CLADDING TECHNOLOGY SHANXI CO., LTDStrip Electrode Cladding Process on 16MnR Low-Alloy Steel Research and Application
Literature Overview
This 2006 publication in Rocket Propulsion by Guo Huimin and Li Wanwan from Xi'an Aerospace Engine Factory addresses the application of strip electrode cladding technology on 16MnR low-alloy steel. The work is significant for its practical orientation in aerospace propulsion component manufacturing, where 16MnR is widely used for pressure vessel and chamber components requiring surface hardening or corrosion resistance.
Process Description and Parameters
Strip electrode cladding is a submerged arc welding (SAW) variant that uses a continuous metal strip instead of a wire electrode. The strip electrode provides several advantages over wire electrode SAW: higher deposition rate, better mechanical properties due to reduced dilution, and more consistent composition control. The process involves feeding a strip of the desired cladding material (typically stainless steel, nickel-based alloy, or high-alloy steel) into the arc along with a self-shielded or flux-shielded consumable electrode.
The study examines the cladding of 16MnR steel, which is a low-carbon manganese-molybdenum steel with the following composition: 0.12-0.20% C, 1.20-1.60% Mn, 0.40-0.65% Si, 0.070-0.125% Mo. This steel is widely used for pressure vessels and aerospace structural components due to its good weldability and mechanical properties.
| Process Parameter | Typical Range | Effect on Cladding Quality |
|---|---|---|
| Welding Current (A) | 400-700 | Controls deposition rate and dilution |
| Arc Voltage (V) | 28-38 | Affects strip melting and penetration |
| Travel Speed (mm/min) | 200-400 | Influences bead width and profile |
| Strip Width (mm) | 12-25 | Determines coverage area per pass |
| Flux Type | Rutile or basic | Affects arc stability and slag properties |
| Preheat Temperature (°C) | 100-200 | Prevents cold cracking in HAZ |
Microstructure and Performance
The microstructure of the strip electrode cladding layer on 16MnR depends on the specific cladding material selected. For stainless steel cladding (e.g., 304 or 316L strips), the overlay microstructure consists of austenite with varying amounts of ferrite depending on the dilution from the 16MnR base metal. The ferrite content is typically controlled using the Schaeffler diagram, targeting 5-15% delta ferrite to prevent hot cracking.
The mechanical properties of the cladding layer show a gradient from the overlay surface to the fusion line. Near the overlay surface, the microstructure closely resembles the strip electrode material, while near the fusion line, dilution from the 16MnR base metal creates a mixed microstructure. The hardness typically ranges from 200-250 HV for stainless steel cladding to 350-450 HV for martensitic stainless steel or high-alloy cladding.
Key Technical Challenges
The primary challenges in strip electrode cladding on 16MnR include:
- Dilution control: The high thermal conductivity of steel and the large volume of base metal affect dilution rates. Strip electrode cladding typically achieves 20-35% dilution in the first pass, which is higher than wire electrode SAW but lower than oxy-fuel methods.
- Cracking susceptibility: 16MnR contains carbon and alloy elements that can promote cold cracking in the HAZ. Preheating to 100-200°C and controlled cooling rates (below 150°C/s) are essential to prevent hydrogen-induced cracking.
- Bond strength: The metallurgical bond between the cladding layer and 16MnR must be verified through bond strength testing. The typical shear bond strength for SAW strip electrode cladding on 16MnR exceeds 150 MPa, meeting ASME and GB/T requirements.
- Surface quality: Strip electrode cladding produces a relatively smooth surface with minimal spatter compared to wire electrode processes, which is advantageous for subsequent machining or direct service application.
Application in Aerospace Propulsion
The application context in aerospace propulsion components is particularly demanding. Components such as combustion chambers, turbopump housings, and propellant tanks require both high mechanical integrity and surface corrosion resistance. The strip electrode cladding process enables the application of corrosion-resistant or wear-resistant surfaces on 16MnR pressure vessels without compromising the bulk mechanical properties.
The study demonstrates that multi-pass strip electrode cladding can build up overlay layers of 5-15 mm thickness with consistent mechanical properties. The first pass has the highest dilution and should be followed by subsequent passes that progressively reduce dilution to below 10% for the final surface layer.
Quality Control and Inspection
Non-destructive testing (NDT) is critical for strip electrode cladding quality assurance:
- Magnetic particle testing (MT): Detects surface and near-surface cracks in the overlay and HAZ
- Ultrasonic testing (UT): Evaluates bond strength and subsurface defects
- Radiographic testing (RT): Identifies porosity, lack of fusion, and inclusion defects
- Visual testing (VT): Assesses surface profile, spatter, and cosmetic quality
The study emphasizes the importance of establishing a comprehensive welding procedure specification (WPS) with qualified welder performance qualifications (WPQ) in accordance with NB/T 47014 and ASME IX requirements.
Study Insights
The strip electrode cladding process represents a mature and reliable technology for surface modification of low-alloy steel components. Its advantages in deposition rate, cost-effectiveness, and mechanical property consistency make it well-suited for aerospace and pressure vessel applications. The key to successful implementation lies in rigorous process parameter control, particularly dilution management and interpass temperature control. This work provides valuable process data that can be directly applied to engineering practice for 16MnR component cladding in demanding service environments.