A study on nanoscale gradient alloying induced by a punching deformation process on low carbon steel

• A gradient alloying is fabricated by PDR process on mild steel.
• The PDR process can induce defects, which promote the Cr element diffusion.
• A gradient alloying exhibit fine grain, Cr solution and hard phase of (Fe,Cr)7C3.

The gradient alloying surface produced on a low-carbon steel material by a punching deformation and recovery process is investigated using scanning electron microscopy, energy disperse spectroscopy and X-ray diffraction. The mechanical properties of the gradient alloying surface are studied using nanoindentation and microhardness testers. The surface layer is observed to contain a (Fe,Cr)7C3 phase. There is also a decrease in Cr content as grain size increases from the top surface to the matrix. These results can be attributed to defects in the microstructure induced by the punching deformation process, which promote diffusion of Cr in the matrix. The gradient alloying surface also exhibited increased hardness due to the grain refining process, the Cr solution used and the presence of the hard (Fe,Cr)7C3 phase.

The chemical analysis by EDS indicates that the new gray domains contain about 48 at% ferrum and 52 at% chromium. It may be Cr-rich phase ((Fe,Cr)xCy) since the atomic ratio of Cr/Fe is about 1. These new phases are α-Fe (JCPDS card No. 06-0696) and (Fe,Cr)7C3 (JCPDS card No. 05-0720), which are supported by XRD analysis.Figure optionsDownload as PowerPoint slide