UA80009C2 - Process for production of high-test, high-plastic alloyed carbonaceous steel - Google Patents

Abstract

Strain-hardened steel alloys having a high tensile strength are prepared by cold working of alloys whose microstructure includes grains in which laths of martensite alternate with thin films of stabilized austenite. Due to the high dislocation density of this microstructure and the tendency of the strains to move between the martensite and austenite phases, the strains created by cold working provide the microstructure with unique mechanical properties including a high tensile strength. Surprisingly, this is achieved without the need for intermediate heal treatments (patenting, in the case of steel wire) of the steel between cold working reductions.

Description

Description of the invention

This invention relates to technological processes of processing low-carbon and medium-carbon alloyed 9 steels and, in particular, steels of high strength and impact toughness, as well as the ability of such steels to undergo deformation in a cold state.

An important stage in the technological process of steels with high operational characteristics is deformation in the cold state, which usually consists of a number of compression and/or stretching operations used in such processes as drawing, extrusion, cold drawing and rolling. Cold mechanical 70 processing causes plastic deformation of the steel, as a result of which the steel acquires strain hardening when giving it the shape of the final product. Cold deformation, which in the case of steel wire production is wire drawing, usually consists of a series of successive stages with intermediate heat treatment operations, which in this case is called patenting.

High-strength steel wire is an example of a high-performance steel and 12 is used in a variety of mechanical structures, including tire cords, wire ropes, and wire strands for reinforcing prestressed concrete. Medium-carbon and high-carbon steel are usually used in high-strength steel wire. The typical process of manufacturing such a wire consists of several stages of cold drawing of hot-rolled rods with pearlite microstructure and intermediate patenting in order to soften the pearlite for carrying out a continuous process of cold drawing. At the same time, for example, hot-rolled rods with a diameter of approximately 5.5 mm pass through rough drawing in several stages to a diameter of approximately Zmm. After that, patenting is carried out at temperatures of 8502C, during which austenization of steel occurs, followed by a transformation of its structure at 500-5502C; on thin lamellar pearlite. Next, the steel is subjected to etching, for example, with hydrochloric acid to remove carbon deposits formed during patenting. Etching is followed by several further stages of drawing to reduce the diameter to approximately 1 mm, and then patenting and etching are carried out again. Go)

After that, the final drawing is carried out in several stages to the desired final diameter, which can be, for example, 0.4 mm, to give the wire the desired properties and, mainly, strength. After that, depending on the purpose of the manufactured product, such operations as twisting into jute, etc., can be carried out. F

The purpose of the initial patent is to obtain wire drawing rods with a thin lamellar (α) pearlite structure that requires a low transformation temperature. To ensure the desired temperature control, this process is, of course, carried out in a bath of molten lead. In subsequent stages, the wire is stretched to a degree of true strain (as defined below) of 6-7 to obtain high levels (a) of strength, approximately 300MPa. In the case of a wire with a pearlite structure, such high values of deformation and strength can be achieved only with the use of a number of patenting operations. Without such co-patenting, cold drawing leads to shear cracking of pearlite plates. Due to the need to use a bath of molten lead, this whole process is expensive and associated with the risk of environmental pollution. « du Cold deformation is also used in the manufacture of expandable steel pipes, that is, pipes that expand at the place of their operation, which is often underground. c Recently, in the sector of alloyed steels, developments were carried out on the formation of microstructures containing both martensitic and austenitic phases alternating with each other, and the martensite in them has the form of rails, separated by thin films of austenite. These microstructures were fused grains, and each of the grains contained several laths of martensite, separated by thin austenite films, and in some cases was surrounded by an austenite shell. These structures are called "dislocated lath martensitic" structures or "packet lath martensitic-austenitic" structures. This type of microstructure was first described in the following US patents, which are incorporated herein in their entirety by reference: IMo 4,170,497 ((Zagevyi Tpotaz, Vapdagi M.M. Kas), issued on October 9, 1979, based on an application filed on 24 August 1977; (av) 50 Mo4,170,499 (Sage(p Tpotaz, Vapdagi M.M. Kas), issued on October 9, 1979 based on the application submitted on September 14, 1978 as a partial continuation of the above application, submitted on August 24, 1977;

Mo4,671,827 (Sage(y Tpotavz, Musk y). Cat, Katatoogiyu Katevzi), issued in June 1987. according to the application submitted on October 11, 1985;

Mob, 273,968 B1 (Sage(y Tpotaz), issued on August 14, 2001 based on an application submitted on March 28, 2000.

Along with the fact that these microstructures give certain advantages in terms of operational properties and,

HF) especially, high anti-corrosion resistance, until then it was not known that in the presence of these microstructures, stage 7 processing, usually applied to alloy steels, can be simplified or excluded from the technological process.

