Ductile Cast Iron Microstructure Adjustment by Means of Heat Treatment

• Published in: Archives of foundry engineering Vol. 20; no. 3; p. 37
• Main Authors: Mróz, M, Orłowicz, A W, Tupaj, M, Kupiec, B, Kawiński, M
• Format: Journal Article
• Language: English
• Published: Katowice Polish Academy of Sciences 01.01.2020
• Subjects: Cast iron; Castings; Cementite; Cooling rate; Dilatometry; Disintegration; Hardness; Heat treating; Heat treating furnaces; Heat treatment; Knowledge acquisition; Nodular iron; Pearlite; Precipitates
• ISSN: 1897-3310; 2299-2944
• DOI: 10.24425/afe.2020.133327

The study presented in this paper concerned the possibility to apply a heat treatment process to ductile cast-iron thin-walled castings in order to remove excessive quantities of pearlite and eutectic cementite precipitates and thus meet the customer’s requirements. After determining the rates of heating a casting up to and cooling down from 900°C feasible in the used production heat treatment furnace (vh = 300°C/h and vc = 200°C/h, respectively), dilatometric tests were carried out to evaluate temperatures Tgr, TAc1start, TAc1end, TAr1start, and TAr1end. The newly acquired knowledge was the base on which conditions for a single-step ferritizing heat treatment securing disintegration of pearlite were developed as well as those of a two-step ferritization process guaranteeing complete disintegration of cementite and arriving at the required ferrite and pearlite content. A purely ferritic matrix and hardness of 119 HB was secured by the treatment scheme: 920°C for 2 hours / vc = 60°C/h / 720°C for 4 hours. A matrix containing 20–45% of pearlite and hardness of 180–182 HB was obtained by applying: 920°C for 2 hours or 4 hours / vc = 200°C/h to 650°C / ambient air.