Method of heat treatment of steel
Method of heat treatment of steel
The outer ring component of the constant speed universal joint that constitutes the motor vehicle driving mechanism is generally manufactured by the following operations: the carbon steel workpiece made of cylinder is successively extruded into shape by forward extrusion, upset forging and reverse extrusion, and the carbon steel workpiece is plastic deformed into the shape of the outer ring part. In addition, it is sometimes necessary to heat the carbon steel workpiece to a predetermined temperature before forging. G type, in the case of the outer ring part, will sometimes have to be heated or heated.
The resulting outer ring parts are cooled to room temperature and transported to the heat treatment equipment. Therefore, in order to soften the outer ring parts and improve their deformation capacity, or to achieve homogenization of hardness, low-temperature annealing, spheroidizing annealing or normalizing shall be carried out in the heat treatment equipment.
Then, a shot peening process is performed to remove the oxide skin produced during the heat treatment above, and a chemical coating film is formed on the outer surface of the outer ring parts by the formation of a lubricant composed of zinc phosphate, etc. However, the outer ring parts are machined by reducing the diameter (finishing forming), thus finishing the final size of the outer ring parts. In addition, the reduction extrusion process is usually cold forging.
In the case of these manufacturing processes, however, there must be extensive space for the outer ring components to be used for storage prior to the implementation of these heat treatments, and preservation purposes to ensure that space is economically disadvantaged.
In addition, heat treatment is carried out at the same time as transferring the outer ring parts loaded on the conveyor belt to the continuous heating furnace, while the time from the outer ring parts being fed into the continuous heating furnace to being sent out from the continuous heating furnace, in other words, the processing time is long, so the outer ring part obviously exists
Poor production efficiency of 3 pieces. In addition, even changing the heating furnace to batch heating furnace cannot shorten the processing time.
Furthermore, the heat treatment equipment used for low-temperature annealing, spheroidization annealing or normalizing must be large equipment, so the equipment investment is huge.
However, if heat treatment is omitted in order to avoid these undesirable conditions, it will neither soften the outer ring parts nor uniform hardness, thus causing cracks in the reduction extrusion process, or reduce the dimensional accuracy of the tooth part when the tooth part is set on the shaft of the outer ring part.
From the above point of view, people are eager to establish a short time can be completed and simple
For example, in the bulletin no. 5-302117 of Japan, a scheme of tempering only without quenching is proposed. In addition, the following scheme was made public in bulletin no. 5-255739 in Japan: steel workpiece shall be machined at a temperature between Acr Ac3 to a degree of plastic deformation of 45-65%, and then air cooling (naturally placed cooling) shall be carried out.
, according to an implementation mode of the present invention provides a method of heat treatment of steel, the method of heat treatment of steel materials include the following process: first, the first step will be to plastic deformation of sex as the processing and processing heat of steel, heat processing from the residual heat of the moment, to keep the above the temperature of the steel in the Ad - Ac3 between points; And the second process, in which the steel is heated and maintained, is cooled at a rate of 5-45"/ min until the pearlite is formed
The temperature at the end, where the holding time in the first process mentioned above is IO minutes or shorter, but is greater than o minutes.
After the plastic deformation process, the metal structure will be slightly affected in the cooled steel
Uneven. In the present invention, the steel is kept at a temperature between the points of acl-ac3, and the metal structure in which the austenite and the ferrite coexist is thus approximately uniform. That is, by maintaining the temperature, the metal structure of the steel can be roughly uniform.
In addition, through the first and second processes, the steel is softened, and the hardness of the steel is roughly the same regardless of the location and distance from the surface. In other words, it is possible to deform all parts to approximately the same degree in subsequent processes, such as reduction extrusion forming. Therefore, it is difficult to crack the formed body, and the size accuracy of the formed body is good.
Furthermore, since heat treatment is carried out at the moment of residual processing heat, i.e., the moment of self-heating of processing, there is no need to preserve the steel for plastic deformation processing. Therefore, since there is no need to prepare space for storage, space can be effectively used for other purposes.
In addition, as the holding time is less than IO minutes, the scale of heat treatment equipment can be smaller than the previous heat treatment equipment such as spheroidizing annealing equipment. Thus, huge equipment investment is avoided. On this basis, the efficiency of heat treatment is improved, so the energy required for heat treatment is reduced, and the production efficiency is also improved. As a result, it is cost-effective. In addition, in the present invention, "plastic deformation processing" includes the process of exerting pressure on the steel to produce plastic deformation. Specifically, examples are: forging, forging and rolling.
Here, the end temperature of the pearlitic release of steel is based on the cooling rate in the second process and
The type of steel varies from 600 to 680. In the range of C. Therefore, the second process to 600-68(TC) is sufficient.
The preferred cooling rate for the second process is 5-l(TC/ min). In this case, the tissue becomes more fine and, as a result, further inhibits the inhomogeneity of hardness.
In the case of plastic deformation of steel by raising the temperature of the steel to the ACl point or higher, the heating (heating up) of the steel is preferably initiated at the point when the steel is at An point or lower and in the range of 50(TC or higher).
Ai ^ point is defined as: when cooling steel from austenite to ferrite and cementite eutectoid transformation temperature. As a result, the metal tissue falling to Ar, point or lower is roughly uniform tissue containing ferrite and pearlite. Thus, the final metal structure of the steel after the second process is further homogenized to obtain steel with roughly equal properties.
Furthermore, in the case of plastic deformation of the steel when the steel is heated to a temperature below the ACl point, the heating (heating up) of the steel is preferred to start at a temperature of 50(TC or higher).
Here, in the case of cold forging, heating can be started at the moment when self-heating of the process is maintained, that is, the temperature is the temperature before plastic deformation or higher.
Therefore, in the first process above, the heating rate is preferably 15-5(TC/ min) until the steel reaches the temperature between ad-ac3 points. If below 15"C/ min, the efficiency of heat treatment decreases. And, if higher than 5(TC/ min), the steel and metal tissue sometimes produces defects.