Particularly close to this invention are the two US patents listed below that disclose cold 60 deformation of steel rods and wire without patent operations:

IMo 4,613,385 (Sage(y Tpotaz, Amip N. Makadamza), issued on September 23, 1986 based on an application filed on December 9, 1982;

Mo4,619,714 (Sage(yy Tpotavz, dae-Nyap Ipp, Mask-doop Kit), issued Oct. 28, 1986 on application filed Nov. 29, 1984 as a continuation-in-part of application filed Aug. 6, 1984 | because yes are themselves incorporated herein in their entirety by reference.The microstructures of the steels covered by these patents are significantly different from the microstructures of the steels described in the first four patents cited above.

The authors of the invention found that the packet-rail martensitic-austenitic microstructure is unique in terms of its crystallographic properties and the ability to control these properties by deformation in the cold state. Due to the high dislocation density of this microstructure and the ease with which deformations in the structure are able to move between the martensitic and austenitic phases, cold deformation allows the creation of a microstructure with unique mechanical properties, including a high tensile strength. This allows such alloys to be cold worked without intermediate heat treatment steps and to obtain tensile strength levels comparable to those of conventional 70 alloy steels cold worked with intermediate heat treatment operations. As far as the steel wire with a packet-rail martensitic-austenitic microstructure is concerned, the present invention consists in discovering the fact that cold deformation of such materials can be carried out without intermediate patenting. Therefore, according to the present invention, alloyed carbon steels having a packet lath martensite-austenite microstructure, i.e. those whose microstructure contains laths of martensite alternating with thin films of residual austenite, undergo cold forming, preferably without intermediate operations heat treated to a degree, to a degree of crimping, sufficient to produce a tensile strength of not less than about 150 psi, which is equivalent to about 103MPa (1MPa-1N/mm32). Of particular interest is the cold deformation to a tensile strength of 2000 MPa (290 psi) and above, a level that the present invention can reach and far exceed.

The implementation of which in practice allowed to obtain a tensile strength of 3000 MPa (435 kilo-pounds per square inch) and 4000 MPa (580 kilo-pounds per square inch). These values are approximate: the conversion factor to the nearest thousand is 6.895MPa-1 kilopound-force/sq.in.

The advantages of this invention extend to packet lath martensitic austenite microstructures containing no or small amounts of ferrite, as well as to microstructures containing packet lath grains, Ha alloyed with ferrite grains, and variants of these structures, including those packed - lath grains surrounded by austenite shells, those that do not contain interphase carbide precipitates, and those in which austenite o films have a uniform orientation. The discovery of the ability of packet lath martensitic-austenitic microstructures to respond to cold working in the manner described above is rather surprising in light of the descriptions of the above-cited US patents MoMo 4,613,385 and 4,619,714, since the ferrite in the microstructures according to these F) patents has a yield strength lower than that of martensite If so, then the ferrite must absorb the stress created by cold deformation, and the martensite must not respond to cold deformation until the ferrite phase is mechanically hardened to a level above the martensite yield strength. In the microstructures on which av! directed the present invention, a relatively low level of ferrite or its absence, when there is no ferrite, causes the absorption of stress by martensite at an early stage of the cold deformation process. Martensite and ferrite differ quite noticeably in their crystal structures and mechanical hardening characteristics. with

In the following, these and other features, goals, advantages and examples of practical implementation of this invention are considered in more detail.

Figure 2 shows graphs of tensile strength vs. true total strain for two alloy steels with a two-phase packet lath martensitic-austenitic microstructure after cold 70 deformation according to the present invention without intermediate heat treatment operations. - c Fig. 1 shows graphs of the dependence of tensile strength on the true total deformation for three alloyed steels with a three-phase batch-bar martensite-austenite-ferrite microstructure and one alloy steel with a two-phase batch-bar martensite-austenite microstructure after cold deformation according to the present invention without intermediate heat treatment operations.

Cold deformation according to the present invention can be performed with the help of technologies and equipment that are usually used for cold processing of other alloyed steels with other microstructures.

The process of cold deformation of steel blanks of a square cross-section, bars, flat rolled o or sheets can be carried out by rolling the steel between rolls or other means of compression for av) reducing the thickness and lengthening the steel. In cases where cold deformation is carried out by rolling, repeated compression is carried out by a series of steel passes through the rolling mill. In a similar way, cold deformation of rod or wire blanks is carried out by means of their cold drawing (Che) or extrusion through matrices. With multiple extrusion, the workpiece is successively passed through a set of matrices of smaller and smaller diameter each time. When drawing pipes, the steel pipe billet is passed through a ring die with a mandrel inside it. With multiple bypasses, the pipe is drawn many times

Through ring dies of ever smaller size with a mandrel placed inside the tube.

