Effect of Hardfacing Speed on Three-Dimensional Hardfacing Forming Quality

Literature Overview

This research by Shi Chuanrui and colleagues from the School of Mechanical Engineering at Xinjiang University, published in Hot Working Technology in 2019, investigates the influence of hardfacing travel speed on three-dimensional forming quality through combined numerical simulation and experimental validation. Funded by the Xinjiang Uygur Autonomous Region Natural Science Foundation (Project No. 2017D01C038), the study employs finite element modeling of single-pass multi-layer hardfacing to map residual stress distributions and correlate them with observable forming defects. The work is particularly relevant to engineers dealing with multi-pass overlay welding on thick sections where residual stress management is critical to preventing cracking and distortion.

Numerical Simulation Approach and Key Results

The study establishes a finite element model of single-pass multi-layer hardfacing using Visual-Environment three-dimensional simulation software. The simulation captures the sequential deposition of weld beads and the thermal-mechanical evolution at each pass. The resulting residual stress maps reveal two distinct and somewhat counterintuitive trends as hardfacing speed increases:

1. In the direction perpendicular to the weld bead, tensile stress at the bead location decreases with increasing speed.
2. In the direction along the weld bead, residual stress at the bead-to-substrate interface gradually increases with speed, while stress in the stable welding region gradually decreases.

These trends can be explained through thermal analysis. At lower travel speeds, the heat input per unit length is higher, creating a larger heat-affected zone and more uniform but higher overall residual stresses. At higher speeds, the heat input per unit length decreases, concentrating thermal effects near the bead surface and creating steeper thermal gradients. The perpendicular stress reduction reflects the reduced overall heat input, while the longitudinal stress increase at the interface reflects the more localized thermal contraction of the bead relative to the cooler base material.

The experimental validation confirmed the simulation predictions, demonstrating that high-speed hardfacing produces better efficiency but suffers from degraded surface quality and more frequent arc start and stop defects. Low-speed hardfacing yields superior surface quality but at the cost of productivity. The study identifies 6 mm/s as the optimal hardfacing speed under the specific experimental conditions, representing a balanced compromise among residual stress levels, productivity, and surface quality.

Process Optimization Analysis

The identification of an optimal speed requires a multi-objective analysis that weighs competing requirements. Residual stress is not merely a numerical value; it has direct consequences for service performance. High tensile residual stresses at the bead-to-substrate interface can initiate fatigue cracks under cyclic loading, promote stress corrosion cracking in aggressive environments, and contribute to post-weld distortion that affects dimensional accuracy. However, excessively low speeds increase heat input, which can lead to undesirable microstructural coarsening, increased dilution, and reduced hardness in the overlay layer.

The arc start and stop defects observed at high speeds are particularly significant in multi-pass applications. Each pass termination creates a localized region of incomplete fusion, porosity, or undercut that can serve as a crack initiation site. In a multi-pass build-up, these defects accumulate and can compromise the structural integrity of the entire overlay. Engineers should implement proper start and stop procedures—including preheating at start points, overlap of at least 25% of bead width at stop points, and controlled ramp-up and ramp-down of travel speed—to mitigate these defects regardless of the nominal travel speed.

From a practical welding procedure development standpoint, this study supports the use of finite element simulation as a tool for optimizing travel speed before committing to full-scale welding trials. The simulation can predict residual stress distributions for a range of speeds without consuming consumables or machine time, allowing engineers to narrow the search space before experimental validation. This approach aligns with the PDCA cycle: Plan the optimal speed range through simulation, Do the experimental welding, Check the results against predictions, and Act by refining the procedure.

Engineering Practice Integration

In industrial hardfacing operations, travel speed is often set based on operator experience or generic welding procedure specifications rather than through systematic optimization. This study demonstrates that travel speed has a measurable and predictable influence on residual stress distribution, surface quality, and defect incidence. Engineers should incorporate travel speed as a critical process variable in welding procedure specifications, with explicit acceptance criteria for residual stress levels and surface quality.

For pipeline and pressure vessel applications, where residual stress management is governed by codes such as ASME B31.3 or NB/T 47014, the findings of this study have direct relevance. Post-weld stress relief treatment is often specified to reduce residual stresses below code limits, but understanding the relationship between travel speed and initial residual stress allows engineers to minimize the severity of the required stress relief cycle. Lower initial stresses can be achieved with appropriate speed selection, potentially reducing thermal distortion during stress relief and improving dimensional stability.

The study's emphasis on three-dimensional forming quality is particularly relevant to applications where overlay thickness and contour accuracy are critical, such as valve seat hardfacing, pump impeller repair, and wear plate fabrication. In these applications, the interplay between travel speed, bead geometry, and residual stress determines whether the finished component meets dimensional tolerances after machining.

Study Insights and Reflections

The most significant contribution of this paper is its demonstration that travel speed optimization is not a simple linear problem but a multi-variable trade-off requiring systematic evaluation. The identification of 6 mm/s as optimal under specific conditions underscores that the optimal speed is application-dependent and must be determined through analysis of the specific geometry, material, and service requirements. Engineers should not transfer speed recommendations from one application to another without re-evaluating the underlying process parameters.

The study also highlights an important gap in conventional welding procedure qualification. Most standard qualification procedures focus on mechanical properties and defect detection but do not systematically evaluate residual stress distributions as a function of travel speed. Incorporating residual stress assessment into procedure qualification, as advocated by this research, would improve the predictive reliability of welding procedures for critical applications.

In conclusion, this research provides a rigorous methodology for optimizing hardfacing travel speed through the integration of numerical simulation and experimental validation. The key engineering insight is that travel speed must be selected as a deliberate process variable that balances residual stress, productivity, and surface quality, rather than as a secondary parameter set to accommodate other process choices. This systematic approach to speed optimization can significantly improve the quality and reliability of hardfacing operations in demanding industrial applications.