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Alloying and Heat-treatment of Ultrahigh Carbon Steel

Author: LiLei
Tutor: LiuHuaShan
School: Central South University
Course: Materials Science
Keywords: Ultrahigh carbon steels modification alloying heat treatment wear
CLC: TG156
Type: Master's thesis
Year: 2013
Downloads: 31
Quote: 0
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Abstract


Ultrahigh carbon steels (UHCS), which are hyper-eutectoid steels containing1.0-2.1%C, have been of great interest. These steels have a remarkable combination of mechanical properties, e.g. high hardness, strength and wear resistance, good ductility, and superplasticity. The high volume fraction of carbides with high connectivity in the matrix makes ultrahigh carbon steels quite brittle after conventional solidification processes. In this paper, a new type of modifier is employed to the UHCS. The effect of alloying and heat-treatment on the microstructure and properties of the UHCS have been researched. The results are summarized as follows:(1) By adding modifier in the UHCS, the eutectic carbide network structure was broken up and became blocky. With the increase of Mo content, alloy carbide M23C6was found in the as-cast microstructure. The appearance of M23C6suppresses the formation of massive cementite and makes spheroidized fine carbides dispersed uniformly in the matrix after heat-treatment. When the content of Mo increases to0.8wt%, retained austenite and lower bainite were found in the as-cast microstructure.(2) Divorced Eutectoid Transformation (810℃×15min furnace cooling to730℃×2h)、isothermal annealing (1050℃×3h+650℃×15min) and normalizing(1000℃×2h) were applied to the samples. The microstructure and properties of the alloys after quenching and tempering were studied. After isothermal annealing (1050℃×3h+650℃×15min)、quenching (850℃×1h) and tempering (400℃×2h), the alloy with0.5wt%Mo obtained the ideal microstructure. It has the highest impact toughness (18.4J cm-2), despite the hardness remaining around50HRC(3) The friction coefficient of UHCS after heat treatment was higher than that of the as-cast alloy. The friction coefficient was changed by the increasing of loads. At the load of80N, the UHCS has the highest friction coefficient.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > Heat treatment > Heat treatment process
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