Numerical Simulation of Preheating Effects on Cooling Temperature Field and Residual Stress in Medium-High Carbon Steel Weld Overlay
1. Definition and Fundamental Principles
Numerical simulation of weld overlay processes on medium and high carbon steel substrates is an advanced computational engineering capability that employs finite element analysis (FEA) to predict and optimize the thermal and mechanical behavior of weld overlay operations. This specific technical competency focuses on quantifying how preheating parameters influence the cooling temperature field and residual stress distribution during the weld overlay of medium carbon steel (typically 0.25–0.60% C) and high carbon steel (0.60–1.00% C) base materials.
The fundamental principles underlying this simulation capability are rooted in coupled thermo-mechanical finite element modeling. The process involves the following core phenomena:
- Thermal Field Modeling: Simulation of transient heat transfer during welding, including heat input from the arc, convective and radiative heat losses, and conductive heat flow into the base material and deposited layers.
- Phase Transformation Modeling: Prediction of martensitic and bainitic phase transformations that occur during cooling of medium and high carbon steel, which generate volumetric expansion and contribute significantly to residual stress.
- Plastic Deformation Modeling: Computation of thermal plastic strain accumulation and elastic-plastic stress development during both heating and cooling cycles.
- Preheating Effect Quantification: Systematic evaluation of how initial substrate temperature modifies the cooling rate, phase transformation kinetics, and final residual stress state.
The cooling temperature field is governed by the heat conduction equation with moving heat sources, while the stress field is derived from the constitutive relationship coupling thermal strain, plastic strain, and transformation strain. In medium and high carbon steels, the critical cooling rate for martensite formation is relatively low, making the thermal history particularly sensitive to preheating conditions.
2. Category and Business Positioning
This capability falls within the company's Process Engineering and Qualification Development domain, serving as a critical analytical bridge between theoretical metallurgy and practical weld overlay production. It is positioned as follows within the company's three core technology routes:
- TIG/MIG Weld Overlay Route: Provides process parameter optimization for overlay welding on medium and high carbon steel equipment such as crankshafts, gears, bearings, and structural components. The simulation directly informs WPS (Welding Procedure Specification) development by predicting preheat requirements, interpass temperature limits, and post-weld heat treatment (PWHT) conditions.
- Hydraulic Explosive Bonding Route: Contributes to understanding the thermal and residual stress state of clad plate assemblies where medium or high carbon steel serves as the base layer, particularly when post-bonding weld overlay repairs or transition layers are required.
- Explosion Welding Route: Supports the analysis of residual stress states in explosively welded laminates containing carbon steel layers, and informs the design of subsequent weld overlay operations on such substrates.
In terms of business value, this simulation capability positions Cladding Technology Shanxi Co., Ltd. as a technically sophisticated provider capable of offering predictive process engineering rather than purely empirical trial-and-error approaches. This is particularly valuable when qualifying new WPS procedures for critical applications or when addressing customer requirements for documented process justification.
3. Technical Purpose and Value
3.1 Primary Technical Objectives
- Establish quantitative relationships between preheat temperature, cooling rate, and residual stress magnitude in medium and high carbon steel weld overlay.
- Identify critical cooling rate thresholds that trigger martensitic transformation and associated cracking risks.
- Optimize preheating strategies to minimize residual stress while maintaining acceptable microstructure in both the overlay deposit and the heat-affected zone (HAZ).
- Provide computational evidence to support WPS qualification parameters, reducing the number of physical coupon tests required.
- Enable predictive assessment of new applications before physical trials, reducing development time and material costs.
3.2 Customer and Operational Value
The simulation capability delivers measurable value through:
- Risk Reduction: Predicting hot cracking, cold cracking, and distortion risks before production welding begins, thereby preventing costly rework and component rejection.
- Efficiency Gains: Optimizing preheat and interpass temperature parameters to minimize fuel consumption, reduce welding time, and lower post-weld stress relief requirements.
- Qualification Support: Providing documented analytical justification that strengthens WPS packages submitted to customer or third-party approval authorities.
- Knowledge Retention: Converting individual operator experience into documented, transferable engineering knowledge through simulation-based learning and analysis.