Cold deformation is carried out at a temperature below the lowest temperature at which it occurs

F, recrystallization. Therefore, suitable temperatures for this are those that do not cause any phase changes in the co-structure of the steel. Recrystallization of carbon steels, of course, occurs at approximately 1000 C (18322), therefore cold deformation according to the present invention is carried out at temperatures well below 60 of this level. In the best versions, such cold deformation is performed at temperatures of approximately 5002 (9322) and below, even better - at 100922 (2122) and below, and best of all - within the range of approximately 2523 ambient temperature.

Cold deformation can be carried out in one pass or by successive numerous passes. In both cases, intermediate heat treatment (which is called "patenting" when steel wire is drawn) 65 can be performed in order to further improve the properties, but the properties of the processed material after only cold deformation (without intermediate heat treatment) are sufficiently high and do not require intermediate heat treatment The degree of compression per pass is not critical for this invention and can vary widely. But at the same time, the crimp must be large enough to avoid hardening the steel to such an extent that it will become weak to break after a small total crimp. In most cases, the best crimp is about 20956 per pass, even better is at least 2595 per pass, and best is about 2595 to 5095 per pass. Crimping per pass depends at least in part on factors such as die angle and draw efficiency. The greater the die angle, the greater the minimum crimp required to avoid destructive cracking in the central zone. But the smaller the coefficient of drawing efficiency, the smaller is the maximum crimping of steel with a given 7/0 exponent of strain hardening. The compromise, of course, lies between these two conflicting factors. In view of the tensile strength of the final product, it is preferable to cold work to values of this parameter in the range of, approximately, 150 psi to 500 psi.

The process according to the present invention can be applied to alloyed carbon steels with a /5 packet lath martensitic-austenitic microstructure described in the above patents, as well as in the corresponding (US patent applications MoMo 10/017,847, filed on December 15, 2001 (under the title "Thiriye -RNase

Mapo-Sotroziie Z(eeiv) (Three-phase nanocomposite steels), authors KyvipeKi, ()., RoMPaskK, O., Tpotav, 0.), and 10/017,879, filed on December 15, 2001. (under the title "Mapo-Sotroziie Magiepeziis 5ieeЇiv " (Nanocomposite martensitic steels), authors KyvipekKki, (.)., RoMask, O., Tpotavz, (3.)), included here in their entirety

By reference. To ensure the possibility of the formation of a packet-railed martensitic-austenitic microstructure, the composition of the steel, of course, has a temperature Me of the beginning of the martensitic transition, approximately, 3002 or higher, and in the best versions - 35023 or higher. It is known that, in general, the temperature of Me is influenced by alloying elements, and among them carbon is characterized by the strongest influence on Me. Therefore, in order for Me to be kept above the level of З00 С, the carbon content in the steel composition should not exceed su 0.3590 (wt). In the best embodiments of the invention, the carbon content is in the range, approximately, from 0.0395 (wt.) o to 0.3590 (wt.), and in the most preferred - in the range, approximately, from 0.0590 (wt.) to 0 ,3395 (mass). Other alloying elements, such as molybdenum, titanium, niobium and aluminum, can be used in amounts sufficient to provide the required number of nucleation centers and thus produce a fine-grained structure of the material, but in a concentration low enough to avoid their influence on the properties of the final (o) alloy. The concentration of alloying elements must also be low enough to avoid the formation of inclusions and other coarse particles that can make the steel prone to failure in the early stages of cold deformation. In some embodiments of the invention, it is beneficial to include one or more I av austenite-stabilizing elements, such as nitrogen, manganese, nickel, copper, and zinc, in the composition of the steel. Particularly suitable among them are manganese and nickel. If nickel is present in the steel composition, its concentration should be within the range of, approximately, from 0.2590 (wt.) to 59b (wt.), and if manganese is present, the concentration of the latter should lie within the (se) range, approximately, from 0, 2595 (mass) to boOb (mass). In many embodiments of the invention, the composition of the steel also includes chromium, the concentration of which, of course, is maintained in the range, approximately, from O0.595 (wt.) to 1296 (wt.).

Some embodiments of the invention are directed to alloys that, in addition to the martensitic-austenitic grains, contain a ferritic phase (three-phase alloys), while others contain only 70 martensitic-austenitic grains and do not contain a ferrite phase (two-phase alloys ). In the general case, the presence or absence of a ferrite phase is determined by the type of heat treatment at the initial stage of austenization. By an appropriate choice of temperature, the structure of the steel can be transformed into a single-phase austenitic one or a two-phase one containing both austenite and ferrite. In addition, the composition of the steel can be selected or adjusted to account for the formation of ferrite during the initial cooling of the alloy from the austenitic phase, or to prevent the formation of ferrite during such cooling, i.e. to prevent the formation of (ee) ferrite grains before further cooling of austenite to form a banded-banded microstructure. o As noted above, in some cases it may be advantageous to use steels with banded-banded martensite a microstructure in which all the austenite films in the packet grain have (а) approximately the same orientation, although their crystallographic orientation may be different, or steels in which all the austenite films in the packet grain have the same orientation of the crystal planes .

