Martensite single-phase precipitation hardening steel and preparation process thereof

Abstract

The invention relates to the technical field of steelmaking, in particular to martensite single-phase precipitation hardening steel and a preparation process thereof. The preparation technology of the martensite single-phase precipitation hardening steel comprises the following steps that a steel billet is subjected to hot rolling and then quenched, the martensite single-phase precipitation hardening steel is obtained after two times of tempering, and the quenching medium is water. According to the method, the hot-rolled steel billet is rapidly quenched, a layered structure is formed in the inner grain structure of the steel billet, and then the step of secondary tempering is utilized, so that the breaking stress of the steel is improved, and the prepared martensite single-phase precipitation-hardened steel has high toughness on the premise that the strength is not lost.

Description

Technical Field

[0001] The invention relates to the technical field of steelmaking, and in particular to a martensitic single-phase precipitation hardening steel and a preparation process thereof. Background Art

[0002] As a martensitic single-phase precipitation hardening steel, copper-containing high-strength steel not only has high strength but also can maintain good toughness. It is widely used in aerospace, shipbuilding and bridge construction. With the increasing requirements for safety, durability and processing performance in high-end application fields, martensitic single-phase precipitation hardening steel is required to show high strength and high toughness during service. At present, most of the martensitic single-phase precipitation hardening steels are improved in toughness by increasing the tempering temperature. However, due to the high tempering temperature, on the one hand, the originally fine and evenly distributed precipitation phases are aggregated and grown, and the distribution is uneven, and the hindering effect of the larger precipitation phase on the dislocation is weakened, resulting in a decrease in the strength of the material. On the other hand, the higher tempering temperature leads to rough grain boundaries, which is not conducive to the high strength of martensitic single-phase precipitation hardening steel. At the same time, at a higher tempering temperature, the solid solubility is increased. Although the toughness can be improved, the content of the precipitated strengthening phase is reduced, thereby weakening the strength of the martensitic single-phase precipitation hardening steel. This results in a relationship between the strength and toughness of the martensitic single-phase precipitation hardening steel.

[0003] The prior art discloses an ultra-high strength and high toughness maraging steel. The raw materials are smelted and refining, and then subjected to homogenization heat treatment combined with multiple hot forgings, so that a copper-rich phase and a Ni3Ti core-shell structure are formed in the obtained maraging steel alloy, thereby achieving composite strengthening of soft and hard nanoparticles without losing the toughness of the maraging steel. However, the toughness is still poor. Summary of the invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defect of poor toughness performance of martensitic single-phase precipitation hardening steel in the prior art, thereby providing a martensitic single-phase precipitation hardening steel and a preparation process thereof.

[0005] On the one hand, the present invention provides a preparation process of martensitic single-phase precipitation hardening steel, comprising the following steps: hot rolling the steel billet and then quenching it, and tempering it twice to obtain the martensitic single-phase precipitation hardening steel, wherein the quenching medium is water.

[0006] Compared with the embodiment of the present invention which uses water cooling as the medium, the quenching process using air cooling or oil as the medium has a too slow quenching rate, which not only fails to form martensitic steel, but also results in poor toughness of the formed steel.

[0007] In some embodiments, the tempering temperature of the double tempering is lower than the austenite transformation temperature of the steel billet.

[0008] In some embodiments, the hot rolling temperature is 1100° C.-1200° C., and the hot rolling holding time is 1 h-2.5 h.

[0009] In some of the embodiments, the final rolling temperature of the hot rolling is 800℃-950℃, preferably 850℃-900℃. The final rolling temperature refers to the temperature of the metal material when it passes through the rolling mill for the last time during the hot rolling process. The final rolling temperature has a direct impact on the microstructure, mechanical properties, dimensional accuracy and surface quality of the product. Controlling the final rolling temperature is one of the key factors to ensure that the steel has good processing performance and meets the final product specification requirements. Too high or too low final rolling temperature may lead to poor internal structure of the material. The present invention controls the final rolling temperature to 800℃-950℃, and the more optimal final rolling temperature is 850℃-900℃, which can achieve an increase in the strength of the steel.

[0010] In order to further improve the toughness of the martensitic monomer phase precipitation hardening steel, in some embodiments, the primary tempering temperature is set to 450°C-550°C, preferably 500°C-550°C, and the primary tempering holding time is 0.25h-1h, preferably 0.5h-1h.

