A heat treatment method for grain refinement of 34CrNi3Mo steel

Abstract

This invention provides a heat treatment method for refining the grain size of 34CrNi3Mo steel, belonging to the field of structural steel heat treatment technology. The heat treatment method includes the following steps: placing the 34CrNi3Mo steel to be heat-treated directly in an environment of 880-900 ℃, cooling it to 840-860 ℃ and holding it at that temperature for 30-50 min, followed by water quenching after removal from the furnace; the 34CrNi3Mo steel to be heat-treated is in a normalized state. Compared with existing technologies, the heat treatment method provided by this invention is stable, efficient, and has good repeatability, and is suitable for the heat treatment of alloy structural steels with high Ni content.

Description

Technical Field

[0001] This invention relates to a heat treatment method for refining the grains of 34CrNi3Mo steel, belonging to the field of structural steel heat treatment technology. Background Technology

[0002] 34CrNi3Mo is a high-strength alloy structural steel mainly used in engine rotors, steam turbine impellers, rail transportation, pressure vessels, and automobile manufacturing. Its composition includes 0.30%-0.40% C, 0.70%-1.10% Cr, 2.75%-3.25% Ni, 0.25%-0.40% Mo, 0.17%-0.37% Si, and 0.50%-0.80% Mn, with P and S contents both ≤0.035%. After quenching and tempering, its tensile strength can reach 900-1200 MPa, and its yield strength is 720-1100 MPa.

[0003] Currently, most heat treatment methods for 34CrNi3Mo steel employ slow-heating processes to achieve grain refinement, exhibiting a certain path dependence. For example, Chinese patent application CN111809038A discloses a heat treatment method for strengthening and toughening the spindle matrix. This patent application uses 34CrNi3Mo steel as the spindle material, and its heat treatment steps are: pretreatment—first ordinary quenching—second sub-temperature quenching—first tempering—second tempering; the heating rate in each step is controlled at 100℃ / h, and multiple heating and cooling cycles are used to avoid austenite inheritance. Such processes often require long heating times, resulting in lower final heating efficiency and higher energy consumption.

[0004] According to the thermal stress calculation formula: σ=E·α·ΔT σ: Thermal stress (MPa) E: Elastic modulus (MPa) α: Coefficient of thermal expansion (1 / ℃) ΔT: Instantaneous temperature difference between surface and interior (°C) It is known that placing low-temperature metals in a high-temperature environment with an excessive ΔT will result in extremely high thermal stress, which often leads to metal cracking and deformation. It is difficult to imagine using a high-temperature environment for heat treatment.

[0005] Therefore, how to provide a new heat treatment approach that can significantly simplify the heat treatment process and improve the heat treatment efficiency while refining the grain size of 34CrNi3Mo steel is one of the technical problems that those skilled in the art expect to solve. Summary of the Invention

[0006] This invention addresses the common practice in existing technologies of using heating rates ≤100℃ / h for the heat treatment of 34CrNi3Mo steel. It provides a heat treatment method for refining the grain size of 34CrNi3Mo steel, significantly simplifying the heat treatment process and improving efficiency. The technical solution to the above-mentioned problems is as follows: A heat treatment method for refining the grain size of 34CrNi3Mo steel includes the following steps: The 34CrNi3Mo steel to be heat-treated is placed directly in an environment of 880-900 ℃, cooled to 840-860 ℃ and held for 30-50 min, and then removed from the furnace and water-cooled and quenched. The 34CrNi3Mo steel to be heat-treated is in the normalized state.

[0007] The 34CrNi3Mo steel comprises the following components by weight: 0.30%-0.40% C, 0.70-1.10% Cr, 2.75-3.25% Ni, 0.25-0.40% Mo, 0.17-0.37% Si and 0.50-0.80% Mn, while the P and S contents are both ≤0.035%.

[0008] More preferably, the 34CrNi3Mo steel comprises the following components in parts by weight: 0.31% C, 1.10% Cr, 2.77% Ni, 0.39% Mo, 0.18% Si and 0.80% Mn.

[0009] Preferably, the 34CrNi3Mo steel to be heat-treated is placed directly in an environment of 880 ℃, cooled to 860 ℃, and then held for 30 min.

[0010] Preferably, the cooling rate is ≤100℃ / h.

[0011] Preferably, the cooling rate is 60°C / h.

[0012] The beneficial effects of this invention are as follows: This invention achieves rapid heating during the austenitization stage by controlling the way the workpiece is fed into the furnace, thereby suppressing the inheritance phenomenon of reverse austenite structure. By using a high-temperature furnace feeding method, the workpiece forms spherical reverse austenite under high heating rate conditions, effectively avoiding the merging and growth of acicular austenite, thus obtaining a fine-grained structure with a grain size of 7-9 and uniform structure. Attached Figure Description

[0013] Figure 1 The image shows the metallographic structure of 34CrNi3Mo steel obtained by the heat treatment method in Example 1 of this invention. Figure 2 The image shows the metallographic structure of the 34CrNi3Mo steel obtained by the heat treatment method in Comparative Example 1. Figure 3 The image shows the metallographic structure of the alloy steel obtained by the heat treatment method in Comparative Example 2. Figure 4 The image shows the metallographic structure of the alloy steel obtained by the heat treatment method in Comparative Example 3. Detailed Implementation

[0014] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0015] Example 1 In this embodiment, the 34CrNi3Mo steel used has the following composition: 0.36% C, 0.92% Cr, 2.90% Ni, 0.30% Mo, 0.20% Si and 0.50% Mn, with P and S contents both ≤0.035%.

