A cold-formed steel with high yield strength

Abstract

The present invention discloses a cold-formed steel with high yield strength. The material to be processed is prepared by smelting. The material is rapidly cooled to 200-300 °C and then heated to 500-600 °C, and deformed steel bars are prepared through multiple cold extrusions. Compared with the traditional hot rolling process, the cold deformation process below 600 °C is adopted in this application to modify the metallographic structure, so as to obtain the properties similar to those of forged steel obtained by forging process. At the same time, processes such as cold heading and shot peening are adopted to improve the internal stress condition of the material, so as to present a certain degree of compressive stress on the surface of the material. Finally, the thread features are formed by cold extrusion, so as to better improve the structural strength and grain distribution of the cold-formed steel.

Description

Technical Field

[0001] The present invention relates to cold-pressed forming steel with high yield strength. Background Art

[0002] In the process of steel preparation, in order to obtain high yield strength and high production efficiency, high-temperature heat treatment is often used. And in the high-temperature hot rolling process, the deformation of the steel is accelerated and the properties of the steel are adjusted by hot rolling.

[0003] The grain forming method in this way is mainly to generate austenite at a high temperature (about 1000 °C), and then transform austenite into ferrite by cooling, and obtain a smaller grain composition and a relatively dense metallographic distribution structure through the precipitation of the second phase, so as to improve the yield strength and tensile strength of the steel.

[0004] However, with the maturity of the cold extrusion process, in the cold extrusion process, through the action of impact force and extrusion force, the metallographic structure can also be deformed to a certain extent, so as to obtain a metallographic structure with a dense structure. Moreover, compared with hot rolling, the safety and the upper limit of the mechanical properties of the material of the cold extrusion form have been greatly improved.

[0005] This form of steel processing technology has been commercially trial-produced in Australia and the United States around 1990. The patent ZL95193842.8 applied by Tabimax Australia Pty Ltd has disclosed and monopolized a process for modifying steel at a temperature below 500 °C, and this process can slightly (30 - 50 MPa) improve the yield strength of the section steel. However, limited by the production capacity of cold plastic deformation at that time, the cold extrusion process could not be applied to the processing of steel with a yield strength of 600 and above. Summary of the Invention

[0006] The purpose of the present invention is to solve the above-mentioned deficiencies of the prior art and propose cold-pressed forming steel with high yield strength.

[0007] A kind of cold-pressed forming steel with high yield strength is obtained by melting and preparing the material to be processed. The material is rapidly cooled to 200 - 300 °C, heated to 500 - 600 °C, and processed through multiple cold extrusions to obtain deformed steel bars;

[0008] Among them, the components added during melting are as follows:

[0009] 0.10% ≤ C ≤ 0.25%;

[0010] 0.75% ≤ Si ≤ 1.75%;

[0011] 1.35% ≤ Mn ≤ 2.7%;

[0012] 0.0% ≤ Ni ≤ 0.35%;

[0013] 0.001% ≤ N ≤ 0.010%;

[0014] The balance is Fe and inevitable trace impurities.

[0015] The main preparation process of this cold-pressed steel includes the following steps:

[0016] Rapidly heat the material quenched to 200 - 300 °C to 500 - 550 °C at a heating rate of 50 - 80 °C / min. After the heating is completed, perform multi-pass cold extrusion. When cold extruding, control the pass deformation amount to be 5 - 8%, and control the temperature of the press roller at 500 °C;

[0017] After cold extrusion, keep the surface temperature of the steel above 400 °C and hold for 30 - 45 min;

[0018] After holding, cool down to 200 - 250 °C. After standing for a period of time, perform cold heading. Control the temperature during cold heading at 25 - 45 °C. The cross-section before cold heading is irregular, and the cross-section shape after cold heading is circular;

[0019] After cold heading, use high-speed shot peening to impact a uniform distribution of craters on the surface of the deformed steel bar. After the impact is completed, perform surface cold extrusion. The surface cold extrusion temperature is 200 - 300 °C, and the thread features are extruded and formed on the surface of the deformed steel bar.

[0020] In order to further improve the grain size and uniformity during primary crystallization, a refining agent is added for refining after melting. When adding the refining agent, argon is introduced into the melt for deoxidation.

[0021] Furthermore, the refining agent is a low-nitrogen alloy.

[0022] Furthermore, a step-by-step heating method is adopted during melting. First, heat to 800 - 860 °C to precipitate the vaporized substances. After heat preservation treatment for 25 ± 5 min, perform the second heating. The second heating is to 1100 ± 10 °C for short-time overheating treatment. After the treatment time of 10 ± 5 min, cool down to 1000 ± 50 °C to keep the melt in a molten state. This heating method is different from the traditional heating method. Using the overheating method will bring the defect of excessive grain growth, which needs to be avoided in hot processing. However, during cold processing, since a large number of deformation zones will be generated in the subsequent cold plastic deformation stage, a larger grain range can better adapt to the performance improvement of the deformation zone. And during the melting process, using the overheating melting method can better remove impurities, thus obtaining a pure molten substance.

