Effect of Tempering Temperature on Wear Resistance of Overlay Welding Molds

Literature Overview

This study by Xu Wujiao, Ding Yongfeng, and Wang Pengcheng from Chongqing University, published in Metal Heat Treatment (Vol. 38, No. 4, 2013, pp. 85-87), investigates the influence of tempering temperature on the wear resistance of overlay-welded molds used in the intermediate shaft manufacturing of micro vehicles. The research employed universal testing machines, optical microscopy, hardness testers, and friction-wear testing machines to systematically evaluate mechanical properties, microstructure, and tribological behavior at different tempering conditions. The classification code TG156.5 indicates this work falls under heat treatment of alloy steels, and the keywords—overlay welding, tempering temperature, wear resistance, and particle-reinforced composite layer—clearly delineate the technical scope.

Core Findings and Technical Interpretation

The central conclusion is that a tempering temperature of 500°C yields the optimal balance of tensile strength, hardness, and wear resistance in the overlay weld deposit. At this temperature, carbide particles are uniformly and finely dispersed within the matrix, forming what the authors term a "particle-reinforced composite layer." This microstructural configuration provides superior resistance to abrasive wear, which is the dominant degradation mechanism in the intermediate shaft forming process.

Microstructural Mechanism

The formation of a particle-reinforced composite layer at 500°C can be understood through the following metallurgical reasoning:

• At lower tempering temperatures, carbide particles may not have fully precipitated or may retain metastable configurations that do not optimally strengthen the matrix.
• At 500°C, the carbon activity and diffusion kinetics favor the precipitation of fine, uniformly distributed carbides (likely Fe₃C and possibly M₇C₃ or M₂₃C₆ depending on the alloying elements in the overlay consumable).
• At temperatures above 500°C, coarsening (Ostwald ripening) of carbide particles begins, reducing the density of particle-matrix interfaces and consequently diminishing the Hall-Petch-type strengthening contribution from particle dispersion.

Engineering Practice Implications

In production environments where overlay-welded molds are subjected to repeated forming cycles, the selection of tempering temperature is not merely a laboratory parameter but a critical process control variable. The 500°C window aligns well with the tempering ranges commonly specified for medium-carbon and low-alloy steels (typically 500-650°C per GB/T 3077 and ASTM A29), but the specificity of 500°C for overlay deposits underscores that weld metal tempering behavior differs from base metal due to segregation, dilution, and non-equilibrium solidification effects.

Key Questions and Reflections

Several questions arise from this work that warrant further investigation:

1. The study does not explicitly report the chemical composition of the overlay consumable or the base metal of the mold. Without knowing the alloy system (e.g., whether the overlay is a high-carbon martensitic steel, a high-speed steel type, or a cobalt-based alloy), it is difficult to generalize the 500°C optimum to other overlay systems.
2. The wear test methodology is not fully described in the abstract. The tribological conditions—counterface material, load, sliding speed, and test duration—significantly influence wear mechanism dominance (abrasive vs. adhesive vs. fatigue wear), and therefore the optimal tempering temperature.
3. The study focuses on a single application (micro vehicle intermediate shaft), but the fundamental principle of particle-reinforced composite layer formation through controlled tempering is applicable to a broader range of wear-resistant overlay applications, including mining equipment, cement mill liners, and paper mill components.

Study Insights and Implications for Practice

From my experience with overlay welding quality control, I emphasize that the tempering step following overlay welding is frequently underestimated in industrial practice. Many shops apply a blanket tempering temperature based on the base material specification without considering the weld deposit's specific precipitation behavior. This study provides a clear demonstration that the tempering temperature must be optimized for the overlay alloy system, not merely inherited from the base metal heat treatment schedule.

A practical recommendation derived from this work is to implement a systematic tempering temperature qualification protocol for any new overlay welding application. This protocol should include:

• Tensile and hardness testing at tempering temperatures spanning 400°C to 650°C in 50°C increments.
• Metallographic examination at each temperature to identify the carbide precipitation and coarsening threshold.
• Pin-on-disc or dry sand rub wear testing under conditions representative of the actual service environment.
• Documentation of the optimal tempering window and inclusion in the welding procedure specification (WPS).

The concept of a particle-reinforced composite layer is particularly relevant to modern overlay welding consumable design, where engineered carbide-forming elements (Cr, Mo, V, W) are deliberately added to create in-situ reinforcement. The tempering temperature controls the size, shape, and distribution of these reinforcing particles, and thus directly governs the service life of the overlay.

This study, though focused on a specific application, reinforces a fundamental principle in welding metallurgy: the as-deposited microstructure of a weld overlay is a transient state, and post-weld heat treatment is an integral part of the overlay process, not an optional add-on. Engineers must treat the combination of welding and tempering as a unified process chain when specifying wear-resistant overlay solutions.