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Chemical corrosion in coal mines substantially affects the mechanical properties of rocks such as sandstone and may trigger the instability of roadways. In this article, the effects of chemical corrosion on the Mode I fracture toughness of sandstone are investigated using semicircular bending tests. The two experimental factors involved in this article are the pH value of the soaking solution and the soaking time. Based on the peak load and the shape parameters of specimens, the Mode I fracture toughness of sandstone under chemical corrosion is estimated as a function of the pH value of the soaking solution and the soaking time. In soaking tests, the relationships between the pH value of the soaking solution and the soaking time and the relative quality and porosity of sandstone are determined. The results indicate that chemical corrosion weakens the mechanical properties of sandstone specimens but enhances the ductility of sandstone specimens. The Mode I fracture toughness of sandstones decreases with an increase in the soaking time. The Mode I fracture toughness of sandstones initially increases but then decreases with an increase in the pH value. When the pH value is 7, the Mode I fracture toughness of sandstone attains the maximum value. The damage to sandstone specimens shares the same mechanical mechanism as the deterioration of the Mode I fracture toughness of sandstone. The results are significant for establishing a coupling damage model for the mechanical–hydrochemical behaviors of rocks.

Numerical simulations and experiments were utilized to study the removal of oxide scale formed on 300 M steel special-shaped hot forging surfaces during heating at elevated temperature by a high-pressure water descaling process. Specifically, the experimental setup of the special-shaped hot forging was designed and manufactured according to the descaling parameters and simulation results obtained from the hot rolling process. The force states of three typical hot forging surfaces impinged by high-pressure water jets were analyzed. Moreover, the mechanism of the high-pressure water descaling process was proposed based on the research results. The numerical simulations and experimental results revealed that the velocity distribution of the high-pressure water jets is relatively different in various areas of the special-shaped hot forging surfaces. Therefore, the descaling performance is synergistically influenced by the velocity of the high-pressure water jet and the shape of the special-shaped hot forging. Given a certain spray pressure, the value of impact force Fi plays a significant role in the descaling of the typical hot forging. The larger the value of Fi on the typical hot forging surface, the easier it is to remove the oxide scale, and vice versa. Accordingly, the difficulty of removing the oxide scale formed on the 300 M steel special-shaped hot forging surfaces during heating at elevated temperature by a high-pressure water descaling process is in the following order: plane surface < convex surface < concave surface. Additionally, only the inner-layer FeO of the oxide scale remained after the high-pressure water descaling process due to the appearance of FeO-Fe2SiO4 eutectic in the FeO layer.

A new manufacturing method of hot stamping tool with CCC is proposed in this study. A pair of optimal hot stamping tool should have long service life, low manufacturing cost and good cooling performance simultaneously. The CuCrZr alloy and Fe-based alloy is selected as interlayer layer (IL) and surface layer (SL) respectively. The maximum stress of new tool was less than the yield strength of the corresponding welding materials, which demonstrated that new tool manufactured by surfacing technology could satisfy the strength requirement and deserve further research.