SU1052551A1 - Method of spheroidizing treatment of strip rolled stock of carbon steels - Google Patents

Description

sd y

O1

The invention relates to the heat treatment of rolled metal and is intended for use in o Rolling rolled rolled products, in particular, for svvidizing the treatment of rolled strip (up to 11 mm thick) made of carbonaceous autoeutectoid steel (0, carbon) for clean cutting and supplied on TU 14-1-1535-76, which should have a low temporary tensile strength and almost completely spheroidized structure (no more than 10% of lamellar pearlite) with uniform distribution of cementite. There is a method of annealing cold-rolled steel, in accordance with which the steel is heated with intermediate exposure, finally kept at 680-710 ° C for at least 15-22 hours, and the heating rate is 0 to 16-0.25 ° C / min and cool give l. The application of the known method allows to obtain a low temporary resistance in the absence of plate-like perlite in the structure. However, the processing time is long and is 48-72 hours. A method of treating carbon and alloyed steels is also known, according to which the steel is quenched, heated to a temperature above Ac, maintained at this temperature, cooled below Ag, maintained at this temperature and finally C23., The disadvantage of this analog is the high temporary resistance and a sharp increase in the amount of plate-like perlite, with an increase in the manganese content of 0.2-0.3%, the closest to that proposed by the technical generality is rolled sferoydizIRUyuschey processing method comprising interrupted quenching, heating to A + (), shutter speed, cooling below the A, resists ku and cooling in air. The temperature of the end of interrupted quenching (at the center of the product) is 700400С, the total annealing time is 3-4 h, the isothermal holding time is 1.5 h. This method provides a spheroidized structure of the SP, the disadvantages of the known method are the heterogeneity of the properties and structure over the cross section, the increased temporary resistance and the hardness of the surface of the Siyev hire, which leads the cleist cutting to the formation of chips on the cut surface. These deficiencies are due to the use of interrupted quenching, resulting in heterogeneity of the structure and the inadequacy of the single annealing of the hardened metal, resulting in increased temporal resistance. The purpose of the invention is to reduce the strength properties and ensure uniformity of properties over the cross section. This goal is achieved by the fact that according to the method of spheroidizing treatment of rolled strip of carbon steels, mainly up to 11 mm thick, including quenching, heating to A + (515 ° C), exposure, cooling below A, exposure and cooling in air, hardening the steel on martensite, and heating to A + {5-15s) is about-. There are steps, up to. at a speed of 80-600 s / min and in the interval (A) - A at a speed of O, 5-1, O s / min. Pre-quenching of martensite allows, in the case of heating at a rate exceeding VO C / min to A: -30 ° C, to obtain austenite in carbon steel at a temperature below (before), and this austenite is unstable and in the process of holding at temperatures below Acw decays. Heating from A to A with an average speed not exceeding 1 ° C / min allows, by the time of heating to point A, to guarantee the completion of the decomposition of metastable austenite formed during accelerated heating, and, accordingly, re-formation of austenite at temperatures above A, t, e, determines the possibility of carrying out double phase recrystallization (annealing) and, accordingly, reducing the temporal resistance. The implementation of quenching martensite provides, in contrast to interrupted quenching, a uniform, the cross section of the structure, but limits the maximum strip thickness (in zavisimoeti of carbon content) to effect tempering martensite necessary to use continuous furnace and spreyernogo cooling device. In addition, it is possible to use quenching with rolling heating. To achieve heating to A with a speed exceeding 80 s / min, multi-zone furnaces or salt baths are not required, or; devices For contact heating or heating of high-frequency current (for rolling large amounts of steel),. To perform heating from Ai to A at a speed not exceeding 1 C / min, multi-zone pass-through furnaces or slug-type devices (chamber furnace) are necessary. performing both fast and slow heating, it is also necessary to measure the heating temperature with an accuracy of no less. For the implementation of slow cooling and isothermal holding, any device is needed in which possible slow cooling with variable speed through-pass multi-zone or chamber furnaces. The choice of the limiting parameter of the heating temperature — the minimum temperature accelerated by heating (at a speed exceeding 80 s / min) —is caused by the dependence of the decrease in the onset temperature 0. (Г transformation on the carbon content. For hardened carbon steel Eutectoid composition is reached in steel (in steel U8 with, which is g less than temperature A-,), and a decrease or increase in the carbon content leads to a decrease in the temperature of the initial NIN. Selecting the face Because of the fact that the maximum reduction in the temperature of the onset of conversion in hardened carbon steels is achieved at a rate of continuous heating / V 100 s / min, In the case of non FYREN heating on increasing the heating rate, , but if, after heating to A ;, (even at a speed of 6000 s / min), isothermal exposure or heating is carried out with a speed of no more than 30-50 s / min, the transformation occurs at this temperature. A decrease in the heating rate of less than 80 C / min leads to a sharp reduction in the temperature range of the formation of the metastability of austenite, i.e. eliminates the possibility of double phase recrystallization (annealing) with a single heating and leads to an increase in temporal resistance. An increase in the heating rate above BOO s / min during furnace heating sharply limits the thickness of rolled metal and requires higher furnace temperatures. The choice of the boundary parameters of the heating rate to temperature A is due to the need to complete the decomposition of the metastable austenite in the process of slow heating. Heating at a rate higher than l / 1 s / min leads to preservation in the structure at the time of transition across the point A of a certain amount of austenite and, accordingly, an increase in temporal resistance. Increasing the temperature to which rapid heating is effected (in the range of A) requires y-ct to complete. Transformation of slow speed heating. Heating at a rate of less than 0.5 s / min leads to an increase in the duration of heating and a reduction in equipment performance. Annealing according to the method can be realized with the help of a through-passage multi-zone furnace. Or with the help of a continuous-periodic heat treatment unit containing a through-type furnace with a transfer chamber and auxiliary chambers located on both sides of the continuous furnace with a thermal mode of their own. Example. The strips made of V8 steel with a thickness of 8 mm, steel 45 with a thickness of 6 mm and steel 20 with a thickness of 4 mm are processed by quenching in water from a temperature of 820 ° C, 850 ° C and 920 ° C, respectively, and annealing. Annealing is carried out in two chamber furnaces H-30. The temperature of the furnace in which the heating is carried out is changed from 750 to 1100 ° C, and the temperature of the furnace in which the slow heating and cooling is carried out is from 700 to. Preliminary measurements indicate the temperature at which the onset of the transformation is for. The steel U8 is, for steel 45 -, for steel 20 - 6660 ° C at a heating rate of l / thous / min. The bands are heated in the same furnace at different speeds up to 700 s (that is, approximately 30 C below temperature A). and transferred to another furnace with a temperature of 700-71 o C / and then heated with an oven to various speeds, then heated with an oven to 740 ° C with a speed, maintained for 0.5 h, cooled to a speed of 50-150 s / h, kept at this temperature for 2-8 hours, finally cooled with a stove before and in air. The results of processing are presented in table. 1. When processed according to a known method, the strips are subjected to interrupted quenching (the temperature of the end of cooling in water at the center of the strip is 400-500 s), heated to 730 ° C, kept for 40 minutes, cooled with a furnace at a rate of 150 ° C / h to 680 690 s and maintained at this temperature; ; for 1.5 hours, the chain Comparison to the treatment according to this method is also carried out isothermal aging for 2 and 8 hours. The results of the treatment are presented in table. 2. As can be seen from the presented data, the application of the proposed method helps to reduce the temporal resistance (compared to the prototype) by at least 4-5 kgf / mm2l of steel 45, by 12 kgf / mm for steel 20 and by 25 kgf / mm2 for steel V8 (extract By a known method, it was not increased to 2-8 hours). At the same time, the uniformity of the properties is provided (in different sections. The hardness yarn did not exceed Znv) and the structure over the cross section (in the case of ensuring uniform quenching), whereas in the case of interrupted quenching, having distinguished in hardness after annealing over the cross section of the strip, it can reach 2ONB (the size of the globules cementite increases from the surface to the center of the strip. From the presented data it also follows that accelerated heating at a rate lower than VO C / min leads to an increase in the temporal resistance of Lenin. Increasing the speed of accelerated heating to 350 ° C / min (with furnace heating EVE} has practically no effect on the properties of the metal. A further increase in the heating rate is up to BOO-BOOO C / min (heating of quenched samples with a diameter of 6-8 mm to 700-715 C with the use of an electrotactic plant, heating in a furnace to 730 ° C speeds of about 3 C / min and heated to 740 ° C, 30 minutes exposure, furnace cooling to 150 s / h, exposure for 8 hours and air cooling, although it does not affect the properties of the steel (temporary resistance is 50-52 kgf / mm-2 for steel 45 58 (-60 kgf / mm for steel U8), however, an increase in heating rate would be b. About C / min makes it difficult to adjust the heating temperature accelerated completion.

