Grain refining process of 20Cr1Mo1VTiB steel and bolt

Abstract

The invention discloses a grain refinement process of 20Cr1Mo1VTiB steel and a bolt. The grain refinement process comprises the following steps: preparing a grain refinement agent; the method comprises the following steps: (1) isothermal normalizing: S1, heating a quenched and tempered coarse grain bolt to 950-980 DEG C, and preserving heat for 3-5 hours; s2, discharging, cooling to 720 + / -10 DEG C at a cooling speed of not less than 250 DEG C / h, and preserving heat for 3-5 hours; s3, discharging and air-cooling to room temperature; (2) quenching and tempering: quenching and high-temperature tempering: S4, heating the bolt to 700 DEG C + / -10 DEG C, and preserving heat for 2-2.5 hours; s5, the temperature is increased to 970-1000 DEG C, and heat preservation is conducted for 0.5-1 h; s6, discharging and water-cooling to room temperature; s7, heating to 700-710 DEG C, preserving heat for 5-8 hours, discharging from the furnace, and air-cooling to room temperature; according to the scheme, the problems that coarse grains appear after existing bolt quenching and tempering treatment, and the grain refining effect of a conventional heat treatment mode is poor can be solved.

Description

Technical Field

[0001] The invention relates to the technical field of engineering materials, and in particular to a grain refinement process of 20Cr1Mo1VTiB steel and a bolt. Background Art

[0002] 20Cr1Mo1VTiB steel is a high-temperature bolt steel developed by my country. It has good comprehensive mechanical properties, anti-relaxation performance and thermal strength. Due to the addition of stable carbide elements V and Ti, and the use of B to strengthen the grain boundary, it not only has high long-lasting strength, but also has high long-lasting plasticity. With the development of high-temperature and high-pressure units, more and more of this material is used. However, this material often has coarse grains after quenching and tempering. The existing conventional grain refinement process cannot completely solve the problem of coarse grains and cannot meet the use requirements of some occasions (grain size ≧ 5 levels). Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a grain refining process for 20Cr1Mo1VTiB steel, which can solve the problem that coarse grains appear after the existing bolt tempering treatment, and the grain refining effect of the conventional heat treatment method is poor.

[0004] The present invention adopts the following technical solutions:

[0005] A grain refinement process for 20Cr1Mo1VTiB steel, comprising:

[0006] (1) Isothermal normalizing

[0007] S1: Heat the quenched and tempered coarse-grained bolts to a temperature of 950°C-980°C and keep them warm for 3h-5h;

[0008] S2: Cool down to 720℃±10℃ at a cooling rate of ≥250℃ / h after exiting the furnace, and keep warm for 3h-5h;

[0009] S3: Take out of the oven and cool to room temperature;

[0010] (2) Tempering treatment is quenching and high temperature tempering

[0011] S4: Heat the bolts to 700℃±10℃ and keep them warm for 2h-2.5h;

[0012] S5: Heat to 970℃-1000℃, keep warm for 0.5h-1h;

[0013] S6: Take out of the furnace and cool to room temperature;

[0014] S7: Heat to 700℃-710℃, keep warm for 5h-8h, take out of the furnace and air cool to room temperature.

[0015] As a preferred method, S1: heating the quenched and tempered coarse-grained bolts to a temperature of 965°C and keeping the temperature for 4 hours; S2: cooling the bolts to 720°C at a cooling rate of ≧250°C / h after being taken out of the furnace and keeping the temperature for 4 hours;

[0016] S3: Take out of the oven and cool to room temperature;

[0017] S4: Heat the bolt to 700°C and keep it at this temperature for 2.3h;

[0018] S5: Heat to 985°C and keep warm for 0.75h;

[0019] S6: Take out of the furnace and cool to room temperature;

[0020] S7: Heat to 705℃, keep warm for 6.5h, remove from the furnace and air cool to room temperature.

[0021] As a preferred method, S1: heating the quenched and tempered coarse-grained bolts to 980°C and keeping the temperature for 3 hours; S2: cooling the bolts to 720°C at a cooling rate of ≧250°C / h after being taken out of the furnace and keeping the temperature for 3 hours;

[0022] S3: Take out of the oven and cool to room temperature;

[0023] S4: Heat the bolt to 700°C and keep it at this temperature for 2h;

[0024] S5: Heat to 1000°C and keep warm for 0.5h;

[0025] S6: Take out of the furnace and cool to room temperature;

[0026] S7: Heat to 710℃, keep warm for 5h, remove from the furnace and air cool to room temperature.

