called tenifer process also called tufftrideprocess as described in the durferrit works news issue 35 published in december 1962 by the degussa corp durferrit division frankfurt main west germany can be employed or e g short time gaseous nitration as described e g by g stahli et al in 34 comparative studies on bath nitrated and nicotrated probes 34 published in material und technik 2 1974 no 3 page 126 135 in german in this process the ferro nitride layer 7 commonly designated also as connecting zone is formed in the steel surface containing e g about 10 12 percent weight of nitrogen depending on the duration and the intensity of the nitrogen treatment and on the steel type processed a thickness c of the layer 7 of up to about 50 u03bc e g 5 10 u03bc with a vickers hardness exceeding that of the unhardened steel of e g 100 200 hv e g with a vickers hardness of 400 600 hv can be achieved nitrogen penetrating in small quantities of less than 0 1 percent by weight by diffusion to a depth of several tenth of a mm below the thickness c of the layer can establish a so called diffusion layer in the ferritic steel structure of the unhardened steel subsequently the spinning ring 1 is hardened in the locally limited zones i e is hardened partially only by heating it to.