A heat treatment method for a V+N micro-alloyed high manganese steel frog

Abstract

A heat treatment method for V+N microalloyed high-manganese steel frogs is provided, comprising the following steps: segmented heating and heat preservation; water toughening treatment; and aging treatment. The water toughening process involves controlling the time from when the frog is removed from the furnace after segmented heating and heat preservation to when it is immersed in water to no more than 100 seconds, and then water-cooling to below 400°C followed by air cooling to room temperature or direct water cooling to room temperature. This invention effectively improves the strength of V+N microalloyed high-manganese steel frogs without compromising their toughness, and also extends their service life.

Description

Technical Field

[0001] This invention belongs to the field of chemical metallurgical heat treatment technology, specifically relating to a heat treatment method for V+N microalloyed high manganese steel turnouts. Background Technology

[0002] As a major mode of transportation in the world, railways play an important role in national economic development and our lives. The frog, as a special structure in the railway track, is the intersection of the main line and the branch line, and it plays a key role in railway transportation.

[0003] High-manganese steel is dominant in railway frog selection. It is a special wear-resistant steel with a carbon content of 1.0% to 1.4% and a manganese content of 11% to 14%. The traditional heat treatment of high-manganese steel, also known as water quenching, involves heating the high-manganese steel to about 1050 to 1100°C and then water quenching it to room temperature to obtain a single-phase austenitic structure.

[0004] However, this traditional heat treatment method cannot fully utilize the role of microalloying elements, and the austenitic structure obtained after water quenching of high-manganese steel, with its face-centered cubic crystal structure, makes it difficult to significantly improve its yield strength. Water-quenched high-manganese steel frogs exhibit relatively low yield strength and matrix hardness, failing to meet the requirements of modern railways operating at high speeds, under heavy loads, and in harsh conditions.

[0005] With social development and the increase in railway transportation speed, people have put forward higher requirements for the mechanical performance and service life of railway frogs. Improving the strength and toughness of high manganese steel is of great significance for improving the service life of railway frogs.

[0006] In the existing technology, the patent with publication number CN101429590 proposes a high manganese steel composition design and heat treatment process. The process involves holding at 600-850℃ for 0.1-1 hours and cooling to room temperature at a cooling rate of 5-100℃ / s. The microalloying element utilization efficiency of this process is very low.

[0007] Patent CN104975145A discloses a heat treatment method for microalloyed high-manganese steel. The process involves heating the microalloyed high-manganese steel to 900–1200°C, holding it at that temperature for 15–30 minutes, cooling it to 480–600°C at a cooling rate of 40–65°C / s, and holding it at that temperature for 15–30 minutes; or heating the microalloyed high-manganese steel to 900–1200°C, holding it at that temperature for 15–30 minutes, water quenching it to room temperature, and then tempering it at 480–600°C for 15–30 minutes. This process easily leads to a decrease in the toughness of the high-manganese steel.

[0008] V+N microalloying promotes the precipitation of a large number of V(C,N) nanoclusters in the high-manganese steel matrix, which can significantly improve the yield strength of high-manganese materials. However, at the same time, these elements can also easily lead to the formation of overheated carbides and undissolved carbides. Therefore, the heat treatment process of the novel V+N microalloyed high-manganese steel turnout must be adjusted and strictly controlled to maximize the strength-enhancing effect of the alloying elements while avoiding the formation of harmful structures. The following technical solution is proposed to address this issue. Summary of the Invention

[0009] The technical problem solved by this invention is to provide a heat treatment method for V+N microalloyed high manganese steel frogs, which solves the technical problem of how to improve the strength of V+N microalloyed high manganese steel frogs without damaging their toughness and improving their service life.

[0010] The technical solution adopted in this invention is a heat treatment method for V+N microalloyed high-manganese steel frogs, comprising the following steps:

[0011] S001, Segmented heating and insulation: The cast alloyed high manganese steel turnout is heated and insulated in segments.