An increase in the rate of slow heating above IC / MHH leads to an increase in the temporal resistance (by 3–6 kgf / mm for steel 45), a decrease in the heating rate (less than 0; 5 s / min) practically does not affect the properties of the metal, but unproductively increases processing time.

An increase in temporal resistance with a decrease in the rate of accelerated heating is associated with a decrease in the degree of completeness of the transgeneracy with a metastability of austenization, and with an increase in the rate of slow heating, with a decrease in the degree of decomposition of metastable austenite.

As shown by the data of experimental verification; As a result of using the proposed method, the temporal resistance of steels 45, U8 and 20, as compared with the prototype, decreases accordingly by 4-7 kgf / m, 2-9 kgf / mm; 1-2 kgf / mm in the absence of differences in hardness and structure over the cross section. rolled,. .

Table

54 86

0.5

150 0.5 150 0.5 105 150 187 0.5 150 150 108

1 1.5 150 102

2 115 150 105

0.5 150 187 0.5 50. 187

. 200 0.5 187 0/5 50 150 105 0.2 0.5 150 150 80 80 150 0.5

55

51, 5

49, $;

50

50.5

53

56

50, 5

49.5

52

50

51

66

62

Continued table. one

Claims (1)

METHOD FOR SPHEROIDIZING TREATMENT OF STRIP RENT FROM 'I CARBON STEELS, mainly up to! 11 mm, including quenching, heating to A ^ + (5-15 ° C), holding, cooling below A =,, holding and. cooling in air, with the fact that, with a view to. to reduce the strength properties and ensure uniform cross-section properties, the steel is quenched for martensite, and heating to Αι + (515 ° C) is carried out stepwise, to ι A ₄ -30 ° C at a speed of 80-600 ° C / min, and interval (¾ <-30 ° C) -. A ^ with | a rate of 0.5-1.0 ° C / min. '' Si Yu SL JV>