Multi-Field Coupled Numerical Simulation of Submerged Arc Surfacing Process for Rolling Mill Rolls

Literature Overview

This paper by Li Chang, Huang Qingchun, Chen Xinxue, Liu Zhaotai, and Han Xing from Liaoning University of Science and Technology presents a comprehensive multi-field coupled numerical simulation approach for submerged arc surfacing (SAW) of rolling mill rolls. Published in "China Surface Engineering" (Vol. 34, No. 4, 2021, pp. 117-128), the study establishes a thermal-elastic-plastic-fluid coupled model based on thermomechanical theory and computational fluid dynamics (CFD) to predict the evolution of temperature field, stress field, and flow field during the surfacing process.

Core Technical Innovation

Multi-Field Coupled Modeling Framework

The study addresses a significant gap in surfacing simulation literature by incorporating melt pool flow field analysis, which has been largely neglected in previous research focusing exclusively on temperature or stress fields:

Field	Previous Studies	This Study	Coupling Effect
Temperature field	Well-established	Included	Drives flow and stress
Stress field	Commonly studied	Included	Influenced by thermal gradients
Flow field	Rarely studied	Novel contribution	Affects heat transfer and microstructure
Electromagnetic field	Indirectly considered	Explicitly coupled	Drives melt pool convection

Governing Equations and Coupling Mechanisms

The coupled model incorporates:

Heat transfer equation: Transient heat conduction with moving heat source (Gauss distribution for arc heat input)
Momentum equation: Navier-Stokes equations with source terms for electromagnetic force, buoyancy, and surface tension
Continuity equation: Mass conservation for incompressible melt pool flow
Thermo-elastic-plastic constitutive equation: Von Mises yield criterion with Bauschinger effect for cyclic plasticity

Driving Forces for Melt Pool Flow

The study identifies and quantifies three primary driving forces for melt pool convection:

Force	Magnitude (typical)	Direction	Effect on Flow Pattern
Electromagnetic (Lorentz) force	10³-10⁴ N/m³	Downward and inward	Creates depression and radial flow
Surface tension (Marangoni)	10⁴-10⁵ N/m³	Depends on temperature gradient sign	Outward or inward flow along surface
Buoyancy (natural convection)	10²-10³ N/m³	Upward (hot metal rises)	Vertical circulation in pool

Key Simulation Results

Temperature Field Evolution

The temperature field simulation reveals:

Peak temperature at weld centerline: 1800-2200°C (liquidus to superheat)
HAZ temperature range: 1000-1400°C (austenitization zone)
Peak temperature location shifts slightly ahead of arc center due to travel direction
Temperature gradients are steeper in the depth direction than in the transverse direction

Stress Field Development

Residual stress analysis shows:

Region	Peak Residual Stress	Stress Type	Engineering Concern
Weld centerline	350-450 MPa	Tensile	Cracking risk
HAZ	200-300 MPa	Mixed	Distortion
Base metal (far from weld)	50-100 MPa	Compressive	Low concern
Surface near weld	300-400 MPa	Tensile	Spalling risk

Flow Field Patterns

The melt pool flow analysis reveals complex three-dimensional convection patterns:

Surface flow: Dominated by Marangoni effect, flowing outward from center (negative surface tension temperature coefficient)
Bottom flow: Electromagnetic force drives downward flow at centerline with return flow at pool edges
Circulation cells: Multiple convection cells form depending on the relative magnitude of driving forces
Flow velocity: Maximum velocities of 0.5-1.5 m/s within the melt pool

Effect of Surface Tension Temperature Coefficient

The sign of the surface tension temperature coefficient (dγ/dT) critically determines the flow pattern:

dγ/dT Sign	Flow Pattern	Pool Shape	Crack Risk
Negative (typical)	Outward surface flow	Wide, shallow pool	Lower
Positive (deoxidized)	Inward surface flow	Narrow, deep pool	Higher

Crack Prevention Analysis

The multi-field coupled model enables systematic analysis of cracking mechanisms:

Solidification Cracking

Caused by shrinkage stresses during solidification
Promoted by high sulfur and phosphorus content
Mitigated by: Reducing dilution, controlling cooling rate, adding grain refiners

Thermal Cracking

Caused by thermal stresses exceeding material strength
Promoted by high residual tensile stress and low ductility
Mitigated by: Preheating, post-weld stress relief, reducing heat input

Hydrogen-Induced Cracking

Caused by hydrogen diffusion into HAZ and weld metal
Promoted by high hydrogen content in flux and slow cooling
Mitigated by: Low-hydrogen flux, controlled cooling, bake-out treatment

Process Optimization Recommendations

Based on the simulation results, the following process optimization guidelines are recommended:

Heat input control: Optimize arc power and travel speed to achieve adequate penetration without excessive thermal distortion
Flux selection: Low-hydrogen basic flux to minimize hydrogen-induced cracking
Wire composition: Balanced alloy composition for hardness and toughness (typically 50-60 HRC for work rolls)
Preheating: 200-300°C to reduce thermal gradient and residual stress
Travel speed: 150-250 mm/min depending on wire diameter and desired bead geometry
Multi-pass strategy: Multiple thin passes preferred over single thick pass to reduce residual stress

Application to Rolling Mill Roll Remanufacturing

Roll Types and Surfacing Requirements

Roll Type	Material	Hardness Requirement	Key Performance
Work roll (hot strip)	H13, H21	45-55 HRC	Wear resistance, thermal fatigue
Work roll (cold strip)	H13, H21	50-60 HRC	Surface finish, dimensional accuracy
Backup roll	Alloy steel	35-45 HRC	Compressive strength
Pinch roll	Alloy steel	40-50 HRC	Wear resistance

Quality Control Protocol

A comprehensive quality control protocol for roll surfacing should include:

Pre-surfacing preparation: Roll surface cleaning, defect repair, dimensional verification
Welding procedure qualification: Per AWS D10.9 or equivalent standard
In-process monitoring: Temperature measurement, weld geometry verification
Post-weld inspection: Hardness mapping, macrographic crack examination, dimensional check
Heat treatment: Stress relief and/or hardening as required
Surface finishing: Grinding to specified surface roughness and dimensional tolerance
Final testing: Hardness verification, dimensional inspection, magnetic particle examination

Study Insights and Practical Implications

This paper represents a significant advancement in surfacing simulation methodology by incorporating melt pool flow field analysis into the coupled model. The flow field directly influences heat transfer rates, solidification patterns, and microstructural development, making its inclusion essential for accurate prediction of weld properties.

The practical value of this research lies in its ability to predict and prevent surfacing defects through process optimization before production begins. By understanding how electromagnetic forces, surface tension, and buoyancy interact to create complex flow patterns within the melt pool, engineers can select process parameters that minimize cracking risk while maintaining adequate deposition efficiency.

The thermal-elastic-plastic-fluid coupling framework developed in this study provides a template for analyzing other surfacing applications where melt pool convection plays a significant role. The methodology can be extended to laser surfacing, plasma surfacing, and other processes where precise control of melt pool dynamics is critical for achieving desired weld properties.

The integration of numerical simulation with experimental validation demonstrates the maturity of computational approaches in surfacing technology. As computational resources become more available, simulation-based process development will become increasingly important for reducing development time, minimizing trial-and-error costs, and enabling the design of optimized surfacing procedures for complex applications such as rolling mill roll remanufacturing.