TIG Welding Temperature Field Numerical Simulation and Experimental Verification for 0Cr18Ni10Ti Austenitic Stainless Steel Source Shells
1. Definition and Fundamental Principles
0Cr18Ni10Ti is a titanium-stabilized austenitic stainless steel conforming to Chinese national standard GB/T 4237, with a chemical composition of approximately 17–19% Cr, 9–12% Ni, and 0.08–0.20% Ti. This material is internationally designated as UNS S32100 and corresponds to ASTM A240 Type 321 stainless steel. The titanium addition serves as a carbon scavenger, forming TiC precipitates that prevent chromium carbide formation at grain boundaries, thereby providing superior resistance to intergranular corrosion (IGC) in the 450–850°C sensitization range.
The term "source shell" (源壳) in this context refers to primary containment shells or reactor vessel components used in nuclear power plant systems, where the 0Cr18Ni10Ti material serves as a corrosion-resistant cladding layer or structural component exposed to high-temperature, high-pressure, and chemically aggressive service environments. The integrity of weld joints in these components is critical to reactor safety and operational longevity.
TIG (Tungsten Inert Gas) welding, also known as Gas Tungsten Arc Welding (GTAW), is the predominant process for welding 0Cr18Ni10Ti stainless steel in nuclear-grade applications due to its exceptional control over heat input, arc stability, and weld geometry. The temperature field numerical simulation of TIG welding involves the construction of a finite element model (FEM) that solves the transient heat conduction equation under the moving heat source boundary condition:
ρCp · ∂T/∂t = ∇·(k(T) · ∇T) + Q(x, y, t)
where ρ is density, Cp is specific heat capacity, k(T) is temperature-dependent thermal conductivity, and Q represents the Gaussian or double-ellipsoidal heat source distribution modeling the arc energy deposition. The simulation captures the thermal history at critical locations including the fusion zone, heat-affected zone (HAZ), and base metal, which directly determines residual stress development, microstructural evolution, and weld integrity.
2. Category and Business Positioning
This technical capability falls squarely within the TIG/MIG weld overlay technology route of Cladding Technology Shanxi Co., Ltd., specifically in the domain of nuclear-grade stainless steel welding process development and qualification. The company's three core technology routes are:
- TIG/MIG Weld Overlay — Direct application of this capability for welding and overlay of stainless steel components including source shells, cladding layers, and transition joints
- Hydraulic Explosive Bonding — Complementary route for producing large-area clad plate/pipe where mechanical bonding suffices
- Explosion Welding — High-energy route for thick-section clad products where thermal methods are impractical
The numerical simulation and experimental verification capability serves as the intellectual foundation that differentiates Cladding Technology Shanxi Co., Ltd. from purely manufacturing-oriented competitors. It provides:
- Process optimization prior to physical trials, reducing qualification costs by 30–50%
- Predictive capability for weld distortion, residual stress, and HAZ microstructural changes
- Documentation and traceability required for nuclear-grade WPS (Welding Procedure Specification) qualification
- Technical authority in customer negotiations and regulatory inspections
3. Technical Purpose and Value
3.1 Process Optimization
The primary purpose of conducting TIG welding temperature field numerical simulation for 0Cr18Ni10Ti source shells is to determine optimal welding parameters that minimize adverse metallurgical effects while ensuring full penetration and sound weld geometry. Key optimization objectives include:
- Heat input control — Maintaining heat input within 0.5–2.5 kJ/mm to prevent excessive grain growth in the HAZ and avoid sensitization in the weld metal
- Thermal cycling management — Limiting peak temperature in the HAZ to below 1200°C to prevent excessive austenite grain coarsening
- Distortion prediction — Forecasting angular and longitudinal distortion to design appropriate backing fixtures and post-weld correction procedures
- Multi-pass sequencing — Optimizing the order and parameters of root, fill, and cap passes to manage cumulative heat effects
3.2 Residual Stress Prediction
The thermal simulation provides the thermal history input for coupled thermo-mechanical analysis, enabling prediction of residual stress distributions. For 0Cr18Ni10Ti, which has a coefficient of thermal expansion (CTE) of approximately 17.3 × 10-6 /K and low thermal conductivity (~16 W/m·K at 25°C), residual stresses can reach 200–350 MPa near the fusion boundary. This is critical for stress corrosion cracking (SCC) susceptibility assessment in chloride-containing environments.
