Tool steel heat treatment

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Aldebaran
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Iscritto il: 31/03/2010, 18:26
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Tool steel heat treatment

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Most of our tools in common use, even cutting, require a high hardness Rockwell, approximately 55 Rockwell.
However, manufacturers are supplied in the annealed steel with Rockwell hardness of 20, or about 200-250 Brinell, to facilitate processing.
They must be heat treated to develop the best properties' characteristics, inherent in any type of acciaio.In thus becomes the instrument can withstand certain pressures, impacts and abrasions.
At each stage of the heat cycle is a result secifico on steel, heat treatment is typically 10% of the cost of the instrument, but 'decisive as regards the performance of the instrument.
The structure of most 'rising hardness in steels and' martensite defined, and can not 'be obtained simply by annealing, as defined in the parlance, soft.
The tool steels, in particular, must pass through at least two stages thermal intermediate.
First, the structure ricotta, defined, and it should be heated to high temperatures to transform it into another structure, called austenite.
In turn, retained austenite, by a sort of cooling by relatively short intervals, it becomes martensite.
To achieve these structural changes within the tool steel, is passed through the implementation of primary thermodynamic 4 steps:
preheat austenitising, quenching and tempering.
Warm, also known as slow heating, concrete steel that offers 3 benefits but 'not directly related to the properties' final product.
First, the tool steel and 'more' sensitive to shock termici.Un sudden increase in temperature up to 1500-2000 degrees F., can 'cause cracks in the instrument.
Preheating one or more 'intermediate temperatures, tends to avoid certain phenomena.
Secondly, the tool steels suffer a change of densita'nell'atto transformation from austenite to ferrite.
If this volume change occurs unevenly, can 'cause distortions that would render the instrument unusable.
The tool steel must then be heated to a temperature just below the austenitic (called critical temperature-1500F for steels and tool), then maintained for a time so that suffciente 'is uniform throughout the supericie piece.
A further heating, finally, will make 'tool almost immune from distortions.
Finally, the steel treated with high temperatures, conduct heat more 'fast or heat up a piece prima.Quindi in preheated oven takes less time to cure temperature to achieve uniformity'.
Minimize the time of heat treatment and 'a good compromise to increase the hardness (impact resistance) of the instrument.
In some cases, especially those involving tempering temperatures above 2000 F., the final austenitising can 'be preceded by multiple preheating.
After the changes have appeared in the austenitic structure, and 'a need for additional heating to properly distribute the contents of alloy steels.
Most of the content of alloy steels exists as tiny particles of carbide in the matrix of soft annealed.
These particles must be at least partially dissolved in the matrix of steel during the austenite transformation temperatures during processing or curing.
Regarding the vision chart for detailed analysis of what is said until now, I refer readers to what 'I wrote here:
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In some situations, the temperature can austenitising 'peculiarita'tipiche be changed to suit a certain type of steel, so that' the object scaturitone has an additional wear resistance and greater toughness', for what applications particolari.Tutto 'in general is obtained using a temperature slightly above the average austenitising favoring the dissolution of alloys in the array.
Instead, with temperatures austenitising slightly below average, you will get 'a greater impact strength but a slightly lower hardness.
Once the league and 'dissolved in the matrix of steel, it must be cooled quickly enough to keep the contents of local league and that' the austenite is transformed into martensite with high hardness.
Speed 'to follow the proceedings depends on the chemical composition of the type of steel.
The low alloy tool steel, such as O1, S5, L6richiedono cooling more 'quick and salt water or oil.
The high-alloy tool steel, requiring more cooling 'slow and air, such as A2, D2, M4, 10V.
With regard to tool steel, and when 'cooked at 2000 F, the transition from about 1800F to 1300F must be fast enough not to compromise its hardness.
The trasformazioneda austenite to martensite does not begin before cooling to about 700F.La martensite, at this temperature is defined Martensite Start, Ms.Nella most tool steels, the austenite transforms into martensite between 600F and 200F about.
The amount 'of martensite present in steel is calculated to quantita'di Martensite Finish, Mfche you get further cooling the steel at temperatures more' low until it reaches almost 100% compared to the presence of steel ' austenite.
But that 'not enough to make the instrument usable and to avoid going immediately shattered just put the work; must annealed at temperatures of about 125/150F.
The discovery takes place after hardening, to eliminate and / or harden the residual martensite, and based on the temperature at which and 'implemented hardening due to carbon-iron curves associated with each type of alloy steel, and' better to choose a tempering temperature more 'high as possible.
With regard to tool steels, temper is more better 'than once, up to three, and implement an equal number of discoveries.
Finally, it is to cool at room temperature for two hours.
There may be variations in temperature and time in general if one includes surface treatments such as nitriding, etc..
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