The last of these options can be implemented by limiting the grain size to 100 µm or less. In the best case, the grain size in the above-mentioned cases lies within the range, approximately, from 1μm to 1Ωm, and in the best - within the range, approximately, from 5μm to У9μm.

The process of forming packet-railed martensitic-austenitic microstructures that do not contain ferrite (that is, "two-phase" microstructures) begins with the selection of steel components and the combination of these components in the appropriate proportions specified above. The combined components are subjected to homogenization ("infiltration") over a period of time and at temperatures sufficient for the formation of a homogeneous austenite structure, in which all elements and components are in a state of solid solution. The temperature of heat treatment should be higher than the recrystallization temperature of austenite, and in the best version - at the level at which very small 60 grains are formed. The recrystallization temperature of austenite, of course, depends on the composition of the alloy and, as a rule, can be easily determined by a person skilled in the art. and others applied to this alloy can be performed at this temperature.

Upon completion of homogenization, the steel is subjected to cooling with grain grinding to the desired size, which, as noted above, may be different. Grinding of the grain can be carried out in stages, but the final grinding, of course, is carried out at an intermediate temperature higher than the recrystallization temperature of austenite or close to it. At the same time, the steel can first be subjected to rolling at a homogenization temperature that provides conditions for dynamic recrystallization, and then cooled to an intermediate temperature and again subjected to rolling for further dynamic recrystallization. The specified intermediate temperature lies between the recrystallization temperature of austenite and the upper limit, which is higher by 5023 of the recrystallization temperature of austenite. For a steel composition with an austenite recrystallization temperature of approximately 900 °C, the intermediate temperature to which this steel is cooled is in the range of approximately 9002 to 9502 °C and best - in the range of 90092 to 92520. For the steel composition, the recrystallization temperature of which austenite is approximately 8202C, the preferred intermediate temperature being approximately 85023. Dynamic recrystallization can also be accomplished 70 by forging or other means well known to those skilled in the art. Dynamic recrystallization gives a reduction in grain size by 1095 or more, and in most cases allows to reduce the grain size by approximately 30-90905.

Upon reaching the desired grain size, the steel is subjected to quenching by cooling from a temperature above the recrystallization temperature of austenite to the Me temperature of the beginning of the martensitic transition and further through the 75 interval of the martensitic transition to transform the austenite crystals into a packet-striped martensitic-austenitic microstructure. When there are ferrite crystals between the austenite crystals, this transformation occurs only in the austenite crystals. At the same time, the optimal cooling rate depends on the chemical composition of the steel and, therefore, on its ability to harden. The resulting packets in the microstructure are approximately the same size as the austenite grains formed at the rolling stages, but the austenite in these grains remains only in thin films and in some cases also in the shell surrounding each packet-rail grain . In cases where thin austenite films must have one variant of crystal orientation, this is achieved by adjusting the process so that the grain size is less than 5 Ωm.

An alternative to dynamic recrystallization in grain grinding to the desired size can be heat treatment alone, i.e. without additional influencing factors. To do this, the steel is hardened as described in c above, and then reheated to a temperature approximately equal to or slightly lower than the recrystallization temperature of austenite. After that, the steel is hardened again to obtain or return to the packet-striped martensitic-austenitic microstructure. The temperature of reheating in this case lies within, approximately, 502C from the recrystallization temperature of austenite and is, for example, 87020.

Such stages of the processing process as heating the composition of the steel to the austenitic phase, cooling the steel by (22) controlled rolling or forging to achieve the desired degree of crimping and grain size and quenching around the austenite grains by rapid cooling in the area of the martensitic transition to obtain a packet-rail structure, performed using well-known methods and tools. Such methods include various types of casting, heat treatment and hot machining of steel, for example, forging or rolling with finishing at a controlled temperature for optimal

