Heat treatment method for improving low-temperature impact toughness and grain size of 35CrNi4Mo material forgings

Abstract

The present application relates to a kind of heat treatment method that can improve the low temperature impact toughness and grain size of 35CrNi4Mo material forgings, using normalizing+quenching+intercritical quenching+high temperature tempering heat treatment mode.Normalizing, heating to 880~900 ℃ uniform temperature after heat preservation, after furnace out, blast cooling;Quenching, heating to 880~890 ℃ uniform temperature after heat preservation, after furnace out, oil cooling;Intercritical quenching, heating to 785~795 ℃ uniform temperature after heat preservation, after furnace out, oil cooling;High temperature tempering, heating to 625~665 ℃ heat preservation, after furnace out, air cooling.The present application can heat treat the diameter ≤φ400mm 35CrNi4Mo material forgings.The 35CrNi4Mo material forgings treated by the present application, at the body 1 / 2 radius sampling test, its mechanical properties not only can reach high low temperature impact toughness (A K V2 (-29 ℃)≥80J), but grain size can reach 6 levels and above (≥6 levels), can fully meet the special technical requirements of 35CrNi4Mo steel forgings, and the operability in production process is strong.

Description

Technical Field

[0001] This invention relates to the field of high alloy structural steel forging production technology, and mainly to a heat treatment method that can improve the low-temperature impact toughness and grain size of 35CrNi4Mo forgings. Background Technology

[0002] 35CrNi4Mo forgings are characterized by high strength and high toughness (room temperature toughness), and are commonly used in the plunger pump head body of complete fracturing machines. Due to differences in component ratios and heat treatment methods, the strength, toughness, and grain size of this material vary significantly. Generally, the heat treatment method for Cr-Ni-Mo steel forgings is quenching followed by high-temperature tempering. Specifically, quenching is performed at 850–890℃, with a holding time calculated at 0.9 h / 100 mm. Tempering involves heating to 560–660℃, holding at that temperature for 2.5 h / 100 mm, and then air-cooling after removal from the furnace. Tests showed that the low-temperature impact toughness of forgings treated with this method at -29℃ could only reach 30-50J, with coarse grains (usually grade 4 or 4.5) or mixed grains (usually 50% grade 3.5 + 50% grade 5). Because the low-temperature impact toughness and grain size did not meet the requirements of the special technical conditions (grain size ≥ grade 6), the service life of the forgings was affected.

[0003] When 35CrNi4Mo forgings are used in specific harsh environments, their low-temperature impact performance is not high and their grains are coarse, which can cause the forgings to fracture and fail, thus leading to the scrapping of the entire fracturing machine. Therefore, how to improve the low-temperature impact toughness and grain size of the forgings is a technical problem that must be solved. Summary of the Invention

[0004] The purpose of this invention is to address the above-mentioned situation by providing a heat treatment method that can improve the low-temperature impact toughness and grain size of 35CrNi4Mo forgings.

[0005] The objective of this invention is to provide a heat treatment method that improves the low-temperature impact toughness and grain size of 35CrNi4Mo forgings. The chemical composition of the 35CrNi4Mo forgings, as determined by smelting analysis, is as follows: C: 0.30%–0.38%, Si ≤ 0.35%, Mn: 0.60%–0.90%, P ≤ 0.010%, S ≤ 0.005%, Cr: 1.45%–1.55%, Mo: 0.40%–0.60%, Ni: 4.1%–4.5%, V: 0.05%–0.10%, Nb ≤ 0.10%, and the remaining elements meet the requirements.

[0006] The specific steps of heat treatment are as follows:

[0007] 1) First, heat the 35CrNi4Mo forging to 880-900℃ and hold it at that temperature for 1.0h / 100mm. After taking it out of the furnace, cool it with forced air.

[0008] The 100mm refers to the diameter of the heat-treated forging material.

