Steels with High Temperature Carbides - New Possibilities for Semi-Solid State Processing

Semi-solid processing of steels is typically studied using high-alloy steels with higher carbon levels, as those offer a long freezing range which is favourable for conducting the process. The drawback to their application is their microstructure which typically consists of austenite grains embedded in ledeburitic network. This type of microstructure typically fails in brittle manner by fracturing along the interface of the hard network and ductile austenite grains. This is why a way was sought to altering or even inverting the configuration of the microstructure. Eventually, suitable steel chemistries were found which allow the inverted microstructure to be obtained. With regard to the high content of alloy additions, these steels have to be made by powder metallurgy methods. Five different steels of this kind were selected for the experimental programme. All contained high amounts of alloying elements and a large fraction of carbides. Their carbon content was taken into account as well, ranging from 0.55 to 3.4 %. Differences between the steels consisted in the levels of major alloying elements, namely chromium, vanadium, molybdenum, tungsten and cobalt. After suitable process parameters were found, semi-solid processing was used to prepare demonstration products. The transition through semi-solid state transformed the ferritic matrix to austenitic-martensitic one, in which the high-stability carbides were retained. The resulting microstructures were of unconventional nature where carbide particles were embedded in tough metal matrix. Their configuration was thus inverted in contrast to the ones typically obtained by semi-solid processing of tool steels.

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Mechanical Characterization of Ceramic Nano B4C- Al2618 Alloy Composites Synthesized by Semi Solid State Processing

Transactions of the Indian Ceramic Society ◽

10.1080/0371750x.2018.1506363 ◽

2018 ◽

Vol 77 (3) ◽

pp. 146-149 ◽

Cited By ~ 10

Author(s):

Madeva Nagaral ◽

Shivananda Kalgudi ◽

Virupaxi Auradi ◽

Shivaputrappa Amarappa Kori

Keyword(s):

Solid State ◽

Mechanical Characterization ◽

Semi Solid ◽

State Processing

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Modelling of morphology evolution and macroscopic behaviour of intercalated PET–clay nanocomposites during semi-solid state processing

Composites Science and Technology ◽

10.1016/j.compscitech.2012.12.002 ◽

2013 ◽

Vol 75 ◽

pp. 35-41 ◽

Cited By ~ 9

Author(s):

C. Pisano ◽

Ł. Figiel

Keyword(s):

Solid State ◽

Clay Nanocomposites ◽

Morphology Evolution ◽

Semi Solid ◽

State Processing

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Semi-Solid High Pressure Die Casting of Metal Matrix Composites Produced by Liquid State Processing

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.192-193.61 ◽

2012 ◽

Vol 192-193 ◽

pp. 61-65 ◽

Cited By ~ 3

Author(s):

Lilian Ivanchev ◽

Sigqibo Templeton Camagu ◽

Gonasagren Govender

Keyword(s):

High Pressure ◽

Solid State ◽

Metal Matrix Composites ◽

Liquid State ◽

Metal Matrix ◽

Die Casting ◽

Matrix Composites ◽

Semi Solid ◽

Pressure Die Casting ◽

State Processing

There are two main technologies for manufacturing of particulate reinforced metal matrix composites (MMC), solid state and liquid state processing. The great challenge of producing cast metal matrix composites is to prevent agglomeration of particulates. This tendency is more pronounced with decreasing the particulate size to fine micro- and nano size. A method for producing MMC was successfully implemented for mixing hybrid, nano and low micron sized, reinforcing particles in an aluminium alloy matrix. The hybrid SiC particles were produced by milling 3µm to 5µm SiC particles to a particle size range between 2.5µm and 150 nm. The hybrid particles were mixed with A356 aluminium alloy under combined magneto-hydrodynamic (MHD) and mechanical stirring. The composite was then transferred to a High Pressure Die Casting (HPDC) machine in the semi-solid state. The micron size particles were found to be predominantly in the intergranular eutectic while the nano-particles were predominantly in the primary α-Al grains. Increased ultimate tensile strength, yield strength and hardness were achieved for the new cast metal matrix hybrid component (MMHC) alloy.

