CLADDING TECHNOLOGY SHANXI CO., LTDDomestic Stainless Steel Strip for Strip Electrode Overlay Welding
Literature Overview
This study note addresses the challenges associated with domestic production of stainless steel strip electrodes for strip overlay welding, as reported by Zhang Yong and Wang Jiahui from the General Machinery Research Institute (under the former Ministry of Mechanical and Electrical Industry) in 1991. Strip electrode overlay welding (also known as strip cladding or strip ESW overlay) was being introduced to China's petrochemical and power generation industries during this period, and the availability of suitable stainless steel strip electrode material was a critical bottleneck. At that time, the strip electrode materials required for overlay welding were predominantly imported from Japan and Germany, making them expensive and subject to supply chain constraints. The research addressed the metallurgical and process challenges of developing domestically produced stainless steel strip electrodes that could meet the quality requirements for overlay applications in oil and gas processing equipment.
Core Technical Analysis
The stainless steel strip electrodes used for overlay welding must meet stringent compositional and mechanical requirements. The strip must be thin (typically 0.8–2.0 mm), wide (20–60 mm), and possess a homogeneous microstructure to ensure consistent weld quality. The following table compares the requirements for imported versus domestic strip electrodes:
| Parameter | Imported Strip (e.g., 304L, 316L) | Domestic Strip (Target) |
|---|---|---|
| Thickness tolerance | ±0.05 mm | ±0.10 mm (initial) |
| Surface quality | Mirror finish, no defects | Good finish, minor defects |
| Carbon content (304L) | ≤ 0.03% | ≤ 0.04% (initial) |
| Sulfur content | ≤ 0.015% | ≤ 0.020% |
| Homogeneity | Excellent | Variable (initial) |
| Formability | Excellent | Adequate |
| Cost (relative) | 1.0 (baseline) | 0.4–0.6 (target) |
The primary challenges in domestic strip production included:
- Thickness tolerance control: Rolling mills in China at that time had limited capability to produce strip with the tight thickness tolerances required for ESW. Variations in strip thickness cause fluctuations in current density, which affect penetration and dilution.
- Surface quality: Surface defects such as scratches, scale, and oxidation cause arc instability and slag entrapment during welding.
- Chemical homogeneity: Inconsistent carbon and sulfur content across the strip width leads to localized variations in weld metal composition and corrosion resistance.
- Flatness: Warping or camber in the strip causes uneven contact with the substrate, leading to inconsistent heat input and potential lack of fusion.
Metallurgical Considerations for Strip Electrode Selection
The selection of stainless steel grade for the strip electrode depends on the service environment of the overlay. For general corrosion resistance in non-chloride environments, 304L (S30403) is suitable. For chloride-containing environments or higher temperatures, 316L (S31603) is preferred. For high-temperature applications, 321 (S32101) or 347 (S34701) with titanium or niobium stabilization may be used.
| Grade | Application | Key Alloying Element | Temperature Limit |
|---|---|---|---|
| 304L | General corrosion, water service | Cr 18-20%, Ni 8-12% | ≤ 425 °C |
| 316L | Chloride environments, sulfuric acid | Mo 2-3% | ≤ 425 °C |
| 321 | High-temperature service | Ti stabilization | ≤ 870 °C |
| 347 | High-temperature service | Nb stabilization | ≤ 870 °C |
| 904L | Strong oxidizing acids | Mo 4-5%, Cu 1-2% | ≤ 425 °C |
The carbon content of the strip electrode is particularly critical. For low-carbon grades (304L, 316L), the carbon content must be kept below 0.03% to prevent intergranular corrosion after sensitization. The domestic production process must incorporate vacuum induction melting (VIM) or electroslag remelting (ESR) to achieve the required low carbon and low sulfur levels.
Process Qualification and Quality Control
The qualification of domestic strip electrodes for overlay welding requires a comprehensive testing program per NB/T 47014 or equivalent standards. The following table outlines the required qualification tests:
| Test | Standard | Acceptance Criteria |
|---|---|---|
| Tensile strength | GB/T 228 | ≥ 450 MPa (304L), ≥ 520 MPa (316L) |
| Elongation | GB/T 228 | ≥ 30% |
| Hardness | GB/T 231 | 150–250 HV |
| Intergranular corrosion | ASTM A923 Method 1B | No intergranular attack |
| Bond strength (peel) | NB/T 47014 | ≥ 350 MPa (carbon steel substrate) |
| Impact strength | GB/T 229 | ≥ 47 J at -29 °C |
| Metallographic examination | GB/T 1954 | No cracking, segregation, or excessive grain growth |
The process qualification must also include welds made with the domestic strip on representative substrates (carbon steel, low-alloy steel, and stainless steel) to verify that the strip performs equivalently to imported alternatives. The qualification procedure should include macrographical and micrographical examination of the weld interface, hardness surveys across the overlay, and corrosion testing of the overlay surface.
Study Insights and Reflections
This 1991 study is historically significant as it represents an early effort to overcome the import dependency on strip electrode materials in China's overlay welding industry. The challenges identified—thickness tolerance, surface quality, chemical homogeneity, and flatness—are the same challenges that domestic producers still face today, albeit at a much higher level of capability. The systematic approach to qualification testing described in this work laid the groundwork for the domestic strip electrode industry that now supplies a significant portion of China's overlay welding needs. The document serves as a valuable reference for understanding the evolution of domestic consumable development and the quality assurance framework that was established during this period.