The Effects of Quenching with Clay on the Microstructure and Corrosion Performance of Steel Blades

Coating a sword with a layer of clay prior to water quenching is one way to promote hardening and improve corrosion resistance. In this study, two types of clay coating were prepared on two identical steel swords (L04 and L05) in order to explore the effects of the addition of clay on the microstructure of steel. Samples taken from each blade were compared using metallography, XRD tests, microhardness tests, and electrochemical tests, and the results showed that L04 had a wavy pattern and contained pearlite, martensite, and residual austenite, while L05 had a mesh pattern and consisted of acicular and lath martensite. More importantly, the electrochemical tests indicated that L05 exhibited better corrosion resistance than L04. Each test zone of L05 (with icorr values of 2.48~8.08 μA·cm−2) had lower corrosion rates compared to the corresponding zones of L04 (with icorr values of 2.93~10.44 μA·cm−2). Furthermore, the calculated Rp values of each test zone of L05 (2341~8260 Ω·cm2) were higher than the values of the corresponding zone of L04 (1908~6716 Ω·cm2). These results further demonstrate that the second method of clay coating endowed superior anti-corrosion performance. In addition, the overall strength and toughness of L04 were achieved with a lower hardness back (mean value 320 HV) and a higher hardness edge (mean value 850 HV), whereas the overall strength and toughness of L05 were achieved with a high hardness throughout (mean value 640 HV of the back and 725 HV of the edge).