Numerical Simulation and Experimental Measurement of Temperature and Stress Fields in Hot Rolling Roll Weld Overlay Specimens
1. Definition and Technical Principles
Thermal and residual stress field simulation during weld overlay on hot rolling mill rolls is a multidisciplinary engineering activity that integrates finite element analysis (FEA), thermomechanical modeling, and experimental metrology to predict and validate the transient temperature distribution and residual stress state generated during clad plate or overlay welding operations. The core principle involves solving the coupled heat conduction equation and thermoelastic-plastic constitutive equations in a sequential or fully coupled manner, using the moving heat source model (typically Goldak double-ellipsoidal or Gaussian distribution) to represent the energy input from the welding arc or wire feed process.
For hot rolling mill rolls, the substrate material (typically 4Cr5MoSiNiV or equivalent high-speed steel) exhibits excellent wear resistance and thermal stability at operating temperatures up to 600–800°C. However, the weld overlay layer—typically austenitic stainless steel (309/310) or nickel-based alloy (Inconel 625)—undergoes rapid thermal cycling during deposition. The mismatch in thermal expansion coefficients between the substrate and overlay (Δα ≈ 3–5 × 10⁻⁶/°C) generates significant residual stresses that can compromise cladding integrity, promote cracking, or cause premature delamination in service.
The numerical simulation workflow comprises:
- Thermal analysis phase: Solution of the 3D transient heat conduction equation with a moving heat source, accounting for phase changes, temperature-dependent material properties (thermal conductivity, specific heat, density), and convective/radiative boundary conditions.
- Mechanical analysis phase: Sequential mapping of the thermal history onto a mechanical model using the "elastic-plastic strain decomposition" method, where total strain is decomposed into elastic, thermal, and plastic components. Residual stresses are computed after cooling to ambient temperature with all plastic strains frozen.
- Experimental validation: Verification using thermocouples (Type K or Type N embedded in the specimen), infrared thermography, X-ray diffraction (XRD) residual stress measurement, or hole-drilling method per ASTM E837.
2. Category and Business Positioning
This capability belongs to the Process Qualification and Engineering Development category within the company's technical framework. It serves as the intellectual backbone connecting raw manufacturing execution to certified, repeatable, and code-compliant product delivery. In the context of Cladding Technology Shanxi Co., Ltd., this simulation-and-measurement competency positions the company as a technically sophisticated supplier capable of:
- Providing customers with predictive thermal-mechanical analysis reports that reduce design iterations and eliminate trial-and-error approaches.
- Supporting WPS (Welding Procedure Specification) qualification with quantitative residual stress data, satisfying demanding end-user requirements in the steel, mining, and cement industries.
- Enabling risk-based qualification strategies that minimize destructive testing while maintaining confidence in cladding integrity.
- Differentiating from competitors who rely solely on empirical methods without analytical validation.
3. Technical Purpose and Value
3.1 Residual Stress Prediction and Control
The primary objective is to predict peak tensile residual stresses in the heat-affected zone (HAZ) and overlay weld metal, identifying regions where stress concentrations may exceed the material's yield strength or fracture toughness threshold. For hot rolling roll overlays, residual stresses exceeding 400–500 MPa in the HAZ can initiate microcracking during subsequent grinding, heat treatment, or operational thermal cycling.
3.2 Distortion Prediction
Weld overlay introduces asymmetric thermal expansion that causes angular distortion, bow, and camber in roll blanks. Numerical simulation quantifies these geometric deviations, enabling pre-compensation in the welding sequence or post-weld straightening processes.
3.3 Process Optimization
Simulation results guide optimization of critical process parameters including heat input per pass, interpass temperature, travel speed, wire feed rate, and pass sequencing strategy. By minimizing peak temperatures and controlling thermal gradients, the simulation supports process design that reduces cracking susceptibility and improves metallurgical compatibility at the substrate-overlay interface.
3.4 Customer Value and Risk Reduction
Delivering validated simulation reports alongside physical specimens provides customers with:
- Quantitative assurance that residual stresses remain within acceptable limits for the intended service life.
- A documented engineering basis for accepting the cladding product without requiring full-scale destructive verification on production rolls.
- Accelerated approval timelines by reducing the number of required physical qualification trials.
