Low temperature carbon steel pipe is medium carbon structural steel, cold steel plus low energy are good with good mechanical properties, and low prices, wide sources, so widely used. Its biggest weakness is the low hardenability, cross-sectional dimensions Japan is relatively high workpiece should not be used. Cold steel for low temperature operation, can withstand a certain low temperature impact.
Low temperature quench pipe A3 + (30 ~ 50) ℃, in practice, is usually set to the upper limit. High quenching temperature to low temperature pipe heating speed, reduce surface oxidation, and can improve efficiency. The workpiece is uniform austenite, will require sufficient holding time. If the actual installed furnace capacity, would be appropriate to extend the holding time. Otherwise, there may be insufficient due to uneven heating caused by the hardness of the phenomenon. However, the holding time is too long, will also appear coarse grains, oxidation and decarbonization serious ills affecting quenching quality. We believe that such equipment is greater than the specified process documents furnace, the heating need to extend the holding time of 1/5.
Because the low temperature steel hardenability is low, it should be large cooling rate of 10% salt solution. After the workpiece into the water, it should hardenability, but not chilled, if in cold salt water penetration, it is possible cracking of the workpiece, it is because when the workpiece is cooled to about 180 ℃, the rapid transformation of austenite horse s body tissue caused by excessive stress due. Therefore, when hardened steel rapid cooling to the low temperature region, it should take slow cooling method. As the water temperature is difficult to grasp, accountable experience to operate, when to stop dithering artifacts in the water, the water can be air-cooled (eg oil cooler can be better). In addition, the work should move into the water should not be static, should be in accordance with the geometry of the workpiece, as the rules of sport. Stationary cooling medium plus stationary workpiece, resulting in uneven hardness, stress uneven leaving large deformation of the workpiece, and even cracking.
Cold steel pieces quenched hardness after quenching should reach HRC56 ~ 59, lower section of the possibility of some large, but not less than HRC48, otherwise, it shows the work has not been fully hardened tissues may occur even ferrite sorbitic Organizations, such organizations tempered, still retained in the matrix, which was not quenched purposes. Cryogenic tempering steel after quenching, the heating temperature is usually 560 ~ 600 ℃, hardness is HRC22 ~ 34. Because the goal is to get quenched mechanical properties, so the relatively wide range of hardness. But drawing hardness requirements, it is necessary to adjust by drawing tempering temperature to ensure hardness. For example, some cold steel shafts require high strength, hardness is high; while some gear, shaft parts with keyway, because after quenching but also for milling, insert processing, hardness requirements will be lower. About Tempering time, depending on the hardness and size of the piece, we think, depends on the hardness after tempering tempering temperature, tempering time with little to do, but must return through the general overall at the workpiece Tempering Time more than one hour.
