Objective: Two kinds of fire-resistant steel with different Nb content (Nb-free and 0.03 wt.%) were prepared for studying the effects of Nb addition on the elevated-temperature strength of fire-resistant steel. Methods: Two stages of heat treatment were carried out on the steels to obtain different microstructures. Typical microstructures, dislocation, and precipitates morphology of steels were observed by SEM and TEM. The dislocation density was calculated by the X-ray data from the microstructures. High temperature and room temperature mechanical properties of steels were determined by tensile testing. Results: The results showed that the YS of N2-HR steel (addition of 0.03 wt.% Nb) at RT and 600 °C was higher than N1-HR steel (Nb-free) by about 81 and 30 MPa, respectively. This indicates that Nb is an alloying element as effective as Mo in increasing the elevated-temperature strength of fire-resistant steel. The dominant strengthening mechanisms of Nb addition on elevated-temperature yield strength are precipitation strengthening and bainite strengthening. Conclusions: Theoretical analysis shows that there are two precipitation strengthening stages in fire-resistant steel: (1) increasing dislocation density during hot rolling, and (2) blocking dislocation movement and recovery in tensile testing. The results also show that the effect of fine grain strengthening is not obvious at high temperature, but is obvious at room temperature.

This paper analyzes the intelligent and digital trend of remanufacturing industry, discusses the connotation and characteristics of additive remanufacturing technology, compares and analyzes the application status and application technology of additive remanufacturing technology in China’s military industry, points out that additive remanufacturing technology has broad application prospects in national defense science and technology, and brings higher military and economic benefits.

This article first introduces the characteristics and disadvantages of traditional remote fire extinguishing technology and proposes a remote fire extinguishing system based on electromagnetic ejection. Based on the finite element analysis method and the grid matrix method, a seven-segment electromagnetic launcher model is designed. As the initial energy source, the capacitor can accelerate a 10 kg fire extinguishing bomb to 113 m/s with a range of 2 km. The results show that the electromagnetic catapult designed in this study can meet the needs of fire extinguishing bombs. This paper also designs the overall structure of the vehicle electromagnetic catapult remote fire extinguishing system, discusses its role in the field of firefighting, and prospects the future work.