CLADDING TECHNOLOGY SHANXI CO., LTDMicrostructure and Properties of Wear-Resistant Weld Overlay Layer on Q235 Steel Plate
Literature Overview
This paper by Dong Shengrong from Hunan Industrial Technician College was published in Materials Development and Application in 2018. The research investigates the microstructure and mechanical properties of wear-resistant weld overlay layers deposited on Q235 carbon steel substrate plates. Q235 is a widely used low-carbon structural steel in China, and the development of effective overlay systems for this substrate has significant practical importance for extending the service life of equipment components.
Core Technical Concept
The research addresses the challenge of depositing wear-resistant overlay layers on low-carbon steel substrates, where dilution control and bond line integrity are critical concerns. Q235 steel contains approximately 0.14-0.22% carbon and minimal alloying elements, making it susceptible to significant dilution during overlay welding. The resulting dilution can reduce the hardness and wear resistance of the overlay layer, compromising its protective function.
The overlay material composition and welding parameters are carefully selected to achieve a balance between wear resistance and bond strength. Common wear-resistant overlay materials include:
- High-carbon martensitic steels: Provide high hardness through martensitic transformation
- Cr-based hardfacing alloys: Offer excellent wear resistance through chromium carbide formation
- Ni-based alloys: Provide good corrosion and wear resistance with lower dilution sensitivity
- Composite materials: Incorporate hard particles (WC, TiC, SiC) in a tough matrix
Microstructural Characteristics
The overlay layer microstructure is characterized by several key features:
| Microstructural Feature | Composition | Role in Wear Resistance |
|---|---|---|
| Matrix phase | Martensite or austenite | Provides base hardness and toughness |
| Carbide particles | Cr7C3, Cr3C2, or WC | Primary wear resistance mechanism |
| Bond line | Diluted transition zone | Critical for adhesion strength |
| Heat-affected zone | Modified substrate microstructure | Influences overall component integrity |
The dilution zone at the bond line is a critical area of concern. Excessive dilution reduces the hardness gradient between the overlay and substrate, potentially leading to premature wear at the interface. The research examines the microstructural evolution across the overlay thickness, identifying the depth at which the overlay composition stabilizes.
Mechanical Property Evaluation
The mechanical properties of the overlay layer are evaluated through several testing methods:
- Hardness testing: Vickers or Rockwell hardness measurements across the overlay thickness
- Wear testing: Pin-on-disk or block-on-ring tests to quantify wear resistance
- Bond strength testing: Peel or shear tests to evaluate overlay-substrate adhesion
- Impact testing: Charpy or drop weight tests to assess toughness
Typical results show hardness values of 40-60 HRC for the overlay layer, with a gradual decrease toward the bond line due to dilution. The wear resistance is typically 3-10 times that of the base Q235 steel, depending on the overlay material composition and microstructure.
Engineering Practice Integration
The overlay technology is applied to several industrial components:
- Mining equipment: Conveyor rollers, chute linings, and crusher components
- Construction machinery: Bulldozer blades, grader teeth, and bucket teeth
- Material handling: Hopper linings, chute plates, and feeders
- Agricultural equipment: Plowshares, disc blades, and tillage tools
The overlay process typically involves surface preparation (grinding or shot blasting), preheating, multi-pass welding, and post-weld heat treatment. Quality control includes visual inspection, magnetic particle testing for crack detection, and hardness verification at specified intervals.
Key Questions and Reflections
Several technical challenges remain in the application of wear-resistant overlays on Q235 substrates. First, the low alloy content of Q235 makes it susceptible to cracking during welding, particularly in thick sections or when welding at low temperatures. Second, the dilution rate varies with welding parameters, making it difficult to maintain consistent overlay properties across large production runs.
The research also raises questions about the long-term performance of overlays under cyclic loading conditions. Fatigue cracking at the bond line is a common failure mode in overlay applications, and the microstructural characteristics of the dilution zone play a critical role in fatigue resistance. Additionally, the effect of thermal cycling on overlay properties over extended service periods requires further investigation.
Study Insights and Implications
This research provides valuable insights into the design and application of wear-resistant overlay systems for low-carbon steel substrates. The emphasis on microstructural characterization and property evaluation offers a systematic approach to overlay development that can be adapted to other substrate materials.
For engineers working on equipment maintenance and component refurbishment, the overlay technology offers an economical alternative to component replacement. The ability to extend service life through overlay welding can significantly reduce maintenance costs and downtime, particularly for large or expensive components where replacement is impractical. However, the technique requires careful process control and quality assurance to ensure reliable performance in service.