H1Cr24Ni13 Overlay on Q235A Steel: Fusion Zone Microstructure and Properties Analysis
1. Definition and Technical Background
H1Cr24Ni13 is a high-alloy cast welding electrode classified under the Chinese national standard GB/T 10044, designed for hardfacing and corrosion-resistant overlay applications. The alloy designation denotes approximately 24% chromium and 13% nickel, supplemented by substantial carbon (typically 1.5–3.0%) and trace amounts of molybdenum, tungsten, and vanadium. This composition produces a martensitic to austenitic microstructure upon solidification, depending on cooling rate, with the formation of hard carbide phases (Cr₇C₃, Cr₃C, Ni₃C) that provide exceptional wear resistance and resistance to corrosive media at elevated temperatures.
Q235A steel is a plain-carbon structural steel conforming to GB/T 700, with a maximum carbon content of 0.22% and minimal alloying additions. It is widely used as a base material for structural components, pressure vessels, and equipment supports in industrial environments. The combination of overlaying H1Cr24Ni13 on Q235A represents a classic dissimilar material joining scenario where a high-alloy, high-carbon overlay must be metallurgically bonded to a low-carbon, low-alloy substrate.
The fusion zone (also termed the heat-affected interface or dilution zone) is the region where the base metal and overlay alloy intermix during solidification. Its microstructure, composition, hardness, and residual stress state are critical determinants of the overlay joint's long-term performance. This technical study focuses specifically on characterizing and optimizing the fusion zone microstructure and mechanical properties when H1Cr24Ni13 is deposited on Q235A steel.
2. Technical Purpose and Value
The research and documentation of fusion zone behavior in H1Cr24Ni13-on-Q235A overlay welding serves several critical technical purposes:
- WPS Qualification Foundation: Understanding the dilution behavior and microstructural evolution in the fusion zone is prerequisite to developing a qualified Welding Procedure Specification (WPS) under applicable codes such as ASME Section IX, NB/T 47014, or GB/T 19418. The fusion zone properties must be demonstrated to meet acceptance criteria before production welding can proceed.
- Dilution Rate Control: The base metal dilution into the overlay layer directly affects the final microstructure. Excessive dilution (>30–40%) can lower the hardness and corrosion resistance of the overlay layer by introducing ferrite and reducing carbide density. Controlled dilution is essential for achieving the designed overlay performance.
- Crack Resistance Assessment: The high-carbon, high-chromium composition of H1Cr24Ni13 creates a high carbon activity gradient at the fusion zone, predisposing the interface to hot cracking (solidification cracking) and cold cracking (hydrogen-induced). Quantifying these risks enables the development of effective preheat and interpass temperature protocols.
- Residual Stress Characterization: The large difference in thermal expansion coefficients between the austenitic/martensitic overlay and the ferritic base metal generates significant residual stresses at the fusion zone, which can compromise dimensional stability and fatigue life.
- Customer Value Proposition: Documented fusion zone performance data provides customers with confidence in the long-term reliability of overlay-protected components, particularly in aggressive chemical processing, pulp and paper, and mining applications.
3. Fusion Zone Microstructure and Phase Evolution
3.1 Solidification Behavior
The solidification of the H1Cr24Ni13/Q235A fusion zone is governed by the local composition, which represents a gradient between the pure base metal (Q235A: ~0.2% C, ~0.4% Mn, balance Fe) and the overlay alloy (H1Cr24Ni13: ~2.5% C, 24% Cr, 13% Ni). The dilution ratio—defined as the fraction of base metal in the weld metal—typically ranges from 15% to 35% for single-pass overlay and can decrease to 10–20% for multi-pass builds.
At low dilution rates (<15%), the fusion zone solidifies primarily as austenite (γ) with extensive secondary carbide precipitation (Cr₇C₃, M₇C₃ type). At intermediate dilution (15–30%), a mixed austenite-ferrite (γ + δ) structure develops. At high dilution (>30%), the fusion zone approaches a ferritic (α) structure with reduced carbide volume fraction, significantly degrading hardness and corrosion resistance.
3.2 Hardness Distribution
| Location from Surface | Approximate Dilution (%) | Microstructure | Vickers Hardness (HV) |
|---|---|---|---|
| Overlay surface | 0–5 | Austenite + dense Cr₇C₃/M₇C₃ | 500–650 |
| Mid-overlay | 10–20 | Austenite + carbides + minor δ-ferrite | 400–550 |
| Fusion zone | 25–40 | Mixed γ + δ + carbides | 250–400 |
| Base metal HAZ | 45–60 | Refined ferrite + pearlite | 150–220 |
| Base metal (unaffected) | 100 | Coarse ferrite + pearlite | 120–180 |
3.3 Residual Stress State
The coefficient of thermal expansion (CTE) of the H1Cr24Ni13 overlay (~14×10⁻⁶/K) differs from Q235A steel (~12×10⁻⁶/K). During cooling, the overlay contracts more than the base metal, generating compressive residual stress in the base metal near the fusion zone and tensile residual stress in the overlay. For single-pass overlays on thin sections (<10 mm base thickness), peak tensile residual stresses in the overlay can reach 200–350 MPa, which must be evaluated against the overlay's fracture toughness.