From grain grinding. Controlled rolling is used to solve a variety of problems, including promoting the diffusion of alloying elements to form a homogeneous austenitic crystalline phase and promoting the preservation of strain energy in the grains. During the quenching stages during this process, the controlled rolling brings the freshly formed martensitic phase into a packet lath configuration consisting of martensitic laths separated by thin films of retained austenite. The degree of crimping during rolling can be different and is easily determined by a person skilled in the art. Quenching is better to be carried out quickly enough to avoid the formation of harmful microstructures, such as pearlite, bainite, and particles or precipitates, and especially the formation of "" interphase precipitates and particles, including undesirable carbides and carbonitrides. grains of the retained austenite film should be approximately from 0.590(06.) to 1596(06.) of the volume of the microstructure, and in the best version - approximately from 395(06.) to 1095(06.), and in the best - a maximum of 595 (vol.) from the volume of the microstructure. Because three-phase alloys have a microstructure consisting of two types of grains - ferritic grains and packet-railed martensitic-austenitic grains fused together into a solid mass. As in two-phase alloys, the size of individual grains is not critical here and can vary widely. For best results, the diameter (or other suitable characteristic linear size) of the grains should be in the range of approximately 2 µm to 100 µm, and preferably in the range of approximately 5 µm to 3 µm. The amount of the ferrite phase relative to the martensitic-austenitic phase can be different. However, in most cases the best c results are obtained when the martensitic-austenitic grains comprise from about 595 to 9595 of the three-phase structure, preferably from about 1595 to 6095, and in the best from about 2095 to 4095 by weight. 29 Three-phase steels can be obtained using a process in which the corresponding ones are first combined

GF! components required for the formation of steel of the desired composition, after that they are subjected to mutual impregnation to obtain a homogeneous austenite structure with elements and components in the state of a solid solution, as in the case of obtaining the two-phase steel described above. The seepage temperature is preferably in the range, approximately, from 9002 to 11702C. After the formation of the austenitic phase, the steel composition is cooled to a temperature in the intercritical interval of 60, that is, in the temperature interval where the austenitic and ferritic phases coexist in equilibrium with each other. Thus, this cooling causes some of the austenite to transform into ferritic grains, leaving the rest of the material in the austenitic phase. The relative amounts of each of the two phases in equilibrium vary with the temperature to which the composition is cooled at this stage, and also depend on the levels of alloying elements.

The distribution of carbon between these two phases (also at equilibrium) also varies with temperature. Because the relative amounts of these two phases are not critical for this invention and can vary widely.

The temperature to which the composition is cooled in order to form a two-phase ferritic-austenitic structure is preferably in the range of approximately 8002C to 100090C.

As soon as ferrite and austenite crystals are formed (that is, as soon as equilibrium is reached at a given temperature in the intercritical phase), the alloy is quickly quenched by cooling in the martensitic transition interval to transform the austenite crystals into a packet-lath martensite-austenite microstructure.

The cooling rate during this transition must be high enough to practically avoid any changes in the ferritic phase and undesirable decomposition of austenite. Depending on the composition of the steel and its ability to harden, water cooling may be used to achieve the desired cooling rate, although air cooling is sufficient for some steels. In some steels and, in particular, those that are three-phase and contain 695 C, the required cooling rate is sufficiently low and allows the use of air cooling. The considerations discussed above regarding two-phase alloys are fully valid for three-phase alloys as well.

The best compositions of two-phase steels are those containing, approximately, from 0.04905 (wt.) to 0.1295 (wt.) carbon, 75 From 0 to 11.090 (wt.) chromium, from 0 to 2.09b (wt. ) of manganese and from 0 to 2,090 (wt.) of silicon, the rest is iron.

The best compositions of three-phase steels are those containing, approximately, from 0.0290 (wt.) to 0.1495 (wt.) carbon, from

0 to 3,000 (wt.) silicon, from 0 to 1.590 (wt.) manganese and from 0 to 1.590 (wt.) aluminum, the rest is iron.

The phenomenon of the formation of secretions or other small particles in the microstructure after cooling has received the general name "self-release". In some embodiments of the invention for both two-phase and three-phase steels, self-tempering must be avoided by using a relatively high cooling rate. The minimum cooling rates at which self-tempering can be avoided can easily be determined using a transformation-temperature-as type diagram for a given alloy. A typical diagram of this type plots temperature on the vertical axis, time on the horizontal axis, and curves on the diagram mark areas where each phase exists either by itself or in combination with another phase or phases. One of the diagrams of this type is shown, for example, in the aforementioned (US patent Mob, 273,968 B1 (Trotazv)). In this diagram, the minimum cooling rate follows the line of decreasing temperature with time, which rests on the left of the C-shaped curve. To the right of curve o extends the zone of existence of carbides. Therefore, the rate that avoids the formation of carbide is along one of the lines that remains on the left side of this curve. Thus, the line tangent to this curve with the least steepness defines the lowest cooling rate at which carbide formation can still be avoided.

