| 1. |
- Claesson, Åsa, et al.
(författare)
-
lntegrated Optical Fiber Sensors in Additive Manufactured Metal Components for Smart Manufacturing Applications
- 2019
-
Ingår i: Smart Systems Integration; 13th International Conference and Exhibition on Integration Issues of Miniaturized Systems.
-
Konferensbidrag (refereegranskat)abstract
- This work combines fiber optic sensors with additive manufacturing to enable integration of temperature and strain sensors in metal components. In this paper, we present a fiber optic sensor network integrated in press hardening tools to monitor the contact between the tool and the metal sheet during forming operation. The tools are manufactured through metal powder bed fusion using laser melting processes (PBF-SLM), after which the tools are prepared for sensor integration. A demonstrator press hardening tool with integrated fiber optic sensors was heated using an electric heat foil and the sensor measurements was compared to a thermal simulation model. The sensor technology is based on Fiber Bragg Gratings (FBGs), integrated at several positions along the optical fiber. FBGs are in-fiber sensors that are multiplexed. lt is possible to place hundreds of FBG sensors along one single fiber, thus allowing for quasidistributed sensing of temperature or strain. The optical fiber itself can be less than 100 micrometer in diameter, allowing for sensing at several points in a minimally invasive way, when integrated in a tool or component.
|
|
| 2. |
- Hatami, Sepehr, 1981, et al.
(författare)
-
The Effect of Alloying on Sinter-Hardening Response of Astaloy Mo and Its Diffusion Bonded Derivatives
- 2010
-
Ingår i: World Powder Metallurgy Congress and Exhibition, World PM 2010; Florence; Italy; 10 October 2010 through 14 October 2010. - 9781899072194
-
Konferensbidrag (refereegranskat)abstract
- In this study, sinter-hardening response of different steel powders based on the Astaloy Mo grade (prealloyed with 1.5% Mo) is investigated. In order to understand the effect of alloying, Astaloy Mo was compared to its diffusion bonded derivatives; which are benefiting from an additional 2 wt.% copper (i.e. Distaloy DH) and 2 wt.% Ni (i.e. Distaloy DC). Tensile specimens of each alloy containing 0.55-0.7 wt.% admixed graphite were prepared. All specimens were sintered at 1120°C for 30 minutes and cooled at a rate of 2.5°C/s within the range of 800 to 300°C. Subsequently, the sinter-hardened specimens were stress relieved at 200°C for 60 minutes. Using X-Ray diffraction technique the residual stresses of all specimens were analyzed. In order to understand the relation between microstructure and the obtained mechanical properties, tensile testing and metallographic investigations were performed.
|
|
| 3. |
- Hryha, Eduard, 1980, et al.
(författare)
-
Control of delubrication process for PM components based on prealloyed steel powders
- 2012
-
Ingår i: Proceedings of the 2012 Powder Metallurgy World Congress & Exhibition, Powder Metallurgy Association and Japan Society of Powder and Powder Metallurgy,2013.
-
Konferensbidrag (refereegranskat)abstract
- Reliable in-situ monitoring system for the on-line control of the processing parameters during delubrication of PM steel compacts is presented. The monitoring system is build utilizing sensors (dew-point, CO2 and O2) commonly used in industry. Delubrication of PM steel compacts, based on Cr-alloyed steel powder, was monitored in a number of process gases (inert, reducing and oxygen containing atmospheres) of the different purity (wet and dry gases). Effects of temperature, holding time, heating rate, flow rate and component density were studied. Optimum conditions for efficient delubrication with minimum effect on PM compact properties at lowest processing cost were established. Based on the specimens analysis and gas monitoring profiles in the case of ethylenbisstearamide-based lubricants it is recommended to perform delubrication with low heating rate at temperature around 450°C in nitrogen atmosphere in order to facilitate efficient delubrication and avoid surface oxide during sintering. Rather low flow rate is needed – enough to provide even weak dynamic gas conditions around every component surface.
|
|
| 4. |
- Hryha, Eduard, 1980, et al.
