Stainless Steel Wear-Resistant Overlay Welding on 35 Steel: Microstructure, Properties, and Process Analysis
1. Definition and Technical Principles
1.1 Fundamental Concept
The overlay welding of stainless steel wear-resistant layers onto 35 steel (a medium carbon structural steel per GB/T 699-2015, with 0.32–0.39% carbon content) represents a critical surface engineering technology. This process deposits a functionally graded stainless steel layer onto a ferrous base substrate, creating a composite structure that combines the toughness and weldability of the 35 steel substrate with the corrosion resistance, hardness, and wear resistance of the stainless steel overlay. The resulting clad assembly delivers enhanced surface durability without compromising the structural integrity of the base material.
1.2 Metallurgical Mechanism
The fundamental metallurgical challenge in overlay welding on 35 steel involves managing the dilution rate between the base metal and the deposited overlay. Due to the carbon content differential between 35 steel (medium carbon) and austenitic stainless steel overlay materials (typically low-carbon austenitic grades such as 308, 309, or 316), significant dilution occurs during welding. This dilution directly influences:
- Austenite stability: The carbon and alloying elements from the base metal dilute into the weld metal, potentially reducing the austenite-forming capacity and introducing martensitic phases.
- Microstructural transformation: The weld zone transitions through a gradient of microstructures—from fully austenitic at the overlay surface, through a mixed austenitic-ferritic structure in the intermediate zone, to a martensitic or bainitic region at the fusion boundary with the 35 steel substrate.
- Hardness distribution: Dilution creates a hardness gradient that, if uncontrolled, can produce brittle martensitic zones susceptible to cracking under thermal and mechanical stress.
- Corrosion resistance: The chromium and nickel content at the fusion line is reduced by dilution, potentially compromising the passivation capability of the overlay near the interface.
The study of microstructure and properties in this context is essential for optimizing the dilution control, ensuring adequate overlay thickness to achieve full metallurgical separation, and verifying that the composite structure meets the specified performance criteria for the intended service environment.
2. Category and Business Positioning
2.1 Technology Classification
Stainless steel wear-resistant overlay welding on 35 steel falls within the broader category of Weld Overlay Cladding (WOC) technologies. Within Cladding Technology Shanxi Co., Ltd's capability portfolio, this technology is positioned as a core process within the TIG/MIG Weld Overlay technology route. The study of overlay microstructure and properties represents a foundational knowledge asset that underpins WPS (Welding Procedure Specification) development, qualification testing, and process optimization.
2.2 Strategic Business Value
This technical knowledge contributes to the company's competitive positioning in several ways:
- Process qualification capability: Deep understanding of overlay microstructure enables the company to develop and qualify WPS procedures that meet stringent customer and regulatory requirements.
- Value-added services: The ability to analyze and characterize overlay microstructures provides customers with technical confidence in product performance and extends the company's service offerings beyond simple fabrication to include metallurgical consulting and failure analysis.
- IP development: Proprietary knowledge of dilution control, microstructure optimization, and property enhancement creates intellectual property barriers and differentiates the company from competitors who rely solely on standard procedures.
- Cross-technology transfer: Understanding overlay metallurgy informs process parameters for hydraulic explosive bonding and explosion welding, where interfacial microstructure and bonding quality are equally critical.
3. Technical Purpose and Value
3.1 Primary Engineering Objectives
The overlay welding of stainless steel on 35 steel serves the following primary engineering objectives:
- Wear resistance enhancement: Increasing surface hardness from the base 35 steel typical range of 150–200 HB to overlay hardness levels of 250–350 HB (depending on the specific stainless steel grade and heat treatment).
- Corrosion resistance: Providing a corrosion-resistant barrier layer suitable for aggressive chemical, acidic, or marine environments where the 35 steel substrate would rapidly degrade.
- Service life extension: Extending the operational life of components by 3–10 times compared to unclad 35 steel in abrasive or corrosive service.