The terms "interphase separation" and "interphase separation" used here mean the formation of small alloy particles in the places between the martensite and austenite phases, that is, between the rails and the thin films that separate these rails from each other. The term "interphase separation" does not refer to the austenitic films themselves. At the same time, interphase precipitates should be distinguished from "intraphase precipitates", which are precipitates located inside 3-5 martensitic laths, and not along the separation surfaces between martensitic laths and austenite films. at

Interfacial separations of approximately 500 angstroms or less in diameter are not detrimental to shock viscosity and may even increase it. Thus, the phenomenon of self-release is not necessarily harmful, provided that self-release is limited to intraphase separation and does not cause interphase separation. As used herein, the expression "substantially free of carbides" means that, if carbides are present, their distribution and quantity are such that "

Their influence on the operational characteristics of the steel and, in particular, on the anti-corrosion properties of the final steel is negligibly small. y Depending on the composition of the alloy, the cooling rate that is high enough to prevent the formation of "" carbide or the occurrence of the phenomenon of self-tempering can, in general, be such that it can be achieved by air cooling, or such that it requires water cooling. In the case of compositions alloys in which air-cooling self-tempering can be avoided, air-cooling can be applied even when the levels of some alloying elements are reduced, provided that the levels of other alloying elements are increased.For example, a reduction in carbon, chromium or silicon can be compensated by an increase o the level of manganese. o The processes and conditions proposed in the above-mentioned US patents, and in particular, heat treatment, grinding 5r Grain, online forging and the use of rolling mills for round, flat and other shapes of blanks, o can be used in the practice of implementing this invention for heating the composition of the alloy to austenitic

Ge) phase, cooling the alloy from the austenitic phase to the intercritical phase in the case of three-phase alloys, and then cooling in the interval of the martensitic transition. Rolling is carried out in a regulated mode in two or more stages during the austenization process and the first stage of cooling, for example, to promote the diffusion of alloying elements with the aim of forming a homogeneous austenitic crystalline phase and then deformation of the crystal grains and preservation of deformation energy in these grains, in that while at the second stage of cooling iF) rolling can serve to introduce the freshly formed martensitic phase into a packet-rail configuration of co-martensitic rails separated by thin films of residual austenite. The degree of crimping during rolling can be different and is easily determined by a person skilled in the art. In packet-railed martensitic-austenitic bo crystals, films of residual austenite make up, approximately, from 0.590(06.) to 1590006.) of the volume of the microstructure, in the best version - approximately from 395(ob.6.) to 1095(06.), and in the best - a maximum of 595 (vol.) from the volume of the microstructure. The austenite fraction relative to the entire three-phase microstructure is a maximum of approximately 59b(o6.). The actual width of the residual austenite film is preferably in the range of about 50 angstroms to 250 angstroms and more preferably about 100 angstroms. The fraction of austenite 65 Relative to the entire three-phase structure in the general case is a maximum of 595. The rolling processes mentioned in this paragraph should be distinguished from cold deformation, which is carried out according to the present invention after the formation of a packet lath martensite-austenite microstructure, regardless of whether it is two-phase or part three-phase structure.

Examples of the implementation of this invention, which are exclusively illustrative, are considered below.

Example 1

This example illustrates the deformation of a carbon steel rod with a packet lath martensitic-austenitic microstructure by cold drawing according to the present invention to 9990 crimping along the cross-sectional plane.

The experiment in accordance with this example was carried out with a steel rod with a diameter of mm, the 7/0 composition of which included carbon 0.195 (mass), silicon 2.095 (mass), chromium 0.595 (mass), manganese 0.595 (mass) and the rest - iron, and the microstructure consisted of grains with a diameter of about 5μm, each of which consisted of martensite laths about 100nm thick, alternating with thin films of austenite about 10nm thick, without a ferrite phase, and each grain, in addition, was surrounded by an austenite shell approximately 100 nm thick. The rod was manufactured by the method described in jointly filed US patent application Ser. 75 Meo10/017,879 dated December 14, 2001).

The uncoated steel rod was cleaned and lubricated, then cold drawn through lubricated dies for 15 passes at 259 to a diameter of 0.0095 inch (0.024 cm). At a final wire diameter of 0.0105 inch (0.027 cm), which was obtained from a total of 9995 crimps in the plane of the cross-section, the wire had a tensile strength of 390 psi (2690 MPa). 20 Example 2

In this example, another illustration of cold drawing of carbon steel rods with a packet lath martensitic-austenitic microstructure in accordance with the present invention is presented. In this example, two different alloys were used - Ge/8С/0.05С and Re/251/0.1С - with a microstructure consisting of grains with a diameter of approximately Х0μm, where each grain consisted of martensite laths approximately 25 cm thick. 5 Ohm, alternating with thin films of austenite, approximately 1 Ohm thick, and did not contain a significant amount of ferrite phase. At the same time, each grain was surrounded by an austenite shell with a thickness of approximately 1 Ohm. at

The specified steel rods with a diameter of mm were cleaned and lubricated on the surface, after which they were subjected to cold drawing through lubricated matrices by successive passes at a temperature of 25 °C. The broaching protocol used for the alloy ГРе/8Си/0.05С is given in Table I. A similar protocol Ге») 30 was used for the alloy ГРе/251/0.1С. In this table, A means the initial diameter of the rod, and A is the diameter of the rod after each pass. o "c) and packet-rail martensitic microstructure practically without ferrite so and passage |mm Ip(A/Ao) to o seal battle 00011111110000111110000 11111111 " ю Z -