(författare)
-
Delubrication of PM Components Based on Cr-Prealloyed Steel Powder – Chances and Risks
- 2011
-
Ingår i: Proc. of EURO PM2011 Congress & Exhibition, 9-12 October 2011, Barcelona, Spain. - 9781899072231 ; 3, s. 105-110
-
Konferensbidrag (refereegranskat)abstract
- Utilization of prealloyed powder grades for production of high-performance PM structural parts require reconsidering of specific stages of sintering process like debinding. Modern lubricants are complex organic compounds, decompositions of which leads to production of a number of species – from complex hydrocarbons to carbon oxides. Composition and amount of decomposition products are strongly determined by the temperature profile and processing atmosphere composition/purity. Uncontrolled delubrication process, especially in the case of the PM components containing elements with high-sensitivity to oxygen, can lead to considerable oxidation. Therefore, in-situ monitoring of the processing parameters during delubrication is presented utilizing commonly used in industry sensors (dew-point, CO2 and O2). Delubrication was monitored in a number of inert and reducing gases of the different purity. Based on the specimens analysis and gas monitoring profiles it is recommended to perform delubrication at the temperatures below 500°C in dry inert atmospheres in the case of ethylenbisstearamide-based lubricants.
|
|
| 5. |
- Hryha, Eduard, 1980, et al.
(författare)
-
Effect of active components of sintering atmosphere on reduction/oxidation processes during sintering of Cr-alloyed PM steels
- 2015
-
Ingår i: Journal of the American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 98:11, s. 3561-3568
-
Tidskriftsartikel (refereegranskat)abstract
- Water atomised steel particles are covered by heterogeneous surface oxide, formed by thin (~6 to 8 nm) iron oxide layer covering most of the powder surface, and particulate features formed by thermodynamically stable oxides containing e.g. Cr and Mn with surface coverage about 5%. Development of sufficiently strong inter-particle necks requires as minimum full removal of the iron surface oxide layer that can be achieved by gaseous reducing agents as CO and H2 as well as by carbon typically admixed in the form of graphite. The study evaluates the effect of concentration of reactive components of the sintering atmosphere, with special focus on carbon monoxide, on the reduction/oxidation and carburization/decarburization processes taking place during the whole sintering process. Results of the thermal analysis, SEM analysis of oxide characteristics, metallographic and chemical analysis of the sintered compacts were correlated with thermodynamic simulation of the oxide stability in applied sintering atmospheres. High oxidation potential of the CO-containing atmospheres in case of Cr-alloyed PM steels was detected during heating stage until ~1000 °C. Oxidation potential is linearly increasing with the increasing content of the carbon monoxide in the processing atmospheres and rather severe oxidation is observed if CO-content exceeds 1 vol.%.
|
|
| 6. |
- Jarfors, Anders E.W. 1963-, et al.
(författare)
-
On the Use of Conformal Cooling in High-Pressure Die-Casting and Semisolid Casting
- 2021
-
Ingår i: Technologies. - : MDPI. - 2227-7080. ; 9:2
-
Tidskriftsartikel (refereegranskat)abstract
- Today, tool life in high pressure die casting (HPDC) is of growing interest. A common agreement is that die life is primarily decided by the thermal load and temperature gradients in the die materials. Conformal cooling with the growth of additive manufacturing has raised interest as a means of extending die life. In the current paper, conformal cooling channels’ performance and effect on the thermal cycle in high-pressure die casting and rheocasting are investigated for conventional HPDC and semisolid processing. It was found that conformal cooling aids die temperature reduction, and the use of die spray may be reduced and support the die-life extension. For the die filling, the increased temperature was possibly counterproductive. Instead, it was found that the main focus for conformal cooling should be focused to manage temperature around the in-let bushing and possibly the runner system. Due to the possible higher inlet pressures for semisolid casting, particular benefits could be seen.
|
|
| 7. |
- Karamchedu, Seshendra, 1987, et al.