3.3 Customer Value and Qualification Building
The simulation-and-verification methodology directly supports:
- WPS/PQR Development — Generating qualified Welding Procedure Specifications with documented thermal parameters that satisfy ASME Section IX, NB/T 20001.1, and RCC-M requirements
- Regulatory Compliance — Providing NRC, CNSA (China National Nuclear Safety Administration), and IAEA-compliant documentation for nuclear component fabrication
- Accelerated Qualification — Reducing the number of physical coupon tests through validated simulation predictions, accelerating project timelines
- Knowledge Retention — Building an institutional database of thermal simulation models that can be adapted for similar geometries and material combinations
4. Key Process and Implementation Points
4.1 Material Property Database Requirements
Accurate numerical simulation of TIG welding on 0Cr18Ni10Ti requires comprehensive temperature-dependent material properties. The following table summarizes the essential properties and their temperature ranges:
| Property | Symbol | Range / Value | Temperature Range | Source Standard |
|---|---|---|---|---|
| Density | ρ | 7900–7700 kg/m³ | 25–1500°C | GB/T 228.1 |
| Specific Heat | Cp | 500–850 J/(kg·K) | 25–1500°C | ASTM E1461 |
| Thermal Conductivity | k | 16–35 W/(m·K) | 25–1500°C | ASTM E1530 |
| Thermal Expansion | α | 16.0–19.5 × 10⁻⁶ /K | 25–1500°C | ASTM E228 |
| Melting Temperature | Tm | 1400–1450°C | — | GB/T 4237 |
| Solidus Temperature | Ts | 1395–1410°C | — | ASTM A240 |
4.2 Heat Source Model Selection
The choice of heat source model significantly affects simulation accuracy. For TIG welding of 0Cr18Ni10Ti, the following models are applicable:
| Heat Source Model | Description | Applicability | Accuracy |
|---|---|---|---|
| Gaussian Surface | Simple 2D Gaussian distribution on weld surface | Thin sections, single-pass | Moderate |
| Double Ellipsoidal (Goldak) | 3D ellipsoidal with front/rear asymmetry | Multi-pass, thick sections | High |
| Moving Cone | Cylindrical/conical with depth-dependent distribution | Root pass, full penetration | High |
4.3 Recommended TIG Welding Parameters for 0Cr18Ni10Ti Source Shells
| Parameter | Root Pass | Fill Pass | Cap Pass |
|---|---|---|---|
| Welding Current (A) | 80–120 | 120–180 | 100–150 |
| Welding Voltage (V) | 10–14 | 14–18 | 12–16 |
| Travel Speed (mm/min) | 150–250 | 200–350 | 200–300 |
| Heat Input (kJ/mm) | 0.5–1.0 | 1.0–1.8 | 0.8–1.5 |
| Shielding Gas | Ar (99.99%) | Ar (99.99%) | Ar (99.99%) |
| Gas Flow Rate (L/min) | 10–15 | 12–18 | 12–15 |
| Tungsten Electrode | WCu 2.4mm | WCu 3.2mm | WCu 2.4mm |
| Filler Wire | — (autogenous) | ER321 / S32108 | ER321 / S32108 |
| Filler Wire Diameter (mm) | — | 1.6–2.4 | 1.6–2.0 |
4.4 Finite Element Model Construction
The numerical simulation workflow follows these key steps:
- Geometry Modeling — Create a representative section of the source shell weld joint, typically using a 3D solid model with symmetry boundary conditions to reduce computational cost. Mesh density should achieve 1–2 mm element size in the fusion zone and HAZ regions.
- Material Assignment — Assign temperature-dependent thermophysical properties to both base metal (0Cr18Ni10Ti) and weld metal (ER321/S32108). Implement latent heat of fusion using the enthalpy method to capture the phase change during melting.
- Boundary Conditions — Apply convective heat transfer (h = 5–25 W/m²·K for air convection) and radiative heat transfer (σT⁴, emissivity ε = 0.8–0.95) on exposed surfaces. Apply symmetry or fixed-temperature conditions at model boundaries.
- Heat Source Implementation — Define the moving heat source with calibrated energy efficiency (typically η = 0.7–0.85 for TIG). Implement the heat source movement along the weld path at the specified travel speed.
- Multi-Pass Sequencing — For multi-pass welds, sequentially activate heat sources for each pass, allowing the temperature field to decay between passes according to the interpass time. Implement element birth/death technique for weld metal deposition.
- Thermal History Extraction — Record temperature-time histories at key locations: fusion boundary, HAZ peak temperature points, and base metal reference points. These histories serve as input for microstructural modeling and residual stress analysis.
