Influence of Hydrogen on the Ion Nitriding of Steels
- PDF / 198,186 Bytes
- 5 Pages / 594 x 792 pts Page_size
- 36 Downloads / 218 Views
INFLUENCE OF HYDROGEN ON THE ION NITRIDING OF STEELS P. V. Kaplun
UDC 620.178.112:339.788
We present the results of experimental investigations of the contact durability of specimens of different steels after ion nitriding in hydrogen and hydrogen-free atmospheres tested in the І-20 lubricant. The detrimental influence of hydrogen on the contact durability of steels in rolling friction is demonstrated. Keywords: contact durability, hydrogen, hydrogen brittleness, point contact, ion nitriding, hydrogen atmosphere, rolling friction.
Gaseous hydrogen is one of the most active media because it easily diffuses into metallic materials and accumulates in them affecting their structures, phase compositions, and physicomechanical properties [1–11]. In the course of hydrogenation, we observe a decrease in the plasticity of metals and, therefore, this phenomenon is called hydrogen brittleness [4–8]. As a result of long-term investigations, the researchers established the main regularities of hydrogen brittleness of steels [1–8]. Hydrogen penetrating in steels affects their mechanical properties under long-term and short-term static loads and also under repeated variable and impact loads [1, 5–7, 9] promoting hydrogen embrittlement of the surface [12–15]. This phenomenon can also be caused by the ultralow hydrogen concentrations (< 1 cm 3 /100 g metal). Brittleness becomes irreversible as a certain critical level of hydrogen concentration is exceeded or as the time of its interaction with the metal increases. The degree of embrittlement depends on the level, type, and distribution of stresses and decreases as the strain rate increases. A temperature of 373°K proves to be most favorable for the manifestation of hydrogen embrittlement. The degree of hydrogen brittleness depends on the carbon content of the metal and the stress concentrators enhance the action of hydrogen [10]. Among different manifestations of the effect of hydrogen on the mechanical properties of metals, a special place is occupied by its influence on the crack resistance. The defects absolutely safe under ordinary conditions may become dangerous under the action of hydrogen and lead to the unexpected brittle fractures of products [6]. The distortions of the crystal lattice of the metal caused by elastic and plastic deformations [6, 7, 11] play the role of strong stimulators of hydrogen brittleness. In this connection, it is necessary to distinguish the mechanical characteristics obtained for steel specimens with undistorted lattices preliminarily saturated with hydrogen, for specimens with distorted lattices, and for specimens saturated with hydrogen in the process of deformation [2, 13]. At present, there are numerous hypotheses [4, 5, 8, 12, 14, 15] explaining the influence of hydrogen on the metals. It is believed that the causes of their embrittlement are the increase in the pressure of molecular hydrogen in internal microcavities, weakening of interatomic bonds in the metal by dissolved hydrogen, and decrease in the specific energy of the internal surfac
Data Loading...
