High-hardness and high-toughness steel for garden shears and preparation method of high-hardness and high-toughness steel

Abstract

The invention relates to high-hardness and high-toughness steel for garden shears and a preparation method, and belongs to the technical field of steel preparation. The steel for the garden shears comprises the following chemical components in percentage by mass: 0.65%-0.85% of C, 0.1%-0.4% of Si, 0.5%-0.9% of Mn, less than or equal to 0.015% of P, less than or equal to 0.005% of S, less than or equal to 0.05% of Al, less than or equal to 0.015% of N, 0.1%-0.5% of Cr, 0.05%-0.3% of Mo, 0.01%-0.08% of Nb and a matrix element Fe. Through reasonable chemical component design, the prepared steel for the garden shears has good properties of high hardness, high toughness and tempering softening resistance.

Description

Technical Field

[0001] The present application relates to the technical field of steel preparation, and in particular to a high-hardness and high-toughness steel for garden shears and a preparation method thereof. Background Art

[0002] Gardening shears refer to scissors used for pruning tree branches, flower branches, hedges, etc., including various types of flower shears, tree shears, hedge shears, etc. Gardening shears steel is the steel used to manufacture the scissors part of gardening shears.

[0003] Based on the service characteristics of gardening shears, the performance that gardening shears need to have includes the following aspects. First, high hardness. As a shearing tool, sufficient hardness can ensure sharpness, so that the scissors can effectively shear branches, flower branches and other plants. Second, high toughness. The shearing objects of the scissors are various naturally grown flower branches and branches. The internal tissues of the plants are uneven, and there is a risk of chipping or even breaking during the shearing process. Therefore, the steel needs to have high toughness and toughness. However, there is a contradictory relationship between high hardness and high toughness, which is reflected in the composition of steel and heat treatment process. In terms of steel composition, steel with a lower carbon content has better toughness, but lower hardness; while steel with a higher carbon content has higher hardness, but poorer toughness. In terms of heat treatment process, the tempering process can improve the toughness of the steel, but there will be tempering softening, which will cause the hardness of the steel to decrease. How to prepare scissors with both high hardness and high toughness is a difficult problem in the field of steel for gardening shears. Summary of the invention

[0004] The present application provides a high-hardness and high-toughness steel for gardening shears and a preparation method thereof, in order to solve the following technical problem: how to prepare steel for gardening shears having both hardness and toughness.

[0005] In a first aspect, an embodiment of the present application provides a high-hardness and high-toughness steel for gardening shears. The chemical composition of the steel for gardening shears, measured by mass fraction, includes: C: 0.65% to 0.85%, Si: 0.1% to 0.4%, Mn: 0.5% to 0.9%, P≤0.015%, S≤0.005%, Al≤0.05%, N≤0.015%, Cr: 0.1% to 0.5%, Mo: 0.05% to 0.3%, Nb: 0.01% to 0.08%, and matrix element Fe.

[0006] Optionally, the garden shears steel meets at least one of the following properties: hardness ≥ 55HRC, impact toughness ≥ 3.0J / cm 2 .

[0007] In a second aspect, the present application provides a method for preparing the high-hardness and high-toughness steel for garden shears described in the first aspect, the method comprising:

[0008] Obtain a continuous casting billet with the said chemical composition;

[0009] Subject the said continuous casting billet to heating, rolling, laminar flow cooling, coiling and slow cooling in sequence to obtain a hot rolled coil;

[0010] Subject the said hot rolled coil to pickling and annealing in sequence to obtain an annealed coil;

[0011] Subject the said annealed coil to heat treatment to obtain steel for gardening shears.

[0012] Optionally, the central segregation of the said continuous casting billet is ≤ level 1.0.

[0013] Optionally, the discharging temperature of the said heating is 1220°C to 1280°C, and the residence time in the furnace of the said heating is ≥ 180 min.

[0014] Optionally, the said rolling includes descaling before rough rolling, rough rolling, descaling before finish rolling and finish rolling; wherein, the finishing temperature of the said rough rolling is 1020°C to 1100°C, and the finishing temperature of the said finish rolling is 840°C to 900°C.

[0015] Optionally, the coiling temperature of the said coiling is 570°C to 670°C.

[0016] Optionally, the slow cooling time of the said slow cooling is 24 h to 96 h.

