A heat treatment process for improving the heat treatment quality of a tempered crankshaft blank and application thereof

Abstract

The application relates to a heat treatment process for improving the heat treatment quality of a quenched and tempered crankshaft blank and application; the process requires that a steel plant supplies materials according to three rolling batch numbers of a head, a middle and a tail according to the carbon content of the same furnace batch number; three different quenching and tempering processes are formulated according to the components of the three rolling batch numbers; the 6DM2 engine crankshaft blank is quenched and tempered by using the heat treatment process; the crankshaft blank material is 42CrMo; the application solves the quenching crack problem in the quenching and tempering process of the crankshaft blank, the quenching crack ratio is reduced from 6% to below 0.5%, the quenching crack waste loss is greatly reduced, the mechanical properties of all the pieces are qualified, and no repair is needed.

Description

Technical Field

[0001] This invention belongs to the field of ferrous metal heat treatment technology, and relates to a heat treatment process and its application for improving the heat treatment quality of tempered crankshaft blanks. Background Technology

[0002] The crankshaft is one of the most important internal components of an engine, crucial to its performance and reliability. The quality of its heat treatment directly affects the engine's performance and lifespan. The crankshaft blank for the 6DM2 engine is relatively heavy and requires tempering on a large continuous tempering line. Made of 42CrMo material, two contradictory defects emerged after tempering: one was that the mechanical properties were too low, requiring rework; the other was that the mechanical properties were too high, leading to quenching cracks, which necessitated scrapping the engine. A schematic diagram of the crankshaft blank can be found here. Figure 1 .

[0003] Existing crankshaft blank heat treatment process: quenching + tempering + inspection + flaw detection

[0004] 1. Quenching: The crankshaft blank is placed in a suspended quenching furnace, heated to 860°C for 200 minutes, held for 150 minutes, and then removed from the furnace and vertically placed into a quenching tank (with quenching agent) to cool to room temperature.

[0005] 2. The quenched crankshaft blank is placed in a suspended tempering furnace, heated to 615℃ for 250 minutes, held for 280 minutes, then removed from the furnace, water-cooled, and unloaded into the material box.

[0006] 3. Inspection: Hardness, metallographic properties and mechanical properties.

[0007] 4. Flaw detection: Check for any cracked parts.

[0008] Due to material composition segregation, some parts in the same batch of material have higher mechanical properties after tempering and thus crack during quenching, while others have lower mechanical properties and fail to meet the standards. It is impossible to distinguish which parts have qualified mechanical properties and which have failed within the same batch of material, making normal supply impossible.

[0009] Patent document CN201721188530.9 provides a high-pressure main piston for preventing quenching cracks. The piston has two valve discs with a piston rod between them. The side surface of each valve disc has an oil storage groove with a width of 3.8 mm, and the effective width of each valve disc on one side is 5 mm. The beneficial effect of this patent document is that by modifying the piston dimensions, it can effectively solve the problem of valve disc cracking during carburizing and quenching, with significant results.

[0010] Patent document CN202211044997.1 provides a heat treatment equipment and process for bearing rollers. A placement seat is slidably connected to the bottom of the inner wall of the heat treatment furnace. Slider blocks are installed on both sides of the center of the bottom of the placement seat. A fixing box is installed at the bottom of the heat treatment furnace and at the corresponding position of the sliders. A connecting plate is fixedly connected to the bottom of the sliders and inside the fixing box. A rack is installed on the outer wall of the connecting plate. A drive shaft is rotatably connected inside the fixing box and near the connecting plate. A drive gear is fixedly connected to the outer wall of the drive shaft and at the corresponding position of the rack. A worm gear is fixedly connected to the outer wall of the drive shaft and below the drive shaft. This patent document effectively solves the problem that current heat treatment processes for bearing rollers simply involve quenching and tempering, resulting in poor performance of the manufactured bearing rollers and failure to meet usage requirements.

[0011] Patent document CN202211426715.4 describes a nickel-saving Nb7Ni cryogenic steel for LNG storage tanks and its heat treatment process. This process reduces Ni content by adding the microalloying element Nb and optimizes the heat treatment process of high-temperature quenching + two-phase quenching + high-temperature tempering (QLT). This results in a reversible austenite formation and stability comparable to 9Ni steel, along with similar mechanical properties, especially a transverse impact energy (AKV) ≥ 110J at -196℃. This yields a low-cost, nickel-saving Nb7Ni cryogenic steel to replace 9Ni steel in LNG storage tanks, demonstrating excellent economic applicability.

