CLADDING TECHNOLOGY SHANXI CO., LTDTIG Cold Weld Remelting and Wire Deposition on 1Cr17 Stainless Steel - Microstructure and Performance Study
Literature Overview
This 2021 research by Zheng Shaoxian, Wang Junping, Yang Meijuan, and E Xin from Lanzhou Jiaotong University and Lanzhou Lanshi Testing Technology Co., Ltd. investigates a novel surface modification technique for 1Cr17 (equivalent to 430) stainless steel. The work combines TIG cold welding (a non-melting surface cleaning process) with subsequent remelting and wire deposition, creating a modified surface layer with improved properties. Funded by the National Natural Science Foundation of China (51765030) and Gansu Provincial Natural Science Foundation (20JR5RA416), this study bridges fundamental metallurgy with industrial surface engineering applications.
Technical Background and Core Concept
1Cr17 stainless steel (Chinese standard, equivalent to ASTM 430/EN X12Cr17) is a ferritic stainless steel widely used in chemical equipment, heat exchangers, and pressure vessel components. Its primary limitation is relatively poor resistance to intergranular corrosion and limited mechanical strength compared to austenitic grades. Surface modification through weld overlay is a cost-effective approach to enhance surface properties without changing the base material.
The innovation in this study is the two-step process:
- TIG Cold Welding: The tungsten arc is applied to the surface without melting it, achieving surface cleaning, oxide removal, and microstructural refinement through rapid heating and self-quenching.
- Wire Deposition and Remelting: After cold welding, filler wire is deposited and the combined cold-welded layer and filler material are remelted to form a homogeneous modified layer.
Process Parameters
| Parameter | Cold Welding Step | Remelting/Deposition Step |
|---|---|---|
| Current (A) | 120-180 | 100-150 |
| Arc Voltage (V) | 12-16 | 10-14 |
| Travel Speed (mm/min) | 200-400 | 100-250 |
| Filler Wire | None | SUS409, SUS308, or Ni-based |
| Shielding Gas | Ar | Ar or Ar-2% O₂ |
| Tungsten Electrode | Pure W or Thoria | Pure W or La₂O₃ |
Microstructural Evolution
The modified layer exhibits a distinct multi-zone microstructure:
Zone Analysis
| Zone | Location | Microstructure | Hardness (HV) |
|---|---|---|---|
| Modified Surface Layer | Top 50-150 μm | Ultrafine ferrite + martensite | 400-550 |
| Transition Zone | 150-300 μm | Mixed ferrite + martensite | 300-400 |
| HAZ | 300-500 μm | Coarse ferrite + grain boundary carbides | 200-280 |
| Base Metal | Below 500 μm | Original ferrite + carbides | 180-220 |
The cold welding step alone produces a refined microstructure through rapid thermal cycling, but the remelting step with appropriate filler wire allows further property optimization. When SUS308 (austenitic) wire is used, the modified layer transforms to a duplex ferrite-austenite microstructure, significantly improving toughness while maintaining hardness.
Performance Evaluation
Mechanical Properties
| Property | Base Metal | Cold Weld Only | Remelting + SUS308 | Remelting + Ni-Based |
|---|---|---|---|---|
| Hardness (HV) | 200 | 380-450 | 350-420 | 450-550 |
| Wear Resistance | Baseline | 2-3× improvement | 1.5-2× improvement | 3-4× improvement |
| Corrosion Resistance | Baseline | Slight improvement | Significant improvement | Excellent improvement |
Corrosion Behavior
The intergranular corrosion resistance (65% HNO₃ test per ASTM A923) shows marked improvement in the modified layer. The base 1Cr17 steel, being prone to chromium carbide precipitation at grain boundaries, typically fails the intergranular corrosion test. After TIG cold welding and remelting with austenitic or nickel-based filler, the modified layer passes the test due to:
- Homogenization of chromium distribution
- Reduction of grain boundary carbide precipitation
- Formation of protective oxide films during the thermal cycle
Quality Control Considerations
For industrial implementation of this surface modification technique, the following quality assurance measures are essential:
- Pre-treatment: Surface must be cleaned to SA 2.5 grade per ISO 8501-1 to ensure proper arc interaction
- Process monitoring: Real-time current and voltage monitoring to ensure consistent heat input
- Post-treatment: Solution heat treatment (1050-1100°C, water quench) may be required for optimal corrosion resistance
- Inspection: Hardness traverse, metallographic examination, and corrosion testing per relevant standards
Engineering Applications
This technology has direct relevance to:
- Pressure vessel internals: Extending service life of ferritic stainless steel components in corrosive environments
- Heat exchanger tubes: Improving wear and corrosion resistance of 430-type tubing
- Chemical processing equipment: Surface hardening of stirred vessels and pipe fittings
- Hydrogenation reactors: Enhancing resistance to hydrogen-induced cracking in ferritic stainless steels
Study Insights
The elegance of this approach lies in its simplicity—a single TIG process, applied in two stages, achieves significant property enhancement without requiring specialized equipment beyond standard TIG welding capability. The concept of "cold welding" to refine surface microstructure before "hot welding" to deposit and alloy the surface layer represents a creative process philosophy that could be extended to other materials. For engineers in the bimetallic products and pressure vessel industries, this study demonstrates that surface modification is not merely about depositing a different alloy but can also involve thermally modifying the existing surface to create beneficial microstructural changes. The combination of microstructural refinement and compositional modification offers a synergistic improvement in both mechanical and corrosion properties.