TY - THES

T1 - Carbonitriding of Gear Components

AU - Hetzenauer, Thomas

N1 - embargoed until 25-06-2023

PY - 2018

Y1 - 2018

N2 - For construction tools, it is necessary to increase the power-to-weight ratio of its tools. Diamond drilling tools, especially, have large transmission gearboxes that are charged with high loads during drilling. The goal of the project is to increase the maximum load of the gearwheels, so that lighter tools with more power can be offered and a leading market position ensured for the company in this business. It was proven in previous laboratory testing that carbonitriding with controlled atmospheric conditions led to a significantly higher content of stabilized retained austenite (RA). Also, an increase in the tooth root load capacity as well as flank load carrying capacity was observed in this previous research study. Reference samples were manufactured by an research partner and should be reproduced at an existing production plant. In the metallographic part of the thesis, different characterization methods for RA are investigated and compared. To gain information for further weight optimization, mechanical tests were conducted using prototype machines. The reproduction of all reference microstructures was possible on an upgraded furnace. X ray diffraction delivers accurate results for the determination of RA. Image analysis of Beraha etched microstructures seems to be most precise for a medium level of about 30% RA content. Above and below this level, the amount is underestimated. As RA in the surface increases, the signal detected by the magnetic-inductive method also increases. Under certain circumstances and by using established standards, basic determination of RA content is feasible with the Feritscope. Carbonitriding with the goal of increasing the content of RA is beneficial for gearwheels used at uniform and unilateral loads. For a high double-sided load, as required in application, the carbonitrided microstructure is not advantageous. The formation of coarse carbonitrides needs to be avoided. This is especially difficult for higher case-hardening depths, which require longer carbonitriding times. To offer carbonitriding for higher case-hardening depths or higher loads, further investigations need to be conducted.

AB - For construction tools, it is necessary to increase the power-to-weight ratio of its tools. Diamond drilling tools, especially, have large transmission gearboxes that are charged with high loads during drilling. The goal of the project is to increase the maximum load of the gearwheels, so that lighter tools with more power can be offered and a leading market position ensured for the company in this business. It was proven in previous laboratory testing that carbonitriding with controlled atmospheric conditions led to a significantly higher content of stabilized retained austenite (RA). Also, an increase in the tooth root load capacity as well as flank load carrying capacity was observed in this previous research study. Reference samples were manufactured by an research partner and should be reproduced at an existing production plant. In the metallographic part of the thesis, different characterization methods for RA are investigated and compared. To gain information for further weight optimization, mechanical tests were conducted using prototype machines. The reproduction of all reference microstructures was possible on an upgraded furnace. X ray diffraction delivers accurate results for the determination of RA. Image analysis of Beraha etched microstructures seems to be most precise for a medium level of about 30% RA content. Above and below this level, the amount is underestimated. As RA in the surface increases, the signal detected by the magnetic-inductive method also increases. Under certain circumstances and by using established standards, basic determination of RA content is feasible with the Feritscope. Carbonitriding with the goal of increasing the content of RA is beneficial for gearwheels used at uniform and unilateral loads. For a high double-sided load, as required in application, the carbonitrided microstructure is not advantageous. The formation of coarse carbonitrides needs to be avoided. This is especially difficult for higher case-hardening depths, which require longer carbonitriding times. To offer carbonitriding for higher case-hardening depths or higher loads, further investigations need to be conducted.

KW - Carbonitrieren

KW - Restaustenit

KW - Zahnräder

KW - Carbonitriding

KW - Gear Wheel

KW - Retained Austenite

M3 - Master's Thesis

ER -