[0012] The aforementioned patent documents are not highly relevant to this application. Summary of the Invention

[0013] The technical problem to be solved by this invention is that some crankshaft blanks crack after quenching and tempering, resulting in a high scrap rate and serious losses. Some parts have low mechanical properties and are unqualified, requiring rework. This invention provides a heat treatment process and application to improve the heat treatment quality of quenched and tempered crankshaft blanks.

[0014] It should be noted that in this paper, relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations.

[0015] Moreover, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0016] To solve the above-mentioned technical problems, the present invention is implemented using the following technical solution:

[0017] A heat treatment process to improve the heat treatment quality of quenched and tempered crankshaft blanks requires steel mills to supply materials from the same batch of heats in three rolling batches: the head of the material, the middle of the material, and the tail of the material, based on the carbon content. Three different quenching and tempering processes are formulated according to the composition of the three rolling batches.

[0018] Furthermore, the quenching and tempering process is determined for the batch number of the blank: the crankshaft blank is loaded into a suspended quenching furnace, heated for 230 to 290 minutes to 835°C to 845°C, held for 100 to 160 minutes, cooled for 12 to 32 minutes to 815°C to 825°C, held for 34 to 54 minutes, and then vertically transferred to a quenching tank to cool to room temperature; it is then transferred to a suspended tempering furnace, heated for 270 to 330 minutes to 625°C to 635°C, held for 320 to 380 minutes, and then water-cooled before being unloaded into the material box.

[0019] Furthermore, the heat treatment process is determined for the batch number of the material: the crankshaft blank is loaded into a suspended quenching furnace, heated for 230 to 290 minutes to 835°C to 845°C, held for 100 to 160 minutes, cooled for 12 to 32 minutes to 830 to 840°C, held for 34 to 54 minutes, and then vertically transferred to a quenching tank to cool to room temperature; it is then transferred to a suspended tempering furnace, heated for 270 to 330 minutes to 595°C to 605°C, held for 320 to 380 minutes, and then water-cooled before being unloaded into the material box.

[0020] Furthermore, the tail roll batch is assigned a tempering process: the crankshaft blank is loaded into a suspended quenching furnace, heated for 230 to 290 minutes to 835°C to 845°C, held for 100 to 160 minutes, cooled for 12 to 32 minutes to 845°C to 855°C, held for 34 to 54 minutes, and then vertically transferred to a quenching tank to cool to room temperature; it is then transferred to a suspended tempering furnace, heated for 270 to 330 minutes to 575°C to 585°C, held for 320 to 380 minutes, and then water-cooled before being unloaded into a material box.

[0021] Preferably, the batch number of the raw material is used to determine the tempering process: the crankshaft blank is loaded into a suspended quenching furnace, heated to 840°C for 260 minutes, held for 130 minutes, cooled to 820°C for 22 minutes, held for 44 minutes, and then vertically placed into a quenching tank to cool to room temperature; it is then placed into a suspended tempering furnace, heated to 630°C for 300 minutes, held for 350 minutes, and then water-cooled before being unloaded into a material box.

[0022] Preferably, the heat treatment process is determined by the batch number of the material: the crankshaft blank is loaded into a suspended quenching furnace, heated to 840°C for 260 minutes, held for 130 minutes, cooled to 835°C for 22 minutes, held for 44 minutes, and then vertically placed into a quenching tank to cool to room temperature; it is then placed into a suspended tempering furnace, heated to 600°C for 300 minutes, held for 350 minutes, and then water-cooled before being unloaded into a material box.

[0023] Preferably, the tail roll batch number is used to determine the tempering process: the crankshaft blank is loaded into a suspended quenching furnace, heated to 840°C for 260 minutes, held for 130 minutes, heated to 850°C for 22 minutes, held for 44 minutes, and then vertically placed into a quenching tank to cool to room temperature; it is then placed into a suspended tempering furnace, heated to 580°C for 300 minutes, held for 350 minutes, and then water-cooled before being unloaded into a material box.

[0024] Furthermore, the quenching tank contains a quenching agent.

[0025] An application of a heat treatment process to improve the heat treatment quality of quenched and tempered crankshaft blanks, wherein the 6DM2 engine crankshaft blanks are quenched and tempered using the heat treatment process described above.

