Tubular Welding Wire for Cladding Applications and Its Technical Characteristics

Literature Overview and Background

This 2003 publication by Zhu Runsheng from the Hardfacing Technology Branch of the Shanghai New Materials Association, published in "Powder Metallurgy Industry," focuses on the development and application of tubular (flux-cored) welding wire for cladding operations. The paper addresses a significant evolution in cladding technology—the transition from solid wire and strip cladding to tubular wire cladding, which offers superior deposition rates, improved process stability, and enhanced metallurgical properties. At the time of publication, tubular wire cladding was gaining traction in industrial applications but lacked comprehensive technical documentation. This paper fills that gap by providing detailed information on wire composition, process parameters, and application-specific recommendations.

Tubular Wire Structure and Composition

Tubular welding wire for cladding consists of a steel casing filled with flux powder. The casing provides structural integrity and electrical conductivity, while the flux powder serves multiple functions: it generates a protective gas shield, refines the weld grain structure, and introduces alloying elements to the weld metal. The paper categorizes tubular wires into two main types based on their filling mechanism: gas-shielded tubular wire (FCAW-G) and self-shielded tubular wire (FCAW-S).

The following table compares the key characteristics of the two types:

The flux composition in tubular wire is critical for achieving the desired overlay properties. For stainless steel cladding, the flux typically contains ferroaluminum, ferrochromium, and ferromanganese to ensure the correct chromium and nickel content in the weld metal. For nickel-based alloy cladding, the flux includes nickel powder and chromium oxide to maintain the alloy integrity. The paper emphasizes that the flux-to-casing ratio must be carefully controlled; a typical ratio for stainless steel tubular wire is 30–40% flux by mass, while for nickel-based alloys, the ratio can be as high as 50–60%.

Process Parameters and Welding Procedure

The paper provides detailed welding procedure recommendations for tubular wire cladding. The process parameters are highly dependent on the base material, overlay composition, and application requirements. The following table presents typical parameter ranges for common cladding applications:

The paper stresses the importance of preheating and interpass temperature control. For low-carbon steel base materials, a preheat temperature of 100–150 °C is recommended to reduce the risk of hydrogen-induced cracking. For high-strength steels, preheating to 200–300 °C may be necessary. The interpass temperature should not exceed 200 °C for stainless steel overlays and 150 °C for nickel-based overlays to prevent grain growth and sensitization.

Applications and Case Studies

The paper documents several successful applications of tubular wire cladding. One notable case involves the cladding of a sulfuric acid pump impeller with 316L stainless steel tubular wire. The impeller, originally made of cast iron, was subject to severe corrosion in 98% sulfuric acid at 80 °C. After cladding with 316L tubular wire to a thickness of 5 mm, the impeller demonstrated a service life increase from 3 months to over 24 months, representing an 800% improvement in corrosion resistance. The cladding was deposited using a multi-pass technique with a root pass of solid wire followed by fill and cap passes with tubular wire, achieving a deposition rate of 12 kg/h and a bond strength exceeding 300 MPa.

Another application discussed is the hardfacing of a mining shovel bucket edge with a chromium-carbon tool steel tubular wire. The original bucket edge, made of plain carbon steel, wore out in 200 hours of service in abrasive limestone. After hardfacing with the tubular wire to a depth of 8 mm, the service life increased to 1,500 hours. The weld metal hardness achieved was 58–62 HRC, with excellent spalling resistance due to the fine carbide distribution in the microstructure.

Quality Control and Defect Prevention

The paper identifies several common defects associated with tubular wire cladding and provides countermeasures. Porosity is the most prevalent defect, caused by inadequate gas shielding or flux degradation. The recommended countermeasure is to ensure proper gas flow rate (15–20 L/min for FCAW-G) and to use fresh wire from sealed packaging. Lack of fusion at the interface between the base metal and the first overlay pass is another concern, addressed by using a higher current density (30–40 A/mm²) for the root pass and ensuring thorough edge preparation. Undercut at the weld toe can be minimized by reducing the travel speed and increasing the wire feed speed slightly, which increases the arc force and improves wetting.

Study Insights and Practical Implications

This paper represents an important milestone in the documentation of tubular wire cladding technology. The comprehensive coverage of wire composition, process parameters, and application case studies provides practical guidance for engineers selecting and implementing tubular wire cladding solutions. In my experience, the transition from solid wire to tubular wire cladding has been one of the most significant process improvements in the field, offering deposition rates that are 2–3 times higher than solid wire GTAW while maintaining superior metallurgical properties. The paper's emphasis on flux composition and its impact on weld metal quality is particularly valuable, as it highlights the often-overlooked importance of filler metal chemistry in achieving the desired overlay performance. Engineers should carefully evaluate tubular wire cladding as a viable alternative to solid wire processes, particularly for large-area cladding applications where productivity is a critical concern.