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Embrittlement occurs during tempering when, through a specific temperature range, the steel experiences an increase in hardness and a reduction in ductility, as opposed to the normal decrease in hardness that occurs on either side of this range. The first type is called tempered martensite embrittlement (TME) or one-step embrittlement.
An increase in the carbon content will cause a significant increase in the hardness and tensile strength of iron. Maximum hardness of 65 R c is achieved with a 0.6% carbon content, although the alloy has low tensile strength. [132] Because of the softness of iron, it is much easier to work with than its heavier congeners ruthenium and osmium. [17]
Below 912 °C (1,674 °F), iron has a body-centered cubic (bcc) crystal structure and is known as α-iron or ferrite.It is thermodynamically stable and a fairly soft metal. α-Fe can be subjected to pressures up to ca. 15 GPa before transforming into a high-pressure form termed ε-Fe discussed below.
Cast iron is made from pig iron, which is the product of melting iron ore in a blast furnace. Cast iron can be made directly from the molten pig iron or by re-melting pig iron, [4] often along with substantial quantities of iron, steel, limestone, carbon (coke) and taking various steps to remove undesirable contaminants.
Forging temperature is the temperature at which a metal becomes substantially more soft, but is lower than the melting temperature, such that it can be reshaped by forging. [1] Bringing a metal to its forging temperature allows the metal's shape to be changed by applying a relatively small force, without creating cracks.
Wide ranges in strength and ductility are possible. High temperature heat treatment (>400C) results in high ductility, good impact toughness, with a yield strength around 500 MPa. Lower temperatures (~260C) results in a higher yield strength of 1400 MPa and high hardness but much lower ductility. [1]
The invar range was described by Westinghouse scientists in 1961 as "30–45 atom per cent nickel". [ 6 ] Common grades of Invar have a coefficient of thermal expansion (denoted α , and measured between 20 °C and 100 °C) of about 1.2 × 10 −6 K −1 ( 1.2 ppm /°C ), while ordinary steels have values of around 11–15 ppm/°C.