[0009] The mm refers to the diameter unit for heat treatment of material forgings;

[0010] 2) Heat the 35CrNi4Mo forgings that have been cooled to room temperature in step 1) to 880-890℃ and hold them at that temperature for 1.0h / 100mm; then quench them after removing them from the furnace.

[0011] The 100mm refers to the diameter of the heat-treated forging material.

[0012] The quenching method is oil cooling, and the oil cooling time is calculated at 13s / mm.

[0013] The mm refers to the diameter unit for heat treatment of material forgings;

[0014] 3) Heat the 35CrNi4Mo forgings that have been cooled to room temperature in step 2) to 785-795℃ and hold them at that temperature for 1.0h / 100mm; then quench them after removing them from the furnace.

[0015] The 100mm refers to the diameter of the heat-treated forging material.

[0016] The quenching method is oil cooling, and the oil cooling time is calculated at 13s / mm.

[0017] The mm refers to the diameter unit for heat treatment of material forgings;

[0018] 4) Heat the 35CrNi4Mo forgings quenched in step 3) to 625–665℃ and hold for 2.5 h / 100 mm. Air-cool after removal from the furnace to obtain high low-temperature impact toughness (A). K Forgings of 35CrNi4Mo material with V2 (-29℃) ≥80J and grain size ≥6;

[0019] The 100mm refers to the diameter of the heat-treated forging material.

[0020] The mm refers to the diameter unit for heat treatment of material forgings.

[0021] The heat treatment method of this invention is normalizing to improve the microstructure and prepare it for quenching; quenching, using oil-cooled furnace quenching, aims to refine the grains; sub-temperature quenching aims to further refine the grains and interrupt microstructure inheritance; and high-temperature tempering is performed immediately after the second quenching. This heat treatment process can achieve high low-temperature impact toughness (A). K V2 (-29℃) ≥ 80J) and fine grain size (grain size ≥ grade 6).

[0022] This invention effectively solves the technical problems of poor low-temperature impact toughness, coarse grains, and mixed grains in high-alloy 35CrNi4Mo steel forgings after heat treatment.

[0023] This invention can heat-treat forgings made of materials with a diameter ≤ φ400mm. Forgings of 35CrNi4Mo material heat-treated according to this invention, when sampled at 1 / 2 radius of the body, exhibit mechanical properties that not only achieve high low-temperature impact toughness (A... K The V2 (-29℃) ≥ 80J, and the grain size can reach level 6 or above (≥ level 6), which can fully meet the special technical requirements of 35CrNi4Mo steel forgings for complete fracturing machines, and the production process is highly operable. Detailed Implementation

[0024] The chemical composition of the 35CrNi4Mo forgings used in this invention, as determined by smelting analysis, is as follows: C: 0.30%–0.38%, Si ≤ 0.35%, Mn: 0.60%–0.90%, P ≤ 0.010%, S ≤ 0.005%, Cr: 1.45%–1.55%, Mo: 0.40%–0.60%, Ni: 4.1%–4.5%, V: 0.05%–0.10%, Nb ≤ 0.10%, and the remaining elements meet the requirements.

[0025] The heat treatment of the forgings of this invention adopts a heat treatment method of normalizing + quenching + sub-critical quenching + high-temperature tempering. Normalizing involves heating to 880-900℃, holding at that temperature, and then air-cooling after removal from the furnace; quenching involves heating to 880-890℃, holding at that temperature, and then oil-cooling after removal from the furnace; sub-critical quenching involves heating to 785-795℃, holding at that temperature, and then oil-cooling after removal from the furnace; high-temperature tempering involves heating to 625-665℃, holding at that temperature, and then air-cooling after removal from the furnace.

[0026] The applicant conducted low-temperature impact toughness (-29℃) and grain size tests on 35CrNi4Mo forgings with an effective cross-section ≤φ400mm after heat treatment using this invention. The sampling location of the specimen was at 1 / 2 radius from the surface of the specimen centerline. The low-temperature impact toughness (-29℃) test result reached ≥80J, and the grain size test result reached ≥6.

