Meeting with Stefano on stress relieving for Ti and SS parts

Wednesday 9 Jul 2025, 15:00 → 16:00 Europe/Zurich

Participants: Nicholas Lusa, Nicolas Peray, José Ferradas and Stefano Sgobba in meeting room of building 112 (2nd floor).

Topic: Stress relieving treatment for stainless steel 304L and titanium grade 5 (materials used for BOND coil components and reaction mold)

Stainless steel:

• The best solution would be to use 316LN because it keeps high mechanical properties at high temperature but it is very expensive and more difficult to machine
• The final choice is to adopt 304L because it is cheaper and already widely used to the manufacturing of other mould (11T impregnation mold, MQXFA reaction and impregnation molds, etc...) 
• The preferred option is to perform vacuum firing of the material at 900-950°C for 2 hours to release internal stress (vacuum level 10^-5/10^-6). Otherwise, it would be possible to perform the same heat treatment in air atmosphere but this would induce the formation of oxydes on the surface and would require a deeper machining after heaqt treatment (not the preferred solution).

 

Titanium grade 5:

• Using raw material solution annealed preferably --> make sure that Pierre will check together with Stefano the material certificates of the raw material the company will procure for the machining of the parts 
• The asymmetry of the machining of the different parts will induce internal stresses. We need to remove them as much as possible if we want to have components with a stable geometry after RHT.
• Titanium grade 5 stress relieving cycle is between 480°C and 650°C for 1h to 4h (the higher the temperature the shorter the duration) under vacuum 10^-5-10^-6. It is very important to have a good vacuum to prevent as much as possible the oxyde formation. However, still oxydation problems may derive from the ratio surfacfe/volume. FOr this reason it is important to perform the heat treatment cycle before the finishing pass leaving around 1mm extra material everywhere.
• That being said the heat treatment foreseen for the titanium components is at 650°C for 1h under vacuum 10^-5/10^-6, before the finishing pass leaving enough extra material to remove the oxydes on the surface and brings the parts to the final geometry according to the related drawing.
• During the reaction heat treatment of the coils, it is preferable to have a flow of Argon that can bring outside the sarcophagus the pollutants and the organic gasses so to lower the oxydation of the titanium.

 

The choice of using stainless steel 416 was discussed, as this alloy was studied by US collegues from LBNL. Stefano's advice is that this tyoe of stainless steel is not a good choice for the RHT mold because it is a ferritic-martensitic steel and during the heat treatment phase changes occur leading to sensibilitation of the steel (the precipitation of carbides at grain boundaries), causing a decrease of the resilience. In addition, the martensitic phase would experience unpredictable volumetric change during the heat treatment.

15:00 → 15:20 Discussion with Stefano

Speakers: Jose Ferradas Troitino (CERN), Nicholas Lusa (CERN), Nicolas Peray

Participants: Nicholas Lusa, Nicolas Peray, José Ferradas and Stefano Sgobba in meeting room of building 112 (2nd floor).

Topic: Stress relieving treatment for stainless steel 304L and titanium grade 5 (materials used for BOND coil components and reaction mold)

Stainless steel:

• The best solution would be to use 316LN because it keeps high mechanical properties at high temperature but it is very expensive and more difficult to machine
• The final choice is to adopt 304L because it is cheaper and already widely used to the manufacturing of other mould (11T impregnation mold, MQXFA reaction and impregnation molds, etc...) 
• The preferred option is to perform vacuum firing of the material at 900-950°C for 2 hours to release internal stress (vacuum level 10^-5/10^-6). Otherwise, it would be possible to perform the same heat treatment in air atmosphere but this would induce the formation of oxydes on the surface and would require a deeper machining after heaqt treatment (not the preferred solution).

 

Titanium grade 5:

• Using raw material solution annealed preferably --> make sure that Pierre will check together with Stefano the material certificates of the raw material the company will procure for the machining of the parts 
• The asymmetry of the machining of the different parts will induce internal stresses. We need to remove them as much as possible if we want to have components with a stable geometry after RHT.
• Titanium grade 5 stress relieving cycle is between 480°C and 650°C for 1h to 4h (the higher the temperature the shorter the duration) under vacuum 10^-5-10^-6. It is very important to have a good vacuum to prevent as much as possible the oxyde formation. However, still oxydation problems may derive from the ratio surfacfe/volume. FOr this reason it is important to perform the heat treatment cycle before the finishing pass leaving around 1mm extra material everywhere.
• That being said the heat treatment foreseen for the titanium components is at 650°C for 1h under vacuum 10^-5/10^-6, before the finishing pass leaving enough extra material to remove the oxydes on the surface and brings the parts to the final geometry according to the related drawing.
• During the reaction heat treatment of the coils, it is preferable to have a flow of Argon that can bring outside the sarcophagus the pollutants and the organic gasses so to lower the oxydation of the titanium.

 

The choice of using stainless steel 416 was discussed, as this alloy was studied by US collegues from LBNL. Stefano's advice is that this tyoe of stainless steel is not a good choice for the RHT mold because it is a ferritic-martensitic steel and during the heat treatment phase changes occur leading to sensibilitation of the steel (the precipitation of carbides at grain boundaries), causing a decrease of the resilience. In addition, the martensitic phase would experience unpredictable volumetric change during the heat treatment.