4. Key Process and Implementation Points
4.1 Simulation Methodology
The numerical simulation follows a rigorous coupled thermo-mechanical analysis workflow:
- Geometry Modeling: Creation of a representative weld overlay geometry including substrate, deposited layers, and boundary conditions reflecting the actual production configuration.
- Material Property Definition: Input of temperature-dependent thermal conductivity, specific heat, elastic modulus, yield strength, and thermal expansion coefficient for both base material and weld metal. Phase transformation parameters (transformation temperature, volumetric expansion) are defined according to the specific carbon steel grade.
- Heat Source Modeling: Implementation of a moving heat source model (e.g., Goldak double-ellipsoid or Gaussian) calibrated to match measured bead geometry and thermal cycles from production trials.
- Thermal Analysis: Transient heat transfer simulation capturing the welding sequence, including preheating, multi-pass deposition, interpass cooling, and post-weld cooling.
- Mechanical Analysis: Sequential coupling of thermal results to compute residual stress and strain, accounting for elastic-plastic behavior and phase transformation strain.
- Parametric Study: Systematic variation of preheat temperature, heat input, interpass temperature, and welding speed to map the full process window.
4.2 Critical Simulation Parameters
| Parameter | Typical Range (Medium Carbon Steel) | Typical Range (High Carbon Steel) | Influence on Cooling/Stress Field |
|---|---|---|---|
| Preheat Temperature | 150–300 °C | 250–450 °C | Reduces peak cooling rate; lowers peak residual stress by 15–35%; delays martensite start temperature |
| Heat Input | 0.8–2.5 kJ/mm | 1.2–3.5 kJ/mm | Higher heat input increases weld pool size and reduces cooling rate; may increase distortion |
| Interpass Temperature | 150–350 °C | 250–450 °C | Controls cumulative thermal cycles; prevents excessive cooling between passes |
| Cooling Rate (800→500 °C) | Target: <15 °C/s | Target: <5 °C/s | Critical threshold for martensite avoidance; directly controlled by preheat and heat input |
| Peak Residual Stress | Without preheat: 300–450 MPa | Without preheat: 350–550 MPa | Reduced by 20–40% with optimized preheating; critical for cracking resistance |
| Welding Speed | 3–8 mm/s (TIG) | 2–5 mm/s (TIG) | Slower speed increases heat input and reduces cooling rate; affects bead profile |
4.3 Preheating Strategy Optimization
The simulation reveals several key findings regarding preheating effectiveness:
- Localized vs. Global Preheating: Localized preheating (torch or induction) is effective for thin sections but may create thermal gradients that introduce additional stress. Global preheating (oven) provides uniform thermal conditions but is impractical for large components. Simulation quantifies the stress trade-offs for each approach.
- Preheat Temperature Plateaus: Beyond a critical preheat temperature (typically 250–350 °C depending on carbon equivalent), the marginal reduction in peak residual stress diminishes significantly. The simulation identifies this plateau to avoid unnecessary energy expenditure.
- Preheat Maintenance: Simulation demonstrates that maintaining preheat temperature during multi-pass welding is more effective than a single initial preheat, as the substrate cools significantly between passes in large thermal mass components.
- Preheat and PWHT Interaction: The simulation evaluates combined preheat-PWHT strategies, showing that moderate preheating with subsequent full stress relief achieves the best residual stress reduction with manageable distortion.
4.4 Material-Specific Considerations
| Carbon Steel Grade | Carbon Equivalent (CE) | Key Metallurgical Concern | Simulation-Informed Preheat | Acceptable Cooling Rate |
|---|---|---|---|---|
| Q345 (GB/T 1591) | 0.40–0.45 | Martensite in HAZ; cold cracking | 150–200 °C | <25 °C/s (800→500 °C) |
| 42CrMo (GB/T 3077) | 0.55–0.60 | Quench cracking; HAZ embrittlement | 250–350 °C | <10 °C/s (800→500 °C) |
| 45 Steel (GB/T 699) | 0.45–0.50 | Martensite formation; residual stress | 200–300 °C | <15 °C/s (800→500 °C) |
| 50CrVA (GB/T 3077) | 0.55–0.65 | Hardness exceedance; cracking | 300–400 °C | <8 °C/s (800→500 °C) |
| High Carbon Tool Steel | 0.80–1.00 | Severe cracking; quench sensitivity | 350–500 °C | <5 °C/s (800→500 °C) |
5. Applicable Standards and Acceptance Criteria
5.1 Process Qualification Standards
- NB/T 47014—Qualification Rules for Welding Procedures and Welders of Pressure Vessels: Governs WPS qualification for pressure vessel applications where medium and high carbon steel weld overlay may be required. Simulation results can support the selection of preheat and PWHT parameters within the qualified range.
