Quantitave alternative method of determining hardness of carburized steel annealed or quenched by a CO2-laser on the basis of carbon-dependent correlation between hardness and thermal diffusivity

A quantitative nondestructive testing method is proposed for imaging thermally treated steel. A theoretical model and experimental data on visualizing an optical beam deflected by a metal sample heated by a Gaussian beam are given. An analytic solution of heat equations obtained in the corresponding approximation gives a theoretical expression for the surface temperature, important for understanding the experimental process. Attention is concentrated to measurements, which make it possible to clarify correlation between mechanical parameters and local thermal characteristics of the sample. For the purpose of establishing a simple theoretical correlation between the steel microhardness and the thermal diffusivity in accordance with variations of the structure and composition of steel, a theoretical procedure of inverting the dependence between the thermal diffusivity and the photothermal deflection observed experimentally is proposed and a methodological comparison of the results is carried out.