4. Key Process and Implementation Points
4.1 Simulation Setup Parameters
| Parameter | Typical Value / Range | Notes |
|---|---|---|
| Substrate material | 4Cr5MoSiNiV / H13 / High-speed steel | Temperature-dependent properties required |
| Overlay material | 309L / 310 / Inconel 625 / Stellite 6 | Dependent on application |
| Heat source model | Goldak double-ellipsoidal | η_front = 0.6–0.8 |
| Heat input | 0.5–3.0 kJ/mm | Per pass, TIG/MIG dependent |
| Peak temperature (simulated) | 1200–1600°C | At weld centerline |
| Peak residual stress (simulated) | 200–550 MPa | In HAZ / weld root region |
| Interpass temperature | 150–300°C | Controlled to manage ΔT |
| Element size (near weld) | 0.3–0.5 mm | Refined mesh at weld zone |
| Element size (far field) | 2.0–5.0 mm | Progressive coarsening |
4.2 Experimental Measurement Methods
| Measurement Method | Standard Reference | Measurement Target | Accuracy / Resolution |
|---|---|---|---|
| Embedded thermocouples (Type K) | ASTM E220 | Temperature-time history at defined depths | ±2°C accuracy, 0.1 Hz sampling |
| IR thermography | ISO 18436 | Surface temperature distribution | ±5°C, spatial resolution 0.5 mm |
| X-ray diffraction (XRD) | ASTM E975 | Residual stress at surface and near-surface | ±20 MPa, 0.2–1.0 mm penetration |
| Incremental hole-drilling | ASTM E837 | Residual stress through-thickness | ±30 MPa, depth resolution 0.5–2.0 mm |
| Neutron diffraction | ASTM E1426 | Deep-subsurface residual stress | ±15 MPa, up to 10 mm depth |
| Strain gauge measurement | ASTM E2228 | Distortion / angular deformation | ±0.1 με resolution |
4.3 Simulation-to-Experiment Correlation Protocol
- Geometry definition: Replicate the exact specimen geometry (typically a flat coupon or cylindrical roll segment, 100 × 50 × 25 mm minimum) in the FEA model with identical boundary conditions to the physical fixture.
- Material property calibration: Obtain temperature-dependent thermal conductivity, specific heat, elastic modulus, yield strength, and plastic strain-hardening curves from the actual substrate and overlay materials used in the physical trial (via Gleeble testing or literature data validated by DSC/DTA).
- Thermal boundary condition matching: Apply convective heat transfer coefficients (h = 10–50 W/m²·K for air cooling) and radiation boundary conditions (ε = 0.7–0.9 for oxidized steel surfaces) consistent with the laboratory environment.
- Heat input calibration: Use the experimentally recorded arc power, travel speed, and wire feed rate to define the moving heat source magnitude. For TIG: I = 80–160 A, V = 12–18 V, v = 100–300 mm/min. For MIG: I = 120–220 A, V = 18–28 V, v = 200–600 mm/min.
- Thermal validation: Compare simulated temperature-time curves at thermocouple locations against experimental data. Acceptable agreement: peak temperature within ±50°C, cooling rate within ±20%.
- Mechanical validation: Compare simulated residual stress profiles (σ_x through-thickness) against XRD or hole-drilling measurements. Acceptable agreement: stress magnitude within ±50 MPa, stress gradient within ±20%.
- Model refinement: Adjust material properties, boundary conditions, or constitutive model parameters to achieve convergence between simulation and experiment. Document all iterations.
4.4 Critical Analysis Considerations for Hot Rolling Rolls
- Thermal history of multi-pass overlay: Each subsequent pass re-heats the previous weld metal, modifying the residual stress state. The simulation must model all passes sequentially, accounting for the superposition of thermal cycles.
- Thermo-mechanical fatigue: Hot rolling rolls experience cyclic heating during operation (ambient → 600–800°C → ambient). Residual stresses superimposed on thermal cycling stresses may accelerate crack initiation. The simulation should assess the combined stress state.
- Phase transformation effects: In martensitic substrate steels, non-isothermal phase transformations during cooling generate additional transformation plasticity strains that modify residual stress. The simulation must include phase-transformation kinetics (e.g., JMA equation for austenite decomposition).
- Grinding residual stresses: Post-weld grinding of the overlay surface introduces additional residual stresses. These can be modeled separately or included in a sequential analysis.
5. Applicable Standards and Acceptance Criteria
5.1 Simulation and Analysis Standards
- ASME BPVC Section VIII, Division 2, Part 5: Rules for fitness-for-service and residual stress assessment in pressure equipment (applicable by analogy for cladding integrity assessment).
- ASME BPVC Section IX, QW-401 through QW-452: Qualification requirements for welding procedures, including the need for documented residual stress data when specified by the end user.
