Impact of Magnetic-Pulse and Chemical-Thermal Treatment on Alloyed Steels’ Surface Layer

The relevant problem is searching for up-to-date methods to improve tools and machine parts’ performance due to the hardening of surface layers. This article shows that, after the magnetic-pulse treatment of bearing steel Cr15, its surface microhardness was increased by 40–50% compared to baseline. In this case, the depth of the hardened layer was 0.08–0.1 mm. The magnetic-pulse processing of hard alloys reduces the coefficient of microhardness variation from 0.13 to 0.06. A decrease in the coefficient of variation of wear resistance from 0.48 to 0.27 indicates the increased stability of physical and mechanical properties. The nitriding of alloy steels was accelerated 10-fold that of traditional gas upon receipt of the hardened layer depth of 0.3–0.5 mm. As a result, the surface hardness was increased to 12.7 GPa. Boriding in the nano-dispersed powder was accelerated 2–3-fold compared to existing technologies while ensuring surface hardness up to 21–23 GPa with a boride layer thickness of up to 0.073 mm. Experimental data showed that the cutting tool equipped with inserts from WC92Co8 and WC79TiC15 has a resistance relative to the untreated WC92Co8 higher by 183% and WC85TiC6Co9—than 200%. Depending on alloy steel, nitriding allowed us to raise wear resistance by 120–177%, boriding—by 180–340%, and magneto-pulse treatment—by more than 183–200%.

Microanalysis of Worn Surfaces of Selected Rotating Parts of an Internal Combustion Engine

The present paper analyzes the damage of surfaces at spots of frictional contact, namely, the friction nodes on a camshaft and the connecting rod pins of a crankshaft. The resulting wear of the monitored friction nodes reduces the technical life of the machines, which can lead to the decommissioning of the machine. Wear was assessed by measuring roughness and microhardness and by observing the microstructures of the materials. The results of the experiments show that the rotating parts displayed visible wear on the cams, as well as on the connecting rod pins. The experiments revealed that wear was caused by the heating of the material to a high temperature during the operation of the machine and that there was a gradual cooling and tempering of the material, which led to a reduction in the microhardness of the monitored object. Lower microhardness values can be a cause of greater wear of the monitored objects. When comparing the microhardness of the used and the new camshaft, the hardened layer of the new camshaft from secondary production has a significantly smaller thickness compared to worn cams, which leads to the finding of a different material quality compared to the original parts from primary production. This fact indicates that the wear of a new camshaft as a spare part can contribute to the shortening of the technical life of friction nodes.

Investigation of the Technological Possibility of Laser Hardening of Stainless Steel 14Cr17Ni2 to a Deep Depth of the Surface

The article presents the results of a research of the process of laser hardening of steel 14Cr17Ni2 (AISI 431) by radiation of a high-power fiber laser LS-16. Assessment of the theoretically possible maximum depth in laser processing without additional beam transformations, the use of additional coatings and devices were shown. The results of experiments on increasing the depth of the hardened layer during laser processing by using scanning of the laser beam and optimally selected mode parameters without scanning are demonstrated. The influence of the number of passes on the depth of the hardened layer is investigated. The microstructure of hardened samples was studied and quantitative estimation of structural components was carried out. The microhardness of hardened samples at different modes of laser hardening was measured.