[0017] Optionally, the peak temperature of the said annealing is 690°C to 750°C.

[0018] Optionally, by volume fraction, the metallographic structure of the said hot rolled coil includes: ferrite: 0% to 5%, pearlite: 95% to 100%.

[0019] Optionally, the lamellar spacing of the said pearlite is 100 nm to 300 nm.

[0020] Optionally, the depth of the decarburized layer on one side of the said hot rolled coil is ≤ 1.5% of the plate thickness of the said steel for gardening shears.

[0021] Optionally, the metallographic structure of the said annealed coil includes ferrite and granular carbides distributed on the said ferrite, and the particle size of the said granular carbides is 1 μm to 2 μm.

[0022] The above technical solutions provided by the embodiments of the present application have the following advantages compared with the prior art:

[0023] An embodiment of the present application provides a steel for high-hardness and high-toughness gardening shears. In terms of mass fraction, the chemical composition of the steel for gardening shears includes: C: 0.65% - 0.85%, Si: 0.1% - 0.4%, Mn: 0.5% - 0.9%, P ≤ 0.015%, S ≤ 0.005%, Al ≤ 0.05%, N ≤ 0.015%, Cr: 0.1% - 0.5%, Mo: 0.05% - 0.3%, Nb: 0.01% - 0.08%, and the matrix element Fe. By precisely controlling the content of C, the steel has sufficient hardness and good toughness; adding Mn refines the steel structure, improves the steel strength, and increases the hardenability of the steel; adding Cr ensures the hardenability of the steel, ensuring that the steel obtains martensite structure from the surface to the core of the thickness after quenching heat treatment to have sufficient hardness; adding Mo resists the softening phenomenon of the steel during multiple tempering processes; through the combined action of Nb and other alloying elements, the original austenite structure during the heat treatment process and the carbide size during the tempering process are refined, and the carbide hardness is increased to improve wear resistance, ensuring that the steel has excellent properties with both high strength and high toughness after quenching and multiple tempering heat treatments. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings herein are incorporated into the specification and constitute a part of this specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0026] Figure 1 It is a schematic flow chart of a preparation method of a steel for high-hardness and high-toughness gardening shears provided by an embodiment of the present application;

[0027] Figure 2 It is the metallographic structure of a hot-rolled coil provided by an embodiment of the present application;

[0028] Figure 3 It is the metallographic structure of an annealed coil provided by an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0029] To make the objectives, technical solutions and advantages of the embodiments of this application clearer, the following will, with reference to the accompanying drawings in the embodiments of this application, clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the described embodiments are some but not all of the embodiments of this application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in this application without creative efforts shall fall within the scope of protection of this application.

[0030] The various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be construed as a rigid limitation on the scope of this application; therefore, it should be considered that the described range description has specifically disclosed all possible sub-ranges and individual values within that range; for example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and individual numbers within that range, such as 1, 2, 3, 4, 5, and 6, regardless of the range; additionally, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0031] In this document, terms such as "including" mean "including but not limited to". Relative terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. "And / or" describes the associated relationship of associated objects and indicates that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, or B exists alone; where A and B may be singular or plural. "At least one" means one or more, and "multiple" means two or more; "at least one kind", "at least one of the following items (pieces)" or similar expressions refer to any combination of these items, including any combination of single item (piece) or plural items (pieces); for example, "at least one of a, b, or c", or "at least one of a, b, and c" can both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively. "Part representation methods" such as weight parts and mass parts represent the proportional relationship between components. In the proportional relationships involved in this document, the parameters that need to be described by proportion should be understood as the antecedents of the proportional formula in the order of description, and the proportional numbers should be understood as the consequents of the proportional formula. For example, if the mass ratio of substance A, substance B, and substance C is 1:2:3, then substance A, substance B, and substance C should correspond one by one with the proportional numbers in the proportional formula in the order of description, that is, the mass of substance A: the mass of substance B: the mass of substance C = 1:2:3.

[0032] Unless otherwise specified, various raw materials, reagents, instruments, and equipment used in this article can be obtained through market purchases or can be prepared by existing methods.