[0011] In some embodiments, the secondary tempering temperature is 425° C.-500° C., preferably 450° C.-475° C., and the holding time is 1 h-2.5 h, preferably 1 h-2 h.

[0012] In some of the embodiments, the method for preparing the steel billet includes the following steps: vacuum melting and forging various metal materials and carbon in a certain proportion.

[0013] Preferably, the metal material includes copper, nickel, manganese, chromium, molybdenum and vanadium.

[0014] In some of the embodiments, the mass fractions of the raw materials for preparing the steel ingot are: carbon powder 0.04%-0.06%, copper block 1.45%-3.24%, nickel block 8.8%-9.5%, manganese block 0.5%-0.7%, chromium block 0.8%-0.95%, molybdenum block 0.8%-0.95%, vanadium block 0.15%-0.3%, and the rest are iron blocks.

[0015] Preferably, the mass fraction of the raw materials for preparing the steel ingot is: carbon powder 0.05%-0.055%, copper block 1.5%-3%, nickel block 9%-9.2%, manganese block 0.55%-0.6%, chromium block 0.85%-0.9%, molybdenum block 0.85%-0.9%, vanadium block 0.2%-0.25%, and the rest is iron block.

[0016] In some embodiments, the vacuum melting temperature is 1530° C.-1600° C., and the melting time is 0.5 h-1 h.

[0017] In some embodiments, the forging temperature is 1100° C.-1150° C., and the forging holding time is 1 h-2.5 h.

[0018] On the other hand, the present invention provides a martensitic single-phase precipitation hardening steel prepared by the above preparation method, comprising the following components in parts by mass: C: 0.023%~0.03%, Cu: 1.5%~3%, Ni: 8.59%~9%, Mn: 0.55%~0.6%, Cr: 0.85%~0.9%, Mo: 0.85%~0.9%, V: 0.2%~0.25%, and the rest is Fe.

[0019] The technical solution of the present invention has the following advantages:

[0020] 1. The present invention provides a preparation process of a martensitic single-phase precipitation hardened steel, comprising the following steps: hot-rolling a steel billet and then quenching it, and tempering it twice to obtain a martensitic single-phase precipitation hardened steel, wherein the quenching medium is water. The present invention rapidly quenches the hot-rolled steel billet with water as the medium to form a layered structure in the internal grain structure of the steel billet, and then uses the step of secondary tempering to increase the fracture stress of the steel, so that the obtained martensitic single-phase precipitation hardened steel has strong toughness without losing strength.

[0021] 2. The present invention provides a preparation process for a martensitic single-phase precipitation hardened steel, wherein the tempering temperature of the two temperings is lower than the austenite transformation temperature of the steel billet. The present invention not only omits the austenitization step in the conventional process through the direct quenching step, but also reduces the tempering temperature, reduces the difficulty of operation, saves resources, and can further improve the strength of the martensitic single-phase precipitation hardened steel by reducing the tempering temperature.

[0022] 3. The present invention provides a preparation process for a martensitic single-phase precipitation hardened steel, wherein the hot rolling final rolling temperature is 800°C-950°C, preferably 850°C-900°C. The present invention controls the hot rolling final rolling temperature at 800°C-950°C, especially when the final rolling temperature is 850°C-900°C, the grain size in the steel can be controlled to meet the standard, thereby improving the strength of the steel.

[0023] 4. The present invention provides a preparation process for a martensitic single-phase precipitation hardened steel, wherein the primary tempering temperature is 500°C-550°C, and the holding time is 0.25h-0.75h; and / or the secondary tempering temperature is 425°C-475°C, and the holding time is 1h-2.5h. The present invention controls the temperature and time of the primary tempering and the secondary tempering within a certain range, which can ensure that the steel with a layered structure has a toughening effect on the one hand, and can further improve the strength of the steel on the other hand. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0025] Figure 1 This is a microscopic morphology of the martensitic single-phase precipitation hardened steel obtained in Example 1 of the present invention;

[0026] Figure 2 This is a microscopic morphology of the martensitic single-phase precipitation hardening steel obtained in Comparative Example 1 of the present invention;

[0027] Figure 3 This is a microscopic morphology of the martensitic single-phase precipitation hardening steel obtained in Comparative Example 2 of the present invention;

[0028] Figure 4 This is a microscopic morphology of the martensitic single-phase precipitation hardening steel obtained in Comparative Example 3 of the present invention;

