Zhuojin Pipe Fitting Co., LtdEffect of Heat Treatment on Microstructure and Properties of D256 Self-Modified Overlay Welding Electrode Deposited Layer
Literature Overview
This paper published in Surface Technology (表面技术, Vol. 42, Issue 2, 2013, pp. 104-107) by Cong Shulin, Han Yanchao, Liu Lixin, and Shi Haifang from Liaoning Institute of Science and Technology, China Nonferrous (Shenyang) Metallurgical Machinery Co., Ltd., Jinzhou Titanium Industry Co., Ltd., and Liaoning Technical University investigates the effect of modifying D256 welding electrode flux with titanium iron, vanadium iron, boron carbide, and rare earth elements, followed by heat treatment, on the microstructure and wear resistance of the overlay deposited layer on high manganese steel components.
Background and Technical Challenge
High manganese steel (Hadfield steel) components frequently experience abrasive failure under medium-to-low loading conditions where the work-hardening mechanism is insufficient to provide adequate wear resistance. The D256 electrode, a standard consumable for overlay welding on manganese steel, produces deposited layers with limited hardness and wear resistance. This study addresses this limitation through flux modification and subsequent heat treatment.
Modification Strategy and Results
The D256 electrode flux was modified with the following additive composition:
| Additive | Content | Primary Function |
|---|---|---|
| Ti-Fe | 12% | Forms TiC/TiB₂ hard phases |
| V-Fe | 12% | Forms VC/V₂C hard phases |
| B₄C | 6% | Generates self-formed borides |
| Rare earth elements | Trace | Refines grain structure |
Microstructural and Mechanical Property Comparison
| Condition | Grain Size | Hardness | Wear Resistance |
|---|---|---|---|
| Unmodified D256 | Coarse | ~45 HRC | Baseline |
| Modified (as-welded) | Refined | 53 HRC | Improved |
| Modified + Solution Aging | Ultra-fine | 49 HRC | Further improved |
Metallurgical Analysis
The modification strategy operates through multiple synergistic mechanisms:
- Self-formed hard phase generation: During arc welding, Ti-Fe and V-Fe react with carbon in the molten pool to form fine TiC and VC particles, while B₄C decomposes to produce self-generated borides (TiB₂, VB). These hard phases are distributed throughout the austenite matrix.
- Grain refinement: The addition of rare earth elements acts as nucleation sites during solidification, promoting finer grain structures. The as-welded modified layer exhibits significantly refined grains compared to the unmodified D256 deposit.
- Heat treatment effect: Solution aging treatment further refines the microstructure and promotes more uniform distribution of carbide particles. Although hardness decreases from 53 HRC to 49 HRC, the improved microstructural uniformity results in enhanced wear resistance.
Engineering Practice Considerations
This research has direct applications in the repair of:
- Crushers and grinding equipment: High manganese steel components in mineral processing that fail under medium-load abrasion.
- Mining equipment: Wear plates, bucket teeth, and conveyor components.
- Cement industry: Crusher jaws and liner plates.
The trade-off between hardness and wear resistance observed in this study is particularly instructive. The as-welded condition achieves higher hardness (53 HRC) but the solution-aged condition provides superior wear resistance despite lower hardness (49 HRC). This suggests that microstructural uniformity and hard phase distribution are more critical for wear performance than peak hardness alone.
Key Reflections
The concept of "self-forming" hard phases through welding metallurgical reactions is elegant in its simplicity. Rather than relying on pre-formed hard particles that may not integrate well with the deposited matrix, the flux modification approach ensures that hard phases nucleate and grow during solidification, achieving intimate bonding with the surrounding matrix. This approach also avoids the issues of particle clustering and interface debonding that plague powder-based overlay systems.
The finding that heat treatment can improve wear resistance despite reducing hardness challenges the conventional assumption that higher hardness always correlates with better wear performance. In abrasive wear applications, the ability of the matrix to support hard phase particles without cracking is equally important as the intrinsic hardness of those particles.
Summary
This research demonstrates that strategic modification of D256 electrode flux with Ti-Fe, V-Fe, B₄C, and rare earth elements, combined with post-weld solution aging treatment, effectively addresses the medium-load abrasive wear failure of high manganese steel components. The self-forming hard phase mechanism provides a cost-effective and metallurgically sound approach to enhancing overlay layer performance, with practical implications for extending service life of critical equipment in mining, cement, and aggregate processing industries.