(författare)
-
Changes in the surface chemistry of chromium-alloyed powder metallurgical steel during delubrication and their impact on sintering
- 2015
-
Ingår i: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136. ; 223, s. 171-185
-
Tidskriftsartikel (refereegranskat)abstract
- Changes induced in the surface chemistry of metal powder during the delubrication stage affect the subsequent sintering process and hence the final properties of the sintered compacts. The different stages during delubrication were characterized by means of in situ visual observation of components made by compacting chromium-alloyed water-atomized steel powder with lubricant additions. A strong correlation is found between this visual observation of changes of the compact appearance during the delubrication and the component chemistry depicted via the monitoring of the exhaust gases composition (CO2, O-2 and H2O), thermogravimetric analysis, and changes in powder surface composition (X-ray photoelectron spectroscopy combined with scanning electron microscopy and energy dispersive X-ray analysis). The compacts were delubricated at different conditions and the effect of different parameters was studied, including temperature (300, 450 and 900 degrees C) and processing gas (N-2 or air). Delubricated compacts were further sintered at 1120 degrees C in N-2/3%H-2 mix to evaluate the effect of delubrication on the properties of the sintered components. The mechanical properties, chemistry and microstructure obtained after sintering show a strong relation to the surface changes induced during delubrication. The results indicate that delubrication at 450 degrees C in dry N-2 preserves the original surface condition of the powder and upon sintering the compacts exhibit optimum properties. Sintered compacts delubricated at 450 degrees C in air and at 900 degrees C in N-2 exhibited inferior properties. In the former case, this was related to the growth of Fe-oxide on the powder surfaces. In the latter case, the initial thin Fe-oxide layer, covering most of the powder surfaces, was reduced and oxygen made available was transferred into stable Cr-Mn-Si-rich oxide particles. Delubrication at 300 degrees C resulted in insufficient lubricant removal along with soot formation contributing to inferior mechanical properties after sintering as well. (C) 2015 Elsevier B.V. All rights reserved.
|
|
| 8. |
- Karamchedu, Seshendra, 1987
(författare)
-
Critical Aspects of Delubrication and Sintering of Chromium-alloyed Powder Metallurgy Steels
- 2015
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The cost efficiency and performance of Powder Metallurgy (PM) steels can be improved by replacing conventionally used alloying elements such as copper and nickel with chromium. Utilizing chromium imposes a challenge in terms of processing due to its effect on powder compressibility and high oxygen affinity, the latter of which, to a certain extent, is dealt with by introducing chromium in prealloyed form that decreases its activity. Therefore, each stage in the PM processing route has to be reconsidered to satisfy the thermodynamic and kinetic requirements to appropriately sinter components based on chromium alloyed steel powder for manufacturing high-performance PM parts. For conventional PM steels, consolidation is typically achieved by compaction, where the final dimensions of the part are achieved, followed by sintering, where metallurgical bonding between the powder particles takes place. To facilitate compaction, powder is mixed with lubricant, which also improves the tool life; but the lubricant has to be removed prior to sintering. Among the problems encountered during sintering, those concerning delubrication are frequent but are difficult to detect. In the present study, a reliable approach for in-situ monitoring of the delubrication of PM steel compacts is presented. The method is based on continuous monitoring of the process atmosphere using sensors commonly used in the industry (CO2 and O2). Using this method, the effect of various process parameters on lubricant removal has been investigated and the changes occurring in the surface chemistry of the compacts during delubrication and their impact on sintering have been assessed. Based on these studies, delubrication at 450 °C in dry N2 with dynamic gas flow conditions around the sample and a low heating rate were proposed to be optimum for the delubrication of chromium-alloyed PM steels. Sintering of water-atomized chromium-alloyed powder compacts is typically performed in hydrogen-containing atmospheres with nitrogen as the carrier gas. However, attaining good carbon control in these atmospheres is challenging. Hence, the effect of different active constituents in the atmosphere, such as hydrogen, carbon monoxide and propane, on the reduction-oxidation and carburization-decarburization processes during the sintering of chromium-alloyed PM steels was investigated. It was shown that concentration of carbon monoxide above 1 vol.% in the sintering atmosphere results in significant oxidation of the compacts, whereas lower concentrations contribute to counteract the carbon loss and provide for the possibility of carburization during a continuous sintering process. Furthermore, lean atmospheres containing carbon monoxide, hydrogen and hydrocarbons as active constituents, with their total concentration not exceeding 5 vol. %, were shown to be potential candidates for sintering of chromium-alloyed PM steels, since they provide carburization while confining oxidation to acceptable levels.