[0029] Figure 5 This is a physical picture of the martensitic single-phase precipitation hardening steel obtained in Example 1 of Experimental Example 1 of the present invention after the impact test;

[0030] Figure 6 This is a physical picture of the martensitic single-phase precipitation hardening steel obtained in Comparative Example 1 of Experimental Example 1 of the present invention after the impact test;

[0031] Figure 7 This is a physical picture of the martensitic single-phase precipitation hardening steel obtained in Comparative Example 2 of Experimental Example 1 of the present invention after the impact test;

[0032] Figure 8 This is a physical picture of the martensitic single-phase precipitation hardening steel obtained in Comparative Example 3 of Experimental Example 1 of the present invention after the impact test;

[0033] Figure 1-Figure 8 RD represents the rolling direction, and ND represents the vertical rolling direction. DETAILED DESCRIPTION

[0034] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0035] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0036] The austenite temperature (Ac1) of the steel in the embodiment of the present invention is about 630°C.

[0037] Example 1

[0038] This embodiment provides a preparation process of martensitic single-phase precipitation hardening steel, and the specific steps and parameters are as follows:

[0039] (1) Ultrapure metal raw materials of Cu, Ni, Mn, Cr, Mo, V and C are melted in a vacuum induction furnace according to a certain ratio, wherein the melting temperature is 1550° C. and the melting time is 45 min to obtain a steel ingot.

[0040] Among them, there are 0.085kg of carbon powder, 4.5kg of copper blocks, 15.4kg of nickel blocks, 1.0kg of manganese blocks, 1.51kg of chromium blocks, 1.51kg of molybdenum blocks, 0.4kg of vanadium blocks, and the rest are iron blocks, 150kg of iron blocks, which are finally smelted into 170kg steel ingots.

[0041] (2) The steel ingot obtained in step (1) was heated to 1120° C. and maintained for 2 h, hot forged into a forged plate with a thickness of 35 mm, and then air-cooled to room temperature.

[0042] (3) The forged plate obtained in step (2) was kept at 1150° C. for 2 h, and then hot-rolled to 18 mm at 1150° C., with a final rolling temperature of 870° C., and then water-cooled to room temperature to obtain a steel plate.

[0043] (4) The steel plate obtained in step (3) is subjected to a first tempering by keeping the temperature at 500° C. for 0.5 h, and then water-cooled to room temperature to obtain a first rolled plate.

[0044] (5) The first rolled plate obtained in step (4) is subjected to a second tempering by being kept at 450° C. for 2 h, and then air-cooled to room temperature.

[0045] The mass fractions of the components of the martensitic single-phase precipitation hardening steel prepared in this embodiment are detected by inductively coupled plasma mass spectrometry (ICP) method.

[0046] C: 0.03%, Cu: 2.5%, Ni: 8.65%, Mn: 0.58%, Cr: 0.88%, Mo: 0.88%, V: 0.23%, and the rest are Fe and inevitable impurities.

[0047] The micromorphology of the martensitic single-phase precipitation hardened steel obtained in this embodiment is shown in Figure 1As shown, it can be known that the hardened steel prepared by the preparation process of this embodiment has an elongated layered structure along the hot rolling direction, and the effective grain size is 5.66 μm.

[0048] Example 2

[0049] This embodiment provides a preparation process of martensitic single-phase precipitation hardening steel, and the specific steps and parameters are as follows:

[0050] (1) Ultrapure metal raw materials of Cu, Ni, Mn, Cr, Mo, V and C are melted in a vacuum induction furnace according to a certain ratio, wherein the melting temperature is 1600° C. and the melting time is 0.5 h to obtain a steel ingot.

[0051] Among them, there are 0.085kg of carbon powder, 3.4kg of copper blocks, 15.3kg of nickel blocks, 1.02kg of manganese blocks, 1.53kg of chromium blocks, 1.53kg of molybdenum blocks, 0.34kg of vanadium blocks, and the rest are iron blocks, 150kg of iron blocks, which are finally smelted into 170kg steel ingots.

[0052] (2) The steel ingot obtained in step (1) was heated to 1120° C. and maintained for 2 h, hot forged into a forged plate with a thickness of 35 mm, and then air-cooled to room temperature.

[0053] (3) The forged plate obtained in step (2) was kept at 1150° C. for 2 h, and then hot-rolled to 18 mm at 1150° C., with a final rolling temperature of 900° C., and then water-cooled to room temperature to obtain a steel plate.

