Initially widely used in the aerospace industry, AISI 4330 grade steel also found applications in critical equipment in the oil and gas industry. Its increased nickel content compared to low alloyed steel grades gives it very good mechanical properties as well as better resistance to corrosion. However, temperature formability can be modified by such adding and hot cracking problems occur frequently after ingot mold casting followed by open die forging and several conditioning steps. The identified cases of cracking appear mainly during cooling after hot forging. The first investigations exclude the second phases as being responsible for the hot cracking of ingots of steels as it has been reported by many studies. However, it appears that the chemical composition of steel can greatly influence its mechanical behavior during deformation. However, the occurrence of cracks during cooling after steel forging indicates therefore that the cracking mechanisms are due to thermomechanical process. Nevertheless, the literature contains little information on the hot mechanical properties of AISI 4330 steel, as well as the influence of nickel on open die forging and on dynamic mechanisms occurring during deformation. Therefore, the main objectives of this study are interconnected:
- Identify the mechanical response to thermodynamic forging of AISI 4330 steel.
- Characterize the influence of nickel on its mechanical behavior.
- Identify the root cause (s) of cracking of AISI 4330 steel during its open die forging.
Based on data from the industrial partner, it was possible to recreate the forging conditions of the steel by hot compression tests carried out on Gleeble-3800. The results of these simulations allow to determine constitutive equations of AISI 4330 steel grade, and therefore to deduce its softening equations and workability using several physical models widely used in the literature for similar steels. Comparative studies let to identify the influence of nickel on several parameters related to forging and the dynamic mechanics that occur during hot deformation. From these data could be extracted information about the phenomenon of hot cracking of AISI 4330 steel.
| Date | 10 Feb 2020 |
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| Original language | French |
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| Awarding Institution | - École de technologie supérieure
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| Supervisor | Mohammad Jahazi (Supervisor) |
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Bitterlin, M. (Author),
Jahazi (Supervisor),
10 Feb 2020Student thesis: Doctoral thesis › Doctorate in Engineering: Engineering