Full text
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| Author(s): |
Adriano Mendanha
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Escola Politécnica (EP/BC) |
| Defense date: | 2004-08-23 |
| Examining board members: |
Helio Goldenstein;
Carlos Eduardo Pinedo;
Amilton Sinatora
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| Advisor: | Helio Goldenstein |
| Abstract | |
In this work the fracture resistance was evaluated by testing bars with different: diameters, directions, hardening and tempering treatments. Impact four point bending tests were used in round test specimen (both unnotched) and fracture toughness by the method Chevron Notch. It was verified that the distribution and M7C3 eutectic carbide size has effect on fracture resistance for the different methods used and these steels showed hard anisotropy, which depends on the principal directions of mechanical working. The treatments practice showed different results in the test studied. Under impact and fracture toughness in test specimens, the heat treatment with hardening at 1000°C and tempering at 220°C (T1) exhibits more efficient than the hardening at 1080°C and tempering at 540°C (T2) . These results were related to the retained austenite content after hardening (In T2 decreases 15% to 3,9%). The secondary hardening effect and carbide precipitation of the alloying elements result of the increase in T2. Under bending no advantages was verified. In this case, retained austenite didn\'t act or was insufficiently positive. In the bending test using austenization temperatures at: 1020, 1040, 1060 and 1080°C (30 min./oil) with tempered at 540°C (2 x 2h/air). The results showed that the maximum value for the bending strength was obtained after austenitization at 1040°C. The lower toughness values found for 1020, 1060 and 1080°C were discussed in termsof the retained austenite content and secondary hardening effect. The fracture toughness results for Chevron Notch direction L/R (longitudinal/radial) in the test T1 showed increase toughness when compared to direction R/L (radial/longitudinal) with the same thermal treatment in T2 no advantages was verified in toughness and directions. ) The results showed that the toughness decreases with the increase of the bar diameter. The impact test showed better results to the fracture resistance treatment independently. The bending test showed better results in the L/R direction too. (AU) | |