Heat Treatment of Steel Machinery's Handbook, 31st Edition
469
550 500 450 400 350 300 250 200 150
280 240 200 160 120 80 40 0 100 200 300 400 500 Brinell Hardness Number 1
275 250 225 200 175 150 125 100 75
2
Solid curve shows normal- expectancy curve. Broken lines define
Fig. 2.
50 60 70 80 90 100 Yield Point, percent of tensile strength
280 260 240 220 200 180 160 140 120 100 70 60 50 40 30 20 10 Reduction of Area, percent 560 520 480 440 400 360 320 280 240 Normal expectancy curves Carbon Steels, 1000 Series Alloy Steels 1300, 2300, 3100 3200, 4100, 4300 5100, 6100 3 Variations from mean
Fig. 3.
550 500 450 400 350 300 250 200
275 250 225 200 175 150 125 100
Fully hardened,
4
0.40-0.55% carbon
0.30-0.40% carbon
When not fully hardened tempering curve will approach this line
400 600 800 1000 1200 Tempering Temperature
Fig. 4.
Fig. 5.
Hardening Basic Steps in Hardening.— The operation of hardening steel consists fundamentally of two steps. The first step is to heat the steel to some temperature above its transformation point (usually at least 100°F or 56°C above) so that it becomes entirely austenitic in struc ture. The second step is to quench the steel at some rate faster than the critical rate (which depends on the carbon content, the amounts of alloying elements present other than car bon, and the grain size of the austenite) to produce a martensitic structure. The hardness of a martensitic steel depends on its carbon content and ranges from about 460 BHN at
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