4. Key Process Implementation Points
4.1 Welding Process Selection
H1Cr24Ni13 is available in both covered electrode (SMAW) and gas-shielded wire (GTAW/GMAW) forms. For the TIG (GTAW) overlay route, the following process parameters are recommended for Q235A base plates of 6–20 mm thickness:
| Parameter | Recommended Range | Rationale |
|---|---|---|
| Welding current | 120–180 A (DCEN) | Limit heat input to control dilution |
| Travel speed | 40–70 mm/min | Higher speed reduces dilution |
| Wire feed rate | 3–5 m/min | Maintain bead geometry and dilution control |
| Shielding gas | Argon (99.99%) or Ar + 2% O₂ | Argon for pure protection; trace O₂ for fluidity |
| Gas flow rate | 15–20 L/min | Adequate root and cap protection |
| Preheat temperature | 150–250°C | Reduce thermal gradient, prevent cold cracking |
| Interpass temperature | ≤250°C | Control grain growth, manage residual stress |
| Heat input | 0.8–1.5 kJ/mm | Minimize dilution while ensuring wetting |
4.2 Transition Layer Strategy
For thick overlays (>3 mm) or applications requiring high corrosion resistance, a transition layer of E309L (austenitic 309L composition) or E310L may be deposited between the Q235A base and the H1Cr24Ni13 overlay. This strategy:
- Reduces the carbon activity gradient at the base/overlay interface, decreasing hot crack susceptibility
- Provides a ductile buffer zone that accommodates differential thermal contraction
- Improves wetting of the high-carbon overlay onto the low-carbon substrate
- Allows the H1Cr24Ni13 layer to solidify with lower dilution, preserving hardness and corrosion properties
4.3 Multi-Pass Build Strategy
For overlay thicknesses exceeding 2 mm, a multi-pass approach is recommended:
- Pass 1 (Wet-in pass): Single stringer bead at minimum heat input to establish a metallurgical bond with controlled dilution (target ≤30%).
- Pass 2 (Build pass): Wider bead deposited over Pass 1, increasing dilution to the overlay alloy. Target dilution ≤20%.
- Pass 3 (Surface pass): Final cap bead with minimal dilution (<10%) to ensure surface hardness and corrosion resistance meet specification.
4.4 Post-Weld Heat Treatment
Post-weld stress relief at 400–500°C for 2 hours (for sections <25 mm) is recommended to reduce residual stresses in the fusion zone. However, temperatures above 550°C must be avoided as they promote carbide coarsening and softening of the overlay layer. For applications requiring maximum hardness, no post-weld heat treatment is applied, and the as-welded condition is accepted.
5. Applicable Standards and Acceptance Criteria
5.1 Material Standards
- GB/T 10044-2006: Cast welding electrodes for hardfacing — specifies composition and performance requirements for H1Cr24Ni13
- GB/T 700-2006: Hot-rolled steel of ordinary quality carbon structural steel — base material specification for Q235A
- ASTM A541/A541M: Standard specification for cast welding electrodes for hardfacing — international equivalent classification
- ASTM A36/A36M: Carbon steel plate, shape, and bar structural — international equivalent of Q235A
5.2 Welding Procedure Standards
- ASME BPV Code Section IX: Qualification of welding procedures and personnel — governs WPS/PQR qualification for overlay welding
- NB/T 47014-2011: Qualification test for welding procedure of pressure vessel — Chinese national standard for WPS qualification
- GB/T 19418-2014: Qualification test for welding procedure of pressure vessel — updated Chinese standard for weld procedure qualification
- ISO 15614-1:2017: Qualification testing of welding procedures for metallic materials — international WPS qualification standard
- EN ISO 14732:2015: Welding — qualification testing of welding procedures — European WPS qualification standard
5.3 Acceptance Criteria
| Test Method | Acceptance Criteria | Standard Reference |
|---|---|---|
| Macrograph examination | No cracks, porosity, lack of fusion; uniform dilution profile | GB/T 1954, ASTM E381 |
| Microhardness traverse | Overlay surface ≥450 HV; no soft zone <200 HV in fusion zone | GB/T 3899.2, ASTM E92 |
| Tensile test (transverse) | UTS ≥350 MPa; elongation ≥10% (for transition layer); overlay layer may exhibit brittle fracture | GB/T 228.1, ASTM E8 |
| Bend test (face bend) | No cracks >1.5 mm on convex surface | GB/T 2651, ASTM E16 |
| Impact test (Charpy V-notch) | ≥27 J at -20°C (if required by specification) | GB/T 229, ASTM E23 |
| Corrosion resistance (salt spray) | No base metal corrosion after 500 h (5% NaCl, 35°C) | GB/T 10125, ASTM B117 |
| NDT — Penetrant testing | No linear indications; pore size ≤0.5 mm | GB/T 18851, ASTM E709 |
| NDT — Ultrasonic testing | No indications exceeding II level per GB/T 11345 | GB/T 11345, ASTM E213 |
6. Common Risks and Controls
6.1 Hot Cracking (Solidification Cracking)
Risk: The high carbon and chromium content of H1Cr24Ni13 creates a wide solidification range with a high volume fraction of solid at the final stages of solidification. Combined with the low sulfur and phosphorus content of Q235A, this creates conditions favorable for interdendritic hot cracking, particularly at the fusion line.
