Niederdruck-Carbonitrieren mit Aminen*

Kurzfassung/AbstractToday case hardening of highly stressed gear wheels is state of the art, to meet the specific load demands at flank and tooth root. The heat treatment is including a carburization and quenching step in liquids or in gaseous media. The result of the heat treatment of gear wheels is strongly impacting the strength and the load capacity at flank and foot of the treated gears. The typical requirement for the microstructure in the surface near case is a well balanced mixture of finely dispersed retained austenite and martensite. Hard intermediate phases like cementite or other carbides are objectionable. Carbonitriding is an up to now unusual thermo-chemical treatment for parts made of case hardening steels. In the past it was typically applied to increase hardness or hardenability of low alloy steels of moderate hardenability. To do so, the treatment atmosphere was modified by the addition of fixed ammonia rates at low treatment temperatures. Newly developed automatically controlled carbonitriding processes make it possible to set up defined carbon-and nitrogen-depth profiles leading into a significant altered phase-composition of the case. The paper will give an overview on different phase compositions being achievable via carbonitriding and will give examples of carbonitrided samples made of case hardening steels, showing the influence of the heat treatment process and its atmosphere parameters. Also a perspective on the latest development of heat treatment technology for a designated set up of independently controlled carbon and nitrogen potentials for defined depth profiles will be given regarding the interdependency of both elements with each other and the alloy elements. n

Section: Wechselwirkung Von Kohlenstoff Und Stickstoff In Fester Lösungunclassified

Neue Randschichtgefüge carbonitrierter Bauteile und deren Festigkeitseigenschaften

Steinbacher¹,

Hoffmann²,

Zoch³

et al. 2015

Prozesstechnische Ansätze zur Optimierung des Wärmebehandlungsergebnisses des Niederdruck-Aufkohlens und des Niederdruck-Carbonitrierens

Franke¹,

Steinbacher

Velten³

et al. 2017

KurzfassungDas Niederdruck-Aufkohlen bietet dem Anwender ein Verfahren, mit dem unter geringem Einsatz von Kohlenwasserstoffen quasi randoxidationsfreie, metallisch blanke Oberflächen erzeugt werden [1]. Die bei diesem Verfahren entstandene randoxidationsfreie Randschicht lässt gegenüber einer durch Randoxidation geschädigten Oberfläche höhere Dauerfestigkeiten erwarten. Allerdings treten andere Effekte auf, die die Lebensdauer vermindern können [2]. An Einsatzstählen der Sorten 18CrNiMo7-6, 20MoCrS4 und 20CrMo4 wurden verschiedene Ansätze zur Verminderung und Unterbindung dieser Effekte untersucht. Es werden Prozessstrategien vorgestellt, die ein bisher ungenutztes Potenzial des Niederdruckaufkohlens ausschöpfen sollen. Zusätzlich wird auf für den Praktiker relevante Ergebnisse eingegangen, die die Prozessübertragbarkeit zwischen den Anlagentypen, Konditionierungseffekte und Wechselwirkungen bei einem Niederdruck-Carbonitrieren behandeln.

Some Aspects of Low Methylamine Partial Pressure Carbonitriding*

Koch

Reimert

Bajohr

2017

Low pressure carbonitriding is a case hardening process under development. At temperatures between 800 °C and 1050 °C and at total pressures below 50 mbar the carbon and nitrogen concentrations in the outer layer of steel parts are increased and the parts are subsequently hardened by quenching. As state of the art, ammonia is used as the nitrogen donor, in combination with a carbon donor gas, mainly acetylene or propane [1–3]. Other possible carbonitriding gases are not mentioned in recent literature with the exception of a Soviet Union patent [4], but no information on the application of this invention was found. At the Engler-Bunte-Institut of the Karlsruhe Institute of Technology, methylamine and dimethylamine were identified as potential carbonitriding gases, and their carbonitriding behavior was experimentally studied using a thermobalance. The experiments proved an increased nitrogen uptake of the steel samples in comparison to the state of the art. The carbon uptakes were in the same order of magnitude to a comparable process with acetylene. In addition to earlier published results for methylamine as the carbonitriding gas [5], this paper focuses on some operational and kinetic effects.