Development of High-Cr Low-Slag Wear-Resistant Overlay Welding Electrodes

Literature Overview

Chen Zhiguo, Min Qingkai, and Zhang Lirong of Shenyang University's School of Mechanical Engineering published this study in 2005 in Hot Working Technology, addressing a practical manufacturing challenge: the development of high-chromium overlay welding electrodes with reduced slag coverage. The motivation is clear from an engineering standpoint – conventional high-Cr overlay electrodes (e.g., D256, D257 type) produce excessive slag that requires aggressive grinding or chipping removal, generating significant waste, environmental burden, and labor cost. For large-scale overlay applications on pressure vessels, heat exchangers, and structural components, slag reduction translates directly to productivity improvement and cost savings.

Core Technical Findings

Electrode Design Philosophy

The authors employed a systematic approach to reduce slag content while maintaining the high-Cr overlay performance. The key design strategies include:

Design Parameter	Conventional Electrode	Low-Slag Electrode	Design Rationale
Cr content (wt%)	25–30	22–26	Slightly reduced to compensate for slag reduction
Slag coverage rate	90–95%	60–70%	Reduced slag volume by 25–35%
Slag basicity (B)	1.5–2.0	1.2–1.5	Lower basicity for thinner slag film
C content (wt%)	1.5–2.5	1.8–2.8	Slightly increased to compensate for reduced dilution
Mo content (wt%)	3–5	4–6	Increased to maintain hardness with less slag
Overlay hardness (HV30)	550–650	580–680	Equivalent or improved
Slag removal effort	High	Moderate-low	Significant reduction

Slag Chemistry Optimization

The slag system was reformulated from a traditional CaO-MgO-SiO2-Al2O3 system to a modified system with increased TiO2 and reduced CaO content. The higher TiO2 content promotes slag fluidity at lower temperatures, ensuring adequate coverage despite reduced slag volume. The lower basicity reduces the thickness of the solidified slag crust while maintaining sufficient oxygen potential control during solidification.

Overlay Performance

The resulting overlay deposits maintain high hardness (580–680 HV30) through the formation of a network of Cr7C3 and Mo2C carbides in a martensitic matrix. The slightly reduced slag coverage introduces a minor risk of surface oxidation in the weld pool, which is mitigated by the increased carbon content that promotes a protective carbonaceous atmosphere. Metallographic examination confirms that the overlay structure is comparable to conventional high-Cr electrodes, with no significant increase in porosity or inclusions.

Welding Process Characteristics

The low-slag electrodes exhibit improved arc stability due to the modified flux composition, with a slightly more concentrated arc that reduces dilution from the base metal. The reduced slag volume also improves deposition efficiency by approximately 5–8%, as less energy is consumed in melting and maintaining the slag pool.

Engineering Practice Implications

For pressure vessel fabrication shops performing extensive overlay welding, the low-slag electrode concept offers tangible benefits:

Productivity improvement – Reduced slag removal time translates to 15–25% faster overlay completion for large-area applications such as vessel internals, pump casings, and valve seats.
Environmental benefit – Reduced slag generation decreases solid waste disposal costs and improves workshop conditions by reducing dust generation during slag chipping.
Cost reduction – Lower slag volume means reduced grinding material consumption and lower labor costs for post-weld cleaning.
Quality consistency – The thinner slag layer allows better visual monitoring of the weld pool, potentially improving operator control and reducing defects.
Standard compliance – The electrodes must be qualified under NB/T 47014 or ASME IX with the same qualification requirements as conventional overlay electrodes, including bend testing, hardness measurement, and corrosion testing of the overlay.

Process Parameters for Low-Slag Electrode Application

Parameter	Recommended Value	Notes
Current type	DCEP (DC electrode positive)	Maximizes deposition rate
Current range	200–350 A	Depends on electrode diameter
Travel speed	150–250 mm/min	Slower for thicker passes
Pass thickness	3–5 mm	Standard overlay pass thickness
Interpass temperature	< 200°C	Prevents softening of previous pass
Preheating	100–150°C for thick sections	Reduces cracking risk

Key Reflections

The practical value of this study lies in its focus on manufacturing efficiency rather than purely on material performance. In the pressure vessel industry, where overlay welding is often performed on large internal surfaces with limited access, the ability to reduce slag removal effort is not a trivial consideration but a significant factor in overall project cost and schedule. The study demonstrates that slag reduction does not necessarily compromise overlay performance, provided that the slag chemistry is carefully reformulated rather than simply reduced in volume. The engineering lesson is that consumable optimization must consider the entire welding cycle – from arc striking to final finishing – rather than focusing solely on the deposited metal properties.