Heat treatment process of G26CrMo4 casting

Abstract

The invention discloses a heat treatment process of a G26CrMo4 casting. Relates to the technical field of metal part heat treatment. The heat treatment process for the G26CrMo4 casting comprises the steps that the casting is heated to a first quenching temperature, heat preservation is conducted for 1-1.5 h, then the casting is cooled to a second quenching temperature, heat preservation is conducted for 2.5-3 h, and water cooling is conducted to the temperature below 50 DEG C; the first quenching temperature is 900-925 DEG C, and the second quenching temperature is 870-900 DEG C; and the casting is subjected to tempering heat preservation treatment, the tempering temperature ranges from 620 DEG C to 660 DEG C, the heat preservation time ranges from 4 h to 5.5 h, and the G26CrMo4 casting is obtained after air cooling. According to the heat treatment process, pre-normalizing treatment does not need to be carried out before quenching and tempering treatment, so that the performance of the G26CrMo4 casting can meet the requirements of the standard EN 10293-2015, the heat treatment procedures are reduced, and the production cost is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of heat treatment of metal parts, and more specifically to a heat treatment process for a G26CrMo4 casting. Background Art

[0002] G26CrMo4 is a low alloy cast steel with high tensile strength, yield strength and corrosion resistance. It is widely used in rail transit vehicle bogie running parts, especially load-bearing parts. Its chemical composition and mechanical properties comply with standard EN 10293-2015.

[0003] At present, the heat treatment process of G26CrMo4 castings is: pre-normalizing followed by quenching and tempering (quenching followed by tempering). The heat treatment process curve is as follows: Figure 1 and 2 Specifically, the process steps and parameters are as follows:

[0004] (1) Pre-normalizing: Pre-normalizing temperature 880℃-920℃, holding time 4h-5h; cooling method: air cooling. Pre-normalizing can improve the metallographic structure (converting the as-cast structure to the normalized structure and refining the grains) and prepare for subsequent quenching and tempering.

[0005] (2) Quenching: The quenching temperature is 880℃-910℃, and the holding time is 3.5-4.5h; Cooling method: water cooling after leaving the furnace, and the water temperature is controlled not higher than 45℃.

[0006] (3) Tempering: Tempering is required in time after quenching, and the time interval should not exceed 8 hours; the tempering temperature is 630℃-650℃, and the holding time is 4h-5h; Cooling method: air cooling after tempering.

[0007] In the prior art, the heat treatment process of G26CrMo4 castings requires pre-normalizing before tempering to make the castings meet the requirements of the standards. The multiple heat treatment procedures are cumbersome and the production cost is high. Therefore, on the basis of ensuring that the mechanical properties meet the requirements, it is of great application value to study a low-cost heat treatment processing technology. Summary of the invention

[0008] The purpose of the present invention is to overcome the defects and shortcomings of the existing G26CrMo4 casting heat treatment process, such as complicated process and high cost, and to provide a G26CrMo4 casting heat treatment process, which can make the processed material meet the requirements of standard EN 10293-2015 by optimizing the quenching and tempering process and omitting the pre-normalizing process.

[0009] Another object of the present invention is to provide a G26CrMo4 casting made by the above heat treatment process.

[0010] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0011] The present invention protects a G26CrMo4 casting heat treatment process, including quenching and tempering processes, specifically comprising the following steps:

[0012] S1, quenching: heating the casting to the first quenching temperature and keeping it for 1-1.5h, then cooling it to the second quenching temperature and keeping it for 2.5-3h, and water cooling it to below 50°C; the first quenching temperature is 900-925°C, the second quenching temperature is 870-900°C, and the temperature difference between the first quenching temperature and the second quenching temperature is 20-40°C;

[0013] S2, tempering: subjecting the casting obtained in step S1 to tempering and heat preservation treatment, the tempering temperature is 620-660°C, the heat preservation time is 4-5.5h, and the G26CrMo4 casting is obtained after air cooling.

[0014] The G26CrMo4 casting heat treatment process of the present invention does not need to be pre-normalized before the quenching and tempering treatment. The quenching stage of the quenching and tempering is divided into two stage treatments with different temperatures. By optimizing the temperature parameters of the heat treatment, the performance of the G26CrMo4 casting can meet the requirements of the standard, and the heat treatment process is reduced, thereby reducing the production cost.

[0015] In some embodiments, in step S1, the temperature difference between the first quenching temperature and the second quenching temperature is 25-35°C, preferably 26-30°C.

[0016] In some embodiments, in step S1, the first quenching temperature is 905-915°C, and the second quenching temperature is 877-887°C.

[0017] Preferably, the first quenching temperature is 908-912°C, and the second quenching temperature is 880-884°C.

