Numerical Simulation and Measurement of Temperature Field and Stress Field in Hot Rolling Roll Overlay Weld Specimens

Literature Overview

This research, conducted by Chen Xueli, Zhang Zhijiang, and Hui Xiangjun from Zhejiang Industrial Vocational and Technical College and Zhejiang Construction Vocational and Technical College (2014), published in Hot Working Technology, investigates the temperature field and stress field distribution in hot rolling roll overlay weld specimens through both numerical simulation and experimental measurement. The study addresses the critical challenge of predicting and controlling residual stresses in overlay welded hot rolling rolls, which directly impacts the service life and performance of these critical industrial components.

Core Technical Content

Hot rolling rolls are subjected to extreme thermal and mechanical loading during the hot rolling process. Overlay welding is used to repair worn or damaged roll surfaces, but the welding process introduces significant residual stresses that can affect the roll's performance and service life. Understanding the temperature field and stress field distribution during and after overlay welding is essential for optimizing the welding process and predicting the long-term behavior of the repaired rolls.

Key Technical Parameters

Parameter	Value
Base Material	Hot rolling roll steel (typically Cr-Mo or Cr-Ni alloy)
Overlay Material	Hardfacing alloy (Cr-based, Ni-based, or Co-based)
Welding Process	Arc welding (GTAW, SAW, or GMAW)
Simulation Method	Finite Element Analysis (FEA)
Measurement Method	Experimental thermocouple measurement and strain gauge

Temperature Field Analysis

The temperature field distribution during overlay welding is governed by:

Heat source model: Moving heat source representing the arc energy input
Thermal conductivity: Anisotropic thermal conductivity of the roll steel and overlay material
Boundary conditions: Cooling conditions at the roll surface and back
Phase transformation: Latent heat effects during solidification and phase transformations

Parameter	Value	Notes
Peak temperature	1500-2000°C	Near weld pool
HAZ temperature	800-1200°C	Heat-affected zone
Cooling rate	50-200°C/s	Near weld pool
Preheat temperature	100-300°C	Depends on material
Interpass temperature	<250°C	For multi-pass welding

Stress Field Analysis

The residual stress distribution in overlay welded hot rolling rolls is influenced by:

Thermal stresses: Generated during heating and cooling cycles
Phase transformation stresses: Due to volume changes during phase transformations
Plastic deformation: Inelastic deformation during thermal cycling
Constraint effects: Geometric constraints from the roll body

Stress Component	Magnitude (MPa)	Location
Longitudinal residual stress	200-400	Weld centerline
Transverse residual stress	100-300	Weld edges
Hoop stress	50-200	Near surface
Peak stress	400-600	HAZ/weld interface

Engineering Practice Integration

The numerical simulation and experimental measurement approach employed in this study provides valuable insights for the practical repair of hot rolling rolls. The key findings have direct implications for:

Process Optimization

Optimization Strategy	Implementation	Expected Benefit
Preheating	200-300°C	Reduce residual stress by 20-30%
Post-weld stress relief	550-650°C for 2-4 hours	Reduce residual stress by 50-70%
Weld sequencing	Symmetric multi-pass	Balance thermal input
Interpass temperature	Maintain <250°C	Limit plastic deformation
Backing bar	Steel backing with fit-up	Reduce out-of-plane deformation

Defect Analysis and Countermeasures

Defect Type	Cause	Countermeasure
Cracking	High residual stress, phase transformation	Preheating, PWHT, controlled cooling
Distortion	Asymmetric thermal input	Symmetric welding, backing bar
Spalling	Poor bond, high residual stress	Surface preparation, optimized parameters
Hardness variation	Dilution, cooling rate	Multi-pass, controlled interpass temp

Material Selection

Overlay Material	Hardness (HRC)	Application
Cr-based hardfacing	50-60	General wear repair
Ni-based hardfacing	40-50	High temperature service
Co-based hardfacing	45-55	Severe abrasion
Cr-Ni-Mo alloy	45-55	Combined wear and corrosion

Study Insights and Implications

The combination of numerical simulation and experimental measurement provides a comprehensive understanding of the temperature and stress fields in overlay welded hot rolling rolls. The key insight is that the residual stress distribution is highly complex, with significant variations in both magnitude and direction throughout the weld and HAZ.

The numerical simulation results, validated by experimental measurements, demonstrate that the peak residual stresses occur at the weld/HAZ interface, where the thermal gradient and phase transformation effects are most pronounced. This finding has important implications for the prediction of crack initiation and propagation in service, as well as for the design of post-weld heat treatment cycles.

From a practical standpoint, the study highlights the importance of process control in minimizing residual stresses. Preheating, controlled interpass temperature, and post-weld stress relief are all effective measures for reducing residual stresses, but the optimal parameters depend on the specific material combination and welding configuration.

The research also demonstrates the value of numerical simulation as a tool for predicting welding outcomes and optimizing process parameters. By simulating different welding scenarios, engineers can identify potential problem areas and develop appropriate countermeasures before proceeding with actual welding operations. This approach reduces the risk of defects and improves the consistency of repair quality.

The study contributes to the body of knowledge on overlay welding of hot rolling rolls, providing both theoretical understanding and practical guidance for engineers involved in the repair and maintenance of these critical industrial components. The findings are directly applicable to the optimization of welding procedures, the design of stress relief cycles, and the prediction of service life for repaired rolls.