[0054] (4) The steel plate obtained in step (3) is subjected to a first tempering by being kept at 550° C. for 0.5 h, and then water-cooled to room temperature to obtain a first rolled plate.

[0055] (5) The first rolled plate obtained in step (4) is subjected to a second tempering by being kept at 475° C. for 2 h, and then air-cooled to room temperature.

[0056] The mass fractions of the components of the martensitic single-phase precipitation hardening steel prepared in this embodiment are detected by ICP method:

[0057] C: 0.023%, Cu: 1.8%, Ni: 8.60%, Mn: 0.55%, Cr: 0.89%, Mo: 0.85%, V: 0.20%, and the rest are Fe and inevitable impurities.

[0058] Example 3

[0059] This embodiment provides a preparation process of martensitic single-phase precipitation hardened steel. The specific steps and parameters are the same as those in Example 1, except that the final rolling temperature in step (3) is 850°C.

[0060] Example 4

[0061] This embodiment provides a preparation process of martensitic single-phase precipitation hardened steel. The specific steps and parameters are the same as those in Embodiment 1, except that the final rolling temperature in step (3) is 800°C.

[0062] Example 5

[0063] This embodiment provides a preparation process of martensitic single-phase precipitation hardened steel. The specific steps and parameters are the same as those in Embodiment 1, except that the final rolling temperature in step (3) is 950°C.

[0064] Example 6

[0065] This embodiment provides a preparation process of martensitic single-phase precipitation hardened steel. The specific steps and parameters are the same as those in Embodiment 1, except that the first tempering temperature in step (4) is 650°C.

[0066] Example 7

[0067] This embodiment provides a preparation process of martensitic single-phase precipitation hardened steel. The specific steps and parameters are the same as those in Embodiment 1, except that the first tempering temperature in step (4) is 450°C.

[0068] Example 8

[0069] This embodiment provides a preparation process of martensitic single-phase precipitation hardened steel. The specific steps and parameters are the same as those in Embodiment 1, except that the first tempering time in step (4) is 1 hour.

[0070] Example 9

[0071] This embodiment provides a preparation process of martensitic single-phase precipitation hardened steel. The specific steps and parameters are the same as those in Example 1, except that the first tempering time in step (4) is 0.25 h.

[0072] Example 10

[0073] This embodiment provides a preparation process of martensitic single-phase precipitation hardened steel. The specific steps and parameters are the same as those in Example 1, except that the second tempering temperature in step (4) is 500°C.

[0074] Embodiment 11

[0075] This embodiment provides a preparation process of martensitic single-phase precipitation hardened steel. The specific steps and parameters are the same as those in Example 1, except that the second tempering temperature in step (4) is 425°C.

[0076] Example 12

[0077] This embodiment provides a preparation process of martensitic single-phase precipitation hardened steel. The specific steps and parameters are the same as those in Embodiment 1, except that the second tempering time in step (4) is 2.5 h.

[0078] Embodiment 13

[0079] This embodiment provides a preparation process of martensitic single-phase precipitation hardened steel. The specific steps and parameters are the same as those in Embodiment 1, except that the second tempering time in step (4) is 1 hour.

[0080] Embodiment 14

[0081] This embodiment provides a preparation process of martensitic single-phase precipitation hardening steel. The specific steps and parameters are the same as those in Example 1, except that in step (1), the smelting temperature is 1530° C. and the smelting time is 1 h to obtain a steel ingot.

[0082] Embodiment 15

[0083] This embodiment provides a preparation process of martensitic single-phase precipitation hardening steel, and the specific steps and parameters are as follows:

[0084] (1) Ultrapure metal raw materials of Cu, Ni, Mn, Cr, Mo, V and C are melted in a vacuum induction furnace according to a certain ratio, wherein the melting temperature is 1550° C. and the melting time is 45 min to obtain a steel ingot.

[0085] Among them, there are 0.0935kg of carbon powder, 2.55kg of copper blocks, 15.64kg of nickel blocks, 0.95kg of manganese blocks, 1.45kg of chromium blocks, 1.45kg of molybdenum blocks, 0.34kg of vanadium blocks, and the rest are iron blocks, 150kg of iron blocks, which are finally smelted into 170kg steel ingots.

[0086] (2) The steel ingot obtained in step (1) was heated to 1120° C. and maintained for 2 h, hot forged into a forged plate with a thickness of 35 mm, and then air-cooled to room temperature.