4.5 Experimental Verification Methodology
The numerical simulation results must be validated through physical experiments. The verification program typically includes:
- Thermocouple Instrumentation — Embed K-type or N-type thermocouples at predetermined locations in the test coupon (3–10 mm from fusion boundary) to record thermal cycles during actual TIG welding. Thermocouple wire should be insulated with ceramic or glass fiber to prevent arc damage.
- Thermal Spray Coating — For surface temperature measurement, apply a thin layer of thermochromic paint or use infrared thermography to capture surface temperature distributions during welding.
- Weld Geometry Measurement — Measure weld bead width, reinforcement height, and penetration depth using profile projection or CT scanning. Compare measured geometry with simulation-predicted fusion boundary.
- Macro/Microstructural Examination — Perform metallographic examination of transverse sections to verify HAZ width, grain structure, and absence of defects. HAZ width measured microscopically should correlate with simulation-predicted 800°C isotherm width.
- Hardness Profiling — Measure Vickers hardness (HV0.2) across the weld cross-section at 0.5 mm intervals. Compare experimental hardness profile with simulation-predicted thermal history-based hardness predictions.
5. Applicable Standards and Acceptance Criteria
5.1 Welding Procedure Standards
| Standard | Title / Scope | Key Requirements |
|---|---|---|
| ASME BPV Section IX | Qualification of Welding Procedures | WPS/PQR qualification, essential variables, performance tests |
| ASME BPV Section III, NB-3200 | Welding Requirements for Nuclear Components | Weld qualification, repair procedures, inspection requirements |
| GB/T 12469 | Steel and Nickel Alloy Welding — Qualification of Welding Procedures | Chinese national WPS qualification procedure |
| NB/T 20001.1 | Nuclear Power Plant Welding — General Requirements | Nuclear-grade welding procedure requirements |
| NB/T 20001.2 | Nuclear Power Plant Welding — TIG Welding | Specific requirements for GTAW of nuclear components |
| RCC-M (M3-4) | French Nuclear Code — Welding Qualification | European nuclear welding qualification framework |
| ISO 15614-1 | Qualification Testing of Welding Procedures for Metallic Materials | International WPS qualification methodology |
| EN ISO 9606-1 | Qualification Testing of Welders — Arc Welding | Welder skill qualification |
5.2 Material Standards for 0Cr18Ni10Ti
- GB/T 4237 — Stainless steel plates, sheets, and strips
- GB/T 14976 — Cold-rolled seamless stainless steel tubes
- ASTM A240 / A240M — Chromium and chromium-nickel stainless steel plate, sheet, and strip
- ASTM A313 — Austenitic stainless steel bars and shapes
- ASME SA-240 / SA-313 — Boiler and pressure vessel stainless steel materials
- NB/T 21035 — Nuclear-grade stainless steel materials
5.3 Weld Filler Metal Standards
- GB/T 8110 — Welding consumables for TIG welding (ER321 equivalent)
- ASTM A5.9 — Carbon and low-alloy steel electrodes (reference for classification system)
- ASME SFA-5.9 — Specifications for stainless steel welding electrodes and rods
- NB/T 21035 — Nuclear-grade welding consumables
5.4 Non-Destructive Testing Standards
- GB/T 11345 — Ultrasonic testing of welds
- GB/T 3323 — Radiographic testing of welds
- ASME Section V, Article 2/4/9 — Radiographic, ultrasonic, and magnetic particle examination
- ASME Section XI, Appendix I — In-service inspection of welds in nuclear power plants
- NB/T 47013 — NDT methods for pressure vessels and components
5.5 Acceptance Criteria
For 0Cr18Ni10Ti source shell welds, acceptance criteria are governed by the applicable design code:
- ASME Section III, NB-3300 — Welds shall be free of cracks, undercut exceeding 0.5 mm, porosity exceeding 0.1% of weld area, and lack of fusion. Acceptance per ASME Section V, Article 4, T-274 (Level 2 radiographic acceptance).
- NB/T 20001.2 — Nuclear-grade welds require 100% radiographic and ultrasonic examination with acceptance per Level 1 criteria (stricter than ASME).
- RCC-M — Weld acceptance per RCC-M M3-4, with requirements for visual, radiographic, ultrasonic, and penetration testing.
