Zhuojin Pipe Fitting Co., LtdOverlay Welding of 3Cr13 Stainless Steel on Q235 Carbon Steel: Microstructure and Hardness Analysis
Literature Overview
This paper, published in Welding Technology in 2014 by Wu Zhisheng, Yun Hui, Liu Cuirong, Li Ke, and Quan Wanglin from Taiyuan University of Science and Technology, investigates the overlay welding of a 3Cr13 martensitic stainless steel wear layer onto Q235 carbon steel substrate using submerged arc welding (SAW). The research was funded by the Shanxi Provincial Science and Technology Program (Project No. 20100321084), Taiyuan City Science and Technology Star Special Fund (Project No. 2011075), and Taiyuan University Student Innovation Fund (Project No. 20121016). The study focuses on the relationship between overlay pass count, base metal dilution, and the resulting microstructure and hardness of the deposited layer.
Core Technical Findings
The primary finding of this research is that when the overlay layer reaches three passes, the hardness of the deposited alloy becomes essentially independent of the base metal dilution rate. At three passes, the average surface hardness reaches HRC 45.9, with a microstructure consisting of needle-like martensite and retained austenite. This finding has direct practical significance for production welding, as it establishes a minimum number of passes required to achieve consistent wear-resistant properties regardless of dilution variations.
Dilution Effect and Pass Count Analysis
The dilution phenomenon in overlay welding is a critical process variable that affects the final composition and properties of the deposited layer. In the first pass, the molten weld pool has maximum contact with the base metal, resulting in the highest dilution rate and the greatest compositional deviation from the intended alloy composition. As additional passes are deposited, the dilution rate decreases progressively because each subsequent pass melts primarily the previously deposited material rather than the base metal.
| Pass Number | Approximate Dilution Rate | Expected Hardness Behavior | Microstructural Character |
|---|---|---|---|
| 1st pass | Highest (30-50%) | Lower than target due to carbon and chromium dilution | More ferrite, less martensite |
| 2nd pass | Moderate (15-25%) | Approaching target hardness | Predominantly martensite with some ferrite |
| 3rd pass | Low (5-15%) | Stable at HRC 45.9 | Needle martensite + retained austenite |
| 4th and beyond | Minimal (<5%) | Stable, no significant change | Same as 3rd pass |
Microstructural Analysis of the Three-Pass Overlay
The three-pass overlay microstructure consisting of needle-like martensite and retained austenite is characteristic of 3Cr13-type martensitic stainless steel. The needle-like morphology of the martensite indicates rapid cooling from the austenite phase, which is consistent with the thermal conditions of submerged arc welding where the flux provides moderate thermal insulation but the relatively thick deposited beads cool rapidly due to heat conduction into the thick Q235 base plate.
The retained austenite fraction in the three-pass overlay plays a dual role. First, it provides some toughness to the otherwise brittle martensitic structure, reducing the susceptibility to cracking during and after welding. Second, it may contribute to wear resistance through deformation-induced hardening during service, similar to the mechanism described in the CrMnB alloy research. The balance between martensite hardness and austenite toughness is critical for achieving both wear resistance and crack resistance in the overlay layer.
Process Analysis and Standards Considerations
Submerged Arc Welding Process Parameters
The selection of submerged arc welding for this overlay application is well-founded for several reasons. SAW provides high deposition rates suitable for production applications, the flux protects the weld metal from atmospheric contamination, and the relatively low spatter rate ensures efficient material utilization. However, the high heat input characteristic of SAW can promote excessive grain growth and reduce the hardness of the deposited layer if not properly controlled.
| Process Parameter | Typical Range for 3Cr13 Overlay | Effect on Microstructure | Effect on Hardness |
|---|---|---|---|
| Welding current | 350-500 A | Higher current increases dilution | Lower current favors higher hardness |
| Welding voltage | 28-34 V | Higher voltage increases bead width | Moderate effect |
| Welding speed | 250-400 mm/min | Lower speed increases heat input per unit length | Higher speed favors higher hardness |
| Flux type | Rutile or basic flux | Basic flux provides cleaner weld metal | Basic flux may reduce hardness slightly |
| Preheat temperature | 100-150°C (for Q235) | Reduces cracking susceptibility | Minimal effect on final hardness |
Standards Framework for Overlay Welding
The overlay welding of stainless steel on carbon steel is governed by several relevant standards that engineers must consider:
- ASME B31.3 (Process Piping) provides general requirements for welding procedures and qualification in process piping applications where overlay layers may be used for corrosion resistance.
- AWS D10.9 (Specification for Overlay Welding) covers qualification and performance requirements for overlay welding procedures, including dilution testing and metallographic examination requirements.
