Effect of Tempering Temperature on Wear Resistance of Overlay-Welded Molds

Literature Overview

This study, published in Metal Heat Treatment (Jinshu Reshuli) in 2013 by Xu Wujiao, Ding Yongfeng, and Wang Pengcheng from the School of Materials Science and Engineering, Chongqing University, investigates the critical relationship between post-weld heat treatment (tempering) temperature and the wear resistance performance of overlay-welded tool and die applications. Overlay welding is extensively used in the manufacture of molds, forming tools, and wear-resistant components where a hard, wear-resistant surface layer is deposited onto a tougher substrate material. The post-weld heat treatment of such components is essential for relieving residual stresses, optimizing microstructure, and achieving the desired balance of hardness and toughness.

Core Technical Content

Microstructural Evolution with Tempering Temperature

The wear resistance of overlay-welded deposits is primarily governed by the microstructure of the overlay layer, which is strongly influenced by the tempering temperature applied after welding. The study examines how different tempering temperatures affect:

Carbide morphology and distribution: The type, size, shape, and distribution of carbides (typically cementite Fe3C, or complex carbides such as M7C3, M2C, and MC depending on alloy composition) are critical determinants of wear resistance.
Matrix hardness: The hardness of the matrix phase surrounding carbides affects the overall wear performance.
Phase transformation: The tempering process may involve decomposition of retained austenite, precipitation of new phases, or coarsening of existing carbides.

Typical Tempering Temperature Ranges and Effects

Based on the study and general engineering knowledge of overlay welding heat treatment:

Tempering Temperature (°C)	Microstructural Changes	Hardness Trend	Wear Resistance Trend
200-300	Stress relief, minimal microstructural change	Slight decrease	Slight decrease
400-500	Carbide precipitation, retained austenite decomposition	Moderate decrease	May increase due to refined carbides
550-600	Significant carbide coarsening, temper embrittlement risk	Substantial decrease	Decrease
650-700	Severe carbide coarsening, significant softening	Large decrease	Significant decrease

Wear Mechanisms in Overlay-Welded Deposits

The wear resistance of overlay deposits depends on the dominant wear mechanism under service conditions:

Abrasive wear: Resistant to hard, fine-distributed carbides in a tough matrix. High-volume fraction of hard carbides provides resistance to material removal by hard particles.
Adhesive wear: Resistant to materials with high melting point phases and appropriate surface chemistry.
Fatigue wear: Resistant to materials with appropriate toughness to resist crack initiation and propagation.
Corrosive wear: Requires both mechanical hardness and chemical stability.

Process Analysis and Heat Treatment Optimization

Selection of Tempering Temperature

The optimal tempering temperature for overlay-welded components depends on several factors:

Overlay alloy composition: High-carbon high-chromium alloys (e.g., Cr12, Cr12MoV) have different temper response compared to medium-carbon alloys or nickel-based alloys.
Substrate material: The substrate may impose constraints on maximum allowable temperature to avoid softening of the base material.
Service conditions: The dominant wear mechanism and operating temperature determine the required microstructure.
Component geometry and residual stress state: Thick sections or complex geometries may require specific tempering temperatures for effective stress relief.

Recommended Heat Treatment Practices

For typical high-carbon high-chromium overlay alloys used in mold applications:

Application	Overlay Alloy	Recommended Tempering Temperature	Expected Hardness
Cold work molds	Cr12MoV equivalent	500-560°C	58-62 HRC
Hot work molds	H13 equivalent	540-580°C	48-52 HRC
Wear plates	High-Cr cast iron equivalent	400-500°C	55-60 HRC
General wear parts	Medium-Cr alloy	550-600°C	45-50 HRC

Multi-Stage Tempering Considerations

For critical applications, multi-stage tempering may be employed:

First temper (higher temperature): Primary stress relief and microstructural stabilization.
Second temper (lower temperature): Fine-tuning of hardness and suppression of secondary carbide precipitation.
Third temper (if required): Additional refinement for precision applications.

Engineering Practice Integration

Quality Control Parameters

The following quality parameters should be monitored during and after tempering of overlay-welded components:

Hardness profile: Cross-sectional hardness measurements from overlay surface through to substrate interface.
Microstructural examination: Metallographic analysis at multiple depths to verify carbide distribution and phase composition.
Residual stress measurement: X-ray diffraction or hole-drilling method to confirm stress relief.
Dimensional stability: Post-temper dimensional checks to ensure no unacceptable distortion.

Common Defects and Countermeasures

Defect	Cause	Countermeasure
Insufficient hardness after temper	Over-tempering or inadequate initial hardness	Verify tempering temperature; check initial as-welded hardness
Cracking during tempering	Excessive residual stress; too rapid cooling from temper	Increase pre-temper stress relief; control cooling rate
Soft spots in overlay	Incomplete melting or excessive dilution	Optimize welding parameters; ensure proper consumable selection
Excessive distortion	Thermal mismatch between overlay and substrate	Use back-up plates; control welding sequence

Key Technical Insights and Reflections

The Hardness-Toughness Trade-off

The fundamental challenge in optimizing tempering temperature for overlay-welded molds is the inverse relationship between hardness and toughness. Higher hardness (achieved at lower tempering temperatures) provides superior wear resistance but reduced fracture toughness, while lower hardness (higher tempering temperature) improves toughness but reduces wear resistance. The optimal temperature must balance these competing requirements based on the specific service conditions.

Practical Implications for Mold Manufacturing

For mold manufacturers employing overlay welding technology, this study provides clear guidance that:

Post-weld heat treatment is not merely a stress-relief operation but a critical process step that determines final performance.
The tempering temperature must be selected based on systematic understanding of microstructure-property relationships, not merely on convention.
Different tempering temperatures may be appropriate for different functional requirements within the same component (e.g., higher hardness in wear zones, higher toughness in high-stress zones).

Study Insights and Implications

The relationship between tempering temperature and wear resistance in overlay-welded deposits is a manifestation of fundamental metallurgical principles applied to a specific manufacturing context. Engineers should approach the optimization of tempering parameters with a systematic methodology: first characterize the as-welded microstructure, then determine the service requirements, and finally select the tempering temperature that achieves the optimal balance of properties for the intended application. The study reinforces the principle that in overlay welding, the heat treatment step is as important as the welding step itself in determining final component performance.