45 narrative 40Cr steel quenched and tempered steel and heat treatment process
DATE:2016/1/16 HITS:2764
45 40Cr steel quenched and tempered steel and heat treatment process
Quenched quenching and tempering of double heat treatment, which aims to make the workpiece has good mechanical properties.
Quenched and tempered steels are carbon steel and alloy quenched and tempered steel two categories, either carbon steel or alloy steel, the carbon content is more stringent control. If the carbon content is too high, the strength of the workpiece after quenching is high, but the toughness is not enough, as the carbon content is too low, toughness and lack of strength. In order to get a good piece quenched overall performance, the general control of the carbon content of 0.30% to 0.50%.
When the tune of hardened, requires the entire cross section of the workpiece quenching, the workpiece obtained as fine needles quenched martensite microstructure dominated. By tempering, to obtain an even tempered sorbite microstructure dominated. Small factories do not every furnace metallurgical analysis, generally for hardness testing, that is to say, the hardness after quenching quenching hardness of the material must meet hardness requirements to check Figure tempering.
   1, 45 quenched and tempered steel
   45 steel is carbon steel, hot and cold workability are good, good mechanical properties, and low prices, wide source, so widely used. Its biggest weakness is the low hardenability, cross-sectional dimensions Japanese requirements are relatively high workpiece should not be used.
   45 steel quenching temperature in A3 + (30 ~ 50) ℃, in practice, is usually taken ceiling. High quenching temperature allows the workpiece heating speed, reduce surface oxidation, and can improve work efficiency. To make the workpiece austenite homogenization, we need sufficient holding time. If the actual installed furnace capacity, would be appropriate to extend the holding time. Otherwise, it may occur due to uneven heating caused by insufficient hardness phenomenon. But the holding time is too long, it will also appear coarse grains, oxidation and decarbonization of serious ills affecting quenching quality. We believe, as installed furnace is greater than a predetermined process documents, heating holding time for an extended 1/5.
  Because 45 steel quenching low, it should be large cooling rate 10% saline solution. Workpiece into the water, should hardenability, but not cold through, if the workpiece thoroughly in cold salt water, it is possible to crack the workpiece, it is because when the workpiece is cooled to about 180 ℃, the austenite into martensite caused rapid tissue caused by excessive stress. Thus, when the fast-cooling to the hardening of the workpiece temperature region, it should take slow cooling method. Because the water temperature is difficult to grasp, it must depend on experience operating, shake the water when the workpiece stop, the water can be air-cooled (if oil cooling 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 regular exercise. Stationary cooling medium plus stationary parts, resulting in uneven hardness, stress leaving uneven workpiece deformation, even cracking.
 45 pieces of quenched and tempered steel hardness after quenching should reach HRC56 ~ 59, the possibility of some large low-profile, but not less than HRC48, otherwise, it shows the workpiece is not fully hardened tissue may occur even ferrite sorbite organizations, such organizations by tempering, still retained in the matrix, less than quenching purposes.
 45 steel tempering after quenching, the heating temperature is usually 560 ~ 600 ℃, hardness is HRC22 ~ 34. Because the goal is to get quenched mechanical properties, so a relatively wide range of hardness. But the drawings have hardness, it is necessary to adjust the tempering temperature by drawing, in order to ensure hardness. If some shaft parts requiring high strength, hardness is high; and some gear, shaft with keyway, because after quenching but also for milling, insert processing, hardness to be lower. About tempering holding time, depending on the hardness and size of the workpiece, in our view, it depends on the hardness after tempering tempering temperature, tempering time with little to do, but it must go back through the general total holding time at tempering the workpiece more than one hour.
   Quenched and tempered steel processing 2,40Cr
   Cr to increase steel hardenability, improve the strength and stability of steel tempering, with excellent mechanical properties. Big or important cross-sectional dimension of quenching the workpiece, should adopt Cr steel. But Cr steel has a second temper brittleness.
   40Cr quenched and the quenching and tempering workpieces, various parameters have predetermined process card, we realized in practice are:
  (A) should be adopted after 40Cr quenching oil cooling, 40Cr steel hardenability better cooling can be hardened in oil, and deformation of the workpiece, cracking tendency is small. But small businesses in tight supply situation, the shape is not complicated workpieces can be quenched in water, they found no cracking, but the operator must strictly control their experience into the water, the water temperature.