[0026] Furthermore, the crankshaft blank material is 42CrMo.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] This invention solves the problem of quenching cracks in crankshaft blanks during the quenching and tempering process. The quenching crack ratio has been reduced from 6% to below 0.5%, greatly reducing the loss of quenching crack scraps. All parts have qualified mechanical properties and do not require rework. Attached Figure Description

[0029] The invention will now be further described with reference to the accompanying drawings:

[0030] Figure 1 This is a schematic diagram of a crankshaft blank;

[0031] Figure 2 This is a quenching and tempering process curve diagram for the heat treatment process used to improve the heat treatment quality of quenched and tempered crankshaft blanks according to the present invention.

[0032] Figure 3 This is a flow chart of the heat treatment process for improving the heat treatment quality of tempered crankshaft blanks according to the present invention. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be described in more detail below with reference to the accompanying drawings.

[0034] In the accompanying drawings, the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout.

[0035] The described embodiments are some, but not all, of the embodiments of the present invention. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0036] Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this invention. The embodiments of this invention will now be described in detail with reference to the accompanying drawings.

[0037] In the description of this invention, it should be understood that the terms "center", "longitudinal", "lateral", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the scope of protection of this invention.

[0038] The present invention will now be described in detail with reference to the accompanying drawings:

[0039] The technical solution of this invention is: quenching + tempering + inspection + flaw detection. The quenching + tempering process curve is shown below. Figure 2 .

[0040] Design concept and implementation method:

[0041] During the smelting process, the raw materials of the same batch exhibit compositional segregation and uneven composition. Parts treated with the same quenching and tempering process may have different carbon contents, resulting in cracking after quenching and tempering, or lower carbon contents, leading to substandard mechanical properties after quenching and tempering.

[0042] To resolve this issue, see [link / reference] Figure 3 The steel mill was required to supply materials from the same heat batch in three rolling batches—head, middle, and tail—based on their carbon content. Three different quenching and tempering processes were developed based on the composition of each of the three batches. This process completely resolved the problems of substandard mechanical properties and quenching cracks.

[0043] The chemical composition of the material at the beginning, middle, and end of the feed differs, with the beginning having a higher chemical composition, the end having a lower chemical composition, and the middle having a chemical composition between the beginning and end. The hardenability of these three states of material is mainly determined by eight elements: C, Si, Mn, Cr, Ni, Cu, Mo, and V. The DI value is the ideal critical diameter, as shown in Table 1.

[0044] Table 1

[0045] Material condition feedstock Material End of material C(％) 0.43-0.46 0.40-0.43 0.37-0.40 Hardenability DI 5.4-6.0 5.0-5.4 4.6-5.0

[0046] 1. Quenching + Tempering

[0047] (1) Setting the batch number of the blank and heat treatment process: The crankshaft blank is loaded into the suspended quenching furnace, heated for 230 minutes to 290 minutes to 835℃ to 845℃, held for 100 minutes to 160 minutes, cooled for 12 minutes to 32 minutes to 815℃ to 825℃, held for 34 minutes to 54 minutes, and then vertically entered into the quenching tank (with quenching agent) to cool to room temperature; then entered into the suspended tempering furnace, heated for 270 minutes to 330 minutes to 625℃ to 635℃, held for 320 minutes to 380 minutes, then water-cooled and unloaded into the material box.

[0048] (2) The batch number of the material is determined and the tempering process is determined: The crankshaft blank is put into the suspended quenching furnace, heated for 230 minutes to 290 minutes to 835℃ to 845℃, held for 100 minutes to 160 minutes, cooled for 12 minutes to 32 minutes to 830℃ to 840℃, held for 34 minutes to 54 minutes, and then vertically put into the quenching tank (with quenching agent) to cool to room temperature; then put into the suspended tempering furnace, heated for 270 minutes to 330 minutes to 595℃ to 605℃, held for 320 minutes to 380 minutes, then water cooled and unloaded into the material box.

[0049] (3) Setting the batch number of the tail roll and heat treatment process: The crankshaft blank is loaded into the suspended quenching furnace, heated for 230 minutes to 290 minutes to 835℃ to 845℃, held for 100 minutes to 160 minutes, cooled for 12 minutes to 32 minutes to 845℃ to 855℃, held for 34 minutes to 54 minutes, and then vertically entered into the quenching tank (with quenching agent) to cool to room temperature; then entered into the suspended tempering furnace, heated for 270 minutes to 330 minutes to 575℃ to 585℃, held for 320 minutes to 380 minutes, then water cooled and unloaded into the material box.

