High-hardness and high-toughness steel as well as heat treatment process and application thereof

Abstract

The invention provides high-hardness and high-toughness steel and a heat treatment process and application thereof, and belongs to the technical field of steel heat treatment. According to the method, the steel is subjected to high-temperature austenitizing firstly, the structure in the steel can be converted into an austenitic structure, then the austenitized steel is subjected to isothermal quenching treatment, and quenching treatment is conducted at the high temperature by controlling the temperature and time of isothermal quenching treatment; most austenite structures in the steel can be converted into bainite structures, a small part of austenite structures can be converted into martensite structures, a small amount of austenite structures are left, finally tempering treatment is conducted, the internal stress of the steel is reduced, and the structures in the obtained steel are bainite + martensite + retained austenite structures, the bainite structure has high toughness, the martensite structure can improve the hardness of the steel, the steel with high hardness and high toughness is finally obtained, and the comprehensive performance is excellent.

Description

Technical Field

[0001] The present invention relates to the technical field of heat treatment of steel materials, and in particular to a high-hardness and high-toughness steel material and a heat treatment process and application thereof. Background Art

[0002] For a long time, in the production activities of rare earth mineral exploration and mining, the traditional "Gannan Drill" has been used for exploration and sampling. The traditional "Gannan Drill" has a simple structure, mainly consisting of a drill barrel (consisting of a knife edge, a sample storage barrel, a drill bit welding rib, and a guide joint), a drill rod, a handle, and a joystick. During the use of the traditional "Gannan Drill", the knife edge is downward, and its sharp knife edge is conducive to penetrating soil and rock layers. The space inside the drill barrel is large, and more mineral samples can be stored. At the same time, workers will knock the knife edge of the drill barrel outward to form a "trumpet shape". The "trumpet-shaped" knife edge makes the knife edge diameter larger than the drill barrel diameter. The drill barrel drills downward, and the rock and soil enter the drill barrel. The diameter of the drill barrel becomes smaller, and the pressure of the barrel wall on the rock and soil and the inside of the rock and soil increases, and the friction increases, so that the rock and soil in the drill barrel will not fall off during the process of lifting the drill barrel upward. The failure of traditional "Gannan Drill" is mainly due to blade curling, cracking and severe wear, so the service life of the blade directly affects the service life of the entire "Gannan Drill". The blade of the traditional "Gannan Drill" is made of 45 steel, which has poor hardness, wears quickly during use, and is easy to curl. The penetration effect on harder geological layers such as semi-weathered layers is very poor. The advantage is that it has high toughness and is not easy to crack during use. If curling occurs, it can be repaired manually to extend the service life. At present, with the development of the rare earth mineral exploration industry, there is an increasing demand for exploration and sampling of harder geological layers such as semi-weathered layers and even slightly weathered layers. The performance of traditional "Gannan Drill" is slightly insufficient for such service conditions.

[0003] After analysis, it is found that the performance of steel materials is mainly affected by the composition ratio and heat treatment process. Taking 45# steel as an example, the appropriate addition of alloying elements such as Cr, Mo, etc. can improve the strength and hardness. Secondly, the heat treatment process of steel is generally quenching + tempering / tempering treatment. The quenching temperature is generally below 80°C, which is lower than the Ms point temperature. Therefore, the structure obtained after quenching is martensite + residual austenite, of which the residual austenite accounts for a small proportion, mainly martensite. The hardness of martensite is higher but the toughness is poor. There are mature steel grades such as 42CrMo and 40Cr on the market. The hardness is higher than that of 45# steel, but its plastic toughness is poor and its impact resistance is low, which can no longer meet the technical requirements.

