Study On Technology & Properties Of Pack Boriding Of Stainless Steels

The pack boriding process has carried on the 20Cr13,95Crl8 and 316 stainless steels at 880℃,910℃, and 940℃ for 5,7,9 and 11h. SiC was used as a boron agent in the boronizing formula. In order to obtain the best formula, the proportion of boron and activator agent and the composition of filler and catalyst were improved. The boride layers of three different stainless steels were characterized by metallographic analysis, SEM, EDS, XRD analysis and tested by Vickers indenters. Meanwhile, the thickness of boride layers was measured to carry out the kinetic study of the three steels and the contour diagrams were drawn to predict the relationships of boride layers’ thickness and processing parameters. To study the high-temperature wear resistance of the boride layers on stainless steels substrate, the high-temperature wear testing method was used on boride layers.The results showed that the boride layer had appropriate thickness with compact structure when the proportion of boron and activator agent was 1:1. The thickness of boride layers increased with decreasing holes after adding rare earth. However, the amount of holes increased when adding NH4CI to the boronizing formula. After being borided with the optimal formula, the three stainless steels’ microstructure results showed the boride layers were smooth without dentate structure. X-ray diffraction analysis of boride layers on the surface of martensite stainless steel revealed the existence of Fe2B, FeB and CrB compounds, however an additional Ni2B on austenitic stainless steel. The diffusion activation energy of 20Cr13, 95Cr18 and 316 was respectively 111 kJ/mol,191 kJ/mol and 236 kJ/mol, indicating that the Q was related with the structure and element contents of the steel substrate. The reciprocating wear experiments and high temperature friction and wear test showed the borided steel’s wear quality was 50% of the original one and boride layers at 200℃ still had a good antifriction effect, proving that the wear resistance of stainless steel was greatly improved.