Effects of low-temperature treatments on surface hardness, retained austenite content, residual stress condition and the resulting tooth root bending strength of case-hardened 18CrNiMo7-6 gears

2019 ◽  
Vol 233 (21-22) ◽  
pp. 7350-7357
Author(s):  
D Kratzer ◽  
F Dobler ◽  
T Tobie ◽  
T Hoja ◽  
M Steinbacher ◽  
...  
Keyword(s):  
Residual Stress ◽  
Low Temperature ◽  
Retained Austenite ◽  
Stress Condition ◽  
Bending Strength ◽  
Surface Hardness ◽  
Tooth Root ◽  
Austenite Content ◽  
Temperature Levels ◽  
Low Temperature Treatments

This paper contains parts of the research project FVA 612 and investigates the correlation between low-temperature treatments of case-hardened gears made from the material 18CrNiMo7-6 and the resulting surface hardness, retained austenite content, and residual stress condition. These parameters were further investigated with regard to the tooth root bending strength obtained with pulsating test rigs. The tested gears were subjected to various low-temperature treatments including different temperature levels before or after tempering. Other investigated parameters were the application of a shot blasting treatment and the effect of low-temperature treatments on gears with increased retained austenite content after the carburizing process.

Heat Treatment Effects on Distortion, Residual Stress, and Retained Austenite in Carburized 4320 Steel

2014 ◽  
Vol 783-786 ◽  
pp. 692-697 ◽  
Author(s):  
Andrew Clark ◽  
Randy J. Bowers ◽  
Derek O. Northwood
Keyword(s):  
Heat Treatment ◽  
Residual Stress ◽  
Retained Austenite ◽  
Compressive Residual Stress ◽  
Surface Residual Stress ◽  
Depth Profiles ◽  
Size And Shape ◽  
Austenite Content ◽  
Treatment Conditions ◽  
The Difference

The effects of heat treatment on distortion, residual stress, and retained austenite were compared for case-carburized 4320 steel, in both the austempered and quench-and-tempered condition. Navy C-ring samples were used to quantify both size and shape distortions, as well as residual stress. The austempering heat treatment produced less distortion and a higher surface residual stress. Both hoop and axial stresses were measured; the difference between them was less than seven percent in all cases. Depth profiles were obtained for residual stress and retained austenite from representative C-ring samples for the austempered and quench-and-tempered heat treatment conditions. Austempering maintained a compressive residual stress to greater depths than quench-and-tempering. Quench-and-tempering also resulted in lower retained austenite amounts immediately beneath the surface. However, for both heat treatments, the retained austenite content was approximately one percent at depths greater than 0.5 mm.

Some Factors Influencing the Pitting, Micro-Pitting (Frosted Areas) and Slow Speed Wear of Surface Hardened Gears

1981 ◽  
Vol 103 (2) ◽  
pp. 499-505 ◽  
Author(s):  
H. Winter ◽  
T. Weiss
Keyword(s):  
Residual Stress ◽  
Carbon Content ◽  
Retained Austenite ◽  
White Layer ◽  
Load Capacity ◽  
Influence Factors ◽  
Surface Hardness ◽  
Considerable Influence ◽  
Slow Speed ◽  
Factors Influencing

Surface hardness and hardening depth are the most important influence factors for the load capacity of surface hardened gears. Besides the structure of the hardening pattern, it’s carbon content, amount of retained austenite, residual stress and white layer (nitrided gears) have a considerable influence. Lubricant and material of the mating gear as well as roughness of the tooth flanks have a different influence on pitting, micro-pitting and wear.

scholarly journals Influence of grinding zones on the tooth root bending strength of case carburized gears

2021 ◽  
Author(s):  
Karl Jakob Winkler ◽  
Thomas Tobie ◽  
Karsten Stahl
Keyword(s):  
Residual Stress ◽  
Stress State ◽  
Bending Strength ◽  
Decisive Role ◽  
Experimental Investigations ◽  
Tooth Root ◽  
Industrial Practice ◽  
Application Range ◽  
Residual Stress State ◽  
Root Area