[0050] 2. Inspection: Hardness, metallographic properties and mechanical properties.

[0051] 3. Flaw detection: Check for any cracks or fractures in the parts.

[0052] Example 1

[0053] 1. Quenching + Tempering

[0054] (1) Setting the batch number of the blank and heat treatment process: The crankshaft blank is loaded into the suspended quenching furnace, heated to 835°C for 230 minutes, held for 100 minutes, cooled to 815°C for 12 minutes, held for 34 minutes, and then vertically entered into the quenching tank (with quenching agent) to cool to room temperature; it is then put into the suspended tempering furnace, heated to 625°C for 270 minutes, held for 320 minutes, and then water-cooled and unloaded into the material box.

[0055] (2) The batch number of the material is determined and the tempering process is as follows: The crankshaft blank is loaded into the suspended quenching furnace, heated to 835°C for 230 minutes, held for 100 minutes, cooled to 830°C for 12 minutes, held for 34 minutes, and then vertically inserted into the quenching tank (with quenching agent) to cool to room temperature; it is then inserted into the suspended tempering furnace, heated to 595°C for 270 minutes, held for 320 minutes, and then water-cooled and unloaded into the material box.

[0056] (3) Setting the batch number of the tail roll and heat treatment process: The crankshaft blank is loaded into the suspended quenching furnace, heated to 835°C for 230 minutes, held for 100 minutes, heated to 845°C for 12 minutes, held for 34 minutes, and then vertically entered into the quenching tank (with quenching agent) to cool to room temperature; it is then put into the suspended tempering furnace, heated to 575°C for 270 minutes, held for 320 minutes, and then water-cooled and unloaded into the material box.

[0057] 2. Inspection: Hardness, metallographic properties and mechanical properties.

[0058] 3. Flaw detection: Check for any cracks or fractures in the parts.

[0059] Example 2

[0060] 1. Quenching + Tempering

[0061] (1) Crankshaft blanks of the material head: The crankshaft blanks are loaded into a suspended quenching furnace, heated to 840°C for 260 minutes, held for 130 minutes, cooled to 820°C for 22 minutes, held for 44 minutes, and then vertically placed into a quenching tank (with quenching agent) to cool to room temperature; then placed into a suspended tempering furnace, heated to 630°C for 300 minutes, held for 350 minutes, then removed from the furnace and water-cooled, and unloaded into the material box.

[0062] (2) Crankshaft blank in the material: The crankshaft blank is loaded into a suspended quenching furnace, heated to 840°C for 260 minutes, held for 130 minutes, cooled to 835°C for 22 minutes, held for 44 minutes, and then vertically inserted into a quenching tank (with quenching agent) to cool to room temperature; it is then placed into a suspended tempering furnace, heated to 600°C for 300 minutes, held for 350 minutes, and then water-cooled and unloaded into the material box.

[0063] (3) Crankshaft blank at the tail end: The crankshaft blank is loaded into a suspended quenching furnace, heated to 840°C for 260 minutes, held for 130 minutes, heated to 850°C for 22 minutes, held for 44 minutes, and then vertically inserted into a quenching tank (with quenching agent) to cool to room temperature; it is then placed into a suspended tempering furnace, heated to 580°C for 300 minutes, held for 350 minutes, and then water-cooled and unloaded into a material box.

[0064] 2. Inspection: Hardness, metallographic properties and mechanical properties.

[0065] 3. Flaw detection: Check for any cracks or fractures in the parts.

[0066] Example 3

[0067] 1. Quenching + Tempering

[0068] (1) Setting the batch number of the blank and heat treatment process: The crankshaft blank is loaded into the suspended quenching furnace, heated to 845°C for 290 minutes, held for 160 minutes, cooled to 825°C for 32 minutes, held for 54 minutes, and then vertically entered into the quenching tank (with quenching agent) to cool to room temperature; it is then put into the suspended tempering furnace, heated to 635°C for 330 minutes, held for 380 minutes, and then water-cooled and unloaded into the material box.