- Cost optimization: Achieving the performance of a fully stainless steel component at a fraction of the material cost by utilizing a low-cost carbon steel substrate with a thin, high-performance overlay.
3.2 Technical Value in Qualification and Delivery
The systematic study of overlay microstructure and properties directly supports the company's qualification building efforts. When a customer requires a qualified overlay procedure for a specific application (e.g., a pump housing, valve body, or wear plate), the company must demonstrate through metallurgical examination that the overlay meets the specified hardness, corrosion resistance, and structural integrity requirements. Knowledge of microstructure-property relationships enables the company to:
- Pre-select appropriate overlay consumables based on dilution calculations.
- Predict and control the resulting microstructure through parameter optimization.
- Design efficient NDT and metallographic examination protocols.
- Provide technical justification for acceptance criteria in customer-specific specifications.
4. Key Process and Implementation Points
4.1 Overlay Material Selection
The selection of stainless steel overlay consumables is the most critical process decision. The following table summarizes common overlay material options for 35 steel substrates:
| Overlay Material | Composition Type | Typical Hardness (HB) | Dilution Sensitivity | Primary Application |
|---|---|---|---|---|
| E308 (GB/T 983) | Austenitic Cr-Ni | 200–250 | High | General corrosion/wear |
| E309 (GB/T 983) | High-Cr-Ni Austenitic | 220–280 | Medium | Carbon steel to SS transition |
| E310 (GB/T 983) | High-Cr-Ni Austenitic | 200–250 | Low | High-temperature wear/corrosion |
| E316 (GB/T 983) | Austenitic Cr-Ni-Mo | 200–260 | Medium | Chemical/pulp industry |
| E410 (GB/T 983) | Martensitic | 350–450 (as-welded) | Low | Abrasive wear resistance |
| E414 (GB/T 983) | Precipitation-Hardening | 350–400 (aged) | Low | High-strength wear/corrosion |
4.2 Multi-Pass Overlay Strategy
Effective overlay welding on 35 steel requires a multi-pass strategy to manage dilution and achieve the target microstructure. The typical approach involves:
- Transition layer (if required): A first pass using a high-alloy consumable such as E309 or E310 to reduce dilution from the carbon steel substrate. This layer serves as a metallurgical buffer, reducing the carbon and manganese dilution into subsequent passes.
- Build-up passes: Subsequent passes using the target overlay material (e.g., E308, E316, or E410) are deposited with controlled overlap (typically 50–75% of bead width) to ensure full fusion and minimize dilution from the previous pass.
- Final cap pass: The topmost pass is optimized for surface quality and maximum dilution resistance, often using a lower heat input to minimize base metal melting.
4.3 Critical Process Parameters
| Parameter | TIG (GTAW) Range | MIG (GMAW) Range | Impact on Microstructure |
|---|---|---|---|
| Heat Input (kJ/mm) | 0.5–2.0 | 1.0–4.0 | Higher input increases dilution and grain growth |
| Travel Speed (mm/min) | 80–250 | 200–600 | Lower speed increases dilution; higher speed may cause incomplete fusion |
| Wire Feed Speed (MIG) | N/A | 300–700 m/h | Affects deposition rate and bead geometry |
| Current (A) | 80–250 | 150–400 | Higher current increases penetration and dilution |
| Shielding Gas | Ar or Ar/2% O₂ | Ar/5% CO₂ or Ar/2% CO₂ | Gas composition affects bead profile and microstructure |
| Interpass Temperature | ≤150°C | ≤200°C | Higher interpass temp reduces residual stress but may affect hardness |
4.4 Pre-Weld Preparation
- Substrate cleaning: The 35 steel surface must be free of rust, scale, oil, and contaminants. Mechanical grinding to bare metal (Sa 2.5 per ISO 8501-1) is recommended for maximum bond strength.
- Preheating: For thick sections (≥25 mm) or restricted geometries, preheating to 100–150°C is advisable to reduce thermal gradients and minimize cracking risk at the fusion boundary.