[0027] The present invention will now be described in detail with reference to specific embodiments.

[0028] Example 1:

[0029] The heat-treated 35CrNi4Mo forging has a diameter of φ100mm and its chemical composition (smelting analysis) is as follows: C: 0.35%, Si: 0.20%, Mn: 0.60%, P: 0.008%, S: 0.005%, Cr: 1.45%, Mo: 0.55%, Ni: 4.1%, V: 0.07%, Nb: 0.02%, and the remaining elements meet the requirements.

[0030] The specific steps of heat treatment are as follows:

[0031] 1) First, heat the 35CrNi4Mo forging to 890℃ and hold it at that temperature for 1.0h / 100mm. After taking it out of the furnace, cool it with forced air.

[0032] The 100mm refers to the diameter of the heat-treated forging material.

[0033] The mm refers to the diameter unit for heat treatment of material forgings;

[0034] 2) After cooling to room temperature in step 1), the 35CrNi4Mo forging is heated to 885℃ and held at that temperature for 1.0h / 100mm for 1.0h. Then it is taken out of the furnace and quenched.

[0035] The 100mm refers to the diameter of the heat-treated forging material.

[0036] The quenching method is oil cooling, and the oil cooling time is calculated at 13s / mm, with an oil cooling time of 22 minutes.

[0037] The mm refers to the diameter unit for heat treatment of material forgings;

[0038] 3) After cooling to room temperature in step 2), the 35CrNi4Mo forging is heated to 790℃ and held at that temperature for 1.0h / 100mm. Then it is taken out of the furnace and quenched.

[0039] The 100mm refers to the diameter of the heat-treated forging material.

[0040] The quenching method is oil cooling, and the oil cooling time is calculated at 13s / mm, with an oil cooling time of 22 minutes.

[0041] The mm refers to the diameter unit for heat treatment of material forgings;

[0042] 4) The 35CrNi4Mo forgings quenched in step 3) are heated to 625℃ and held at that temperature for 2.5 hours per 100mm. After quenching, the forgings are air-cooled to obtain high low-temperature impact toughness (A). K Forgings of 35CrNi4Mo material with V2 (-29℃) ≥80J and grain size ≥6;

[0043] The 100mm refers to the diameter of the heat-treated forging material.

[0044] The mm refers to the diameter unit for heat treatment of material forgings.

[0045] Low-temperature impact toughness A of the heat-treated 35CrNi4Mo forging in this embodiment K V2 (-29℃): 99J, 101J, 98J; Grain size: 7.5 grade.

[0046] Example 2: Same as Example 1, except that...

[0047] The heat-treated 35CrNi4Mo forging has a diameter of φ200mm and its chemical composition (smelting analysis) is as follows: C: 0.36%, Si: 0.25%, Mn: 0.90%, P: 0.010%, S: 0.004%, Cr: 1.51%, Mo: 0.60%, Ni: 4.2%, V: 0.06%, Nb: 0.05%, and the remaining elements meet the requirements.

[0048] The specific steps of heat treatment are as follows:

[0049] 1) First, heat the 35CrNi4Mo forging to 890℃ and hold it at that temperature for 2.0 hours, calculated as 1.0h / 100mm. After removing it from the furnace, cool it with forced air.

[0050] 2) After cooling to room temperature in step 1), the 35CrNi4Mo forging is heated to 885℃ and held at that temperature for 2.0 hours (calculated as 1.0h / 100mm). Then, it is removed from the furnace and quenched.

[0051] The quenching method is oil cooling, and the oil cooling time is calculated at 13s / mm, so the oil cooling time is 43 minutes.

[0052] 3) After cooling to room temperature in step 2), the 35CrNi4Mo forging is heated to 790℃ and held at that temperature for 2.0 hours (calculated as 1.0h / 100mm). Then, it is taken out of the furnace and quenched.