[0016] The normalized 34CrNi3Mo steel was placed directly in an environment of 890℃, cooled to 850℃ for 38 minutes, held for 40 minutes, and then removed from the furnace and water-quenched.

[0017] Example 2 In this embodiment, the 34CrNi3Mo steel used has the following composition: 0.40% C, 0.72% Cr, 3.20% Ni, 0.26% Mo, 0.36% Si and 0.67% Mn, with P and S contents both ≤0.035%.

[0018] The normalized 34CrNi3Mo steel was placed directly in an environment of 900℃, cooled to 840℃ for 36 minutes, held for 50 minutes, and then removed from the furnace and water-quenched.

[0019] Example 3 In this embodiment, the 34CrNi3Mo steel used has the following composition: 0.31% C, 1.10% Cr, 2.77% Ni, 0.39% Mo, 0.18% Si and 0.80% Mn, with P and S contents both ≤0.035%.

[0020] The normalized 34CrNi3Mo steel was placed directly in an environment of 880℃, cooled to 860℃ for 20 minutes, held for 30 minutes, and then removed from the furnace and water-quenched.

[0021] Comparative Example 1 The only difference between this comparative example and Example 1 is the heat treatment method, specifically: The normalized 34CrNi3Mo steel was heated to 890℃ at a heating rate of 100℃ / h, cooled to 850℃ after 38 minutes, held at that temperature for 40 minutes, and then removed from the furnace and water-quenched.

[0022] Comparative Example 2 The only difference between this comparative example and Example 1 is the composition of the 34CrNi3Mo steel, specifically: The alloy steel used has the following composition: 0.42% C, 1.25% Cr, 2.60% Ni, 0.45% Mo, 0.20% Si and 0.30% Mn, with P and S contents both ≤0.035%.

[0023] Comparative Example 3 The only difference between this comparative example and Example 1 is the heat treatment method, specifically: The normalized 34CrNi3Mo steel was heated to 890℃ at a heating rate of 200℃ / h, cooled to 850℃ after 38 minutes, held for 40 minutes, and then removed from the furnace and water-quenched.

[0024] Comparative Example 4 The only difference between this comparative example and Example 1 is the heat treatment method, specifically: The normalized 34CrNi3Mo steel was placed in an environment of 850℃ for 78 min and then removed from the furnace and water-cooled for quenching.

[0025] Test case This invention measures the grain size of the heat-treated metals obtained in each embodiment and comparative example, and performs penetrant testing to confirm whether the workpieces are cracked. The grain size is measured according to GB / T6394-2017 standard, and the impact performance is tested according to GBT229-2020 Charpy impact test method for metallic materials. The results are as follows: Table 1. Grain size test results of the examples and comparative examples

[0026] As can be seen from the table above, the impact performance of the samples obtained in Examples 1-3 of this invention is significantly better than that of the comparative examples, which illustrates that the grain refinement method and refinement effect provided by this invention are closely related to the mechanical properties.

[0027] Comparing Example 1 and Comparative Example 1, it can be seen that both use room temperature steel after normalizing for heat treatment. The main difference is that Example 1 uses direct heating in a high-temperature environment, while Comparative Example 1 uses low-speed heating. From the perspective of the final steel grain size, the grain size of Example 1 at level 8 is significantly higher than that of Comparative Example 1 at level 5. At the same time, Comparative Example 1 cracked after water quenching, making it unusable, and its impact performance was also relatively poor. It can be seen that the heat treatment method provided by the present invention has the advantages of being fast and effective compared with the prior art.

[0028] Comparing Example 1 with Comparative Example 2, it can be seen that the two used steels with different compositions for heat treatment. The results show that, under the same heat treatment method, due to the different composition content of the steel, the final obtained steel grain size decreased and the grain size difference was huge, with multiple grain sizes present. This indicates that the heat treatment method of the present invention depends on specific steel composition.

[0029] Comparing Example 1 with Comparative Example 3, it can be seen that Comparative Example 3 uses a high-speed heating method. From the perspective of the final steel grain size, the grain size of Example 1 at level 8 is significantly higher than that of Comparative Example 3 at level 6. It can be seen that the high-speed heating method in the prior art is still significantly different from the technical effect achieved by the present invention. At the same time, Comparative Example 3 also cracked after water quenching, making it unusable.

[0030] Comparing Example 1 with Comparative Example 4, it can be seen that the temperature at which the steel is first placed in a high-temperature environment has a significant impact on the heat treatment effect. Comparative Example 4 uses an environment of 850°C. While keeping the total heating time constant, the grain size of the steel in Comparative Example 4 decreased sharply, showing the worst grain size value and impact performance data.

[0031] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A heat treatment method for grain refinement of 34CrNi3Mo steel, characterized in that, Includes the following steps: The 34CrNi3Mo steel to be heat-treated is placed directly in an environment of 880-900 ℃, cooled to 840-860 ℃ and held for 30-50 min, and then removed from the furnace and water-quenched; the cooling rate is ≤100℃ / h. The 34CrNi3Mo steel to be heat-treated is in the normalized state.

2. The heat treatment method according to claim 1, characterized in that, The 34CrNi3Mo steel comprises the following components in parts by weight: 0.31% C, 1.10% Cr, 2.77% Ni, 0.39% Mo, 0.18% Si and 0.80% Mn.

3. The heat treatment method according to claim 1, characterized in that, The 34CrNi3Mo steel to be heat-treated was placed directly in an environment of 880 ℃, cooled down to 860 ℃ and held for 30 min.

4. The heat treatment method according to claim 1, characterized in that, The cooling rate is 60 °C / h.

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