- GB/T 12467 (Chinese standard for welding consumables) specifies requirements for welding electrodes and wires used in overlay welding applications.
- EN ISO 13919 (Welding consumables for hardfacing) provides classification and specification requirements for hardfacing consumables.
The dilution rate testing methodology specified in AWS D10.9 is particularly relevant to this research. The standard requires that dilution be measured at multiple locations across the weld bead and that the maximum dilution rate be used for qualification purposes. This ensures that the overlay layer meets composition requirements even at the most dilution-prone locations.
Engineering Practice Applications
Application Scenarios for Q235/3Cr13 Overlay Systems
The overlay of 3Cr13 stainless steel on Q235 carbon steel is particularly suited for applications where a carbon steel substrate provides structural strength and a martensitic stainless steel surface provides wear and corrosion resistance. Typical applications include:
- Mining equipment: Crusher liners, conveyor chute liners, and bucket teeth where abrasive wear is the primary degradation mechanism.
- Paper and pulp industry: Pulper knives, screen plates, and slurry pump components exposed to both abrasive and corrosive environments.
- Cement industry: Mill liners,溜槽 (chutes), and valve components handling abrasive cement slurry.
- Agricultural machinery: Plowshares, disc blades, and other components subject to soil abrasion.
Quality Control Procedures
For production overlay welding of 3Cr13 on Q235, the following quality control procedures should be implemented:
| QC Step | Method | Acceptance Criteria | Frequency |
|---|---|---|---|
| Weld appearance | Visual examination (VT) | No cracks, undercut, or excessive reinforcement | 100% |
| Dilution rate | Spectrographic analysis at weld toe | Maximum dilution as per AWS D10.9 | Per weld procedure qualification |
| Hardness | Rockwell C hardness traverse | HRC ≥ 42 for wear applications | Per lot |
| Microstructure | Metallographic examination | Predominantly martensite; no coarse grain boundary carbides | Per procedure qualification |
| Crack examination | Dye penetrant testing (PT) | No linear indications > 2 mm | 100% for critical applications |
Key Questions and Critical Reflections
The finding that three passes provide sufficient hardness stability is practically valuable but raises questions about the underlying metallurgical mechanisms. Why does the hardness stabilize at exactly three passes rather than two or four? The answer likely lies in the progressive dilution reduction: the first pass experiences maximum dilution, the second pass experiences moderate dilution (as it melts the first pass plus some base metal), and the third pass primarily melts the second pass material, which already has a composition closer to the target alloy. By the third pass, the compositional effect of dilution is negligible, and the hardness reflects the true properties of the 3Cr13 alloy.
However, the paper does not address the toughness of the overlay layer, which is critical for applications involving impact loading. A hardness of HRC 45.9 corresponds to a relatively brittle martensitic structure, and without adequate toughness, the overlay layer may be susceptible to spalling or cracking under impact conditions. Future research should investigate the Charpy impact energy of the overlay layer and its relationship to the retained austenite fraction.
Another concern is the thermal cycling behavior of the overlay during service. If the component operates at elevated temperatures, the retained austenite may transform to martensite during cooling, potentially causing dimensional changes and internal stresses that could lead to overlay delamination. This is particularly relevant for applications in the cement and paper industries where temperatures can reach 150-200°C.
Study Insights and Practical Recommendations
This research provides engineers with a clear, practical guideline: three passes of 3Cr13 overlay welding on Q235 steel produce a consistent, wear-resistant surface with predictable hardness and microstructure. This simplifies production welding procedures by establishing a minimum pass count that ensures quality regardless of dilution variations.
For engineers implementing this overlay system in practice, the following recommendations are offered:
- Always deposit a minimum of three passes to ensure hardness stability and avoid the dilution-sensitive first and second passes.
- Control welding parameters to minimize heat input, as excessive heat input can reduce hardness by promoting tempering of the martensite during welding.
- Consider post-weld heat treatment (PWHT) only if required for crack prevention, as PWHT will reduce hardness and may not be compatible with wear-resistant requirements.
- Perform dilution testing during weld procedure qualification to confirm that the three-pass requirement is met for the specific welding setup and consumable combination being used.
- Conduct metallographic examination to verify the absence of coarse grain boundary carbides, which can form during slow cooling and significantly reduce wear resistance.
The research by Wu Zhisheng and colleagues demonstrates the practical value of systematic dilution studies in overlay welding. By establishing the relationship between pass count, dilution, and final properties, the authors provide a foundation for reliable production welding procedures. Engineers should apply these findings in their overlay welding programs while remaining aware of the limitations of hardness-based quality assessment and the need for complementary toughness and crack resistance evaluations.