Volume 6, Issue 1 (January 2009)
Energy Efficient and Eco-friendly Intensively Quenched Limited Hardenability Low Alloy Steels
Low and limited hardenability (LH) steels are plain carbon steels characterized by a low content of alloying elements (Cr, Ni, Mo, W, V, etc.). The use of LH steels with an intensive quenching method allows full elimination of the carburization process for a variety of steel parts, such as, gear and bearing products, tools, low-wear parts for different applications. This is based on the steel super strengthening phenomenon and creation of high residual compressive stresses at the surface of intensively quenched steel parts. Both of these factors allow replacing expensive alloy steels with plain carbon steels. The unique characteristic of limited hardenability steels is that these alloys only harden to a shallow depth when heated and quenched. The main idea of this paper involves the creation of the optimal depth of a hardened shell which provides optimal stress distribution in quenched steel parts. Since the LH steel core does not harden significantly, a relatively high ductility of the core is maintained. The grain sizes of LH steels are greater than ASTM 8. Several patents on LH steels have been issued in Europe. A number of technical papers utilizing LH steels for gears and bearing products have been published in the Ukraine and Russia. Elimination of carburizing saves energy and prevents the emissions of thousands of tons of CO2 gases. Furthermore, the high level of compressive surface residual stresses and the steel super strengthening phenomenon eliminates the need for secondary shot peening or surface induction operations. Also, carburized alloy steels can be successfully replaced by LH steels to increase service life and decrease materials cost.