6. Common Risks and Controls
6.1 Metallurgical Risks
| Risk | Cause | Effect | Control Measure |
|---|---|---|---|
| Intergranular Corrosion (IGC) | Excessive heat input causing Cr₂₃C₆ precipitation at grain boundaries in sensitization range (450–850°C) | Reduced corrosion resistance, grain boundary dissolution | Limit heat input below 2.5 kJ/mm; use Ti-stabilized filler (ER321); control interpass temperature below 150°C; perform 10% CuSO₄ acid dye test per ASTM A923 |
| Sigma Phase Formation | Prolonged exposure to 600–900°C during multi-pass welding | Brittle intermetallic phase, reduced ductility and toughness | Minimize time in sensitization range; optimize multi-pass sequence; consider post-weld solution treatment (1050–1100°C, water quench) |
| Hot Cracking | Solidification cracking due to high sulfur/phosphorus content or inappropriate filler metal | Cracks in weld metal centerline | Use low-S, low-P base metal (S < 0.03%, P < 0.045%); select appropriate filler (ER321); control weld bead geometry (avoid wide flat beads) |
| Excessive HAZ Grain Growth | Peak temperature exceeding 1300°C in HAZ | Reduced toughness, increased SCC susceptibility | Control heat input; use low-current, high-speed parameters; simulate to verify HAZ peak temperature distribution |
| Stress Corrosion Cracking (SCC) | High residual stress combined with chloride environment and sensitized microstructure | Intergranular or transgranular cracking in service | Control residual stress via simulation-guided parameter optimization; consider PWHT if code-permitted; ensure proper passivation per ASTM A967 |
6.2 Process Risks
- Porosity — Caused by insufficient shielding gas coverage, contaminated base metal, or moisture in tungsten electrode. Control: maintain minimum gas flow rate of 10 L/min, use trailing gas shield, ensure tungsten is dry and properly ground.
- Undercut — Excessive heat input at weld toes causing base metal melting and recession. Control: reduce current, increase travel speed, optimize torch angle (typically 75–90° from horizontal).
- Weld Distortion — Differential thermal expansion causing angular and longitudinal distortion. Control: use simulation to predict distortion magnitude; design appropriate backing fixtures; implement symmetric welding sequence; consider back-step welding for thin sections.
- Welding Crater Defects — Cracks or shrinkage porosity at weld termination. Control: implement crater fill technique; use pulse TIG for termination; maintain constant travel speed throughout.
6.3 Simulation-Specific Risks
- Material Property Uncertainty — Temperature-dependent properties from literature may not match actual batch material. Control: perform DSC (Differential Scanning Calorimetry) and laser flash analysis on actual material to calibrate thermal properties.
- Heat Source Model Simplification — Idealized heat source distributions may not capture actual arc behavior. Control: calibrate heat source parameters against measured weld geometry and thermocouple data from physical trials.
- Boundary Condition Approximation — Convective and radiative heat transfer coefficients are estimated. Control: perform sensitivity analysis; use actual measured cooling rates to validate boundary conditions.
- Mesh Convergence — Inadequate mesh density leads to numerical diffusion of temperature field. Control: perform mesh convergence study with element sizes of 0.5, 1.0, and 2.0 mm in the weld region.
7. Application Across the Three Technology Routes
7.1 TIG/MIG Weld Overlay Route
This is the primary application domain for the temperature field simulation capability. In the context of 0Cr18Ni10Ti source shells:
- Direct Welding — The simulation directly supports WPS development for butt joints, fillet joints, and repair welds on source shell components. Thermal history predictions guide the selection of interpass temperature limits and multi-pass sequences.
- Cladding Overlay — When 0Cr18Ni10Ti is applied as a TIG weld overlay cladding layer on carbon steel or low-alloy steel substrate, the simulation predicts dilution ratios, HAZ hardness, and bonding layer microstructure. The simulation identifies optimal number of passes (typically 2–3 layers) to achieve desired dilution (10–30% for first pass, decreasing with subsequent passes).
- Transition Welding — For dissimilar metal joints (e.g., 0Cr18Ni10Ti to P91 or 15CrMo), the simulation predicts the thermal gradient at the interface, which determines the risk of cracking and the required transition layer strategy.
7.2 Hydraulic Explosive Bonding Route
While hydraulic explosive bonding is a solid-state joining process that does not involve melting, the temperature field simulation capability contributes indirectly:
- Post-Bonding Weld Repair — Defects or non-bonded areas in hydraulically bonded clad plates require TIG weld repair. The simulation supports development of qualified repair welding procedures that minimize additional thermal effects on the bonded interface.
- Edge Sealing — Edge welding of bonded clad plates to prevent delamination requires simulation-optimized TIG parameters to avoid thermal separation of the bonded interface.
- Preheating Assessment — For thick-section bonded assemblies, preheating may be required before subsequent fabrication welds. Simulation determines the preheat temperature and thermal distribution to prevent interfacial debonding.