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Semi-Solid Processing of Powder Steels in Cryogenically-Cooled Die

Materials Science Forum ◽

10.4028/www.scientific.net/msf.783-786.801 ◽

2014 ◽

Vol 783-786 ◽

pp. 801-806 ◽

Cited By ~ 3

Author(s):

Bohuslav Masek ◽

David Aišman ◽

Kateřina Rubešová ◽

Hana Jirková

Keyword(s):

Solid State ◽

Rapid Solidification ◽

Test Sample ◽

Initial Structure ◽

Metastable Austenite ◽

Lateral Extrusion ◽

First Case ◽

Solid Region ◽

Semi Solid ◽

State Processing

By processing steels in the semi-solid state it is possible to achieve unconventional structures even with commonly used steels. This can be demonstrated on X210Cr12 tool steel. After semi-solid state processing, 96% of the microstructure can consist of metastable austenite. In the microstructure, there are polyhedral grains embedded in a ledeburitic network. A combination of semi-solid state processing and rapid solidification is a new method for modifying the microstructure more substantially. In the present experiment, two tool steels, CPM 15V and CPM S30V, were processed by an unconventional method. Since the steels are made by powder metallurgy, their initial structure contains globular carbides in ferritic matrix. Both materials have high levels of carbon and alloying elements, namely vanadium and chromium. The unconventional processing was carried out by mini-thixoforming which enables the use of a small amount of metal. After heating into the semi-solid region, the material was rapidly forced by lateral extrusion into a cavity of a metal die where rapid solidification and rapid cooling took place. Two cooling schedules were employed. In the first case, the die was at room temperature, whereas in the second one it was pre-cooled to-196°C using liquid nitrogen. Since the test sample was cooled from both sides and its thickness was 3 mm, immensely high cooling rates were achieved. The influence of the cooling rate was also noticeable in the microstructures containing high fractions of metastable austenite, martensite and carbides.

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In Situ Microstructure Observation of Steel Grades in the Semi-Solid State for Thixoforging Process by Using Confoncal Laser Scanning Microscopy

Solid State Phenomena ◽

10.4028/www.scientific.net/ssp.217-218.15 ◽

2014 ◽

Vol 217-218 ◽

pp. 15-22 ◽

Cited By ~ 1

Author(s):

Guo Chao Gu ◽

Raphaël Pesci ◽

Eric Becker ◽

Laurent Langlois ◽

Régis Bigot

Keyword(s):

High Temperature ◽

Solid State ◽

Microstructure Evolution ◽

Laser Scanning ◽

Diffusion Rate ◽

Laser Scanning Microscopy ◽

Alloying Elements ◽

Steel Grades ◽

Semi Solid

It is necessary to well understand the microstructure evolution during high speed heating and forming for steel thixoforging, since it determines the thixotropic flow behavior of materials in the semi-solid state. A new in situ technique - high temperature Confocal Laser Scanning Microscopy (CLSM) - was developed and used for studying the microstructure evolution directly at high temperature where the microstructure in the semi-solid state could not be preserved by quenching experiments for conventional 2D characterization. Several steel grades (C38LTT, 100Cr6 and M2) were investigated during heating from the as-received state to the semi-solid state and finally cooled to the solid state).It has been found that there is a significant difference in diffusion rate of alloying elements between these grades during heating and cooling. In M2, thanks to the high content of alloying elements and their low diffusion rate, the semi-solid temperature range is greater and its microstructure in the semi-solid state could be preserved by quenching or even at a low cooling rate, which means the microstructure of M2 in the semi-solid state can be characterized in room temperature on quenched M2 samples. On the contrary, the microstructure of other steel grades 100Cr6 and C38LTT in semi-solid state can only be revealed by CLSM at high temperature because of the lower volume fraction of alloying elements and their high diffusion rate. It is very interesting to use high temperature CLSM to in situ investigate the microstructure evolution in the semi-solid state, especially at low liquid fraction.

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