| dc.description.abstract | The surface hardness of the material is one part that is often considered in the industrial field. In its application, certain specifications are often required, such as Gear which is often used in the industrial world. There are 2 ways to increase surface hardness, namely induction hardening and flame hardening. A good method is flame hardening because this method is not like induction hardening which only uses the factor of heating and cooling the material quickly, instead there is a transfer of carbon elements from acetyline gas which is used in the flame hardening process. The carbon element is useful for hardening the material because the more carbon elements the harder the material will be. The aim of this study was to determine the effect of the duration of the heating time and the cooling medium used on the hardness of the ss400 steel material. In the heating process using a carburizing flame by combining oxygen gas and acetylene gas then the torch is directed to the heated specimen using the progressive method over the entire surface of the sample for 5 minutes, 15 minutes and 25 minutes. After that, quenching was carried out using air, oil and water cooling media. The heating temperature and the final temperature after cooling are taken using a thermocouple as the data for the rate of increase and decrease in temperature. The highest temperature was obtained at a variation of heating time for 25 minutes with an oil cooling medium of 828°C. Then the samples were tested for metallography using an optical microscope to obtain microstructural images. Specimens with a heating time of 25 minutes with oil cooling media obtained a 50% martensite microstructure and water obtained an 80% martensite microstructure according to the TTT diagram used. After that, the hardness was tested using the Vickers method. In this test, the highest hardness value was obtained on the specimen with a water cooling medium of 452HV then 333HV oil with a decrease in hardness with increasing distance between the inside of the material and the surface of the material. Then the SEM test was carried out to re-identify the depth of hardening. Differences in grain size were found in the specimens where the surface of the specimen that was exposed to flame hardening had a small grain size and the part of the specimen that was inside the specimen was getting bigger. This results in data that there is a limit to the depth of hardening. In its application, specimens with high hardness values but not too high to avoid low toughness values and the deepest depth of hardening are found in specimens with a heating time of 25 minutes with oil cooling media. | en_US |
