Search

The stability of gradient grain microstructure on the surface of low carbon steel was studied by different annealing temperature and high temperature friction and wear experiments. The results showed that the surface grain of the low-carbon steel was refined, and the microhardness reached 250 HV. An increase in the annealing temperature, the gradient refined grain microstructure of the surface layer gradually disappeared. When the annealing temperature was lower than 300 °C, the average grain size increased continuously from the surface to the center without obvious interface. The surface layer hardness could reach about 220 HV. However, when the annealing temperature reached 500 °C, the refined microstructure of the surface layer completely disappeared. At the same time, the grain boundaries could be seen clearly indicating the refined grain in the surface layer had recrystallized. Compared with the as-prepared, the grain size of the surface layer grew up and the microhardness reduced to about 150 HV. Moreover, the wear behavior of the gradient refined grain microstructure at high temperature also proved that the disappearance of the surface refined grain leads to an increase in the wear volume at higher temperature.

The present research investigated the effect of annealing temperature on surface gradient fine microstructure and wear resistance of low-carbon steel. The results depicted that the optimized annealing temperature from 300 °C to 400 °C can facilitate the formation of a stable fine microstructure. The fine grain size is about 0.2 μm on the topmost surface layer, and the percentage of grain boundary with misorientation angle of 1.5° is 26 %. The full width at half maximum values gradually decreases with increasing temperature from room temperature to 600 °C. In addition, the abrasive wear dominates the entire process for samples annealed at 300-400 °C. The wear mechanism gradually switches to adhesive wear and even delamination wear when the annealing temperature is increased to 500-600 °C.

Cold deformation is an effective approach for enhancing the strength of many metallic materials. Efforts continue to be expended to improve existing processes for manufacturing non-quenched and tem...

The high-temperature wear properties of the gradient microstructure formed by ultrasonic impact treatment (UIT) on the surface of low-carbon steel are investigated. The dominant wear mechanism of the sample is oxidation wear and adhesive wear as the temperature increased from 300 °C to 500 °C. The wear mechanism of the sample changed from abrasive wear to fatigue wear as the applied load increased from 15 N to 95 N. The improvement in the high-temperature wear properties is due to the gradient nanocrystallization, which is helpful for forming an oxide film during wearing. As well as due to presence of the grain boundary wetting phase transitions of cementite, which can effectively delay the crack initiation.

Purpose This paper aims to investigate the friction and wear properties of Cr-Ni-Mo-V steel against 440C stainless steel under both water and water–silica mixture lubricant. Design/methodology/approach The Cr-Ni-Mo-V steel specimens were taken from a forged steel brake disc with the process of quenching at 900°C and tempering at 600°C. The tribological testing was performed using a contact configuration of ball-on-flat with a liquid cell according to the ASTM standard. Detailed examinations on the worn surface were analyzed using a scanning electron microscope. Findings The results indicate that the friction coefficient and friction damage of the steel sliding under water–silica mixture are higher than those under water. The friction coefficient decreases with increasing load and increases with the sliding speed for the two lubricants. The mass wear rate presents a rising trend with both sliding load and speed. The wear mechanisms of the Cr-Ni-Mo-V steel sliding under the two lubricants are oxidation wear, abrasive wear and fatigue wear. Research limitations/implications Because of the chosen tribological testing approach, the research results could not describe the tribological performance of the brake disc accurately during actual braking process of the high-speed train. Therefore, researchers are encouraged to test the proposed propositions further. Originality/value This study shows that the tribology behavior of the Cr-Ni-Mo-V steel with water or water–silica mixture lubrications helps the industrial firms and academicians to work on the wear of the brake disc in rainwater or wet environment.

As compared with the untreated one, the low-carbon steel with gradient alloying produced by impact peening showed an increase in corrosion resistance. Specifically, when the corrosion potential increased from-1061 mV to-603.5 mV, the corrosion current density decreased from 1.579×10-3 A/cm2 to 6.703×10-4 A/cm2, the capacitive arc radius increased, and there was no corrosion products viewed on the surface. The improvement in corrosion resistance could be attributed to the diffusion of Cr allowed by the large number of defects induced by the impact peening deformation. This also resulted in the formation of Fe-Cr solid solution, which helped to promote the formation of a passivation film.

In this study, the gradient grain induced by punching deformation and recovery treatment on a cupronickel alloy surface sample were investigated, and their effects on corrosion resistance were measured by atom force microscopy (AFM), X-ray diffraction (XRD), electrochemical measurement, electron work function (EWF), and contact electrical resistance (CER). The cupronickel alloy surface experienced punching deformation for 60 min and recovery at 300 °C for 1 h to produce gradient surface. The grain size measured by XRD is bigger than that measured by AFM, due to X-ray intensity of 95 % produced at the depth of 12–20 μm for the crystal planes of (111), (200), and (220). The gradient grain surface, compared to the original surface, shows a 13.7-fold decrease in passivation current density (i p), and corrosion potential (E C) increases by approximately 9.8 %. These results are attributable to the increase in EWF and formation of passivation film with better adhesion and compactness after treatment.

