone and tensile stresses in the surrounding material.
2. Phase transformation effects: If the base material or overlay alloy undergoes phase transformations during cooling, volume changes associated with these transformations contribute to the residual stress state.
3. Plastic deformation: The intense local plastic deformation in the weld zone during solidification and subsequent cooling creates a complex stress distribution that depends on the constraint conditions imposed by the surrounding structure.
4. Sequential welding effects: In multi-pass cladding operations, each subsequent pass is deposited on a pre-stressed substrate, creating a cumulative stress state that evolves with each pass.

Dynamic Stress Characteristics

The dynamic stress component during the cladding process differs fundamentally from the residual stress that remains after cooling. Dynamic stresses arise from:

• Rapid thermal loading during the welding arc application
• Mechanical forces from wire feed and torch movement
• Thermal shock from the interaction of the hot weld pool with cooler surrounding material
• Vibration and oscillation of the large structure under welding-induced thermal gradients

Numerical Simulation Approach

The finite element analysis (FEA) approach used in this type of study typically involves:

1. Thermal analysis: Modeling the temperature field evolution during welding, including heat input, heat transfer, and phase transformation effects.
2. Mechanical analysis: Coupling the thermal results to a thermo-elastoplastic analysis that accounts for plastic deformation, creep, and phase transformation strains.
3. Sequential welding simulation: Modeling each welding pass individually, transferring the stress state from one pass to the next as boundary conditions.

Key modeling assumptions include:

• Elastic-plastic material behavior with appropriate temperature-dependent properties
• Small-strain formulation (valid for moderate distortions)
• Perfect bond between overlay and substrate (no debonding)
• Adiabatic or semi-adiabatic conditions during the welding process

Engineering Practice Implications

The findings from this type of stress analysis have direct practical significance for the fabrication of large clad structures:

1. Welding sequence optimization: The welding sequence must be carefully planned to minimize cumulative distortion and residual stress. Alternating directions, symmetric sequences, and step-back welding are common strategies.
2. Preheat and interpass temperature control: Maintaining appropriate preheat temperatures (typically 100–250°C for carbon steel substrates) reduces thermal gradients and minimizes the risk of cold cracking while also reducing peak residual stresses.
3. Post-weld stress relief: For critical applications, post-weld stress relief (PWSR) is essential. Typical PWHT parameters include:

• Temperature: 580–650°C for carbon steel structures
• Holding time: 1 hour per 25 mm thickness (minimum 2 hours)
• Heating rate: Limited to prevent thermal shock
• Cooling rate: Controlled to prevent reformation of high stresses

1. Distortion control: For large frame structures, distortion control measures such as temporary bracing, backing bars, and拘束 devices are essential to maintain dimensional accuracy within specified tolerances.

Key Questions and Reflections

A fundamental challenge in cladding large frame structures is the interaction between stress relief and overlay integrity. Post-weld stress relief at elevated temperatures can potentially weaken the bond between the overlay layer and the substrate, particularly if the overlay alloy has a significantly different thermal expansion coefficient from the substrate. This is particularly relevant for dissimilar metal cladding where the coefficient of thermal expansion mismatch can be substantial.

Another important consideration is the effect of residual stresses on the long-term service behavior of the clad structure. High residual tensile stresses in the overlay layer can:

• Accelerate fatigue crack initiation and propagation
• Promote stress corrosion cracking in aggressive environments
• Reduce the effective fatigue life of the component
• Interact with service loads to create local stress concentrations

The study raises the question of whether in-situ stress measurement techniques—such as hole-drilling strain gauge methods, neutron diffraction, or X-ray diffraction—can be practically implemented on large structures to verify that residual stress levels are within acceptable limits.

Study Insights and Conclusion

This research contributes valuable understanding of the stress development mechanisms during cladding of large structures, providing a foundation for improved welding sequence design and distortion control. The key insight for practicing engineers is that residual stress management must be integrated into the overall fabrication strategy rather than treated as a post-fabrication correction. A systematic approach that combines welding procedure optimization, sequence planning, real-time monitoring, and post-weld treatment can significantly improve the dimensional accuracy and long-term reliability of large clad structures. The numerical simulation capabilities demonstrated in this work provide a powerful tool for predicting and controlling welding-induced stresses before fabrication begins, reducing the need for costly corrective measures after the fact.