[0027] As a preferred method, S1: heating the quenched and tempered coarse-grained bolts to 950°C and keeping the temperature for 5 hours; S2: cooling the bolts to 720°C at a cooling rate of ≧250°C / h after being taken out of the furnace and keeping the temperature for 5 hours;

[0028] S3: Take out of the oven and cool to room temperature;

[0029] S4: Heat the bolt to 700°C and keep it warm for 2.5h;

[0030] S5: Heat to 970°C and keep warm for 1h;

[0031] S6: Take out of the furnace and cool to room temperature;

[0032] S7: Heat to 700℃, keep warm for 8h, take out of the furnace and air cool to room temperature.

[0033] Compared with the prior art, the present invention has the following advantages: the coarse-grained 20Cr1Mo1VTiB bolt is heated to a higher temperature than the conventional normalizing process and kept warm, so that the coarse-grained bolt structure can be more fully austenitized, and then cooled to about 720°C at a cooling rate of ≧250°C / h and kept warm for a long time, so that the austenite can be converted into finer pearlite and ferrite structures, and TiC and VC second phase particles are precipitated at the same time, and these second phase particles can pin the grain boundaries and hinder the growth of grains; then the bolt is heated to 970°C-1000°C and kept warm for 0.5h-1h for water cooling, and the quenching temperature is 40°C-70°C lower than the conventional quenching temperature (1040°C), so that the growth of grains can be avoided during the high-temperature heat preservation process; in addition, the quenching cooling medium uses faster tap water, which can improve the cooling effect and ensure the performance of the material after quenching. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a temperature schematic diagram of the first stage of the grain refinement process of the present invention;

[0035] Figure 2 Schematic diagram of the temperature in the second stage of the grain refinement process of the present invention. DETAILED DESCRIPTION

[0036] In order to facilitate the understanding of the technical solution of the present invention, a detailed description is given below in conjunction with the accompanying drawings and specific embodiments.

[0037] like Figure 1-2 As shown, a grain refinement process of 20Cr1Mo1VTiB steel includes (1) isothermal normalizing, (2) quenching and tempering treatment;

[0038] Among them, (1) isothermal normalizing specifically includes:

[0039] S1: Heat the quenched and tempered coarse-grained bolts to a temperature of 950°C-980°C and keep them warm for 3h-5h to make the coarse-grained bolts more fully austenitized;

[0040] S2: Cool down to 720℃±10℃ at a cooling rate of ≥250℃ / h after being taken out of the furnace, and keep warm for 3h-5h, which can transform austenite into finer pearlite and ferrite structures, and at the same time precipitate TiC and VC second phase particles, which can pin the grain boundaries and hinder the growth of grains;

[0041] S3: Take out of the oven and cool to room temperature;

[0042] (2) The quenching and tempering treatment is specifically quenching and high temperature tempering, including:

[0043] S4: Heat the bolts to 700℃±10℃ and keep them warm for 2h-2.5h;

[0044] S5: Heat up to 970℃-1000℃, keep warm for 0.5h-1h. The quenching temperature is 40℃-70℃ lower than the conventional quenching temperature (1040℃) to avoid grain growth during high temperature insulation;

[0045] S6: Water-cooling to room temperature after the furnace is taken out. The quenching cooling medium uses faster tap water, which can improve the cooling effect and ensure the performance of the material after quenching;

[0046] S7: Heat to 700℃-710℃, keep warm for 5h-8h, take out of the furnace and air cool to room temperature.

[0047] After treating the bolts with coarse grains after quenching and tempering according to the above grain refining process, the grain size of the bolts can be effectively refined and the grain size is ≥ 5 levels (the average grain diameter is 62um).

[0048] Example 1

[0049] Bolt specifications used in Example 1: Chemical composition: C is 0.19%, Si is 0.47%, Mn is 0.47%, S is 0.001%, P is 0.008%, Mo is 0.77%, Cr is 0.96%, Ni is 0.23%, Cu is 0.03%, V is 0.49%, Ti is 0.2%, B is 0.003%. The grain size after quenching and tempering is level 2 (average grain diameter 180um), other room temperature mechanical properties: Rp 0.2 762MPa, R m is 843MPa, A is 19%, Z is 65%, AKu is 32J and 24J, HBW is 260, and Rp 0.2 is the yield strength, R m is the tensile strength, Z is the area reduction, AKu is the impact value, A is the elongation, and HBW is the Brinell hardness.