[0023] Furthermore, when heating and melting the material to be melted in a stepwise heating manner, slag removal and argon gas introduction are carried out during the heat preservation stage.

[0024] Furthermore, after the melted material is cast into shape, the cast component is rapidly cooled by water through a water injector. The cooling water in the water injector is injected onto the surface of the material under a certain pressure and instantaneously vaporizes to cool the material.

[0025] Furthermore, the water volume adjustment of the water injector is calculated based on the specific surface area of the material. When the specific surface area of the material is large, the water injection volume is set to a low value. Beneficial effects

[0026] Compared with the traditional hot rolling process, the present application uses a cold deformation process below 600 °C to modify the metallographic structure, thereby obtaining properties similar to those of forged steel obtained by the forging process. At the same time, processes such as cold heading and shot peening are used to improve the internal stress condition of the material, so as to present a certain degree of compressive stress on the surface of the material. Finally, the thread features are formed by cold extrusion, thereby better improving the structural strength and grain distribution of the cold-pressed steel.

[0027] Compared with hot-rolled ribbed steel with similar compositions, under the condition of adding the same trace elements, the yield strength of the ribbed steel formed by cold extrusion is increased by about 50 - 80 MPa. Moreover, in the production of ribbed steel with a yield strength of 600 MPa, the yield strength can still be increased by 30 - 50 MPa, thereby obtaining ribbed steel with better yield strength. Brief description of the drawings

[0028] Figure 1 It is the mechanical property diagram in Embodiments 1 to 3. Detailed implementation manners

[0029] In order to deepen the understanding of the present invention, the present invention will be further described in detail below in conjunction with embodiments and drawings. The embodiments are only used to explain the present invention and do not constitute a limitation on the protection scope of the present invention. Embodiment

[0030] A cold-pressed steel with high yield strength, and the components added during melting are as follows:

[0031] C: 0.15%;

[0032] Si: 1.05%;

[0033] Mn: 1.95%;

[0034] Ni: 0.25%;

[0035] N: 0.005%;

[0036] The remainder is Fe and inevitable trace impurities.

[0037] During smelting, a step-by-step heating method is adopted. Firstly, it is heated to 850 °C to precipitate the vaporized substances. After heat preservation treatment for 25 ± 5 min, the second heating is carried out. The second heating is to 1106 °C for short-time overheat treatment. After the treatment time of 10 ± 5 min, it is cooled to 1000 °C to keep the melt in a molten state.

[0038] The molten material is cast into shape. The temperature of the formed material is about 800 degrees Celsius, and then it is rapidly cooled to 260 °C through water cooling and heat preservation is carried out;

[0039] After heat preservation for 25 min, it is rapidly heated to 500 - 550 °C at a heating rate of 50 - 80 °C / min. After the heating is completed, 30 passes of cold extrusion are carried out. During cold extrusion, the deformation amount per pass is controlled at 5 - 8%, and the temperature of the pressure roller is controlled at 500 °C;

[0040] After cold extrusion, the surface temperature of the steel is kept above 400 °C and heat preservation is carried out for 30 - 45 min;

[0041] After heat preservation is completed, it is cooled to 200 - 250 °C. After standing for a period of time, cold heading is carried out. The temperature during cold heading is controlled at 25 - 45 °C. The cross-section before cold heading is irregular, and the cross-section shape after cold heading is circular;

[0042] After cold heading, uniform crater distribution is impacted on the surface of the deformed bar through high-speed shot peening. After the impact is completed, surface cold extrusion is carried out. The surface cold extrusion temperature is 200 - 300 degrees Celsius, and the thread features are extruded and formed on the surface of the deformed bar. Example

[0043] A cold-pressed formed steel with high yield strength, and the components added during smelting are as follows:

[0044] C: 0.20%;

[0045] Si: 1.15%;

[0046] Mn: 2.05%;

[0047] Ni: 0.30%;

[0048] N: 0.005%;

[0049] The remainder is Fe and inevitable trace impurities.

[0050] During smelting, a step-by-step heating method is adopted. First, it is heated to 850 °C to precipitate the vaporized substances. After heat preservation treatment for 25 ± 5 min, the second heating is carried out. The second heating is to 1106 °C for short-time overheat treatment. After the treatment time of 10 ± 5 min, it is cooled to 1000 °C to keep the melt in a molten state.

[0051] The molten material is cast into shape. The temperature of the formed material is about 800 degrees Celsius, and then it is rapidly cooled to 260 °C through water cooling and heat preservation is carried out;

[0052] After heat preservation for 25 min, it is rapidly heated to 500 - 550 °C at a heating rate of 50 - 80 °C / min. After the heating is completed, 25 passes of cold extrusion are carried out. During cold extrusion, the pass deformation amount is controlled at 5 - 8%, and the temperature of the pressure roller is controlled at 500 °C;

[0053] After cold extrusion is completed, the surface temperature of the steel is kept above 400 °C and heat preservation is carried out for 30 - 45 min;

[0054] After heat preservation is completed, it is cooled to 200 - 250 °C. After standing for a period of time, cold heading is carried out. The temperature during cold heading is controlled at 25 - 45 °C. The cross-section before cold heading is irregular, and the cross-section shape after cold heading is circular;

[0055] After cold heading, uniform crater distribution is impacted on the surface of the deformed steel bar by high-speed shot peening. After the impact is completed, surface cold extrusion is carried out. The surface cold extrusion temperature is 200 - 300 degrees Celsius, and the thread features are extruded and formed on the surface of the deformed steel bar. Example

[0056] A cold-pressed formed steel with high yield strength, in which the components added during smelting are as follows:

[0057] C: 0.25%;

[0058] Si: 1.65%;

[0059] Mn: 2.65%;

[0060] Ni: 0.30%;

[0061] N: 0.005%;

[0062] The balance is Fe and inevitable trace impurities.