[0033] In a first aspect, an embodiment of the present application provides a steel for high-hardness and high-toughness gardening shears. In terms of mass fraction, the chemical composition of the steel for gardening shears includes: C: 0.65% - 0.85%, Si: 0.1% - 0.4%, Mn: 0.5% - 0.9%, P ≤ 0.015%, S ≤ 0.005%, Al ≤ 0.05%, N ≤ 0.015%, Cr: 0.1% - 0.5%, Mo: 0.05% - 0.3%, Nb: 0.01% - 0.08%, and the matrix element Fe.

[0034] Positive effects of the mass fraction of C being 0.65% - 0.85%: Within this mass fraction range, it can ensure that the gardening shears prepared from the steel after heat treatment have sufficient hardness and good toughness. When the mass fraction of C is greater than the maximum value of the range endpoints, it will lead to an increase in brittleness and a higher risk of fracture after heat treatment of the steel; when the mass fraction of C is less than the minimum value of the range endpoints, it will lead to insufficient hardenability of the steel, too low hardness after heat treatment, and insufficient sharpness of the prepared gardening shears. Exemplarily, the mass fraction of C can be 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, etc.

[0035] Positive effects of the mass fraction of Si being 0.1% - 0.4%: Within this mass fraction range, it can ensure that the steel achieves a good solution strengthening effect, improves the hardenability, elastic limit, and tempering resistance of the steel. When the mass fraction is greater than the maximum value of the range endpoints, it will lead to an increase in the difficulty of controlling the surface quality of the steel, an increase in the adhesion force of the scale, making it difficult to remove, and resulting in surface quality problems after the scale is pressed in; when the mass fraction is less than the minimum value of the range endpoints, it will lead to insufficient solution strengthening effect and insufficient improvement in the toughness and tempering resistance of the steel. The mass fraction of Si can be 0.1%, 0.2%, 0.3%, 0.4%, etc.

[0036] Positive effects of the mass fraction of Mn being 0.5% - 0.9%: Within this mass fraction range, it can ensure that the steel has sufficient strength and hardenability. When the mass fraction is greater than the maximum value of the range endpoints, it will lead to an increase in the difficulty of controlling the surface quality of the steel, an increase in the adhesion force of the scale, making it difficult to remove, and resulting in surface quality problems after the scale is pressed in; when the mass fraction is less than the minimum value of the range endpoints, it will lead to insufficient solution strengthening effect and insufficient improvement in the toughness and tempering resistance of the steel. The mass fraction of Mn can be 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, etc.

[0037] Positive effects of P ≤ 0.015%: Within this mass fraction range, P generally dissolves in ferrite, with a strong solid solution strengthening effect, which can be used to increase the strength of the steel, thereby reducing the toughness of the steel. When the mass fraction exceeds the maximum value at the upper end of this range, excessive P will segregate at grain boundaries, weakening the grain boundaries and being unfavorable for welding performance. The mass fraction of P can be 0.03%, 0.05%, 0.07%, 0.09%, 0.011%, 0.013%, 0.015%, etc.

[0038] Positive effects of S ≤ 0.005%: Within this mass fraction range, excellent formability of the steel can be ensured. When the mass fraction exceeds the maximum value at the upper end of this range, a large amount of sulfides will form, and the size of the formed sulfides will be relatively large, which is unfavorable for the fatigue resistance of the steel. The mass fraction of S can be 0.001%, 0.002%, 0.003%, 0.004%, 0.005%, etc.

[0039] Positive effects of Al ≤ 0.05%: Al ≤ 0.05% as a deoxidizer can reduce the O content in the steel grade and inhibit the formation of oxide inclusions. When the mass fraction exceeds the maximum value at the upper end of this range, the graphitization tendency and decarburization sensitivity of the steel will increase. The mass fraction of Al can be 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, etc.

[0040] Positive effects of N ≤ 0.015%: Ensure the plasticity and toughness of the steel and control the formation of TiN inclusions. When the mass fraction exceeds the maximum value at the upper end of this range, the plasticity and toughness of the steel will be reduced, and the content of TiN inclusions will increase. The mass fraction of N can be 0.03%, 0.05%, 0.07%, 0.09%, 0.011%, 0.013%, 0.015%, etc.

