Hydrogen Effect on Strength and Plasticity of Steels After Ion Nitriding in Hydrogen and Hydrogen-Free Environments
- PDF / 923,353 Bytes
- 7 Pages / 594 x 792 pts Page_size
- 111 Downloads / 219 Views
HYDROGEN EFFECT ON STRENGTH AND PLASTICITY OF STEELS AFTER ION NITRIDING IN HYDROGEN AND HYDROGEN-FREE ENVIRONMENTS P. V. Kapluna,1 and B. A. Lyashenkob
UDC 621.726
The authors present the results of experimental investigations of strength and plasticity characteristics, as well as fracture nature, of the specimens of different steels under tension after ion nitriding in hydrogen (nitrogen with hydrogen) and hydrogen-free (nitrogen with argon) environments. The obtained characteristics are compared with those before nitriding. It is established that during ion nitriding in the hydrogen-free environment, tensile strength of the specimens has increased by 4–11%, whereas relative elongation and contraction have decreased by 1.1–3 times based on the nitriding mode and steel type. The authors have built the tensile stress-strain diagram for the specimens made of steel St3, 40Kh, and 12Kh18N10T without chemical and thermal treatment, ion nitriding in the hydrogen and hydrogen-free environments. The influence of hydrogen concentration in the saturation environment on the strength and plasticity characteristics has been defined. Under concentrations higher than 10 vol.% there is embrittlement with the decrease of strength characteristics (to 15%) and a significant decrease of plasticity (to 40%) for low-alloyed steels. For high-alloyed steels, the negative influence of hydrogen on the strength characteristics does not increase by 3%, while the influence on the plasticity characteristics – by 8%. The authors have investigated the initiation and propagation of microcracks under external loading on the steel with nitride layers. Keywords: strength, plasticity, hydrogen, hydrogen brittleness, tension, ion nitriding, hydrogen and hydrogen-free environment. Introduction. Gaseous hydrogen is one of the most active media affecting the physical and mechanical properties of metals. From the gaseous phase, it adsorbs onto the surface of friction in the form of ions and atoms [1]. In the ionized state, hydrogen diffuses simply into metal (as positive ions). Besides diffusion, it can penetrate the metal center via defects of the crystal lattice and sometimes at the crystal boundaries. Diffusion increases with the temperature rise, strain increase of the crystal lattice and length of the boundaries, as well as metal pollution. In the context of the Trojan-Orioni dislocation-adhesive concept, hydrogen, which got into metal, occupies the most favorable places (from the energetic point of view) – kernels of dislocations. Here there is a decrease in cohesion in the kernel of the crack-forming dislocation, cluster formation, and occurrence of metal-hydrogen links of hydride type. The total effect of these three activities is the main mechanism of the decohesion influence of hydrogen on the metal lattice. The theoretical concepts on the mechanism of hydrogen effect on fracture [1–9] link the fracture facilitation of metals with one (or several) of the following factors [10]: the pressure of molecular hydrogen in metal micropores; hydrogen d
Data Loading...
