### 14.11 Thermal contact coefficient

The thermal contact coefficient B_{M} accounts for the influence of the material
properties of pinion and gear:

For martensitic steels the range of heat conductivity, λ_{M}, is 41 to 52 N/sK and
the product of density times the specific heat per unit mass, ρ_{M} ⋅ c_{M} is about
3.8N∕[mm^{2}K], so that the use of the average value B_{
M} = 13.6N∕mms^{0.5}K for
such steels will not introduce a large error when the thermal contact coefficient is
unknown.