Twinning induced plasticity (TWIP) steels with excellent strength and elongation properties are expected to be the next generation of automotive high-strength steels. The present work investigates endogenous inclusions formed in Fe-25Mn-3Si-3Al TWIP steels in laboratorial ingot, mold casting after AOD steelmaking and electroslag remelting (ESR) process at industrial plant, respectively. The research shows that AlN and Al 2 O 3 inclusions are found as dominating inclusions, and most of them are AlN, but the number, distribution, size shape of inclusions have big differences in different metallurgical processes. The AlN inclusions in laboratorial ingot mainly present cluster states and have larger size, but after AOD or ESR process most of AlN inclusions are uniformly distributed, this would reduce harm to steel quality. From the point of view of thermodynamics, the research finds that the generation of AlN inclusions in Fe-25Mn-3Si-3Al steels is different from that of most of other high-Al steels or Al-killed steels, because many publications reported that the precipitation of AlN inclusions took place at solidifying front or solid phase, but AlN inclusions formed in Fe-25Mn-3Si-3Al steels generate in liquid steel, and related experimental results prove this point.

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Online rapid detection of a fertilizer solution’s type and concentration is crucial for intelligent water and fertilizer machines to realize intellectual precision variable fertilization. In this paper, a cylindrical capacitance sensor was designed based on the dielectric properties of the fertilizer solution, and an online rapid detection method of fertilizer type and concentration was proposed based on the characteristic frequency response mode. Three fertilizer solutions, potassium chloride, calcium superphosphate, and urea, were used as test objects. Ten concentrations of each fertilizer solution in the 10~100 g/L range were taken as the test fertilizer solution. Then, under the action of a series of sine wave excitation signals from 1 kHz to 10 MHz, the sensor’s amplitude-frequency/phase-frequency response data were obtained. The detection strategy of ‘first type, then concentration’ was adopted to realize rapid online detection of fertilizer type and concentration. Experimental results indicated that the maximum relative error of the sensor stability test was 0.72%, and the maximum error of concentration detection was 7.26%. Thus, the intelligent water and fertilizer machine can give feedback on the information of a fertilizer solution in real-time during the process of precise variable fertilization, thus improving the intelligence of water and fertilizer machines.

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