Category Archives: News

Fatigue Properties of Modified Steels Carburized at High Temperatures

The objective of phase XI is to compare the performance of carburized steel in bending and axial fatigue loading conditions. Carburization is a surface heat treatment process which adds carbon to the surface of a material to increase its hardness … Continue reading

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Neuber Stress Plots

This article explains how a “Neuber Stress” is calculated from fatigue test data obtained from un-notched axially-loaded specimen. In the presence of a geometric stress concentration feature on a part, the fatigue life of that part is often under-predicted as … Continue reading

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Mechanical Properties versus Carburization Depth

In this article we will examine the relationship between ultimate tensile strength, fatigue strength, and elongation versus the depth of carburization. The data for this comparison was taken from several iterations discussed in previous articles and shown in Table 1. … Continue reading

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Through Carburized 20MoCr4 Steel, 26-Hour Atmosphere Cycle versus 36-Hour Vacuum Cycle

In this article we will compare two through-carburized 20MoCr4 steel iterations. The composition of the 20MoCr4 steel is shown below in Table 1. Iteration #137 was atmosphere through carburized using the traditional 927 °C, twenty-six hour cycle which provides a … Continue reading

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The Effect of Bainite on Strength and Fatigue in Through-Carburized SAE 8620 Test Bars

A case microstructure may consist of martensite, retained austenite and bainite, and depends upon alloy and cooling rate. The impact of bainite on fatigue is not well known.  Sometimes carburized parts are intentionally austempered to increase the amount of bainite … Continue reading

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Atmosphere versus Vacuum Through-Carburized Boron Steels

In this article we will compare two through-carburized boron steels which were both atmosphere and vacuum heat treated. As in previous axial fatigue tests; approximately 30 test samples were prepared to ensure there were three replicate tests at a minimum … Continue reading

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A Look Ahead at Bar Fatigue in 2018

The SMDI Bar Steel Fatigue subcommittee is celebrating 20 years of working together to provide the industry with much needed fatigue data for critical applications. Past work includes the completion of over 200 iterations; 164 released to the public. This … Continue reading

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2017 Bar Fatigue Blog – Year in Review

During 2017 the SMDI Bar Steel Fatigue sub-committee continued work on numerous studies, test protocols, as requested by the committee members who represent key ground vehicle OEMs and suppliers. The committee continues to concentrate test efforts on those steel grades … Continue reading

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Carburized Case-Core Samples

In this article we will examine Iterations #62, #63 and #70. These are carburized samples with a case/core composite to simulate an actual carburized part. Until now, all of the carburized samples we have looked at have been through carburized … Continue reading

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Mechanical Properties and Fatigue Strength of the Early Through-Carburized Samples

In this article we will examine the mechanical properties and fatigue strength of the early through-carburized iterations in the SMDI fatigue program. During this time period the test bars were typically ground and polished after carburizing in order to eliminate … Continue reading

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