[0087] (3) The forged plate obtained in step (2) was kept at 1150° C. for 2 h, and then hot-rolled to 18 mm at 1150° C., with a final rolling temperature of 870° C., and then water-cooled to room temperature to obtain a steel plate.

[0088] (4) The steel plate obtained in step (3) is subjected to a first tempering by keeping the temperature at 500° C. for 0.5 h, and then water-cooled to room temperature to obtain a first rolled plate.

[0089] (5) The first rolled plate obtained in step (4) is subjected to a second tempering by being kept at 450° C. for 2 h, and then air-cooled to room temperature.

[0090] The mass fractions of the components of the martensitic single-phase precipitation hardening steel prepared in this embodiment are detected by inductively coupled plasma mass spectrometry (ICP) method.

[0091] C: 0.03%, Cu: 1.6%, Ni: 8.59%, Mn: 0.55%, Cr: 0.85%, Mo: 0.85%, V: 0.21%, and the rest are Fe and inevitable impurities.

[0092] Example 16

[0093] This embodiment provides a preparation process of martensitic single-phase precipitation hardening steel, and the specific steps and parameters are as follows:

[0094] (1) Ultrapure metal raw materials of Cu, Ni, Mn, Cr, Mo, V and C are melted in a vacuum induction furnace according to a certain ratio, wherein the melting temperature is 1550° C. and the melting time is 45 min to obtain a steel ingot.

[0095] Among them, there are 0.09kg of carbon powder, 5.1kg of copper blocks, 15.3kg of nickel blocks, 1.0kg of manganese blocks, 1.53kg of chromium blocks, 1.53kg of molybdenum blocks, 0.45kg of vanadium blocks, and the rest are iron blocks, 150kg of iron blocks, which are finally smelted into 170kg steel ingots.

[0096] (2) The steel ingot obtained in step (1) was heated to 1120° C. and maintained for 2 h, hot forged into a forged plate with a thickness of 35 mm, and then air-cooled to room temperature.

[0097] (3) The forged plate obtained in step (2) was kept at 1150° C. for 2 h, and then hot-rolled to 18 mm at 1150° C., with a final rolling temperature of 870° C., and then water-cooled to room temperature to obtain a steel plate.

[0098] (4) The steel plate obtained in step (3) is subjected to a first tempering by keeping the temperature at 500° C. for 0.5 h, and then water-cooled to room temperature to obtain a first rolled plate.

[0099] (5) The first rolled plate obtained in step (4) is subjected to a second tempering by being kept at 450° C. for 2 h, and then air-cooled to room temperature.

[0100] The mass fractions of the components of the martensitic single-phase precipitation hardening steel prepared in this embodiment are detected by inductively coupled plasma mass spectrometry (ICP) method.

[0101] C: 0.03%, Cu: 3%, Ni: 9%, Mn: 0.59%, Cr: 0.9%, Mo: 0.9%, V: 0.25%, and the rest are Fe and inevitable impurities.

[0102] Comparative Example 1

[0103] This comparative example provides a preparation process of a martensitic single-phase precipitation hardened steel, and the specific steps and parameters are as follows:

[0104] (1) According to the proportion of step (1) of Example 1, ultrapure metal raw materials of Cu, Ni, Mn, Cr, Mo, V and C are smelted in a vacuum induction furnace, wherein the smelting temperature is 1550° C. and the smelting time is 45 min to obtain a steel ingot, wherein the carbon powder is 0.085 kg, the copper block is 4.5 kg, the nickel block is 15.4 kg, the manganese block is 1.0 kg, the chromium block is 1.51 kg, the molybdenum block is 1.51 kg, the vanadium block is 0.4 kg, and the rest is iron block, and finally smelted into a 170 kg steel ingot.

[0105] (2) The steel ingot obtained in step (1) was heated to 1120° C. and maintained for 2 h, hot forged into a forged plate with a thickness of 35 mm, and then air-cooled to room temperature.

[0106] (3) The forged plate obtained in step (2) was kept at 1150° C. for 2 h, and then hot-rolled to 18 mm at 1150° C., with a final rolling temperature of 870° C., and then air-cooled to room temperature to obtain a steel plate.

[0107] (4) The steel plate was heated to 900°C and kept at this temperature for 1 hour, then water-cooled, tempered at 450°C for 2 hours, and then air-cooled to room temperature.

[0108] The microstructure of the martensitic single-phase precipitation hardening steel obtained in this comparative example is shown in FIG. Figure 2 shown.

