Regular Article

Short time austenitizing effects on the hardenability of 0.55 wt. pct. Carbon steels

Advanced Steel Processing and Products Research Center, Department of Metallurgical and Materials Engineering, Colorado School of Mines, Golden, 80401 Colorado, USA

^* e-mail: rcryderm@mines.edu

Received: 5 December 2017
Accepted: 4 April 2018

Abstract

Three laboratory melted steels containing 0.55 wt. pct. C were preconditioned by austenitizing at 900 °C and oil quenching. The oil quenched specimens were induction heated at a rate of 50 °C/s to 850 °C and the hardenability was determined for austenitizing times of 2 and 10 s. Alloy compositions of the three steels in wt. pct. were 0.8 Mn, 0.2 Mn–2.1 Ni, and 0.8 Mn–0.5 W. The changes in transformation behavior were determined on a quenching dilatometer and are described by CCT diagrams, hardness, and metallographic examination. The progression of transformation to austenite on heating was determined by metallographic examination of specimens quenched from several peak-heating temperatures. Changes in austenite grain size with the induction heating time were also characterized. The quench rate required to attain fully martensitic microstructures increased as the austenitizing time was reduced from 10 to 2 s. Conventional hardenability calculation methods did not accurately forecast the hardness and microstructure under conditions of rapid induction hardening.