Crack Propagation Behavior of Impact Fracture in Case Hardening Steel Subjected to Combined Heat Treatment with Excess Vacuum Carburizing and Subsequent Induction Hardening

Abstract

The Charpy impact value of case hardening steel subjected to combined heat treatment with excess vacuum carburizing and subsequent induction hardening was evaluated. The purpose of this study is to clarify the relation between the crack propagation behavior and the microstructure in steels having different amounts of retained austenite and cementite. The vacuum carburizing treatment is performed at the hyper-eutectoid composition of 1.3 mass% C. Three different heating temperatures were chosen for induction hardening in the two-phase (austenite, cementite) region between A cm and A 1 to obtain different amounts of retained austenite and cementite. Decreasing the induction heating temperature from 1 143 K to 1 043 K, increased crack propagation resistance by around 30% on average in both the quenched-only and the quenched-and-tempered specimens. The high crack propagation resistance of the samples with the low induction heating temperature was caused by the arrest effect of undissolved θ. By contrast, in the sub-zero treated specimens, crack propagation resistance showed an almost constant value irrespective of the induction heating temperature. That constant propagation resistance was attributed to the repeated bending and branching occurring during crack propagation.

Simultaneous Improvement of Toughness and Fatigue Life in a Typical Ultrahigh Strength Steel by a New Deep Cryogenic Treatment Process

“…The primary factors affecting the fracture of carbon steel are both the content and morphology of martensite, RA, and carbides. [31][32][33][34] Thus, the causes of the varied mechanical properties from the different treatment processes were analyzed through the microstructures. In the following, the process of traditional heat treatment (QTT), the process with the worst mechanical properties (QCTT), and the process with the best mechanical properties (QTC) will be discussed in detail.…”

Effect of Rolling and Alloying Elements on the Impact Properties of Hypereutectoid Steels

“…The fraction of the retained γ phase was measured using X-ray diffraction (XRD) with Cr Kα radiation at 30 kV and 10 mA by using MSF-3M (RIGAKU). Note that Cr Kα radiation is generally used in the measurement of the retained γ phase with this equipment 21,22) . The retained γ phase was measured in the angle range of 115°-141°, for a dwell time of 100 s, whereas the α phase was measured in the angle range of 143°-169° for 30 s. The volume fraction of the retained γ phase was determined by the integrated intensity of (220) γ and (211) α peaks with the following equation:…”