|
|
| 9. |
- Karamchedu, Seshendra, 1987
(författare)
-
Delubrication of Chromium Prealloyed Powder Metallurgy Steels
- 2013
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Consolidation of steel components produced by means of powder metallurgy (PM) is achieved typically through compaction and sintering. During consolidation, final dimensions of the part are already achieved after compaction, while sintering imparts strength to the components. Prior to the compaction stage, lubricants are added to the metal powder to reduce the inter-particle and die-wall friction during pressing and hence improve powder compressibility and ejection of the component from the compaction tool. These lubricants have to be safely removed after compaction since they are source of oxygen and carbon that can negatively affect further sintering process as well as final performance of the sintered components. Lubricants commonly used for PM steels are based on ethylene bis-stearamide (EBS) and their removal is achieved through thermolysis in the initial zone of the sintering furnace. With increasing demands on the achievable densities and performance of PM components, lubricants and possible risks of improper delubrication have received interest. Among the problems encountered during sintering, those concerning delubrication are frequent but difficult to detect. Hence previous studies have aimed at improving the efficiency of lubricant removal and predicting the same. Delubrication being a complex process still poses problems in practice and its proper control requires a system which monitors the delubrication sequence and can be incorporated into a closed loop control.In the present work, a reliable approach for in-situ monitoring of delubrication of PM steel compacts is presented. The method is based on continuous monitoring of the processing atmosphere using sensors commonly used in the industry (CO2 and O2). It was demonstrated that the initial stages of lubricant removal can be monitored using the oxygen sensor based on zirconia ceramics and the later stages can be detected utilizing CO2 sensor based on infrared cell technology. Based on the established methodology, a systematic study on the effect of various process parameters on lubricant removal in the processing of chromium prealloyed PM steels has been conducted. Effect of temperature, holding time, heating rate, process gas composition (inert, reducing and oxygen containing atmospheres) and purity (wet and dry gases), flow rate and graphite addition was evaluated. Additionally, change in surface chemistry of the base powder occurring during delubrication and its effect on sintering have been studied using X-ray photoelectron spectroscopy and scanning electron microscopy combined with the energy dispersive X-ray analysis. Based on the experimental results it is recommended to perform delubrication at ~ 450 °C applying low heating rates in dry-nitrogen atmosphere with flow sufficient enough to provide dynamic gas conditions around the component surface. This is especially important in the case of powder prealloyed with oxygen sensitive elements like chromium.
|
|
| 10. |
- Karamchedu, Seshendra, 1987, et al.
(författare)
-
Effect of active constituents in the atmosphere on the sintering of chromium-alloyed PM steels
- 2016
-
Ingår i: World Powder Metallurgy 2016 Congress and Exhibition, World PM 2016; Hamburg; Germany; 9 October 2016 through 13 October 2016. - 9781899072484
-
Konferensbidrag (refereegranskat)abstract
- Sintering of chromium-alloyed PM steels in atmospheres containing hydrogen and carbon monoxide has been studied. Thermogravimetric analysis was performed on PM steel compacts in atmospheres containing the gaseous constituents individually and when present together. Oxidation/reduction and carburization/decarburization of the compacts was evaluated based on thermogravimetric analysis complemented with bulk carbon and oxygen analysis of the samples. The results suggest that hydrogen promotes the reduction of the iron oxide layer covering the powder surface below 650 °C, the effectiveness of which improves with an increase in the concentration of hydrogen in the atmosphere. When hydrogen was additionally present, an enhancement in the reduction and carburization behavior was observed in the case of carbon monoxide containing atmospheres.
|
|
| 11. |
- Karamchedu, Seshendra, 1987, et al.
(författare)
-
Effect of Delubrication Process Parameters on Surface Characteristics of Cr- alloyed PM steels
- 2012
-
