No abstract

Purpose -The purpose of this paper is to characterize carbide coatings obtained by thermo reactive diffusion (TRD) method on AISI 52100 and 440C bearing steels, which are extensively used in industry, and to study wear behaviour of coated steels at elevated temperatures. Design/methodology/approach -For coatings of vanadium and titanium carbides, TRD treatment is performed on AISI 52100 and 440C steels using pack method at 9508C for 3 h. Carbide coatings are characterized using X-ray diffraction (XRD). The Daimler-Benz Rockwell-C adhesion test and micro-Knoop indenter is used to assess the adhesion and hardness of the carbide layers, respectively. Ball-on-disc arrangement is used for determination of tribological properties of carbide-coated steels. Friction and wear tests are carried out against Si 3 N 4 ball at elevated temperatures up to 6008C under 5 N load, for sliding speed of 0.3 m/s. Findings -The presence of carbides formed on AISI 52100 (Ti 6 C 3.75 and VC 0.88 phases) and on AISI 440C (Ti 6 C 3.75 , VC 0.88 and minor Cr 23 C 6 and Cr 7 C 3 phases) is confirmed by XRD analysis. Hardness values of titanium and vanadium carbides on the 52100 and 440C steels are about 2,175-2,464 and 2,128-2,433 HK 0.05 , respectively. Friction experiments show that this type of coating is more effective than the substrates in regards to achieving lower friction up to 3008C. Above this temperature, the effect of substrate is more dominant on the friction coefficient. Scanning electron microscopy and energy-dispersive X-ray analysis results show the presence of the compact oxide layers at elevated temperatures as a result of increased sintering and oxidation of the wear debris.Research limitations/implications -This paper deals with only characterization of vanadium and titanium carbide coatings and high temperature wear properties of the coated steels. Practical implications -Carbide coatings obtained by TRD method are satisfactory in terms of high temperature tribological applications in comparison with those produced vapor deposition processes, which are expensive and complicated equipment. Originality/value -There is no literature about high temperature wear and friction behaviour of TRD carbide-coated 52100 and 440C steels. In this study, there are new results on high temperature wear of TRD carbide-coated steels.

No abstract

In the present study, the production of dual phase steel structure in the core of surface borided SAE 1020 steel and the effect of martensite volume fraction (MVF) on tensile, microhardness and microstructure were investigated. For the purposes, specimens were divided into two groups. The first group of specimens was subjected to intercritical annealing at temperatures between 720 and 820°C. Specimens from the second group were first borided at 900°C for 2 h, and then without removing the specimens from the furnace, they were annealed at different intercritical heat treatment temperatures from 720 to 820°C. During the intercritical annealing process, the specimens of both groups were kept in the furnace for 30 min. Thermal processes were followed by microstructural analysis of the specimens. The MVFs of the specimens were calculated after intercritical annealing. Heat treatment temperatures that resulted in common MVFs were found for the two groups. In the first and second groups of specimens, dual phase microstructures were obtained after heat treatment. Up to 83 μm thick boride layer was obtained on the surface of the borided specimens, and a ferrite–martensite microstructure was produced in the matrix. In addition, an X-ray diffraction test was applied to the borided specimens. According to microhardness tests, a hardness value of up to 1530 was obtained on the boride layer.

Èññëåäóåòñÿ âëèÿíèå ìîðôîëîãèè ñòðóêòóðû ôåððèòà è åãî îáúåìíîãî ñîäåðaeàíèÿ íà ìåõàíè÷åñêèå ñâîéñòâà è âÿçêîñòü ðàçðóøåíèÿ äâóõôàçíûõ ñòàëåé. Äëÿ îïðåäåëåíèÿ çíà÷åíèé âÿçêîñòè ðàçðóøåíèÿ èñïîëüçîâàëè íå ñòàíäàðòíûé, à àëüòåðíàòèâíûé ïîäõîä. Ñòàëè ïîäâåðãàëè ãîìîãåíèçèðóþùåé òåðìîîáðàáîòêå. Ïóòåì ïîëíîãî îòaeèãà èëè çàêàëêè ñòàëåé èç àóñòåíèòíîãî ñîñòîÿíèÿ äî ïðèìåíåíèÿ äîêðèòè÷åñêîãî îòaeèãà â àóñòåíèòíîé îáëàñòè ïîëó÷åíû äâå ðàçëè÷íûå èñõîäíûå ìèêðîñòðóêòóðû. Ïîëó÷åíû äâóõôàçíûå ñòàëè ñ äâóìÿ òèïàìè ìîðôîëîãèè (êðóïíî-è ìåëêîçåðíèñòàÿ) ñ 40-, 20-è 10%-íûì îáúåìíûì ñîäåðaeàíèåì ôåððèòà â çàâèñèìîñòè îò èñõîäíîé ìèêðîñòðóêòóðû. Îòïóùåííûå îáðàçöû ñ 10%-íûì îáúåìíûì ñîäåðaeàíèåì ôåððèòà èìåëè áîëåå âûñîêèå çíà÷åíèÿ âÿçêîñòè ðàçðóøåíèÿ ïî ñðàâíåíèþ ñ òàêîâûìè äðóãèõ îáðàçöîâ èç ýòèõ ñòàëåé.