Zhuojin Pipe Fitting Co., LtdWear-Resistant Overlay Welding on Plungers of Large Cylinder Compressors
Literature Overview
The paper by Zhang Junlin, Wang Junlin, and Chen Zhuohua, published in Welding (No. 8, 1990), describes the development and application of wear-resistant overlay welding on the plungers of large cylinder compressors used in high-pressure gas cylinder manufacturing. The authors, affiliated with Taiyuan Heavy Machinery Plant, document their experimental work on welding parameters, overlay composition, and the resulting hardness and wear resistance of the overlay weld.
Background and Application Context
High-pressure gas cylinder compressors are critical equipment in the manufacturing of gas cylinders, particularly for applications such as diving equipment, medical oxygen cylinders, and industrial gas storage. These compressors operate under extreme conditions, with the plungers experiencing high cyclic loading, friction, and wear. The plungers are typically fabricated from carbon steel or low-alloy steel, which is prone to wear under the severe operating conditions of the compressor.
The plungers described in the paper have diameters ranging from φ200 mm to φ1000 mm, indicating that they are used in large, high-capacity compressors. The wear-resistant overlay welding is applied to the surface of the plungers to extend their service life and reduce maintenance costs.
Overlay Weld Composition and Selection
The authors selected a 2Cr13-based overlay composition for the wear-resistant overlay welding. 2Cr13 is a martensitic stainless steel with the following approximate composition:
| Element | Content (wt%) |
|---|---|
| C | 0.15–0.25 |
| Cr | 12.0–14.0 |
| Mn | ≤1.0 |
| Si | ≤0.6 |
| Fe | Balance |
The 2Cr13 overlay was selected for its excellent combination of hardness, wear resistance, and corrosion resistance. The martensitic microstructure of 2Cr13 can be hardened to 45–55 HRC through heat treatment, providing good wear resistance. The chromium content provides corrosion resistance against the compressed gas media, which may contain moisture or other corrosive components.
Experimental Investigation
The authors conducted a systematic experimental investigation to optimize the welding parameters and overlay composition. The key variables studied included:
- Welding current: Varied over a range of values to determine the effect on overlay hardness and microstructure.
- Welding voltage: Adjusted in conjunction with current to control the arc stability and heat input.
- Travel speed: Varied to control the cooling rate and the resulting microstructure.
- Electrode diameter: Different electrode sizes were tested to determine the optimal size for the plunger diameter range.
- Number of passes: Multiple passes were used to build up the overlay thickness, with the number of passes optimized for each plunger diameter.
The experimental results showed that the overlay hardness was strongly influenced by the welding current. Higher currents produced coarser microstructures and lower hardness, while lower currents produced finer microstructures and higher hardness. However, very low currents resulted in poor wetting and incomplete fusion, which reduced the bond strength between the overlay and the base metal.
Optimal Welding Parameters
Based on the experimental results, the authors recommended the following welding parameters for the wear-resistant overlay welding of the plungers:
| Parameter | Recommended Value |
|---|---|
| Welding current | 120–180 A |
| Welding voltage | 22–28 V |
| Travel speed | 200–300 mm/min |
| Electrode diameter | φ3.2–φ4.0 mm |
| Interpass temperature | <150°C |
| Number of passes | 2–4 (depending on plunger diameter) |
The overlay thickness was typically 3–5 mm, which provided adequate wear resistance while minimizing the risk of cracking due to thermal stresses. The multi-pass welding procedure was designed to minimize the thermal gradient between adjacent passes and to ensure uniform hardness throughout the overlay thickness.
Microstructure and Hardness Analysis
The microstructure of the 2Cr13 overlay weld was analyzed using optical microscopy and X-ray diffraction. The overlay weld metal consisted primarily of martensite with some retained austenite and chromium carbides. The hardness of the overlay was measured using Vickers and Rockwell hardness tests, and the results showed that the hardness was in the range of 40–50 HRC, depending on the welding parameters and the heat treatment condition.
The hardness distribution across the overlay thickness was not uniform. The surface of the overlay was typically harder than the interior, due to the faster cooling rate at the surface. This hardness gradient was beneficial for wear resistance, as the surface is the region that experiences the highest wear.
The bond strength between the overlay and the base metal was also evaluated. The bond strength was found to be adequate for the service conditions of the compressor, with no evidence of delamination or cracking under cyclic loading.
Engineering Practice Integration
The application of wear-resistant overlay welding to plunger surfaces is a well-established practice in the compressor industry. However, the specific challenges of large-diameter plungers (φ200–φ1000 mm) require careful consideration of several practical factors:
- Access and positioning: Large plungers may require special fixtures or jigs to hold them in position during welding. The welding position may need to be varied to ensure uniform heat input and to avoid excessive distortion.
- Distortion control: The large diameter of the plungers makes them susceptible to thermal distortion during welding. The welding sequence should be designed to minimize distortion, and post-weld machining may be required to restore dimensional accuracy.
- Heat treatment: The overlay weld may require post-weld heat treatment to achieve the desired hardness and microstructure. The heat treatment must be carefully controlled to avoid cracking or distortion.
- Inspection: The overlay weld should be inspected for cracks, porosity, and incomplete fusion using appropriate NDT methods such as magnetic particle testing (MT) or liquid penetrant testing (PT).
Key Questions and Reflections
The paper raises several questions about the long-term performance of the wear-resistant overlay welding. First, the wear resistance of the overlay was evaluated under laboratory conditions, but the actual wear behavior in service may be different due to the complex loading and environmental conditions in the compressor.
Second, the paper does not extensively discuss the cost-effectiveness of the overlay welding compared to other wear protection methods such as surface hardening, coatings, or the use of wear-resistant materials for the entire plunger. The overlay welding is a cost-effective solution for extending the life of existing plungers, but the cost of the welding procedure, inspection, and maintenance must be considered in the overall cost analysis.
Third, the paper does not address the environmental and safety aspects of the welding procedure. The welding of 2Cr13 overlay produces fumes that contain chromium and other metals, which can be hazardous to the welder's health. Proper ventilation and personal protective equipment are essential to ensure the safety of the welding operation.
Study Insights and Implications
The fundamental insight from this paper is that wear-resistant overlay welding is an effective method for extending the service life of compressor plungers. The selection of the 2Cr13 overlay composition, the optimization of welding parameters, and the careful control of the welding procedure are all essential for achieving the desired performance.
The paper also highlights the importance of experimental investigation in welding engineering. The systematic variation of welding parameters and the careful analysis of the resulting microstructure and hardness provide valuable data for optimizing the welding procedure. This approach is applicable to other welding applications where the performance of the weld is critical.
For modern applications, the principles outlined in this paper can be extended using advanced techniques such as laser cladding for more precise and uniform overlay deposition, plasma arc welding for higher productivity, and computational welding mechanics for predicting distortion and residual stress. However, the fundamental understanding of wear-resistant overlay welding remains unchanged, making this paper a valuable reference for both experienced engineers and those new to the field.