Submerged Arc Welding Overlay Process for Port Machinery Funnel Liners

Literature Overview

Port machinery, particularly grab bucket and funnel assemblies used in bulk material handling terminals, experience severe abrasive and corrosive wear due to continuous contact with sand, ore, coal, and other abrasive media. The study of submerged arc welding (SAW) automatic overlay processes for funnel liners addresses the need for cost-effective, high-throughput surface hardening solutions that extend component service life while maintaining structural integrity. The literature reviewed here examines the process parameters, weld metal composition, microstructural evolution, and field performance of multi-pass SAW overlay applied to carbon steel funnel shells in port environments.

Core Technical Points

Process Parameters and Welding Configuration

The SAW overlay process for funnel liners typically employs a multi-pass build-up strategy. The base material is usually Q235 or Q345 structural carbon steel, and the overlay wire is selected to provide a hard, wear-resistant surface layer. Common filler wires include H10Mn2 (high carbon manganese) or H13Cr2Mo, with fluxes such as SJ101 or HJ431.

Parameter	Typical Range	Notes
Welding current	450–650 A	DCEN polarity for better penetration
Welding voltage	28–36 V	Depends on wire diameter and flux type
Travel speed	300–500 mm/min	Slower for deeper dilution control
Wire diameter	1.6–2.4 mm	Larger wire for higher deposition rate
Number of passes	2–4	First pass for transition, subsequent for hardening
Interpass temperature	≤250 °C	Critical for preventing softening
Dilution rate	20–40%	Must be controlled for hardness

The automatic SAW machine is configured with a track-guided or pendulum oscillation system to ensure uniform bead width and consistent overlap across the curved funnel surface. For funnel assemblies with typical diameters of 1.5–3.0 m, the track follows the circumferential and longitudinal directions, requiring careful setup of the torch height and alignment.

Microstructure and Hardness Control

The wear resistance of the overlay layer is governed by the hardness profile, which depends on the dilution between the base metal and the weld metal. With a dilution of approximately 30%, the overlay layer typically achieves a hardness of 450–550 HV, while the transition zone exhibits a gradient from 250 HV to 450 HV. The microstructure of the overlay consists of martensite and retained austenite, with carbide particles (M7C3 and M3C) providing abrasion resistance.

The interpass temperature is a critical variable. Exceeding 250 °C during multi-pass welding causes tempering of the martensite formed in earlier passes, reducing the final hardness by 50–80 HV. Maintaining the interpass temperature below 200 °C through controlled travel speed and pass sequencing is essential for achieving the target hardness uniformly across the overlay.

Common Defects and Countermeasures

Defect Type	Root Cause	Countermeasure
Excessive dilution (>40%)	Low travel speed, high current	Reduce current, increase speed, use low-dilution flux
Cracks in overlay	High carbon equivalent, low toughness	Preheat to 100–150 °C, use low-hydrogen flux
Porosity	Flux contamination, moisture	Dry flux at 300 °C for 2 h, ensure proper shielding
Uneven bead profile	Torch misalignment, vibration	Calibrate pendulum oscillation, stabilize track
Hardness below spec	Excessive interpass temperature	Enforce temperature monitoring with infrared gun

Integration with Engineering Practice

In actual port terminal operations, funnel liners are exposed to materials with Mohs hardness up to 7 (quartz-containing ore). Field tests demonstrated that SAW overlay liners with surface hardness of 500 HV achieved service lives of 18–24 months, compared to 6–8 months for uncladded carbon steel. The cost-benefit analysis shows that the overlay process reduces replacement frequency by a factor of three, with the initial cladding cost representing less than 15% of the total lifecycle cost of the funnel assembly.

The automatic SAW configuration is particularly advantageous for funnel liners because of the large surface area and repetitive geometry. A single operator can manage the automatic welding machine for multiple passes, achieving a deposition rate of 6–10 kg/h compared to 1–2 kg/h for manual methods. The process also ensures consistent quality across the entire cladded surface, which is difficult to achieve with manual welding on curved surfaces.

Key Questions and Reflections

The transition zone between the base metal and the overlay layer remains a potential weak point. Although the dilution rate is controlled, the carbon steel base may still exhibit localized softening due to the heat input of the SAW process. For funnels operating under cyclic loading (grab bucket cycles), fatigue cracking at the transition zone is a concern that requires further investigation through fatigue testing under realistic loading spectra.

Another consideration is the residual stress distribution. SAW overlay generates significant longitudinal and transverse residual stresses due to the high heat input and rapid solidification. For thin-walled funnel shells (typically 10–14 mm), these stresses may cause distortion or even buckling. Post-weld stress relief at 550–600 °C is often necessary, but this must be carefully controlled to avoid further softening of the overlay layer.

Study Insights and Implications

The SAW overlay process for port machinery funnel liners represents a mature, economical, and highly effective solution for abrasive wear protection. The key to success lies in the precise control of dilution rate, interpass temperature, and process parameters to achieve a consistent hardness profile of 450–550 HV across the entire overlay surface. Engineers should pay particular attention to the transition zone properties, residual stress management, and the long-term fatigue behavior of the cladded assembly under cyclic operational loading. The automatic configuration significantly improves productivity and quality consistency, making it the preferred method for large-scale industrial applications in port and bulk material handling environments.