[0018] In some embodiments, the quenching water volume is ≥ 0.1 m 3 ;

[0019] Optionally, the quenching water volume is 0.1-0.5m 3 , in the laboratory environment, the processed samples meet the requirements.

[0020] Optionally, the quenching water volume is 50-60m 3 In the implementation at the production site, the processed workpieces can also meet the requirements, which proves that the G26CrMo4 casting heat treatment process of the present invention can be applied to large-scale industrial production.

[0021] In some embodiments, in step S2, the tempering temperature is 625-635°C. Preferably, the tempering temperature is 628-632°C.

[0022] In some embodiments, in step S1, the heating rate of the casting to the first quenching temperature is ≤180°C / h.

[0023] In some embodiments, in step S2, the heating rate of the casting to the tempering temperature is ≤180°C / h.

[0024] In some embodiments, the chemical composition of the G26CrMo4 is as follows: C 0.22-0.29%, Si≤0.60%, Mn 0.50-0.80%, S≤0.020%, P≤0.025%, Cr 0.80-1.20%, Ni≤0.40%, Mo0.15-0.30%, Cu≤0.30%, Al 0.02-0.08%, V≤0.05%, and the balance is Fe.

[0025] Preferably, the carbon equivalent CE of the G26CrMo4 is 0.58-0.76, more preferably 0.6-0.7, and the calculation of the carbon equivalent CE refers to standard TB / T 2942.1-2020.

[0026] In some embodiments, the chemical composition of the G26CrMo4 is as follows: C 0.22-0.26%, Si 0.32-0.48%, Mn 0.64-0.80%, S≤0.015%, P≤0.018%, Cr 0.85-1.05%, Ni 0.05-0.12%, Mo 0.15-0.20%, Cu 0.03-0.05%, Al 0.03-0.06%, V≤0.05%, and the balance is Fe.

[0027] A G26CrMo4 casting is made by a heat treatment process of the G26CrMo4 casting.

[0028] In some embodiments, the tensile strength is 700-850Mpa, the yield strength is ≥550Mpa, the elongation after fracture is ≥10%, the cross-sectional shrinkage is ≥35%, the impact absorption energy at 20°C is ≥18J, and the hardness is 200-260HBW; its tempered structure is level 4-6; among the types of non-metallic inclusions, the fine series of types I and III are level 2-3, the coarse series of types I and III are level 1-1.5, type II is level 0.5-2, and type IV is level 0-2.

[0029] Preferably, the G26CrMo4 casting has a tensile strength of 700-761 MPa, a yield strength of 539-615 MPa, an elongation after fracture of 18.5-28.5%, a cross-sectional shrinkage of 61-66%, an impact absorption energy of 100-138 J at 20°C, and a hardness of 211-237 HBW.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The invention provides a G26CrMo4 casting heat treatment process. No pre-normalizing treatment is required before the quenching and tempering treatment. The quenching and tempering stage is divided into two stage treatments with different temperatures. By optimizing the temperature parameters of the heat treatment, the performance of the G26CrMo4 casting can meet the requirements of the standard EN 10293-2015, and the heat treatment process is reduced, thereby reducing the production cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a pre-normalizing process curve diagram in the prior art.

[0033] Figure 2 It is a quenching and tempering process curve diagram in the prior art.

[0034] Figure 3 It is a heat treatment process curve diagram of the G26CrMo4 casting of the present invention.

[0035] Figure 4 The metallographic structure diagrams of the G26CrMo4 castings after quenching and tempering in the heat treatment process of Examples 1-3 of the present invention are shown in order from top to bottom: the materials of Example 1, Example 2 and Example 3; the left diagram is 100 times magnified; the right diagram is 500 times magnified.

[0036] Figure 5 The metallographic structure diagram of the G26CrMo4 casting after quenching and tempering in the heat treatment process of Examples 4-6 of the present invention. From top to bottom, the materials of Example 4, Example 5 and Example 6 are shown, the left side diagram is 100 times magnified, and the right side diagram is 500 times magnified.

[0037] Figure 6 This is the metallographic structure diagram of the G26CrMo4 casting after quenching and tempering in the heat treatment process of Comparative Example 1 of the present invention.

[0038] Figure 7 This is the metallographic structure diagram of the G26CrMo4 casting after quenching and tempering in the heat treatment process of Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0039] The present invention is further described below in conjunction with specific embodiments, but the embodiments do not limit the present invention in any form. Unless otherwise specified, the raw materials and reagents used in the embodiments of the present invention are conventionally purchased raw materials and reagents.

