Steel wire is an important product in modern industries and is widely used in different applications. Where higher strength or durability is required, a heat treatment known as patenting is applied. This heat treatment uses molten lead as a coolant to form a fine-lamellar pearlite microstructure. Since lead is toxic, there are constant efforts to make the process environment as safe as possible as well as to replace lead baths. The first step for a possible replacement is a good understanding of the current boundary conditions. Therefore, an experimental setup was designed to measure the cooling curve of wire samples with different wire diameters and steel grades directly at two industrial lead baths. Furthermore, an inverse calculation method was developed to calculate the heat transfer coefficients from the cooling curves. The experimental setup, the evaluation method, and the resulting heat transfer coefficients are presented. The results show that the heat transfer coefficients vary with the sample diameter and velocity but not the lead bath temperature or steel grade. In addition, a comparison with correlations from literature was conducted.