- ISO 15614-1: Qualification of welding procedures for metallic materials—general requirements for simulation-based qualification support.
- GB/T 19418: Chinese national standard for weld overlay qualification procedures.
- API 579-1/ASME FFS-1: Fitness-for-service assessment methodology incorporating residual stress.
5.2 Residual Stress Acceptance Criteria
| Component / Location | Acceptance Limit | Basis |
|---|---|---|
| Overlay weld metal (surface) | Peak tensile σ_x ≤ 350 MPa | Industry practice for hot rolling rolls |
| HAZ (substrate side) | Peak tensile σ_x ≤ 450 MPa | Below yield strength of 4Cr5MoSiNiV (≈600 MPa at RT) |
| Interface region | No sustained tensile stress > 200 MPa | To prevent interface cracking / delamination |
| Distortion (flat coupon) | Angular distortion ≤ 0.5°/100 mm | Manufacturing tolerance for roll straightening feasibility |
| Simulation-experiment correlation | Temperature: ±50°C; Stress: ±50 MPa | Model validation acceptance threshold |
5.3 Measurement Standards
- ASTM E975: Determination of residual stress by X-ray diffraction.
- ASTM E837: Determination of residual stress by the hole-drilling strain gauge method.
- ISO 19220: Metalworking—determination of residual stresses by X-ray diffraction.
- GB/T 17043: Chinese standard for residual stress measurement by XRD.
- NACE MR0175/ISO 15156: Materials for H₂S environments—relevant when nickel-based overlays are used in sour service.
6. Common Risks and Controls
| Risk Category | Description | Mitigation / Control Measure |
|---|---|---|
| Material property uncertainty | Temperature-dependent properties of overlay alloys (especially Inconel 625, Stellite) are poorly characterized above 800°C in commercial databases. | Conduct Gleeble or DIL805 testing on actual materials; use sensitivity analysis to bound property uncertainty; document data sources. |
| Heat source model inaccuracy | Goldak model assumes axisymmetric energy distribution; actual MIG arc with shielding gas shows asymmetric heat input. | Calibrate heat source against experimental thermocouple data; use inverse analysis to optimize η_front and η_rear; validate with IR thermography. |
| Phase transformation neglect | Omitting austenite-to-martensite transformation in the substrate HAZ underestimates residual stress by 30–60%. | Include JMA or Koistinen-Marburger transformation kinetics; validate transformation temperatures by DSC on actual substrate. |
| Boundary condition mismatch | Simulation assumes adiabatic or uniform convection; actual fixture has localized constraints (clamping, backing bar contact). | Model actual fixture geometry; apply localized contact boundary conditions; perform parametric study of h-value. |
| Cracking prediction gap | Residual stress alone does not predict cracking; hydrogen content,拘束度 (restraint factor), and strain rate also matter. | Combine residual stress analysis with cracking susceptibility assessment (e.g., TCR method, hydrogen embrittlement analysis per ISO 3676). |
| Multi-pass superposition errors | Simplified sequential analysis may not capture interaction between passes in thick overlays (>5 mm). | Use "birth and death" element technique; model each pass as a discrete deposition event; validate against multi-thermocouple measurements at different depths. |
| Post-weld treatment effects | Post-weld heat treatment (PWHT) or stress-relief annealing modifies residual stress but is sometimes omitted from analysis. | Include PWHT cycle in simulation (e.g., 600°C × 2h for 309L overlay); predict post-PWHT residual stress distribution; validate by XRD post-PWHT. |
7. Application Across the Company's Three Technology Routes
7.1 TIG/MIG Weld Overlay Route
The simulation-and-measurement capability is most directly applicable to the TIG/MIG weld overlay route, which constitutes the company's primary manufacturing method for hot rolling mill roll cladding. Key applications include:
- WPS qualification support: Provide quantitative residual stress predictions to satisfy ASME Section IX or GB/T 19418 qualification requirements, reducing the number of destructive tests needed.
- Pass sequencing optimization: Use simulation to determine optimal pass sequence (e.g., spiral, transverse, longitudinal) that minimizes peak residual stress and angular distortion for large-diameter rolls (D500–D1000 mm).
- Heat input management: Predict peak temperature at the substrate-overlay interface to ensure it remains below the critical temperature for microstructural degradation (typically 850°C for 4Cr5MoSiNiV to avoid excessive grain growth).
- Post-weld straightening prediction: Quantify residual distortion to determine required straightening force and energy, optimizing post-weld machining operations.
