| 1. |
- Hoseiny, Seyyed Mohammad Hamed, 1980, et al.
(författare)
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Machinability evaluation of pre-hardened plastic mould steels
- 2012
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Ingår i: International Journal of Machining and Machinability of Materials. - 1748-5711 .- 1748-572X. ; 11:4, s. 327-341
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Tidskriftsartikel (refereegranskat)abstract
- There are multiple demands placed upon plastic mould steels, depending on the application they will have. Among these requirements, machinability has generally a great economic importance in mould steels and in pre-hardened mould steels in particular. The machining cost can exceed more than half of the cost of a mould. Nevertheless, to avoid subsequent heat treatment, distortion and dimensional inaccuracy, there has been the tendency to use even higher hardness in the pre-hardened mould steels, a hardness range of 38-40 HRC instead of 30-32 HRC. In this work, machinability of some of the most popular grades of pre-hardened plastic mould steel at 38-40 HRC is compared in two milling and two drilling operations. The materials have shown very different properties in different machining operations. This, beside the high requirements upon the plastic mould steels, such as polishability, hardness, impact toughness etc. makes it very complicated to improve these types of steels to be superior in all mould applications.
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| 2. |
- Hoseiny, Seyyed Mohammad Hamed, 1980, et al.
(författare)
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Machinability evaluation of prehardened plastic moulding steels
- 2008
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Ingår i: Proceedings of the Swedish Production Symposium (SPS) - 2008.
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Konferensbidrag (refereegranskat)abstract
- There are multiple demands placed upon plastic mould steels, depending on the application they will have. Among these requirements, machinability is of great economic importance. Mould steel influences the cost of plastic parts more through its machinability, since machining cost exceeds more than half of the cost of a mould. Milling and drilling are the machining operations that are mostly used in production of a mould and the highest volume of material removal performs through these two categories of operations and specially milling. Recently, there has been a high tendency to use prehardened mould steels with the hardness range of 38-40 HRC, for the higher demands on mechanical properties and wear resistance. Additionally, to avoid distortion and dimensional inaccuracy, the mould steels are supplied in prehardened condition which impairs their machinability. In this work, machinability of some of the most popular grades of prehardened plastic mould steels is compared in two milling and two drilling operations. The materials have shown very different properties in different machining operations. This, beside the high requirements upon the plastic mould steels, such as polishability and hardness, impact toughness and etc. makes it very complicated to improve these types of steels to be superior in all mould applications in addition to that material selection becomes crucial with respect to mould making cost.
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| 3. |
- Hoseiny, Seyyed Mohammad Hamed, 1980, et al.
(författare)
-
The effect of the martensitic packet size on the machinability of modified AISI P20 prehardened mold steel
- 2012
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Ingår i: Journal of Materials Science. - : Springer Science and Business Media LLC. - 0022-2461 .- 1573-4803. ; 47:8, s. 3613-3620
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Tidskriftsartikel (refereegranskat)abstract
- The effect of martensitic packet size on the machinability of prehardened mold steel at a hardness of similar to 40 HRC (typical hardness for prehardened mold steels) was studied in terms of cutting force and tool life. The machinability tests were performed in end milling using coated, cemented carbide tools at three different cutting speeds. The results showed that an increase in the martensite packet size led to higher cutting force and shorter tool life. The increase in cutting force was related to the increase of work hardening. The work material with a coarser martensite packet size showed a higher amount of work hardening that can explain the higher cutting force. The longer tool life in the workpieces with finer structure was correlated to smaller amplitude of the variation in cutting force.
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| 4. |
- Hoseiny, Seyyed Mohammad Hamed, 1980, et al.