- GB/T 985.1—Rules for Welding Qualification: Specifies qualification requirements including preheat temperature, interpass temperature, and PWHT conditions that must be verified through simulation or physical testing.
- ASME BPV Section IX—Qualification Standards for Welding, Brazing, and Filler Metal Performance: Provides the framework for WPS qualification in ASME-coded pressure equipment. Simulation data supports the justification of procedure variables.
- ISO 15614—Qualification Testing of Welding Procedures for Metallic Materials: International standard for welding procedure qualification. Simulation provides supplementary evidence for procedure parameters.
- EN ISO 9606—Qualification Testing of Welders: Relevant when welder qualification is required for overlay welding on carbon steel components.
5.2 Material and Welding Standards
- GB/T 5185—Welding Technical Terminology: Defines terminology for preheating, interpass temperature, and residual stress measurements.
- GB/T 3375—General Terms of Welding: Provides standardized definitions for weld overlay terminology.
- ASTM A372—Standard Specification for Carbon and Alloy Steel Plate for Weld-Overlay: Defines substrate requirements for weld overlay applications.
- API 579—Fitness-for-Service: Relevant for assessment of residual stress in in-service components undergoing overlay repair.
- ISO 10042—Metallic and Ceramic Materials—Determination of Residual Stresses: Standard methods for residual stress measurement to validate simulation predictions.
- NACE MR0175/ISO 15156—Materials for Use in H2S Environments: May apply when overlay welding on carbon steel for sour service, with simulation informing PWHT requirements to control hardness.
5.3 Acceptance Criteria Derived from Simulation
| Acceptance Parameter | Criterion | Verification Method | Standard Reference |
|---|---|---|---|
| Peak Residual Stress | ≤ 0.6 × Yield Strength of base material | Simulation prediction validated by XRD or hole-drilling | ISO 10042 |
| HAZ Hardness | ≤ 250 HV (general); ≤ 22 HRC (sour service) | Simulation-informed PWHT schedule | NACE MR0175 |
| Cooling Rate (800→500 °C) | Below critical rate for specific steel grade | Thermocouple measurement; simulation validation | GB/T 985.1 |
| Preheat Temperature | Within qualified range per WPS | Thermocouple/infrared measurement | NB/T 47014 |
| Interpass Temperature | Within specified limits | Surface thermocouple monitoring | ASME BPV IX |
6. Common Risks and Controls
6.1 Metallurgical Risks
- Cold Cracking (Hydrogen-Induced Cracking): Medium and high carbon steels are highly susceptible to cold cracking when cooling rates exceed critical thresholds. Control: Simulation identifies the minimum preheat temperature required to keep cooling rates below the critical threshold. Hydrogen control through low-hydrogen consumables and adequate preheating is mandated.
- Hot Cracking: Excessive preheating combined with high heat input can increase hot cracking susceptibility in certain overlay alloys. Control: Simulation optimizes the preheat-heat input combination to minimize the time spent in the hot cracking temperature range (1200–800 °C).
- Excessive HAZ Hardness: Rapid cooling in high carbon steel HAZ produces hard martensitic structures prone to cracking. Control: Simulation-informed PWHT schedules (typically 550–650 °C for 2–4 hours depending on thickness) are prescribed to achieve ferrite-pearlite transformation and hardness reduction.
- Dissimilar Metal Dilution: In overlay applications on carbon steel, base metal dilution can alter the overlay composition and properties. Control: Simulation predicts dilution levels based on bead geometry and heat input, informing the selection of overlay alloy chemistry.