The gradient alloying surface produced on a low-carbon steel material by a punching deformation and recovery process is investigated using scanning electron microscopy, energy disperse spectroscopy and X-ray diffraction. The mechanical properties of the gradient alloying surface are studied using nanoindentation and microhardness testers. The surface layer is observed to contain a (Fe,Cr) 7 C 3 phase. There is also a decrease in Cr content as grain size increases from the top surface to the matrix. These results can be attributed to defects in the microstructure induced by the punching deformation process, which promote diffusion of Cr in the matrix. The gradient alloying surface also exhibited increased hardness due to the grain refining process, the Cr solution used and the presence of the hard (Fe,Cr) 7 C 3 phase.

The present research investigated the effect of loads on high-temperature wear behavior of carbon steel with gradient microstructure. The results demonstrated that the gradient grain refinement was obtained, with grain size ranging from 0.1 to 3 μm. An increase in the coefficient of friction and wear volume was observed with the load increased. The wear mechanism of the sample changed from oxidation wear to delamination wear, with the load increased from 15 N to 75 N. Moreover, under low loads, it was found that a continuous oxide film was formed on the gradient surface, which retained the favorable high temperature wear properties. However, under high loads, the gradient layer was completely penetrated, and the low binding strength between the oxide film and the matrix resulted in the initiation and propagation of cracks, thereby exhibiting a poor wear performance of the sample.

Ultrasonic impact treatment (UIT) fabricated a gradient microstructure surface layer on carbon steel. The microstructural features were characterized by scanning electron microscopy, electron backscatter diffraction, and X-ray diffraction; the microhardness and wear behavior of the gradient microstructure surface were also studied. Results showed that an approximately 250 μm thick gradient microstructure was clearly observed, with low-angle grain boundaries and strong texture. The microhardness exhibited a gradient change of a depth of 269 HV in the top surface layer to 160 HV in the matrix. The wear mechanism changed from abrasive to fatigue wear when the sliding speed increased from 10 mm/s to 30 mm/s. Under sliding speeds of 10 mm/s and 20 mm/s, better wear resistance was attributable to the formation of oxides on the gradient microstructure surface. However, under the high speed of 30 mm/s, the gradient layer exhibited a high friction coefficient and wear rate.

The effect of ageing on the mechanical and impact properties of non-quenched and tempered steel wire strengthened by cold forming to an area reduction of 25.5% was investigated by tensile testing, charpy impact tests and scanning electronic microscopy. It was found that when the specimen was aged at 300 °C for 2 h, its tensile strength, yield strength, elongation and impact absorption energy increased by 10.8, 18.1, 44.8 and 19.6%, respectively. In addition the ductile-brittle transition temperature decreased by 5 °C. These improved properties are attributed to the decreasing dislocation density, the formation of sub-grains in a stable condition and the uniform dispersion of a fine precipitation phase during the ageing treatment.

The punching severe deformation is a recently developed surface treatment that forms alloying by inducing a greater compressive equivalent stress field. Despite its proven utility, there has been little attention devoted to the accurate modeling of this process. In this work, a 3D-DEFORM finite element analysis was used to model the equivalent stress distribution induced by the punching process on a low-carbon steel surface. A majority of the controlling parameters of the process were taken into account. The effect of punching number, punching tip size, punching velocity and punching pressure on the equivalent stress distribution was evaluated. The results show that an equivalent stress distribution much higher than the conventional surface severe deformation can be obtained by optimizing the punching severe deformation process. The reported simulation results can successfully predict the punching severe deformation used to create an alloying layer on the surface of low-carbon steel.

The shaft parts surface was treated by ultrasonic surface machining (USM) technology after surface induction hardening and tempering. In order to study the surface strengthening mechanism of ultrasonic punching on the surface of induction quenching and tempering, nano-intendation, X-ray diffraction, and scanning electron microscopy equipped with energy dispersive spectroscopy were utilized to evaluate the mechanical and corrosion properties of untreated and USM-treated surface. The results indicated that the surface treated by USM had an obviously gradient plastic deformation layer and the grain of lath martensite was refined by this deformation. The surface mircohardness of USM-treated sample had a gradient trend, and the surface highest hardness was increased. Surface residual stress of USM-treated specimen was higher than untreated surface. The surface of USM-treated specimen also exhibited a lower friction coefficient, and a smaller wear scar. In addition, the surface of USM-treated sample had better corrosion resistance than untreated surface.

The grain size variation in a gradient surface produced by a punching and recovery process on a Cu-30Ni alloy has been observed by atomic force microscopy. The friction characteristics of the gradient surface in a 3.5 wt% NaCl solution were investigated using a micro-indenter probe, a pin-on-disc type tribometer, a strain sensor and an optical microscope. The results showed that the hardness and grain size can be well represented by the Hall–Petch relationship when the gain size is more than 30 nm. The wear rate, friction coefficient and adhesive force all increase depth below the surface. These variations are attributed to a gradual increasing grain size with depth. The morphologies of the worn track were also studied to understand further the corrosive wear behaviour of gradient surfaces.