[0053] The quenching method is oil cooling, and the oil cooling time is calculated at 13s / mm, so the oil cooling time is 43 minutes.

[0054] 4) The 35CrNi4Mo forgings quenched in step 3) are first heated to 300-350℃ and held for 2 hours, then heated to 640℃ and held for 5 hours. The holding time is calculated as 2.5h / 100mm, and the holding time is 5.0h. After being removed from the furnace and air-cooled, high low-temperature impact toughness (A) is obtained. K Forgings of 35CrNi4Mo material with V2 (-29℃) ≥80J and grain size ≥6;

[0055] Low-temperature impact toughness A of the heat-treated 35CrNi4Mo forging in this embodiment K V2 (-29℃): 96J, 93J, 98J; Grain size: 6.5 grade.

[0056] Example 3: Same as Example 1, except that...

[0057] The heat-treated 35CrNi4Mo forging has a diameter of φ300mm and its chemical composition (smelting analysis) is as follows: C: 0.38%, Si: 0.30%, Mn: 0.85%, P: 0.008%, S: 0.004%, Cr: 1.50%, Mo: 0.55%, Ni: 4.4%, V: 0.08%, Nb: 0.03%, and the remaining elements meet the requirements.

[0058] The specific steps of heat treatment are as follows:

[0059] 1) First, heat the 35CrNi4Mo forging to 890℃ and hold it at that temperature for 3.0 hours, calculated as 1.0h / 100mm. After removing it from the furnace, cool it with forced air.

[0060] 2) After cooling to room temperature in step 1), the 35CrNi4Mo forging is heated to 885℃ and held at that temperature for 3.0 hours (calculated as 1.0h / 100mm). Then, it is taken out of the furnace and quenched.

[0061] The quenching method is oil cooling, and the oil cooling time is calculated at 13s / mm, with an oil cooling time of 65 minutes.

[0062] 3) After cooling to room temperature in step 2), the 35CrNi4Mo forging is heated to 790℃ and held at that temperature for 3.0 hours (calculated as 1.0h / 100mm). Then, it is taken out of the furnace and quenched.

[0063] The quenching method is oil cooling, and the oil cooling time is calculated at 13s / mm, with an oil cooling time of 65 minutes.

[0064] 4) The 35CrNi4Mo forgings quenched in step 3) are heated to 650℃ and held at that temperature for 7.5 hours (calculated as 2.5 hours / 100mm). After removal from the furnace and air-cooled, high low-temperature impact toughness (A) is obtained.K Forgings of 35CrNi4Mo material with V2 (-29℃) ≥80J and grain size ≥6;

[0065] Low-temperature impact toughness A of the heat-treated 35CrNi4Mo forging in this embodiment K V2 (-29℃): 95J, 97J, 91J; Grain size: 6.5 grade.

[0066] Example 4: Same as Example 1, except that...

[0067] The heat-treated 35CrNi4Mo forging has a diameter of φ350mm. Its chemical composition (smelting analysis) is as follows: C: 0.38%, Si: 0.30%, Mn: 0.85%, P: 0.008%, S: 0.005%, Cr: 1.55%, Mo: 0.55%, Ni: 4.2%, V: 0.08%, Nb: 0.08%, and the remaining elements meet the requirements.

[0068] The specific steps of heat treatment are as follows:

[0069] 1) First, heat the 35CrNi4Mo forging to 890℃ and hold it at that temperature for 3.5 hours, calculated as 1.0h / 100mm. After removing it from the furnace, cool it with forced air.

[0070] 2) After cooling to room temperature in step 1), the 35CrNi4Mo forging is heated to 885℃ and held at that temperature for 3.5 hours (calculated as 1.0h / 100mm). Then, it is removed from the furnace and quenched.