Controls:
- Maintain preheat at 150–250°C to slow cooling rate
- Use narrow, short arc with high travel speed to reduce heat input per pass
- Apply a transition layer of E309L/E310L to buffer the composition gradient
- Avoid weaving; use stringer beads to minimize pool width and solidification time
- Ensure base metal is clean and free of sulfur/phosphorus segregations
6.2 Cold Cracking (Hydrogen-Induced Cracking)
Risk: Although Q235A has low carbon, the high dilution zone can create a locally high-hardness region susceptible to hydrogen-induced cracking if hydrogen from moisture (flux, atmosphere, or base metal surface contamination) is not adequately controlled.
Controls:
- Preheat to 150–250°C and maintain interpass temperature
- Use dry electrodes/wire and ensure shielding gas is free of moisture
- Clean base metal surface of oil, rust, and moisture before welding
- Apply post-weld bake at 250–300°C for 1–2 hours for hydrogen diffusion if required
6.3 Excessive Dilution
Risk: Over-dilution (>35–40%) transforms the fusion zone microstructure to predominantly ferritic, reducing hardness below 250 HV and compromising corrosion resistance. This is particularly problematic in single-pass overlays on thick base plates.
Controls:
- Minimize heat input by using lower current and higher travel speed
- Use a backing plate or backing bar to prevent root penetration
- Employ a multi-pass build with the first pass providing minimal wetting
- Use a transition layer to achieve effective overlay thickness with controlled dilution
6.4 Residual Stress and Distortion
Risk: Differential thermal expansion between the overlay and base metal generates high residual stresses, potentially causing distortion in thin sections or cracking in thick sections under subsequent thermal cycling.
Controls:
- Use balanced welding sequences (alternate beads, symmetric patterns)
- Apply post-weld stress relief at 400–500°C (below overlay softening temperature)
- Use backing plates and clamping to constrain distortion during welding
- Consider shot peening of the overlay surface to introduce beneficial compressive stresses
7. Application Scenarios Across Technology Routes
7.1 TIG/MIG Weld Overlay Route
The H1Cr24Ni13-on-Q235A fusion zone research directly supports the TIG/MIG weld overlay technology route of Cladding Technology Shanxi Co., Ltd. Key applications include:
- Chemical processing equipment: Pumps, valves, and pipe fittings where the Q235A structural body requires localized corrosion/wear protection at valve seats, impeller surfaces, or pipe ends. The overlay provides resistance to mineral acids, sulfuric acid, and oxidizing environments at temperatures up to 600°C.
- Pulp and paper industry: Wear plates, chipper knives, and screen bars where Q235A substrates are overlay welded with H1Cr24Ni13 to resist abrasive slurry and chemical attack simultaneously.
- Oil and gas equipment: Drill collars, subsea connectors, and wellhead components where the base material is Q235A and the overlay provides resistance to H₂S corrosion and erosion-corrosion.
- Power generation: Boiler tubes and heat exchanger tubes where localized areas require high-temperature oxidation resistance. The fusion zone integrity is critical for maintaining pressure containment.
The fusion zone study enables the company to develop qualified WPS documents with documented dilution control, preheat requirements, and acceptance criteria that satisfy customer specifications and regulatory requirements under ASME, NB/T, and GB standards.
7.2 Hydraulic Explosive Bonding Route
While H1Cr24Ni13 is not typically used as a cladding strip for hydraulic explosive bonding (due to its brittle, high-carbon nature), the fusion zone research provides valuable comparative data for the company's hydraulic explosive bonding route. Specifically:
- Performance benchmarking: The hardness, corrosion resistance, and dilution characteristics of weld overlay are benchmarked against hydraulic explosive bonded cladding (e.g., 304L/316L stainless on Q235A) to demonstrate the unique advantages of each technology.
