Cyclic annealing versus continuous annealing of 20 wt.% chromium white cast iron

To destabilize as-cast microstructure of 20 wt.% chromium white iron, cyclic annealing involving repeated austenitization for short duration of 0.6 h at 900, 950, 1000, 1050 and 1100 °C followed by forced air cooling is conducted as an alternative to continuous annealing requiring austenitization for longer period of 4–6 h at the said temperatures followed by furnace cooling. Continuous austenitization destabilizes the austenite matrix through precipitation of secondary carbides and transforms the alloy depleted austenite to pearlite on furnace cooling, thereby reducing the as-cast hardness from HV 669 to HV466. In contrast, repeated austenitization not only destabilizes the austenite matrix through precipitation of secondary carbides followed by its transformation to martensite on forced air cooling, but also causes disintegration of longer eutectic carbides to shorter segments with subsequent increase in hardness to as high as HV 890. Notched impact toughness after both continuous and cyclic annealing remains uniformly at 12.0 J as compared to as-cast value of 6.0 J. Besides, an unexpected rise in abrasive wear resistance after cyclic annealing treatment makes the alloy superior than that obtained by continuous annealing treatment as practiced in industries.

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The Joint Effects of Nitriding and Parameters Related to the Destabilisation of Austenite on Wear Resistance in White Cast Iron with 25% Cr

Metals ◽

10.3390/met11010085 ◽

2021 ◽

Vol 11 (1) ◽

pp. 85

Author(s):

Alejandro González-Pociño ◽

Florentino Alvarez-Antolin ◽

Juan Asensio-Lozano

Keyword(s):

Wear Resistance ◽

Cast Iron ◽

White Cast Iron ◽

Nitrided Layer ◽

Erosive Wear ◽

Air Cooling ◽

Cast Irons ◽

Eutectic Carbides ◽

Noticeable Increase ◽

Ionic Nitriding

In this article, the effects of an ionic nitriding treatment are analysed, together with deliberate variation of different thermal parameters associated with the destabilisation of austenite, on erosive wear resistance of white cast irons with 25% Cr. The methodology followed in this research was an experimental design, where six factors were analyzed by performing eight experiments. The thickness of the nitrided layer is much smaller than in white cast iron with lower percentages in Cr, never reaching 20 microns. The nitriding treatment entails considerable softening of the material underneath the nitriding layer. This softening behaviour becomes partially inhibited when the destabilisation temperature of austenite is 1100 °C and dwell times at such temperature are prolonged. This temperature seems to play a significant role in the solubilization of non-equilibrium eutectic carbides, formed during industrial solidification. The nitriding treatment leads to additional hardening, which, in these cases, favours a second destabilisation of austenite, with additional precipitation of secondary carbides and the transformation of retained austenite into martensite. Despite softening of the material, the nitriding treatment, together with air-cooling after destabilisation of the austenite, allows a noticeable increase in resistance to erosive wear.

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Microstructure and Tempering Behaviour of 28Cr-2.5C-1W Cast Irons

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.283.116 ◽

2018 ◽

Vol 283 ◽

pp. 116-123

Author(s):

Sasitorn Yeekew ◽

Amporn Wiengmoon ◽

Torranin Chairuangsri ◽

John T.H. Pearce

Keyword(s):

Carbide Precipitation ◽

Air Cooling ◽

Austenite Matrix ◽

Secondary Carbide ◽

Cast Irons ◽

High Chromium ◽

X Ray ◽

Secondary Carbides ◽

Cooling Phase ◽

Scanning Electron

In this work, the effects of 1 wt.% tungsten addition and variation in tempering times on the microstructure and hardness of nominal 28 wt.%Cr high chromium irons were investigated. As-cast samples were destabilised at 1050 °C for 4 hours and then hardened by air cooling. Tempering after destabilisation was carried out at 450 °C for 2, 4 and 6 hours followed by air cooling. X-ray diffractometry, light microscopy and scanning electron microscopy were used to characterize the microstructures of the irons. The results show that the as-cast microstructure of the iron without W addition consisted of primary austenite dendrites with eutectic M7C3 and eutectic austenite partially transformed to martensite. The iron with 1 wt.%W addition contained primary M7C3 and eutectic M7C3 in an austenite matrix. Destabilisation treatment of the austenite matrix in both irons allowed precipitation of secondary carbides and transformation to martensite during air cooling. Phase transformation of eutectic M7C3 was also found in the iron with W addition. The formation of primary M7C3 in the 1 wt.%W iron increased the as-cast macro-hardness from 500 (no W) to 576 HV30. Destabilisation increased the macro-hardness up to 736 (no W) and 780 HV30 (1 wt.%W) since secondary carbide precipitation allowed austenite to transform to essentially martensitic matrices. At longer tempering times, the macro-hardness further increased up to about 820 HV30.