Ingår i: Materials for Tomorrow 2012.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Utilizing chromium as an alloying element in structural powder metallurgy (PM) steel parts provides advantages in terms of profitability and recyclability but poses a challenge in terms of processing due to high chromium affinity to oxygen. From the previous investigations it is known that water-atomized chromium prealloyed PM steel powders after reduction annealing are dominantly covered by a thin Fe-oxide layer with fine particulate oxides in between [1-2], meaning good powder sinterability. However, transformation of the surface iron oxide into more thermodynamically stable ones during the consolidation can inhibit the formation of sintering necks which determine the strength of the parts. Hence, the surface chemical changes during each stage of sintering have to be evaluated in order to carefully design the process in a way that proper sintering is ensured and re-oxidation of the powder is avoided. Delubrication in PM processing precedes the high temperature sintering step and aims at efficient removal of the admixed lubricant. At the same time, the process has to be performed in a way to avoid/minimize changes in surface oxide chemistry and amount. In the present work the surface chemical analysis of chromium prealloyed steel Astaloy CrM (Fe-3Cr-0.5Mo) admixed with 0.6 ethylene bis-steramide lubricant is performed after delubrication under different processing conditions. Experimental techniques used were X-ray photoelectron spectroscopy (XPS) in combination with high-resolution scanning electron microscopy (HR SEM) and energy dispersive X-ray spectroscopy (EDX). Investigation of the surface chemical characteristics has been performed on samples delubricated in dry nitrogen atmosphere at 450 and 900°C and in air at 450°C. Delubricated in N2 at 450°C compacts showed the best surface condition similar to that of the base powder. XPS analysis revealed the presence of much higher concentration of Cr and Mn oxides on the surface of the sample delubricated at 900°C. SEM and EDX analysis confirmed the presence of particulate oxides containing the aforementioned elements indicating the growth of undesirable thermodynamically stable oxides at this temperature at the expense of the pre-existing Fe-oxide layer. After delubrication in air at 450°C the thickness of the Fe-oxide layer on the powder particle surfaces increased by a few nanometers in the center and a six fold increase in the oxide layer thickness at the edge of the samples was observed. High magnification SEM imaging on the sample showed presence of regions with the oxide thickness more than 100 nm near the edge of the sample compared to initial 6 nm, characteristic for the base powder. Based on the results from this investigation it is strongly recommended to perform delubrication at~450°C in an inert atmosphere since the as-received surface condition of the powders is retained and no undesirable changes occur.References:1. Chasoglou, Dimitris. PhD Thesis, Surface Chemical Characteristics of Chromium-alloyed Steel Powder and Role of Process Parameters during Sintering. s.l. : Chalmers University of Technology, 2012. ISBN 978-917385-711-6.2. Karlsson, Henrik. PhD Thesis, Role of Surface Oxides in Sintering of Chromium-Alloyed Steel Powder. s.l. : Chalmers University of Technology, 2005. ISBN 91-7291-703-2.
|
|
| 12. |
- Karamchedu, Seshendra, 1987, et al.
(författare)
-
Influence of delubrication process on the properties of sintered PM components
- 2013
-
Ingår i: Proceedings of Euro PM2013. ; 2, s. 163-168
-
Konferensbidrag (refereegranskat)abstract
- Problems associated with improper delubrication are frequently encountered during the manufacturing of sintered components but are very difficult to identify in a continuous sintering process. The effect of delubrication parameters on the final properties of chromium prealloyed PM steels has been studied by varying the delubrication processing conditions (thermo-profile and processing atmosphere) followed by sintering in Ar/10%H2 mixture at 1120 ºC. The best results after sintering were obtained for the compacts delubricated at 450 °C in dry nitrogen. Increasing the delubrication temperature to 900 °C resulted in slightly higher impact energy and as-sintered oxygen content but high carbon loss and lower hardness. Delubrication in air resulted in high carbon losses and the lowest impact energy and hardness values. These effects were related to considerable surface oxide changes during delubrication detected by HR SEM+EDX analyses. Delubrication at 300 °C was insufficient resulting in soot formation and inferior as-sintered mechanical properties.
|
|
| 13. |
- Karamchedu, Seshendra, 1987, et al.
(författare)
-
INFLUENCE OF PROCESS PARAMETERS ON DELUBRICATION OF PM STEELS
- 2011
-
Ingår i: Powder Metallurgy Progress. - 1335-8987. ; 11:1-2, s. 90-96
-
Tidskriftsartikel (refereegranskat)abstract
- A systematic study of the effect of various process parameters on lubricant removal in the processing of chromium prealloyed PM steels has been conducted. Improper delubrication affects the densification process and can also lead to blistering, sooting and deposition of decomposition products inside the furnace and on the PM compacts. Current work is focused on defining optimum conditions for efficient delubrication with minimum effect on PM compact properties at lowest processing cost. Effect of temperature, holding time, heating rate, process gas composition (inert, reducing and oxygen containing atmospheres), purity (wet and dry gases) and flow rate was evaluated based on in-situ continuous monitoring of the dew-point, carbon dioxide and oxygen content using industrial sensors. For ethylenebissteramide based lubricants, delubrication at temperature around 450°C with a low heating rate in an inert processing atmosphere with rather low flow rates (enough to provide weak dynamic gas conditions) is recommended.
|
|
| 14. |
- Karamchedu, Seshendra, 1987, et al.