FABRICATION AND WEAR BEHAVIOR OF PEC/N HARDENED LAYER ON PURE IRON

In this paper, the antifriction carbonitriding (PEC/N) layers were prepared on pure iron by cathodic plasma electrolytic treatment (PET) in glycerin and carbamide aqueous solution under 360[Formula: see text]V for 1, 3 and 10[Formula: see text]min. Influence of discharge time on morphology, structure, surface roughness and microhardness of PEC/N layer was analyzed. The tribological performance of the PEC/N layer, growth mechanism and diffusion process during PEC/N treatment was investigated. The thickness of the PEC/N layer grew to 48[Formula: see text][Formula: see text]m for 10[Formula: see text]min treatment and the growth of the saturation layer met the parabolic law. The highest microhardness of the surface was up to 811 HV, which was 5 times of that of iron substrate. The PEC/N layer consisted of [Formula: see text]-Fe, Fe[Formula: see text]N, Fe4N, Fe3C, Fe5C2 phases and a little FeO phase. The wear rate of the PEC/N layer reduced by five-sixes comparing with the iron substrate and the surface of the wear track was much smoother. The temperature close to the surface during PEC/N fitted by the tested temperature values inside the sample was 801∘C (1074[Formula: see text]K), and the combination diffusion rate of C and N into pure iron during PET at 360[Formula: see text]V reached [Formula: see text][Formula: see text]m2/s. The electron temperature fluctuates between 3000[Formula: see text]K and 8000[Formula: see text]K. The antifriction PEC/N layer displayed a very good wear resistance and the higher diffusion rate makes plasma electrolytic carbonitriding a very effective technique for surface modification of pure iron.

Increasing wear resistance of the protective sleeve of the centrifugal pump made of gray cast iron by surface hardening

One of the weak spots that reduce the guaranteed operating time of centrifugal pumps is the assembly that includes the seal and protective sleeves. The main purpose of the bushings in the rotor kit is to protect the shaft from corrosion, erosion and wear. The sleeve operates under abrasive wear conditions by packing elements and abrasive particles that get into the liquid pumped by the pump. The protective sleeves made of gray cast iron do not meet the service life in connection with accelerated surface wear. Goal. The purpose of the work is to ensure high wear resistance of cast iron pump parts by heat treatment. Method. The chemical composition was determined on a portable laser analyzer Laser Z200 C +. The structure was studied using an optical microscope. The wear was investigated by the roller-block method on a friction machine. Surface quenching was carried out with a high-frequency lamp generator in a single-turn inductor. Results. The microstructure of gray cast iron as cast consists of pearlite, ferite, double phosphide eutectic and inclusions of lamellar graphite. Microhardness of small-lamellar pearlite is Н50 = 1550–2220 MPa, microhardness of phosphide eutectic is Н50 = 6500–8000 MPa. Surface induction quenching by high-frequency currents followed by low tempering is an effective way to increase the wear resistance of cast iron products of small cross-section and does not cause warping. Cast iron for surface quenching should have a pearlite structure, and graphite should be contained in the form of small inclusions. The optimal heating temperature for induction hardening was determined as 900 °С, which made it possible to obtain the microstructure of the hardened layer – martensite, double phosphide eutectic and graphite. Scientific novelty. The developed modes of surface quenching make it possible to preserve a double phosphide eutectic in the structure of the surface layer, which makes it possible to obtain high hardness and wear resistance of the hardened layer. Practical significance. Surface induction quenching with low tempering of cast gray iron increased its wear resistance by 2,4 times. The previous normalization had practically no effect on the durability of cast iron, since its structure contains less than 10% ferrite.

Селективный магнитный контроль толщины и степени упрочнения поверхностных слоев на стальных объектах

The dependences of measured locally magnetic characteristics of surface-hardened steel objects on the thickness and physical properties of their surface layers are studied. It is shown theoretically and experimentally that a change in the thickness of the hardened layer on the surface of steel objects affects on the magnitude of the tangential field component on the surface of the object in the interpolar space significantly , as well as the change in the strength properties of the layer affects the magnitude of the magnetic flux in the "transducer-object" circuit. It is proposed to use this difference in magnetic parameters for selective testing of the surface hardening quality. It is shown that the coercive force measured locally by the internal field and the maximum value of the magnetic flux, which can be measured using a single transducer in single measuring cycle, can be used as diagnostic parameters.

Effects of Hybrid Surface Treatment Composed of Plasma Nitriding and CrN Coating on Friction-Wear Properties of Stainless Steel

This study was conducted to investigate the effect of hybrid surface treatment composed of plasma nitriding (PN) and chromium nitride (CrN) coating on the friction-wear properties, the adhesion strength of AISI 316L stainless steel. The CrN coatings with the thickness of 1.0 µm and 2.2 µm were formed on the surfaces of both substrates with plasma nitriding (PN/CrN coating) and without plasma nitriding (CrN coating). The plasma nitriding, CrN coatings, and the hybrid treatment improved markedly the friction-wear properties of the stainless steel. The plasma nitriding generated a hardened layer between the soft substrate and the thin hard coatings and improved markedly friction-wear properties of the CrN-coated stainless steel and the adhesion of the CrN coatings.