[0040] The chemical compositions of the castings in the following embodiments and comparative examples are shown in Table 1 by mass percentage:

[0041] Among them, the calculation formula of carbon equivalent CE is: CE = C + (Mn + Si) / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15 (refer to standard TB / T 2942.1-2020). Carbon equivalent CE is the content of various alloy elements in steel converted into carbon. The carbon equivalent CE can be used to evaluate the strength performance of steel.

[0042] Table 1 Chemical composition of casting materials

[0043]

[0044] Examples 1 to 6

[0045] This embodiment provides a series of G26CrMo4 casting heat treatment processes, and its process curve is as follows: Figure 3 As shown, the following steps are included:

[0046] S1, heating the casting for quenching and heat preservation treatment, the heating rate is ≤180℃ / h, wherein the quenching temperature is divided into two different temperature stages, and the casting is water-cooled after being taken out of the furnace; in the water cooling treatment, the temperature of the water used is ≤45℃, and the volume of the water tank used at the production site is: 5000mm*4000mm*3000mm;

[0047] S2, subjecting the casting obtained in step S1 to tempering and heat preservation treatment, and air cooling, to obtain a G26CrMo4 casting, wherein the size of the casting is 700mm*600mm*350mm.

[0048] Examples 1-3 are processed in a laboratory environment, and Examples 4-6 are processed on-site. The quenching temperature and the holding time of the two stages, as well as the tempering temperature and the holding time of the two stages of all examples are shown in Table 2.

[0049] Table 2

[0050]

[0051] Comparative Example 1

[0052] A heat treatment process for G26CrMo4 castings. In this comparative example, no pre-normalizing treatment is performed before quenching and tempering treatment. The heat treatment process curve is as follows: Figure 2 shown. Specifically,

[0053] Take the G26CrMo4 casting for heat treatment. The casting size and specifications are the same as those in Example 4. The casting material is selected from C-1 material. The heat treatment process steps and parameters are as follows:

[0054] (1) Quenching: Quenching temperature is 890℃, holding time is 4h; Cooling method: water cooling out of the furnace, water temperature is controlled not higher than 45℃; heating rate to quenching temperature is ≤180℃ / h; quenching water volume is 55m3.

[0055] (2) Tempering: Temper the castings promptly after quenching; the tempering temperature is 630℃ and the holding time is 4.5h; cooling method: air cooling after tempering; the heating rate to the tempering temperature is ≤180℃ / h.

[0056] Comparative Example 2

[0057] A heat treatment process for G26CrMo4 castings. This comparative example adopts pre-normalizing and quenching and tempering treatment. The heat treatment process curve is as follows: Figure 1 and Figure 2 shown. Specifically,

[0058] Take the G26CrMo4 casting for heat treatment. The casting size and specifications are the same as those in Example 5. The casting material is selected from C-2 material. The heat treatment process steps and parameters are as follows:

[0059] (1) Pre-normalizing: pre-normalizing temperature 900℃, holding time 4h; cooling method: air cooling; heating rate ≤180℃ / h.

[0060] (2) Quenching: The quenching temperature is 890℃, and the holding time is 4h. Cooling method: water cooling after leaving the furnace, and the water temperature is controlled not higher than 45℃. The heating rate from the heating temperature to the quenching temperature is ≤180℃ / h. The quenching water volume is 55m3.

[0061] (3) Tempering: Temper the castings promptly after quenching; the tempering temperature is 630°C and the holding time is 4.5h; cooling method: air cooling after tempering; the heating rate to the tempering temperature is ≤180°C / h.

[0062] Performance Testing

[0063] 1. Mechanical properties

[0064] The G26CrMo4 castings of Examples 1-6 and Comparative Examples 1-2 were subjected to performance tests, and the results are shown in Table 3.

[0065] The tensile strength, yield strength, elongation after fracture and reduction of area are tested according to the reference standard GB / T 228.1-2010 "Tensile test of metallic materials Part 1: Room temperature test method".

[0066] The reference standard for impact absorption energy is GB / T 229-2007 "Charpy Pendulum Impact Test Method for Metallic Materials".

[0067] The hardness is tested according to the standard GB / T 231.1 "Brinell hardness test for metallic materials - Part 1: Test method".

[0068] Table 3

[0069]

[0070] The G26CrMo4 casting of the present invention has a tensile strength of 700-761 MPa, a yield strength of more than 539 MPa, an elongation after fracture of more than 18.5%, a cross-sectional shrinkage of more than 61%, and has good impact absorption energy and plasticity, meeting the requirements of standard EN10293-2015.

[0071] Comparing Examples 1-3 and 4-6, it can be seen that both the laboratory environment (quenching water volume 0.1m3) and the production site (quenching water volume 55m3) can make the casting performance of G26CrMo4 meet the requirements.