(författare)
-
Lean atmospheres for sintering chromium alloyed PM steels
- 2013
-
Ingår i: Proceedings of Euro PM2013. ; 2, s. 353-358
-
Konferensbidrag (refereegranskat)abstract
- Hydrogen and carbon monoxide are effective reducing agents at different temperature ranges and there is only scarce experimental and theoretical data about their interaction and combined reducing effect at dry conditions and low amount. The work presents experimental and theoretical evaluation of the reducing and carburizing activity of lean nitrogen-based atmospheres containing hydrogen, carbon monoxide and small additions of hydrocarbons with their total content in the range of 0.3 to 5 vol%. Effect of carbon content (0 and 0.4 wt%) and temperature profile in the case of sintering of chromium prealloyed PM steels was evaluated. Results indicate that the carbon pickup increases with increasing CO content in the atmosphere, however it brings significant risk of oxidation. Atmospheres with low content of CO and H2 (
|
|
| 15. |
- Karamchedu, Seshendra, 1987, et al.
(författare)
-
Lean Atmospheres for Sintering of Chromium Alloyed Powder Metallurgy Steels
- 2015
-
Ingår i: Journal of the American Ceramic Society. - : Wiley. - 0002-7820 .- 1551-2916. ; 98:11, s. 3588-3595
-
Tidskriftsartikel (refereegranskat)abstract
- Thermodynamic evaluation of the reducing and carburizing activities of N-2-based lean sintering atmospheres containing CO, H-2, and small amounts of hydrocarbons with their total content not exceeding 5vol% was performed with regard to sintering of chromium alloyed PM steels. Based on the thermodynamic evaluation, three sintering atmosphere compositions were chosen for experimental studies. For the chosen sintering atmospheres, the effect of graphite addition, sintering temperature, holding time and cooling rate on the microstructure, and final oxygen and carbon contents was studied. The compacts without admixed graphite exhibited a microstructure with pearlitic, and in some cases bainitic regions, with their content varying according to the temperature profile and increasing with increase in CO concentration in the atmosphere. These results are indicative of the carburizing ability of the atmospheres which was also supported by the results from chemical analysis. Pearlitic-bainitic microstructures were observed in the compacts admixed with graphite after sintering which suggests that the proposed atmospheres provide conditions sufficient for at least partial reduction of the surface iron oxide during sintering. The final oxygen content obtained after sintering in the proposed lean atmospheres was higher than that obtained in the case of nitrogen/hydrogen mix but still was within acceptable limits. The results obtained suggest that the proposed lean CO and H-2 containing sintering atmosphere compositions are promising candidates for robust sintering of chromium alloyed PM steels.
|
|
| 16. |
- Karamchedu, Seshendra, 1987, et al.
(författare)
-
SINTER-HARDENING RESPONSE OF SINTERED STEEL BASED ON ASTALOY MO AND ITS DIFFUSION BONDED DERIVATIVES
- 2014
-
Ingår i: Powder Metallurgy Progress. - 1339-4533. ; 14:3, s. 93-99
-
Tidskriftsartikel (refereegranskat)abstract
- This study addresses the sinter-hardening response of sintered steel based on Astaloy Mo grade (prealloyed with 1.5 wt.% Mo) and its derivatives Distaloy DH- diffusion bonded with 2 wt.% copper and Distaloy DC- diffusion bonded with 2 wt.% Ni, respectively. Compacts of these powder grades were sintered at 1120°C for 30 minutes and cooled at a rate of 2.5 °C/s within the range of 800 to 300 °C followed by stress relieving at 200 °C for 60 minutes. In order to understand the relation between microstructure and the obtained mechanical properties, tensile testing and metallographic investigations were performed. It is shown that the distribution of the alloying elements as expected has a crucial impact on the microstructure development where regions lean in Cu or Ni become bainitic while regions with Cu or Ni become martensitic. Also, despite of the fact that Cu is more homogeneously distributed into the DH material, while Ni partly remains in Ni-rich regions in the DC material, both alloys show similar sinter-hardenability. The compensating effects by carbon redistribution upon bainite formation and Ni on C activity are supposed to be key factors in this context.
|
|
| 17. |
- Vattur Sundaram, Maheswaran, 1987, et al.