[0004] Therefore, how to improve the toughness of steel without reducing its hardness, so that the "Gannan Drill" blade has a higher drilling depth in the semi-weathered layer, has become a technical problem that needs to be urgently solved in this field. Summary of the invention

[0005] The purpose of the present invention is to provide a high-hardness and high-toughness steel and its heat treatment process and application. The heat treatment process provided by the present invention can significantly improve the toughness and wear resistance of the steel without almost affecting the hardness of the steel. The "Gannan Drill" blade prepared from the steel has a higher drilling depth in the semi-weathered layer.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a heat treatment process for high-hardness and high-toughness steel, comprising the following steps:

[0008] (1) subjecting the steel to a high-temperature austenitizing treatment to obtain an austenitized steel; the holding temperature of the high-temperature austenitizing treatment is 850 to 900° C., and the holding time of the high-temperature austenitizing treatment is 20 to 60 minutes;

[0009] (2) subjecting the austenitized steel obtained in step (1) to isothermal quenching and cooling in sequence to obtain a quenched steel; the isothermal quenching treatment is performed at a holding temperature of 260 to 300° C. and the isothermal quenching treatment time is 90 to 150 min;

[0010] (3) The quenched steel obtained in step (1) is tempered to obtain a high-hardness and high-toughness steel.

[0011] Preferably, the steel material in step (1) is 45# steel, 42CrMo steel or 40Cr steel.

[0012] Preferably, the steel is processed into a "Gannan drill" blade shape before the high-temperature austenitizing treatment in step (1).

[0013] Preferably, the holding temperature of the high-temperature austenitizing treatment in step (1) is 870° C., and the holding time of the high-temperature austenitizing treatment is 30 minutes.

[0014] Preferably, the holding temperature of the isothermal quenching treatment in step (2) is 280-300° C., and the time of the isothermal quenching treatment is 120 min.

[0015] Preferably, the isothermal quenching treatment in step (2) is carried out in a salt bath, and the salt used in the salt bath is molten nitrate.

[0016] Preferably, the molten nitrate is prepared by mixing potassium nitrate and sodium nitrate in a mass ratio of 1:1.

[0017] Preferably, the holding temperature of the tempering treatment in step (3) is 220-250° C., and the holding time of the tempering treatment is 90-150 min.

[0018] The present invention provides a high-hardness and high-toughness steel material prepared by the heat treatment process described in the above technical solution, wherein the structure of the high-hardness and high-toughness steel material is bainite+martensite+residual austenite structure.

[0019] The present invention provides a high-hardness and high-toughness steel material prepared by the heat treatment process described in the above technical solution or the application of the high-hardness and high-toughness steel material described in the above technical solution in "Gannan Drilling".

[0020] The invention provides a heat treatment process for high-hardness and high-toughness steel, comprising the following steps: (1) subjecting the steel to high-temperature austenitizing treatment to obtain austenitized steel; the holding temperature of the high-temperature austenitizing treatment is 850-900°C, and the holding time of the high-temperature austenitizing treatment is 20-60 minutes; (2) subjecting the austenitized steel obtained in the step (1) to isothermal quenching treatment and cooling in sequence to obtain quenched steel; the holding temperature of the isothermal quenching treatment is 260-300°C, and the time of the isothermal quenching treatment is 90-150 minutes; (3) subjecting the quenched steel obtained in the step (1) to tempering treatment to obtain high-hardness and high-toughness steel. The present invention first subjects the steel to high-temperature austenitization, which can transform the structure in the steel into an austenite structure, and then subjects the austenitized steel to isothermal quenching treatment. By controlling the temperature and time of the isothermal quenching treatment and performing quenching treatment at a relatively high temperature, most of the austenite structure in the steel can be transformed into a bainite structure, and a small part of the austenite structure can be transformed into a martensite structure, with a small amount of austenite structure remaining. Finally, a tempering treatment is performed to reduce the internal stress of the steel. The structure of the obtained steel is bainite + martensite + residual austenite structure. The bainite structure has high toughness, and the martensite structure can improve its hardness, and finally a steel with both high hardness and high toughness is obtained, with excellent comprehensive performance. The results of the embodiment show that by using the heat treatment process of the present invention, when the steel is 45# steel, the Rockwell hardness of the obtained "Gannan Drill" blade is greater than 43HRA, and the impact absorption energy KV 2 >19J, semi-weathered layer drilling depth>10m, compared with the conventional quenching process, the semi-weathered layer drilling depth is increased by about 12.5%, when the steel is 42CrMo steel or 40Cr steel, the Rockwell hardness of the "Gannan Drill" blade is>50HRA, and the impact absorption energy KV 2 >16J, semi-weathered layer drilling depth>22m, compared with conventional quenching process, impact absorption energy KV 2 The improvement is 30-35%, and the drilling depth of the semi-weathered layer is increased by 55-60%, which is a significant improvement. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is an electron microscope image of the steel obtained in Example 1;

