| 1. |
|
|
| 2. |
|
|
| 3. |
|
|
| 4. |
|
|
| 5. |
|
|
| 6. |
- Temmel, Cornelius, 1973
(författare)
-
Fatigue Anisotropy in Forged Components
- 2007
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ever-growing requirements on combustion engine efficiency of motor vehicles demand increasing service loads in powertrain components. Optimization of component material is therefore inevitable. A major detriment with many forged transmission components is their anisotropic mechanical behavior, not least during cyclic loading. Any forging operation will introduce material flow and therewith orientation into the material. With the bulk material also non-metallic inclusions will be deformed. This orientation of the microstructure is held responsible for mechanical anisotropy.Manganese sulfides (MnS) in engineering steel are indigenous non-metallic inclusions which appear according to chemical specifications. These sulfides may generate benefits during component machining and are therefore widely accepted. Microstructural investigations on several materials showed that manganese sulfides deform excessively during any hot deformation operation of the steel. However, by solid solution hardening of the sulfides with calcium (Ca), original inclusion shapes can be maintained throughout a deformation operation.The present investigation is concerned with the examination of the influence of deformed MnS inclusions on fatigue anisotropy. Experimental as well as commercial medium carbon steels with standard and low sulfur (S) contents and therewith different sulfide populations have been hot deformed. Hardened test specimens of those steels, taken in short-transverse and longitudinal directions with respect to the deformation direction, were then fatigue tested. For material with standard S content, fatigue limits in longitudinal test direction are generally twice as high as in short transverse direction. Fractographic investigations showed that fatigue crack initiation is dominated by sulfide inclusions which ultimately can be held responsible for material anisotropy. The very poor fatigue resistance in short transverse direction can be attributed to the appearance of clustered sulfides, where the geometry of such clusters is not accessible by any established metallographic procedure. Diminishing of sulfide inclusions did improve isotropy. Yet, the most powerful measure to increase isotropy of the material proved to be an additional Ca treatment of the sulfides. Thus, quasi isotropic material could be created.In-situ tensile testing in a scanning electron microscope chamber showed that manganese sulfides bond very poorly to the steel matrix. Manganese sulfides in a steel matrix should therefore be seen as inherent micro-cracks. The nature of discoid sulfides being micro-cracks matters also during material hardening where current production material shows a considerably higher quench crack propensity as compared with low S material. Quench cracks initiate at flattened sulfides.Machinability of low S material did not show to be problematic at high cutting speeds. It is believed that an optimization of cutting parameters can balance the disadvantages of low S material during machining operations with low cutting speeds.
|
|
| 7. |
|
|
| 8. |
|
|
| 9. |
- Temmel, Cornelius, 1973, et al.
(författare)
-
Fatigue Isotropy in Cross-Rolled, Hardened Isotropic-Quality Steel
- 2008
-
Ingår i: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science. - : Springer Science and Business Media LLC. - 1073-5623. ; 39A:5, s. 1132-1144
-
Tidskriftsartikel (refereegranskat)abstract
- Deformation and forging operations often introduce microstructural orientation and, therewith, mechanical anisotropy to steel. Flattened manganese sulfide inclusions are held responsible for a great part of fatigue anisotropy. Isotropic-quality (IQ) steel maintains the mechanical isotropy of the material, even after a deformation operation. Isotropic material generally contains little S and, therewith, few manganese sulfides. Further, the IQ steels used in this investigation were Ca treated. The Ca treatment improves the shape stability of the sulfides, even during a hot-working deformation. Two commercial materials were compared for their fatigue response, a standard medium-carbon steel with 0.04 wt pct S and a low-sulfur variant that underwent IQ treatment. The two batches were cross-rolled to plates with a deformation ratio of 4.5, leading to in-plane isotropy. Tension-compression fatigue testing was performed in longitudinal and short transversal directions relative to the rolling plane. The results showed strong anisotropy of the fatigue behavior for the standard material. The performance in the short transverse direction, with the principal stress perpendicular to the flattened inclusions, was inferior. The IQ material with nearly spherical inclusions was almost perfectly isotropic, with only slightly worse fatigue response in the short transverse direction. © The Minerals, Metals & Materials Society and ASM International 2008.
|
|
| 10. |
- Temmel, Cornelius, 1973, et al.
(författare)
-
Investigation on Manganese Sulfide Inclusion Sizes in 50CrMo4 Steels by means of Fractography, Micrograph Analysis and Immersion Ultrasound
- 2009
-
Ingår i: Praktische Metallographie/Practical Metallography. - : Walter de Gruyter GmbH. - 0032-678X. ; 46:3, s. 123-136
-
Tidskriftsartikel (refereegranskat)abstract
- Increasing loads in powertrain components have put manganese sulfide inclusions in the spotlight of engineers. The indigenous sulfides are accounted responsible for the poor fatigue performance of highly loaded steel parts. In order to relate fatigue performance to manganese sulfide inclusion size, an accurate geometrical description of the sulfides is necessary. Fatigue testing generally reveals maximum inclusion sizes, since the largest inclusions will initiate fatigue failure. Micrograph analysis and immersion ultrasonic testing have been carried out in order to compare those methods with the referenced values of fatigue testing. It showed that immersion ultrasound is not capable of detecting manganese sulfide inclusions of the present sizes. Micrograph analysis, however, is applicable, if analysis data is modified subjectively.
|
|
