CLADDING TECHNOLOGY SHANXI CO., LTDMicrostructure and Properties of Stainless Steel Wear-Resistant Overlay on 35 Steel
Literature Overview and Application Context
The study "Microstructure and Properties of Stainless Steel Wear-Resistant Overlay on 35 Steel" investigates the metallurgical behavior and mechanical performance of stainless steel overlay layers deposited on 35 steel (a medium carbon steel with approximately 0.35% C) substrate. This combination is of significant practical importance because 35 steel is widely used as a base material for structural components, shafts, gears, and wear-critical machine parts, while stainless steel overlays provide corrosion resistance and enhanced wear performance. The study addresses the fundamental challenge of achieving a metallurgically sound bond between dissimilar materials while maintaining the desired properties in both the overlay and the heat-affected zone.
Base Material and Overlay System Characterization
35 steel is a low-alloy medium carbon steel with typical composition of 0.32–0.37% C, 0.50–0.80% Mn, and 0.17–0.37% Si. Its microstructure in the as-supplied condition consists of ferrite and pearlite, with a hardness of approximately 200–250 HV. The carbon content is sufficient to provide moderate strength and good weldability, but it also means that the heat-affected zone (HAZ) is susceptible to hardening and potential cracking during welding operations.
The stainless steel overlay system studied is typically based on austenitic stainless steel compositions such as 304, 316, or a modified variant with elevated carbon content for enhanced wear resistance. The specific composition affects the microstructure of the overlay layer and the dilution behavior at the interface.
| Component | 35 Steel Base | Stainless Steel Overlay | Interface Zone |
|---|---|---|---|
| Carbon (wt%) | 0.32–0.37 | 0.08–0.15 (304) or 0.20–0.40 (modified) | 0.15–0.30 |
| Chromium (wt%) | 0.30–0.60 | 18.0–20.0 | 5.0–12.0 |
| Nickel (wt%) | 0.30–0.60 | 8.0–10.5 (304) | 2.0–6.0 |
| Hardness (HV) | 200–250 | 250–350 (as-deposited) | 350–500 |
| Microstructure | Ferrite + Pearlite | Austenite + Ferrite | Martensite + Austenite |
Microstructural Analysis and Dilution Effects
The most critical aspect of this study is the characterization of the dilution zone at the interface between the 35 steel base and the stainless steel overlay. During the welding process, base metal melts and mixes with the overlay material, creating a gradient composition zone that can significantly affect both the corrosion resistance and mechanical properties of the overlay.
The dilution rate is typically 15–35% for single-pass overlays and decreases to 10–20% for multi-pass deposits. The dilution zone microstructure is particularly important because it often contains martensite formed from the high carbon content of the base metal diluted into the overlay. This martensite can be hard (500–700 HV) but brittle, creating a potential crack initiation site.
The study identifies three distinct zones in the overlay structure:
- Overlay zone: Predominantly austenitic structure with some delta ferrite, providing good corrosion resistance and moderate wear resistance.
- Dilution zone: Mixed microstructure of austenite, martensite, and delta ferrite, with elevated hardness but reduced ductility.
- Heat-affected zone in base metal: Partially recrystallized ferrite and pearlite with some martensite formation near the fusion line.
The transition from the dilution zone to the overlay zone is critical. If the dilution zone is too wide or too hard, it can become a weak link in the overlay system, leading to delamination or cracking under service loading.
Mechanical Properties and Wear Performance
The mechanical properties of the overlay system are governed by the interplay between hardness, toughness, and bond strength. The study reports the following typical values:
| Property | Overlay Layer | Dilution Zone | Base Metal HAZ | Base Metal |
|---|---|---|---|---|
| Hardness (HV) | 280–350 | 400–550 | 280–380 | 200–250 |
| Tensile Strength (MPa) | 550–650 | 600–750 | 450–550 | 490–590 |
| Impact Energy (J) | 30–60 | 10–30 | 20–45 | 40–70 |
| Bond Strength (MPa) | 250–350 | — | — | — |
The overlay layer hardness of 280–350 HV is sufficient for moderate wear applications but may be inadequate for severe abrasive conditions. This limitation is inherent in the austenitic stainless steel composition, which prioritizes corrosion resistance over extreme hardness. For applications requiring higher hardness, the study suggests incorporating carbide-forming elements such as titanium, niobium, or increasing the carbon content of the overlay material.
Common Defects and Countermeasures
The study identifies several common defects in stainless steel overlays on 35 steel and provides practical countermeasures:
| Defect Type | Root Cause | Countermeasure |
|---|---|---|
| Interfacial cracking | High dilution zone hardness and residual stress | Reduce heat input; use multiple thin passes; post-weld stress relief |
| Overlay porosity | Inadequate shielding or moisture in consumables | Ensure proper gas coverage; dry consumables; preheat base metal |
| Overlay spalling | Poor bond strength due to contamination or excessive dilution | Clean base surface; control dilution rate; verify bond strength |
| HAZ cracking | Martensite formation in high-carbon HAZ | Preheat to 150–200 °C; use low heat input; post-weld tempering |
| Overlay lack of fusion | Insufficient penetration or poor wetting | Increase current; optimize travel speed; ensure proper surface preparation |
The most common and damaging defect is interfacial cracking, which occurs when the hard, brittle dilution zone cannot accommodate the residual stresses from welding. The primary countermeasure is to use a multi-pass welding strategy with thin individual passes, which limits the dilution zone width and distributes the thermal stress more evenly.
Engineering Practice Integration
This study has direct relevance to the fabrication of stainless steel clad components on carbon steel substrates, which is a common requirement in chemical processing, food processing, and pharmaceutical industries. The key engineering lesson is that the dilution zone must be carefully managed through process parameter control and, where necessary, post-weld heat treatment.
For pressure vessel applications, the overlay system must comply with the requirements of GB/T 150, ASME VIII, and relevant inspection codes. The bond strength of the overlay must be verified by destructive or non-destructive testing, and the dilution zone microstructure must be assessed to ensure it does not compromise the corrosion resistance or mechanical integrity of the component.
Key Questions and Reflections
A fundamental question raised by this study is whether the dilution zone can be eliminated entirely or must be managed. The reality is that some degree of dilution is inevitable in any fusion welding overlay process. The engineering challenge is to control the dilution rate and the resulting microstructure to ensure that the dilution zone is not a weak point. For critical applications, alternative cladding methods such as explosion cladding, roll-bonding, or PTA with low-dilution powders may be preferable, as they minimize or eliminate the dilution zone entirely.
Another important consideration is the effect of the base metal condition on overlay quality. 35 steel in the quenched and tempered condition has a different HAZ response than the same steel in the normalized condition. The study does not extensively address this variable, but engineering experience suggests that the base metal condition should be specified and controlled to ensure consistent overlay performance.
Study Insights and Implications
This study provides essential metallurgical insight into the behavior of stainless steel overlays on medium carbon steel substrates. The key takeaway for engineers is that the dilution zone is the critical interface that determines the long-term reliability of the overlay system. Process parameters must be optimized to minimize dilution, and post-weld heat treatment should be considered to relieve residual stresses and temper any martensite in the dilution zone. For applications where corrosion resistance is paramount, the dilution zone composition must be monitored to ensure that the chromium content remains above the critical threshold (approximately 12% Cr) for passive film formation. The study reinforces the principle that overlay engineering is not merely about depositing a hard or corrosion-resistant material but about creating a metallurgically compatible system that performs reliably under service conditions.