[0022] Figure 2 This is an electron microscope image of the steel obtained in Example 2;

[0023] Figure 3 This is an electron microscope image of the steel obtained in Example 3;

[0024] Figure 4 This is an electron microscope image of the steel obtained in Comparative Example 1;

[0025] Figure 5 This is an electron microscope image of the steel obtained in Comparative Example 2;

[0026] Figure 6 This is an electron microscope image of the steel obtained in Comparative Example 3;

[0027] Figure 7 This is a transmission electron microscope image of the steel obtained in Example 2;

[0028] Figure 8 This is a transmission electron microscope magnified image of the steel obtained in Example 2;

[0029] Fig. 9 The TEM lens of the steel obtained in Example 2;

[0030] Fig.10 This is a magnified transmission electron microscope image of the steel obtained in Example 2. DETAILED DESCRIPTION

[0031] The present invention provides a heat treatment process for high-hardness and high-toughness steel, comprising the following steps:

[0032] (1) subjecting the steel to a high-temperature austenitizing treatment to obtain an austenitized steel;

[0033] (2) subjecting the austenitized steel obtained in step (1) to isothermal quenching and cooling in sequence to obtain a quenched steel;

[0034] (3) The quenched steel obtained in step (1) is tempered to obtain a high-hardness and high-toughness steel.

[0035] The present invention subjects the steel to high-temperature austenitizing treatment to obtain the austenitized steel.

[0036] In the present invention, the steel material is preferably 45# steel, 42CrMo steel or 40Cr steel. The present invention has no particular limitation on the specific composition and source of the 45# steel, 42CrMo steel or 40Cr steel, and commercial products well known to those skilled in the art can be used.

[0037] The present invention preferably processes the steel into the shape of a "Gannan drill" blade before high-temperature austenitizing treatment. The present invention does not specifically limit the specific operation of processing the steel into the shape of a "Gannan drill" blade, and the operation familiar to those skilled in the art can be adopted. The present invention processes the steel into the shape of a "Gannan drill" blade, so that the steel can be directly welded to the "Gannan drill" for use after the heat treatment is completed, thereby avoiding the influence of mechanical deformation during the processing on the performance of the steel.

[0038] In the present invention, the holding temperature of the high-temperature austenitizing treatment is 850-900°C, preferably 870°C; the holding time of the high-temperature austenitizing treatment is 20-60min, preferably 30-40min; the heating rate to the high-temperature austenitizing treatment temperature is preferably 8-15°C / min, more preferably 10°C / min. The present invention can transform all the structures in the steel into austenite structures through high-temperature austenitizing treatment; by controlling the parameters of the high-temperature austenitizing treatment, the conversion efficiency can be further improved; by controlling the heating rate, the temperature rise is too fast to cause excessive internal stress.

[0039] After obtaining the austenitized steel, the present invention sequentially performs isothermal quenching treatment and cooling on the austenitized steel to obtain the quenched steel.

[0040] In the present invention, the holding temperature of the austempering treatment is 260-300°C, preferably 280-300°C; the time of the austempering treatment is 90-150min, preferably 120min. The present invention can transform most of the austenite structure in the steel into bainite and martensite structure through austempering treatment; by controlling the process parameters of the austempering treatment, most of the austenite structure can be transformed into bainite structure, a small part of the austenite structure can be transformed into martensite structure, and part of the austenite structure can be retained, so as to obtain a steel with a structure of bainite + martensite + residual austenite structure.

