Papers by Keyword: Surface Hardening

Abstract: We study the effect of the grain refinement on the elemental composition and nanohardness of the surface layers in AISI 316L austenitic steel processed by ion-plasma hardening. Ion-plasma hardening of the samples with (1) grain-subgrain (with high dislocation density) and (2) coarse-grained structures causes a surface hardening and formation of the composite layers with a thickness of about 20 μm. The nanohardness and depth profiles of elemental concentration of nitrogen, carbon and oxygen in the ion-plasma hardened layers depends on pretreatment regime of the steel specimens. Cold rolling causes an increase in the grain and subgrain boundaries fraction and dislocation density in steel specimens, provides more intensive accumulation of interstitial atoms in thin surface 5 μm-layer, leads to additional surface hardening and suppress carbon diffusion into depth of the specimens as compared with coarse-grained structure.

Abstract: The quality of heat-exchange tubes is one of the most important factors affecting the technical condition and the durability of steam generators at nuclear power plants. The combined influence of the aggressive environment and stresses in heat-exchange tubes during the exploitation of steam generators leads to corrosive cracking of tubes. This results from the residual stresses (RS) stretching tube walls. The production of heat-exchange tubes involves the following operations: boring and grinding hot-rolled pipe billet, cold rolling middle-sized pipes, heating, rolling final-sized pipes, straightening, electro-polishing the inner surface and burnishing the outer surface, checking the final quality. The operation modes of straightening and burnishing predetermine the residual stresses in pipes in the delivery state. The paper presents the results of the studies on the residual stresses and surface hardening caused by the finishing operations. The paper also shows the need for exceptions to the production techniques for heat-exchange pipes, i.e. a series of operations increasing tensile residual stresses.

Abstract: The present paper examines the influence of the tribofinishing process on the surface state of steel parts XC48, while taking into account the variation in hardness and mass. The tribofinishing process is a mechanical-chemical process, which comprises the use of low frequency impact vibration in the presence of abrasive and chemical additives [1]. The treatment regime (frequency and amplitude) has a great influence on geometrical, mechanical and metallographic treated surfaces. The improvement of the surface quality is determined as a function of the treatment time from 30 to 240 minutes. The tribofinishing process has many technical and economic advantages for the treatment of mechanical parts of simple and complex shapes, which have a better surface finish and improved life of parts etc.

Abstract: The work analyzes application perspectives of Ti-based alloy VT6 (Ti-6Al-4V) with an ultrafine-grained structure with different grain sizes as structural material to produce high-load machine parts. The paper considers technological factors for ensuring quality of parts with account of assumed conditions of their exploitation, differently directed change of mechanical properties with reduction of an average grain size and choice of surface hardening technique.

Abstract: Abstract. A promising method for improving wear resistance of metal cutting tools including pre-heating and a subsequent impact of the pulsed magnetic field of high intensity on the cutting tool is proposed. The experimental setup and methods of research are described. Experimental studies of surfaces of carbide reversible cutting plates of the VK8, T15K6 alloy and drills of high speed steel R6M5 to assess the effectiveness of the proposed method were performed. An increase in wear resistance of cutting tools made of the T15K6 hard-alloy plates by 30% and made of the VK8 alloy plates by 13% was revealed while wear resistance of drills made of steel R6M5 increased on average by 58% The proposed method can be of practical interest for hardening the surface of other types of tools and machine parts for further experimental verification.

Abstract: To conduct high production hardening modification of iron-carbon and titanium alloy surface layers a laser-plasma method (LPM) is developed. The method is based on the use of optical pulse discharge plasma. A discharge is ignited with laser pulses repeated with a high frequency by a CO₂-laser oscillator - amplifier system. A laser pulse is focused on the treated surface. To form plasma in alignment with the beam in the laser head, a high velocity gas flow (air, nitrogen, argon, and carbon dioxide) is created. The pressure of the plasma-forming gas can reach 0.5 MPa, and the output speed of the laser head can be 300 m/s.The results of the experiment on the impact of laser-plasma action on the structure and microhardness of the structural steel surface are presented. Laser-plasma treatment leads to the formation of a layer with the martensitic structure on the surface of structural low-alloyed steel 40Kh. This layer is formed due to quenching in a liquid state (QLS) and quenching in a solid state (QSS). The microhardness of the martensitic layer is 11-13 GPa, the hardened zone depth reaches 0.3 mm. It is proposed to use laser-plasma treatment of structural steel as a method for the local surface hardening of machine parts and tools.

Abstract: Quenching of steel 45 using high-frequency induction-heating (440000 Hz) with simultaneous shower water cooling was studied. The possibility of liquid-phase creation in the bulk (appr. 0.2 mm) in the material being treated in the absence of melting on the surface was clearly demonstrated by both numerical simulation of the temperature field in the material during hardening and experimental results

Abstract: In this paper, diffusional surface hardening processes utilized to overcome the poor tribological performance of titanium and its alloys is briefly introduced. More specifically, surface treatments known as thermal oxidation, nitriding and boriding offering the advantage of producing graded surfaces comprising hard compound layer and diffusion zone by diffusion of interstitial atoms (oxygen, nitrogen and boron) are overviewed.

Abstract: Specimens of austenitic stainless steel hardness changing were tested. The used hardening technology was a modified explosive treatment. During the hardening tests the explosive exploded different distance from surface. Same setup was tested with 2, 3 and 4 mm holder. The hardness improving and the plastic deformation were different as function of the holder size. The hardness was measured by Vickers hardness tester. The amount of strain induces martensite was detected magnetically. It can suppose that the microstructure changed during high rate strain. Results showed that the strain rate and result hardness depend on the holder size. We found that the bigger holder size in case of the tested setup provoke higher hardening. To determine the hardness properties it’s important to use an optional setup.

Abstract: With the aim of developing a durable tool for friction stir processing (FSP) of cast iron, the durability of a Ti (C,N)-Ni cermet tool has been investigated and compared with that of a WC-Co cemented carbide tool. Results of exposure tests in air revealed that the WC-Co cemented carbide sample oxidized rapidly above 973 K, whereas the cermet material showed little oxidization even after holding at a temperature of 1103 K. When these tools were used for the FSP of cast iron surfaces, it was found that an oxide layer of over 100 μm was generated on the lateral faces of the WC-Co cemented carbide tool after it was used to work a length of 400 mm. In contrast, a thin oxide layer of only 5 μm was generated after the cermet tool worked a length of 2400 mm. Cross sections of the iron casts (FC250) subject to FSP using these tools showed that in a bowl-shaped region approximately 1.5 mm deep the initial pearlite structures changed to martensite structures. The martensite structures in this region had a Vickers hardness of 600 to 800 HV, while that of the initial pearlite structure was about 280 HV.