6.2 Process Risks
- Distortion: High preheat temperatures and large heat inputs can cause significant component distortion, particularly in thin-walled or asymmetric geometries. Control: Simulation predicts distortion magnitude and direction, enabling fixture design and post-weld machining allowances.
- Preheat Inadequacy: Insufficient or non-uniform preheating leads to localized high cooling rates and cracking. Control: Simulation maps the thermal field to identify minimum effective preheat zones and temperature uniformity requirements.
- Interpass Temperature Drift: In multi-pass overlay welding, interpass temperatures may drop below required levels between passes. Control: Simulation quantifies interpass cooling rates to establish maximum allowable interpass times or supplementary heating requirements.
6.3 Simulation-Specific Risks
- Material Property Uncertainty: Temperature-dependent material properties may be imprecise for specific steel grades. Control: Sensitivity analysis is performed on key material properties; critical properties (transformation temperature, yield strength) are measured experimentally for specific heats of material.
- Boundary Condition Simplification: Simulation models may oversimplify actual welding conditions. Control: Validation against measured thermocouple data and residual stress measurements from physical trials is mandatory before relying on simulation for production decisions.
- Phase Transformation Model Limitations: Simplified transformation models may not capture complex microstructural evolution in alloyed steels. Control: For critical applications, simulation results are supplemented with dilatometry data and metallographic verification.
7. Application Scenarios Across Technology Routes
7.1 TIG/MIG Weld Overlay Applications
The simulation capability has direct and extensive application in the TIG and MIG weld overlay route:
- Overlay Welding on Crankshafts and Shafts: Medium carbon steel (e.g., 42CrMo, 40Cr) crankshafts require overlay repair of worn journals. Simulation determines preheat and PWHT parameters to prevent cracking while maintaining dimensional accuracy. Typical application: overlay of Stellite or nickel-based alloys on 42CrMo shafts for wear resistance.
- Gear and Sprocket Repair: High carbon steel gears (e.g., 20CrMnTi after carburization) require careful overlay welding. Simulation predicts the thermal influence zone and residual stress to ensure overlay adhesion and minimize distortion of gear geometry.
- Valve Seat and Plug Overlay: Carbon steel valve bodies require overlay of cobalt-based or tungsten carbide alloys. Simulation optimizes preheat to prevent cracking in the high carbon steel body while ensuring proper metallurgical bonding.
- Transition Layer Welding: When overlaying austenitic or nickel-based alloys on high carbon steel, a transition layer (e.g., 309L) is required. Simulation predicts the thermal cycle through the multi-layer sequence to optimize each layer's parameters.
- Multi-Pass Build-Up Welding: For significant material buildup on carbon steel, simulation models the entire multi-pass sequence including cumulative thermal effects, interpass cooling, and final residual stress state.
7.2 Hydraulic Explosive Bonding Applications
- Post-Bonding Weld Overlay: When hydraulic explosive bonding produces clad plates with carbon steel base layers, subsequent weld overlay of functional alloys (e.g., nickel, tungsten carbide) may be required on the cladding surface. Simulation predicts the thermal interaction between the overlay weld and the bonded interface, ensuring the bonding interface is not compromised by excessive thermal input.
- Clad Plate Repair Welding: Simulation guides the welding parameters for repairing damaged areas on carbon steel clad plates, including preheat requirements to prevent cracking in the carbon steel substrate while preserving the bond quality at the interface.
- Edge Preparation Welding: When clad plates require edge welding or tack welding for assembly, simulation predicts the residual stress interaction between the weld and the pre-existing bonding interface residual stresses.
7.3 Explosion Welding Applications
- Explosively Welded Laminates with Carbon Steel: When carbon steel serves as one layer in an explosion-welded laminate, simulation predicts the residual stress state of the laminate and informs subsequent welding or overlay operations that may be performed on the assembled structure.
- Post-Explosion Welding: For structures assembled from explosion-welded components that require additional weld overlay (e.g., wear-resistant overlay on an explosion-welded carbon steel/copper laminate), simulation models the combined residual stress field from both the explosion bonding and the subsequent welding.