[0041] In the present invention, the isothermal quenching treatment is preferably carried out in a salt bath; the salt used in the salt bath is preferably a molten nitrate. The present invention does not specifically limit the specific type of the nitrate, and it can be selected according to the technical common sense of those skilled in the art. As an embodiment of the present invention, the molten nitrate can be prepared by mixing potassium nitrate and sodium nitrate in a mass ratio of 1:1; the preparation method of the molten nitrate is preferably to first mix potassium nitrate and sodium nitrate, then heat and melt them, and then control the temperature to the insulation temperature of the isothermal quenching treatment. The present invention can ensure that the nitrate is a liquid melt at the temperature of the isothermal quenching treatment by controlling the type and amount of the nitrate.

[0042] The present invention preferably turns the austenitized steel material during the isothermal quenching treatment or uses a flowing molten nitrate for salt bathing. The present invention can ensure the uniformity of the isothermal quenching treatment by the above-mentioned method.

[0043] The present invention preferably detects the temperature of the steel material by an external infrared thermal imager during the isothermal quenching process. The present invention can ensure that the temperature of the steel material is always within the required temperature range by constantly detecting the temperature of the steel material.

[0044] After the isothermal quenching treatment is completed, the product of the isothermal quenching treatment is preferably cleaned. The specific operation of the cleaning is not particularly limited in the present invention, and the surface salt can be filtered out.

[0045] In the present invention, the cooling method is preferably natural cooling at room temperature. The present invention has no particular limitation on the cooling time, as long as it can be cooled to room temperature. As an embodiment of the present invention, the cooling time can be 20 to 60 minutes, or 30 to 40 minutes.

[0046] After the quenched steel is obtained, the present invention performs a tempering treatment on the quenched steel to obtain a high-hardness and high-toughness steel.

[0047] In the present invention, the holding temperature of the tempering treatment is preferably 220-250°C, more preferably 230-250°C; the holding time of the tempering treatment is preferably 90-150 minutes, more preferably 100-120 minutes. The present invention can reduce the internal pressure of the steel by performing the tempering treatment; by controlling the temperature and time of the tempering treatment and performing the low-temperature short-time tempering treatment, the hardness and toughness of the steel can be further improved.

[0048] The present invention has no particular limitation on the cooling method of the tempering treatment, as long as it can be cooled to room temperature. As an embodiment of the present invention, the cooling method is preferably natural cooling at room temperature.

[0049] In the present invention, the tempering treatment is preferably carried out in a heat treatment furnace. The present invention has no particular limitation on the specific model and source of the heat treatment furnace, and a commercially available heat treatment furnace well known to those skilled in the art can be used.

[0050] The present invention firstly performs high-temperature austenitization on the steel material, so that the structure in the steel material can be transformed into an austenite structure, and then the austenitized steel material is subjected to isothermal quenching treatment. By controlling the temperature and time of the isothermal quenching treatment, the quenching treatment is performed at a relatively high temperature, so that most of the austenite structure in the steel material can be transformed into a bainite structure, and a small part of the austenite structure can be transformed into a martensite structure, and a small amount of austenite structure remains. Finally, tempering treatment is performed to reduce the internal stress of the steel material. The structure of the obtained steel material is bainite+martensite+residual austenite structure, the bainite structure has higher toughness, and the martensite structure can improve its hardness, and finally a steel material with both high hardness and high toughness is obtained, and the comprehensive performance is excellent.

[0051] The present invention also provides a high-hardness and high-toughness steel obtained by the heat treatment process described in the above technical solution. The structure of the high-hardness and high-toughness steel provided by the present invention is bainite+martensite+residual austenite structure.

[0052] The present invention also provides a high-hardness and high-toughness steel obtained by the heat treatment process described in the above technical solution or the application of the high-hardness and high-toughness steel described in the above technical solution in "Gannan Drilling".

[0053] The present invention has no special limitation on the specific application method. The steel is processed into the shape of the blade of the "Gannan Drill", and then directly welded to the "Gannan Drill" after a heat treatment process for use.