And" 64111611

Tensile strength was measured on the original rod and after each pass, and based on the obtained (a) results, graphs of the dependence on the true total deformation were constructed, shown in Fig. 2, where the squares o correspond to the Re/8C/0.05C alloy, and the diamonds to the alloy Re/251/0.1С. It can be seen from these graphs that the tensile strength of both alloys reaches approximately 2000 MPa at the end of the drawing process with a total (α) 50 crimp over a cross-sectional area of 9790. s Example C

This example illustrates the process of cold deformation in accordance with the invention when using carbon steel rods with a packet-band martensite-austenite microstructure, which contained a third phase in the form of ferrite crystals (in addition to martensite rails and thin films of austenite, i.e. in a three-phase 59 microstructure) .

ГФ) In this example, the deformation of Re/251/0.1C steel with a microstructure consisting of ferrite 7 alloyed with packet lath grains, similar to those described above in Examples 1 and 2, containing martensitic laths alternating with thin films, was carried out austenite, and the grains were surrounded by an austenite shell.

The rods were produced by the method described in US Patent Application No. 10/017,847, filed December 14, 2001, because using a reheat temperature of 9502 to achieve a ferrite content of 7095 per microstructure volume. The initial diameter of the rod was 0.220 in. (5.55 Ω) and cold working was done by drawing these rods through lubricated taper dies at 25 C in 15 passes with a crimp of approximately 3695 per pass to a final diameter of 0.037 in. (0.94 mm). 65 The stretching protocol used in this example is given in Table II, where A 5 denotes the initial diameter of the rod, A is the diameter of the rod after each pass.

: passage |mm Ip(A/Ab) o to echatovyyu battle 00000000 a yuyu vm sho 00803811 vzh yaz

The tensile strength of the final wire was 2760 MPa (400 psi). high school

Example 4

This example is another illustration of the cold deformation of carbon steel rods, i) the microstructure of which consisted of packet lath martensitic-austenitic and ferritic crystals in accordance with the present invention.

A round rod made of Re/251/0.1C steel was subjected to cold deformation, as in Example 3, with a microstructure, Ge! which consisted of ferrite alloyed with packet lath grains, similar to those described above in Examples 1 and 2, containing martensitic laths alternating with thin films of austenite, and surrounded by an austenitic shell. A rod of the specified composition was produced using the general method described in US patent application No. 10/017,847, filed December 14, 2001. In this case, the rod was first hot rolled to a diameter of 0.25 inches (6.35 mm), and then heated to 11502 and kept at this temperature

335 temperature for approximately 30 minutes to austenize the composition, and then quenched in an ice-cold Ge) salt solution to transform the austenite into practically 10095 martensite, after which the rod was again rapidly heated to transform its structure into approximately 7095 ferrite and 3095 austenite Next, the rod was quenched in an ice-cold salt solution to transform austenite into a martensitic-austenitic packet-striped structure. The rod was then cold drawn in 7 passes of 3590" crimps per pass to a final diameter of 0.055" (1.4 Ω) resulting in a tensile strength of 1875 MPa (272 psi). In a parallel experiment, a rod of the same composition, given a similar initial treatment, was cold drawn in 13 passes with 3595 "" crimps per pass to a final diameter of 0.015 in. (0.37 mm), resulting in a tensile strength of 2480 MPa (360 kilolb- force/sq.in).

Example 5 o This example is another illustration of the process of cold deformation of carbon steel rods, the microstructure of which consisted of lath martensite-austenitic and ferritic crystals in accordance with the present invention, where the effect of varying the relative amounts of lath martensite o martensite-austenite is demonstrated and ferrite.

The object of the experiment was alloyed steel ГРе/251/0.1С, as in Examples 3 and 4, and the rods were made as described in Example 4, using different reheating temperatures, which gave different levels

Ge) of the ferrite content - 095, 56905, 6690 and 7590, which corresponded to the content of the packet-striped martensitic-austenite phase - 10095, 4495, 3595 and 2595 by volume. All four microstructures were drawn according to a protocol similar to that given in Table II, and the resulting tensile strength values are presented in the form of graphs of true total strain in Fig. 1, where the squares correspond to the alloy with a 10090 packet-rail structure, the triangles correspond to alloy with a 4495 packet-rail structure, circles and F) correspond to an alloy with a 3495 packet-rail structure, diamonds - an alloy with a 2595 packet-rail structure. It can be seen on these graphs that all four microstructures had a tensile strength significantly higher than 2000MPa, and those in which the batch-banded martensitic-austenitic part of the structure exceeded 2590, because they demonstrated values of tensile strength higher than the microstructure in which the batch- the rail part was 2590.