- Hybrid cladding strategies: For components requiring both a thick corrosion-resistant layer (achieved by hydraulic explosive bonding of 316L on Q235A) and a localized wear-resistant surface (achieved by TIG overlay of H1Cr24Ni13), the fusion zone research provides the metallurgical basis for the overlay-on-bonded-cladding sequence.
- Qualification cross-reference: Understanding the dilution and microstructure in weld overlay helps define the performance envelope that explosive bonding must exceed for certain applications, strengthening the technical case for selecting explosive bonding where dilution-free bonding is required.
7.3 Explosion Welding Route
Explosion welding (explosive cladding) provides a dilution-free metallurgical bond between dissimilar materials, which is fundamentally different from the fusion zone behavior studied in this research. However, the fusion zone study contributes to the explosion welding route in the following ways:
- Surface preparation for post-explosion overlay: Components produced by explosion welding (e.g., 304L/316L on Q235A) may require additional surface hardening via TIG overlay of H1Cr24Ni13. The fusion zone research provides the metallurgical basis for this secondary overlay, ensuring compatibility between the explosion-bonded interface and the weld overlay.
- Comparative qualification data: The fusion zone properties (hardness, residual stress, corrosion resistance) of weld overlay are documented alongside explosion welding properties to provide customers with a comprehensive comparison for technology selection.
- Repair and maintenance procedures: When explosion-welded components require localized repair or re-cladding, TIG overlay of H1Cr24Ni13 may be applied to the explosion-bonded surface. The fusion zone study provides WPS development data for this repair scenario.
8. Contribution to Qualification Building and Customer Value
8.1 Qualification Building
The documented fusion zone microstructure and properties research directly contributes to the company's qualification portfolio in the following ways:
- PQR Development: The research data (macrographs, micrographs, hardness traverses, tensile results, corrosion test data) constitutes the primary evidence for Performance Qualification Records (PQRs) submitted under ASME Section IX, NB/T 47014, or GB/T 19418.
- WPS Standardization: The optimized process parameters derived from fusion zone analysis are incorporated into standardized WPS documents that govern production welding, ensuring consistent quality across all production sites.
- Third-Party Certification: Documented fusion zone performance data supports applications for third-party certification bodies (e.g., TUV, DNV, CNAS-accredited labs) to validate the company's overlay welding capabilities.
- Scope Expansion: Qualification of H1Cr24Ni13 on Q235A establishes a foundation for extending the WPS scope to similar base materials (Q345, Q345R, 16Mn) and similar overlay alloys (H1Cr24Ni30, H1Cr20Ni12) under ASME Section IX essential variables.
8.2 Product Delivery
The fusion zone research enables the company to deliver overlay-clad products with guaranteed performance:
- Hardness guarantee: Documented hardness profiles (≥450 HV at surface, ≥250 HV in fusion zone) provide a measurable quality criterion for product acceptance.
- Corrosion resistance guarantee: Salt spray test data (≥500 h without base metal corrosion) provides a quantifiable corrosion resistance specification for customer acceptance.
- Dimensional stability: Residual stress data and distortion control measures ensure that overlay-clad components meet dimensional tolerances after welding and any subsequent machining.
- Longevity prediction: Understanding the microstructure and residual stress state enables the company to provide customers with predicted service life data for specific operating environments.
8.3 Customer Value
The technical depth of this fusion zone research translates into direct customer value:
- Risk mitigation: Customers are protected from premature overlay failure due to cracking, spalling, or corrosion breakthrough, reducing unplanned downtime and maintenance costs.
- Design optimization: Detailed dilution and hardness data allows customers to optimize overlay thickness, reducing material usage while maintaining performance, thereby lowering component costs.
- Regulatory compliance: Documented WPS/PQR data satisfies regulatory requirements in nuclear, pressure vessel, and offshore applications, enabling customers to pass inspections and audits.
- Competitive differentiation: The company's documented fusion zone expertise positions it as a technically superior supplier compared to competitors who may lack metallurgical documentation and qualification data.
9. Conclusion
The research on H1Cr24Ni13 overlay fusion zone microstructure and properties on Q235A steel represents a fundamental technical asset for Cladding Technology Shanxi Co., Ltd. It provides the metallurgical foundation for WPS qualification, establishes measurable acceptance criteria for product quality, enables risk-informed process control, and supports technology selection across the company's three cladding routes (TIG/MIG weld overlay, hydraulic explosive bonding, and explosion welding). The documented data and optimized parameters directly contribute to building a robust qualification portfolio, ensuring reliable product delivery, and delivering measurable value to customers in chemical processing, oil and gas, power generation, and heavy industry sectors.