[0071] The quenching method is oil cooling, and the oil cooling time is calculated at 13s / mm, so the oil cooling time is 76 minutes.

[0072] 3) After cooling to room temperature in step 2), the 35CrNi4Mo forging is heated to 790℃ and held at that temperature for 3.5 hours (calculated as 1.0h / 100mm). Then, it is taken out of the furnace and quenched.

[0073] The quenching method is oil cooling, and the oil cooling time is calculated at 13s / mm, so the oil cooling time is 76 minutes.

[0074] 4) The 35CrNi4Mo forgings quenched in step 3) are heated to 665℃ and held at that temperature for 8.75 hours (calculated as 2.5 hours / 100mm). After removal from the furnace, they are air-cooled to obtain high low-temperature impact toughness (A). K Forgings of 35CrNi4Mo material with V2 (-29℃) ≥80J and grain size ≥6;

[0075] Low-temperature impact toughness A of the heat-treated 35CrNi4Mo forging in this embodimentK V2 (-29℃): 87J, 86J, 89J; Grain size: Grade 6.

[0076] Example 5: Same as Example 1, except that...

[0077] The heat-treated 35CrNi4Mo forging has a diameter of φ400mm. Its chemical composition (smelting analysis) is as follows: C: 0.37%, Si: 0.22%, Mn: 0.83%, P: 0.009%, S: 0.005%, Cr: 1.52%, Mo: 0.58%, Ni: 4.5%, V: 0.09%, Nb: 0.07%, and the remaining elements meet the requirements.

[0078] The specific steps of heat treatment are as follows:

[0079] 1) First, heat the 35CrNi4Mo forging to 890℃ and hold it at that temperature for 4.0 hours, calculated as 1.0h / 100mm. After removing it from the furnace, cool it with forced air.

[0080] 2) The 35CrNi4Mo forgings cooled to room temperature in step 1) are heated to 885℃ and held at that temperature for 4.0 hours (calculated as 1.0h / 100mm). Then, the forgings are removed from the furnace and quenched.

[0081] The quenching method is oil cooling, and the oil cooling time is calculated at 13s / mm, so the oil cooling time is 87 minutes.

[0082] 3) After cooling to room temperature in step 2), the 35CrNi4Mo forging is heated to 790℃ and held at that temperature for 4.0 hours (calculated as 1.0h / 100mm). Then, it is taken out of the furnace and quenched.

[0083] The quenching method is oil cooling, and the oil cooling time is calculated at 13s / mm, so the oil cooling time is 87 minutes.

[0084] 4) The 35CrNi4Mo forgings quenched in step 3) are first heated to 300-350℃ and held for 2 hours, then heated to 665℃ and held for 10 hours. The forgings are then air-cooled after removal from the furnace to obtain high low-temperature impact toughness (A). K Forgings of 35CrNi4Mo material with V2 (-29℃) ≥80J and grain size ≥6;

[0085] Low-temperature impact toughness A of the heat-treated 35CrNi4Mo forging in this embodiment K V2 (-29℃): 85J, 83J, 81J; Grain size: 6.

[0086] The applicant applied a conventional quenching and high-temperature tempering heat treatment process to the 35CrNi4Mo forgings in Examples 1-5. Specifically, the process involved heating to 850-870℃ for quenching, with a holding time of 0.9h / 100mm. Tempering was performed by heating to 550-660℃ and holding for 2.5h / 100mm, followed by air cooling after removal from the furnace. Comparative experiments 1-5 are described below. Specifically, comparative experiments 1-5 did not use step 1) of "heating to 880-900℃ and holding for 1.0h / 100mm, followed by forced air cooling after removal from the furnace"; did not use the quenching temperature range of step 2 of "heating to 880-890℃ and holding for 1.0h / 100mm", and did not use step 3 of "heating to 785-795℃ and holding for 1.0h / 100mm, followed by oil quenching (sub-temperature quenching) after removal from the furnace".

