DE2311283A1 - FAST HEAT TREATMENT OF STEEL - Google Patents

Description

DR. INO. E. HOFFMANN · I> IPL. ING. W. EITLE · DP. RER. NAT. K. HOFFMANN PATKNTAN WlLTt D-8000 MDNCHEN 81 · ARABELLASTRASSE 4 · TELEPHONE (Olli) »11087 * · ^ '' * - ° ^

Licencia Talälmänyokat Ertekesitö Vällalat Budapest / Hungary

Rapid heat treatment of steels

The invention relates to a rapid heat treatment process as a substitute for long endurance and slow cooling existing stress relief annealing, furnace annealing or hardening and tempering existing tempering, patenting of plastically deformed and hardened, unalloyed or alloyed steel with low, medium or high carbon content manufactured semi-finished and finished products, such as wires, strips, rods, tubes, plates and the like.

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In most of the steel-made Haibund end products used, the machinability is with plastic deformation and the mechanical properties required for use by the well-known structure of the Steel secured after being in the relatively soft, plastically formable ferrite of chemical composition of the Steel depending on several or fewer brittle cementite or other carbide grains or platelets in proportion can be found evenly distributed. This steel is mostly used in the course of processing into a semi-finished or finished product cold, plastically deformed. During the individual deformation processes, the steel should be used for further cold deformation, or at the end of the deformation processes in order to ensure the mechanical properties required for use be heat treated. This heat treatment is a so-called consisting of long endurance and slow cooling Furnace annealing or tempering consisting of hardening and subsequent tempering or patenting.

The furnace annealing is carried out on the steel in large coils and is a, a significant furnace capacity, Large workshop floor area, labor-intensive work process requiring many material movements. The temper hardening or patenting consists of several stages and involves a more intricate series of operations than furnace annealing, the first process of which is a rather long high temperature annealing, which very often involves scaling and Causes decarbonization difficulties. The subsequent faster or slower cooling may cause Cracks and almost always coolant problems. The starting or endurance that follows after the deterrent is one that Long process similar to furnace annealing. The cost of these multi-tiered, intricate ones Heat treatment is complicated by having

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related devices associated with high investment costs still increased.

With the method according to the present invention can both furnace annealing and tempering or patenting with a single one, with those in the steel during of the annealing occurring structural changes are replaced according to the same, short endurance. That The new process is based on the better utilization of the properties in the steel during the plastic deformation and the subsequent one The process of annealing changes in structure, and its essence is as follows: In the course of processing into a semi-finished or finished product the steel is cold, plastically deformed. For plastic deformation it is necessary that the material has been previously is in a soft state. This state is due to the warm plastic that occurs during the cold deformation Deformation, or during the subsequent slow cooling, or as a result of a separate furnace annealing heat treatment The structure developing in the steel is secured. In this structure is the ferrite suitable for plastic deformation, in a soft, easily cold-deformable condition. The structure depends on the chemical composition of the steel The presence of more or less cementites and other carbides are relatively coarse-grained and have a non-uniform Distribution on. Cold plastic deformation has three effects on the structure of this steel:

1. The ferrite that enables the deformation solidifies.

2. The more or less coarse cementite or carbide grains and platelets present in the structure crumble.

3. Under the action of the significant, 3o to 8o percent plastic deformation flatten the grain groups occurring between the individual cementite or carbide grains wider ferrite zones to narrow strips, so that

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the larger distances between the carbide grains decrease significantly and their original coarse-grained, uneven distribution is actually corrected.

The solidification of the ferrite, the crumbling of the more or less give carbide grains and flakes and theirs Even distribution in the structure results in the tensile strength and yield point, but especially the plasticity of the material are so small that the steel can no longer be plastically deformed economically in this state. Because of its low ductility, it cannot be sold as an end product. Before those secured by the present invention Possibilities were known in the case when because of further plastic deformation, or because of consumption Final product in the annealed state was required, in the case of the cold-formed, solidified material, from relatively slow heating, from a cementite and often present other carbide also dissolving, long-term endurance at a correspondingly high temperature and from one, with the furnace at the same time cooling using existing furnace annealing

at

det, whereby steel with a higher carbon content creates scale and decarbonization was avoided by providing a suitable protective gas atmosphere. In the course of the heat treatment the ferrite was annealed and recrystallized, while the cementite or the carbide if it were during endurance was dissolved, separating from the solution during the slow cooling, relatively coarse-grained or lamellar, and the The amount of perlite and the dimensions of the ferrite grains are accordingly unevenly distributed! became.

Because of the soft ferrite, this material was excellently suited for further plastic deformation. Because of the coarse-grained, Irregularly distributed cementite or perlite, however

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the strength properties have dropped unnecessarily to values that are too small, and this was already an obstacle the increase in strength that can be achieved in the course of further deformation and improves the quality of the end product. Particularly The lowering of the strength values of such a material, which is the end product in the annealed state, was harmful should be sold. The goal would be, the greater the plasticity, the greater the yield point or Maintain tensile strength of the material.

However, one must reckon with these problems because of the limited possibilities resulting from furnace annealing. If that Material as the end product is not required in the annealed state, but a much greater tensile strength and Yield strength and, as a compromise, a moderate one, for consumption but sufficient plasticity, elongation, contraction were required have those used prior to the present invention Heat treatment process - temper hardening, plating - the task is solved in such a way that the, im In the course of earlier technological work processes, the properties and structure of the steel developed in the first Heat treatment stage were completely "washed off". In the course of the heating to the hardening temperature and the endurance namely, first of all, the hardened ferrite, which usually withstands plastic deformation, is annealed. After that, the Carbides (in the first place the cementite) dissolved. During the subsequent Deterrence, because a completely new one arises during the tempering or perseverance, the requirements corresponding structure securing mechanical properties.

