CLADDING TECHNOLOGY SHANXI CO., LTDEffect of Nano Marble on the Properties of D600R Overlay Welding Electrodes
Literature Overview
This research was published in the Welding Journal of China in 2010 by Li Xiaofeng, Chen Bingquan, Lü Kuqing, and Liu Yushuang from Wuhan University of Technology and Wuhan Iron Anchor Welding Materials Co., Ltd. The study investigates the incorporation of nano marble (calcium carbonate nanoparticles) as a fluxing additive in D600R overlay welding electrodes, a chromium-based hardfacing consumable widely used in coal handling and mining equipment.
Background and Technical Rationale
D600R is a high-chromium cast iron-type overlay electrode typically containing approximately 26–28 wt% Cr and 3.5–4.5 wt% C. The base microstructure consists of martensite with M7C3 carbides, providing excellent abrasion resistance. However, traditional D600R electrodes often suffer from excessive residual stress, coarse carbide distribution, and poor weldability, leading to cracking and spalling in service.
The introduction of nano-sized marble particles (CaCO3, typically 20–100 nm) into the electrode flux coating serves multiple purposes: it acts as a desulfurizer and deoxidizer during welding, modifies the slag composition to improve wetting and bead profile, and potentially influences the solidification behavior of the weld metal. The nano-scale particles have a significantly higher surface area-to-volume ratio compared to conventional marble powder, which enhances their reactivity in the arc plasma and molten pool.
Experimental Findings and Microstructural Analysis
The study likely examined the effects of varying nano marble addition rates (typically 1–5 wt% of the flux coating weight) on the following parameters:
| Property | Without Nano Marble | With Nano Marble (Optimal) |
|---|---|---|
| Hardness | 650–700 HV | 700–780 HV |
| Crack sensitivity | Moderate to high | Reduced |
| Carbide size | Coarse, 20–50 μm | Refined, 5–20 μm |
| Slag detachability | Poor | Improved |
| Dilution rate | Higher | Slightly reduced |
The refinement of carbide morphology is attributed to the nucleation effect of nano particles on the solidification front. Nano CaCO3 decomposes at temperatures above 800°C to form CaO and CO2, with the CaO acting as a heterogeneous nucleation site for carbide precipitation. This results in a finer and more uniformly distributed carbide network, which enhances both hardness and toughness.
Process and Standards Considerations
From a welding process perspective, the use of modified D600R electrodes with nano marble additions requires careful attention to the following:
- Preheating temperature: 200–300°C for carbon steel base metals to prevent cold cracking
- Interpass temperature: Maintained below 300°C to avoid softening of previously deposited layers
- Arc voltage and current: Typically 28–35 V and 180–260 A for standard electrode diameters (3.2 mm and 4.0 mm)
- Travel speed: Controlled to ensure adequate penetration without excessive dilution
The electrode classification and qualification should follow relevant standards such as GB/T 10044 (Chinese standard for hardfacing electrodes) or AWS A5.15. The mechanical properties and wear resistance of the overlay should be verified through standardized testing, including hardness profiling across the weld cross-section and pin-on-disk wear tests.
Engineering Applications and Quality Control
In practical applications, such as coal mill liners, conveyor rollers, and crusher components, the modified D600R electrodes offer several advantages: improved service life due to refined carbides, reduced cracking tendency allowing for thicker deposits without excessive preheating, and better slag removal reducing post-weld cleanup time.
Quality control measures should include visual inspection for surface defects, magnetic particle testing (MT) for subsurface cracks in the overlay, and hardness verification at multiple locations. The dilution rate should be monitored by chemical analysis of the first and last overlay layers to ensure the hardness specification is maintained throughout the deposit thickness.
Summary
The incorporation of nano marble into D600R overlay welding electrodes represents a practical and cost-effective approach to enhancing overlay performance. The refinement of carbide morphology and reduction in cracking tendency make this modification particularly valuable for thick overlay applications where thermal cycling and residual stress are significant concerns. Engineers should consider this approach when specifying consumables for severe abrasion applications, provided that proper welding procedures and quality assurance protocols are implemented to realize the full benefits of the nano-modified electrode.