[0041] Positive effects of Cr with a mass fraction of 0.1% - 0.5%: Within this mass fraction range, sufficient hardenability and good surface quality of the steel can be ensured. When the mass fraction exceeds the maximum value at the upper end of this range, it will increase the difficulty of controlling the surface quality of the steel, enhance the adhesion of scale, making it difficult to remove, resulting in surface quality problems after scale is pressed in. When the mass fraction is less than the minimum value at the lower end of this range, the hardenability of the steel will be insufficient, and martensite structure will not be formed in the core of the part thickness after heat treatment quenching. The mass fraction of Cr can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, etc.

[0042] The positive effect of Mo mass fraction of 0.05% to 0.3% is that within this mass fraction range, the steel can be guaranteed to have sufficient toughness and resistance to temper softening. When the mass fraction value is greater than the maximum value of the endpoint of the range, the steel cost will increase too much; when the mass fraction value is less than the minimum value of the endpoint of the range, the steel's resistance to temper softening will be insufficient, and the garden shears parts produced will be severely tempered and softened during the tempering stage, resulting in insufficient hardness of the finished product. The mass fraction of Mo can be 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, etc.

[0043] The positive effect of Nb mass fraction of 0.01% to 0.08% is that within this mass fraction range, the steel can be guaranteed to have fine structure and high wear resistance. When the mass fraction value is greater than the maximum value of the endpoint of the range, coarse micron-sized Nb-containing carbides will be formed, which is not conducive to toughness; when the mass fraction value is less than the minimum value of the endpoint of the range, it will not play a sufficient role in refining the structure and forming a sufficient number of Nb-containing carbides to improve the wear resistance of the steel. The mass fraction of Nb can be 0.01%, 0.03%, 0.05%, 0.07%, 0.08%, etc.

[0044] Fe is a matrix element. The specific content / content range of Fe can be obtained by the upper and lower limit formula of the component, that is:

[0045] The sum of the percentages of the contents of each component in a composition should be equal to 100%, and the content ranges of several components should meet the following conditions: the upper limit value of a component + the lower limit value of other components ≤ 100; the lower limit value of a component + the upper limit value of other components ≥ 100.

[0046] In some embodiments, the garden shears steel meets at least one of the following properties: hardness ≥ 55HRC, impact toughness ≥ 3.0J / cm 2 .

[0047] Figure 1 A schematic flow chart of a method for preparing high-hardness and high-toughness steel for garden shears provided in an embodiment of the present application.

[0048] See also Figure 1 In a second aspect, the present application provides a method for preparing the high-hardness and high-toughness steel for garden shears described in the first aspect, the method comprising:

[0049] S1, obtaining a casting billet having the chemical composition;

[0050] In some embodiments, the center segregation of the ingot is ≤ 1.0 level.

[0051] S2, sequentially heating, rolling, laminar cooling, coiling and slow cooling the ingot to obtain a hot-rolled coil;

[0052] In some embodiments, the tapping temperature of the heating is 1220°C to 1280°C, and the residence time of the heating in the furnace

[0053] ≥180 min.

[0054] In the embodiments of the present application, the positive effect of the tapping temperature of the heating being 1180°C to 1260°C is to ensure the uniformity of the overall temperature of the billet and prepare the austenite structure for hot rolling; when the value of the temperature is greater than the maximum value of the endpoints of this range, it will cause the austenite grains to be coarse, severe decarburization, and in severe cases, overheating and burning defects will occur; when the value of the temperature is less than the minimum value of the endpoints of this range, it will cause the temperature of the billet to be too low, increase the subsequent hot rolling resistance, and the uneven temperature of the billet will make the tissue properties of the steel uneven.

[0055] In some embodiments, the rolling includes descaling before rough rolling, rough rolling, descaling before finish rolling, and finish rolling; wherein, the finishing temperature of the rough rolling is 1020°C to 1100°C, and the finishing temperature of the finish rolling is 840°C to 900°C.

[0056] In the embodiments of the present application, the positive effect of the finishing temperature of the rough rolling being 1020°C to 1100°C is to ensure the reduction of the rough rolling and the temperature of the subsequent finish rolling; when the value of the temperature is greater than the maximum value of the endpoints of this range, the reduction of the rough rolling is limited, resulting in the rolling effect of the rough rolling not being suitable to meet the standard; when the value of the temperature is less than the minimum value of the endpoints of this range, the temperature of the subsequent finish rolling is too low, resulting in difficult rolling and unable to ensure suitable structure and properties.