(författare)
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The Influence of Heat Treatment on the Microstructure and Machinability of a Prehardened Mold Steel
- 2015
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Ingår i: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science. - : Springer Science and Business Media LLC. - 1073-5623. ; 46A:5, s. 2157-2171
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Tidskriftsartikel (refereegranskat)abstract
- The machinability performance of a modified AISI P20 steel, heat treated to have the same hardness but three different microstructures, lower bainite, tempered martensite, and primary spheroidized carbides in a tempered martensite matrix, was studied. The microstructures were characterized using light optical and scanning electron microscopy and X-ray diffraction, and mechanical properties were compared by means of tensile and Charpy V-notch impact tests. The influence of microstructure and the resultant mechanical properties on machinability was studied in the context of single tooth end milling operation. The results showed that the material containing primary spheroidized carbides exhibited a superior machinability at the expense of a marginal loss of tensile strength and impact toughness, with comparable yield strength to that of the material containing tempered martensite. By contrast, the material with bainitic mi- crostructure showed the lowest yield strength and the poorest machinability performance while having the highest uniform elongation.
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| 5. |
- Rehan, Arbab, et al.
(författare)
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Effect of Austenitization and Tempering on the Microstructure and Mechanical Properties of a 5 wt% Cr Cold Work Tool Steel
- 2016
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Ingår i: Steel Research International. - : Wiley. - 1611-3683 .- 1869-344X. ; 12:1 December, s. 1609-1618
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Tidskriftsartikel (refereegranskat)abstract
- The effects of austenitization and tempering temperatures for a 5 wt% Cr cold work tool steel are studied with an aim of understanding the influence on microstructure and mechanical properties. Microstructures are characterized with scanning electron microscopy and light optical microscopy. Retained austenite contents and martensite start temperatures are measured by X-ray diffraction and dilatometry, respectively. Hardness, impact toughness, and compressive yield strength are also determined. When the austenitization temperature is increased from 1020 or 1050 to 1075 °C, followed by tempering at 525 °C, significant hardness is gained while there is no increase in compressive yield strength. Higher austenitization temperatures also produce larger amounts of retained austenite. At the same time, the impact toughness is reduced due to coarsening of the martensitic microstructure. When the steel is tempered at 200 °C, a higher impact toughness and a higher volume fraction of retained austenite are observed. Retained austenite is not found after tempering at temperatures of 525 °C or above. It is concluded that the best combination of mechanical properties is achieved by austenitization at 1020 or 1050 °C followed by tempering at 525 °C.
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| 6. |
- Rehan, Arbab
(författare)
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Effect of heat treatment on microstructure and mechanical properties of a 5 wt.% Cr cold work tool steel
- 2019
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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.
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| 7. |
- Rehan, M. Arbab, et al.
(författare)
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EBSD Analysis of Blocky Structures in Hardened and Tempered Microstructures of a 5 wt.% Cr Cold Work Tool Steel
- 2021
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Ingår i: Metallography, Microstructure, and Analysis. - : Springer Science and Business Media LLC. - 2192-9270 .- 2192-9262. ; 10:6, s. 862-875
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Tidskriftsartikel (refereegranskat)abstract
- The hardened microstructure of 5 wt.% Cr cold work tool steels is mainly martensitic with significant amount of retained austenite and some undissolved carbides. Whereas the microstructure after tempering shows significant amounts of angular shaped blocky regions, which are interpretated as retained austenite or fresh martensite. The distinction between the phases is difficult due to the morphological similarities. Therefore, the blocky regions are characterized by electron backscatter diffraction to better understand the microstructures. The results showed that the characterisation of blocky structures in the microstructure of a 5 wt.% Cr cold work tool steels varied according to the austenitisation and tempering temperatures as well as the holding time at the tempering temperature. Electron backscatter diffraction of as-quenched microstructures revealed that the blocky structures were either retained austenite, fresh martensite or a combination of large part of fresh martensite with minute amounts of retained austenite. The blocky structures were entirely retained austenite after tempering at 200 °C. Tempering at 525 °C, for holding times of 0.1 or 0.5 h, more blocky regions were retained austenite contrasting to the blocky regions for holding times of 1 or 2 h, which were largely fresh martensite. It was further concluded that electron backscatter diffraction is a suitable technique for characterisation of blocky structures provided that the specimens are prepared by electro-polishing while X-ray diffraction is best suited for a bulk measurement of retained austenite.
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| 8. |
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