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Influence of the chemical composition on the mechanical properties of forged microalloyed steels

V. GEANTĂ1,* , M. TACĂ2, D. DAISAb2, I. VOICULESCU1, R. STEFĂNOIU1, D.M. CONSTANTINESCU1, D. SAVASTRU3

Affiliation

  1. POLITEHNICA University of Bucharest, 313 Splaiul Independenţei, 060042, Bucharest, Romania
  2. METAV-CD Bucharest, Romania
  3. National Institute for Research and Development in Optoelectronics, INOE 200, 409 Atomistilor st., Magurele, Romania

Abstract

The microalloying process applied to the steels is a common practice for obtaining high quality grades of steels that can be used in the production of parts for the automotive industry. The most significant chemical elements used for micro-alloying are: vanadium, niobium, titanium and zirconium. Microalloying of carbon steels with small amounts of elements having high affinity to carbon and nitrogen (usually less than 0.1%), results in a significant improvement of the mechanical properties. By microalloying process, stable compounds as carbides, carbo-nitrides or nitrides in the form of finely dispersed particles are formed in the solid solution of the solidified steel. These precipitates can slow the austenite grain growth and can block the dislocations movement during deformation process. The microalloying process of steels allows the increasing of some mechanical properties at lower cost compared with those of low and medium alloyed steels. If the metallurgical processes are appropriate (obtaining, refining and thermo mechanical processing such as rolling, forging etc.), the precipitates reaches the appropriate dimensions and dispersion, being localized mostly in the grain volume and not on the grain boundary, and can act as reinforcement elements in the metallic matrix, by blocking the grains growth and by increasing the local tension at the site level, which increase the hardness and can improve the thermal stability characteristics, at high temperatures. In the paper are presented and discussed several results of research, related to the obtaining of the micro-alloyed steels using a vacuum induction furnace, the selection of the alloying elements according the particular type of metallurgical treatment, the establishment of the optimal V/Nb ratio and the analyze of the cooling speed after deformation, in order to optimize the final characteristics of the experimental steels..

Keywords

Microalloyed steels, Steelmaking, Vacuum induction furnace, Forging, Mechanical properties, V/Nb ratio.

Submitted at: April 9, 2015
Accepted at: June 24, 2015

Citation

V. GEANTĂ, M. TACĂ, D. DAISAb, I. VOICULESCU, R. STEFĂNOIU, D.M. CONSTANTINESCU, D. SAVASTRU, Influence of the chemical composition on the mechanical properties of forged microalloyed steels, Journal of Optoelectronics and Advanced Materials Vol. 17, Iss. 7-8, pp. 1004-1011 (2015)