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Influence of Ni Content on Erosive Wear and Destabilization Heat Treatment Conditions Behavior of Multi Component White Cast Iron

Materials Science Forum ◽

10.4028/www.scientific.net/msf.998.48 ◽

2020 ◽

Vol 998 ◽

pp. 48-54

Author(s):

Kenta Kusumoto ◽

Kazumichi Shimizu

Keyword(s):

Heat Treatment ◽

Wear Resistance ◽

Cast Iron ◽

White Cast Iron ◽

Erosive Wear ◽

Wear Property ◽

Eutectic Carbides ◽

Secondary Carbides ◽

Ni Content ◽

Ni Addition

This study investigated the influence of nickel (Ni) addition on erosive wear property of multi-component white cast iron with good erosive wear resistance. Multi-component white cast irons (MWCIs) with 2 mass % of carbon (C), 5 mass % of chromium (Cr), molybdenum (Mo), tungsten (W), niobium (Nb) and 0, 3, 5 mass % of Ni were prepared as experimental materials. The heat treatment condition was quenching by forced air cooling after keeping the specimens at 1123K for 3.6ks. Specimens with size of 50mm×50mm×10mm were tested using a suction-type blasting machine. The test was conducted with impact angle of 30, 60 and 90 deg. at room temperature. Collision particles were irregular steel grids with average particle diameter of 770μm and hardness of 810HV1. The speed of air flow was about 100m/s while the speed of impact particles was around 20.0g/s and the total time of each experiment was 3600 sec.. According to the result, erosion rate was decreased with the increase of Ni content in all of the impact angles. Especially, MWCIs which contain 5 mass % Ni showed the most excellent erosive wear resistance. As reasons, it can be considered that with Ni addition, the volume fraction of eutectic carbides and secondary carbides was increased which enhanced the matrix structure and suppressed the surface deformation of the experimental surface. Therefore, the increasing of eutectic carbides and secondary carbides can be considered as the reason of erosive wear resistance increased.

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Heat Treatment in High Chromium White Cast Iron Ti Alloy

Journal of Metallurgy ◽

10.1155/2014/856408 ◽

2014 ◽

Vol 2014 ◽

pp. 1-9 ◽

Cited By ~ 6

Author(s):

Khaled M. Ibrahim ◽

Mervat M. Ibrahim

Keyword(s):

Heat Treatment ◽

Tensile Strength ◽

Wear Resistance ◽

Cast Iron ◽

Impact Toughness ◽

White Cast Iron ◽

High Chromium ◽

Eutectic Carbides ◽

Secondary Carbides ◽

Ti Addition

The influence of heat treatment on microstructure and mechanical properties of high chromium white cast iron alloyed with titanium was investigated. The austenitizing temperatures of 980°C and 1150°C for 1 hour each followed by tempering at 260°C for 2 hours have been performed and the effect of these treatments on wear resistance/impact toughness combination is reported. The microstructure of irons austenitized at 1150°C showed a fine precipitate of secondary carbides (M6C23) in a matrix of eutectic austenite and eutectic carbides (M7C3). At 980°C, the structure consisted of spheroidal martensite matrix, small amounts of fine secondary carbides, and eutectic carbides. Titanium carbides (TiC) particles with cuboidal morphology were uniformly distributed in both matrices. Irons austenitized at 980°C showed relatively higher tensile strength compared to those austenitized at 1150°C, while the latter showed higher impact toughness. For both cases, optimum tensile strength was reported for the irons alloyed with 1.31% Ti, whereas maximum impact toughness was obtained for the irons without Ti-addition. Higher wear resistance was obtained for the samples austenitized at 980°C compared to the irons treated at 1150°C. For both treatments, optimum wear resistance was obtained with 1.3% Ti.

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Air circulation in a gastrointestinal light source box and endoscope in the era of SARS-CoV-2 and airborne transmission of microorganisms

Endoscopy International Open ◽

10.1055/a-1336-3280 ◽

2021 ◽

Vol 09 (03) ◽

pp. E482-E486

Author(s):

Stanislas Chaussade ◽

Einas Abou Ali ◽

Rachel Hallit ◽

Arthur Belle ◽

Maximilien Barret ◽

...

Keyword(s):

Light Source ◽

Cooling System ◽

Air Cooling ◽

Airborne Transmission ◽

Plastic Tube ◽

Care Workers ◽

Air Cooling System ◽

Forced Air ◽

Air Circulation ◽

Closed Environment

Abstract Background and study aims The role that air circulation through a gastrointestinal endoscopy system plays in airborne transmission of microorganisms has never been investigated. The aim of this study was to explore the potential risk of transmission and potential improvements in the system. Methods We investigated and described air circulation into gastrointestinal endoscopes from Fujifilm, Olympus, and Pentax. Results The light source box contains a lamp, either Xenon or LED. The temperature of the light is high and is regulated by a forced-air cooling system to maintain a stable temperature in the middle of the box. The air used by the forced-air cooling system is sucked from the closed environment of the patient through an aeration port, located close to the light source and evacuated out of the box by one or two ventilators. No filter exists to avoid dispersion of particles outside the processor box. The light source box also contains an insufflation air pump. The air is sucked from the light source box through one or two holes in the air pump and pushed from the air pump into the air pipe of the endoscope through a plastic tube. Because the air pump does not have a dedicated HEPA filter, transmission of microorganisms cannot be excluded. Conclusions Changes are necessary to prevent airborne transmission. Exclusive use of an external CO2 pump and wrapping the endoscope platform with a plastic film will limit scatter of microorganisms. In the era of pandemic virus with airborne transmission, improvements in gastrointestinal ventilation systems are necessary to avoid contamination of patients and health care workers.

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