(författare)
-
Vacuum sintering of chromium alloyed powder metallurgy steels
- 2019
-
Ingår i: Metal Powder Report. - : Mark Allen Group. - 0026-0657 .- 1873-4065. ; 74:5, s. 244-250
-
Tidskriftsartikel (refereegranskat)abstract
- Modern developments in vacuum furnace technologies have led to an increased interest in vacuum sintering of powder metallurgy (PM) steel components owing to the robustness, productivity and the possibility to integrate heat-treatment into the process at an attractive cost. In the present study, the potential for vacuum sintering of chromium-alloyed PM steels and the effect of the vacuum level on the final properties of the components are evaluated. The studies were performed on Fe-1.8 wt.% Cr powder and the sintering experiments were performed in a dilatometer. Four different vacuum levels: 10, 1, 10−2 and 10−4 mbar were studied and the effect of density and carbon content were also examined. The results indicate an efficient oxide reduction and process robustness at intermediate vacuum levels whereas high-temperature sintering in high vacuum brings the risk of Cr-sublimation. Furthermore, industrial trails were performed at 10 and 1 mbar vacuum levels and their mechanical properties were evaluated. Vacuum sintering proved to be an attractive alternative to process Cr-alloyed steel powders.
|
|
| 18. |
- Vattur Sundaram, Maheswaran, 1987, et al.
(författare)
-
Vacuum Sintering Studies On Chromium Alloyed PM Steels
- 2016
-
Ingår i: World Powder Metallurgy 2016 Congress and Exhibition, World PM 2016; Hamburg; Germany; 9 October 2016 through 13 October 2016.
-
Konferensbidrag (refereegranskat)abstract
- Recent advancements in vacuum furnace technologies have led to an increased interest in vacuum sintering of Powder Metallurgy (PM) steel components owing to the robustness, productivity and the possibility to integrate heat-treatment into the process at an attractive cost. In the present study the potential for vacuum sintering of chromium-alloyed PM steels and the effect of the vacuum level on the final properties of the components is evaluated. The studies were performed on Fe-1.8 wt.% Cr powder and the sintering experiments were performed in a dilatometer. Four different vacuum levels: 1, 10, 10-2 and 10-4 mbar were studied and the effect of density and carbon content were also examined. The results indicate an efficient oxide reduction and process robustness at intermediate vacuum levels whereas high-temperature sintering in high vacuum brings risk of Cr-sublimation. Still, applying proper conditions, vacuum sintering proved to be an attractive alternative to process Cr-alloyed steel powders. The influence of vacuum level on the sintering efficiency of chromium-alloyed PM steels is studied.
|
|
| 19. |
- Wendel, Johan, 1989, et al.
(författare)
-
Effect of Powder Processing on the Sintering Mechanisms of Carbonyl and Water-atomized Iron Powders
- 2016
-
Ingår i: World Powder Metallurgy 2016 Congress and Exhibition, World PM 2016; Hamburg; Germany; 9 October 2016 through 13 October 2016. - 9781899072484
-
Konferensbidrag (refereegranskat)abstract
- Metal injection molding (MIM) is an attractive alternative for net-shape manufacturing of components with high demands on shape complexity. Spherical powders with small particle sizes and a wide size distribution are generally preferred for MIM parts. In this study, the sintering behavior of an annealed spherical carbonyl iron powder, a standard carbonyl iron, and a sieved (-45 µm) water-atomized iron powder was investigated. Injection molded compacts made from the respective powders were sintered in a dilatometer in a hydrogen atmosphere to study the shrinkage behavior. The shrinkage of the powder during heating stage was related to the surface area, morphology and surface chemistry of the powders. Surface composition of the powders was studied by X-ray photoelectron spectroscopy (XPS) and high-resolution scanning electron microscopy (HR SEM) combined with energy dispersive X-ray analysis (EDX). Results show strong correlation between the sintering activity to the surface chemical composition of the powder and surface area.
|
|
| 20. |
- Yuan, Miwen, 1990, et al.
(författare)
-
A Case Study for a Worn Tool Steel in the Hot Stamping Process
- 2023
-
Ingår i: Journal of Materials Research and Technology. - : Elsevier BV. - 2238-7854. ; 22, s. 1065-1075
-
Tidskriftsartikel (refereegranskat)abstract
- A good understanding of failure mechanisms can help us improve the lifetime of the dies. This paper presents a case study investigating the wear behavior of a QRO90 die insert utilized for stamping uncoated boron-alloyed high-strength steel sheets. Topography and microstructure were characterized by means of scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), hardness measurement and X-ray photoelectron spectroscopy (XPS). Severe galling due to accumulated layers transferred from the boron-alloyed steel workpieces occurred on the die surface. Material softening was detected in the sublayer of the tool steel (up to ∼200 μm). In addition, white layers with a in a thickness of 1-2 μm were frequently observed on the surface of the round corner of the tool. The main wear mechanisms are discussed. Galling caused by surface softening and the spallation of white layers are considered to be the primary wear mechanisms for the tool.
|
|
| 21. |
- Yuan, Miwen, 1990, et al.
