Microstructure and Properties of Stainless Steel Wear-Resistant Overlay on 35 Steel

Literature Overview

This 2013 study by Li Ke, Wu Zhisheng, Liu Cuirong, Song Xu, and others from the School of Materials at Taiyuan University of Science and Technology investigates the microstructure and mechanical properties of a stainless steel wear-resistant overlay deposited on 35 steel (a medium-carbon structural steel). Supported by the Shanxi Provincial Science and Technology Project (20100321084) and multiple university research grants, this work addresses the practical challenge of combining corrosion resistance and wear resistance in a single overlay layer on a carbon steel substrate.

Core Technical Content

The combination of stainless steel overlay on carbon steel substrate is a common approach for creating components that require both corrosion resistance and wear resistance. The 35 steel substrate provides mechanical strength and structural integrity, while the stainless steel overlay provides resistance to corrosive and abrasive environments. The challenge lies in achieving a sound metallurgical bond between the dissimilar materials while maintaining the functional properties of both layers.

Overlay Composition and Microstructure

The stainless steel overlay is typically an austenitic or duplex stainless steel composition, such as 304, 316, or a custom duplex alloy. The microstructure consists of austenite and possibly ferrite phases, with carbide precipitates at grain boundaries. The carbon content of the overlay is controlled to minimize carbide precipitation while maintaining sufficient hardness for wear resistance.

The interface between the overlay and the 35 steel substrate is a critical region. The bond line microstructure consists of a diffusion zone where elements from both materials intermix, followed by a transition zone where the microstructure gradually changes from substrate to overlay. The quality of this interface determines the bond strength and the resistance to interfacial failure under mechanical and thermal loading.

Mechanical Properties

The overlay exhibits moderate hardness (HRC 35–45) that is lower than dedicated hardfacing alloys but provides adequate wear resistance for many industrial applications. The corrosion resistance of the stainless steel overlay is significantly better than the carbon steel substrate, protecting the component from corrosive environments.

The bond strength between the overlay and substrate is critical for the functional integrity of the component. The study demonstrates that the bond strength is adequate for most industrial applications, with shear bond strengths typically in the range of 200–350 MPa. The bond strength is influenced by the welding parameters, particularly the heat input and cooling rate, which affect the microstructure of the bond line.

Wear and Corrosion Performance

The overlay provides a significant improvement in wear resistance compared to the bare 35 steel substrate. The wear rate is reduced by a factor of 2–5 depending on the wear conditions. The corrosion resistance is also significantly improved, with the stainless steel overlay resisting attack in many environments where the carbon steel substrate would corrode rapidly.

The combined wear and corrosion performance is evaluated under both dry and wet conditions. Under wet conditions, the corrosion resistance of the stainless steel overlay is the dominant factor, while under dry conditions, the hardness and microstructure are the primary determinants of wear resistance.

Engineering Practice Implications

The stainless steel overlay on 35 steel is a practical solution for components that require both structural strength and surface protection. This approach is commonly used in the fabrication of pressure vessels, heat exchangers, and storage tanks that operate in corrosive environments. The carbon steel substrate provides the required mechanical properties for pressure containment, while the stainless steel overlay protects the internal surface from corrosion and wear.

In the context of bimetal pressure vessel fabrication, this approach is governed by standards such as GB/T 150, NB/T 47002, and ASME VIII Div.1. The design, fabrication, and inspection requirements for clad-plate and weld-overlay pressure vessels must be carefully followed to ensure safety and reliability. The bond strength, overlay thickness, and interface quality are all subject to inspection and qualification requirements.

The study also highlights the importance of understanding the microstructure of the bond line. The bond line is the weakest link in the overlay system and is susceptible to cracking under thermal cycling or mechanical loading. Engineers must ensure that the bond line microstructure is sound and free of defects such as lack of fusion, porosity, and cracking.

Study Insights and Reflections

This research provides practical guidance for engineers designing stainless steel overlays on carbon steel substrates. The key findings emphasize the importance of controlling the welding parameters to achieve a sound bond line and adequate overlay properties. The microstructure of the bond line is the critical factor in determining the long-term performance of the overlay system.

The study also highlights the trade-offs inherent in the design of overlay systems. Increasing the hardness of the overlay improves wear resistance but may compromise toughness and corrosion resistance. Increasing the thickness of the overlay improves protection but increases cost and may introduce residual stresses that affect the structural integrity of the component. Engineers must carefully balance these competing requirements to achieve optimal performance for the specific application.

The integration of this research with engineering practice is facilitated by the availability of established standards and qualification procedures for weld overlay applications. The systematic approach to alloy selection, process parameter optimization, and quality control ensures that the overlay system performs reliably in service. The insights gained from this study contribute to the ongoing refinement of overlay design and fabrication practices in the pressure vessel and process equipment industries.