[0054] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0055] Example 1

[0056] A heat treatment process for high hardness and high toughness steel is:

[0057] (1) processing 45# steel into a "Gannan drill" blade shape, and then placing it in a high-temperature box furnace for high-temperature austenitization treatment to obtain an austenitized steel; the holding temperature of the high-temperature austenitization treatment is 870° C., and the holding time of the high-temperature austenitization treatment is 30 min; the heating rate of heating to the high-temperature austenitization treatment temperature is 10° C. / min;

[0058] (2) subjecting the austenitized steel obtained in step (1) to isothermal quenching treatment in a salt bath, filtering off the salt stains on the surface, and finally cooling naturally in air for 30 minutes to obtain quenched steel; the salt bath contains flowing molten nitrate; the molten nitrate is prepared by heating and melting a mixture of potassium nitrate and sodium nitrate in a mass ratio of 1:1, and then controlling the temperature to be 300° C.; the isothermal quenching treatment is carried out at a holding temperature of 300° C. and for a time of 120 minutes; and the temperature of the steel is detected by an external infrared thermal imager during the isothermal quenching treatment;

[0059] (3) The quenched steel obtained in step (1) is tempered in a heat treatment furnace, and finally naturally cooled at room temperature to obtain a high-hardness and high-toughness steel; the holding temperature of the tempering treatment is 250° C., and the holding time of the tempering treatment is 120 min.

[0060] Example 2

[0061] A heat treatment process for high hardness and high toughness steel is:

[0062] (1) processing 42CrMo steel into a "Gannan drill" blade shape, and then placing it in a high-temperature box furnace for high-temperature austenitization treatment to obtain an austenitized steel; the holding temperature of the high-temperature austenitization treatment is 870° C., and the holding time of the high-temperature austenitization treatment is 30 min; the heating rate to the high-temperature austenitization treatment temperature is 10° C. / min;

[0063] (2) subjecting the austenitized steel obtained in step (1) to isothermal quenching treatment in a salt bath, filtering off the salt stains on the surface, and finally cooling naturally in air for 30 minutes to obtain quenched steel; the salt bath contains flowing molten nitrate; the molten nitrate is prepared by heating and melting a mixture of potassium nitrate and sodium nitrate in a mass ratio of 1:1, and then controlling the temperature to be 300° C.; the isothermal quenching treatment is carried out at a holding temperature of 300° C. and for a time of 120 minutes; and the temperature of the steel is detected by an external infrared thermal imager during the isothermal quenching treatment;

[0064] (3) The quenched steel obtained in step (1) is tempered in a heat treatment furnace, and finally naturally cooled at room temperature to obtain a high-hardness and high-toughness steel; the holding temperature of the tempering treatment is 250° C., and the holding time of the tempering treatment is 120 min.

[0065] Example 3

[0066] A heat treatment process for high hardness and high toughness steel is:

[0067] (1) processing 40Cr steel into a "Gannan drill" blade shape, and then placing it in a high-temperature box furnace for high-temperature austenitization treatment to obtain an austenitized steel; the holding temperature of the high-temperature austenitization treatment is 870° C., and the holding time of the high-temperature austenitization treatment is 30 min; the heating rate of heating to the high-temperature austenitization treatment temperature is 10° C. / min;

[0068] (2) subjecting the austenitized steel obtained in step (1) to isothermal quenching treatment in a salt bath, filtering off the salt stains on the surface, and finally cooling naturally in air for 30 minutes to obtain quenched steel; the salt bath contains flowing molten nitrate; the molten nitrate is prepared by heating and melting a mixture of potassium nitrate and sodium nitrate in a mass ratio of 1:1, and then controlling the temperature to be 300° C.; the isothermal quenching treatment is carried out at a holding temperature of 300° C. and for a time of 120 minutes; and the temperature of the steel is detected by an external infrared thermal imager during the isothermal quenching treatment;

[0069] (3) The quenched steel obtained in step (1) is tempered in a heat treatment furnace, and finally naturally cooled at room temperature to obtain a high-hardness and high-toughness steel; the holding temperature of the tempering treatment is 250° C., and the holding time of the tempering treatment is 120 min.