[0050] The specific grain refinement process includes the following steps:

[0051] S1: Heat the quenched and tempered bolts to 965°C and keep them warm for 4 hours;

[0052] S2: Cool down to 720℃ at a cooling rate of ≥250℃ / h after exiting the furnace, and keep warm for 4h;

[0053] S3: Take out of the oven and cool to room temperature;

[0054] S4: Heat the bolt to 700°C and keep it at this temperature for 2.3h;

[0055] S5: Heat to 985°C and keep warm for 0.75h;

[0056] S6: Take out of the furnace and cool to room temperature;

[0057] S7: Heat to 705℃, keep warm for 6.5h, remove from the furnace and air cool to room temperature.

[0058] The bolt grain size obtained by the above grain refinement process is 5.5 (average grain diameter 52um), and other room temperature mechanical properties: Rp 0.2 780MPa, R m It is 854MPa, A is 19.5%, Z is 67%, AKu is 56J and 47J, HBW is 262, and the performance can meet the standard requirements.

[0059] Comparative Example: According to the conventional grain refinement process, the bolt was heated to 930℃ and kept for 4 hours, then air-cooled to room temperature, then heated to 700℃, kept isothermal for 2 hours, then heated to 1040℃, kept for 0.5 hours, then oil-cooled to room temperature, and then heated to 710℃ and kept for 6 hours for tempering. The obtained bolt grain size is level 4 (average grain diameter 90um), and other room temperature mechanical properties: Rp 0.2 790MPa, R m It is 865MPa, A is 19%, Z is 65.5%, AKu is 35J and 38J, and HBW is 266.

[0060] The grain size and mechanical properties of Example 1 and the comparative example are compared as follows:

[0061]

[0062] Example 2

[0063] Bolt specifications used in Example 2: Chemical composition: C is 0.19%, Si is 0.47%, Mn is 0.47%, S is 0.001%, P is 0.008%, Mo is 0.77%, Cr is 0.96%, Ni is 0.23%, Cu is 0.03%, V is 0.49%, Ti is 0.2%, B is 0.003%. The grain size after quenching and tempering is level 2 (average grain diameter 180um), other room temperature mechanical properties: Rp 0.2 762MPa, R m It is 843MPa, A is 19%, Z is 65%, AKu is 32J and 24J, and HBW is 260.

[0064] The specific grain refinement process includes the following steps:

[0065] S1: Heat the quenched and tempered bolts to 980°C and keep them warm for 3 hours;

[0066] S2: Cool down to 720℃ at a cooling rate of ≥250℃ / h after being taken out of the furnace, and keep warm for 3h;

[0067] S3: Take out of the oven and cool to room temperature;

[0068] S4: Heat the bolt to 700°C and keep it at this temperature for 2h;

[0069] S5: Heat to 1000°C and keep warm for 0.5h;

[0070] S6: Take out of the furnace and cool to room temperature;

[0071] S7: Heat to 710℃, keep warm for 5h, remove from the furnace and air cool to room temperature.

[0072] The bolt grain size obtained by the above grain refinement process is level 5 (average grain diameter 62um), and other room temperature mechanical properties: Rp 0.2 765MPa, R m It is 854MPa, A is 20%, Z is 68%, AKu is 54J and 52J, HBW is 256, and the performance can meet the standard requirements.

[0073] Example 3

[0074] Bolt specifications used in Example 3: Chemical composition: C is 0.19%, Si is 0.47%, Mn is 0.47%, S is 0.001%, P is 0.008%, Mo is 0.77%, Cr is 0.96%, Ni is 0.23%, Cu is 0.03%, V is 0.49%, Ti is 0.2%, B is 0.003%. The grain size after quenching and tempering is level 2 (average grain diameter 180um), other room temperature mechanical properties: Rp 0.2 762MPa, R m It is 843MPa, A is 19%, Z is 65%, AKu is 32J and 24J, and HBW is 260.