[0063] During smelting, a step-by-step heating method is adopted. First, it is heated to 850 °C to precipitate the vaporized substances. After heat preservation treatment for 25 ± 5 min, the second heating is carried out. The second heating is to 1106 °C for short-time overheat treatment. After the treatment time of 10 ± 5 min, it is cooled to 1000 °C to keep the melt in a molten state.

[0064] The molten material is cast and formed. The temperature of the formed material is about 800 degrees Celsius, and then it is rapidly cooled to 260 °C by water cooling and kept warm.

[0065] After keeping warm for 25 minutes, it is rapidly heated to 500 - 550 °C at a heating rate of 50 - 80 °C / min. After the heating is completed, 20 passes of cold extrusion are carried out. When carrying out cold extrusion, the reduction per pass is controlled at 5 - 8%, and the temperature of the pressure roller is controlled at 500 °C.

[0066] After the cold extrusion is completed, the surface temperature of the steel is kept above 400 °C and kept warm for 30 - 45 minutes.

[0067] After the heat preservation is completed, it is cooled to 200 - 250 °C. After standing for a period of time, cold heading is carried out. The temperature during cold heading is controlled at 25 - 45 °C. The cross-section before cold heading is irregular, and the cross-section shape after cold heading is circular.

[0068] After cold heading, uniform crater distributions are impacted on the surface of the deformed steel bar by high-speed shot peening. After the impact is completed, surface cold extrusion is carried out. The surface cold extrusion temperature is 200 - 300 degrees Celsius, and the thread features are extruded and formed on the surface of the deformed steel bar.

[0069] The above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. Cold-formed steel with high yield strength, characterized in that, The material to be processed is prepared by smelting. The material is quenched to 200 - 300 °C, then heated to 500 - 600 °C, and deformed steel bars are prepared through multiple cold extrusions. The components added during smelting are as follows: 0.10%≤C≤0.25%； 0.75% ≤ Si ≤ 1.75%; 1.35% ≤ Mn ≤ 2.7%; 0.0% ≤ Ni ≤ 0.35%; 0.001%≤N≤0.010%； The balance is Fe and inevitable trace impurities; The cold extrusion includes the following steps: The material quenched to 200 - 300 °C is rapidly heated to 500 - 550 °C at a heating rate of 50 - 80 °C / min. After the heating is completed, multiple passes of cold extrusion are carried out. During cold extrusion, the pass deformation amount is controlled at 5 - 8%, and the roll temperature is controlled at 500 °C. After cold extrusion, the surface temperature of the steel is maintained above 400 °C and heat-insulated for 30 - 45 min. After heat insulation, the temperature is lowered to 200 - 250 °C. After standing for a period of time, cold heading is carried out. The temperature during cold heading is controlled at 25 - 45 °C. The cross-section before cold heading is irregular, and the cross-section shape after cold heading is circular. After cold heading, uniform crater distribution is impacted on the surface of the deformed steel bar by high-speed shot peening. After the impact is completed, surface cold extrusion is carried out. The surface cold extrusion temperature is 200 - 300 °C, and the thread features are extruded and formed on the surface of the deformed steel bar.

2. The cold-pressed formed steel with high yield strength according to claim 1, characterized in that, After smelting is completed, a refining agent is added for refining. When adding the refining agent, argon gas is introduced into the melt for deoxidation.

3. The cold-pressed forming steel with high yield strength according to claim 2, characterized in that, The refining agent described is a low-nitrogen alloy.

4. The cold-pressed forming steel with high yield strength according to claim 1, characterized in that, During smelting, a step-by-step heating method is adopted. First, it is heated to 800 - 860 °C to precipitate the vaporized substances therein. After heat-insulating treatment for 25 ± 5 min, the second heating is carried out. The second heating is to 1100 ± 10 °C for short-time overheating treatment. After the treatment time of 10 ± 5 min, the temperature is lowered to 1000 ± 50 °C to keep the melt in a molten state.

5. The cold-pressed forming steel with high yield strength according to claim 4, characterized in that, When heating and melting the material to be melted by the step-by-step heating method, slag removal and argon gas introduction treatment are carried out during the heat-insulating stage.

6. The cold-pressed forming steel with high yield strength according to claim 1, characterized in that, After the smelted material is formed by casting, the cast component is rapidly cooled by water through a water-piercing device. The cooling water in the water-piercing device is injected onto the surface of the material under a certain pressure and instantaneously vaporizes to cool the material.

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