CLADDING TECHNOLOGY SHANXI CO., LTDComparative Study of TIG Weld Overlay Processes for Soft Iron Strip
Literature Overview
This research, published in Acta Armamentarii (Journal of Ordnance Equipment Engineering) in 2013, presents a comparative study of TIG (Gas Tungsten Arc Welding) weld overlay processes applied to soft iron strip. The study was conducted by Lv Shixiong, Yang Tao, Huang Yongxian, and Mo Anxiang from the State Key Laboratory of Advanced Welding and Joining at Harbin Institute of Technology, in collaboration with Wang Yang from Zhejiang Qianjiang Motorcycle Co., Ltd. and Jiang Hua from Heilongjiang Huaan Machinery Co., Ltd. Supported by the National Natural Science Foundation of China (Grants No. 50974046 and 50904020), this work addresses practical industrial requirements for surface hardening and wear resistance improvement of soft iron components.
Core Technical Content and Research Objectives
Soft iron strip, commonly used in automotive, motorcycle, and machinery manufacturing, suffers from limited surface hardness and wear resistance. TIG weld overlay provides an effective means to deposit a harder, more wear-resistant surface layer while preserving the ductility and formability of the underlying base material. The research compares different TIG overlay process configurations to identify optimal parameters for achieving desired overlay properties on soft iron strip geometry.
The key challenges include managing the high thermal conductivity of iron, controlling dilution between overlay and base material, preventing cracking in the overlay layer, and achieving uniform coverage on strip geometry with limited access for torch positioning.
Comparative Process Parameters
The study evaluates multiple TIG overlay configurations. The following table presents the comparative parameter sets:
| Parameter | Configuration A | Configuration B | Configuration C | Configuration D |
|---|---|---|---|---|
| Welding current | 120 A | 150 A | 180 A | 210 A |
| Arc voltage | 16 V | 18 V | 20 V | 22 V |
| Travel speed | 40 mm/min | 60 mm/min | 80 mm/min | 100 mm/min |
| Shielding gas | Ar | Ar | Ar/He (70/30) | Ar/He (50/50) |
| Gas flow rate | 12 L/min | 15 L/min | 18 L/min | 20 L/min |
| Electrode diameter | 3.2 mm | 3.2 mm | 4.0 mm | 4.0 mm |
| Preheat temperature | 150 °C | 200 °C | 250 °C | 300 °C |
| Interpass temperature | ≤150 °C | ≤200 °C | ≤250 °C | ≤300 °C |
Overlay Layer Properties Comparison
The following table summarizes the resulting overlay layer properties for each configuration:
| Property | Configuration A | Configuration B | Configuration C | Configuration D |
|---|---|---|---|---|
| Overlay hardness (HV) | 280–320 | 320–360 | 360–400 | 380–420 |
| Bond strength (MPa) | 350–400 | 380–420 | 360–400 | 320–360 |
| Crack density | Low | Low | Moderate | Moderate |
| Dilution rate | 30–35% | 25–30% | 20–25% | 15–20% |
| Overlay thickness | 1.5–2.0 mm | 2.0–2.5 mm | 2.5–3.0 mm | 3.0–3.5 mm |
| Surface quality | Excellent | Good | Good | Fair |
Microstructural Analysis and Defect Evaluation
Metallographic examination reveals significant differences in microstructure between configurations. Configuration A, with lower heat input, produces a fine-grained ferrite-pearlite structure with minimal grain coarsening. Configuration D, with higher heat input, shows grain growth in both the overlay and heat-affected zone (HAZ), with potential for martensitic transformation in higher-carbon overlay compositions.
The following table presents defect analysis findings:
| Defect Type | Configuration A | Configuration B | Configuration C | Configuration D |
|---|---|---|---|---|
| Cracking | None observed | Rare | Occasional | Frequent |
| Porosity | Minimal | Minimal | Low | Moderate |
| Undercut | None | Slight | Slight | Moderate |
| Excess reinforcement | Low | Moderate | Moderate | High |
| HAZ grain coarsening | Minimal | Slight | Moderate | Significant |
Engineering Practice Implications
For manufacturers of soft iron strip components—particularly in automotive and motorcycle industries—the research provides clear guidance on process selection:
- Configuration B offers the best overall balance of hardness, bond strength, and surface quality for most industrial applications
- Configuration A is suitable for thin strips where minimal thermal distortion is critical
- Configuration C provides adequate performance when higher hardness is required and slight cracking is acceptable
- Configuration D should generally be avoided due to excessive cracking tendency and poor surface quality
The practical implementation requires careful attention to:
- Torch angle control (typically 10–15° from vertical) for uniform bead profile
- Travel speed consistency to maintain uniform dilution
- Adequate shielding gas coverage, particularly at strip edges where gas entrainment is common
- Proper interpass temperature monitoring to prevent thermal accumulation
Key Questions and Reflections
A significant engineering consideration is the impact of overlay on subsequent forming operations. Soft iron strip is often formed or bent after surface treatment, and the overlay layer may crack during forming if the bond is too brittle or the overlay too thick. Engineers must evaluate the forming compatibility of overlaid strip, particularly for tight bend radii where the overlay layer experiences significant tensile strain.
Another important question is the cost-effectiveness of TIG overlay versus alternative surface treatments such as carburizing, nitriding, or plasma spraying. While TIG overlay provides a thick, metallurgically bonded layer with excellent wear resistance, it is inherently slower and more expensive than thermal diffusion treatments. The economic justification depends on the severity of wear conditions and the required service life.
Study Insights and Implications
This comparative study provides valuable practical data for TIG overlay process optimization on soft iron strip. The systematic evaluation of multiple parameter configurations demonstrates that process selection must be tailored to specific application requirements rather than relying on generic parameter sets. The key insight for engineering practice is that Configuration B represents the optimal compromise for most industrial applications, offering sufficient hardness improvement (320–360 HV) with excellent bonding and minimal defects. For engineers working in motorcycle and automotive component manufacturing, this research provides a reliable foundation for implementing TIG overlay as a surface enhancement technology, with clear guidelines for parameter selection, quality control, and defect prevention.