Enhancement of Fatigue Life in St37 Steels by Carburizing Process

Carburizing is a heat treatment process, which used widely for surface hardening. In this process, the parts are placed in a concentrated atmosphere of Carbon atoms. The carbon atoms diffuse in the samples from the surface. In the present article, the effects of carburizing temperature on fatigue life will be studied. The St37 steel material is selected for study due to its wide range of usage in industry and little attention on the carburizing of this material. The samples are prepared by implementing the carburizing process at different temperatures (300, 400, 500, and 600 °C). The holding time is 1 hour for all samples. The two-point bending fatigue tests had been carried out on constant loading stresses. The results of the fatigue life test show that the fatigue life enhances the carburizing process. The fatigue life improved from about 45000 cycles to about 65000 cycles (about 44% increase) by increasing the temperature from 300°C to 600°C. Holding at higher temperatures leads to an increase in fatigue life smoothly due to the increase in the diffusivity coefficient. Also, the fracture surface demonstrates that the crack initiation starts from outer surfaces very slowly and failure happens as a brittle fracture in the samples.

ST37 Steel Carburization with Coconut Charcoal

The carburization process is a surface hardening process where carbon is added to the surface without changing the core properties of the material. This process is carried out at the austenite temperature so that the carbon can diffuse into the phase. This process can only be done on low carbon steels with content below 0.25%. This research was conducted on ST37 steel, which is steel with low carbon content with 0.18% carbon content. This type of steel is surface hardened with a carburizing temperature of 850 C with a long lasting time of 1 hour, then it is carried out under moderate cooling with outside air media. And change its mechanical properties from the comparison of the initial mechanical properties of the specimen. The highest hardness value occurs in the carburizing process of coconut shell charcoal, but this hardness value occurs not because of the carburization process but because of the enlarged grain size caused by heating at temperatures below 723⁰ C, thus reducing the elongation properties of the material. Carburizing with battery stone media is more efficient than coconut shell charcoal at temperatures below 723 C. Because the temperature is below the austenite temperature, the absorbed carbons cannot diffuse as happened in the carburization process, but the absorbed carbons can bind the grain boundaries and change their hardness by 4%. In the microstructure research that occurs in this process nothing can change its phase because the temperature does not reach the austenite temperature. However, there are differences in the microstructure between the carburization process with coconut shell charcoal media.

Microstructural and Mechanical Evaluations of SAW By Manufactured Granular Basic Bonded Cr, Mo, and Cr-Mo Active Fluxes on ST37 Low Carbon Steel

Bead-on-plate submerged arc welding was conducted on St37 steel by manufactured Cr, Mo, and Cr-Mo active basic fluxes produced via the unfused bonded method. The base metal heat-affected zone and weld metal (WM) microstructures were identified and characterized by optical microscopy and scanning electron microscopy. Then, the ferrite morphologies volume fraction of WMs were measured. Moreover, the chemical analysis of slag and inclusions was evaluated by point scan energy-dispersive X-ray spectroscopy and extensively discussed. Inclusions number density and size and their effects on the formation of AF were also elaborated. Then, the WMs’ longitudinal tensile strength and Vickers hardness were measured. Finally, the Charpy V-notch test was conducted to determine the impact toughness; the fracture surfaces were investigated, as well.

Pengaruh Suhu dan Waktu Proses Hard Chrome pada Pelat Baja ST37 Terhadap Kekerasan dan Ketebalan Lapisan

The thickness and hardness affect the service life of ST37 steels. The temperature and duration of the coating process affect the hard chrome layer's thickness and hardness. The purpose of this study is to determine the effect of temperature and coating duration of the ST37 steel plate using the hard chrome coating method on the thickness and hardness of the coating. This research is an experimental study in which the treatment used is the temperature and duration of the metal plating process with hard chrome. The temperatures used were 45 °C, 50 °C, and 55 °C, and the coating time was 10 minutes, 20 minutes, and 30 minutes. After the hard chrome plating process is complete, the thickness and hardness of each specimen were tested. This research uses descriptive analysis. The results obtained from the thickness test are the highest average layer thickness of 8.9 µm at 45 °C, 9.1 µm at 50 °C, and 9.2 µm at 55 °C, respectively. The coating hardness test result shows an average value of 323.28 VHN at 45 °C, 333.01 VHN at 50 °C, and 466.51 VHN at 55° C, respectively. It can be concluded that the duration of the metal plating process with the controlled temperatures proportionally affects the thickness and hardness of the coating.Ketebalan dan kekerasan berpengaruh terhadap masa pakai logam baja ST37. Suhu dan lama proses pelapisan mempengaruhi tingkat ketebalan dan kekerasan lapisan hard chrome. Tujuan dari penelitian ini adalah untuk mengetahui pengaruh suhu dan lama pelapisan pelat baja ST37 menggunakan metode pelapisan hard chrome terhadap ketebalan dan kekerasan lapisan. Penelitian ini merupakan penelitian eksperimen di mana perlakuan yang digunakan adalah suhu dan lama proses pelapisan logam dengan hard chrome. Suhu yang digunakan adalah 45°C, 50°C, dan 55°C, dan lama pelapisannya yaitu 10 menit, 20 menit, dan 30 menit. Setelah proses pelapisan hard chrome selesai, selanjutnya dilakukan pengujian ketebalan dan kekerasan lapisan pada masing-masing spesimen. Analisis yang digunakan pada penelitian ini adalah analisis deskriptif. Hasil yang didapatkan dari pengujian ketebalan yaitu menghasilkan nilai rata-rata ketebalan lapisan tertinggi sebesar 8,9µm pada suhu 45°C, 9,1 µm pada suhu 50°C, dan 9,2 µm pada suhu 55°C. Hasil pengujian kekerasan lapisan yang didapatkan yaitu menghasilkan nilai rata-rata sebesar 323,28 VHN pada suhu 45°C, 333,01 VHN pada suhu 50°C, dan 466,51 VHN pada suhu 55°C. Dapat disimpulkan bahwa semakin lama proses pelapisan logam dengan suhu 45°C, 50°C, dan 55°C maka ketebalan dan kekerasan lapisan akan bertambah.