Radev, R. “Numerical Investigations Regarding Necessity of Preforming Steps for Hot Closed Die Forging of Axisymmetrical Part”. Advanced Technologies and Materials, vol. 38, no. 2, Dec. 2013, pp. 125-31, https://jged.uns.ac.rs/index.php/atm/article/view/JTP.2013.38.2.2.