feajob
Aerospace
- Aug 19, 2003
- 161
Hello Everyone,
I'm reaching out for your input. My background is in fatigue life assessments, not materials engineering, so I'd value your thoughts on these statements:
Risks Associated with Machining Pre-Hardened PH13-8Mo:
Do you agree with the above statements? If not, please provide details so I can improve my understanding.
Thank you,
Ali
I'm reaching out for your input. My background is in fatigue life assessments, not materials engineering, so I'd value your thoughts on these statements:
Risks Associated with Machining Pre-Hardened PH13-8Mo:
- Increased Residual Stresses:
- Machining hardened material generates higher cutting forces and heat, leading to significant residual stresses. These stresses can be tensile, potentially initiating or propagating cracks, especially in fatigue-sensitive applications.
- These residual stresses can also lead to distortion during subsequent heat treatments (if any) or in service.
- Reduced Fatigue Life:
- The combination of residual stresses and the inherent stress concentrations from machining operations can significantly reduce fatigue life.
- The surface integrity, critical for fatigue performance, can be compromised by the higher machining forces.
- Increased Risk of Cracking:
- PH13-8Mo, while strong, can be susceptible to cracking if machined aggressively in the hardened state.
- Existing microcracks or imperfections can propagate more readily under the higher stresses induced by machining.
- Difficulty in Achieving Tight Tolerances:
- Hardened materials are more difficult to machine accurately.
- This can make it challenging to achieve tight tolerances and surface finishes, potentially affecting the functional performance of the part.
- Springback is also a much larger issue.
- Tool Wear and Breakage:
- Machining hardened steel results in significantly higher tool wear and an increased risk of tool breakage. This leads to increased costs and potential surface damage to the workpiece.
- Heat Generation:
- Excessive heat build up during machining can alter the material properties of the steel, and create unwanted localized hardness changes.
- Stress Corrosion Cracking (SCC) Potential:
- Residual stresses can increase the susceptibility of PH13-8Mo to stress corrosion cracking in corrosive environments.
- Solution annealing softens the material, making it much easier to machine.
- It minimizes residual stresses, reducing the risk of distortion and cracking.
- It allows for better control of tolerances and surface finishes.
- The final heat treatment after machining provides the desired strength and hardness without the detrimental effects of machining in the hardened state.
Do you agree with the above statements? If not, please provide details so I can improve my understanding.
Thank you,
Ali