A Comparison between Ultra-high-strength and Conventional High-strength Fastener Steels: Mechanical Properties at Elevated Temperature and Microstructural Mechanisms
Artikel i vetenskaplig tidskrift, 2016

A comparison is made between the mechanical properties of the ultra-high-strength steel KNDS4 of fastener grade 14.9 and of conventional, high-strength steels 34Cr4 of fastener grade 12.9 and 33B2 of grade 10.9. The results show that the ratio of the yield strength at elevated temperatures to the yield strength at room temperature is higher for the ultra-high-strength steel than for both conventional high strength steels, especially at 500 degrees C. Moreover, the results show a trend in which the nano-indentation creep rate is lower as the strength of the steels is higher. The improved mechanical properties of the KNDS4 steel compared to the conventional high-strength steels are related to the smaller size of the alloy carbides in the KNDS4 steel. Furthermore, the effect of an alternative (industrial) heat-treatment on the evolution of the microstructure and hardness of the KNDS4 steel was investigated. Changing the industrial heat treatment can increase the hardness of KNDS4 by about 8%, since more alloy carbides can nucleate and grow. However, the standard industrial heat treatment results in a refinement of the martensite microstructure (grain size), which might be more beneficial for the toughness of the steel. Independent of the heat treatment, the mechanical performance of KNDS4 fasteners at elevated temperature and the low nano-indentation creep rates are two strong indicators that fasteners made from KNDS4 steel might be used at higher service temperatures than traditional high strength fasteners.

nano-indentation

creep

alloy carbide

temperature resistance

martensite

strength

microstructure

Författare

Ceic Ohlund

Organisation okänd

M. Lukovic

Organisation okänd

Jonathan Weidow

Chalmers, Fysik, Materialens mikrostruktur

Mattias Thuvander

Chalmers, Fysik, Materialens mikrostruktur

S. E. Offerman

Organisation okänd

ISIJ International

0915-1559 (ISSN)

Vol. 56 10 1874-1883

Ämneskategorier

Bearbetnings-, yt- och fogningsteknik

Metallurgi och metalliska material

DOI

10.2355/isijinternational.ISIJINT-2016-120

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Senast uppdaterat

2018-10-31