SU688529A1 - Method of manufacturing spring plates - Google Patents

Description

(54) METHOD OF MANUFACTURING RESESSION SHEETS

one

The invention relates to the field of metallurgy and mechanical engineering, in particular to methods for manufacturing and heat treating spring leaves, and can be used in the manufacture of vehicle suspensions.

A known method of manufacturing spring sheets, comprising heating them to quenching temperature, bending them, and cooling the dies by immersing them together with spring leaves in oil and high tempering.

This method is laborious and leads to decarburization of the surface of the sheet, which reduces the iridostnoe properties of multi-leaf springs.

A method is also known that the spring leaves are subjected to induction heating to quenching temperatures. In this case, a foot of spring leaves is heated in an inductor, from where they are transferred one by one to a bending-quenching device, in which they are bent and quenched in oil. After quenching, high tempering and shot hardening are carried out. This method reduces decarburization by reducing the heating time for quenching. However, the springs collected from the sheets.

manufactured in a known manner, have insufficient fatigue strength.

The aim of the invention is to improve the fatigue strength of the springs. This is achieved by the fact that in a known method, including induction heating to quenching temperatures, bending, cooling, tempering and sticking with shot, the spring leaves after gnbka are subjected to jetting, for example, water-jet, followed by self-tapping of the surface with 100 to 350 ° C for the time required to achieve the temperature difference between the core and the surface of the spring leaf, equal to 30-100 ° C, after which high-speed surface hardening is performed to a depth of 0.1-0.3 thickness of the spring leaf and tempering at 180-350 ° WITH.

Only one side of the spring leaf that experiences tensile stresses during operation can be subjected to surface heating. Vacation after surface quenching is carried out at 180-350 ° C for 0.5-1.5 hours. Cooling after high-speed heating is carried out by a jet-water method.

FIG. 1 shows the curve of surface heating and curve b of heating the core of the spring sheet; in fig. Figure 2 shows the distribution of hardness over the cross section of the spring leaf (the ordinate represents the distance from the surface to the point of hardness measurement).

The proposed method allows to increase the strength properties of the spring due to the joint action of two strengthening factors: austeite grinding grain and creating residual compressive stresses in the surface layer, where maximum tensile operating stresses act.

According to the proposed method, heating under bending is used to prepare the initial structure of the steel, which is achieved by intensive cooling after heating and self-tempering. The resulting fine structure on the surface without a structure-free ferrite makes it possible to obtain a very fine grain of austenite during subsequent high-speed surface heating, at the site of which, after quenching, martensite with a crystal size of 1-3 microns is formed. Such a structure has high strength and ductility. The use of jet-water cooling and self-discharging guarantees the absence of cracks during the first quenching, while there is no need for washing, which is necessary for quenching in oil.

To achieve the second hardening factor (creating residual compressive stresses on the surface of the spring leaf) and to obtain a viscous core, it is necessary that the surface hard layer (52-60 PCs) is 0.1 - 0.3 times the thickness of the spring leaf, and the hardness of the core was 30-40 HRc (see the hardness distribution graph for the section of the spring leaf in Fig. 2). At the same time, the surface hardened spring sheet due to the larger volume of martensite with high hardness has residual compressive stresses on the surface. Carrying out a self-tempering in the temperature range of 100-550 ° C for a time during which the temperature difference in the core and on the surface of the spring leaf is set in the interval of 30-100 ° C, and the subsequent high-speed surface heating provides the above requirements for the core and the surface layer.

In the self-tempering temperature range of 100-550 ° C, structural changes in the core can occur in two ways, each of which results in the required hardness of 30-40 ARc.

At surface self-tempering temperatures in the range of 100-180 ° C, the core is cooled to temperatures at which martensitic turning in spring steels occurs 50% or more. This

martensite at high-speed surface heating is released. In order to leave higher, the temperature difference in the core and on the surface is 30-100 ° before surface heating.

Due to this, even with the superficial character of the high-speed heating, the core of the spring sheet is heated to 600-650 ° C and released to a hardness of 36-40

MDS. As a result, there is no spring l, having after final tempering at 180-350 ° С on the surface a hardness of 58-60 PKC and in the core 36-40 PPC, which ensures the presence of high

residual compressive stress in places of action of tensile operating stresses.

