CLADDING TECHNOLOGY SHANXI CO., LTDOverlay Welding Repair of 1350 Roughing Mill Universal Joint Fork Head
Literature Overview and Industrial Application
This 1994 publication by Liu Chengmin from Baosteel Technology documents the overlay welding repair of a universal joint fork head from a 1350 roughing mill at a major steel production facility. The study is significant for its demonstration of overlay welding technology applied to critical heavy industrial equipment repair, where downtime costs are extremely high and component replacement may be impractical or prohibitively expensive. Roughing mills are among the heaviest and most heavily loaded equipment in steel mills, operating under extreme conditions of high temperature, heavy impact loading, and abrasive wear. The universal joint fork head is a critical drivetrain component that transmits high torque from the motor to the mill rolls.
Component Description and Failure Analysis
The 1350 roughing mill universal joint fork head is a large forged steel component, typically made from a low-alloy steel such as 42CrMo or 40CrNiMo. The component experiences the following service conditions:
| Service Parameter | Typical Value |
|---|---|
| Operating torque | 50,000-80,000 N·m |
| Operating speed | 50-120 rpm |
| Ambient temperature | 40-80°C |
| Impact loading | Repeated heavy impact |
| Wear mechanism | Abrasive + adhesive |
| Lubrication | Oil bath, partially submerged |
The failure mode identified was progressive wear of the fork head bearing surfaces, leading to excessive clearance and vibration. The wear was concentrated on specific contact areas where the sliding contact between the fork head and the universal joint cross caused material removal through a combination of abrasive and adhesive mechanisms.
Repair Methodology and Process Selection
The repair methodology involved the following systematic steps:
- Surface preparation: The worn surfaces were ground to remove all damaged material and establish a sound base for overlay welding. The ground surface was cleaned with solvent and inspected for cracks using magnetic particle testing (MT).
- Welding procedure qualification: A welding procedure qualification was performed in accordance with applicable standards, using a combination of SMAW for打底焊 (root pass) and SAW or FCAW for fill and cap passes. The qualified procedure specified the following parameters:
| Process | Application | Current | Voltage | Travel Speed |
|---|---|---|---|---|
| SMAW (root) | First pass on prepared surface | 200-280A | 22-28V | 150-250mm/min |
| FCAW (fill) | Fill passes to build thickness | 280-380A | 28-34V | 200-350mm/min |
| FCAW (cap) | Final cap pass for surface quality | 250-350A | 26-32V | 200-300mm/min |
- Overlay material selection: A high-carbon martensitic steel electrode composition was selected, providing a hardness of 45-55 HRC in the as-deposited condition. The composition included 2.0-2.5% carbon, 5-8% chromium, 0.5-1.0% molybdenum, and 0.3-0.5% vanadium.
- Welding execution: The overlay was applied in multiple passes, with each pass thoroughly cleaned before the next pass was deposited. Interpass temperature was maintained below 200°C to control the microstructure and prevent excessive grain growth.
Post-Weld Heat Treatment
The repaired component underwent a post-weld heat treatment consisting of:
- Stress relief at 550-600°C for 2 hours per 25mm of section thickness
- Followed by tempering of the overlay layer at 550°C for 1-2 hours to reduce hardness to the target range and improve toughness
Quality Verification and Performance Results
The repaired component was verified through the following inspection methods:
- Visual inspection: No surface defects, undercuts, or excessive reinforcement observed.
- Magnetic particle testing (MT): No indications of cracks or other discontinuities at the bond line or in the overlay layer.
- Ultrasonic testing (UT): No indications of lack of fusion or volumetric defects.
- Hardness testing: Overlay layer hardness measured at 48-52 HRC, meeting the specification requirement.
- Dimensional verification: The repaired surfaces were machined to the specified dimensions and surface finish.
The repaired universal joint fork head was returned to service and operated for an extended period without further wear-related failures, demonstrating the effectiveness of the overlay welding repair approach.
Study Insights and Engineering Reflections
This case study demonstrates the significant economic and operational benefits of overlay welding repair for heavy industrial equipment. The cost of overlay welding repair is typically a fraction of the cost of component replacement, and the downtime associated with repair is significantly shorter than the lead time for replacement parts. The systematic approach to repair methodology, from failure analysis through process qualification to quality verification, provides a template that can be applied to similar repair situations in other heavy industrial applications. The study reinforces the importance of proper process qualification and quality verification in ensuring the reliability of repaired components, particularly for critical safety-related equipment.