[0057] The positive effect of the finishing temperature of the finish rolling being 840°C to 900°C is to make the rolling process match the deformation and temperature change process of the steel; when the value of the temperature is greater than the maximum value of the endpoints of this range, it will force the rolling speed to be too high, affecting the rolling stability and the subsequent cooling process, and thus affecting the properties of the steel; when the value of the temperature is less than the minimum value of the endpoints of this range, it will cause the deformation resistance to increase in the later stage of rolling, affecting the rolling stability and disturbing the phase transformation of the steel cooling process.

[0058] In some embodiments, the coiling temperature is 570°C to 670°C.

[0059] In the embodiments of the present application, the slab after finish rolling is subjected to laminar cooling and then coiled, and the coiling temperature is 570°C to 670°C. Within this coiling temperature range, the phase transformation of the steel can be controlled to prepare a suitable structure; when the value of the temperature is greater than the maximum value of the endpoints of this range, it will cause the phase transformation temperature to be too high, the structure to be coarse, and the target properties cannot be obtained; when the value of the temperature is less than the minimum value of the endpoints of this range, it will cause the phase transformation temperature to be too low, easily form upper bainite structure, the target properties cannot be obtained, and it will cause difficult coiling, and the hot rolled strip is prone to cracking problems.

[0060] In some embodiments, the slow cooling time is 24 h to 96 h.

[0061] In the embodiments of the present application, the positive effect of the slow cooling time being 24 h to 96 h is to release the internal stress in the steel and make the steel structure more uniform; when the value of the time is greater than the maximum value of the range of the endpoints, it will cause the evolution of the steel structure and affect the production rhythm; when the value of the time is less than the minimum value of the range of the endpoints, it will cause the steel structure to be non-uniform and the internal stress to be too large.

[0062] In some embodiments, by volume fraction, the metallographic structure of the hot-rolled coil includes: ferrite: 0% to 5%, pearlite: 95% to 100%.

[0063] The positive effect of the volume fraction of ferrite being 0% to 5%: Ferrite has good plasticity and preferentially deforms under external force conditions, reducing the brittleness of the steel and improving the plasticity and toughness of the steel; when the volume fraction value is greater than the endpoint value of the range, it will cause insufficient strength and hardness of the steel.

[0064] The positive effect of the volume fraction of pearlite being 95% to 100%: It provides sufficient carbon content to ensure the hardness of martensite after quenching of the steel, and the precipitation of a sufficient amount of fine carbides after tempering to ensure the strength and hardness of the steel; when the volume fraction value is less than the endpoint value of the range, it will cause insufficient hardenability of the steel and insufficient hardness.

[0065] In some embodiments, the lamellar spacing of the pearlite is 100 nm to 300 nm.

[0066] The positive effect of the lamellar spacing of pearlite being 100 nm to 300 nm: It ensures good subsequent spheroidizing annealing process performance; when the value of the lamellar spacing is greater than the endpoint value of the range, it will cause the structure to be coarse in the subsequent spheroidizing annealing process and heat treatment process, resulting in an increase in the brittleness of the steel; when the particle size value is less than the endpoint value of the range, it will cause the strength of the hot-rolled steel to be too high, resulting in difficult rolling and prone to edge cracking problems in hot-rolled strip steel.

[0067] In some embodiments, the depth of the single-sided decarburized layer of the hot-rolled coil ≤ 1.5% of the plate thickness of the steel for gardening shears.

[0068] In the embodiments of the present application, the depth of the single-sided decarburized layer of the hot-rolled coil ≤ 1.5% of the plate thickness of the steel for gardening shears is to ensure sufficient hardenability and hardenability on the surface of the steel; when the depth of the single-sided decarburized layer of the hot-rolled coil is greater than 1.5% of the plate thickness of the steel for gardening shears, it will cause insufficient hardenability on the surface of the steel, resulting in non-martensite structure or quenching soft spots on the surface, leading to uneven surface hardness and insufficient sharpness of the gardening shears.

[0069] S3. Successively pickle and anneal the hot-rolled coil to obtain an annealed coil;

[0070] In some embodiments, the peak temperature of the annealing is 690°C to 750°C.

