CLADDING TECHNOLOGY SHANXI CO., LTDStudy on Cladding Performance of Crankshaft Die Material
Literature Overview
The study by Sun Jianli and Gao Wenliang from the Department of Aeronautical Manufacturing, Chengdu Aeronautical Polytechnic College, published in 2015 in the journal "Foundry Technology," investigates the cladding (weld overlay) performance of crankshaft die materials. Crankshaft dies are critical tooling components in the automotive and aerospace industries, used to form the complex geometry of crankshafts through cold or warm forging operations. The die surfaces are subjected to extreme contact pressures, abrasive wear, and thermal loading, making them prone to rapid wear and failure. The application of wear-resistant overlay layers on die surfaces is a well-established method for extending die life, but the cladding performance of the specific die materials used in crankshaft manufacturing has not been extensively studied. This research fills that gap by systematically evaluating the weldability, microstructure, and mechanical properties of overlay layers applied to crankshaft die materials.
Die Material Characterization
Crankshaft dies are typically manufactured from high-carbon high-chromium die steels such as Cr12MoV, H13 (4Cr5MoSiV), or 5CrNiMo. These materials are selected for their high hardness (typically 58–62 HRC in the tempered condition), good wear resistance, and adequate toughness. However, these materials also present significant challenges for overlay welding due to their high carbon equivalent, high hardenability, and susceptibility to cracking during welding.
| Die Material | Composition (wt%) | Hardness (HRC) | Carbon Equivalent (CE) | Weldability Assessment |
|---|---|---|---|---|
| Cr12MoV | C: 1.45–1.65, Cr: 11.0–12.5, Mo: 0.4–0.6, V: 0.15–0.35 | 58–62 | 0.75–0.85 | Poor |
| H13 | C: 0.32–0.45, Cr: 4.75–5.50, Mo: 1.10–1.75, V: 0.80–1.20 | 48–53 | 0.45–0.55 | Moderate |
| 5CrNiMo | C: 0.45–0.55, Cr: 0.40–0.60, Ni: 1.40–1.70, Mo: 0.12–0.25 | 48–52 | 0.35–0.42 | Moderate |
The high carbon equivalent of Cr12MoV (0.75–0.85) presents a severe cracking risk during welding. The formation of hard, brittle martensite in the heat-affected zone (HAZ) is inevitable without careful preheating and post-weld heat treatment. The H13 and 5CrNiMo materials have lower carbon equivalents, making them more amenable to overlay welding, but they still require careful process control to prevent HAZ cracking.
Overlay Welding Process Development
The authors evaluated multiple overlay welding processes for the crankshaft die materials, including GTAW (Gas Tungsten Arc Welding), GMAW (Gas Metal Arc Welding), and plasma arc welding. The selection of overlay alloy composition was based on the specific service conditions of the crankshaft die:
- Abrasive wear resistance: Required for dies subjected to high contact pressures and sliding contact
- Hot hardness: Required for warm forging applications where die temperatures exceed 200 °C
- Bond strength: Critical to prevent overlay spalling during die service
- Thermal fatigue resistance: Required to withstand repeated thermal cycling
The overlay alloys evaluated included:
| Overlay Alloy | Key Alloying Elements | Hardness (HV) | Application |
|---|---|---|---|
| Fe-Cr-C | Cr: 12–18, C: 2–4 | 700–900 | High abrasive wear |
| Fe-Cr-Mo | Cr: 8–12, Mo: 2–4 | 550–700 | Moderate wear, good toughness |
| Co-Cr-W | Co: 60–70, Cr: 15–20, W: 5–10 | 600–800 | High temperature wear |
| Ni-Cr-C | Ni: 60–70, Cr: 15–20, C: 2–4 | 650–850 | High temperature, corrosion |
Welding Parameters and Process Optimization
The welding parameters were optimized through a series of trial welds, with the goal of minimizing cracking, porosity, and dilution while ensuring adequate bond strength. The key process parameters for each die material are summarized below:
| Parameter | Cr12MoV | H13 | 5CrNiMo |
|---|---|---|---|
| Preheat temperature (°C) | 300–400 | 150–250 | 150–200 |
| Interpass temperature (°C) | 200–300 | 100–200 | 100–150 |
| GTAW current (A) | 60–100 | 80–130 | 80–130 |
| Travel speed (mm/min) | 100–200 | 150–300 | 150–300 |
| Shielding gas | Ar (99.99%) | Ar or Ar/CO2 | Ar or Ar/CO2 |
| Post-weld heat treatment | 600–650 °C × 2h | 550–600 °C × 2h | 550–600 °C × 2h |
The preheat temperature is the most critical parameter for Cr12MoV, where temperatures of 300–400 °C are required to reduce the cooling rate in the HAZ and minimize martensite formation. The post-weld heat treatment is essential for all three materials to relieve residual stresses, temper the HAZ martensite, and reduce the risk of delayed cracking.
Microstructure and Performance Evaluation
The microstructural analysis of the overlay layers and HAZ revealed several important observations:
- Overlay layer: The Fe-Cr-C overlay exhibited a ledeburitic structure with abundant cementite (Fe3C) particles in a martensitic matrix, providing excellent abrasive wear resistance. The Co-Cr-W overlay showed a cellular dendritic structure with carbide precipitation at cell boundaries, offering good hot hardness.
- Heat-affected zone: The HAZ of Cr12MoV exhibited a mixed microstructure of martensite, bainite, and retained austenite. The hardness in the HAZ was typically 600–700 HV, significantly higher than the base material, indicating the formation of hard, brittle martensite. The post-weld heat treatment reduced the HAZ hardness to 450–550 HV, improving toughness.
- Fusion boundary: The fusion boundary between the overlay and the base material was examined for lack of fusion, cracking, and intermetallic compound formation. No intermetallic compounds were observed at the fusion boundary for the Fe-based overlays, but the Co-Cr-W overlay showed a thin layer of Co-Cr intermetallics at the fusion boundary, which slightly reduced bond strength.
Defect Analysis and Countermeasures
| Defect Type | Root Cause | Detection Method | Countermeasure |
|---|---|---|---|
| HAZ cracking | High CE, rapid cooling | MT, RT | Increase preheat, reduce heat input |
| Overlay porosity | Gas pickup, poor shielding | RT, UT | Improve shielding gas coverage, reduce travel speed |
| Overlay spalling | Insufficient bond strength, thermal fatigue | Visual, MT | Optimize welding parameters, post-weld heat treatment |
| Dilution-induced softening | Excessive base metal dilution | Hardness testing | Use lower heat input, multiple thin passes |
| Residual stress-induced distortion | Uneven thermal expansion | Strain gauges | Symmetric welding sequence, stress relief treatment |
Study Insights and Practical Implications
This research provides practical guidance for the overlay welding of crankshaft die materials, with particular emphasis on the challenges posed by high-carbon die steels such as Cr12MoV. The key lessons for practicing engineers are: (1) preheating is non-negotiable for Cr12MoV overlay welding—temperatures below 300 °C are insufficient to prevent HAZ cracking; (2) the selection of overlay alloy must be matched to the specific service conditions—Fe-Cr-C overlays are optimal for abrasive wear at room temperature, while Co-Cr-W overlays are preferred for high-temperature applications; (3) post-weld heat treatment is essential for all die materials to relieve residual stresses and temper the HAZ martensite; (4) the bond strength of the overlay must be verified through bend testing or shear testing, particularly for Co-based overlays where intermetallic compound formation can reduce bond strength. The research also highlights the importance of systematic process qualification—each combination of base material, overlay material, and welding parameters must be individually qualified through trial welds and performance testing before production application.