[0109] Comparative Example 2

[0110] This comparative example provides a preparation process of a martensitic single-phase precipitation hardened steel. The specific steps and parameters are the same as those of Example 1, except that the first tempering is not provided, that is, the steel plate after water cooling in step (3) is kept at 450°C for 2h and air-cooled to room temperature to obtain a martensitic single-phase precipitation hardened steel.

[0111] The microstructure of the martensitic single-phase precipitation hardening steel obtained in this comparative example is shown in FIG. Figure 3 shown.

[0112] Comparative Example 3

[0113] This comparative example provides a preparation process of a martensitic single-phase precipitation hardened steel, and the specific steps and parameters are as follows:

[0114] (1) According to the proportion of step (1) of Example 1, ultrapure metal raw materials of Cu, Ni, Mn, Cr, Mo, V and C are smelted in a vacuum induction furnace, wherein the smelting temperature is 1150° C. and the smelting time is 45 min to obtain a steel ingot, wherein the carbon powder is 0.085 kg, the copper block is 4.5 kg, the nickel block is 15.4 kg, the manganese block is 1.0 kg, the chromium block is 1.51 kg, the molybdenum block is 1.51 kg, the vanadium block is 0.4 kg, and the rest is iron block, and finally smelted into a 170 kg steel ingot.

[0115] (2) The steel ingot obtained in step (1) was heated to 1120° C. and maintained for 2 h, hot forged into a forged plate with a thickness of 35 mm, and then air-cooled to room temperature.

[0116] (3) The forged plate obtained in step (2) was kept at 1150° C. for 2 h, and then hot-rolled to 18 mm at 1150° C., with a final rolling temperature of 870° C., and then air-cooled to room temperature to obtain a steel plate.

[0117] (4) The steel plate is heated to 900°C and kept at this temperature for 1 hour, then water-cooled, and then kept at 500°C for 0.5 hour for the first tempering, and then water-cooled to room temperature to obtain the first rolled plate.

[0118] (5) The first rolled plate obtained in step (4) is subjected to a second tempering by being kept at 450° C. for 2 h, and then air-cooled to room temperature.

[0119] The microstructure of the martensitic single-phase precipitation hardening steel obtained in this comparative example is shown in FIG. Figure 4 shown.

[0120] Comparative Example 4

[0121] This comparative example provides a preparation process of a martensitic single-phase precipitation hardened steel. The specific steps and parameters are the same as those of Example 1, except that air cooling is used instead of water cooling in step (3).

[0122] Comparative Example 5

[0123] This comparative example provides a preparation process of martensitic single-phase precipitation hardening steel. The specific steps and parameters are the same as those of Example 1, except that step (4) and step (5) are not included, that is, the steel plate prepared in step (3) is martensitic single-phase precipitation hardening steel.

[0124] Experimental Example 1

[0125] The martensitic single-phase precipitation hardening steels obtained in Example 1 and Comparative Examples 1-3 were subjected to impact tests in accordance with the National Standard of the People's Republic of China GB / T 229-2020.

[0126] The impact test was conducted on a V-notch sample for Charpy impact test along the rolling direction, with a size of 10mm×10mm×55mm. The experimental temperature was -84°C, and the sample was placed in a gas liquid nitrogen tank. When the temperature reached -84°C, the temperature was maintained for 0.5h, and then the sample was taken out and struck within 5s (the equipment for the impact test was a pendulum instrumented impact tester, model NI750C).

[0127] See the actual image and microscopic morphology scan after impact test. Figure 5-Figure 8 ,

[0128] It can be seen that the martensitic single-phase precipitation hardening steel obtained by the preparation process provided in the embodiment of the present invention has a stratified morphology on the fracture after the impact test, while the martensitic single-phase precipitation hardening steel obtained in comparative examples 1-3 does not show a stratified morphology after the impact test, which proves that the martensitic single-phase precipitation hardening steel obtained by the preparation process provided in the present invention has good toughness.

