Plenary Lecture

Plenary Lecture

On Thermal Equilibrium, Optimal Chemical Composition and Residual Stresses during Quenching of Steels


Dr. Nikolai Kobasko
IQ Technologies Inc, Akron
USA and Intensive Technologies Ltd
Kyiv, Ukraine
E-mail: nikobasko@yahoo.com


Abstract: Hardening of steel is very important technology when alloy elements are dissolved in austenite during equilibrium establishment at high temperatures (800 1000oC). Then steel parts are rapidly cooled by water, water jets, oils, polymers and other liquids to room temperature where again new thermal equilibrium is established. When hardened through, often cracks are appearing due to tensile residual tresses are formed at the surface. To prevent crack formation, slow cooling in oils is widely used. During slow cooling material is not enough strengthened, that is why more alloy elements are added to the steel to provide needed strengthening. In the plenary lecture principally new approach of steel hardening is proposed. It is based on generalized equation for cooling time evaluation which allows calculating time of transition from high temperature equilibrium to room temperature equilibrium. The equation also calculates appropriate interruption time to provide optimal quenched layer. Using the generalized equation and CCT diagrams, the method for optimizing chemical composition of steels is developed to obtain optimal residual stress distribution throughout the section of steel part. The advantage of this method consists in the opportunity to use plain carbon steels instead of expensive alloy steels and calculate ideal critical size for a big variety of geometries on the basis of using respective CCT diagrams which are used at optimizing chemical composition of steels. It is discussed in detail optimal depth of hardened layer which provides high compressive residual stresses at the surface and not big residual tensile stresses in the core. Simultaneously during intensive quenching, the superstrengthening of a material in outer layers is occur. The method allows developing the new technologies to save materials, increase service life of steel parts, and use environmentally friendly liquids, just plain water, as a quenchant. The service life of steel parts increases due to high compressive residual stresses at the surface and improved mechanical properties. Taking all of these facts into account, a new approach for hardening of steel parts in the heat treating industry has been developed and applied into the practice.

Brief Biography of the Speaker:
Dr. Nikolai Kobasko received his PhD from the National Academy of Sciences of Ukraine in 1969. He is a leading expert on quenching and heat transfer during the hardening of steels. He is the author and co-author of more than 250 scientific and technical papers, several books and brochures, and more than 30 patents and certificates. In 2004, Dr. Nikolai Kobasko received the Da Vinci Diamond Award and Certificate in recognition of an outstanding contribution to thermal science. Dr. Nikolai Kobasko is Co-Editor of the WSEAS TRANSACTIONS on HEAT and MASS TRANSFER and is a member of Editorial Board for International Journal of Mechanics (NAUN) and Journal of ASTM International (JAI). He was the Head of the laboratory of the Thermal Physics Institute of the National Academy of Sciences of Ukraine. He is co-founder of two consulting companies: IQ Technologies Inc. Akron, USA (1999) and Intensive Technologies Ltd, Kiev, Ukraine (2000). The aim of both companies is material savings, ecological problems solving and increaing service life of steel parts. In 2009 for substantial and innovative contributions to thermal science and heat treating technologies, including development of novel quenching methods and application of computational models to thermal processes Dr. Nikolai Kobasko was elected as ASM International Fellow (FASM). At present he is the Director of Technology and R&D of IQ Technologies Inc., Akron, USA and also President of the Intensive Technologies Ltd., Kiev, Ukraine. More information is provided in http://www.intensivequench.com and http://www.itl.kiev.ua.

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