The method according to the present invention is based on this on the recognition that to achieve the desired result such complex, costly and therefore many

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Work processes that present difficulties and possible errors are unnecessary.

When working out the method according to the invention, it became clear that in order to achieve the further plastic deformation securing soft state - for softening, recrystallization of the originally suitable for deformation plastic ferrite - the lengthy furnace annealing is not required, but this condition during a single, appropriately regulated heat treatment process consisting of rapid heating and short-term, perhaps only momentary endurance can be designed.

The new process solves the above-mentioned technical and economic problems of temper hardening and patenting by heating to the tempering temperature with a heating rate of at least 50 ° C./sec., Advantageously 2oo to 100,000 ° C./sec., And the duration and The tempering temperature is limited to a maximum of 300 seconds, advantageously 0.4 to 3 seconds, or to a maximum of 0.85, advantageously 0.5 to 0.75 of the melting or solidus temperature measured in Kelvin degrees so that the ferrite that enables the deformation and solidified during the deformation is annealed and recrystallized to the desired extent, while the brittle cementite and other carbides that are present in the structure and crumble during the deformation are only extremely limited to the extent required for the final mechanical properties to be resolved.

After the plastic deformation of the steel has mostly over approximately the same physical properties that are desired by consumers. Its strength values are even better, only the plasticity is worse. So it seems

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the idea, of course, that such a heat treatment is required to ensure that the requirements placed on the end product are met should be used, which does not deteriorate the strength values, and the plasticity numbers in desired mass improved. The method according to the invention solves the problem with one, of a single one rapid glowing and heat treatment consisting of short-term endurance at moderate temperatures, in which Run the ferrite, which enables the deformation and which has hardened during the deformation, anneals to the desired extent, but only the brittle cementite or other carbides present in the structure, which may have crumbled in the course of the deformation Solved to a small extent or not at all. The short-term endurance should not necessarily be achieved through fast or slow ones Cooling take place. During such heat treatment, plasticity, elongation and elongation improve significantly Contraction of the alloy, while the strength values, tensile strength and yield point only decrease to such an extent that the material meets the consumer's requirements. These properties can be influenced by the heating rate and holding temperature as well as holding time are regulated accordingly, so that greater elongation - smaller ones Strength or smaller elongation - greater strength can be achieved as required.

The following examples are available for implementing the method according to the invention:

1. A 1 mm thick, 10 mm wide, manganese alloyed, 0.2 % carbon containing steel strip of C52 quality according to the Hungarian standard should be annealed before the final finish rolling, as it is too hard as a result of the previous cold rolling process and for further deformation is unsuitable. The annealing takes place on the basis of the method according to the invention

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as follows: the cold-rolled, smooth, bare strip runs from a reel between two 15 mm wide contact rollers, each 200 mm in diameter. The contact rollers are made of tin bronze. The contact surfaces of the rollers are soldered with tungsten-silver plates or segments containing 20% silver in order to ensure the complete transfer of current and to avoid the risk of burn-in caused by sparks. The tape running out of the contact rollers runs after a distance of 2,000 mm into a molten lead bath at about 35 ° C, the task of which is to secure the corresponding electrical contact. A terminal of a direct current source of 4o V is connected to the contact rollers and to the lead bath. A current of about 600 A flows along the 2ooo mm long section between the two contacts, and the Joule effect of the current glows the section to 700 ° C. The tape runs between the two contacts at such a speed that each point on the tape covers the 2,000 mm distance within 20 seconds. Therefore, it takes about 2 seconds to reach the temperature of 700 ° C and 18 seconds to endure. Between the two contacts, the tape runs between two graphite plates to prevent oxidation and decarbonization. The tape running out of the lead contact is guided between "lead-removing" plates, also made of graphite, and from here into the cooling oil bath. The elongation of the strip heat-treated in this way is at least 25 %, which already enables further plastic deformation.

2. The steel strip described in the previous example is to be used as the end product with dimensions of 0.8 χ Io mm. The tensile strength of the tape previously cold-formed to 70% is Io5 kp / mm, its elongation is 2 %. The requirement for the end product, however, is a tensile strength of at least 8o kp / mm and a length extension of 12 %.

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The cold-formed strip is passed through the device described in the previous example in such a way that the distance between the two contacts amounts to a total of 200 mm. The voltage is 6 V, the current flowing through it has a strength of 800 A. The speed of the tape is the same as in the previous example, so that each point of the tape covers the distance between the contacts within 2 seconds. The Joule effect of the current heats the tape to 76o ° C in about 1 second, and the tape remains at this temperature for 1 second. At the end of the work process, the tensile strength of the material is 85 to 90 kgf / mm and its elongation is 14 to 18 %.

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Claims (1)

Claim Rapid heat treatment process as a substitute for one that consists of long endurance and slow cooling Stress-relieving annealing, furnace annealing, or temper hardening consisting of hardening and tempering, patenting of plastic deformed! and solidified, unalloyed or alloyed Semi-finished and finished products made of steel with low, medium or high carbon content, such as wire, Strips, rods, tubes, plates and the like, characterized in that the tempering temperature is used with a heating rate of at least 50 C / sec., advantageous 200 to 100,000 ° C / sec., Heats up and the duration and temperature of the tempering to a maximum of 300 sec., Advantageous o, o4 to 3 seconds, or to a maximum of 0.85th, advantageously 0.5 to 0.75th of the melting or melting point measured in Kelvin degrees. Solidus temperature limited, so that the deformation enabling and solidified during the deformation ferrite in the desired The mass is annealed and recrystallized, while that which is present in the structure crumbles in the course of the deformation brittle cementite and other carbides but only extremely limited in the amount required for final mechanical properties Mass to be dissolved. 309838/0938