[0012] S002, Water cooling treatment: The time from opening the furnace door to the frog entering the water after the segmented heating and insulation is controlled to be no more than 100 seconds, and the water cooling is cooled to below 400℃ and then air-cooled to room temperature or directly water-cooled to room temperature.

[0013] S003. Aging treatment: Heat the water-treated turnout to 400-500℃ and age it for 2-4 hours.

[0014] In the above technical solution, furthermore: the chemical composition and mass percentage of the V+N microalloyed high-manganese steel frog are as follows: C: 0.6-1.2, Mn: 14.0-19.0, Cr: 1.0-2.5, Mo: 0.5-1.2, V: 0.3-0.5, Si: 0.3-0.7, N: 0.008-0.016, P: ≦0.035, S: ≦0.03, with the remainder being Fe, and the stacking fault energy of the V+N microalloyed frog steel is 15-45 mJ / m. 2 .

[0015] In the above technical solution, further: step S001, segmented heating and heat preservation, includes the following steps:

[0016] S101: Place the cast alloyed high manganese steel frog into a resistance furnace or gas heating furnace with a furnace temperature not exceeding 300℃, and preheat it to 600-800℃ at a heating rate not exceeding 80℃ per hour for 2-3 hours.

[0017] S102: After the heat preservation is completed, the temperature is raised to 1050-1100℃ at a rate of no more than 200℃ per hour for water-cooled heating and heat preservation for 2-5 hours.

[0018] In the above technical solution, further: the V+N microalloyed high manganese steel frog structure after heat treatment according to the method is an austenitic matrix and a large number of nano- to micron-sized carbonitrides dispersed on the austenitic matrix.

[0019] In the above technical solution, further: the V+N microalloyed high manganese steel turnout after heat treatment according to the method is rated according to GB / T13925-2010 standard: overheated carbides ≤ G2 grade, undissolved carbides ≤ W3 grade, precipitated carbides ≤ X3 grade; the size of precipitated carbonitrides is below 50nm.

[0020] In the above technical solution, the mechanical properties of V+N microalloyed high manganese steel turnouts after heat treatment according to the method are: yield strength ≥500MPa, tensile strength ≥800MPa, elongation ≥40%, and impact value (20℃) ≥200J.

[0021] Advantages of this invention compared to existing technologies:

[0022] 1. The heat treatment method of the present invention can avoid cracking of the fork during the heating process, and at the same time can avoid excessive levels of overheated carbides, undissolved carbides and precipitated carbides in the structure after heat treatment.

[0023] 2. The heat treatment method of this invention can promote the dispersed precipitation of a large number of nano-sized precipitates in the high-manganese steel matrix. These precipitates significantly improve the yield strength of the high-manganese steel fork by hindering dislocation movement, while also inhibiting twin formation and increasing the critical stress for twin formation. This promotes twin formation at higher strains, allowing the material to undergo continuous strain hardening over a wider strain range, resulting in high toughness. Furthermore, the V and N-promoted nano-carbonitrides can inhibit the formation of deformation twins, while a reasonable stacking fault energy design allows the alloy to generate a large number of deformation twins during deformation. Therefore, the dispersed precipitation of nano-carbonitrides results in very fine deformation twins, which is beneficial for improving the strength and toughness of the alloy material.

[0024] 3. This invention improves the strength of V+N microalloyed high manganese steel frogs without damaging their toughness, and also increases their service life. Detailed Implementation

[0025] The technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] Example 1:

[0027] A heat treatment method for V+N microalloyed high-manganese steel frogs includes the following steps:

[0028] Step S001, Segmented Heating and Heat Preservation: The cast alloyed high-manganese steel frog is heated and heat-preserved in segments. In the above embodiment, further, step S001, segmented heating and heat preservation, includes the following steps: Step S101: The cast alloyed high-manganese steel frog is placed in a resistance furnace or gas-fired furnace with a furnace temperature not exceeding 300°C, and preheated to 650°C at a heating rate of 60°C per hour for 2 hours. Step S102: After heat preservation, the temperature is further increased to 1070°C at a heating rate of 150°C per hour for 2 hours of water quenching.