[0075] The specific grain refinement process includes the following steps:

[0076] S1: Heat the quenched and tempered bolts to 950°C and keep them at this temperature for 5 hours;

[0077] S2: Cool down to 720℃ at a cooling rate of ≥250℃ / h after exiting the furnace, and keep warm for 5h;

[0078] S3: Take out of the oven and cool to room temperature;

[0079] S4: Heat the bolt to 700°C and keep it warm for 2.5h;

[0080] S5: Heat to 970°C and keep warm for 1h;

[0081] S6: Take out of the furnace and cool to room temperature;

[0082] S7: Heat to 700℃, keep warm for 8h, take out of the furnace and air cool to room temperature.

[0083] The bolt grain size obtained by the above grain refinement process is 5.5 (average grain diameter 52um), and other room temperature mechanical properties: Rp 0.2 794MPa, R m It is 875MPa, A is 19.5%, Z is 68%, AKu is 56J and 47J, HBW is 270, and the performance can meet the standard requirements.

[0084] The above are only preferred embodiments of the present invention. The protection scope of the present invention shall be based on the scope defined by the claims. Several improvements and modifications made by those skilled in the art without departing from the spirit and scope of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A grain refinement process for 20Cr1Mo1VTiB steel, characterized in that: include; S1: Heat the quenched and tempered coarse-grained bolts to a temperature of 950°C-980°C and keep them warm for 3h-5h; S2: Cool down to 720℃±10℃ at a cooling rate of ≥250℃ / h after exiting the furnace, and keep warm for 3h-5h; S3: Take out of the oven and cool to room temperature; S4: Heat the bolts to 700℃±10℃ and keep them warm for 2h-2.5h; S5: Heat to 970℃-1000℃, keep warm for 0.5h-1h; S6: Take out of the furnace and cool to room temperature; S7: Heat to 700℃-710℃, keep warm for 5h-8h, take out of the furnace and air cool to room temperature.

2. The grain refinement process of 20Cr1Mo1VTiB steel according to claim 1, characterized in that: S1: Heat the quenched and tempered coarse-grained bolts to 965°C and keep them warm for 4 hours; S2: Cool down to 720℃ at a cooling rate of ≥250℃ / h after exiting the furnace, and keep warm for 4h; S3: Take out of the oven and cool to room temperature; S4: Heat the bolt to 700°C and keep it at this temperature for 2.3h; S5: Heat to 985°C and keep warm for 0.75h; S6: Take out of the furnace and cool to room temperature; S7: Heat to 705℃, keep warm for 6.5h, remove from the furnace and air cool to room temperature.

3. The grain refinement process of 20Cr1Mo1VTiB steel according to claim 1, characterized in that: S1: Heat the quenched and tempered coarse-grained bolts to 980°C and keep them warm for 3 hours; S2: Cool down to 720℃ at a cooling rate of ≥250℃ / h after exiting the furnace, and keep warm for 3h; S3: Take out of the oven and cool to room temperature; S4: Heat the bolt to 700°C and keep it at this temperature for 2h; S5: Heat to 1000°C and keep warm for 0.5h; S6: Take out of the furnace and cool to room temperature; S7: Heat to 710℃, keep warm for 5h, remove from the furnace and air cool to room temperature.

4. The grain refinement process of 20Cr1Mo1VTiB steel according to claim 1, characterized in that: S1: Heat the quenched and tempered coarse-grained bolts to 950°C and keep them at this temperature for 5 hours; S2: Cool down to 720℃ at a cooling rate of ≥250℃ / h after exiting the furnace, and keep warm for 5h; S3: Take out of the oven and cool to room temperature; S4: Heat the bolt to 700°C and keep it warm for 2.5h; S5: Heat to 970°C and keep warm for 1h; S6: Take out of the furnace and cool to room temperature; S7: Heat to 700℃, keep warm for 8h, take out of the furnace and air cool to room temperature.

5. The grain refinement process of 20Cr1Mo1VTiB steel according to claim 1, characterized in that: Chemical composition: C is 0.17%~0.23%, Si is 0.40%~0.60%, Mn is 0.40%~0.65%, S is ≤0.025%, P is ≤0.025%, Mo is 0.75%~1.00%, Cr is 0.90%~1.30%, Ni is ≤0.30%, Cu is ≤0.25%, V is 0.45%~0.65%, Ti is 0.16%~0.28%, and B is 0.001%~0.005%.

6. A bolt made of 20Cr1Mo1VTiB steel, characterized in that: The product is manufactured by using the grain refining process described in any one of claims 1 to 5.

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