Effect of Water Glass Baumé Degree on Microstructure and Properties of Composite Powder Particle and Solid Wire Cladding Alloys

Literature Overview and Background

This study systematically investigates how the Baumé degree (concentration) of water glass flux affects the microstructure and mechanical properties of cladding alloys produced through two different consumable configurations: composite powder particles and solid wires. Water glass (sodium silicate solution) serves as a flux in submerged arc welding (SAW) and flux-cored welding (FCAW) overlay processes, and its concentration directly influences the slag chemistry, shielding effectiveness, deoxidation behavior, and ultimately the quality of the deposited cladding layer.

The research addresses a practical problem encountered in cladding production: the optimization of flux concentration for different consumable geometries. Composite powder particles (typically spherical or irregular particles formed by atomization or agglomeration of alloy powders) and solid wires (continuous rods of alloy composition) have different melting behaviors, heat transfer characteristics, and dilution patterns, which necessitate different flux optimization approaches.

Water Glass Baumé Degree and Slag Chemistry

Baumé Degree	SiO2/Na2O Ratio	Slag Viscosity (1400°C)	Basicity (CaO/SiO2)	Deoxidation Capacity
25°Bé	2.8–3.2	1.2–1.8 Pa·s	0.6–0.8	Low
30°Bé	3.0–3.5	1.5–2.2 Pa·s	0.7–0.9	Moderate
35°Bé	3.2–3.8	1.8–2.8 Pa·s	0.8–1.0	Moderate-High
40°Bé	3.5–4.0	2.2–3.5 Pa·s	0.9–1.2	High

The Baumé degree of water glass directly determines the SiO2/Na2O ratio in the resulting slag, which governs the slag's viscosity, basicity, and chemical reactivity. Higher Baumé degrees produce more viscous slags with higher basicity, which enhances deoxidation but may also increase the risk of slag inclusions and reduce slag fluidity.

Microstructural Effects of Flux Concentration

Cladding Property	Low Baumé (25°Bé)	Medium Baumé (30°Bé)	High Baumé (35°Bé)
Hardness (HV)	350–420	420–500	480–560
Grain size (μm)	30–50	20–35	15–25
Carbide distribution	Coarse, segregated	Moderate, semi-uniform	Fine, uniform
Inclusion content	High	Moderate	Low
Cracking tendency	Low	Low-Moderate	Moderate-High
Dilution rate	25–35%	18–28%	12–20%

The study reveals that medium Baumé degrees (30–35°Bé) generally provide the optimal balance between deoxidation, grain refinement, and crack resistance for both composite powder and solid wire cladding. However, the optimal range differs slightly between the two consumable types due to their different melting and solidification behaviors.

Comparative Analysis: Composite Powder vs. Solid Wire

Parameter	Composite Powder Particles	Solid Wire
Melting behavior	Rapid, uniform melting	Sequential melting along length
Heat input distribution	More uniform	More concentrated at wire tip
Dilution control	Easier (lower dilution)	Harder (higher dilution)
Optimal Baumé degree	30–33°Bé	33–37°Bé
Maximum achievable hardness	550–620 HV	500–580 HV
Surface quality	Rougher (particle texture)	Smoother (continuous bead)
Deposition rate	Higher	Lower
Cost per kg deposited	Lower	Higher

The composite powder particle consumable offers advantages in deposition rate and dilution control, making it suitable for thick cladding builds. The solid wire consumable provides better surface finish and more consistent bead geometry, making it preferable for thin, precision cladding applications. The different optimal Baumé degree ranges reflect the need for higher flux concentration with solid wires to compensate for their greater tendency toward dilution and oxidation.

Process-Structure-Property Relationships

The study establishes clear process-structure-property relationships for both consumable types:

Flux concentration → Slag chemistry → Deoxidation efficiency → Inclusion content → Toughness

Higher Baumé degrees improve deoxidation but may increase slag inclusion retention if viscosity is too high.

Flux concentration → Slag viscosity → Heat transfer → Cooling rate → Grain size → Hardness

More viscous slags (higher Baumé) reduce heat transfer to the slag pool, increasing cooling rate and producing finer grains with higher hardness.

Flux concentration → Slag basicity → Sulfur removal → Hot cracking susceptibility → Service life

Higher basicity improves sulfur removal but excessive basicity can promote certain types of solidification cracking.

Quality Control Considerations

Quality Parameter	Acceptance Criteria	Test Method	Rejection Criteria
Surface hardness	Within ±50 HV of target	Vickers hardness test	Outside specification range
Inclusion level	≤2.0 per GB/T 10561	Metallographic examination	Exceeds 3.0
Crack content	Zero cracks	MT/PT examination	Any crack detected
Dilution rate	<25% (high Cr alloys)	Spark OES or wet chemistry	>30%
Bond strength	≥200 MPa (shear)	Shear test coupon	<150 MPa

Study Insights and Implications

This research provides valuable quantitative data for the optimization of water glass flux in cladding operations. The finding that different consumable geometries require different optimal flux concentrations is particularly significant for production environments where both consumable types may be used for different cladding thicknesses or surface finish requirements.

The study reinforces the principle that flux optimization cannot be treated as a generic parameter adjustment but must be tailored to the specific consumable geometry, welding process, and desired cladding properties. This systematic approach to flux optimization—varying one parameter at a time while measuring the complete property set—is directly applicable to other cladding process development activities, including the optimization of flux composition for electroslag welding overlay or the selection of shielding gas composition for gas metal arc welding overlay.