[0029] Step S002, Water tempering treatment: The time from opening the furnace door to the water entry of the frog after segmented heating and heat preservation is controlled within 55 seconds, and the water tempering is cooled to room temperature.

[0030] Step S003, Aging Treatment: Heat the water-treated turnout to 450℃ and aging it for 2.5 hours.

[0031] In the above embodiments, furthermore: the chemical composition and mass percentage of the V+N microalloyed high-manganese steel frog are: C: 1.1, Mn: 15.3, Cr: 2.1, Mo: 0.6, V: 0.4, Si: 0.35, N: 0.016, with the remainder being Fe, and the stacking fault energy of the V+N microalloyed frog steel is 42 mJ / m 2 .

[0032] Example 2:

[0033] A heat treatment method for V+N microalloyed high-manganese steel frogs includes the following steps:

[0034] Step S001, Segmented Heating and Heat Preservation: The cast alloyed high-manganese steel frog is heated and heat-preserved in segments. In the above embodiment, further: Step S001, the segmented heating and heat preservation includes the following steps: Step S101: The cast alloyed high-manganese steel frog is placed in a resistance furnace or gas-fired furnace with a furnace temperature not exceeding 300°C, and preheated to 700°C at a heating rate of 40°C per hour for 3 hours. Step S102: After the heat preservation is completed, the temperature is further increased to 1100°C at a heating rate of 130°C per hour for 2.5 hours of water-cooled heating and heat preservation.

[0035] Step S002, Water tempering treatment: The time from opening the furnace door to the frog entering the water after the segmented heating and heat preservation is controlled within 80 seconds, and the water tempering is cooled to 450℃ and then air-cooled to room temperature.

[0036] Step S003, Aging treatment: Heat the water-treated turnout to 400℃ and age it for 5 hours.

[0037] In the above embodiments, furthermore: the chemical composition and mass percentage of the V+N microalloyed high-manganese steel frog are: C: 0.7, Mn: 14.7, Cr: 1.0, Mo: 1.0, V: 0.35, Si: 0.55, N: 0.008, with the remainder being Fe, and the stacking fault energy of the V+N microalloyed frog steel is 18 mJ / m 2 .

[0038] Example 3:

[0039] A heat treatment method for V+N microalloyed high-manganese steel frogs includes the following steps:

[0040] Step S001, Segmented Heating and Heat Preservation: The cast alloyed high-manganese steel frog is heated and heat-preserved in segments. In the above embodiment, further: Step S001, the segmented heating and heat preservation includes the following steps: Step S101: The cast alloyed high-manganese steel frog is placed in a resistance furnace or gas-fired furnace with a furnace temperature not exceeding 300°C, and preheated to 750°C at a heating rate of 40°C per hour for 3 hours. Step S102: After the heat preservation is completed, the temperature is further increased to 1050°C at a heating rate of 110°C per hour for 5 hours of water-cooled heating and heat preservation.

[0041] Step S002, Water tempering treatment: The time from opening the furnace door to the frog entering the water after the segmented heating and heat preservation is controlled within 88 seconds, and the water tempering is cooled to room temperature.

[0042] Step S003, Aging Treatment: Heat the water-treated turnout to 500℃ and aging it for 3.5 hours.

[0043] In the above embodiments, furthermore: the chemical composition and mass percentage of the V+N microalloyed high-manganese steel frog are: C: 0.9, Mn: 18.2, Cr: 2.5, Mo: 1.2, V: 0.3, Si: 0.68, N: 0.008, with the remainder being Fe, and the stacking fault energy of the V+N microalloyed frog steel is 23 mJ / m 2 .

[0044] The mechanical properties and metallographic structure ratings of the V+N microalloyed high manganese steel turnouts prepared in specific embodiments 1-3 of this invention are shown in Table 1.

[0045] Table 1

[0046]

[0047] In any of the above embodiments, further: the V+N microalloyed high manganese steel frog structure after heat treatment according to the method is an austenitic matrix and a large number of nano- to micron-sized carbonitrides dispersed on the austenitic matrix.

