Effect of Surfacing Current on Microstructure and Properties of 16Mn Steel Plate Overlay Layer

Literature Overview

This paper, authored by Wang Chunhua and He Xinghua from Liaoning Technical University and Shenyang Aerospace University respectively, was published in Hot Working Technology (Vol. 47, No. 5, 2018, pp. 173-176) under the National Natural Science Foundation of China (Grant No. 51374120). The study investigates the influence of SMAW (Shielded Metal Arc Welding) current intensity on the microstructure, hardness, wear resistance, and toughness of overlay layers deposited on 16Mn steel plates, which simulate the middle trough of a scraper conveyor used in coal mining applications. The research is highly relevant to engineers dealing with wear-resistant surfacing in heavy-duty mining and material handling equipment.

Core Technical Content and Methodology

The experimental design employed SMAW surfacing on 16Mn steel plates that matched the material grade and heat treatment condition of the actual scraper conveyor middle trough. Multiple current intensities were tested, with 150 A identified as the optimal parameter. Metallographic examination, mechanical property testing, hardness measurement, wear testing, and fracture surface analysis were conducted on the resulting overlay layers.

Microstructural Analysis

The overlay layer microstructure consists of martensite, retained austenite, and carbide phases. The key finding is that as surfacing current increases, the retained austenite content decreases while martensite becomes coarser. This relationship between current intensity and microstructural evolution is critical for process optimization.

Wear Resistance Mechanism

The study identifies that the 150 A current condition produces the best wear resistance, primarily because retained austenite plays a supporting role during the wear process. This is a significant insight: retained austenite undergoes strain-induced martensitic transformation during wear, providing work hardening and maintaining a balance between hardness and toughness.

Fracture Surface Analysis

All overlay layers, regardless of current intensity, exhibited river-pattern fracture morphology in impact testing, indicating that toughness is generally low across all tested conditions. This is inherent to the martensitic nature of the overlay and is an important limitation to consider in engineering applications.

Engineering Practice Implications

For scraper conveyor middle trough applications, the following observations are relevant:

1. The 150 A current represents a practical balance between wear resistance and acceptable toughness for mining conveyor applications where impact loading is present.
2. The river-pattern fracture morphology across all conditions suggests that the overlay layer itself is brittle, and the base metal's contribution to overall toughness becomes important in service.
3. In field applications, the transition zone between overlay and base metal should be carefully monitored, as stress concentration at this interface can initiate crack propagation.

Key Technical Insights and Reflections

The retained austenite content serves as a critical microstructural variable that governs wear performance in martensitic overlay layers. This finding aligns with well-established metallurgical principles where retained austenite provides transformation toughening under mechanical loading. However, the study also highlights a fundamental trade-off: increasing current raises hardness but simultaneously reduces toughness and retained austenite content.

For engineering practice in mining equipment repair and maintenance, this research provides a clear parameter window. The optimal 150 A current should be considered as a starting point, but field conditions such as ambient temperature, base metal preheating, and layer thickness may require adjustments. The brittleness inherent in the overlay layer means that proper design of the transition from overlay to base material is essential to prevent premature failure.

This study reinforces the importance of matching surfacing parameters to service conditions rather than simply maximizing hardness. A wear-resistant overlay that is too brittle will fail through cracking rather than gradual wear, defeating its purpose in dynamic mining environments.

Study Value and Outlook

The research provides practical guidance for field technicians and engineers responsible for scraper conveyor maintenance. Future work should explore multi-layer surfacing strategies, post-weld heat treatment to optimize the retained austenite/martensite ratio, and the effect of filler metal composition on overlay performance. The findings also suggest that combining SMAW surfacing with controlled cooling rates could further optimize the microstructure for specific service conditions.