Why low carbon steel is not sensible for heat treatment?
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Considering plain carbon steels alone for the sake of this answer, classification of such steels could be done, three ways (Low, Medium and High).
Yes, Low carbon Steels are ductile, malleable, tough, machinable and weldable. It implies that they are great for Cold Working. Cold working or as I rather prefer calling it, strain hardening is the phenomenon that involves hardening a ductile metal as it is plastically deformed at temperatures relatively cold to the absolute melting temperature.
When we consider heat treating here, we are looking at the “Hardening” operation alone.
When we do that, that is, hardening the same steel via. heat treatment, we are looking at an operation that involves heating the steel to temperatures around 850–900 degrees centigrade and quenching them to achieve a Martensitic Microstructure.
Yes I am aware of the fact that Martensite is produced from alloys systems that do not contain neither Fe nor C at all. As a matter of fact, Martensitic Transformation is possible with just pure Iron. But here is the problem. For attempting such a feat successfully, quenching rates in an excess of 35,000 degrees Centigrade/Second are required. (Refer: M.J. Bibby and J. Gordon Parr, The Martensitic Transformation in Pure Iron, Journal of the Iron and Steel Institute, 1964, Vol 202, p100–104)
Now hardening via. heat treatment for low carbon steels might not be that extreme. Heat treatments to form martensite are generally applied to steels containing more than 0.3% C. In these steels, the gains in hardness are most substantial.
But, steels containing less than 0.3% C are difficult to harden in heavy sections but are still hardenable in sheets and thin plates to provide excellent combinations of strength and toughness after tempering.
I am hoping that this answer helps.
Yes, Low carbon Steels are ductile, malleable, tough, machinable and weldable. It implies that they are great for Cold Working. Cold working or as I rather prefer calling it, strain hardening is the phenomenon that involves hardening a ductile metal as it is plastically deformed at temperatures relatively cold to the absolute melting temperature.
When we consider heat treating here, we are looking at the “Hardening” operation alone.
When we do that, that is, hardening the same steel via. heat treatment, we are looking at an operation that involves heating the steel to temperatures around 850–900 degrees centigrade and quenching them to achieve a Martensitic Microstructure.
Yes I am aware of the fact that Martensite is produced from alloys systems that do not contain neither Fe nor C at all. As a matter of fact, Martensitic Transformation is possible with just pure Iron. But here is the problem. For attempting such a feat successfully, quenching rates in an excess of 35,000 degrees Centigrade/Second are required. (Refer: M.J. Bibby and J. Gordon Parr, The Martensitic Transformation in Pure Iron, Journal of the Iron and Steel Institute, 1964, Vol 202, p100–104)
Now hardening via. heat treatment for low carbon steels might not be that extreme. Heat treatments to form martensite are generally applied to steels containing more than 0.3% C. In these steels, the gains in hardness are most substantial.
But, steels containing less than 0.3% C are difficult to harden in heavy sections but are still hardenable in sheets and thin plates to provide excellent combinations of strength and toughness after tempering.
I am hoping that this answer helps.
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