- Fillet preparation: A fillet or chamfer preparation at the edge of the overlay area is recommended to ensure full fusion and prevent undercut at the overlay edge.
- Consumable drying: All welding consumables must be stored and handled per manufacturer specifications. Rutile-coated electrodes should be stored at 100–150°C; basic electrodes at 350–400°C.
5. Applicable Standards and Acceptance Criteria
5.1 Welding Procedure and Qualification Standards
- GB/T 983-2012: "Solid electrodes for gas shielded arc welding of stainless steels and heat-resistant steels" — specifies consumable classification, composition, and mechanical properties.
- GB/T 19420-2008: "Qualification testing of welding procedure for fusion welding" — defines PQR (Procedure Qualification Record) requirements.
- GB/T 3375-2008: "Welding, brazing and cutting — Terms" — standard terminology for overlay welding.
- ASTM A5.4/A5.4M: "Specification for Welding Consumables for Gas Shielded Arc Welding of Stainless Steels and Heat-Resistant Steels."
- ASME BPV Section IX: "Qualification Rules for Welding, Brazing, and Fusing" — WPS/PQR qualification requirements for pressure vessel applications.
- ISO 15614-1:2017: "Qualification testing of welding procedures for metallic materials — Arc and gas welding."
- NB/T 47014-2011: "Qualification test rules for welding procedure of pressure vessels and pressure piping" — Chinese national standard for pressure equipment WPS qualification.
5.2 Material and Product Standards
- GB/T 699-2015: "Technical delivery conditions for carbon structural steels" — specifies 35 steel composition and properties.
- GB/T 2554-2017: "Technical conditions for weld overlay cladding" — defines cladding product requirements including thickness, dilution, and performance.
- ASTM A743/A743M: "Standard Specification for Castings, Austenitic, for Elevated Temperature Service."
- API 6D: "Specification for Line Pipe" — relevant for clad pipe applications.
- EN 1561: "Weld overlay cladding — Technical delivery conditions" — European standard for cladding products.
5.3 Acceptance Criteria
| Acceptance Parameter | Typical Requirement | Test Method | Standard Reference |
|---|---|---|---|
| Overlay thickness | ≥3 mm (minimum for full metallurgical separation) | Micrograph measurement | GB/T 2554-2017 |
| Dilution rate | ≤5% (final pass), ≤10% (average) | Spark OES or wet chemistry | GB/T 2554-2017 |
| Overlay hardness | Per specified grade (e.g., 250–350 HB for E308) | Vickers or Brinell | GB/T 231.1 / GB/T 4340.1 |
| Impact energy (if required) | ≥27 J at −40°C (for low-temperature service) | Charpy V-notch | GB/T 229-2020 |
| Corrosion resistance | Potential difference test, salt spray, or specific immersion test | Electrochemical or immersion | GB/T 10125 / ASTM B117 |
| Weld defects | No cracks, porosity, or incomplete fusion per acceptance level | PT, MT, RT, or UT | GB/T 11345 / EN ISO 17635 |
| Interfacial bonding | Full fusion, no interfacial cracks or delamination | Macro/micrograph examination | GB/T 2554-2017 |
5.4 NDT Requirements
Non-destructive testing of overlay welds on 35 steel must address the specific challenges posed by the dissimilar material interface:
- Penetrant Testing (PT): Per GB/T 18851-2015 or ASTM E709, for surface-breaking defects. Essential for detecting cracks at the overlay edge and fusion boundary.
- Magnetic Particle Testing (MT): Per GB/T 26055-2010 or ASTM E1444, for surface and near-surface defects. Effective for the 35 steel substrate but limited at the fully austenitic overlay surface.
- Ultrasonic Testing (UT): Per GB/T 11345-2013 or EN ISO 17635, for volumetric defects. Requires careful calibration due to acoustic impedance mismatch at the steel/stainless interface.