[0070] Comparative Example 1

[0071] A heat treatment process for steel with a "Gannan Drill" blade shape is:

[0072] (1) processing 45# steel into a "Gannan drill" blade shape, and then placing it in a high-temperature box furnace for high-temperature austenitization treatment to obtain an austenitized steel; the holding temperature of the high-temperature austenitization treatment is 870° C., and the holding time of the high-temperature austenitization treatment is 30 min; the heating rate of heating to the high-temperature austenitization treatment temperature is 10° C. / min;

[0073] (2) quenching the austenitized steel obtained in step (1), and then naturally cooling it in air for 30 minutes to obtain a quenched steel; the quenching medium is quenching oil, the quenching temperature is 80° C., and the quenching time is 30 minutes; during the quenching process, the temperature of the steel is detected by an external infrared thermal imager;

[0074] (3) The quenched steel obtained in step (1) is tempered in a heat treatment furnace, and finally naturally cooled at room temperature to obtain a "Gannan Drill" blade-shaped steel; the holding temperature of the tempering treatment is 300° C., and the holding time of the tempering treatment is 180 min.

[0075] Comparative Example 2

[0076] A heat treatment process for steel with a "Gannan Drill" blade shape is:

[0077] (1) processing 42CrMo steel into a "Gannan drill" blade shape, and then placing it in a high-temperature box furnace for high-temperature austenitization treatment to obtain an austenitized steel; the holding temperature of the high-temperature austenitization treatment is 870° C., and the holding time of the high-temperature austenitization treatment is 30 min; the heating rate to the high-temperature austenitization treatment temperature is 10° C. / min;

[0078] (2) quenching the austenitized steel obtained in step (1), and then naturally cooling it in air for 30 minutes to obtain a quenched steel; the quenching medium is quenching oil, the quenching temperature is 80° C., and the quenching time is 30 minutes; during the quenching process, the temperature of the steel is detected by an external infrared thermal imager;

[0079] (3) The quenched steel obtained in step (1) is tempered in a heat treatment furnace, and finally naturally cooled at room temperature to obtain a "Gannan Drill" blade-shaped steel; the holding temperature of the tempering treatment is 300° C., and the holding time of the tempering treatment is 180 min.

[0080] Comparative Example 3

[0081] A heat treatment process for steel with a "Gannan Drill" blade shape is:

[0082] (1) processing 40Cr steel into a "Gannan drill" blade shape, and then placing it in a high-temperature box furnace for high-temperature austenitization treatment to obtain an austenitized steel; the holding temperature of the high-temperature austenitization treatment is 870° C., and the holding time of the high-temperature austenitization treatment is 30 min; the heating rate of heating to the high-temperature austenitization treatment temperature is 10° C. / min;

[0083] (2) quenching the austenitized steel obtained in step (1), and then naturally cooling it in air for 30 minutes to obtain a quenched steel; the quenching medium is quenching oil, the quenching temperature is 80° C., and the quenching time is 30 minutes; during the quenching process, the temperature of the steel is detected by an external infrared thermal imager;

[0084] (3) The quenched steel obtained in step (1) is tempered in a heat treatment furnace, and finally naturally cooled at room temperature to obtain a "Gannan Drill" blade-shaped steel; the holding temperature of the tempering treatment is 300° C., and the holding time of the tempering treatment is 180 min.

[0085] The properties of the steels prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were tested, wherein the Rockwell hardness test standard was GB / T 230, the impact absorption energy test standard was GB / T 9096, and the test method for the drilling depth of the semi-weathered layer was as follows: the “Gannan Drill” blade-shaped steel was directly welded to the “Gannan Drill”, and then drilling was performed in the semi-weathered layer area, and other conditions during the drilling process were controlled to be the same, and the drilling depth of the semi-weathered layer was obtained as shown in Table 1:

[0086] Table 1 Properties of steels prepared in Examples 1 to 3 and Comparative Examples 1 to 3

[0087]

[0088] It can be seen from the comparison between Example 1 and Comparative Example 1, Example 2 and Comparative Example 2, and Example 3 and Comparative Example 3 in Table 1 that, for the same kind of steel, although the heat treatment process provided by the present invention will not significantly improve the hardness of the steel, it can significantly improve its impact absorption energy (i.e., toughness) while ensuring that the hardness remains basically unchanged or decreases slightly. When the obtained "Gannan Drill" blade is used for drilling in the semi-weathered layer, the excavation depth can be significantly improved; among them, when the steel is 45# steel, the drilling depth of the semi-weathered layer is improved by about 12.5%, and when the steel is 42CrMo steel or 40Cr steel, the toughness is improved by 30-35%, and the drilling depth of the semi-weathered layer is improved by 55-60%, which is a large improvement.

