| 1. |
- Rehan, Arbab
(författare)
-
Effect of heat treatment on microstructure and mechanical properties of a 5 wt.% Cr cold work tool steel
- 2019
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This work presents investigations related to phase transformations occurring inthe 5 wt.% Cr cold work tool steel Caldie during hardening and tempering treatments. The influence of austenitisation temperature, cooling rate, sub-zero cooling, isothermal treatment during cooling, tempering temperature and holding time on the microstructure and mechanical properties were investigated.The hardened microstructure of the investigated steel consisted of a mixture ofplate and lath martensite, minor amounts of bainite, blocky and thin retained austenite and M7C3 carbides. Increasing austenitisation temperature from 1020°Cto 1050°C was found useful as it provided higher hardness, good compressive strength and sufficient toughness. However, a further increase to 1075°C resulted in large prior austenite grains which produced coarse martensite containing somewhat increased carbon content. This was found to reduce the impacttoughness of the steel. Significant amounts of retained austenite were present after tempering for 2x2 h between 200°C and 500°C while tempering at 525°C or higher, reduced retained austenite content to below 2%. During holding at tempering temperature carbides precipitated in martensite and possibly in retained austenite. The retained austenite was thereby destabilised and transformed to martensite on cooling. This fresh martensite was tempered by following tempering treatments. It was concluded that tempering at 525°C for 2x2 h was suitable to achieve a good combination of hardness, compressive strength and impact toughness. Retained austenite was also found to transform during holding at 600°C for longer times. Initially, carbides formed in the austenite and after some time transformation of retained austenite to ferrite and carbides took place. Results were used to discuss alternative heat treatment procedures for the 5wt.% Cr cold work tool steel Caldie and some changes of current heat treatment recommendations were suggested.
|
|
| 2. |
- Steffenburg-Nordenström, Joachim, 1962-
(författare)
-
Process chain simulation of forming, welding and heat treatment of Alloy 718
- 2017
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Manufacturing of aero engine components requires attention to residual stress and final shape of the product in order to meet high quality product standards.This sets very high demands on involved manufacturing steps to meet design requirements. Simulation of manufacturing processes can therefore be animportant tool to contribute to quality assurance.The focus in this work is on simulation of a manufacturing process chain comprising of sheet metal forming, welding and a stress relief heat treatment.Simulation of sheet metal forming can be used to design a forming tool design that accounts for the material behaviour, e.g. spring back, and avoid problems such as wrinkling, thinning and cracking. Moreover, the simulation can also show how the material is stretched and work hardened. The residual stresses after forming may be of local character or global depending on the shape that is formed. However, the heat affected zone due to welding is located near the weld.The weld also causes large residual stresses with the major component along the weld. It is found that the magnitude of the residual stresses after welding is affected by remaining stresses from the previous sheet metal forming. The final stress relieve treatment will relax these residual stresses caused by e.g. forming and welding. However, this causes additional deformations.The main focus of this study is on how a manufacturing process step affects the subsequent step when manufacturing a component of the nickel-based super alloy 718. The chosen route and geometry is a simplified leading edge of an exhaust case guide vane. The simulations were validated versus experiments. The computed deformations were compared with measurements after each manufacturing step. The overall agreement between experiments and measurement was good. However, not sufficiently accurate considering the required tolerance of the component. It was found from simulations that the residual stresses after each process affects the subsequent step. After a complete manufacturing process chain which ends with a stress relief heat treatment the residual stresses were not negligible. VIII Special experiments were performed for studying the stress relief in order to understand how the stresses evolve through the heat treatment cycle during relaxation. It was found that the stresses were reduced already during the beginning of the heating up sequence due to decreasing Young´s modulus and yield stress with increasing temperature. Relaxation due to creep starts when a certain temperature was reached which gave a permanent stress relief.
|
|
| 3. |
- Öberg, Anna, 1979, et al.
(författare)
-
The Influence of Correct Transfer of Weld Information on Production Cost
- 2012
-
Ingår i: 5th Swedish Production Symposium 2012, SPS12. - Linköping. - 9789175197524 ; , s. 295-302
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This study aims at identifying the causes for deviations between actual and theoretical weld weight. Previous performed studies have shown examples of up to 40% extra weld consumables used in some cases. One consequence is of course higher production cost but it can also give increased weight leading to higher fuel consumption and decreased payload. An interesting aspect is that generous margins on specific production measures dilute important feedback of process variation information preventing and prolonging structural root cause analysis.The causes for the observed deviations can heritage from several areas, both technical and within the information handling. The investigation shows that single components of the information structure and system, such as unsuitable demands as well as incapable evaluation methods, significantly influences the reliability of the entire manufacturing process. The common factor concerning when problems occur, seems to be the ability of correct information transfer between different functions in the organisation preventing the mismatch to appear in the interface. Suggestions for improving this situation include cross functional agreements as well as new measuring methods.
|
|
| 4. |
- Andersson, Jörgen, 1973, et al.