7.3 Explosion Welding Route
The simulation capability supports explosion welding applications in the following ways:
- Post-Explosion Welding — Explosion-welded clad components often require machining and subsequent welding operations. The temperature field simulation guides the development of welding procedures for attachment of nozzle assemblies, flanges, and other components to explosion-welded clad vessels.
- Defect Repair — When explosion welding produces local defects (laminations, voids), TIG weld repair is required. Simulation supports repair procedure qualification by predicting thermal effects on the surrounding explosion-bonded interface.
- Process Integration — In hybrid processes combining explosion welding with TIG weld overlay (explosion welding for bulk cladding, TIG for final surface preparation), the simulation ensures thermal compatibility between the two processes.
8. Contribution to Qualification Building and Product Delivery
8.1 WPS Qualification Acceleration
The numerical simulation and experimental verification methodology significantly accelerates WPS qualification for 0Cr18Ni10Ti source shell welds:
- Parameter Window Definition — Simulation identifies the acceptable parameter range (current, voltage, travel speed, gas flow) that produces sound welds within code limits. This reduces the number of trial welds from 10–15 to 3–5.
- Essential Variable Justification — Simulation results provide technical justification for essential variable ranges in the WPS, supporting expedited qualification under ASME Section IX, QW-101 or ISO 15614-1.
- Coupon Design Optimization — Simulation predicts the thermal effects on different coupon geometries, enabling optimal coupon design that maximizes qualification coverage while minimizing material and testing costs.
8.2 Product Quality Assurance
For production welds on source shell components, the simulation capability enables:
- Weld Map Generation — Predicting residual stress and distortion for each weld on the component, enabling proactive mitigation through fixture design and welding sequence optimization.
- Dimensional Control — Predicting cumulative distortion from multiple welds on a source shell assembly, enabling accurate pre-setting of dimensional tolerances.
- Repair Procedure Development — Rapid development of qualified repair procedures for in-process defects, minimizing production downtime.
8.3 Regulatory and Customer Confidence
- Nuclear Regulatory Submissions — Simulation documentation supports regulatory submissions for new component designs, demonstrating that welding procedures have been technically validated.
- Customer Technical Reviews — Simulation results provide quantitative evidence for customer design reviews, enhancing confidence in the company's technical competence.
- Lessons Learned Database — Each simulation-verification cycle builds institutional knowledge that accelerates future projects with similar geometries and materials.
9. Implementation Recommendations
- Software Selection — Use validated finite element software (ANSYS Mechanical, Abaqus, or Deform-3D) with proven track record in welding simulation. Ensure the software supports moving heat source, element birth/death, and coupled thermo-mechanical analysis.
- Material Property Validation — Establish an in-house material property database through DSC, laser flash, and thermomechanical analysis testing on actual production material batches. Do not rely solely on literature values.
- Simulation-Experiment Integration — Adopt an iterative approach where simulation results guide experimental design, and experimental results calibrate simulation models. Target within 15% agreement between predicted and measured thermal cycles.
- Documentation and Traceability — Maintain complete simulation documentation including model files, input parameters, material property data, boundary conditions, and validation reports. Ensure documentation meets nuclear-grade quality record requirements per ASME NQA-1.
- Personnel Qualification — Assign qualified welding engineers and simulation specialists with demonstrated competence in both TIG welding practice and finite element analysis. Cross-training between simulation and shop-floor teams ensures practical relevance of simulation results.
- Continuous Improvement — Establish a feedback loop where production weld quality data (NDT results, dimensional measurements, failure analyses) feeds back into simulation model refinement.
10. Conclusion
The TIG welding temperature field numerical simulation and experimental verification for 0Cr18Ni10Ti stainless steel source shells represents a critical technical capability that bridges theoretical welding science with practical manufacturing execution. By accurately predicting thermal histories, residual stress distributions, and microstructural evolution, this capability enables:
- Optimized welding parameters that minimize metallurgical risks while ensuring code compliance
- Accelerated WPS/PQR qualification with reduced physical testing
- Proactive distortion and residual stress management for complex source shell geometries
- Technical authority in nuclear-grade component fabrication and regulatory compliance
For Cladding Technology Shanxi Co., Ltd., this capability strengthens the TIG/MIG weld overlay technology route while providing essential support to the hydraulic explosive bonding and explosion welding routes through repair procedure development and process integration. The simulation-and-verification methodology is not merely an academic exercise but a production-ready tool that directly contributes to product quality, qualification efficiency, and customer value in the highly regulated nuclear power industry.