English: A small, magnified segment of the iron-carbon phase diagram showing the beta "phase" of iron. Reference: ASM Handbook, Vol. 3: Alloy Phase Diagrams, ASM International, 1992, p 2.210, ISBN 0-87170-381-5. The odd curvature of the alpha-graphite solvus in this figure is due to the curve-smoothing function of Microsoft Excel acting on a small number of data points. The solvus in the ASM Handbook appears to dwindle to ~zero percent carbon below 400°C, but the equilibrium solubility of C in Fe is about 0.008% at 0°C, according to W.F. Smith, Structure and Properties of Engineering Alloys, McGraw-Hill, 1981, p 5, ISBN 0-07-058560-1.