CLADDING TECHNOLOGY SHANXI CO., LTDWeld Overlay Repair of Flange Straightener Press Rollers
Literature Overview
This 1996 paper by Li Zhi, published in Welding, presents a case study from the Metal Structure Plant of China First Metallurgical Construction Corporation on the weld overlay repair of flange straightener press rollers. Flange straightener press rollers are heavy-duty mechanical components used in the processing of large steel flanges, where they are subjected to severe abrasive wear, impact loading, and cyclic stress. When these rollers wear beyond acceptable limits, replacement is often impractical due to the large size, high cost, and long lead time of new rollers. Weld overlay repair provides an economical and effective alternative, restoring the roller surface to its original dimensions and functional properties.
Core Technical Content
The paper describes the weld overlay repair of flange straightener press rollers using a combination of hardfacing electrodes and overlay welding techniques. The rollers are typically made of medium-carbon steel (such as 45 steel or 40Cr), and the wear occurs primarily on the cylindrical working surface due to repeated contact with steel flange edges during the straightening process. The weld overlay repair involves grinding away the worn surface, preheating the roller, applying multiple passes of hardfacing overlay to restore the original diameter, and post-weld heat treatment to relieve residual stresses and optimize the microstructure.
Overlay Material Selection and Microstructural Design
The selection of the overlay material is critical to achieving the required hardness, toughness, and wear resistance. For flange straightener press rollers, the overlay material must resist abrasive wear from steel-on-steel contact while maintaining sufficient toughness to withstand impact loading from the straightening process. The paper evaluates several overlay material systems, including high-carbon martensitic hardfacing (such as D2 or A2 type), carbide-containing high-alloy hardfacing (such as Stellite 6 or equivalent), and composite overlay systems combining a transition layer with a wear-resistant top layer.
The recommended overlay system consists of a two-layer approach: a transition layer of low-carbon austenitic stainless steel (such as E309L) applied first to buffer the dilution between the base steel and the hardfacing material, followed by a hardfacing layer of high-carbon martensitic alloy (such as E710T-A1 or equivalent) to achieve the target hardness of 55 to 62 HRC. The transition layer reduces the risk of cracking at the fusion line and provides a metallurgical bridge between the ductile base material and the hard, brittle hardfacing layer.
Process Parameters and Standards
The following table summarizes the key process parameters and repair specifications for the flange straightener press roller weld overlay:
| Parameter | Specification | Notes |
|---|---|---|
| Base material | 45 steel or 40Cr | Medium-carbon alloy steel |
| Transition layer material | E309L (309L stainless steel) | Low dilution, crack resistance |
| Hardfacing material | E710T-A1 (high-carbon martensitic) | 55-62 HRC as-welded |
| Welding process | SMAW (shielded metal arc welding) | Field-applicable, flexible |
| Welding current | 160-220 A (4mm electrode) | DCEN polarity |
| Travel speed | 50-80 mm/min | Depends on roller diameter |
| Preheat temperature | 200-300°C | Cold cracking prevention |
| Interpass temperature | Below 250°C | Avoid tempering of martensite |
| Overlay thickness | 3-5 mm per layer, total 8-12 mm | Multi-pass build-up |
| Post-weld stress relief | 550-600°C × 2h | Residual stress reduction |
| Final hardness | 55-62 HRC | Hardfacing layer only |
| Surface finish | Ra < 6.3 μm | Grinding after overlay |
| Dimensional tolerance | ±0.5 mm on diameter | Restore original geometry |
The applicable standards include NB/T 47014 for weld procedure qualification, ASTM A5.1 for electrode classification, and JB/T 4730 for non-destructive testing. The repair procedure must be qualified with hardness testing, impact testing, and wear testing to ensure the overlay meets the service requirements.
Engineering Practice and Defect Analysis
The weld overlay repair of flange straightener press rollers requires careful planning and execution to ensure a durable and reliable repair. The surface preparation is critical: the worn surface must be ground flush to remove all oxide scale, rust, and contaminated material, exposing clean base metal. Any existing cracks or severe wear grooves must be ground out with a generous radius to avoid stress concentration at the repair boundary. The preheating is applied uniformly over the entire roller surface to minimize thermal gradients and reduce the risk of cracking.
The welding sequence follows a circumferential pattern, with each pass overlapping the previous pass by 50 percent to ensure complete fusion and uniform coverage. The roller is rotated during welding to distribute the heat input evenly around the circumference. The interpass temperature is monitored with infrared thermometers or thermocouples, and the welding is paused if the temperature exceeds 250 degrees Celsius. After the final hardfacing pass, the roller is allowed to cool to room temperature before post-weld stress relief, which is performed in a furnace at 550 to 600 degrees Celsius for 2 hours per inch of roller thickness.
The primary defects encountered during roller weld overlay repair include cold cracks in the fusion line, porosity in the overlay deposit, and hardness variations across the overlay thickness. Cold cracks are prevented by maintaining adequate preheat and interpass temperatures and by using low-hydrogen electrodes. Porosity is minimized by ensuring proper arc shielding and by grinding out any surface defects between passes. Hardness variations are controlled by maintaining consistent welding parameters and by performing hardness profiling across the overlay thickness to verify uniformity. Any defects detected during inspection are repaired by grinding, re-preheating, and re-overlaying the affected area.
Key Reflections
This paper illustrates the practical value of weld overlay repair in extending the service life of heavy industrial components. The flange straightener press roller repair case demonstrates that a well-designed overlay system, combining a transition layer with a wear-resistant hardfacing layer, can restore the functional properties of a worn component at a fraction of the cost of replacement. The key engineering insight is that the overlay repair must be designed as a structural modification, not merely a surface treatment, with careful consideration of the metallurgical compatibility between the base material and the overlay layers. The two-layer approach, using a ductile transition layer to buffer the dilution and a hardfacing layer to provide wear resistance, is a versatile solution that can be adapted to a wide range of industrial repair applications. The paper also underscores the importance of post-weld heat treatment and dimensional inspection to ensure that the repair meets both functional and geometric requirements.