For greater spring sheet thickness (25 mm) at self-tempering temperatures in

And in the range of 100-180 ° C to reduce the hardness of the core, it is possible to apply and reheat additional tempering 450-600 ° C and rapid surface cooling to increase the temperature difference on the surface and in the core of the spring sheet.

When self-tempering in a different temperature range, namely 180-550 ° C, austenite remains in the core during the aging;

which decays during and after high-speed surface heating, in which the core heats up to 650-700 ° C. This decomposition occurs due to the fact that austenite, which has been for some time at relatively low temperatures of 180-550 ° C and further heated to elevated temperatures of 650-700 ° C, becomes unstable. In this case, repeated heating of the spring leaf with a temperature difference between the core and the surface of 30-100 ° provides a more complete decomposition of austenite. In this process, after the final tempering at 180-350 ° C, the hardness on the surface of the spring is also 52-60 PNC, and in the core 30-35 HRc.

Thus, in the manufacture of spring leaves according to the inventive method, in the surface layer of the spring leaf it is possible to obtain fine grain and significant residual stresses due to the difference in the specific volumes of the surface layer and core. Moreover, these stresses extend to the depth of the surface hardening layer, which is 0.1-0.3 times the thickness of the spring sheet. Such a layer can not be erased when the spring leaves are worn during operation.

Conducting a blast-hardening work hardening that creates residual compressive stresses in a thin surface layer, 0.1-0.2 mm in depth, is also necessary. This increases the level of residual compressive stress in the decarbonized

a layer of sheets with a depth of 0.1-0.2 mm, arising in the process of metallurgical production.

The use in quenching after high-speed surface heating of jet-water cooling, which provides high cooling rates, makes it possible to use steel with fewer alloying elements for the manufacture of springs.

Example. The sheets included in the spring kit of the ZIL-130 car, made of 60C2 steel with a thickness of 10 mm, were successively heated using high frequency currents up to 870 ° C, bent over the required radius according to the drawing, and then subjected to jet water cooling for 3 s . This cooling time allowed self-tempering to pass at 100 ° C for 0.3 minutes (see Fig. 1 curve a). At the same time, the temperature in the core was 130 ° C (see Fig. 1, curve b). After this exposure, the spring sheet was heated superficially at a speed of 300 degrees / s to 820 ° C to a depth of 2.5 mm. In the middle of the spring leaf, the temperature reached 650 ° C. During subsequent water jet cooling at a critical speed, the surface was quenched to martensite with a hardness of 65 PKc, and the core had a tempering martensite structure with a hardness of 35-40 HRc.

Metallographic analysis of the surface layer showed that the martensite formed there has a needle size of 1-3 microns. After quenching, tempering was carried out at 250 ° C for 1.5 hours. The hardness in the surface layer is 58 HRc, in the core 38 HRc (Fig. 2).

Spring leaves were collected in spring and tested for fatigue on the machine company "Schenk on the program that simulates the load on the road, covered with cobblestones. Serial springs, obtained by processing by the proposed method, survived without failure such a number of loading cycles, which corresponds to the mileage

the car is 7200 km, while the springs, processed by a known method, weathered 4600 km.

Thus, the described method of manufacturing springs allows an almost 1.5-fold increase in the durability of the springs. Providing the same durability of the springs obtained by the known and proposed methods, the latter allows reducing the weight of the springs.

The proposed method can be used in the manufacture of springs, torsions and other products experiencing significant cyclic loads.

Claims (3)

1. A method of manufacturing spring sheets, including induction heating to quenching temperature, bending, quenching, tempering, and shot hardening, characterized in that, in order to increase the fatigue strength of the spring leaves, they are subjected to bend cooling after bending followed by self-chilling at 100-550 ° WITH for the time required to achieve a temperature difference between the core and the surface of 30-100 ° C, after which high-speed surface hardening to a depth of 0.1-0.3 of the spring sheet thickness and tempering are carried out. 2. A method according to claim 1, characterized in that the high-speed surface hardening exposes one side of the spring sheet. 3. The method according to claim 1, characterized in that the speed surface hardening carried out by induction ignition and jet water cooling.