AbstractKnowledge of the expected tooth root bending strength plays a decisive role in the design of gear sets. Due to dimensional and shape changes resulting from distortion due to the heat treatment, unintentional, partial grinding in the tooth root area may occur, particularly in the application range of large gears. The influences of an unintentional grinding zone on the tooth root bending strength have not yet been clarified with sufficient accuracy. As a result, grinding zones lead to uncertainties when evaluating the tooth root bending strength and thus to a loss of time and cost in the field of industrial practice.This paper presents experimental investigations on the influence of grinding zones on the tooth root bending strength of case carburized gears. For the experimental investigations, there are three unground reference variants with different blasting treatments: non-blasted, mechanical cleaned by shot blasting and shot peened. The unground reference variants are examined regarding their tooth root bending strength. For the other test gear variants, different grindings zones are applied resulting in light and strong material removal by grinding. The variants with the different grinding zones are examined analogously regarding their tooth root bending strength and are subsequently compared to the reference variants.The results of the experimental investigations show that grinding zones can have diverse influences on the tooth root bending strength of case carburized gears– Non-blasted gears do not show changes regarding the tooth root bending strength with regard to light or strong grinding zones applied within this investigation.– Shot blasted (mechanical cleaned) gears show no change in the tooth root bending strength for light grinding zones (grinding application does not significantly alter the original residual stress state in the tooth root area).– Shot blasted (mechanical cleaned) gears show a reduction of the tooth bending strength of up to 20 % with regard to strong grinding zones (grinding application does significantly alter the original residual stress state in the tooth root area).– Shot peened gears show a behavior similar to that of shot blasted gears with reductions of the tooth root bending strength of up to 30 %.– Shot peening the strong grinding zones as a repair measure can increase the reduced tooth root bending strength again. However, for the investigated test gears, the resulting tooth root bending strength was below the shot blasted reference variant.The results of this paper help to evaluate the influence of grinding zones on the tooth root bending strength of case carburized gears more precisely compared to the generalized reductions of current standards and classifications. The results can be incorporated in standards such as DIN 3390 as well as ISO 6336 and can be applied in the field of industrial practice. Eventually, the findings help to reduce the current loss of time and cost caused by uncertainties regarding grinding zones.

Vacuum Carburizing of AISI S7 Tool Steel

2006 ◽  
Vol 118 ◽  
pp. 91-96 ◽  
Author(s):  
Liu Ho Chiu ◽  
Yu Jen Chen ◽  
Chang Hui Wu ◽  
Heng Chang
Keyword(s):  
Fracture Toughness ◽  
High Temperature ◽  
Low Temperature ◽  
Tool Steel ◽  
Retained Austenite ◽  
Surface Hardness ◽  
Vacuum Carburizing ◽  
Modest Increase ◽  
Gas Quenching ◽  
Quenching And Tempering

The effects of vacuum carburizing under an acetylene atmosphere at 950 and 1000, followed by gas quenching and tempering at various temperatures on the properties of AISI S7 shock-resistant tool steel were studied. As carburized specimens undergo low temperature tempering, the surface hardness of the quenched specimens carburized at 1000 is lower than those of the specimens carburized at 950, due to the large amount of retained austenite in specimens carburized at 1000. Under high temperature tempering, specimens carburized at 1000 have higher surface hardness than specimens carburized at 950. As specimens are tempered in the range between 450 to 550, the surface hardness of carburized specimens show a modest increase due to the secondary hardening effects. According to the fracture toughness data, the toughness of carburized specimens peaked at tempering at 600.

Influence of Low Temperatures on Material Properties and Tooth Root Bending Strength of Case-Hardened Gears

2015 ◽  
Author(s):  
Florian Dobler ◽  
Thomas Tobie ◽  
Karsten Stahl
Keyword(s):  
Heat Treatment ◽  
Material Properties ◽  
Low Temperatures ◽  
Treatment Process ◽  
Bending Strength ◽  
Heat Treatment Process ◽  
Tooth Root ◽  
Almost All ◽  
Relevant Material ◽  
Low Temperature Treatments

This paper presents the main results of performed investigations and discusses the possible influences of different low temperature treatments on relevant material characteristics in correlation with the obtained tooth root bending strength of case-hardened gears made of materials 18CrNiMo7-6, 20MnCr5 and 15NiCr13. Most of the investigations were performed on gears that were exposed to low temperatures after heat treatment. Additionally, the effect of low temperatures within the heat treatment process was examined. For shot blasted gears, which were treated by low temperatures after heat treatment process, all examined materials showed no decrease of the tooth root bending strength. In contrast, for almost all gears which were cooled down to low temperatures within the heat treatment, a decrease in the tooth root bending strength was observed in unpeened as well as in shot blasted condition. Additional investigations show a correlation of tooth root bending strength and relevant material properties.