- Process Window Definition: Simulation helps define the acceptable thermal budget for post-explosion welding operations, ensuring that the explosive bond interface is not subjected to temperatures or stresses that could compromise its integrity.
8. Contribution to Qualification Building, Product Delivery, and Customer Value
8.1 Qualification Building
- WPS Development Acceleration: Simulation reduces the number of physical qualification trials by providing predictive guidance on preheat temperature, heat input, and PWHT parameters. This accelerates WPS qualification timelines by 30–50% while maintaining full compliance with NB/T 47014, ASME BPV IX, or ISO 15614 requirements.
- Procedure Justification Documentation: Simulation results provide quantitative analytical support for procedure parameters, creating a robust technical dossier that satisfies customer and regulatory requirements for process justification.
- Capability Expansion: Simulation enables the company to qualify new material combinations and overlay specifications without extensive physical trial campaigns, expanding the certified capability matrix efficiently.
8.2 Product Delivery Enhancement
- Reduced Rework Rates: By predicting cracking and distortion risks before production, the simulation capability reduces rework rates significantly, improving on-time delivery performance.
- Optimized Resource Utilization: Simulation-informed preheat and PWHT parameters minimize energy consumption and furnace time while achieving the required metallurgical outcomes.
- Consistent Quality: Simulation establishes clear process control limits, enabling consistent quality across different production batches and operators.
8.3 Customer Value Creation
- Technical Credibility: The ability to provide simulation-based process justification enhances the company's technical credibility with demanding customers, particularly in power generation, petrochemical, and energy sectors where documented process engineering is mandatory.
- Customized Solutions: Simulation enables tailored process development for each customer's specific application, material grade, and geometry, rather than applying generic procedures.
- Cost Optimization: By optimizing preheat and PWHT parameters, the company delivers solutions that minimize total cost of ownership for the customer's equipment.
- Knowledge Transfer: Simulation results can be presented to customers as part of the technical deliverable, demonstrating engineering rigor and building long-term trust.
9. Implementation Roadmap and Best Practices
9.1 Simulation Validation Protocol
- Establish baseline material property database for all carbon steel grades in production scope, including temperature-dependent properties and phase transformation parameters.
- Conduct thermocouple-instrumented physical trials to generate measured thermal cycle data for model calibration.
- Validate thermal predictions against measured thermocouple data with acceptable deviation (±10% on peak temperature, ±15% on cooling rate).
- Validate residual stress predictions against X-ray diffraction or neutron diffraction measurements with acceptable deviation (±20% on peak stress magnitude).
- Document validation results and establish confidence levels for simulation predictions in production decision-making.
9.2 Process Control Integration
Simulation outputs should be integrated into production process control through:
- Standardized preheat temperature specifications for each material grade and component type.
- Interpass temperature monitoring requirements with defined upper and lower limits.
- PWHT schedules (temperature, soak time, cooling rate) prescribed based on simulation predictions.
- Post-weld residual stress verification requirements for critical applications.
- Documentation templates for recording actual process parameters against simulation predictions for continuous improvement.
9.3 Continuous Improvement Cycle
The simulation capability should be continuously refined through a feedback loop: production data (measured thermal cycles, residual stress measurements, cracking incidence) feeds back into model refinement, improving prediction accuracy over time. This creates a compounding knowledge asset that becomes increasingly valuable as the company's production volume and material diversity grow.
10. Conclusion
The numerical simulation of preheating effects on cooling temperature field and residual stress in medium-high carbon steel weld overlay represents a sophisticated analytical capability that bridges fundamental metallurgical science with practical manufacturing execution. For Cladding Technology Shanxi Co., Ltd., this capability strengthens the company's position as a technically advanced provider of clad and overlay solutions, enabling predictive process engineering that reduces risk, accelerates qualification, and delivers optimized, documented solutions to demanding customers. The systematic application of simulation across all three technology routes—TIG/MIG weld overlay, hydraulic explosive bonding, and explosion welding—creates a unified engineering framework that maximizes knowledge transfer and process consistency across the entire product portfolio.