University of Oulu

Haiko, O.; Kaijalainen, A.; Pallaspuro, S.; Hannula, J.; Porter, D.; Liimatainen, T.; Kömi, J. The Effect of Tempering on the Microstructure and Mechanical Properties of a Novel 0.4C Press-Hardening Steel. Appl. Sci. 2019, 9, 4231. http://dx.doi.org/10.3390/app9204231

The effect of tempering on the microstructure and mechanical properties of a novel 0.4C press-hardening steel

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Author: Haiko, Oskari1; Kaijalainen, Antti1; Pallaspuro, Sakari1;
Organizations: 1Materials and Mechanical Engineering, Centre for Advanced Steels Research, University of Oulu,90014 Oulu, Finland
2Raahe Works, SSAB Europe, 92100 Raahe, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 4.5 MB)
Persistent link: http://urn.fi/urn:nbn:fi-fe2019102134062
Language: English
Published: Multidisciplinary Digital Publishing Institute, 2019
Publish Date: 2019-10-21
Description:

Abstract

In this paper, the effects of different tempering temperatures on a recently developed ultrahigh-strength steel with 0.4 wt.% carbon content were studied. The steel is designed to be used in press-hardening for different wear applications, which require high surface hardness (650 HV/58 HRC). Hot-rolled steel sheet from a hot strip mill was austenitized, water quenched and subjected to 2-h tempering at different temperatures ranging from 150 °C to 400 °C. Mechanical properties, microstructure, dislocation densities, and fracture surfaces of the steels were characterized. Tensile strength greater than 2200 MPa and hardness above 650 HV/58 HRC were measured for the as-quenched variant. Tempering decreased the tensile strength and hardness, but yield strength increased with low-temperature tempering (150 °C and 200 °C). Charpy-V impact toughness improved with low-temperature tempering, but tempered martensite embrittlement at 300 °C and 400 °C decreased the impact toughness at −40 °C. Dislocation densities as estimated using X-ray diffraction showed a linear decrease with increasing tempering temperature. Retained austenite was present in the water quenched and low-temperature tempered samples, but no retained austenite was found in samples subjected to tempering at 300 °C or higher. The substantial changes in the microstructure of the steels caused by the tempering are discussed.

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Series: Applied sciences
ISSN: 2076-3417
ISSN-E: 2076-3417
ISSN-L: 2076-3417
Volume: 9
Issue: 20
Article number: 4231
DOI: 10.3390/app9204231
OADOI: https://oadoi.org/10.3390/app9204231
Type of Publication: A1 Journal article – refereed
Field of Science: 216 Materials engineering
Subjects:
Funding: This research has been done within the program Steel Ecosystem for Focused Applications (StEFA). We gratefully acknowledge financial support from Business Finland and the companies participating in the program.
Copyright information: © 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
  https://creativecommons.org/licenses/by/4.0/