Tempering, of steel

If martensite is reheated to between 200 and 300 °C for an appropriate time and is then requenched, a partial crystallization of FeaC occurs, and a tough steel, sorbite, with properties intermediate between martensite and pearlite or bainite, is obtained. This process is known as the tempering of steel.12... 

The Leeds Northrup Co. has developed a two-couple continuous curve recorder for automatically heating furnaces to definite temperatures. As applied in carburizing and tempering of steel one thermocouple is placed in the furnace chamber and the other in contact with the steel piece. The controller automatically maintains the furnace for instance at 1,000°C. until the steel has reached 900°C. and then it drops the furnace to 900 C. Such an arrangement for control can be applied to a great many processes. 

The Romans were skilled metallurgists and it is evident that already before the Christian era they were familiar not only with iron. but with the tempering of steel. Virgil in his Aeneid , written about 36 b.c. describes a smithy in full blast —... 

EXAMINATION OF THE KINETICS OF MAGNETIC PROPERTIES IN TEMPERING STRUCTURAL STEELS WITH SPECIAL REFERENCE TO ACTIVE INSPECTION OF THEIR QUALITY by E.S. Gorkunov and I.n. Batuklitina, Vol. 23, No.3, pp. 177-183... 

Steels develop exceUent combinations of strength and toughness if heat-treated by quenching to martensite, foUowed by tempering (see Steel). 

Ferrophosphoms is produced as a by-product in the electrothermal manufacture of elemental phosphoms, in which iron is present as an impurity in the phosphate rock raw material. The commercial product contains ca 23—29% P and is composed primarily of Fe2P [1310-43-6] and Fe P [12023-53-9] along with impurities such as Cr and V. Ferrophosphoms is used in metallurgical processes for the addition of phosphoms content. Low concentrations (up to - 0.1%) of phosphoms in wrought and cast iron and steel not only increases the strength, hardness, and wear resistance but also improves the flow properties. In large stmctural members and plates, it is desirable to use a type of steel that does not need to be quenched or tempered, and thus does not exhibit weld-hardening. This property is afforded by the incorporation of a small quantity of phosphoms in steel. Ferrophosphoms from western U.S. phosphoms production is used as a raw material for the recovery of vanadium (see Vanadiumand vanadiumalloys). 

The tendency toward lower carbon steels has minimized the utilization of peadite as a stmctural constituent. The growing use of HSLA steels has greatiy reduced the quenching and tempering of carbon steels to provide slightly stronger materials without the use of expensive alloys. Normalizing is stiU used to reduce variability in hot-roUed material if the economics can be justified. 

Fig. 5. Micrographs of the microstructure of fully hardened and tempered tool steels produced by the powder metallurgy technique, showing uniform distribution and fine carbide particles in the matrix, (a) M-42 (see Table 6) and (b) cobalt-free AlSl T-15 having a higher concentration of fine carbide...

Heat treatment by quenching and tempering improves the low temperature ductility of steels such as 0.5 Cr, 0.5% Mo, 1% Ni Type V. For lower-temperature application (below -196°C), up to 9% nickel is used as the sole alloying element. 

The structures and phase transformations observed in steels have been dealt with in some detail not only because of the great practical importance of steels, but also because reactions similar to those occurring in steels are also observed in many other alloy systems. In particular, diifusionless transformations (austenite -> martensite), continuous precipitation (austenite -> pearlite) and discontinuous precipitation (austenite -> bainite and tempering of martensite) are fairly common in other alloy systems. 

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