- Radiographic Testing (RT): Per GB/T 3323-2005 or ASTM E94, for volumetric defects. Note that stainless steel has different radiographic absorption than carbon steel, requiring exposure technique adjustments.
6. Common Risks and Controls
6.1 Cracking Risks
- Hot cracking: Austenitic stainless steel overlay welds are susceptible to solidification cracking (hot cracking) due to the narrow solidification range and low ductility of the interdendritic liquid films. Controls: Optimize heat input to ensure a single-phase austenitic solidification; avoid high sulfur and phosphorus content in consumables; ensure adequate overlap between passes.
- Cold cracking (hydrogen-induced cracking): The 35 steel substrate, with its medium carbon content, is susceptible to hydrogen-induced cracking in the heat-affected zone (HAZ). Controls: Preheat the substrate to 100–150°C; use low-hydrogen consumables; apply post-weld heat treatment (PWHT) at 200–300°C for 1–2 hours to diffuse residual hydrogen; limit interpass temperature.
- Interfacial cracking: Cracks can initiate at the fusion boundary between the 35 steel and the overlay due to thermal stress from differential thermal expansion coefficients. Controls: Use a transition layer; employ multi-pass welding with controlled interpass temperatures; consider post-weld stress relief.
6.2 Dilution and Microstructural Risks
- Excessive dilution: High dilution rates introduce carbon and manganese from the 35 steel into the overlay, potentially forming brittle martensite or reducing corrosion resistance. Controls: Use multi-pass overlay with high-alloy transition layers; minimize heat input; use consumables with high alloy content (E309 or E310 for transition); maintain adequate overlay thickness (≥3 mm).
- Sigma phase formation: In high-chromium austenitic overlays, prolonged exposure to temperatures in the 600–800°C range can cause sigma phase precipitation, embrittling the microstructure. Controls: Avoid excessive heat input; limit interpass temperature; select overlay grades with lower chromium content for high-temperature service.
- Sensitization: If the overlay weld metal passes through the sensitization temperature range (450–850°C) during welding or subsequent service, chromium carbide precipitation at grain boundaries can reduce local chromium content below the passivation threshold. Controls: Use low-carbon consumables (E308L, E316L); minimize time in the sensitization range; consider stabilizing grades (E347 with niobium) for high-temperature applications.
6.3 Process Risks
- Incomplete fusion: Poor fusion at the overlay/substrate interface or between overlay passes can create stress concentrators and reduce bond strength. Controls: Ensure adequate cleaning; maintain proper travel speed and current; use appropriate bead overlap (50–75%); perform visual inspection of each pass.
- Porosity: Gas porosity from contamination or shielding gas breakdown can weaken the overlay. Controls: Thorough surface cleaning; ensure adequate shielding gas coverage (especially at the trailing edge); use dry consumables; maintain proper gas flow rates.
- Residual stress and distortion: The thermal gradient between the overlay and the 35 steel substrate generates significant residual stresses. Controls: Use back-step welding sequence; apply interpass temperature control; consider post-weld stress relief at 600–650°C (for the overlay) or 550–600°C (for the substrate), selecting the lower temperature to avoid sensitization.
7. Application Scenarios Across Company Technology Routes
7.1 TIG/MIG Weld Overlay Applications
Weld overlay is the primary technology route for applying stainless steel wear-resistant layers to 35 steel components. Key application scenarios include:
- Pump impellers and casings: 35 steel pump bodies with stainless steel overlay on the wetted surfaces to resist cavitation erosion and corrosion in water treatment, chemical processing, and oil/gas applications.
- Valve components: Valve bodies and trim made from 35 steel with overlay on sealing surfaces and flow paths for service in aggressive chemical media.
- Mining equipment: Wear plates, scraper blades, and conveyor components made from 35 steel with overlay for abrasive wear resistance in mining and material handling applications.
- Power generation: Boiler tube sections, turbine casing components, and heat exchanger tubes where 35 steel structural components require localized wear and corrosion protection.
