Determination of Hardness and Other Mechanical Properties of Thin-Sheet TRIP Steel by Indenting

In this paper, we studied the microstructure and mechanical properties of thin-sheet TRIP steel VNS9-Sh obtained by cold rolling of a hot rolled sheet for several transitions with intermediate heat treatment and supplied in the form of a strip with a thickness of 250–260 μm. The structure of the TRIP steel is deformation martensite and metastable hardened austenite. On the basis of the average grain size (35 μm) and the strip thickness, the optimum loading of the Vickers pyramid equal to 1 kgf (9.81 N) was determined when determining the hardness. Under this load, the indent covers several grains of steel and the ratio of the tape thickness to the indent depth is at least 20, which excludes the influence of the substrate (the instrument stage or other equipment) on the hardness values. To evaluate other mechanical properties, a kinetic (instrumental) indentation by a spherical diamond indenter with a radius of 0.2 mm was used. A methodolgy for determining the normal elastic modulus, yield stress, and time resistance is proposed. It is shown that the maximum deviation of the values of the indicated mechanical characteristics found by instrumented indentation from the values of these characteristics determined by the sample tension test did not exceed ±7%.