Numerical Simulation and Measurement of Temperature and Stress Fields in Hot Rolling Mill Roll Cladding Test Specimens

Literature Overview

This study presents a comprehensive investigation into the thermal and mechanical behavior of hot rolling mill roll cladding through the combined use of finite element numerical simulation and experimental temperature and strain measurement. Hot rolling mill rolls operate under extreme conditions involving high temperatures, heavy contact stresses, and thermal cycling, making the integrity of the cladding layer critical for roll life and product quality. The research employs thermocouples and strain gauges embedded in test specimens during the cladding process, with results validated against a three-dimensional transient thermal-structural coupled finite element model. This dual approach of simulation and measurement provides a rigorous methodology that other engineers can replicate for their own cladding process optimization.

Numerical Simulation Methodology

The finite element model was constructed using ABAQUS with a 3D transient coupled thermal-stress analysis. The roll blank was modeled as a 45CrMo steel cylinder with a diameter of 450 mm and a length of 600 mm, while the overlay layer was represented as a nickel-based alloy deposit with a nominal thickness of 6 mm. The thermal boundary conditions included convective and radiative heat transfer from the weld pool, with a moving heat source modeled as a Gaussian distribution. The weld travel speed was set at 0.8 m/min, and the heat input was calibrated at 15 kJ/mm based on experimental measurements.

The following table presents the key material properties used in the simulation:

The simulation was performed in two stages: first, a transient thermal analysis to obtain the temperature history at each node, followed by a structural analysis using the thermal results as body loads. This sequential coupled approach was selected for computational efficiency while maintaining acceptable accuracy for the temperature ranges encountered in the cladding process.

Experimental Measurement Approach

The experimental setup included K-type thermocouples with 0.5 mm diameter wires, embedded at various distances from the weld centerline (3, 6, 10, 15, and 25 mm) and at different depths within the roll blank (surface, 5 mm, 15 mm, and 30 mm from surface). Strain gauges of foil type were applied on the roll surface at corresponding locations to measure the residual stress evolution during and after welding. The measurement system sampled data at 10 Hz to capture the rapid temperature changes during the welding process.

The measured peak temperatures at the weld centerline surface reached approximately 1850 degrees Celsius, with a rapid decay to below 600 degrees Celsius within 5 mm from the centerline. The cooling rate at the weld centerline was measured at approximately 35 degrees Celsius per second, while at 15 mm from the centerline, it decreased to about 8 degrees Celsius per second. These cooling rates have direct implications for the microstructure evolution and residual stress distribution in the overlay and heat-affected zone.

Temperature and Stress Field Analysis

The comparison between simulated and measured temperature fields showed excellent agreement, with deviations within 5 percent for most measurement points. The maximum discrepancy occurred at the peak temperature region, where the simulation slightly underestimated the peak by approximately 80 degrees Celsius. This deviation is attributed to the simplified heat source model and the neglect of phase change effects in the weld pool. The residual stress distribution, however, showed more variation between simulation and measurement, with the simulation predicting higher tensile residual stresses in the overlay layer by approximately 15 to 25 MPa.

The residual stress analysis revealed that the overlay layer experiences significant tensile residual stresses in the longitudinal direction, reaching values of 280 to 350 MPa, while the transverse residual stresses are lower at 150 to 200 MPa. The base metal experiences compressive residual stresses beneath the overlay, which are beneficial for fatigue resistance but may lead to distortion in thin-walled roll components. The stress distribution is asymmetric due to the directional nature of the welding process, with higher stresses near the start and end of the weld.

Practical Implications for Rolling Mill Roll Cladding

The findings of this study have direct implications for the design and fabrication of hot rolling mill rolls. The high tensile residual stresses in the overlay layer, combined with the thermal cycling during rolling service, can lead to fatigue cracking at the overlay-base metal interface. The study recommends the incorporation of a stress-relieving heat treatment at 620 degrees Celsius for 2 hours per inch of thickness, followed by controlled cooling in a furnace. This treatment reduces the residual stresses by approximately 60 to 70 percent without significantly affecting the hardness of the overlay layer.

Furthermore, the thermal gradient analysis highlights the importance of controlling the welding sequence. For large-diameter rolls, a spiral or multi-pass welding sequence that progressively builds up the overlay thickness can reduce the thermal shock and minimize the risk of cracking. The study also suggests that the use of a backing plate with improved thermal conductivity can help to moderate the cooling rate and reduce residual stresses.

Study Insights and Recommendations

The most significant insight from this study is the validation that numerical simulation, when properly calibrated with experimental data, can serve as a powerful predictive tool for cladding process optimization. However, the study also cautions that simulation results should always be validated with physical measurements, particularly for residual stress predictions where material constitutive models introduce significant uncertainties. Engineers are encouraged to adopt a hybrid approach: use simulation to explore process parameter variations efficiently, then confirm critical findings with targeted experimental measurements.

The methodology presented in this study can be extended to other cladding applications, including weld overlay on pressure vessel internals and heat exchanger tubes. The key is to establish a reliable measurement protocol that captures the essential thermal and mechanical histories, and to develop material property databases that are accurate over the relevant temperature range. This study exemplifies the rigorous engineering approach that is essential for advancing the science and practice of weld overlay technology in heavy industry.