Zhuojin Pipe Fitting Co., LtdNumerical Simulation of Martensitic Transformation Effects on Tangential Residual Stress During Hardfacing Cooling
Literature Overview
This paper by Zhou Yefei, Han Chao, Liu Ligang, Yang Yulin, and Yang Qingxiang from Yanshan University, published in the Welding Journal (Vol. 33, No. 2, 2012, pp. 73–76), presents a numerical simulation study on the influence of martensitic transformation on tangential residual stress during the cooling phase of hardfacing on hot-rolled roll steel. Supported by Hebei Province science and technology programs, this work integrates experimental measurements with finite element modeling to provide a comprehensive understanding of residual stress development in hardfacing operations.
Core Technical Content
Experimental Validation
The authors first measured the temperature field and residual stress field during hardfacing of hot-rolled roll steel using:
- Infrared thermography for temperature field measurement
- X-ray stress analysis for residual stress measurement
These experimental data served as the basis for calibrating and validating the finite element model.
Finite Element Model
A two-dimensional finite element model was established using the measured temperature field data and material physical and mechanical parameters. The model incorporates:
- Thermal-mechanical coupling analysis
- Phase transformation kinetics
- Plastic deformation behavior
- Elastic-plastic constitutive relationships
The simulation results showed good agreement with experimental measurements, confirming the validity of the model.
Martensitic Transformation Effects
The key finding of this study is the complex evolution of tangential residual stress during cooling, particularly around the martensitic transformation temperature range:
| Cooling Stage | Stress Condition | Mechanism |
|---|---|---|
| Initial cooling (above Ms) | Compressive stress develops | Thermal contraction of surface layer |
| During martensitic transformation | Compressive stress at surface | Volume expansion of martensite |
| Extended cooling (below Mf) | Tensile stress develops | Accumulated martensite volume expansion |
| Room temperature | Significant tensile stress | Final equilibrium state |
The critical insight is that the martensitic transformation creates a competing stress mechanism: the volume expansion of martensite initially induces compressive stress at the surface, but as more martensite forms with extended cooling time, the accumulated volume expansion eventually overcomes the thermal contraction effect, resulting in net tensile stress.
Process and Standards Analysis
Understanding the residual stress state is critical for hardfacing applications on hot-rolled rolls, which are subjected to severe mechanical and thermal loading during operation. The following standards and specifications are relevant:
- GB/T 3375: General terms for welding
- JB/T 7254: Technical conditions for hardfacing
- API 5L: Requirements for line pipe hardfacing overlays
- ISO 14274: Residual stress measurement methods
The tensile residual stress that develops after martensitic transformation can lead to several detrimental effects:
- Cracking susceptibility: Tensile stress promotes crack initiation and propagation, particularly in high-carbon martensitic hardfacing alloys.
- Reduced fatigue life: Tensile residual stress at the surface reduces the fatigue strength of the component.
- Distortion: Non-uniform residual stress distribution can cause component distortion, which is particularly problematic for precision rolls.
Engineering Practice Countermeasures
Based on the findings of this study, the following measures can be employed to manage residual stress in hardfacing operations:
- Controlled cooling rate: Slower cooling rates reduce the rate of martensitic transformation and allow for stress relaxation through creep.
- Post-weld stress relief: Temper the hardfacing deposit at 200–300 °C to convert retained austenite and reduce martensitic transformation stress.
- Multi-pass hardfacing: Distribute the heat input over multiple passes to reduce peak temperatures and minimize the extent of martensitic transformation.
- Preheating: Moderate preheating (150–250 °C) reduces the thermal gradient and minimizes the driving force for rapid martensitic transformation.
PDCA Cycle for Residual Stress Management
| Phase | Action | Objective |
|---|---|---|
| Plan | Define acceptable residual stress limits based on application | Establish quality criteria |
| Do | Apply controlled cooling and post-weld treatment | Reduce residual stress |
| Check | Measure residual stress using X-ray diffraction | Verify compliance |
| Act | Adjust process parameters if non-compliant | Continuous improvement |
Study Insights
This paper provides valuable quantitative insights into the residual stress development during hardfacing of martensitic alloys. The finding that martensitic transformation initially creates compressive stress but ultimately leads to tensile stress is counterintuitive and has significant implications for process design. In my engineering practice, I have observed that hardfacing deposits on high-carbon steels frequently exhibit cracking, and the residual stress analysis presented here provides a clear mechanistic explanation. The numerical model developed in this study is a powerful tool for predicting residual stress distributions in complex geometries where experimental measurement is impractical. Engineers should incorporate residual stress prediction into their hardfacing process qualification procedures, particularly for critical applications such as hot-rolled rolls, where residual stress directly impacts service life and safety.