All of the above is primarily illustrative. It is quite clear that the content of this description does not exclude other possible variants of various parameters of the composition of steels, as well as processes and conditions of their processing, which do not contradict the idea and novelty of this invention. Such variations and modifications can be readily implemented by those skilled in the art and are also within the scope of the invention.

Claims (19)

The formula of the invention 1. A process for making a high-strength, high-ductility alloy carbon steel, which includes: 2 (a) creating an alloy carbon steel having a microstructure consisting of laths of martensite alternating with films of retained austenite, and (B) deforming said alloy carbon steel in in the cold state with a crimp sufficient to achieve a tensile strength of at least about 1035 MPa. 2. The process of claim 1, wherein step (b) includes cold forming said 70 alloy carbon steel with a crimp sufficient to achieve a tensile strength of approximately 1035 to 3450 MPa. 3. The process of claim 1, wherein step (B) includes cold forming said alloyed carbon steel with a cross-sectional area crimp of at least 20 95 per pass. 4. The process of claim 1, wherein step (b) includes cold forming said 72 alloyed carbon steel with a cross-sectional area crimp of at least 25 95 per pass. 5. The process of claim 1, wherein step (B) includes cold forming said alloy carbon steel with a cross-sectional area crimp of approximately 25 95 to 50 95 per pass. 6. The process according to claim 1, which differs in that stage (b) includes deformation in the cold state in several passes without heat treatment between passes. 7. The process according to claim 1, which differs in that stage (B) is performed at a temperature not higher than about 100 26. 8. The process according to claim 1, which differs in that stage (B) is performed at an ambient temperature within the range of approximately 25 26. s 9. The process according to claim 1, which differs in that said alloyed carbon steel has the form of a rod or (3) wire, and in stage (p) this alloyed carbon steel is drawn through a matrix. 10. The process according to claim 1, which differs in that said alloyed carbon steel has the form of a sheet, and in stage (b) rolling of this alloyed carbon steel is carried out. zo 11. The process according to claim 1, which is characterized by the fact that stage (a) includes: Ф () creation of alloyed carbon steel of such a composition at which the temperature of the beginning of the martensitic (а) transition is at least approximately ЗО00 2С, and (i) heating of the specified composition of alloyed carbon steel to a temperature high enough to cause its austenization and create a homogeneous austenitic phase with all alloying elements in the state of "(2 zv of solid solution, and so (its) cooling of the specified homogeneous austenitic phase through the interval of the martensitic transition at a rate, high enough for the formation of the specified microstructure, practically avoiding the formation of carbide at the boundaries of the separation between the specified rails of martensite and films of residual austenite. 12. The process according to claim 11, characterized in that said alloyed carbon steel has a composition at which the martensitic transition onset temperature is at least approximately 350°C. - in the village 13. The process according to claim 11, which is characterized in that said residual austenite films have a uniform orientation. :with" 14. The process according to claim 11, which is characterized by the fact that the specified composition of alloyed carbon steel contains iron and alloying elements in the amount: approximately from 0.04 to 0.12 wt. 95 carbon, from O to 11 wt. 95 chromium, from 0 to 2 wt. 95 of manganese and from 0 to 2 wt. 9o silicon. ooo 15. The process according to claim 11, which is characterized by the fact that the temperature at stage (ii) is in the range from approximately 800 C to 1150 20. o 16. The process according to claim 1, which is characterized by the fact that stage (a) includes: o () creating an alloyed carbon steel of such a composition, at which the temperature of the beginning of the martensitic transition is equal to at least approximately ЗО00 2С, and (i) heating the indicated composition of the alloy carbon steel to a temperature high enough to (Che) cause it to austenize and create a homogeneous austenitic phase with all alloying elements in solid solution, (iii) cooling said homogeneous austenitic phase to transform a portion of this austenitic phase into ferrite crystals with the formation as a result of a two-phase microstructure containing ferrite crystals fused with austenite crystals, and F) (im) cooling of the specified two-phase microstructure through the interval of the martensitic transition under conditions that cause the transformation of the specified austenite crystals into a microstructure containing martensite rails alternating with films of residual austenite. in 17. The process according to claim 16, which is characterized in that the stage (ii) includes cooling the specified homogeneous austenite phase to a temperature of approximately 800 C to 1000 es. 18. The process according to claim 16, characterized in that step (ii) includes heating said composition of alloyed carbon steel to a temperature in the range of about 10502 to 11702C, and step (ii) includes cooling this homogeneous austenite phase to a temperature approximately from 800 C to 1000 es. BB 19. The process according to claim 16, which is characterized by the fact that the specified composition of alloyed carbon steel contains iron and alloying elements in the amount: approximately from 0.02 to 0.14 wt. 95 carbon, from 0 to 1.5 wt. 95 manganese, from