Fatigue in low pressure carbonitrided steels
type: CreativeWork
description: Low pressure carbonitriding and pressurized gas quenching heat treatments were conducted on four steel alloys: 20MnCr5, 20MnCr5 + B, SAE 8620 and SAE 8620 + Nb. Bending fatigue tests were performed with Brugger specimens to simulate fatigue on the tooth root of a gear. The heat treatment parameters were modified to ensure the surface hardness and effective case depths were comparable for the four alloys. The profiles for hardness, retained austenite, residual stress, carbon and nitrogen were comparable for all the alloys. However, the fatigue performance of each alloy was different. The highest endurance limit was attained by 20MnCr5+B, followed by 20MnCr5, SAE 8620+Nb, and SAE 8620. The differences in fatigue endurance limit occurred despite similar case depths and surface hardness, indicating that other features were relevant for the fatigue performance in this study. However, the difference between the 20MnCr5 endurance limits was minimal, suggesting the differences in B content in these alloys has little effect. Low magnitude tensile residual stresses were measured near the surface in all conditions. Additionally, non-martensitic transformation products (NMTPs) were observed to various extents near the surface on all the alloys, with a higher volume fraction in SAE 8620 + Nb and lower volume fraction in 20MnCr5 + B. However, there were no differences in retained austenite profiles between the conditions, and the retained austenite was mostly stable against deformation-induced transformation to martensite during fatigue testing near the endurance limit, which is in contrast to some studies on carburized steels where more significant transformation occurs. The presence of NMTPs and tensile residual stress could have occurred due to a low cooling rate during pressurized gas quenching. Residual stress profiles were very similar for all the alloys. Overall, it is interpreted that the difference in fatigue lives between the conditions is due to differences in chemical…
abstract: Low pressure carbonitriding and pressurized gas quenching heat treatments were conducted on four steel alloys: 20MnCr5, 20MnCr5 + B, SAE 8620 and SAE 8620 + Nb. Bending fatigue tests were performed with Brugger specimens to simulate fatigue on the tooth root of a gear. The heat treatment parameters were modified to ensure the surface hardness and effective case depths were comparable for the four alloys. The profiles for hardness, retained austenite, residual stress, carbon and nitrogen were comparable for all the alloys. However, the fatigue performance of each alloy was different. The highest endurance limit was attained by 20MnCr5+B, followed by 20MnCr5, SAE 8620+Nb, and SAE 8620. The differences in fatigue endurance limit occurred despite similar case depths and surface hardness, indicating that other features were relevant for the fatigue performance in this study. However, the difference between the 20MnCr5 endurance limits was minimal, suggesting the differences in B content in these alloys has little effect. Low magnitude tensile residual stresses were measured near the surface in all conditions. Additionally, non-martensitic transformation products (NMTPs) were observed to various extents near the surface on all the alloys, with a higher volume fraction in SAE 8620 + Nb and lower volume fraction in 20MnCr5 + B. However, there were no differences in retained austenite profiles between the conditions, and the retained austenite was mostly stable against deformation-induced transformation to martensite during fatigue testing near the endurance limit, which is in contrast to some studies on carburized steels where more significant transformation occurs. The presence of NMTPs and tensile residual stress could have occurred due to a low cooling rate during pressurized gas quenching. Residual stress profiles were very similar for all the alloys. Overall, it is interpreted that the difference in fatigue lives between the conditions is due to differences in chemical…
author: Vilela Costa, Larissa
language: eng
language: English
keywords: fatigue, low pressure carbonitriding, carbonitriding, steel, low alloy steel
identifier: T 9121
date published: 2021
date modified: 2026-07-24T01:42:11Z
provider: Colorado School of Mines
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: Colorado School of Mines. Arthur Lakes Library

PropertyValue
property ID: Handle
value: https://hdl.handle.net/11124/176454