[0071] In the embodiments of the present application, the positive effect of the peak temperature of the annealing being 690°C to 750°C is to prepare a suitable spheroidized pearlite structure. When the peak temperature of the annealing is greater than the maximum value of the range endpoints, over-spheroidization will occur, the carbide particles will be coarse, and a coarse lamellar structure may be formed; when the peak temperature of the annealing is less than the minimum value of the range endpoints, the spheroidization process cannot be promoted, and the spheroidization rate is too low.

[0072] In some embodiments, the metallographic structure of the annealed coil includes ferrite and granular carbides distributed on the ferrite, and the particle size of the granular carbides is 1 μm to 2 μm.

[0073] In the embodiments of the present application, the positive effect of the particle size of the granular carbides being 1 μm to 2 μm is to ensure the uniformity of the carbides in the annealed coil product, prepare the structure for subsequent heat treatment, and form austenite with uniform composition and suitable grain size during the heat treatment heating process; when the carbide particle size value is greater than the maximum value of the range endpoints, it will cause difficulty in carbide dissolution during the subsequent heat treatment heating process, form austenite with coarse grains, and even cause overheating; when the carbide particle size value is less than the minimum value of the range endpoints, it will cause non-uniform composition of the annealed coil product and form austenite structure with non-uniform grains during subsequent heat treatment.

[0074] S4. Heat-treat the annealed coil to obtain steel for gardening shears.

[0075] In the embodiments of the present application, the heat treatment includes quenching and multiple tempering heat treatments.

[0076] The product prepared by the preparation method of the high-hardness and high-toughness steel for gardening shears is the above-mentioned high-hardness and high-toughness steel for gardening shears. Since the preparation method of the high-hardness and high-toughness steel for gardening shears adopts some or all of the technical solutions of the embodiments of the high-hardness and high-toughness steel for gardening shears, it at least has all the beneficial effects brought by the technical solutions of the embodiments of the high-hardness and high-toughness steel for gardening shears, which will not be elaborated one by one here.

[0077] The following further elaborates the present application in combination with specific embodiments. For the experimental methods without specific conditions indicated in the following embodiments, they are usually determined according to national standards / industry standards; if there are no corresponding national standards / industry standards, they are carried out according to general international standards, conventional conditions, or the conditions recommended by the manufacturer.

[0078] Example 1

[0079] After the hot metal is pretreated, converter smelting, LF refining, RH refining and continuous casting are carried out in sequence to obtain a slab. By mass fraction, the chemical composition of the slab includes: C: 0.74%, Si: 0.26%, Mn: 0.69%, P: 0.011%, S: 0.002%, Al: 0.02%, N: 0.006%, Cr: 0.34%, Mo: 0.09%, Nb: 0.021%, and the matrix element Fe.

[0080] Based on the chemical composition of the slab, this embodiment also provides a preparation method of steel for high-hardness and high-toughness gardening shears, including the following steps:

[0081] Obtain a slab with the said chemical composition;

[0082] Heat, roll, cool, coiling and slow cooling the said slab in sequence to obtain a hot-rolled coil;

[0083] Pickle and anneal the said hot-rolled coil in sequence to obtain an annealed coil;

[0084] Heat-treat the said annealed coil to obtain the steel for gardening shears.

[0085] The tapping temperature of heating is 1260 °C, and the residence time in the furnace for heating is 220 min; the finishing rolling temperature of rough rolling is 1080 °C, and the finishing rolling temperature of finish rolling is 880 °C; the cooling is laminar flow cooling, and the coiling temperature is 600 °C; the slow cooling time is 72 h; the peak temperature of annealing is 730 °C.

[0086] Example 2

[0087] Compare Example 2 with Example 1. The differences between Example 2 and Example 1 are as follows:

[0088] By mass fraction, the chemical composition of the slab includes: C: 0.73%, Si: 0.21%, Mn: 0.67%, P: 0.010%, S: 0.001%, Al: 0.02%, N: 0.006%, Cr: 0.36%, Mo: 0.1%, Nb: 0.022%, and the matrix element Fe.

[0089] The tapping temperature of heating is 1220 °C, and the residence time in the furnace for heating is 180 min; the finishing rolling temperature of rough rolling is 1020 °C, and the finishing rolling temperature of finish rolling is 840 °C; the cooling is laminar flow cooling, and the coiling temperature is 570 °C; the slow cooling time is 24 h; the peak temperature of annealing is 720 °C.