[0072] The G26CrMo4 casting of Comparative Example 1 was directly tempered without pre-normalizing treatment, and its strength, plasticity and toughness indicators were significantly reduced.

[0073] Compared with Example 5, the chemical composition of the G26CrMo4 casting of Comparative Example 2 is equivalent. After quenching and tempering pre-normalizing treatment, its metallographic structure and mechanical properties are close to those of the casting of the present invention, and also meet the requirements of standard EN 10293-2015; in contrast, after the quenching and tempering stage of the present invention is optimized and divided into two stage treatments at different temperatures, the pre-normalizing heat treatment process can be reduced, and the workpiece can have equivalent mechanical properties and meet the requirements of standard EN 10293-2015, thereby achieving the effect of simplifying the heat treatment process and reducing production costs.

[0074] The G26CrMo4 castings of Examples 1-6 and Comparative Examples 1-2 were subjected to metallographic structure tests. Figure 4-7 As shown, the metallographic structure of grade E steel in standard TB / T2942.2-2018 was used for rating, and the results are shown in Table 4.

[0075] Table 4

[0076]

[0077]

[0078] The results show that the quenched and tempered structure of the casting material of the present invention is level 4-6: mainly tempered troostite, partly containing a very small amount of undissolved irregular ferrite, the overall structure is uniform, and the grains are fine. The casting material of Comparative Example 1 is residual as-cast structure level 3: tempered troostite with dendrite distribution, and contains a mixed distribution of multi-directionally distributed needle-shaped and blocky ferrite and tempered troostite. Due to the difference between its microstructure and the quenched and tempered structure, the product has poor fatigue fracture resistance during use, so its metallographic structure is evaluated as unqualified.

[0079] The above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A G26CrMo4 casting heat treatment process, characterized in that: The following steps are involved: S1, heating the casting to a first quenching temperature and keeping it for 1-1.5 hours, then cooling it to a second quenching temperature and keeping it for 2.5-3 hours, and water cooling it to below 50°C; the first quenching temperature is 900-925°C, the second quenching temperature is 870-900°C, and the temperature difference between the first quenching temperature and the second quenching temperature is 20-40°C; S2, subjecting the casting obtained in step S1 to tempering and heat preservation treatment, the tempering temperature is 620-660°C, the heat preservation time is 4-5.5h, and the G26CrMo4 casting is obtained after air cooling.

2. The G26CrMo4 casting heat treatment process according to claim 1, characterized in that: In step S1, the temperature difference between the first quenching temperature and the second quenching temperature is 25-35°C.

3. The G26CrMo4 casting heat treatment process according to claim 1, characterized in that: In step S1, the first quenching temperature is 905-915°C, and the second quenching temperature is 877-887°C.

4. The G26CrMo4 casting heat treatment process according to claim 1, characterized in that: In step S2, the tempering temperature is 625-635°C.

5. The G26CrMo4 casting heat treatment process according to claim 1, characterized in that: In step S1, the heating rate of the casting to the first quenching temperature is ≤180°C / h.

6. The G26CrMo4 casting heat treatment process according to claim 1, characterized in that: In step S2, the heating rate of the casting to the tempering temperature is ≤180°C / h.

7. The G26CrMo4 casting heat treatment process according to any one of claims 1 to 6, characterized in that: The chemical composition of the G26CrMo4 is as follows: C 0.22-0.29%, Si≤0.60%, Mn 0.50-0.80%, S≤0.020%, P≤0.025%, Cr 0.80-1.20%, Ni≤0.40%, Mo 0.15-0.30%, Cu≤0.30%, Al 0.02-0.08%, V≤0.05%, and the balance is Fe.

8. The G26CrMo4 casting heat treatment process according to claim 7, characterized in that: The chemical composition of the G26CrMo4 is as follows: C 0.22-0.26%, Si 0.32-0.48%, Mn 0.64-0.80%, S≤0.015%, P≤0.018%, Cr0.85-1.05%, Ni 0.05-0.12%, Mo 0.15-0.20%, Cu0.03-0.05%, Al 0.03-0.06%, V≤0.05%, and the balance is Fe.

9. A G26CrMo4 casting, characterized in that: The G26CrMo4 casting is made by the heat treatment process described in any one of claims 1-8.

10. The G26CrMo4 casting according to claim 9, characterized in that: The tensile strength is 700-850Mpa, the yield strength is ≥550Mpa, the elongation after fracture is ≥10%, the cross-sectional shrinkage is ≥35%, the impact absorption energy at 20°C is ≥18J, and the hardness is 200-260HBW; its tempered structure is level 4-6; among the types of non-metallic inclusions, the fine series of types I and III are level 2-3, the coarse series of types I and III are level 1-1.5, type II is level 0.5-2, and type IV is level 0-2.

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