[0048] In any of the above embodiments, further: the V+N microalloyed high manganese steel turnouts heat-treated according to the method are rated according to GB / T13925-2010 standard: overheated carbides ≤ G2 grade, undissolved carbides ≤ W3 grade, precipitated carbides ≤ X3 grade; the size of precipitated carbonitrides is less than 50nm.

[0049] In any of the above embodiments, further: the mechanical properties of V+N microalloyed high manganese steel turnouts after heat treatment according to the method are: yield strength ≥500MPa, tensile strength ≥800MPa, elongation ≥40%, impact value (20℃) ≥200J.

[0050] As can be seen from the above description, the heat treatment method of the present invention can avoid cracking of the fork during the heating process, and at the same time, it can avoid excessive levels of overheated carbides, undissolved carbides and precipitated carbides in the tissue after heat treatment.

[0051] Furthermore, the heat treatment method of the present invention can promote the dispersion of a large number of nanoscale precipitates in the high manganese steel matrix. On the one hand, the precipitates significantly improve the yield strength of the high manganese steel fork by hindering dislocation movement, and on the other hand, they also inhibit the formation of twins, increase the critical stress for the formation of twins, and promote the formation of twins at higher strains, thereby enabling the material to continuously strain harden within a larger strain range and obtain high toughness.

[0052] In summary, this invention improves the strength of V+N microalloyed high manganese steel frogs without compromising their toughness, and also increases their service life.

[0053] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A heat treatment method for V+N microalloyed high-manganese steel frogs, characterized in that, Includes the following steps: Step S001, Segmented heating and heat preservation: The cast alloyed high manganese steel turnout is heated and heat-preserved in segments; Step S002, Water tempering treatment: The time from opening the furnace door to the frog entering the water after the segmented heating and heat preservation is controlled to be no more than 100 seconds, and the water tempering is cooled to room temperature. Step S003, Aging treatment: Heat the water-cooled turnout to 400-500℃ and age it for 2-4 hours; Step S001 includes the following steps: Step S101: Place the cast alloyed high manganese steel fork into a resistance furnace or gas heating furnace with a furnace temperature not exceeding 300℃, and preheat it to 600-800℃ at a heating rate not exceeding 80℃ per hour for 2-3 hours. Step S102: After the heat preservation is completed, the temperature is raised to 1050-1100℃ at a rate of no more than 200℃ per hour for water quenching and heat preservation for 2-5 hours. The chemical composition and mass percentage of the V+N microalloyed high-manganese steel frog are as follows: C: 0.6-1.2, Mn: 14.0-19.0, Cr: 1.0-2.5, Mo: 0.5-1.2, V: 0.3-0.5, Si: 0.3-0.7, N: 0.008-0.016, P: ≦0.035, S: ≦0.03, with the remainder being Fe; The V+N microalloyed frog steel has a stacking fault energy of 15-45 mJ / m 2 .

2. The heat treatment method for V+N microalloyed high-manganese steel turnouts according to claim 1, characterized in that: The V+N microalloyed high-manganese steel frog structure after heat treatment according to the method consists of an austenitic matrix and a large number of nano- to micron-sized carbonitrides dispersed on the austenitic matrix.

3. The heat treatment method for V+N microalloyed high-manganese steel turnouts according to claim 1, characterized in that, According to the method described above, V+N microalloyed high-manganese steel turnouts heat-treated according to the following standards are graded as follows: overheated carbides ≤ G2 grade, undissolved carbides ≤ W3 grade, precipitated carbides ≤ X3 grade; precipitated carbonitrides are less than 50 nm in size.

4. The heat treatment method for V+N microalloyed high-manganese steel turnouts according to claim 1, characterized in that, Mechanical properties of V+N microalloyed high manganese steel turnouts after heat treatment according to the method described: yield strength ≥500MPa, tensile strength ≥800MPa, elongation ≥40%, impact value ≥200J at 20℃.

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