[0090] Example 3

[0091] Compare Example 3 with Example 1. The differences between Example 3 and Example 1 are as follows:

[0092] By mass fraction, the chemical composition of the continuous casting billet includes: C: 0.77%, Si: 0.28%, Mn: 0.73%, P: 0.010%, S: 0.001%, Al: 0.02%, N: 0.006%, Cr: 0.38%, Mo: 0.1%, Nb: 0.018%, and the matrix element Fe.

[0093] The heating tapping temperature is 1280 °C, and the heating holding time is 250 min; the finishing rolling temperature of rough rolling is 1100 °C, and the finishing rolling temperature of finish rolling is 900 °C; the cooling is laminar cooling, and the coiling temperature is 670 °C; the slow cooling time is 96 h; the peak temperature of annealing is 750 °C.

[0094] Comparative Example 1

[0095] Compare Comparative Example 1 with Example 1. The differences between Comparative Example 1 and Example 1 are as follows:

[0096] Select a commonly used steel 55MnB for gardening shears as the comparative example.

[0097] By mass fraction, the chemical composition of the continuous casting billet includes: C: 0.56%, Si: 0.30%, Mn: 0.81%, P: 0.019%, S: 0.005%, Al: 0.037%, Cr: 0.12%, B: 0.0025%, and the matrix element Fe.

[0098] Comparative Example 2

[0099] Compare Comparative Example 2 with Example 1. The differences between Comparative Example 2 and Example 1 are as follows:

[0100] Select a commonly used steel SK85 for gardening shears as the comparative example.

[0101] By mass fraction, the chemical composition of the continuous casting billet includes: C: 0.87%, Si: 0.21%, Mn: 0.43%, P: 0.014%, S: 0.003%, Al: 0.02%, Cr: 0.10%, and the matrix element Fe.

[0102] Comparative Example 3

[0103] Compare Comparative Example 3 with Example 1. The differences between Comparative Example 3 and Example 1 are as follows:

[0104] Do not add Mo and Nb alloys.

[0105] Comparative Example 4

[0106] Compare Comparative Example 4 with Example 1. The differences between Comparative Example 4 and Example 1 are as follows:

[0107] The heated tapping temperature is 1300 °C; the final rolling temperature in rough rolling is 1120 °C, and the final rolling temperature in finish rolling is 930 °C; the cooling is laminar cooling, and the coiling temperature is 750 °C.

[0108] The performance of the steel products obtained in Examples 1-3 and Comparative Examples 1-4 was tested respectively, and the results are shown in Table 1.

[0109] Related test methods:

[0110] Decarburized layer depth: The decarburized layer depth of hot-rolled strip steel was determined by the metallographic method specified in GB / T 224-2019 "Determination Method for Decarburized Layer Depth of Steel".

[0111] Hardness: The Rockwell hardness HRC of the finished steel products after heat treatment was measured according to the method specified in GB / T 230.1-2018 "Rockwell Hardness Test for Metallic Materials".

[0112] Impact toughness: The impact toughness of the finished steel products after heat treatment was measured according to the method specified in GB / T 229-2020 "Charpy Pendulum Impact Test Method for Metallic Materials".

[0113] Shearing life: According to the method for garden shears specified in the test method of garden shear manufacturing enterprises, the number of shearing times of the shears for a specific material was measured.

[0114] Table 1

[0115]

[0116] Hardness is the most important performance index of garden shear products. As a cutting tool, hardness is positively correlated with sharpness. The higher the hardness value, the higher the sharpness of the garden shear.

[0117] Impact toughness refers to the ability of a material to absorb plastic deformation work and fracture work under impact load, and is an index characterizing the occurrence of edge chipping and brittle fracture of garden shears during actual use. The higher the impact toughness value, the better the toughness of the garden shear.

[0118] Shearing life is the number of successful shearing times of the garden shear on a specific cylindrical wood tested in the laboratory. When the sharpness of the shear edge is reduced to a certain extent, the wood cannot be sheared smoothly. The higher the number of shearing times, the longer the life of the shear and the more durable the shear.

[0119] As can be seen from Table 1, the chemical compositions and preparation process parameters of Examples 1-3 are all within the required range of the present invention, and the steel has good microstructure and properties.

