Zhuojin Pipe Fitting Co., LtdOverlay Welding Repair of Steam Calciner Guide Wheel Shaft Using 45 Steel
Literature Overview
The article by Zhang Zhande, Lu Yupeng, and Yang Lei from Tangshan Sanyou Chemical Co., Ltd. was published in Soda Ash Industry (2010, Issue 4, pp. 35-37) under ISSN 1005-8370. It addresses a practical engineering problem encountered in the chemical industry: the wear and damage of the guide wheel shaft (挡轮轴) in a steam calciner (蒸汽煅烧炉). The authors conducted a weldability analysis of 45 steel and developed a reasonable overlay welding process to successfully repair the damaged shaft. This work belongs to the category of equipment maintenance and repair welding, classified under TG455.
Weldability Analysis of 45 Steel
45 steel is a medium-carbon structural steel with a carbon content of approximately 0.42-0.50 wt%. Its weldability is fundamentally constrained by the carbon equivalent (Ceq), which for 45 steel typically falls in the range of 0.45-0.55%. This places it in the category of steels with moderate to poor weldability, where the primary concerns during welding are:
- Cracking susceptibility in the heat-affected zone (HAZ) due to martensite formation during rapid cooling
- Sensitivity to hydrogen-induced cold cracking, particularly when the base metal is in a high-strength or high-hardness condition
- Distortion and residual stress accumulation due to the relatively low thermal conductivity of medium-carbon steels
The authors correctly identified that the carbon equivalent serves as a critical threshold indicator. When Ceq exceeds 0.45%, preheating becomes essential to control the cooling rate and suppress the formation of hard, brittle martensite in the HAZ. The cooling rate from 800°C to 500°C (t800-500) should ideally be maintained below 10-15°C/s for 45 steel to ensure adequate diffusible hydrogen embrittlement resistance.
| Parameter | Typical Value for 45 Steel | Engineering Requirement |
|---|---|---|
| Carbon content (wt%) | 0.42-0.50 | - |
| Carbon equivalent (Ceq) | 0.45-0.55 | < 0.45 preferred for welding |
| Preheat temperature | 150-250°C | 200-250°C for repair welding |
| Interpass temperature | 200-300°C | Maintain above 200°C |
| Post-weld heat treatment | 550-650°C | Required for stress relief |
| Recommended electrode type | E5015/E5016 | Low-hydrogen basic electrodes |
Overlay Welding Process Development
The repair strategy employed overlay welding (堆焊) rather than butt welding, which is appropriate for the guide wheel shaft application where the damaged surface is typically a bearing surface or a wear-exposed cylindrical surface. The overlay welding process was designed with the following considerations:
- Surface preparation: The damaged area was ground to remove all worn material, creating a clean, well-defined groove with a V-shaped or U-shaped profile. The groove angle was typically 60-90° with adequate root clearance.
- Preheating: Given the medium carbon content of 45 steel, a preheat temperature of 200-250°C was applied using induction heating or gas torch heating. The preheat was applied uniformly over a zone extending at least 3-5 times the wall thickness from the weld area.
- Welding consumable selection: Low-hydrogen basic electrodes (E5015 or E5016 type) were selected to minimize hydrogen pickup and reduce cold cracking risk. The electrode was kept at a drying temperature of 300-350°C for 1-2 hours prior to use.
- Welding parameters: The authors optimized current, voltage, travel speed, and layer thickness to achieve:
- Low heat input to minimize HAZ softening and grain growth
- Adequate dilution control between layers to build up the required repair thickness
- Uniform weld bead profile to restore the cylindrical geometry
- Post-weld treatment: Stress relief annealing at 550-650°C was applied to reduce residual stresses and improve the toughness of the HAZ.
Engineering Practice Insights
This case study exemplifies a common scenario in chemical plant maintenance: the repair of rotating shaft components that experience severe wear due to friction, abrasion, and thermal cycling. The guide wheel shaft in a steam calciner operates under continuous mechanical loading and elevated temperatures, making it susceptible to surface wear and dimensional degradation.
From a quality control perspective, the following verification steps should be implemented:
- Visual inspection (VT): Check for uniform bead profile, absence of undercut, and proper geometric restoration of the shaft diameter
- Penetrant testing (PT): Apply to the overlay weld surface to detect surface-breaking cracks and porosity
- Hardness testing: Measure hardness in the weld metal, HAZ, and base metal to confirm no excessive hardening (HRC < 30-35 for 45 steel repair)
- Dimensional verification: Confirm the restored shaft diameter meets the original design specifications within tolerance
The practical success of this repair demonstrates that 45 steel, despite its moderate weldability, can be effectively repaired through overlay welding when proper preheating, low-hydrogen consumables, and post-weld heat treatment are employed. The key lesson is that the welding process must be designed to control the cooling rate and hydrogen content simultaneously, as these two factors are the primary drivers of cold cracking in medium-carbon steels.
Study Reflection
This literature provides a straightforward yet valuable case study in industrial repair welding. The methodology follows a systematic approach: material characterization → weldability assessment → process parameter optimization → field implementation → verification. For engineers working in chemical plant maintenance, this approach can be directly adapted to similar repair scenarios involving medium-carbon steel shafts, rollers, and other rotating components. The emphasis on preheating and low-hydrogen consumables is consistent with international welding standards such as AWS D1.1 and ISO 15614, reinforcing the universal applicability of these fundamental principles.