Carbonitriding of low alloy steels: Mechanical and metallurgical responses

Abstract

Metallurgical and mechanical responses to the introduction of carbon and/or nitrogen have been investigated for alloys 16NiCrMo13 and 23MnCrMo5 through atmospheric pressure carbonitriding, carburizing and austenitic nitriding. Treatments were performed at 1173 K using CO − H 2 and/or NH 3 based atmospheres. As-quenched hardness is studied in terms of solid solution interstitial content, which is estimated from electron probe micro-analyses and thermodynamic simulations. This aims to quantify high-temperature precipitation of nitrides, which is accompanied by consumption of nitrogen in solid solution. Plots of as-quenched hardness versus the square root of the total content expressed in atomic fraction of interstitial elements, i.e. the sum of solution carbon and nitrogen, show the complementary character of these elements in determining the mechanical properties of the as-quenched alloys. Tempering of carbon-nitrogen martensite-for both carbonitriding and austenitic nitriding-led to lower hardness loss when compared to the same total content of interstitial carbon in martensite. Transmission electron microscopy analyses highlight precipitation of fine Fe 16 N 2 zones in the nitrogen-rich depth.

A first-principles reassessment of the Fe-N phase diagram in the low-nitrogen limit

“…Nitriding is a gaseous thermochemical treatment that is widely used to improve the surface properties of parts and components made in forging and tool steel. [1,2,3,4] Indeed, during nitriding, a compound layer at the surface and a diffusion zone underneath are formed. In contrast, through-thickness nitriding for improvement of bulk properties is rarely considered.…”

The influence of carbon potential after gas-carbonitriding on the microstructure and fatigue behavior of low alloyed steel

“…The endurance limits of the untreated specimens and the carbonitrided specimens 640 MPa, 740 MPa (for CN11) and 840 MPa (for CN21) correspond respectively to 16% and 32% enhancement, compared to the untreated state. In fact, according to the literature, fatigue strength improves with the increase of hardness and retained austenite [6,7].…”

“…Within this framework, the application of thermo chemical surface treatment enhances the strength of steels and the hardness of the surface [1][2][3]. Generally, case hardness may be considerably increased through the diffusion of carbon and/or nitrogen into the surface, applying thermo chemical treatments (carburizing [2,4,5], carbonitriding [6,7], nitrocarburizing [8] and nitriding processes [9][10][11][12]. In particular, carbonitriding has been employed in order to improve fatigue and wear resistance of steels utilized in many parts of machines [13], such as cam shafts, screws, engine valves and gears crank shafts as well as plates of various kinds of machines, for the purpose of enhancing fatigue strength and increasing wear resistance [14].…”

Design of Experiment Approach in the Industrial Gas Carburizing Process

“…Finally, samples were quenched in the mineral oil at 75°C. The quenching process allows the diffusionless martensitic transformation at the surface [30][31][32]. However, thermal gradient at the core of the sample is significantly less, which allows the bainitic or ferritic transformation to occur in the core of the samples [32,33].…”