(författare)
-
Microstructure development during tempering of the hot-work tool steel Uddeholm QRO 90 Supreme
- 2009
-
Ingår i: Proc. 8th Int Tooling Conf., Eds. P Beiss, C Broeckmann, S Franke and B Keysselitz, RWTH Aachen Univ, Aachen, Germany. - 3861307006 ; II, s. 611-623
-
Konferensbidrag (refereegranskat)
|
|
| 5. |
- Andersson, Oscar
(författare)
-
Process planning of resistance spot welding
- 2013
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Manufacturing engineering in general has experienced an increased demand of process planning in order to optimize processes to reduce costs, environmental impact and increase time efficiency. Resistance spot welding (RSW) is a common and large-scale joining method in several manufacturing industries indicating significant potentials of efficient process planning.The goal of this thesis is to establish new knowledge for updated and improved process planning of RSW in industrial applications. The goal is expressed by two research questions targeting the issues of process variations and potential of numerical methods of the RSW process. The research questions are expressed in terms of weld size, which is the main interest in RSW process planning.As any large-scale manufacturing process, RSW involves variations in results – the weld size is known to vary, both as a result of intentional dependent parameters such as process parameters and as a result of unintentional variations in welding conditions. A series of physical and numerical analysis have been performed in order to gain knowledge of such variations.The unintentional variations, which result in varying weld sizes in apparently identical conditions, were analyzed through both controlled laboratory welding and welding in industrial production environments. The results of the analysis showed the magnitude of standard deviations in both environments and the distribution of weld sizes. The analysis showed that common standard deviations in controlled laboratories and industrial production are approximately 0.3 mm and 0.9 mm, respectively and that weld sizes are distributed showed promising fit to both Normal and Weibull distributions.The intentional variations of weld sizes due to process parameters, which is the most important aspect of RSW process planning, have traditionally been analyzed through physical testing. In the present thesis two numerical methods were evaluated; regression analysis and FE simulations. For the regression analysis several models were generated and showed a standard deviation of residuals between model and physical results of 0.5 mm. For the FE simulations, material models for the RSW were generated and the simulations showed a standard deviation compared to physical testing of 0.68 mm. In conclusion, the present thesis presents results, which help quantify variations in weld sizes and present the capability of numerical methods of the RSW process.
|
|
| 6. |
- Azar, Amin S., et al.
(författare)
-
Effect of crystal orientation and texture on fatigue crack evolution in high strength steel welds
- 2015
-
Ingår i: International Journal of Fatigue. - : Elsevier BV. - 0142-1123 .- 1879-3452. ; 77, s. 95-104
-
Tidskriftsartikel (refereegranskat)abstract
- In the present study, electron backscattered diffraction is used to analyze the fatigue crack evolution in a high strength steel weld that was loaded cyclically in the plastic regime. Three prominent regions of a fatigue crack are investigated separately: crack tip, crack trajectory and crack initiation. Taylor and Schmid factors are mapped with respect to the defined loading matrix. Possible effective mechanisms are proposed based on the local plasticity properties like lattice rotation and misorientation. The analyses of the crack tip and trajectory regions show that although the critical resolved shear stresses in some regions are low, small deformation resistance of these regions can compromise the dislocation immobility and cause local fracture. It is shown that if the crack grows transgranularly, at least one side of the crack may show low lattice rotation or strain equivalent values, which indicates the relaxation of elastic stresses after fracture. The crack initiation is determined to be dominantly controlled by transcrystalline mechanism of initiation that takes place under plastic loading conditions. It is also shown that the secondary < 123 >11 (1) over bar type of slip systems were the most activated under such loading conditions. (C) 2015 Elsevier Ltd. All rights reserved.
|
|
| 7. |
|
|
| 8. |
|
|
| 9. |
|
|
| 10. |
- Dalaei, Kamellia, 1975, et al.
(författare)
-
Stability of Residual stresses Created by Shot Peening of Pearlitic Steel and Their Influence on Fatigue Behaviour
- 2010
-
Ingår i: 10th International Fatigue Congress, FATIGUE 2010; Prague; Czech Republic; 6 June 2010 through 11 June 2010. - : Elsevier BV. - 1877-7058. ; 2:2, s. 613-622
-
Konferensbidrag (refereegranskat)abstract
- In this study the effect of shot peening on the fatigue lifetime of a near pearlitic microalloyed steel was investigated. The fatigue tests were run in strain control with parallel recording of stress relaxation and recovery of the work hardened surface zone at different total strain amplitudes exerted to the test specimens. These relaxation processes were followed versus cycle number up to half of the fatigue life time (N=Nf/2). Provided that the global plastic strain amplitude is lower than about 0.08 % a noticeable increase in life time is seen. Lower plastic strain amplitude increases the life time. At small plastic strain amplitudes it was found that the fatigue life time could be increased more than tenfold by the shot peening process.
|
|
