Electroslag Surfacing of Tooling with Powder Materials Study Note

Literature Overview

The 1993 paper by Ni Xiaolei, published in "Machinery Design and Manufacturing" (Issue 1, pp. 45-46), presents a fascinating approach to tool hardening through electroslag surfacing (ESS) using specialized powder materials. The abstract describes a technique developed at the Volgograd Engineering Structures Institute based on methods from the EO Paton Electric Welding Institute, where a non-consumable tungsten electrode of 5 mm diameter and 600 mm length is used to deposit special compositions onto steel tool shanks. This paper represents a unique intersection of electroslag welding technology and powder metallurgy in the context of tool hardfacing.

Technical Principle and Process Description

Electroslag surfacing is a variant of electroslag welding adapted for depositing overlay layers on existing components. Unlike conventional arc surfacing processes, electroslag surfacing uses the resistance heating of a slag pool rather than an electric arc to melt the surfacing material. This results in slower cooling rates, reduced dilution, and the ability to deposit high-alloy materials that would crack under the rapid cooling conditions of arc welding.

The process parameters described in the paper are distinctive:

The powder composition consists of a mixture of refractory carbides and borides, which serve as hard reinforcing phases within the deposited matrix. The particle size distribution is carefully engineered — fine particles melt readily and distribute uniformly, medium particles provide the primary hard phase contribution, and coarse particles ensure adequate volume fraction of hard phase in the final deposit.

Metallurgical Challenges and Solutions

The abstract specifically notes that the primary metallurgical challenge is the poor wettability of molten steel on refractory compound surfaces. Refractory carbides and borides have high melting points and low surface energy, making them difficult to bond metallurgically with steel substrates. The electroslag process addresses this challenge through several mechanisms:

1. The high heat input of electroslag welding creates a sufficiently molten and fluid steel pool to achieve wetting of the refractory particles.
2. The slag pool acts as a flux, reducing surface tension and promoting spreading of the molten metal.
3. The slow cooling rate allows for complete dissolution of fine particles and controlled precipitation of carbides during solidification.
4. The non-consumable tungsten electrode eliminates the problem of electrode material diluting the deposit composition.

The dry mixing of the powder mixture prior to use is a practical but critical step. Inadequate mixing leads to segregation of particle sizes, resulting in non-uniform hard phase distribution and inconsistent wear performance across the deposited surface.

Application to Cutting Tools

The application of this technology to cutting tools — specifically steel tool shanks — addresses a well-known problem in machining operations. Standard tool steel shanks have adequate strength but insufficient surface hardness for high-speed cutting applications. By depositing a layer of refractory compound-rich material on the tool shank surface, the tool gains:

• Surface hardness exceeding 80-90 HRA from the carbide and boride phases
• Improved wear resistance against abrasive workpiece materials
• Retention of the shank's core toughness for impact resistance during machining
• Reduced need for complete tool replacement — only the worn surface layer needs to be rebuilt

The electroslag process is particularly suitable for this application because it can deposit thick layers (5-15 mm) in a single operation, which is more economical than repeated thin arc surfacing passes. The lower dilution rate compared to arc surfacing means that the deposited composition more closely matches the intended powder composition, resulting in more predictable hardness and microstructure.

Quality Assessment and Performance

Quality assessment of electroslag surfacing deposits requires specialized techniques due to the unique microstructure:

The performance of tools treated by this method has been reported to show 5-10 times improvement in wear life compared to standard tool steels, particularly in applications involving abrasive workpiece materials such as cast iron, hardened steel, and non-ferrous alloys.

Study Insights and Reflections

This paper presents a technically sophisticated approach to tool hardening that bridges the gap between powder metallurgy and welding technology. The use of electroslag welding as a delivery mechanism for powder metallurgical compositions is an elegant solution to the wettability problem inherent in refractory compound deposition. The Paton Institute's contribution to this technology reflects their long-standing leadership in electroslag welding research and development.

The practical implication for tool manufacturing and maintenance is significant. Rather than replacing worn tools entirely, the electroslag surfacing approach allows for in-situ rebuilding of the working surface, reducing material costs and minimizing tool lead time. The ability to deposit thick layers in a single operation also makes this approach economically attractive for high-value tooling where the cost of replacement is substantial. This paper remains a valuable reference for engineers exploring advanced hardfacing technologies for cutting and forming tools.