- Marine and offshore: Propeller shafts, rudder stocks, and structural components where 35 steel components require corrosion and wear protection in marine environments.
- Food processing: Mixing paddles, shafts, and conveyors where 35 steel components require stainless steel overlay for sanitary and corrosion resistance.
7.2 Hydraulic Explosive Bonding Applications
While weld overlay is the dominant technology for stainless steel overlay on 35 steel, hydraulic explosive bonding (water-jet-assisted explosive bonding) offers an alternative approach for specific applications:
- Large-area cladding: Hydraulic explosive bonding can produce uniform clad plates with stainless steel facing on 35 steel backing, suitable for fabricating large components such as heat exchanger plates, reactor linings, and storage tank linings.
- Thick overlay: Where overlay thicknesses of 3–10 mm or greater are required, hydraulic explosive bonding provides a more efficient and consistent alternative to multi-pass weld overlay.
- Low dilution: The mechanical bonding mechanism produces essentially zero dilution at the interface, ensuring the full metallurgical properties of the stainless steel cladding layer are preserved.
- Composite plate production: Cladding Technology Shanxi Co., Ltd can produce 35 steel/stainless steel clad plates via hydraulic explosive bonding for downstream fabrication into custom components.
7.3 Explosion Welding Applications
Explosion welding (explosive cladding) represents another technology route for producing 35 steel/stainless steel clad assemblies:
- Industrial-scale cladding: Explosion welding is suitable for producing large-diameter clad pipes and pipes of 35 steel with stainless steel lining for chemical processing, pulp and paper, and environmental applications.
- Specialty alloys: Where the overlay material is not readily available in welding consumable form, explosion welding can bond stainless steel cladding directly onto 35 steel substrates.
- Uniformity and repeatability: Once the explosive parameters are optimized, explosion welding provides highly uniform cladding quality across the entire bonded area, with consistent microstructure and bonding quality.
- Through-thickness properties: The explosive bonding interface produces a distinctive wave-like microstructure that provides excellent mechanical bonding and resistance to interfacial cracking, complementing the weld overlay approach.
7.4 Technology Route Selection Matrix
| Application Requirement | Recommended Technology Route | Rationale |
|---|---|---|
| Localized overlay on existing components | TIG/MIG Weld Overlay | Flexible, repairable, suitable for complex geometries |
| Large-area uniform cladding | Hydraulic Explosive Bonding | Consistent thickness, low dilution, high productivity |
| Large-diameter clad pipes | Explosion Welding | Scalable, uniform interface, suitable for tubular products |
| Repair of worn/corroded components | TIG/MIG Weld Overlay | On-site capability, minimal preparation, rapid turnaround |
| Thick overlay (≥5 mm) | Hydraulic Explosive Bonding or Explosion Welding | More efficient than multi-pass weld overlay for thick deposits |
| High-precision overlay on critical surfaces | TIG Weld Overlay | Fine control over bead geometry and dilution |
| High-volume production of clad plates | Explosion Welding | Batch production capability, consistent quality |
8. Microstructure Characterization and Quality Assurance
8.1 Metallographic Examination Protocol
Systematic metallographic examination of the overlay weld is essential for verifying microstructure quality and detecting potential defects. The recommended protocol includes:
- Sample preparation: Transverse cross-sections through the overlay weld are prepared by mounting, grinding, and polishing to a mirror finish. Sections should be taken at multiple locations along the weld length.
- Etching: Standard etchants for stainless steel overlay (e.g., 5% HF + 5% HCl) and carbon steel substrate (e.g., 4% Nital) are applied separately to reveal the microstructure of each material. A double-etching technique may be required to distinguish the interface.
- Microstructural features to evaluate:
- Austenite grain size in the overlay (per ASTM E112, target: fine to medium grain size, ≤5).
- Presence of delta ferrite in the overlay (per ASTM E490, target: 3–10% for E308/E309 to prevent hot cracking).
