Study Note on Manual Overlay Welding Hardening Treatment for Tile Molds

Literature Overview

This paper by Wu Jun and Wu Jingshu (1994), published in Welding Technology (Volume 23, Issue 4, p. 41), presents a cost-effective overlay welding solution for ceramic tile forming molds. The authors, from Wuhan Institute of Technology, addressed the economic challenge of low mold life and high replacement costs in wall and floor tile production. Their approach involved using medium-carbon 45 steel as the base material with high-hardness alloy steel overlay welded onto the cutting edge regions, achieving wear resistance superior to Cr12 tool steel at significantly lower cost.

Core Technical Content

The tile molding industry requires molds with exceptional surface hardness and dimensional stability, as the forming process subjects mold edges to repeated contact with ceramic slurry and mechanical forces. The authors identified that conventional tool steel molds (such as Cr12) offered adequate hardness but at prohibitive cost and with limited repairability. Their innovative approach leveraged the economic advantages of 45 steel (a common medium-carbon steel) combined with strategic overlay welding of high-hardness alloy deposits on critical wear zones.

Key Technical Approach

• Base material selection: 45 steel (medium-carbon steel, ~0.42-0.50% C) chosen for cost-effectiveness and machinability
• Overlay material: High-hardness alloy steel with superior wear resistance
• Application method: Manual arc welding (SMAW) for flexibility and accessibility
• Target performance: Hardness and wear resistance exceeding Cr12 while maintaining economic viability

Process Analysis

The manual arc welding (SMAW) process was selected for several practical reasons:

1. Equipment simplicity: No specialized equipment required beyond standard welding machines
2. Flexibility: Suitable for on-site repair of production molds
3. Accessibility: Can reach complex mold geometries that automated processes cannot
4. Cost-effectiveness: Minimal capital investment for consumable development

Critical Process Parameters

The success of this overlay welding approach depends on several key factors:

• Dilution control: The alloy composition of the overlay weld is significantly affected by base metal dilution. Multiple thin passes are preferred over single thick deposits to minimize dilution effects.
• Heat input management: Excessive heat input can cause softening of the overlay material or excessive grain growth in the heat-affected zone. Low-current, short-arc techniques are recommended.
• Preheating: Moderate preheating (100-200°C) helps reduce thermal stresses and minimizes the risk of cracking in the high-carbon overlay deposits.
• Post-weld treatment: Controlled cooling or stress relief may be necessary to prevent delayed cracking, particularly if martensitic transformations occur in the overlay layer.

Engineering Practice Integration

This approach exemplifies a broader engineering philosophy: combining inexpensive base materials with targeted surface enhancement to achieve performance at reduced cost. In modern manufacturing, this concept has evolved into:

• Composite mold design: Using different materials for different functional zones of a mold
• In-situ surface modification: Applying hard coatings or overlay welds to extend mold life without complete replacement
• Predictive maintenance: Monitoring mold wear patterns to schedule overlay repairs before failure

The tile molding application shares several characteristics with other wear-critical applications in the steel and pipe manufacturing industries:

Study Insights and Reflections

This paper, though brief (only one page), encapsulates a powerful engineering principle: the strategic use of overlay welding to transform economical base materials into high-performance components. The approach of using 45 steel as a substrate and building up critical surfaces with hard alloy deposits is fundamentally similar to the principles applied in modern pipe manufacturing, where:

• Pipe mill mandrels are restored through overlay welding rather than replacement
• Forming rolls receive hardfacing treatments to extend service intervals
• Tooling for pipe fitting manufacturing utilizes composite materials approaches

The economic argument presented—achieving Cr12-level performance at significantly lower cost through a combination of cheap base material and targeted overlay—remains compelling in today's cost-conscious manufacturing environment. The key insight is that not all of a component needs to be made from expensive material; only the critical wear surfaces require enhanced properties.

Practical Recommendations

For engineers considering similar approaches in pipe and fitting manufacturing:

1. Material selection: Identify the minimum-cost base material that meets structural requirements, then apply overlay only to wear-critical zones.
2. Consumable matching: Select overlay consumables based on the specific wear mechanism (abrasive, erosive, adhesive, or corrosive).
3. Process optimization: Develop welding procedures that minimize dilution while ensuring sound metallurgical bonding.
4. Quality verification: Implement hardness profiling, microstructural examination, and wear testing to validate overlay performance.

Summary

This study demonstrates that manual overlay welding of high-hardness alloy steel onto 45 steel tile molds achieves wear resistance comparable to or exceeding Cr12 tool steel at substantially lower cost. The approach highlights the economic and practical advantages of surface modification over complete material replacement, a principle with broad applicability across wear-critical industrial components including pipe mill tooling and forming equipment.