Study on vacuum ionic liquid-gas phase boronization bookmark0 Zhang Haijun\ Li Guoqing2 and Ding Ming1 (1. Jiangxi Institute of Machinery Science and Technology, Nanchang 330002, China; 2. Laboratory of Ion Surface Technology, East China Jiaotong University, Nanchang 330013, China) The compound layer and the diffusion layer contain B and Fe2B, and they are in a highly dispersed state, which plays a good role in resisting heavy-load thermal shock, thermal abrasion, and resistance to repeated low-cycle thermal fatigue, and can greatly increase the service life of the hot die. .
When the engine exhaust valve hot dies (3Cr2W8V steel) work, to withstand 16t heavy-duty hot extrusion impact and repeated low cycle thermal fatigue, it is easy to produce early 'corner collapse' at the die cavity corners. Failure: After the heat treatment of the mold, the matrix structure obtained is M+B+A residue+a small amount of carbides, and the hardness value of the matrix meets the requirements.After the failure of the mold, most of the molds' rounded corners collapse and failure is the work of the outer surface of the mold cavity. Damage to the parts, more specifically the shallow surface of the mold cavity, is not associated with the mold base. For this purpose, we conducted a vacuum ionic liquid-gas phase boriding treatment and compared it with the gas nitrocarburizing and ion nitrocarburizing results.
The sample is made of the same material as the exhaust valve hot stamping die. The sample size is 10mm> 40mm> 20mm. The sample is cleaned and dried with the hot die in the same furnace.
The vacuum ionic liquid-vapor phase boronization was performed in a 50 kW bell-type ion nitriding furnace. The seepage agent was trimethyl borate (B(OCH3)3). Argon, hydrogen, nitrogen, and ammonia were used as reaction gases and carrier gas. - The gas-phase mixing reactor is connected to the ion nitriding furnace and can continuously or intermittently supply the liquid-gas mixture to the nitriding furnace. Treatment temperature 550600*C, time 48h. After testing, compound 1050HV0.1. see through layer microstructure; X-ray diffraction phase structure analysis results, white light layer is a-Fe + a small amount of Fe2B; Auger electron spectroscopy surface element C , O, W, Cr, Fe and B, N. methanol + 50% ammonia, heating temperature 530600C, heat preservation 4.5h oil cooling. The detected compound layer was 0.0060.008mm, and diffusion layer was 0.140.18mm. The surface whiteness analysis was mainly carried out by e+Y phase ion nitrocarburization in a 50kW ion-nitriding furnace. The seepage agent was acetone/ammonia gas=1/ 8, furnace pressure 5001000Pa, at 540600*C insulation 48h. After testing, the compound layer 0.010.12mm, diffusion layer 0.140.18mm, the surface phase analysis of white bright layer consisting of N, C phase, hardness value 1186HV0.1. 2 mold The on-site assessment compares the service life of hot niobium of the exhaust valve with the 16t press for the three processes of gas nitrocarburizing, ion nitrocarburizing, and vacuum ionic liquid-gas-phase boriding. The results are shown in Table 1. It can be seen that the vacuum ionic liquid-vapor phase boriding mold has greatly improved the service life of the mold compared with other processes.
Table 1 Effect of Different Treatment Processes on the Service Life of the Die Process Type Service Life (Item) Failure Mode Quenching + Tempering Treatment Collapse Quenching and Tempering + Gas Soft Nitriding Crash Quenching Tempering + Ion Nitriding Crush Quenching and Tempering + Vacuum Ionic Liquid - Vapor-Phase Boronization When the surface of the hot fatigue steel diffuses, C ions seem to be more prone to diffusion than B ions. When the number of C ions is large, diffusion 'barriers' hinder the penetration of B, which will lead to a decrease in the thickness of the permeation B layer. Control of the effective C content can maintain a certain thickness of the infiltrated layer B. The phase analysis of the gas nitrocarburized surface shows that the e+Y phase is formed, and the phase analysis of the surface of the ionic nitrocarburizing shows that the +Y phase is formed. In the actual evaluation of hot dies, it has a certain role, but its use of anti-hot extrusion impact and wear resistance is not very prominent, while the enthalpy of ionic liquid-gas phase B treatment is mainly infiltration of steel surface B. -Fe dissolves in a concentration of 0.00081%B. The gap between a-Fe crystal lattices is small. The active B ion forms a substitutional solid solution in aFe, which causes lattice distortion, increases dislocations and strengthens ferrite; iono-osmotic B metal surface 0.003mm compound In the layer, B particles are not equal in height Scattered in the e-phase, affected by plasma sputtering and excitation, the B-saturated and non-stable e-phase is contained and the decomposition is converted to the e+Y phase morphology. The structure is a Fe2B hard phase embedded in the matrix. According to the theoretical analysis, ion permeation B produces a 'secondary phase strengthening' effect on the metal surface e+Y phase and the matrix, so the ion permeability B layer is a hot die resistant to 'corner collapse' and resistance to heavy-duty hot extrusion impact. The main mechanical support against low cycle thermal fatigue.
