Effect of surface condition on properties of the nitrocarburised layer

U radu je provedena su ispitivanja svojstva nitrokarburiranog sloja u solnoj kupci TENIFER ovisno o stupnju površinske obrade. Rad se sastoji od teorijskog i eksperimentalnog dijela.Teorijski dio bavi se klasifikacijom i detaljnim opisom postojećih metoda čišćenja i pripreme površine. Navode se prednosti i nedostaci svakog postupka kao i moguće primjene. Također se objašnjava postupak nitrokarburiranja u solnoj kupci TENIFER. U eksperimentalnom dijelu rada objašnjena su osnovna svojstva čelika C35, nakon čega je objašnjeno pet različitih priprema ispitnih uzoraka izrađenih iz čelika C35. Potom su provedena ispitivanja tvrdoće, površinske hrapavosti, korozijske postojanosti te analiza mikrostrukture prije i nakon postupka nitrokarburiranja. Usporedbom rezultata ispitivanja te njihovim dovođenjem u direktan odnos s kvalitetom pripreme površine donesen je zaključak o optimalnoj površinskoj pripremi. Ovakav tip istraživanja nije ranije proveden na čeliku C35, a može doprinijeti smanjenju troškova u proizvodnji strojnih dijelova načinjenih od te vrste čelika. Na temelju rezultat provedenih ispitivanja, prije nitrokarburiranja čelika C35 u solnoj kupci TENIFER, preporučuje se priprema površine brušenjem papirima gradacije od #600 do #1200 koje će omogućiti nastanak zone spojeva s najmanjom poroznosti i dobru otpornost na koroziju.The following study deals with the properties of the nitrocarburated layer in TENIFER salt bath taking into consideration the degree of surface treatment. The study consists of a theoretical and experimental part. The theoretical part deals with the classification and provides us with a detailed description of the existing methods of surface cleaning and surface preparation. The advantages and disadvantages of each procedure are explained, as well as the possible applications of each of them. The nitrocarburization process in the salt bath TENIFER is also explained. The experimental part of the study explains the basic properties of steel grade C35, as well as the five different types of sample preparations. Moreover, the hardness, surface roughness, corrosion resistance and microstructure analyses of samples have been carried out before and after the nitrocarburization process. By comparing the test results, and by bringing them into direct correlation with the quality of surface preparation, a conclusion has been reached that specifies the optimal surface preparation. This type of research has not previously been carried out on steel grade C35 and can contribute to reducing costs in the production of machine parts made out of this type of steel. Based on the results of the tests carried out, prior to nitrocarburization of steel C35 in the TENIFER salt bath, it is recommended to prepare the surface by grinding with grading papers that has grit size range from # 600 to # 1200, which will allow the formation of smallest porosity and good corrosion resistance of the compaund zone