[0129] Example 2

[0130] The tensile strength, yield strength, fracture elongation, post-fracture shrinkage and impact energy of the martensitic single-phase precipitation hardening steels obtained in Examples 1-12 and Comparative Examples 1-5 were tested, and the test results are shown in Table 1, wherein the test methods for tensile strength and yield strength refer to the national standard of the People's Republic of China GB / T228.1-2021, and the test was carried out using a Z250 universal testing machine at a strain rate of 2.5×10-4s-1;

[0131] The detection method of the impact energy at -84℃ adopts the national standard of the People's Republic of China GB / T 229-2020, and the V-notch sample for the Charpy impact test is processed along the rolling direction, with a size of 10mm×10mm×55mm. The experimental temperature is -84℃, and the sample is placed in a gas liquid nitrogen tank. When the temperature reaches -84℃, the temperature is maintained for 0.5h, and then the sample is taken out and struck within 5s.

[0132] Table 1 Performance test results of martensitic single-phase precipitation hardening steel

[0133]

[0134]

[0135] According to the results in Table 1, it can be seen that Comparative Example 1 adopts the traditional preparation process, that is, air cooling after hot rolling, and tempering once after keeping warm in an environment higher than the austenite temperature. Comparative Example 4 adds a tempering step on the basis of Comparative Example 1, but the alloy elements in the hardened steel cannot be dissolved due to the air cooling method, resulting in a significant decrease in the impact energy of the hardened steel at -84°C. Comparative Example 2 adopts one tempering on the basis of quenching, and Comparative Example 3 adopts air cooling instead of water cooling to obtain hardened steels with significantly reduced hardness. The present invention adopts direct quenching after hot rolling and cooperates with two tempering steps to form a layered structure on the martensitic hardened steel. The obtained martensitic single-phase precipitation hardened steel can significantly improve the toughness of the steel, especially the toughness at low temperature, while ensuring the strength of the steel.

[0136] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A process for preparing a martensitic single-phase precipitation hardened steel, characterized in that: The following steps are included: The steel billet is hot rolled and quenched, and then tempered twice to obtain martensitic single-phase precipitation hardened steel. The quenching medium is water.

2. The process for preparing the martensitic single-phase precipitation hardened steel according to claim 1, characterized in that: The tempering temperature of the two temperings is lower than the austenite transformation temperature of the steel billet.

3. The process for preparing the martensitic single-phase precipitation hardened steel according to claim 2, characterized in that: The final rolling temperature of the hot rolling is 800°C-950°C, preferably 850°C-900°C.

4. The process for preparing the martensitic single-phase precipitation hardening steel according to any one of claims 1 to 3, characterized in that: The hot rolling temperature is 1100° C.-1200° C., and the hot rolling holding time is 1 h-2.5 h.

5. The process for preparing the martensitic single-phase precipitation hardening steel according to claim 4, characterized in that: The primary tempering temperature is 450°C-550°C, preferably 500°C-550°C. The holding time of the first tempering is 0.25h-1h, preferably 0.5h-1h; and / or, The secondary tempering temperature is 425°C-500°C, preferably 450°C-475°C, and the holding time is 1h-2.5h, preferably 1-2h.

6. The process for preparing martensitic single-phase precipitation hardening steel according to claim 5, characterized in that: The steel billet is prepared by vacuum melting and forging various metal materials and carbon in a certain proportion.

7. The process for preparing the martensitic single-phase precipitation hardening steel according to claim 6, characterized in that: The metal material includes copper, nickel, manganese, chromium, molybdenum and vanadium; and / or, The vacuum smelting has a smelting temperature of 1530° C.-1600° C. and a smelting time of 0.5 h-1 h.

8. The process for preparing martensitic single-phase precipitation hardening steel according to claim 6, characterized in that: The forging temperature is 1100° C.-1150° C., and the forging holding time is 1 h-2.5 h; and / or, In the preparation of steel ingots, the mass fractions of each raw material are: carbon 0.04%-0.06%, copper 1.45%-3.24%, nickel 8.8%-9.5%, manganese 0.5%-0.7%, chromium 0.8%-0.95%, molybdenum 0.8%-0.95%, vanadium 0.15%-0.3%, and the rest is iron.

9. A martensitic single-phase precipitation hardening steel, characterized in that: The steel is prepared by the preparation process of the martensitic single-phase precipitation hardening steel according to any one of claims 1 to 8.

10. The martensitic single-phase precipitation hardening steel according to claim 9, characterized in that: The invention comprises the following components in parts by mass: C: 0.023% to 0.03%, Cu: 1.5% to 3%, Ni: 8.59% to 9%, Mn: 0.55% to 0.6%, Cr: 0.85% to 0.9%, Mo: 0.85% to 0.9%, V: 0.2% to 0.25%, and the rest are Fe and unavoidable impurities.

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