High-temperature mechanical treatment of spring rolled products in a small enterprise

Abstract

On the single-stand mill 180 of the Ukrainian Spring Center, experiments were conducted on high-temperature mechanical treatment (HTMT) of rolled steel during hot rolling of spring strips to the required thicknesses. HTMT of rolled steel 55Cr3, carried out during hot rolling of a strip with a thickness of 14 mm to a thickness of 12 mm, showed the ability to significantly affect the mechanical properties of the rolled steel.

In all modes, HTMT significantly increases the strength of the steel with a satisfactory level of impact toughness and reduced plasticity. Varying the temperature of the end of accelerated cooling and the tempering temperature allows you to influence the mechanical characteristics of the rolled steel, due to which their values ​​were obtained that meet the norms of the TU 8429 standard.

When hardening steel from furnace heating and tempering, the structure contains lamellar troostite with individual microcracks and the effects of high-temperature oxidation. Instead, after HTMO with a post-deformation pause of 0.2 s, the steel acquires a more finely dispersed structure of acicular troostite without the above-mentioned defects. Tempering at a temperature of 470 degrees C reduced the hardness, eliminated residual austenite, and allowed obtaining a finely dispersed structure of tempering sorbite.

Comparison of the mechanical properties and structure of steel with an increase in the post-deformation pause from 0.2 s to 5 s showed an increase in strength and a decrease in the plasticity and toughness of steel, as well as the level of dispersion of the structure. With a pause of 0.2 s, the appearance of cracks after accelerated cooling of the rolled product during the HTMO process was prevented due to the finely dispersed structure and increased toughness of the steel. On the contrary, an increase in the post-deformation pause to 5 s led to the appearance of individual thermal cracks, which are sometimes also observed after quenching of 55Сr3 steel from furnace heating.