Text Appearing Before Image: 1. Normal Steel as Rolled Fig. 3.—Metcalf Test PiecesCarnegie Electric Tool Steel No. 1 *,fe.W HEAT TREATMENT TESTS 4. Overheated Text Appearing After Image: Fig. 4. Full Size Test Piece FracturesCarnegrie Electric Tool Steel No. 1 CARNEQIE STEEL CpMPANY 3. Where the grains are very coarse and bright. These areprogressively larger towards the melted end of the bar and show thegrowth in grain size which takes place when steels are heated abovethe hardening point. Maximum hardness occurs with minimum grain size.To insure this condition steels must be heated above thehardening point. The temperature should be held justabove this point to insure uniform heating throughout thebar, but beyond this point steel should not be heated morethan absolutely necessary. HARDENING POINT. The hardening temperature fortool steels (the point of minimum grain size) varies withthe chemical composition. In carbonless iron it occursat about 1697° F.;in steels of .90 carbon or over, at 1382° F.It is also affected by the presence of alloys. The line of minimum grain size for carbon steels ofdifferent composition is shown on the chart, Fig. 6. Com-panion, Fig. 5,
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