Laser Hardening of Unimax Stainless Steel

Nowdays, laser hardening of materials brings a comparative advantage over the conventional hardening technique. Fast cooling rate due to the heat distribution through its own bulk material, self-quenching property (rapid cooling without external water or oil), environmentally friendly characteristics since the procedure does not exhaust smoke, the localized heat input due to adjustable laser spot size to avoid distortion and minimum time to finish the operation are some of the advantages to mention. NIKO is a company specialized in making electrical products like socket outlets and switches by using injection molding techniques. Unimax is a kind of stainless steel used by the company to prepare some parts of the injection molding components like a Nozzle. This time, the company is using more and more fiber-reinforced polymers throughout their product line. These composites are far stronger than the polymer, but on the downside, the fibers are quite abrasive. The objective of this research was to harden the Unimax stainless steel using Nd:YAG (neodymium-doped yttrium aluminum garnet) laser technique. First, the laser transverse speed and spot size were identified as the primary process parameters. Then, the traverse speed of 100, 150 and 400 mm/min and spot size of 2164, 2169, 2288 and 2412 um were assigned with 3 replications. Afterwards, thermal simulation was done using COMSOL Multiphysics© followed by the real test on the metal bar. Therefore, the highest hardness of 650 HV was obtained at a speed of 150 mm/min and a spot size of 2169 um diameters. Finally, the corresponding depth of hardness and roughness values of 200 um below the surface and unmelt samples respectively were obtained. HIGHLIGHTS Laser hardening of materials brings a comparative advantage over the conventional hardening technique The laser transverse speed and spot size were identified as the primary process parameters. Afterwards, thermal simulation was done using COMSOL Multiphysics© followed by the real test on the stainless steel bar The depth of hardening and Vickers hardness (HV) increased with the smaller spot size and slow traverse speed of the ND:YAG laser, but this resulted in a melt on the surface of the hardened metal One of the problems of making products using injection molding techniques using fiber-reinforced polymers is the abrasive nature of the fibers which widen the injection nozzle GRAPHICAL ABSTRACT

The technology of thermal cyclic electrolytic plasma hardening of steels

This work describes the technology of thermal cyclic electrolytic plasma hardening, as well as describes the design features of the electrolytic plasma heater. There are presented the results of the research of medium-carbon steel hardness treated by thermal cyclic electrolytic plasma hardening under different conditions. An industrial installation for thermal cyclic electrolytic plasma hardening of materials was developed to carry out thermal cyclic electrolytic plasma hardening of steels in an automated mode. Tempered layers were obtained on the surface of the samples with average thickness values from 0.5 to 10 mm and hardness up to 750 HV. Experimentally that the alternation of switching on the electric potential at a voltage of U1 = 320 V and U2 = 200 V provides heating of the product surface to a depth of 10 mm. In this case, the maximum hardness of the surface layer (750 HV) practically does not depend on the thickness of the hardened layer. The hardness of the hardened layer of the product gradually decreases from the maximum (750 HV) to the hardness of the base (280-300 HV). The developed installation allows to vary the electrophysical parameters within a wide range: to set the voltage, the duration of processing, the time of switching on and off the voltage.

Influence of oxide inclusions on the process of interparticle splicing of powder materials

One of the characteristic features of the structure of the powder material is the increased content of oxide inclusions. In most works considering the influence of oxide inclusions on the fracture process, their contradictory role in the processes of crack initiation and development is noted, which consists, on the one hand, in creating concentrators of internal stresses, increasing the tendency of the material to brittle fracture and in reducing the plastic properties of the material, on the other, when oxide inclusions of appropriate dispersion and distribution in the volume of the matrix prevent the sliding of dislocations, thereby contributing to its strengthening. The positive effect of oxide inclusions on the mechanical properties of the material led to the development of the internal oxidation technology as one of the methods of precipitation hardening of materials.

The Effect of Internal Pressure on Radial Strain of Steel Pipe Subjected to Monotonic and Cyclic Loading

Steel pipes in different engineering applications may fail, leading to numerous environmental disasters. During loading, certain mechanical and chemical phenomena develop inside the pipes and cause them to burst. In this study, the influence of internal pressure on the elastic and plastic behaviour of E355 steel pipes was investigated on small specimens with different wall thicknesses. First, the failure modes of pipes subjected to monotonic loading were assessed, and then the behaviour of specimens subjected to cyclic internal pressure was analysed in terms of variation of radial strain. The strain and stress states of pipes were analysed using the finite element method. The results revealed that the hardening of materials inside the pipes increases the risk of cracking and bursting because of elasticity limits being exceeded, causing entry into the plastic domain. The transition of mechanical behaviour can be observed in the microstructure of steel in cracked areas from the inside to the outside of the pipe.