150 8·Iron and Steel croconstituent.The strengthening mechanism in ferrite stainless steels (up to 30%Cr and less than 0.12%C)is then by solid-solu- tion hardening.Still,martensitic stainless steels (for knives or ball bearings)and austenitic stainless steels (containing Ni and Cr)are also frequently manufactured and used if the high price can justify this.For details we refer again to the above-mentioned handbooks. 8.5●Cast Irons Cast iron is the principal material which the old Chinese manu- factured 3000 years ago as a result of increasing the carbon con- tent during the smelting of iron ore.This enabled them to reduce the melting temperature possibly to as low as 1150C,thus gain- ing liquid metal that could be effectively cast(see Chapter 7).Fur- ther,raw cast iron(today called pig iron)is the material that flows out of a blast furnace,as likewise explained in Chapter 7.Specif- ically,iron having a carbon content above 2.11 mass percent is generally referred to as cast iron even though carbon concentra- tions between 2.5 and 4.5%are more typical for practical appli- cations.(See in this context the carbon concentrations of common iron-containing materials shown on the bottom of Figure 8.7.) 1600 T (C) 1400 L+ Graphite 1200 Y+L 1154° (Austenite) 2.08 4.26 1000 Y+Graphite 800 738° 0.68 600 a+Graphite FIGURE 8.7.The equilibrium iron-car- (Ferrite) bon phase diagram showing graphite 400 as the stable phase.Compare to Figure Fe 1 LL人o0 234 100 8.1,in which the metastable inter- (Graphite) metallic phase Fe3C is prominently in- Composition (mass C) cluded.The dashed line marks the sol- ubility of graphite in liquid Fe.Note Tool steels Cast iron the carbon contents of common iron- Alloy steels containing materials,which are shown Construction steels below the phase diagram. Soft ferromagnets150 8 • Iron and Steel croconstituent. The strengthening mechanism in ferrite stainless steels (up to 30% Cr and less than 0.12% C) is then by solid-solu￾tion hardening. Still, martensitic stainless steels (for knives or ball bearings) and austenitic stainless steels (containing Ni and Cr) are also frequently manufactured and used if the high price can justify this. For details we refer again to the above-mentioned handbooks. Cast iron is the principal material which the old Chinese manu￾factured 3000 years ago as a result of increasing the carbon con￾tent during the smelting of iron ore. This enabled them to reduce the melting temperature possibly to as low as 1150°C, thus gain￾ing liquid metal that could be effectively cast (see Chapter 7). Fur￾ther, raw cast iron (today called pig iron) is the material that flows out of a blast furnace, as likewise explained in Chapter 7. Specif￾ically, iron having a carbon content above 2.11 mass percent is generally referred to as cast iron even though carbon concentra￾tions between 2.5 and 4.5% are more typical for practical appli￾cations. (See in this context the carbon concentrations of common iron-containing materials shown on the bottom of Figure 8.7.) 8.5 • Cast Irons 738 1154  + L  + Graphite L + Graphite  + Graphite  1600 1400 1200 1000 800 600 400  (Ferrite)  (Austenite) 0.68 Fe 1 2 3 4 90 100 (Graphite) L 2.08 4.26 Composition (mass % C) Tool steels Cast iron Alloy steels Construction steels Soft ferromagnets T (C) FIGURE 8.7. The equilibrium iron–car￾bon phase diagram showing graphite as the stable phase. Compare to Figure 8.1, in which the metastable inter￾metallic phase Fe3C is prominently in￾cluded. The dashed line marks the sol￾ubility of graphite in liquid Fe. Note the carbon contents of common iron￾containing materials, which are shown below the phase diagram