  After (b) 40Cr quenched and tempered hardness of the workpiece is still high, the second tempering temperature will increase 20 ~ 50 ℃, otherwise, hardness decreased difficult.
  (C) 40Cr workpiece after tempering, complex shape in oil cooling, simply cooled in water in order to avoid the influence of the second temper brittleness. Workpiece rapid cooling after tempering, if necessary, and then subjected to stress relief treatment.
Quality of quenching the workpiece, the operator level is an important factor, at the same time, there are many reasons for equipment, materials and quenched before processing, we believe that:
(A) of the workpiece is transferred from the furnace to a cooling tank slowly, the workpiece into the water temperature has dropped below the critical point Ar3, resulting partially decomposed, the workpiece is not completely get hardened structure, reach hardness. So small parts coolant to pay attention to speed, large parts to the cold time to master.
(B) of the workpiece installed furnace capacity to be reasonable, appropriate level of 1 to 2, resulting in uneven heating of the workpiece overlap, resulting in uneven hardness.
(C) of the workpiece into the water arrangement should maintain a certain distance, too dense vapor membrane rupture near the workpiece is blocked, causing the workpiece near the lower surface hardness.
(D) quenching furnace, quenching can not breath finish, depending on the oven temperature should be the extent of decline, halfway closed furnace re-warming, for consistent hardness after quenching the workpiece.
(V) to pay attention to the temperature of the cooling liquid, 10% higher than the brine temperature such as 60 ℃, it can not be used. Coolant can not have oil, mud and other impurities, otherwise, there will be insufficient hardness or uniformity.
(Vi) unprocessed rough quenched hardness is not uniform, if you want to get good quality quenched and tempered, rough should roughing, rods to forged.
(Vii) strict quality control, low hardness after quenching from 1 to 3 units, tempering temperature can be adjusted to achieve hardness. But after quenching hardness of the workpiece is too low, some even only HRC25 ~ 35, must be re-quenching, must not only subjected to temperature or tempering to achieve the requirements of the drawings bin, otherwise lost meaning quenched, and may have serious consequences.
45 quenched and tempered steel
 45 quenched and tempered steel is the most common type of heat treatment most of us have made. Referred to herein are non-automated production line, require a higher hardness (250HB above). Now some of the common problems in practice process are summarized below, please criticism.
1. Normally the heating temperature is between 830 ~ 850 ℃.
  Because some of my colleagues on the entire quenching mechanism is not fully digested, sometimes blind fear rework the heating temperature to 860 ~ 870 ℃, but basically do not solve the problem. In fact, as long as the full austenitizing heating temperature as low as possible (benefits not discuss). Of course, as far away from the pool and in front of baked appropriate incubation temperature increase to compensate for the cooling distance is not covered in this column.
2. cooling on attention.
Heat treatment of the most important part is to cool, a lot of heat treatment defects are produced during cooling. Such as: cracking, lack of hardness, deformation ultra-poor, local soft spots and so on.
⑴ not hurried when baked, sometimes fear can not hardened and confused. As long as no less than Ar3, is not affected by the surface hardness precipitated ferrite.
⑵ cooling water temperature is very important to strictly control the water temperature should not exceed 30 ℃, if more than 30 ℃, precipitated ferrite is inevitable, no matter how you thereafter cold workpiece through difficult higher hardness 250HB. Therefore, to strictly control the water temperature should not exceed 30 ℃.
⑶ workpiece into the water to keep the water moving to rupture the membrane and increase the vapor above 500 ℃ cooling rate, thereby avoiding precipitation of ferrite or pearlite, thereby affecting the final hardness of the workpiece.
⑷ To avoid cracking complex parts, the temperature is below 300 ℃ can be water cooled air-cooled for a while and then, when the workpiece temperature does not exceed 150 ℃ tempering water.
3. in strict accordance with the tempering temperature tempering 45 steel tempering temperature and generally in the lower side, according to HRc = 62-T × T / 9000 calculated and combined with each of the temperature difference between the furnace itself to make proper adjustments.
By taking these measures, basically solved the 45 high hardness quenched steel rework problem.
For more complex shapes of parts, you can shorten the holding time, and even the temperature does not heat 5-10 minutes or outlet quenching temperature can be baked at 840-850, but as far as about 780-820 quenching
45 # steel after quenching hardness up to HRC55 +, but generally have been tempered when used, depending on the tempering temperature, probably between HRC30 ~~ 45 use, the use of high frequency induction heating surface hardness after quenching It will be higher.

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