[0089] The microstructures of the steels prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were observed using an electron microscope. The results are as follows: Figures 1 to 6 As shown. Figures 1 to 6 It can be seen that after being processed by the heat treatment process provided by the present invention, the structure of the steel is mostly needle-shaped or bamboo-leaf-shaped (longer) bainite, and needle-shaped (shorter) martensite mixed therein, while the structure in the comparative example is mainly shorter needle-shaped martensite.

[0090] Figure 7 and Figure 8 They are transmission electron microscopy of the steel obtained in Example 2 at different magnifications, Fig. 9 and Fig.10 The following are transmission electron microscope images of the steel obtained in Comparative Example 2 at different magnifications. Figure 7 and Figure 8 It can be seen that bainite (B) and martensite (M) do exist in the steel obtained in Example 2, while Comparative Example 2 is mainly martensite (M) without bainite (B). Secondly, there is a small amount of residual austenite (Ar) in Example 2. The strength and hardness of the residual austenite are very low, but the toughness is relatively high. The presence of a small amount of residual austenite (Ar) is helpful to improve the toughness.

[0091] To sum up, after the "Gannan Drill" blade steel is treated with the "high-temperature austenitization-salt bath isothermal quenching-short-time low-temperature tempering" heat treatment process, the structure of the steel can be mainly bainite + martensite structure, so that the steel has both high hardness and toughness, and excellent comprehensive performance.

[0092] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A heat treatment process for high hardness and high toughness steel, comprising the following steps: (1) subjecting the steel to a high-temperature austenitizing treatment to obtain an austenitized steel; the holding temperature of the high-temperature austenitizing treatment is 850 to 900° C., and the holding time of the high-temperature austenitizing treatment is 20 to 60 minutes; (2) subjecting the austenitized steel obtained in step (1) to isothermal quenching and cooling in sequence to obtain a quenched steel; the isothermal quenching treatment is performed at a holding temperature of 260 to 300° C. and the isothermal quenching treatment time is 90 to 150 min; (3) The quenched steel obtained in step (1) is tempered to obtain a high-hardness and high-toughness steel.

2. The heat treatment process according to claim 1, characterized in that: The steel material in step (1) is 45# steel, 42CrMo steel or 40Cr steel.

3. The heat treatment process according to claim 1, characterized in that: Before the high-temperature austenitizing treatment in step (1), the steel is processed into a "Gannan drill" blade shape.

4. The heat treatment process according to claim 1, characterized in that: The holding temperature of the high-temperature austenitizing treatment in the step (1) is 870° C., and the holding time of the high-temperature austenitizing treatment is 30 minutes.

5. The heat treatment process according to claim 1, characterized in that: The holding temperature of the isothermal quenching treatment in step (2) is 280-300° C., and the time of the isothermal quenching treatment is 120 minutes.

6. The heat treatment process according to claim 1, characterized in that: The isothermal quenching treatment in step (2) is carried out in a salt bath, and the salt used in the salt bath is molten nitrate.

7. The heat treatment process according to claim 6, characterized in that: The molten nitrate is prepared by mixing potassium nitrate and sodium nitrate in a mass ratio of 1:

1.

8. The heat treatment process according to claim 1, characterized in that: The holding temperature of the tempering treatment in the step (3) is 220-250° C., and the holding time of the tempering treatment is 90-150 min.

9. The high-hardness and high-toughness steel material prepared by the heat treatment process according to any one of claims 1 to 8, wherein the structure of the high-hardness and high-toughness steel material is bainite + martensite + retained austenite structure.

10. Use of the high-hardness and high-toughness steel prepared by the heat treatment process according to any one of claims 1 to 8 or the high-hardness and high-toughness steel according to claim 9 in "Gannan Drill".

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