- Customer qualification packages: Deliver simulation reports alongside physical test specimens (tensile, hardness traverse, macro/micro etch, XRD residual stress) as a comprehensive qualification dossier.
7.2 Hydraulic Explosive Bonding Route
While hydraulic explosive bonding does not involve welding heat input in the same sense, thermal-stress simulation remains relevant in the following contexts:
- Pre-bonding thermal conditioning: If the substrate or cladding plate is pre-heated to improve formability or reduce yield strength for bonding, simulation predicts the thermal gradients and resulting residual stresses that may affect bond quality.
- Post-bonding stress assessment: The explosive bonding process itself generates significant plastic deformation and residual stresses. Simulation can predict the stress state in the bond interface and validate against XRD measurements to ensure the bond is free of stress-induced delamination risk.
- Thermal expansion mismatch in service: For clad plates used in hot service (e.g., hot rolling mill table rolls), simulation predicts the combined effect of bonding residual stresses and operational thermal cycling on interface integrity.
- WPS qualification for bonded-clad plate welding: When hydraulic explosively bonded clad plates are subsequently welded (e.g., for fabricating a roll shell), the residual stress state from bonding must be incorporated into the welding simulation to predict the final stress distribution.
7.3 Explosion Welding Route
Explosion welding involves higher-energy impacts and more complex thermal-mechanical histories than hydraulic bonding. The simulation capability supports:
- Process parameter optimization: Predict the temperature and stress states at the collision interface during explosion welding (velocities of 2–5 m/s) to ensure metallurgical bonding without excessive heat input that could cause intermetallic formation.
- Residual stress mapping: Model the post-explosion stress distribution through the clad plate thickness, identifying regions of high tensile stress that may require stress-relief treatment.
- Service life prediction: Combine explosion welding residual stresses with operational thermal cycling (for hot rolling rolls) to predict fatigue life at the clad interface using fracture mechanics approaches (e.g., Paris law crack growth under combined residual and cyclic loading).
- Comparison with weld overlay: Quantitatively compare residual stress states achieved by explosion welding versus multi-pass TIG/MIG overlay, providing customers with data-driven selection criteria based on their specific application requirements.
8. Contribution to Qualification Building, Product Delivery, and Customer Value
8.1 Qualification Building
The numerical simulation and experimental measurement capability directly accelerates and strengthens the company's qualification portfolio. By providing analytical validation of residual stress states, the company can:
- Reduce qualification lead time by 30–50% through simulation-guided process design that minimizes trial iterations.
- Expand qualification scope to cover a wider range of substrate-overlay material combinations and thicknesses by extrapolating validated simulation models.
- Meet increasingly stringent customer requirements (particularly from European and Japanese steel mills) that mandate residual stress documentation as part of qualification acceptance.
- Build a proprietary database of validated thermal-mechanical models that becomes an intellectual property asset and competitive barrier.
8.2 Product Delivery
- Enable confident delivery of large-diameter hot rolling mill rolls (up to D1200 mm) with documented residual stress assurance, reducing the need for 100% destructive testing on production articles.
- Support post-weld heat treatment (PWHT) design by predicting the required temperature and duration to reduce residual stresses below acceptance limits.
- Provide customers with predictive service-life models based on validated residual stress data, enhancing confidence in the delivered product.
- Reduce field failures and warranty claims by proactively identifying and controlling residual stress hotspots before product shipment.
8.3 Customer Value
- Risk reduction: Customers receive quantitative assurance that the cladding will not delaminate or crack during service, reducing unplanned downtime.
- Accelerated approval: Comprehensive simulation reports with experimental validation shorten customer engineering review cycles from weeks to days.
- Performance optimization: Simulation-guided process design enables the company to offer customers optimized cladding solutions tailored to their specific thermal cycling, wear, and mechanical loading conditions.
- Technical partnership: The ability to provide analytical support positions the company as a technical partner rather than a commodity supplier, supporting long-term contracts and premium pricing.
9. Conclusion
The capability to perform numerical simulation and experimental measurement of temperature and stress fields in hot rolling roll weld overlay specimens represents a critical engineering competency that underpins the company's ability to deliver qualified, high-integrity cladding products. By integrating validated finite element models with experimental metrology, the company transforms empirical manufacturing into a science-driven process, reducing risk, accelerating qualification, and delivering measurable value to customers across the steel, mining, cement, and power generation industries. This capability is applicable across all three manufacturing routes—TIG/MIG weld overlay, hydraulic explosive bonding, and explosion welding—providing a unified analytical framework for process qualification and product assurance.