[0087] The grain size of Comparative Examples 1-5 was tested using the same grain size testing method as in Examples 1-5, and the test results are as follows:

[0088] Comparative Example 1: Low-temperature impact toughness A of heat-treated 35CrNi4Mo forgings K V2 (-29℃): 48J, 48J, 47J; Grain size: 4.5 grade.

[0089] Comparative Example 2: Low-temperature impact toughness A of heat-treated 35CrNi4Mo forgings K V2 (-29℃): 46J, 40J, 41J; Grain size: 30% grade 4 + 70% grade 4.5.

[0090] Comparative Example 3: Low-temperature impact toughness A of heat-treated 35CrNi4Mo forgings K V2 (-29℃): 41J, 38J, 37J; Grain size: 40% grade 4 + 60% grade 4.5.

[0091] Comparative Example 4: Grain size and low-temperature impact toughness of heat-treated 35CrNi4Mo forgings (A) K V2 (-29℃): 36J, 32J, 30J; Level 4.5.

[0092] Comparative Example 5: Low-temperature impact toughness A of heat-treated 35CrNi4Mo forgings K V2 (-29℃): 30J, 31J, 31J; Grain size: 40% grade 3.5 + 60% grade 4.

[0093] Comparing the results of Examples 1-5 with those of Comparative Examples 1-5, the low-temperature impact toughness and grain size are effectively improved, fully demonstrating that the heat treatment method of the present invention can improve the low-temperature impact toughness (A) of 35CrNi4Mo forgings. KV2 (-29℃) ≥ 80J) and grain size (grain size ≥ grade 6) meet the special technical requirements and satisfy the use requirements of forgings in specific harsh environments.

Claims

1. A heat treatment method that can improve the low-temperature impact toughness and grain size of 35CrNi4Mo forgings, characterized in that: The diameter section of 35CrNi4Mo forgings is φ100mm-φ400mm. The chemical composition analysis is as follows: C: 0.30%~0.38%, Si≤0.35%, Mn: 0.60%~0.90%, P≤0.010%, S≤0.005%, Cr: 1.45%~1.55%, Mo: 0.40~0.60%, Ni: 4.1%~4.5%, V: 0.05%~0.10%, Nb≤0.10%, and the remaining elements are iron and unavoidable impurities. The specific steps of heat treatment are as follows: 1) First, heat the 35CrNi4Mo forging to 880-900℃ and hold it at that temperature for 1.0h / 100mm. After taking it out of the furnace, cool it with forced air. The 100mm refers to the diameter of the heat-treated forging material. The mm refers to the diameter unit for heat treatment of material forgings; 2) Heat the 35CrNi4Mo forgings that have been cooled to room temperature in step 1) to 880-890℃ and hold them at that temperature for 1.0h / 100mm; then quench them after removing them from the furnace. The 100mm refers to the diameter of the heat-treated forging material. The quenching method is oil cooling, and the oil cooling time is calculated at 13s / mm. The mm refers to the diameter unit for heat treatment of material forgings; 3) Heat the 35CrNi4Mo forgings that have been cooled to room temperature in step 2) to 785-795℃ and hold them at that temperature for 1.0h / 100mm; then quench them after removing them from the furnace. The 100mm refers to the diameter of the heat-treated forging material. The quenching method is oil cooling, and the oil cooling time is calculated at 13s / mm. The mm refers to the diameter unit for heat treatment of material forgings; 4) Heat the 35CrNi4Mo forgings quenched in step 3) to 625-665℃ and hold at that temperature until homogeneous. The holding time is calculated at 2.5h / 100mm. After being air-cooled after being removed from the furnace, the low-temperature impact toughness A at -29℃ is obtained. K Forgings of 35CrNi4Mo material with V2≥80J and grain size≥6 grade; The 100mm refers to the diameter of the heat-treated forging material. The mm refers to the diameter unit for heat treatment of material forgings.