The effect of nitriding temperature on hardness and microstructure of die steel pre-treated by ultrasonic cold forging technology
Highlights
► Ultrasonic cold forging technology was used as a pretreatment for plasma nitriding. ► A thicker and harder gradient modification layer was formed. ► An optimized nitriding temperature was recognized as 520 °C.
Introduction
Plasma nitriding, one of well-established commercial surface modification techniques, has been widely used to enhance wear and corrosion behaviour of moulds [1], [2], [3]. Nevertheless, reducing energy consumption still presents a major challenge to surface engineers and researchers, and it also acts as a driving force for the optimization of plasma nitriding process [4]. The thickness, composition and properties of a nitrided layer are dependent on the nitriding conditions as well as on the material [1], [5], [6]. Therefore, there are two ways to improve the plasma nitriding process: one is to find a complex surface modification technology to accelerate the chemical reaction of the material surface and the other is to develop an optimal technological plasma nitriding parameter [1], [5], [6], [7], [8].
It is reported that the surface layer possesses ultrafine grains with a large number of grain boundaries and defect densities, which may act as fast atomic diffusion channels, then the gas nitriding temperature could be reduced [6], [7], [8], [9]. Li et al. [7] reported that the surface mechanical attrition treatment (SMAT) plus plasma nitriding can be successfully used to further improve the properties of AISI 4140 and AISI 316L steel. Ultrasonic cold forging technology (UCFT) utilizes ultrasonic vibration energy to induce severe plastic deformation to a material surface [10], [11]. It could produce outstanding surface hardness, surface roughness (0.08–0.5 μm) and an effect layer with a certain depth (about 300 μm) [10], [11], [12], [13], [14]. Therefore, UCFT could be expected as a highly promising pre-treatment means of plasma nitriding. Meanwhile, the plasma nitriding temperature plays another basic role on the formation of nitrided layer [15], [16], [17], [18]. However, few works on the die steel pre-treated by UCFT and then plasma nitriding are reported so far.
In this study, UCFT was introduced as a pre-treatment of plasma nitriding. Plasma nitriding processes performed at temperature of 350, 450, 500, 520, and 550 °C for 4 h. The effects of plasma nitriding temperature on the modification layer structural properties, including surface morphology, hardness profile, diffusion layer thickness, compound layer thickness and phase content, were investigated. It aims to find an optimized nitriding temperature to the surface combined modification process.
Section snippets
Materials
A commercial available AISI D2 die steel cylinder (∅32 mm × 105 mm) with hardness of about 200 HV was prepared. Table 1 shows its chemical composition.
Ultrasonic cold forging technology treatment
The sketch of the UCFT device is shown in Fig. 1. The principle of the device was developed by Alekhine and Alekhine [14]. It transforms ultrasonic vibratory energy into tens of thousands of strikes per second. The output power is about 1 kW. The dynamic load is 1.5–5 times higher than static load. The total load acting on the specimen is the sum of
UCFT pre-treatment
Cross-section image of the UCFT + Un-nitrided samples was shown in Fig. 1. It can be seen that micro-structural morphology of severe plastic deformation layer is quite different from that of the matrix. An effective layer caused by severe plastic deformation with a depth of about 350 μm was formed.
Fig. 3 illustrates the XRD pattern obtained from the Un-UCFT + Un-nitrided samples and the UCFT + Un-nitrided samples. The Bragg diffraction peaks of the UCFT + Un-nitrided samples are broader than those of
Conclusions
To sum up, the UCFT can be introduced as a pre-treatment means of plasma nitriding to effectively enhance the properties of AISI D2 die steel. Pre-treated by UCFT, the surface of AISI D2 steel samples tends to form a thicker and harder nitride layer with smaller nitrided nano-particles and more nitride phases (ε-Fe2–3N, γ′-Fe4N and CrN).
A higher nitriding temperature promotes the formation of the hard phases (ε-Fe2–3N, γ′-Fe4N and CrN). Meanwhile, to some extent, a high nitriding temperature
Acknowledgments
The authors would like to thank the National Natural Science Foundation of China (51275494), the Fundamental Research Funds for the Central Universities (2012ZY51), the Program for Key International Science and Technology Cooperation Project of China (2010DFR50070) and the Tribology Science Fund of State Key Laboratory of Tribology (SKLTKF11B04).
References (21)
- et al.
RF plasma nitriding of severely deformed iron-based alloys
Mater Sci Eng A
(2003) - et al.
Microstructural, mechanical and corrosion characterization of nitrogen-implanted plastic injection mould steel
Surf Coat Techno
(2005) - et al.
Simultaneous plasma nitriding and ageing treatments of precipitation hardenable plastic mould steel
Mater Dse
(2007) - et al.
Low-temperature nitriding of 38CrMoAl steel with a nanostructured surface layer induced by surface mechanical attrition treatment
Surf Coat Technol
(2008) Nanocrystalline materials
Prog Mater Sci
(1989)- et al.
Gas nitriding of iron with a nanostructured surface layer
Scripta mater
(2007) - et al.
The effect of surface nanocrystallization on plasma nitriding behaviour of AISI 4140 steel
Appl Surf Sci
(2010) - et al.
The formation of ε-Fe2–3N phase in a nanocrystalline Fe
Scripta Mater
(2004) - et al.
Micro-dimpled surface by ultrasonic nanocrystal surface modification and its tribological effects
Wear
(2012) - et al.
Fatigue and mechanical characteristics of nano-structured tool steel by ultrasonic cold forging technology
Mater Sci Eng A
(2007)
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