Serkan Orhan, 030070165, 9th week part3

5)Medium Carbon Steels  12.35 [Group: Material]

[Old]

There are two groups of medium carbon steels:

1.      From 0.3% to 0.5% carbon. These can be heat treated to make them taough and strong.

2.      From 0.5% to 0.8% carbon. These can be heat treated to make them fairlyhard yet remain a degree of toughness(impact resistance)
Medium carbon steels are harder, stronger and tougher than low carbon steels. They are also more
expensive. They cannot be bent or formed in the cold condition to the same extend as low carbon
steels without cracking. However, medium carbon steels hot forge well, but close temperature
control is required to prevent:

·         ‘Burning’  at high tempratures over 1150⁰C, as this leads to embrittlement. The metal cannot be reclaimed and the forging has to be scrapped.

·         Cracking when forging is in the ‘cold’ condition from a forging point o f view.

Medium carbon steels with a carbon content in the 0.5% to 0.8% range are used for such products as wood saws, cold chisels, forged blanks for connecting rods, cranckshafts, gears and other stressed components such as high-tensile pipes and tubes.

(Roger Timings, Fabrication and Welding Engineering, p. 79)

[New][Better]

The medium-carbon steels have carbon concentrations between about 0.25 and 0.60 wt%.Thcse alloys may be heat-treated by austenitizing,quenching,and then tempering to improve their mechanical properties.They are most often utilized in the tempered condition, having microstructures of tempered martensite.The plain medium-carbon steels have low hardenabilities  and can be successfully heat-treated only in very thin sections and with very rapid quenching rates. Additions of chromium nickel, arid molybdenum improve the capacity of these alloys to be heat-treated , giving rise to a variety of strength—ductility combinations.These heat-treated alloys are stronger than the low-carbon steels, but at a sacrifice of ductility and toughness. Applications include railway wheels and tracks, gears, crankshafts, and other machine parts and high-strength structural components calling for a combination of high strength, wear resistance, and toughness. The compositions of several of these alloyed medium corbon steels are presented in Table 13.2a. Some comntent is in order regarding the designation schemes that are

(Fundamentals of Materials Science and Engineering: An Integrated Approach,  William D. Callister,David G. Rethwisch, p.546)