In-depth analysis of crack area characteristics of fisheye failures influenced by the multiaxial stress condition in the tooth root fillet of high-strength gears

2021 ◽  
pp. 095440622110616
Author(s):  
Daniel Fuchs ◽  
Sascha Rommel ◽  
Thomas Tobie ◽  
Karsten Stahl
Keyword(s):  
Residual Stresses ◽  
Stress Condition ◽  
Bending Strength ◽  
High Strength ◽  
Tooth Root ◽  
Multiaxial Stress ◽  
Depth Analysis ◽  
Standard Specimens ◽  
Compressive Residual Stresses ◽  
Model Approach

Modern high-strength gears have to satisfy many requirements, such as improved tooth root bending strength. The process of shot-peening is correlated to the introduction of compressive residual stresses in the surface layer of a gear to achieve a higher tooth root bending strength. However, due to the compressive residual stresses fisheye failures can occur and can have a determining effect on the endurance of high-strength gears. By preventing such failures, it should be possible to increase further the tooth root bending strength of high-strength gears. However, this requires a deeper understanding of the crack initiation and propagation processes. Especially the unique multiaxial stress condition in the tooth root fillet of a gear could influence the crack area characteristics significantly. Though, in the literature there is no proper characterization of crack area characteristics in the tooth root fillet of gears in detail, so far. Furthermore, in previous work a model approach for the evaluation of the tooth root bending strength of gears was presented, which is based on the results of Murakami. A first comparison with experimental data showed a basic applicability of the model approach on gears. However, the derived model approach showed some room for improvement. Questions arose as to whether the approach is really fully applicable to gears, whether further modifications are needed, or whether further extension is even practical, since the fisheye fracture characteristics of gears might differ significantly from those of standard specimens. The aim of this paper is therefore to present an extensive in-depth analysis of the crack area characteristics in the event of tooth root fracture damages caused by a fisheye failure in high-strength gears. Furthermore, a case study is used to verify whether a detailed evaluation of the characteristics of non-metallic inclusions leads to more accurate results of the model approach.

scholarly journals Effect of Cryogenic Treatment on Microstructure, Mechanical Properties and Distortion of Carburized Gear Steels

Metals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1940
Author(s):  
Yongming Yan ◽  
Ke Liu ◽  
Zixiang Luo ◽  
Maoqiu Wang ◽  
Xinming Wang
Keyword(s):  
Mechanical Properties ◽  
Wear Resistance ◽  
Low Temperature ◽  
Wear Mechanisms ◽  
Retained Austenite ◽  
Cryogenic Treatment ◽  
Austenite Content ◽  
Cryogenic Process ◽  
Carburized Gear ◽  
Gear Steels

The effects of cryogenic treatment and low temperature tempering on the microstructure, mechanical properties and distortion of the 20Cr2Ni4A and 17Cr2Ni2MoVNb carburized gear steels were investigated. The results showed that the case hardness of the experimental steels was increased after the cryogenic treatment, due to the decrease of the retained austenite content and the precipitation of the tiny carbides. The wear resistance of the two steels after cryogenic treatment was improved, although the wear mechanisms were different for 17Cr2Ni2MoVNb and 20Cr2Ni4A steels. The distortion of the Navy C-ring specimens underwent shrinkage before expansion during the cryogenic process, and the distortion of 17Cr2Ni2MoVNb steel was smaller than that of 20Cr2Ni4A steel.

scholarly journals Effect of Tempering Conditions on Secondary Hardening of Carbides and Retained Austenite in Spray-Formed M42 High-Speed Steel

Materials ◽  
2019 ◽  
Vol 12 (22) ◽  
pp. 3714 ◽  
Author(s):  
Bowen Liu ◽  
Tian Qin ◽  
Wei Xu ◽  
Chengchang Jia ◽  
Qiuchi Wu ◽  
...  
Keyword(s):  
Electron Microscope ◽  
Carbide Phase ◽  
Retained Austenite ◽  
High Speed ◽  
Bending Strength ◽  
High Speed Steel ◽  
Secondary Hardening ◽  
Electron Backscattered Diffraction ◽  
Scanning Calorimetry ◽  
Austenite Content

In this study, the effect of tempering conditions on microstructure, grain size, and carbide phase compositions of spray-formed high-speed steel after quenching at 1180 °C was studied. The influence of carbide phase, size of carbides, and retained austenite content on secondary hardening of the steel was analyzed by field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), electron backscattered diffraction (EBSD), and differential scanning calorimetry (DSC); the hardness, microhardness of carbide, and bending strength were tested. The results show that M3C, M6C, M7C3, and MC carbides may precipitate at different tempering temperatures and the transformation of the retained austenite can be controlled by tempering. The phase composition of carbides, microstructure, and retained austenite content strongly influences the performance characteristics of M42 high-speed steel after tempering. In contrast, the secondary carbides produced by tempering thrice at 540 °C are mainly M6C carbides rich in W and Mo elements, and the content of retained austenite is effectively reduced. At this stage, the Rockwell hardness reaches 67.2 HRC, bending strength reaches 3115 MPa, and the properties and microstructure are optimal.

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