Microstructure and Hardness Analysis of Q235 Steel Overlay with 3Cr13 Stainless Steel

Literature Overview

The study by Li Ke, Wu Zhisheng, Liu Cuirong, and Yang Dongxing (2013), published in Hot Working Technology (Vol. 42, No. 17, pp. 155-156), investigates the microstructure and hardness distribution of overlay welds produced by automatic submerged arc welding (SAW) of 3Cr13 stainless steel onto Q235 steel substrate. Conducted at the School of Materials Science and Engineering, Taiyuan University of Science and Technology, and the Physical Testing and Measurement Center of Jinxí Industrial Group Co., Ltd., this work was supported by the Shanxi Provincial Science and Technology Project (20100321084), Taiyuan University of Science and Technology Youth Fund (20113001), and Graduate Student Scientific Innovation Project (20111001). The study addresses the practical challenge of combining corrosion-resistant overlay materials with carbon steel substrates.

Weld Joint Characterization

The overlay welds were produced using automatic submerged arc welding, a process well-suited for producing uniform, high-quality overlay deposits on flat or simple geometries. The 3Cr13 stainless steel is a martensitic stainless steel containing approximately 13% chromium, which provides good corrosion resistance and wear resistance when hardened. The Q235 substrate is a low-carbon structural steel commonly used in general fabrication. The hardness distribution across the weld joint was measured using microhardness testing, and the microstructure was characterized using metallographic examination.

The hardness maximum was found in the second overlay layer, reaching 453 HV, which is significantly higher than both the first overlay layer and the substrate. This hardness distribution is consistent with the expected microstructural evolution, where subsequent passes experience lower dilution and higher chromium content, promoting the formation of harder martensitic and carbide phases.

Microstructural Evolution

The microstructure of the weld joint exhibits a clear gradient from the soft substrate through the heat-affected zone to the hard overlay layer. The Q235 substrate retains its ferrite-pearlite microstructure with an average hardness of 132 HV. The heat-affected zone shows features of thermal cycling, including possible Widmanstätten ferrite and acicular ferrite formation, depending on the cooling rate. The overlay layer microstructure is dominated by martensite and chromium carbides, with the hardness increasing from the first to the second pass.

The hardness maximum in the second overlay layer can be attributed to several factors. First, the second pass experiences less dilution from the base metal compared to the first pass, resulting in a higher effective chromium content and more complete martensitic transformation. Second, the thermal cycling from the second pass may refine the microstructure of the first pass, contributing to hardness increase. Third, the carbon content in the second pass may be slightly higher due to the interaction between the overlay material and the first pass, promoting more carbide precipitation.

Welding Process Considerations

Automatic submerged arc welding is an excellent choice for overlay applications due to its high deposition rate, excellent weld quality, and process stability. The flux covering provides excellent protection against atmospheric contamination, resulting in clean welds with low hydrogen content. However, the process has limitations, including the requirement for flat or simple geometries, the need for specialized equipment, and the potential for high heat input that can affect the substrate properties. For 3Cr13 overlay on Q235 steel, the process parameters must be carefully controlled to minimize dilution while ensuring good metallurgical bonding.

The dilution rate in SAW overlay is typically higher than in processes such as plasma arc or laser overlay, which means that the effective composition of the overlay layer is significantly influenced by the base metal. For 3Cr13 overlay, the dilution reduces the chromium content in the weld metal, potentially affecting the corrosion resistance and hardenability. The hardness results in this study confirm that the overlay layer achieves significantly higher hardness than the substrate, but the dilution effect should be considered when predicting corrosion resistance and wear resistance in service.

Engineering Practice Implications

The combination of 3Cr13 stainless steel overlay with Q235 steel substrate is a practical solution for components that require both structural strength and surface corrosion or wear resistance. This approach is commonly used in the fabrication of chemical equipment, mining machinery, and power generation components. The hardness gradient from 132 HV to 453 HV provides a transition zone that can accommodate differential thermal expansion during thermal cycling. Engineers should be aware that the high hardness of the overlay layer may be accompanied by reduced toughness, which could be a concern for impact loading applications. Post-weld heat treatment may be necessary to relieve residual stresses and improve the toughness of the overlay layer.

Study Insights and Reflections

This study provides practical data on the microstructure and hardness of 3Cr13 overlay welds on Q235 steel, which is valuable for engineers designing overlay solutions for industrial applications. The hardness maximum in the second pass is an important finding, as it suggests that multi-pass overlay strategies can be used to optimize the surface properties. The relatively simple experimental methodology, using standard metallographic and microhardness testing, makes the findings readily applicable to industrial quality control and process verification. Engineers should note that the hardness distribution is sensitive to process parameters, substrate preparation, and overlay material composition, and that systematic optimization is recommended for critical applications.

The combination of corrosion-resistant stainless steel overlay with structural carbon steel substrate represents a widely used engineering approach that offers significant economic advantages over using corrosion-resistant materials throughout the entire component. This hybrid approach leverages the structural efficiency of carbon steel while providing the surface protection of stainless steel, making it an attractive solution for many industrial applications. The study confirms that automatic submerged arc welding is a viable process for producing high-quality overlay welds, and the hardness and microstructure data provide a useful reference for process qualification and quality assurance.

Summary and Conclusions

These five studies collectively address key aspects of overlay welding technology, from consumable design and composition optimization to process simulation and joint characterization. The TiC-VC electrode study demonstrates the potential of in-situ carbide formation for improving abrasion resistance while maintaining weldability. The high-chromium overlay study highlights the effectiveness of TiC addition in mitigating dilution effects and improving microstructural uniformity. The plasma arc powder optimization study showcases the power of statistical experimental design in developing high-performance overlay coatings. The laser overlay simulation study provides quantitative insights into thermal behavior that are essential for process optimization. The 3Cr13 overlay study offers practical data on microstructure and hardness for a widely used overlay system. Together, these works represent a comprehensive view of overlay welding technology spanning consumable development, process control, and performance evaluation, and they provide valuable guidance for engineers working in surface engineering and equipment repair applications.