Publish Time: 2022-11-01 Origin: Site
The drill bit is a long, thin, slender rod-shaped tool with a long edge that is subjected to high bending stresses while drilling through dense metal. To prevent breakage or chipping of the drill bit, the material used should have sufficient bending strength and toughness. The main procedure of HSS TWIST DRILL BIT hardening is: preheating (secondary) → heating → cooling → straightening → tempering → straightening → inspection.
Here is the content list:
Preheating
Heating
Cooling
Straightening
Tempering
Test
Preheating is carried out twice, the first time in a chamber furnace and the second time in a medium-temperature salt bath furnace. This is because the HSS TWIST DRILL BIT contains a large number of alloying elements, such as tungsten, chromium, and vanadium, and its poor thermal conductivity; at the same time, the cold drill bit directly heated at a high temperature, is bound to extend its residence time at the high-temperature stage, increasing the tendency of oxidation and decarburization, so before quenching and heating must be preheated to reduce the temperature difference, minimize the distortion.
In addition, we can make the shank hardness reach the technical requirements by adjusting the second preheating heating temperature, time, and cooling mode later. The specific operation is: After the first preheating, the drill is transferred to a medium temperature salt bath furnace, and the drill bit is immersed in the salt bath as a whole, while the heating temperature is increased to 870~900℃ and the heating time is extended to 0.2~0.5min/mm; subsequently, the shank is exposed to natural cooling in the air while the edge is heated.
From the process curve, we know that the heating temperature of the drill edge is 1 220 ℃, this is because most of the alloying elements in HSS TWIST DRILL BIT are in the form and other alloy carbides, these carbides can only be dissolved in austenite at a very high temperature, and the higher the heating temperature, the longer the time, they are dissolved in austenite in the number of the higher the heating temperature, the longer the time, they dissolve into the austenite in the number of martensites, the higher the concentration of martensite alloy after cooling, which can obtain high hardness, high red hardness and wear resistance". However, too high a heating temperature and too long a heating time will lead to coarse drill grain, coarse reticulated carbide, overheating or even overburning, so we use a lower heating temperature and a shorter heating time.
The cracking of HSS TWIST DRILL BIT tends to occur most easily at this stage. We use the graded isothermal quenching method based on the isothermal transition curve characteristics of W6Mo5Cr4V2Al steel. After high-temperature heating, the drill bit is put into the calcium salt at 560~580℃ for a short period, so that the internal and external temperature of the drill bit is the same, and then put into the nitrate salt furnace at 260~280℃ for a longer period, and then air cooled. As the salt bath cooling is faster and more uniform, it can effectively prevent the precipitation of secondary carbides and ensure the required hardness and red hardness of the drill bit after quenching; at the same time, the graded cooling of the drill bit reduces the temperature difference, which decreases the thermal stress and thus reduces the tendency of distortion. Isothermal cooling, so that part of the residual austenite into the lower bainite, not only more effectively reduces the distortion, and cracking tendency, and can improve the toughness of the drill bit.
Immediately after quenching, hot straightening is performed. As the HSS TWIST DRILL BIT contains more residual austenite after isothermal cooling, the hardness is lower and straightening is easier.
To prevent stabilization of the residual austenite, tempering is required promptly and is performed four times. This is because the HSS TWIST DRILL BIT quenching residual austenite more, a tempering is difficult to make its full transformation, after four temperings, can make the residual austenite greatly reduced, to obtain the required performance. In 550 ~ 570 ℃ tempering, can get the best with the performance, so, the tempering temperature selected 560 ℃. As the transformation of residual austenite is in the tempering cooling process, so each tempering is to be slowly cooled to room temperature in the air, to carry out the next tempering.
HSS TWIST DRILL BIT is tempered and then straightened to check if it meets the technical requirements, and this is confirmed by a final inspection.
If you are interested in HSS TWIST DRILL BIT, you can contact us at www.dmcraftools.com, looking forward to your arrival and hope to cooperate with you.