- Martensite formation at the fusion boundary (indicates excessive dilution).
- Carbide precipitation at grain boundaries (indicates sensitization).
- Interfacial bonding quality (full fusion, no cracks or porosity at the interface).
- Overlay thickness and dilution profile (measured from micrographs).
8.2 Chemical Analysis of Dilution
Quantitative chemical analysis of the overlay at various depths from the surface provides critical dilution data:
- Spark OES analysis: Rapid analysis of Cr, Ni, C, Mn, and Mo content at the overlay surface, mid-overlay, and near the fusion boundary.
- Wet chemistry analysis: For critical applications, volumetric analysis of polished sections provides higher accuracy for dilution calculations.
- Dilution calculation: Dilution (%) = [(C_base × thickness_diluted) / (C_overlay × total_overlay_thickness)] × 100, where C represents the carbon content of the respective materials.
9. Qualification Building and Customer Value
9.1 WPS Development and Qualification
The knowledge of overlay microstructure and properties directly supports the company's WPS development and qualification program:
- Essential variables identification: Understanding of microstructure-property relationships enables the company to correctly identify essential variables (heat input range, consumable type, preheat temperature, interpass temperature) for WPS qualification per NB/T 47014-2011 or ASME Section IX.
- Qualification testing design: Knowledge of expected microstructures informs the design of mechanical tests (tension, impact, hardness), corrosion tests, and metallographic examinations required for PQR completion.
- Procedure transfer: Qualified WPS can be transferred to similar applications (different substrate thickness, geometry, or overlay grade) within the established limits, reducing qualification costs and delivery times.
- Multi-technology qualification: The company can maintain qualified procedures across all three technology routes (TIG, MIG, hydraulic explosive bonding, explosion welding), providing customers with flexibility in technology selection based on their specific requirements.
9.2 Product Delivery Enhancement
- Technical documentation: The company provides customers with detailed metallurgical reports including micrographs, hardness profiles, dilution analysis, and corrosion test results, demonstrating the quality and performance of the overlay weld.
- Performance prediction: Based on microstructure analysis, the company can predict overlay performance in specific service environments (temperature, pressure, chemical exposure), providing customers with confidence in the product's long-term reliability.
- Failure analysis capability: The company's metallurgical expertise enables rapid failure analysis of overlay welds, identifying root causes (cracking, corrosion, wear) and recommending corrective actions.
9.3 Customer Value Proposition
The systematic study of overlay microstructure and properties translates into tangible customer value:
- Reduced lifecycle costs: Optimized overlay procedures produce wear-resistant, corrosion-resistant components that extend service intervals, reduce unplanned downtime, and lower total cost of ownership.
- Regulatory compliance: Qualified procedures and documented metallurgical data ensure compliance with industry standards and regulatory requirements (NB/T 47014, ASME Section IX, API, ISO), reducing customer risk.
- Technical partnership: The company's metallurgical expertise positions it as a technical partner rather than a simple fabricator, enabling collaborative design of overlay solutions tailored to specific service conditions.
- Quality assurance: Rigorous metallographic examination and property verification provide customers with documented evidence of overlay quality, supporting their own quality assurance and regulatory compliance programs.
10. Conclusion
The study of microstructure and properties of stainless steel wear-resistant overlay on 35 steel is a foundational technical capability for Cladding Technology Shanxi Co., Ltd. This knowledge underpins the company's ability to develop qualified welding procedures, deliver high-quality overlay products, and provide value-added metallurgical services to customers across multiple industries. By maintaining deep expertise in overlay metallurgy across all three technology routes — TIG/MIG weld overlay, hydraulic explosive bonding, and explosion welding — the company ensures that customers receive technically optimized, standards-compliant, and performance-verified cladding solutions. The systematic approach to microstructure characterization, dilution control, and property verification establishes a quality framework that supports continuous improvement, qualification expansion, and long-term customer trust.