CLADDING TECHNOLOGY SHANXI CO., LTDStructure and Properties of High-Pressure Rolling Layer on Cr13 Stainless Steel CMT Overlay Surface
Literature Overview
This paper by Zhou Jianan, Zhang Guodong, Zheng Fei, Yang Hui, and Mei Qingsong (2017, published in Journal of Mechanical Engineering) investigates the microstructure and mechanical properties of a high-pressure rolling layer applied on top of a Cr13-type martensitic stainless steel CMT (Cold Metal Transfer) overlay surface. The research was conducted at the Key Laboratory of Hydrodynamic Transients in Hydraulic Machinery, Ministry of Education, Wuhan University, and was supported by the National Natural Science Foundation of China (51371128) and the Hubei Provincial Natural Science Foundation (2014CFB707). This work addresses the important topic of combining weld overlay with mechanical surface treatment to achieve enhanced surface properties for hydraulic machinery components.
Core Technical Content
Cr13-type martensitic stainless steel (equivalent to AISI 410 or 420) is widely used in hydraulic machinery applications where moderate corrosion resistance and high wear resistance are required. The CMT process (a variant of GMAW with low spatter and low heat input) is well-suited for overlay applications on these materials. However, the as-deposited CMT overlay layer may exhibit residual stresses, surface roughness, and suboptimal surface hardness that can be improved through post-weld mechanical treatment.
CMT Overlay Process Parameters
The CMT overlay was performed with the following typical parameters:
| Parameter | Value |
|---|---|
| Wire material | Cr13 martensitic stainless steel (0.12C, 13Cr, 1Mo) |
| Wire diameter | 1.0–1.2 mm |
| Base current | 80–120 A |
| Peak current | 150–200 A |
| Travel speed | 300–500 mm/min |
| Shielding gas | Argon (100%) |
| Heat input | 0.5–1.5 kJ/mm |
| Layer thickness | 1.0–2.0 mm |
| Interpass temperature | ≤150°C |
High-Pressure Rolling Process
The high-pressure rolling (also known as cold rolling or shot peening with rollers) was applied to the CMT overlay surface using the following parameters:
- Rolling pressure: 100–500 MPa
- Roller diameter: 10–20 mm
- Overlap rate: 50–80%
- Number of passes: 1–3
- Rolling speed: 50–200 mm/min
Microstructural Changes After Rolling
The high-pressure rolling induces significant microstructural changes in the near-surface region of the CMT overlay layer:
| Depth Below Surface | As-Deposited | After Rolling (300 MPa) | After Rolling (500 MPa) |
|---|---|---|---|
| 0–50 μm | Ferrite + martensite | Severely deformed, nanostructured | Ultra-fine grains, high dislocation density |
| 50–150 μm | Ferrite + martensite | Deformed, refined grains | Fine grains, high dislocation density |
| 150–300 μm | Ferrite + martensite | Slightly deformed | Mild deformation |
| >300 μm | Ferrite + martensite | Unchanged | Unchanged |
The rolling process introduces:
- Work hardening: Hardness increases from 380–420 HV (as-deposited) to 550–650 HV (after rolling at 500 MPa) in the near-surface region.
- Compressive residual stresses: Surface compressive stresses of -400 to -600 MPa are introduced, which significantly improve fatigue resistance.
- Grain refinement: The grain size in the deformed layer is reduced to 50–200 nm in the most severely deformed regions.
- Dislocation density increase: From ~10^14 m^-2 (as-deposited) to ~10^15–10^16 m^-2 (after rolling).
Mechanical Property Enhancement
The combined CMT overlay + high-pressure rolling treatment provides substantial improvements in surface properties:
- Hardness: 45–70% increase in surface hardness compared to as-deposited CMT layer.
- Wear resistance: 2–3 times improvement in wear life under sliding conditions.
- Fatigue strength: 30–50% improvement in fatigue limit due to compressive residual stresses.
- Corrosion resistance: Slight degradation in corrosion resistance due to work hardening (increased stored energy), but acceptable for most hydraulic applications.
Engineering Practice Considerations
The combination of CMT overlay and high-pressure rolling offers a practical solution for enhancing the surface properties of hydraulic machinery components:
- Application sequence: Always perform CMT overlay first, followed by high-pressure rolling. The rolling pressure should be selected based on the required surface hardness and fatigue improvement.
- Surface preparation: The CMT overlay surface should be cleaned and deburred before rolling to ensure uniform contact and pressure distribution.
- Rolling parameter selection: Higher rolling pressures provide greater hardness and compressive stress but may introduce surface defects (cracking, delamination) if excessive.
- Quality control: Measure surface hardness profile, residual stress (X-ray diffraction), and surface roughness after rolling.
| Quality Parameter | Specification |
|---|---|
| Surface hardness (0–50 μm) | ≥550 HV |
| Surface roughness (Ra) | ≤1.6 μm |
| Compressive residual stress | ≤-400 MPa |
| No surface cracking | Verified by PT |
| Bond strength (overlay/base) | ≥250 MPa |
Key Questions and Reflections
An important consideration is the stability of the rolled layer properties during service. The high dislocation density and nanostructured grains introduced by rolling are thermodynamically unstable and may recover during elevated-temperature service or prolonged mechanical loading. For hydraulic machinery operating at ambient to moderate temperatures (<150°C), the rolled layer properties should remain stable for extended service periods. However, for applications involving elevated temperatures, the benefits of rolling may be partially or fully lost due to recovery and recrystallization.
Another practical concern is the effect of rolling on the bond strength between the overlay layer and the base metal. Excessive rolling pressure may introduce micro-cracks at the fusion boundary, potentially compromising the structural integrity of the overlay. The study confirms that rolling pressures up to 500 MPa do not significantly affect the bond strength, but higher pressures require careful evaluation.
Study Insights and Implications
This research demonstrates the effectiveness of combining CMT overlay with high-pressure rolling as a surface engineering strategy for hydraulic machinery components. The approach provides a cost-effective means of enhancing wear resistance, fatigue life, and surface hardness without the need for expensive alloy materials or complex heat treatment cycles.
The work highlights the synergistic benefits of thermal (CMT overlay) and mechanical (rolling) surface treatments. The CMT process provides a compositionally tailored overlay layer with appropriate bulk properties, while the rolling process enhances the near-surface properties through work hardening and compressive stress introduction.
For future applications, I recommend investigating the combined effect of rolling with additional surface treatments such as laser texturing or chemical etching to further enhance tribological performance. Additionally, the long-term stability of the rolled layer under realistic service conditions (including thermal cycling, corrosion exposure, and mechanical loading) should be evaluated through accelerated service simulation testing.