Manual Surfacing Hardening Treatment of Wall and Floor Tile Molds

Literature Overview

This 1994 paper by Wu Jun and Wu Jingshu from Wuhan Institute of Technology, published in Welding Technology (Vol. 23, No. 4, p. 41), addresses the economic challenge of low mold life in wall and floor tile production. The authors propose using medium-carbon 45 steel as the mold body and applying a high-hardness alloy steel overlay on the cutting edge through manual surfacing welding. The resulting molds exhibit wear resistance exceeding that of Cr12 tool steel while significantly reducing material cost. The classification TQ174.6 situates this work in ceramic manufacturing technology, highlighting the cross-disciplinary nature of welding applications.

Core Technical Approach

The problem statement is straightforward: tile molds experience rapid wear at the cutting edge, leading to high replacement frequency and production downtime. Conventional Cr12 tool steel molds, while offering good wear resistance, are expensive and difficult to repair once worn. The authors' solution leverages the lower cost and better weldability of 45 steel for the bulk of the mold, reserving the expensive wear-resistant material only for the critical edge region through surfacing.

Material Selection and Performance Comparison

The following table compares the key properties of the proposed approach with conventional alternatives:

Property	Cr12 Tool Steel Mold	45 Steel + Surfacing Overlay
Material cost	High	Low (45 steel base) + moderate overlay cost
Hardness at edge	HRC 58–62	HRC 60–65 (overlay)
Wear resistance	Good	Excellent (overlay tuned for abrasion)
Repairability	Difficult (full replacement)	Easy (re-surface the edge)
Weldability	Poor	Good (45 steel base)
Cost per unit life	High	Low

The choice of 45 steel as the base material is critical because of its good toughness and weldability. Unlike Cr12, which has high carbon content and poor weldability due to the formation of hard, brittle martensite in the heat-affected zone, 45 steel can be preheated and welded with minimal risk of cracking. The surfacing layer, composed of a high-hardness alloy steel, provides the necessary wear resistance at the cutting edge without requiring the entire mold to be made from expensive tool steel.

Manual Surfacing Process Details

The manual surfacing process involves several critical steps:

The 45 steel mold is machined to final dimensions with a slight allowance at the cutting edge for surfacing buildup.
The edge region is preheated to 200–300 °C to reduce thermal stress and prevent cracking at the weld interface.
The surfacing alloy is deposited in multiple passes using manual arc welding, typically with SMAW or GTAW processes.
Between passes, the interpass temperature is maintained above 200 °C to prevent cold cracking.
After the final pass, the overlay is machined to the precise cutting edge geometry.
Post-weld tempering at 200–300 °C for 2 hours relieves residual stress and improves toughness.

The hardness of the overlay is typically in the range of HRC 60–65, which exceeds the hardness of Cr12 and provides superior resistance to the abrasive action of ceramic slurry during tile forming. The overlay thickness is typically 3–5 mm, providing sufficient material for multiple regrinding cycles during the mold's service life.

Defect Analysis and Countermeasures

The primary defects encountered in manual surfacing of mold edges include:

Defect Type	Cause	Countermeasure
Cracking at weld toe	High cooling rate, low interpass temperature	Increase preheat and interpass temperature
Overlay spalling	Excessive dilution, poor metallurgical bond	Use transition layer, reduce first-pass penetration
Uneven hardness	Inconsistent heat input	Standardize welding parameters, use qualified welders
Porosity	Contaminated electrode or base metal	Thorough cleaning, electrode drying
Excessive HAZ hardness	High carbon content in base near weld	Preheat and post-weld heat treatment

A particularly important consideration is the dilution effect. When welding a high-hardness alloy onto 45 steel, the first pass experiences significant dilution from the base metal, reducing the effective alloy content and hardness of the overlay. The authors implicitly address this by using multiple passes, where subsequent passes experience lower dilution and achieve higher hardness. The final pass, which constitutes the functional cutting edge, achieves the target hardness with minimal dilution.

Study Insights and Implications

This paper exemplifies the engineering principle of using the right material in the right place. By combining a low-cost, weldable base material with a high-performance overlay, the authors achieve a cost-effective solution that outperforms the conventional single-material approach. The methodology is directly transferable to other mold applications where localized wear is the primary failure mechanism, such as extrusion dies, forging dies, and stamping dies. The emphasis on manual surfacing, while seemingly less sophisticated than automated processes, is well-suited to the small-batch, multi-variety production environment typical of tile manufacturing. For modern practitioners, this work underscores the importance of hybrid material design in welding engineering and the economic advantages of repairable component design over replacement-based strategies.