(författare)
-
Characteristics of a modified H13 hot-work tool steel fabricated by means of laser beam powder bed fusion
- 2022
-
Ingår i: Materials Science & Engineering. - : Elsevier Ltd. - 0921-5093 .- 1873-4936. ; 831
-
Tidskriftsartikel (refereegranskat)abstract
- In the present study, a modified H13 hot-work tool steel (M-H13) was fabricated by laser beam powder bed fusion (LB-PBF). The effect of two types of post processing, direct tempering from as-built condition (DT) and conventional quenching followed by tempering (QT), on the microstructure and mechanical properties was evaluated. The typical microstructure in QT condition was tempered martensite with carbides along lath boundaries. In DT condition, melt pool boundaries and cellular structure from as-built condition were still observed. While comparable tensile properties and hardness were obtained, DT samples exhibited significantly lower impact toughness compared to QT samples. This was attributed to the difference in work hardening ability and strain rate sensitivity originating from different microstructures obtained under these two heat treatment conditions. The study was also focused on the softening behavior and the correlation with the microstructure of the two post treatments at the elevated temperatures. It was found that the DT samples showed lower thermal softening compared to QT samples. The evolution of carbides was discussed based on the microanalysis results and the JMatPro simulation. © 2021 The Authors
|
|
| 22. |
- Yuan, Miwen, 1990, et al.
(författare)
-
Softening Behavior of a Cold Work Tool Steel and High-Boron Tool Steel Fabricated by Directed Energy Deposition
- 2024
-
Ingår i: Steel Research International. - 1869-344X .- 1611-3683. ; 95:3
-
Tidskriftsartikel (refereegranskat)abstract
- Prolonging the life of hot stamping dies in the automotive industry is challenging. Surface modification is an effective way to improve the durability of the dies. In this study, two tool steel grades, one cold work tool steel (V4E) and one high-boron tool steel (HBS), are deposited on a tool steel substrate using directed energy deposition, followed by tempering. Softening behavior at high temperatures of 550 and 600 °C is investigated. In the key findings, it is revealed that both steels exhibit remarkable hardness, surpassing the substrate even after extended exposure to high temperatures. HBS shows excellent softening resistance in terms of hardness at 550 °C but experiences a significant drop at 600 °C. V4E demonstrates an overall superior softening resistance due to its thermal stable MC (M represents metal) carbides and the relatively stable dislocation density. Microstructural analysis highlights some unique features, such as borides in HBS and dendritic structures in V4E. In this study, the correlation between microstructure characteristics and hardness evolution is revealed, providing some insights into how these materials resist softening to enhance the longevity and performance of hot stamping dies.
|
|
| 23. |
- Yuan, Miwen, 1990, et al.
(författare)
-
Study of defects in directed energy deposited Vanadis 4 Extra tool steel
- 2022
-
Ingår i: Journal of Manufacturing Processes. - : Elsevier BV. - 1526-6125. ; 76, s. 419-427
-
Tidskriftsartikel (refereegranskat)abstract
- A cold work tool steel with varied number of layers was deposited on a substrate of hot work tool steel for hard-facing by directed energy deposition technique. This study deals with the defects and microstructure in the as-cladded tool steels. Defects, including pores and cracks, were found in the deposited zone, the number of which increased with the building height or number of layers deposited. Large irregular pores were mainly located at the lower regions of the deposited layers. The formation of this type of pores was attributed to the segregation of alloy elements on the pore surface and insufficient heat input. Non-equilibrium eutectic microstructure was a characteristic feature in the regions adjacent to the pores. Cracking, on the other hand, tended to occur in the upper part of the deposited layers. Two important contributing factors were identified for cracking. The first one was the microstructural gradient, which was modified from fine cellular dendrite to columnar dendrite when moving from the bottom to the top deposited layer. Second, the deposited cold work tool steel exhibited a relatively large temperature range of solidification, as simulated by Thermocalc software, leading to high sensitivity to hot cracking.
|
|
