Weld Overlay Repair Process and Performance Study of 45 Steel

Literature Overview

The study focuses on the weld overlay repair technology applied to 45 steel components, which are widely used in mechanical shafts, gears, and structural parts in heavy industry. 45 steel (equivalent to AISI 1045) is a medium-carbon steel with approximately 0.42-0.50 wt% carbon content, offering good strength and machinability but limited corrosion resistance and surface hardness. The literature examines various welding overlay processes—primarily submerged arc welding (SAW), gas metal arc welding (GMAW), and plasma transferred arc (PTA) cladding—to restore or enhance surface properties of worn or damaged 45 steel components. The core objective is to achieve a functional surface layer that combines high hardness, wear resistance, and adequate bond strength with the base metal.

Core Technical Points

Base Metal Characteristics and Weldability Challenges

45 steel presents several weldability challenges that directly influence overlay process selection. The carbon equivalent (CE) value for 45 steel typically ranges from 0.43 to 0.48%, calculated using the formula CE = C + Mn/6 + (Cr+Mo+V)/5 + (Ni+Cu)/15. This CE value indicates moderate susceptibility to hydrogen-induced cracking (HIC) during welding, particularly when the base metal is in the quenched-and-tempered condition. The literature highlights that preheating temperatures of 150-250°C are generally recommended to mitigate cracking risks, while interpass temperature control between 200-300°C is critical for multi-pass overlay builds.

Process Selection and Parameter Optimization

The study compares three primary overlay processes for 45 steel repair applications:

The literature emphasizes that PTA cladding offers the finest control over dilution rates, which is particularly important when overlaying hardfacing alloys onto 45 steel. Dilution rates below 10% are achievable with PTA using proper powder feed rates and arc travel speeds, whereas SAW typically produces dilution rates of 15-25% due to deeper penetration.

Microstructure and Performance Analysis

The overlay layer microstructure is heavily influenced by the cooling rate, which varies significantly between processes. For SAW overlay on 45 steel, cooling rates of approximately 5-15°C/s are typical, producing a coarse ferrite-pearlite matrix with possible martensite formation in high-carbon hardfacing consumables. In contrast, PTA cladding produces cooling rates of 50-200°C/s, yielding finer microstructures with retained austenite and martensite phases that contribute to higher hardness values.

Mechanical testing results reported in the study show that properly designed overlay layers on 45 steel can achieve hardness improvements of 60-100% compared to the as-received base metal condition. Bond strength tests (per ASTM A264 or equivalent) consistently show values exceeding 600 MPa for well-executed SAW and GMAW overlays, while PTA overlays demonstrate bond strengths in the range of 550-700 MPa depending on interpass cleaning procedures.

Defect Analysis and Countermeasures

Common Defects in 45 Steel Overlay Repair

Engineering Practice Insights

From a practical standpoint, the repair of 45 steel components in the field requires careful consideration of the component's service conditions. For rotating shafts and gear components, the residual stress state after overlay welding can significantly affect fatigue life. The literature recommends post-weld stress relief at 580-620°C for 2 hours per 25mm of section thickness to mitigate residual stresses that could lead to premature failure in service.

The study also highlights the importance of consumable selection. Hardfacing alloys such as Cr-C alloy (e.g., D2 equivalent), Ni-Cr-C alloy, or Co-Cr alloy can be used depending on the required wear mechanism resistance. For abrasive wear conditions typical in mining and material handling applications, Cr-C hardfacing alloys with carbide-rich microstructures are preferred, while Ni-Cr-C alloys offer better resistance to oxidative and erosive wear at elevated temperatures.

Study Insights and Implications

This literature provides valuable guidance for selecting appropriate overlay processes for 45 steel repair applications. The key takeaway is that process selection should be driven by the required hardness level, allowable dilution, and production efficiency requirements. For high-volume production repairs where moderate hardness (300-350 HV) is acceptable, SAW offers the best cost-effectiveness. For precision repairs requiring high hardness and low dilution, PTA is the superior choice despite higher equipment costs.

The study reinforces the importance of weld procedure qualification (WPQ) per NB/T 47014 or ASME IX for ensuring consistent overlay quality. Engineers should pay particular attention to preheating protocols, interpass temperature control, and post-weld heat treatment specifications when developing repair procedures for 45 steel components in critical service applications. Understanding the relationship between cooling rate, microstructure, and mechanical properties enables more rational process parameter optimization and defect prevention strategies.