To provide a high hardness and high expansion alloy which has high thermal expansion and high strength as well as thermal settling resistance, a high hardness and high expansion alloy metallic sheet obtained by using the alloy, a production method for the high hardness and high expansion alloy.

The high hardness and high expansion alloy having thermal settling resistance has a composition containing, by mass, ≤0.2% C, ≤1.0% Si, >5.0 to 10.0% Mn, >7.0 to 14.0% Ni, >6.0 to <12.0% Cr, one or two kinds of Mo and W by 0.2 to 2.0% in terms of Mo+1/2W and 0.005 to 0.2% N, and the balance substantially Fe. Further, A value expressed by equation (1): A value = 30C-1.34Si+0.5Mn+ Ni-0.67Cr-Mo-0.5W+20N is <16, and B value expressed by equation (2): B value = Ni+0.65Cr+0.98Mo+0.49W+1.05Mn+0.35Si+12.6(C+N) is 22 to 26, also, its hardness at ordinary temperatures is ≥400 Hv, and the average thermal expansion coefficient at ordinary temperatures to 100°C is 15×10-6/°C or higher.