4 Conclusions 3 Discussion 3.1 Controlling the phase structure of the boronized layer If Fe2B and FeB dual phase structures appear in the boronized layer, they do not differ greatly in hardness, but their expansion coefficients are significantly different. Kunst pointed out that at 200600C, Fe2B The coefficient of expansion is 7.85*10-6K-1, and the coefficient of FeB expansion is 23.00, which is less than -1. The expansion coefficient is 15.60. 10-6K-1. Due to the different expansion coefficients, the Fe2B layer forms compressive stress during the post-wetting cooling process, and tensile stress occurs in the FeB layer, which will lead to vertical matrix cracks between the Fe2B and FeB layers. In the experiment, we effectively controlled the equivalence of the physicochemical reaction equilibrium function between the process state of the single-phase Fe2B transition, the hydrogen-argon ratio, and the input of the liquid-gas mixture when the ion-permeable B was used. At 1/1, the liquid-gas mixture B sees good glow discharge stability, and the free B and C ions after excitation can be converted to Fe2B under an inert atmosphere at a certain temperature; while the liquid-gas mixture seep When the input amount of agent B to the furnace is in a large range, H/Ar fluctuates, the dynamic balance of H/Ar=1/1 is broken, and excess B ions are likely to appear in the cathode region. At this time, the glow discharge stability is poor, resulting in glow. The transition from discharge to arc discharge and the sharp increase in cathode current should be avoided as far as possible. When vacuum ionic liquid-gas phase infiltrate B uses boron trimethyl borate for the minimum amount of boron, the atmosphere balance is destroyed, the atmosphere quickly depletes B, and the iron in the matrix cannot form the Fe2B layer quickly enough. The formation of the diffusion layer is relatively slow.
3.2 Effect of Carbon on Boron Ion Boronization Vacuum Ion Liquid-Vacuum Boron Trichloromethane Mixture The infiltration agent contains some amount of C, and the influence of surface element C from AES Auger spectroscopy is analyzed, and the effect of boron on glow discharge plasma boronization During the process, the B and C ions form a boride hard phase on the metal surface by ionic liquid-gas phase infiltration B, which is the main anti-heavy heat shock, thermal cycle fatigue, and wear-resisting mechanical working part of the hot die corner. The support body plays a role of anti-wear, anti-pressure collapse, thermal fatigue, and long service life.
The homemade trimethyl borate organic activator used at room temperature is safe, non-toxic and non-corrosive for ionic liquid-gas phase boriding, and can be processed at low temperature, and is suitable for industrial production.
The evaluation of the service life of retort physics ionic liquid-gas phase boronization shows that this technology is a new type of practical technology in the process of hot die casting, and has a very high promotion value. E3 (Responsible Editor/Respondent: Zhang Jie), which brings great convenience to the majority of the authors, not only shortens the time of the investment + manuscript, but also reduces the errors in manuscript entry, and improves editorial quality. However, due to the excessive amount of spam on the Internet for a period of time, the identification and handling of +editing has caused great trouble. In order to prevent your e-mail from being incorrectly deleted, the editor of this publication reminds you that when contributing + by e-mail, be sure to include the word â€œmanuscriptâ€ in the subject line of the e-mail. Thank you for your cooperation. +
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