35 Steel Overlay Stainless Steel Wear-Resistant Layer Microstructure and Properties

Literature Overview and Application Context

The study by Li Ke, Wu Zhisheng, Liu Cuirong, and Song Xu from the School of Materials Science at Taiyuan University of Science and Technology investigates the microstructure and properties of a stainless steel wear-resistant overlay layer applied to 35 steel using automatic submerged arc welding (SAW). Published in Thermal Processing Technology in 2013 (Vol. 42, No. 7, pp. 161–162), this research was supported by the Shanxi Provincial Science and Technology Key Project (20100321084), the Taiyuan University of Science and Technology Young Fund (20113001), and the University-level UIT Project (XJ2010029).

The combination of 35 steel substrate and stainless steel overlay is of practical significance in the engineering community. 35 steel is a medium-carbon structural steel widely used for shafts, gears, and structural components, while the stainless steel overlay provides corrosion resistance and wear resistance. This combination is particularly relevant for pipe components and structural steel in corrosive environments where both wear and corrosion are concerns.

Welding Process and Microstructural Analysis

The automatic submerged arc welding process used in this study is well-suited for the production of thick overlay layers on flat or slightly curved surfaces. SAW provides a stable welding arc, high deposition rates, and good penetration, making it an efficient choice for overlay welding applications. The automatic nature of the process ensures consistent welding parameters and uniform weld bead geometry, which is critical for achieving uniform overlay properties.

The microstructure of the overlay weld metal is directly correlated with the hardness distribution. The researchers found that the hardness profile across the overlay layer corresponds to the microstructural variations, with areas of higher hardness associated with harder microstructural phases. The overlay layer achieved the expected hardness values, indicating that the welding process and alloy design were successful in producing the desired performance.

The correlation between microstructure and hardness is a fundamental principle of welding metallurgy. The microstructure of the overlay weld metal is determined by the cooling rate, the alloy composition, and the welding parameters. In the case of stainless steel overlays, the cooling rate is particularly important because it determines the relative amounts of austenite, ferrite, and martensite in the weld metal. A high cooling rate can promote the formation of martensite, which increases hardness but may reduce toughness and increase the risk of cracking.

Engineering Considerations for Dissimilar Metal Overlay Welding

The welding of a stainless steel overlay onto a 35 steel substrate creates a dissimilar metal weld interface that must be carefully managed. The dilution between the overlay and the base material is a critical factor that affects the microstructure, mechanical properties, and corrosion resistance of the overlay layer. Excessive dilution can reduce the chromium content in the weld metal below the level required for corrosion resistance, while insufficient dilution can result in poor fusion and a weak bond between the overlay and the substrate.

The automatic submerged arc welding process offers several advantages for this application. The stable arc and consistent heat input provide good control over the dilution ratio, and the high deposition rate allows for the production of thick overlay layers in a reasonable number of passes. However, SAW also has limitations, including the requirement for a flat or slightly curved surface and the need for a flux supply. For curved pipe surfaces, the welding equipment must be designed to maintain a consistent torch angle and wire position throughout the entire weld circumference.

Quality Control and Performance Verification

A quality control protocol for 35 steel with stainless steel overlay should include the following elements. First, the base material must be verified for proper heat treatment and surface preparation. The surface should be clean, free of rust, scale, and contaminants, and may require machining or grinding to ensure good fusion with the overlay. Second, the welding consumables must be verified for proper composition and quality, including the wire composition and flux characteristics.

Third, the welding process parameters must be tightly controlled, including the welding current, voltage, travel speed, and wire feed speed. Any deviation from the qualified parameters can affect the dilution ratio, microstructure, and ultimate performance of the overlay layer. In-process monitoring of the welding arc stability and wire feeding consistency is recommended.

Fourth, post-weld inspection should include macrographic examination of the weld bead geometry, dilution ratio measurement through cross-sectional analysis, hardness testing at multiple locations across the weld bead, and corrosion testing to verify the corrosion resistance of the overlay layer. The hardness profile should be measured at regular intervals to ensure uniform reinforcement and to identify any areas of excessive dilution or incomplete fusion.

Study Insights and Practical Implications

The research by Li Ke and colleagues, while brief in scope, provides a valuable confirmation of the effectiveness of automatic submerged arc welding for producing stainless steel wear-resistant overlays on 35 steel substrates. The finding that the hardness distribution corresponds to the microstructural variations is a fundamental metallurgical principle that underpins the design and optimization of overlay welding processes.

For engineers working in the steel pipe and fitting industry, this research highlights the potential of SAW for the production of thick, high-quality overlay layers on structural steel components. The automatic nature of the process ensures consistent quality and high productivity, making it well-suited for industrial production environments. However, the research also underscores the importance of careful process control and quality verification to ensure that the overlay achieves the desired performance.

The study is limited in its depth of analysis, focusing primarily on the correlation between microstructure and hardness without providing detailed information on the specific microstructural phases, the dilution ratio, or the wear testing results. For a more comprehensive understanding of the overlay performance, additional research would be needed to characterize the microstructure in detail, measure the dilution ratio, and conduct wear and corrosion testing under relevant service conditions.

Despite these limitations, the research provides a useful baseline for engineers considering the application of stainless steel overlays to 35 steel components. The key takeaways are that automatic SAW can produce overlays with the expected hardness values, that the microstructure and hardness are closely correlated, and that careful process control is essential for achieving consistent quality.