Liang Tang

The integrity of sealing systems in key energy and chemical industry equipment heavily depends on flange gaskets. In practice, complex operating conditions compromise the compressive-resilience behavior of flange gaskets, a process that may perhaps culminate in sealing failure. Therefore, this study conducted hot compression experiments on 304 austenitic stainless steel, aiming to investigate the effects of compressive stress and temperature on the compressive-resilience properties of gaskets. The experiments were performed with applied compressive stresses of 35, 50, and 65 MPa at temperatures of 100, 300, and 500 °C. The results indicate that under a compressive stress of 65 MPa at 500 °C, the specimen exhibits a maximum compression rate of 9.84% and a minimum resilience rate of 22.17%. Based on microstructural analyses, the underlying mechanisms are elucidated. The elastic compression stage is primarily governed by Hooke’s law, where greater compressive stress leads to increased deformation, and higher temperatures result in a lower elastic modulus, which in turn contributes to greater deformation. Unexpectedly, the compressed specimen failed to resilience completely. This is mainly because compressive stress leads to work hardening, plastic deformation, and phase transformation, while the temperature increase further induces plastic deformation, collectively weakening the material’s elastic recovery. Thus, it can be classified as quasi-elastic compression by strict definition.

20CrMnTi carburized steel is widely used in the manufacturing of gear transmission components. Gears often operate under complex working conditions that involve high pressure and temperature, and intermittent alternating loads. The material is frequently subjected to repeated compression and resilience cycles, which significantly affect dimensional accuracy and stability. This study investigates the influence of different temperatures and pressures on the compression resilience properties and microhardness of 20CrMnTi steel. The results indicate that temperature and pressure lead to a nonlinear increase in the compression curve, reduce resilience properties and the microhardness of the carburized layer, and affect the microhardness of the matrix. Microstructural analysis indicated that plastic deformation, carbide coarsening, and a lower elastic modulus led to the enlarged compression and diminished microhardness in the carburized layer. Work hardening, dynamic recrystallization, and plastic deformation in the matrix material weaken resilience properties and influence the distribution of microhardness in the matrix.

Cemented carbide is often used as the pick-tip material for conical picks. The pick-tip often experiences premature failure due to insufficient toughness. This paper aims to improve the impact toughness of cemented carbide through electromagnetic coupled cryogenic treatment. A theoretical model between process parameters and impact toughness is established. The optimal parameters are determined as follows: a cryogenic temperature of −190 °C, cryogenic time of 24 h, magnetization intensity of 1.5 T, and magnetization time of 15 s. The treatment improves the impact toughness by 11.39% compared with the heat treatment. Microstructure analysis indicates a notable increase in dislocations and grain refinement within the Co phase, attributing to the enhanced toughness.

The machining residual stress produced in the cutting process of aluminum alloy parts can easily lead to a scrap of the processed parts. In order to reduce the residual stress of aluminum alloy in the milling process, based on the Taguchi-Grey relational approach, the effects of different milling parameters on the residual stress and surface roughness of 2A12 aluminum alloy were studied. To reduce the residual stress and surface roughness of 2A12 aluminum alloy, optimized milling parameters were obtained. To further reduce the milling residual stress of 2A12 aluminum alloy, the samples processed by the optimized milling parameters were treated by cryogenic treatment and artificial aging. The residual stress of the sample was measured by the blind hole drilling method, and the evolution mechanism of the microstructure to reduce the machining residual stress was revealed. The results show that the combination of deep cooling treatment and oil bath aging can effectively reduce the residual stress on the machined surface of the aluminum alloy and facilitate a more uniform distribution of the residual stress inside the specimen. The effect of the coarse second phase on the residual stress in the microstructure is not significant, and the fine and diffusely distributed precipitation phase is beneficial to the reduction of the residual stress in the aluminum alloy.

In this work, thermo-mechanically treated 42CrMo steel was subjected to cryogenic treatment conducted by means of orthogonal design method, followed by low-temperature tempering to investigate the effect of different parameters of cryogenic treatment on wear resistance of 42CrMo steel and to optimize parameters of cryogenic treatment for improving wear resistance. The results of hardness test and wear test show that cryogenic treatment significantly improves wear resistance with marginal changes in coefficient of friction and hardness. Specifically, cryogenic temperature has the largest impact on wear resistance of 42CrMo steel, holding time has medium impact, and the parameter of treatment cycles has the least impact. The optimum parameters of cryogenic treatment are −196°C for 12 hours with one cycle for improving wear resistance. The results of scanning electron microscopy (SEM) and X-ray diffractometry (XRD) analysis indicate that marginal changes in hardness and coefficient of friction may be owing to little amount of transformation of retained austenite, and the significant influence of cryogenic treatment on improving wear resistance of 42CrMo steel can be mainly attributed to segregation of carbon atoms promoted by cryogenic treatment resulting in more precipitation of carbides in subsequent tempering.