Pre-Placed Additional Filler Metal Plate Submerged Arc Cladding

Literature Overview and Technical Context

This 1997 study by Rao Linping from Jinan Xinli Water Supply Equipment Co., Ltd. describes an innovative submerged arc cladding technique utilizing pre-placed additional filler metal plates. This approach represents a departure from conventional wire-fed or strip-fed submerged arc cladding by introducing a pre-positioned solid metal plate as the primary filler source, with a submerged arc serving as the bonding energy source. The application context—water supply equipment manufacturing—suggests the need for corrosion-resistant surface layers on carbon steel pressure vessels or pipe components intended for water service.

The technique is particularly relevant for producing bimetallic components where the cladding layer thickness exceeds what can be practically achieved with conventional wire or strip feeding, and where the geometry allows for pre-positioning of the filler plate.

Technical Principle and Process Description

Process Configuration

The pre-placed plate method operates on the following principle:

A filler metal plate of the desired cladding composition is positioned on the prepared substrate surface
The substrate is preheated to promote fusion
A submerged arc is directed along the interface between the substrate and the pre-placed plate
The arc melts the interface, bonding the plate to the substrate
Multiple plates may be placed sequentially to build up the required thickness

Process Parameters

Parameter	Typical Value	Impact
Substrate material	Q235B / Q345B	Carbon steel base
Filler plate material	06Cr19Ni10 (304) or 06Cr17Ni12Mo2 (316)	Corrosion resistance
Plate thickness	3-6 mm per plate	Build-up rate
Number of plates	1-3 plates	Total cladding thickness
Arc current	500-700 A	Fusion depth
Arc voltage	28-35 V	Penetration profile
Travel speed	100-200 mm/min	Bonding quality
Flux type	RZ-501 or similar	Slag protection
Preheat temperature	150-250°C	Prevent cracking
Interpass temperature	<250°C	Control cooling rate

Metallurgical Analysis of the Bond Interface

Interface Structure

The bond interface in pre-placed plate cladding exhibits a unique microstructure compared to wire-fed or strip-fed methods:

Zone	Location	Microstructure	Hardness
Substrate HAZ	Base metal near interface	Coarse grain, possible phase transformation	150-200 HV
Fusion zone	Melted interface region	Columnar grains, mixed composition	200-280 HV
Dilution zone	Within filler plate	Gradient composition	180-220 HV
Unaffected filler	Beyond dilution zone	Original filler microstructure	180-200 HV

The key metallurgical concern is the dilution zone within the filler plate. If the arc penetration is too deep, excessive substrate metal mixes into the filler, degrading the corrosion resistance of the cladding layer. The dilution rate in the fusion zone can reach 30-50%, which is significantly higher than the dilution in the final surface layer of wire-fed cladding.

Dilution Control Strategies

Strategy	Implementation	Effectiveness
Multi-pass with reduced penetration	Lower current, higher voltage	Moderate reduction
Sequential plate placement	Bond each plate separately	Good reduction
Final surfacing pass	Wire-fed overlay on final plate surface	Excellent reduction
Reduced travel speed	Slower welding for shallower penetration	Limited benefit
Preheating optimization	Higher preheat for reduced thermal gradient	Moderate improvement

Quality Assessment and Performance Evaluation

Bond Strength Testing

Test Method	Standard Reference	Acceptance Criteria
Peel test	GB/T 3323	>150 MPa
Shear test	ASTM B671	>200 MPa
Macrographic examination	Visual + metallography	No cracks, no lack of fusion
Intergranular corrosion	ASTM A923	<5% grain boundary attack
Salt spray test	ASTM B117	No red rust at 1000 hours

Comparison with Conventional Methods

Parameter	Pre-Placed Plate	Wire-Fed SAW	Strip Cladding
Build-up rate	Very high	High	High
Layer thickness per pass	3-6 mm	3-8 mm	3-6 mm
Dilution control	Moderate	Good	Excellent
Geometric flexibility	Limited	High	Moderate
Cost efficiency	High	Moderate	Low
Surface quality	Requires machining	Requires machining	Requires machining
Applicable geometry	Flat, large surfaces	Any accessible	Flat, large surfaces

Engineering Application and Practical Considerations

The pre-placed plate method is most suitable for:

Large flat surfaces where the geometry permits plate placement
Thick cladding layers (10-20 mm) where wire feeding would be impractical
Applications where build-up rate is more important than dilution control
Batch production where setup time can be amortized over multiple units

For water supply equipment, this technique is particularly applicable to:

Internal cladding of large-diameter water tanks
Pipe fittings with flat surfaces suitable for plate placement
Valve bodies requiring localized corrosion-resistant areas
Pump casings with accessible flat surfaces

The technique requires careful attention to the sequence of plate placement and welding. The first plate must be positioned with precise alignment to the substrate edge, and subsequent plates must overlap the previously welded plate by 5-10 mm to ensure complete fusion bonding.

Study Insights and Implications

Rao Linping's 1997 work represents an innovative approach to achieving thick cladding layers with high build-up rates. While the method has inherent limitations in terms of dilution control and geometric flexibility, it offers a cost-effective solution for specific applications where these limitations are acceptable. The technique essentially transforms the submerged arc welding process from a deposition operation into a bonding operation, which changes the fundamental process physics and the associated quality considerations. For modern practitioners, this work demonstrates that creative adaptation of welding processes to new configurations can yield practical solutions that complement rather than replace conventional approaches, particularly in cost-sensitive manufacturing environments.