[0120] From the data of Comparative Examples 1-4:

[0121] Rational chemical composition design is the primary condition to ensure the performance of steel for gardening shears. Steel with too low carbon content generally exhibits the performance characteristics of "good toughness but low hardness", while steel with too high carbon content generally shows the characteristics of "high hardness but poor toughness". And steel with moderate carbon content but lacking effective microalloy strengthening generally presents the characteristics of "low hardness and poor toughness".

[0122] Rational and strict rolling and annealing processes are necessary conditions to ensure the microstructure and properties of steel. Exceeding the reasonable process range will bring defects in microstructure and properties.

[0123] Appendix Figures 2-3 detailed description:

[0124] Figure 2 is the metallographic structure of the hot-rolled coil provided by the embodiment of the present application; as Figure 2 shown, the structure is a very small amount of proeutectoid ferrite and pearlite, and the proportion of pearlite is 97%. The lamellae inside the pearlite are fine and dense, within the range of sorbite, and it is difficult to distinguish the lamella details under the optical microscope.

[0125] Figure 3 is the metallographic structure of the annealed coil provided by the embodiment of the present application; as Figure 3 shown, the structure is granular carbides distributed on a ferrite matrix, and the average particle size of the carbides is 1.3 μm.

[0126] One or more technical solutions in the embodiments of the present invention at least further have the following technical effects or advantages:

[0127] (1) The steel provided by the embodiment of the present invention not only has the mechanical properties of both high strength and high toughness, but also has the property uniformity of uniform hardness without soft spots.

[0128] (2) The steel prepared by the method of the embodiment of the present invention maintains good sharpness during the whole service process and has a long service life after being further processed into gardening shears.

[0129] (3) The steel provided by the embodiment of the present invention can still maintain the excellent properties of high strength and high toughness after quenching and multiple tempering heat treatments, and is very suitable for manufacturing gardening tools such as gardening shears that require high hardness, high toughness and anti-tempering softening properties.

[0130] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art. The general principles defined in the present application can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown in the present application, but will conform to the widest scope consistent with the principles and novel features claimed in the present application.

Claims

1. A high-hardness and high-toughness steel for garden shears, wherein the chemical composition of the steel for garden shears comprises, by mass fraction: C： 0.65%~0.85%, Si: 0.1%~0.4%, Mn: 0.5%~0.9%, P≤0.015%, S≤0.005%, Al≤0.05%, N≤0.015%, Cr: 0.1%~0.5%, Mo: 0.05%~0.3%, Nb: 0.01%~0.08%, and matrix element Fe.

2. The garden shears steel according to claim 1, characterized in that: The garden shears steel meets at least one of the following properties: hardness ≥ 55HRC, impact toughness ≥ 3.0J / cm 2 .

3. A method for preparing the steel for garden shears according to claims 1 to 2, the method comprising: Obtaining a casting billet having the chemical composition; The ingot is sequentially heated, rolled, laminar cooled, coiled and slowly cooled to obtain a hot-rolled coil; The hot-rolled coil is pickled and annealed in sequence to obtain an annealed coil; The annealed coil is heat treated to obtain steel for garden shears.

4. The method according to claim 3, characterized in that The central segregation of the ingot is ≤1.0 level.

5. The method according to claim 3, characterized in that: The heating furnace temperature is 1220°C to 1280°C, and the heating furnace time is ≥180min; and / or, The rolling process includes descaling before rough rolling, rough rolling, descaling before finish rolling and finish rolling; wherein, The final rolling temperature of the rough rolling is 1020°C to 1100°C, and the final rolling temperature of the fine rolling is 840°C to 900°C.

6. The method according to claim 3, characterized in that The coiling temperature is 570°C to 670°C; and / or, The slow cooling time is 24h to 96h; and / or, The peak temperature of the annealing is 690°C to 750°C.

7. The method according to claim 3, characterized in that Measured by volume fraction, the metallographic structure of the hot-rolled coil includes: ferrite: 0% to 5%, pearlite: 95% to 100%.

8. The method according to claim 7, characterized in that The interlamellar spacing of the pearlite is 100nm to 300nm.

9. The method according to claim 3, characterized in that: The single-side decarburization layer depth of the hot-rolled coil is ≤1.5% of the plate thickness of the garden shears steel.

10. The method according to claim 3, characterized in that The metallographic structure of the annealed coil includes ferrite and granular carbides distributed on the ferrite, and the particle size of the granular carbides is 1 μm to 2 μm.

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