Zhuojin Pipe Fitting Co., LtdSurfacing Composite Manufacturing of Discharge Rolls for Large Hot Rolling Width Shear Press
Literature Overview
This paper by Zhong Yi and Zeng Yibin, published in Plastic Engineering Journal in 2013, addresses a critical industrial challenge: the severe thermal fatigue cracking and metal-to-metal wear experienced by discharge rolls in large hot rolling width shear presses operating at temperatures above 800°C. The authors developed a nitrogen-alloyed surfacing hard-faced flux-cored wire and established a surfacing composite manufacturing process to extend the service life of these critical components. Published by researchers from the Wuhan Iron and Steel (Group) Company Research Institute and the Hot Rolling Plant, this work represents a direct application of surfacing technology to solve a real industrial problem in the steelmaking and rolling industry.
Core Technical Findings
The study developed a surfacing wire with nitrogen alloying and established a manufacturing process that extends the service life of discharge rolls to six months without thermal fatigue cracking. The key performance characteristics are summarized as follows:
| Parameter | Specification |
|---|---|
| Operating temperature | Above 800°C |
| Service life achieved | Six months |
| Thermal fatigue cracks | None observed |
| Metal-to-metal wear | Significantly reduced |
| Surfacing microstructure | Martensite + minor ferrite + alloy compounds |
| Wire type | N-alloyed hard-faced flux-cored wire |
The surfacing layer microstructure consists of martensite, a small amount of ferrite, and alloy compounds. This microstructure provides a combination of high hardness, thermal stability, and resistance to thermal fatigue cracking. The nitrogen alloying plays a critical role in enhancing the high-temperature performance of the surfacing layer.
Metallurgical Analysis of the Surfacing Layer
The martensitic microstructure provides the primary hardness and wear resistance, while the minor ferrite phase contributes to toughness and resistance to thermal fatigue cracking. The alloy compounds—likely including nitrides, carbides, and possibly carbonitrides formed by the nitrogen and carbon in the wire composition—provide additional strengthening and high-temperature stability.
Nitrogen alloying is particularly effective for high-temperature applications because:
- Nitrogen forms stable nitrides (e.g., CrN, MoN, VN) with high melting points that resist dissolution and coarsening at elevated temperatures.
- Nitrogen increases the solid solution strengthening effect in the austenite and martensite phases, maintaining hardness at temperatures where carbon-based strengthening would be lost.
- Nitrogen improves the thermal conductivity of the alloy, reducing thermal gradients and thermal stresses during cyclic heating and cooling.
The presence of minor ferrite in the microstructure is beneficial for thermal fatigue resistance. The ferrite phase has a different thermal expansion coefficient than the martensite, creating a microstructural mechanism that can accommodate thermal strains without cracking. This is analogous to the role of ferrite in duplex stainless steels, where the two-phase microstructure provides excellent resistance to thermal fatigue.
Process Development and Manufacturing Considerations
The surfacing composite manufacturing process involves the following key steps:
- Base roll preparation: The discharge roll is machined to the required geometry, with the surfacing area prepared by grinding to remove surface defects and ensure good adhesion.
- Preheating: The roll is preheated to 200–300°C to reduce thermal gradients and minimize the risk of cracking during surfacing.
- Surfacing deposition: Multiple layers of the N-alloyed flux-cored wire are deposited using submerged arc welding (SAW), with interpass temperature control maintained at 200–300°C.
- Post-weld heat treatment: A tempering treatment at 500–600°C is applied to relieve residual stresses and optimize the microstructure.
- Machining: The surfaced roll is machined to final dimensions, with a minimum overlay thickness of 2–3 mm retained to ensure adequate protection.
The process parameters—welding current, voltage, travel speed, wire feed rate, and interpass temperature—were optimized to ensure complete fusion, uniform microstructure, and minimal residual stress. The use of a flux-cored wire provides inherent shielding and alloying, simplifying the process compared to solid wire surfacing with external flux.
Engineering Practice Implications
This study demonstrates the practical value of surfacing composite manufacturing for extending the life of critical components in the steel industry. The discharge roll is a high-value component that experiences severe thermal and mechanical loading, and conventional replacement strategies are costly and disruptive to production. The surfacing approach offers several advantages:
- Cost reduction: Surfacing extends component life by a factor of 2–3 compared to replacement with new rolls.
- Reduced downtime: Surfacing can be performed during scheduled maintenance windows, minimizing production interruption.
- Material efficiency: Only the wear surface is replaced, preserving the bulk material of the roll.
- Process flexibility: Different surfacing alloys can be selected for different wear conditions, allowing process optimization.
The six-month service life achieved is a significant improvement over the previous practice, which likely involved replacement at intervals of two to three months. This translates to substantial cost savings and reduced operational disruption.
Key Reflections and Insights
This study is a prime example of applied metallurgical engineering, where fundamental knowledge of alloy design, welding metallurgy, and wear mechanisms is integrated to solve a specific industrial problem. The selection of nitrogen alloying is particularly insightful, as nitrogen is often underutilized in surfacing alloys despite its significant benefits for high-temperature applications.
The study also highlights the importance of process optimization in surfacing applications. The microstructure and performance of the surfacing layer are not solely determined by the wire composition but are also influenced by the welding parameters, preheating, and post-weld heat treatment. The systematic development of the manufacturing process is as important as the alloy design.
The approach of using a composite manufacturing strategy—combining a tough base material with a hard, wear-resistant surfacing layer—is a powerful engineering concept that can be applied to many other components in the steel and metallurgical industries.
Summary
This paper presents a successful application of surfacing composite manufacturing to extend the service life of discharge rolls in large hot rolling width shear presses. The development of a nitrogen-alloyed flux-cored wire and the establishment of an optimized surfacing process have resulted in a six-month service life with no thermal fatigue cracking and significantly reduced metal-to-metal wear. This work demonstrates the practical value of integrated alloy design and process optimization in solving real industrial challenges.