PROPERTIES OF TUBES FROM Zr-1% Nb ALLOY AFTER THERMOCHEMICAL TREATMENT AND HYDROGENATION

The influence of treatment in controlled gas environments with subsequent hydrogenation on the physical and mechanical characteristics of the Zr-1% Nb zirconium alloy has been investigated. The surface hardness and the size of the diffusion-hardened layer of the ring-samples cut from fuel tubes from the Zr-1% Nb alloy after treatment in oxygen- and nitrogen-containing gaseous media with subsequent saturation with hydrogen have been established. The influence of the parameters of the gaseous medium and the modes of thermochemical treatment (TCT) of specimens-rings on the destructive stresses under static load at temperatures of 20 and 380 °C is shown. It was revealed that treatment in the investigated gas environment increases the resistance to hydrogen saturation and has a positive effect on the long-term strength of ring specimens from the zirconium alloy Zr-1% Nb.

Surface Characteristics of Low Carbon Steel JIS G3101 SS400 after Sandblasting Process by Steel Grit G25

This research aims to study the surface characteristics of low carbon steel JIS G3101 SS400 processed by sandblasting using steel grit G25. The sandblasting process is conducted at a fixed nozzle pressure of 5 bar and pressure angle of 90o, and varying nozzle-to-surface distances at 15, 25, and 30 cm, and blasting durations of 25, 45, and 120 s. Surface characterization is firstly carried out by conducting observation on the surface’s morphology by SEM and chemical composition by EDS. Subsequently, visual inspection and measurement on surface roughness and hardness profile identification by Rockwell and micro-Vickers hardness tests are conducted. A paint thickness test using ASTM D7091 was undertaken to observe the surface characteristics related to the coating process. Based on the result, SEM found valleys, granules, micro-cracks, and grits embedded on the surface. The visual inspection shows the roughness is within the range of Sa2 - Sa3 of ISO 8501 with values are Ra 18.1 and Ra 21.4 µm. The hardened layer exhibits a maximum hardness value of 332 HV and a depth of more than 50 µm by sandblasting parameters of 15 cm distance and 120 s duration. Both roughness and hardness profiles are confirmed, increasing with closer nozzle-to-surface distance and longer blast duration. It is concluded that sandblasting using steel grit G25 is effective in improving the mechanical strength and surface hardness of low carbon steel SS400. These mechanical properties are essential in the paint coating of machinery applications such as pump, tank, ship, and pipeline.

Hardness Prediction of Grind-Hardening Layer Based on Integrated Approach of Finite Element and Cellular Automata

As an emerging composite processing technology, the grind-hardening process implements efficient removal on workpiece materials and surface strengthening by the effective utilization of grinding heat. The strengthening effect of grind-hardening on a workpiece surface is principally achieved by a hardened layer, which is chiefly composed of martensite. As a primary parameter to evaluate the strengthening effect, the hardness of the hardened layer mostly depends on the surface microstructure of the workpiece. On this basis, this paper integrated the finite element (FE) and cellular automata (CA) approach to explore the distribution and variation of the grinding temperature of the workpiece surface in a grind-hardening process. Moreover, the simulation of the transformation process of “initial microstructure–austenite–martensite” for the workpiece helps determine the martensite fraction and then predict the hardness of the hardened layer with different grinding parameters. Finally, the effectiveness of the hardness prediction is confirmed by the grind-hardening experiment. Both the theoretical analysis and experiment results show that the variation in the grinding temperature will cause the formation to a certain depth of a hardened layer on the workpiece surface in the grind-hardening process. Actually, the martensite fraction determines the hardness of the hardened layer. As the grinding depth and feeding speed increase, the martensite fraction grows, which results in an increase in its hardness value.