[0069] (2) The batch number of the material is determined and the tempering process is as follows: The crankshaft blank is loaded into the suspended quenching furnace, heated to 845°C for 290 minutes, held for 160 minutes, cooled to 840°C for 32 minutes, held for 54 minutes, and then vertically entered into the quenching tank (with quenching agent) to cool to room temperature; it is then put into the suspended tempering furnace, heated to 605°C for 330 minutes, held for 380 minutes, and then water-cooled and unloaded into the material box.

[0070] (3) Setting the batch number of the tail roll and heat treatment process: The crankshaft blank is loaded into the suspended quenching furnace, heated to 845°C for 290 minutes, held for 160 minutes, heated to 855°C for 32 minutes, held for 54 minutes, and then vertically entered into the quenching tank (with quenching agent) to cool to room temperature; it is then put into the suspended tempering furnace, heated to 585°C for 330 minutes, held for 380 minutes, and then water-cooled and unloaded into the material box.

[0071] 2. Inspection: Hardness, metallographic properties and mechanical properties.

[0072] 3. Flaw detection: Check for any cracks or fractures in the parts.

[0073] After the implementation of this process, the problem of quenching cracks in the crankshaft blank during the quenching and tempering process was solved. The quenching crack ratio was reduced from 6% to below 0.5%, which greatly reduced the loss of quenching crack scraps. All parts met the mechanical properties and did not require rework.

[0074] Example 4

[0075] Application Example: A 130 kg crankshaft blank for a 6DM2 engine was heat-treated using the heat treatment process of this invention on a large-scale heat treatment line. The mechanical properties were qualified and there were no quenching cracks.

[0076] Example 5

[0077] Application Example: A 98 kg crankshaft blank for a 6DM2 engine was heat-treated using the heat treatment process of this invention on a large-scale heat treatment line. The mechanical properties were qualified and there were no quenching cracks.

[0078] The crankshaft blank material mentioned above is 42CrMo.

[0079] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be included within the scope of protection of the present invention. Furthermore, all content not described in detail in this specification is prior art known to those skilled in the art.

Claims

1. A heat treatment process for improving the heat treatment quality of quenched and tempered crankshaft blanks, characterized in that: The steel mill is required to supply the same batch of material in three rolling batches based on the carbon content: head, middle, and tail of the material; and to develop three different quenching and tempering processes based on the composition of the three rolling batches. The batch number of the raw material is determined by the following tempering process: The crankshaft blank is loaded into a suspended quenching furnace, heated for 230-290 minutes to 835-845℃, held for 100-160 minutes, cooled for 12-32 minutes to 815-825℃, held for 34-54 minutes, and then vertically transferred to a quenching tank to cool to room temperature. It is then transferred to a suspended tempering furnace, heated for 270-330 minutes to 625-635℃, held for 320-380 minutes, and then water-cooled before being unloaded into the material box. The heat treatment process for the batch number of the crankshaft blank is as follows: The crankshaft blank is placed in a suspended quenching furnace, heated for 230-290 minutes to 835-845℃, held for 100-160 minutes, cooled for 12-32 minutes to 830-840℃, held for 34-54 minutes, and then vertically transferred to a quenching tank to cool to room temperature. It is then placed in a suspended tempering furnace, heated for 270-330 minutes to 595-605℃, held for 320-380 minutes, and then water-cooled before being unloaded and placed in a material box. The tail roll batch number is used to determine the heat treatment process: The crankshaft blank is loaded into a suspended quenching furnace, heated for 230 to 290 minutes to 835°C to 845°C, held for 100 to 160 minutes, cooled for 12 to 32 minutes to 845°C to 855°C, held for 34 to 54 minutes, and then vertically transferred to a quenching tank to cool to room temperature. It is then transferred to a suspended tempering furnace, heated for 270 to 330 minutes to 575°C to 585°C, held for 320 to 380 minutes, and then water-cooled before being unloaded into the material box.

2. The heat treatment process for improving the heat treatment quality of quenched and tempered crankshaft blanks according to claim 1, characterized in that: The batch number of the raw material is determined and the tempering process is as follows: The crankshaft blank is loaded into a suspended quenching furnace, heated to 840℃ for 260 minutes, held for 130 minutes, cooled to 820℃ for 22 minutes, held for 44 minutes, and then vertically placed into a quenching tank to cool to room temperature. It is then placed into a suspended tempering furnace, heated to 630℃ for 300 minutes, held for 350 minutes, and then water-cooled before being unloaded into the material box.

3. The heat treatment process for improving the heat treatment quality of tempered crankshaft blanks according to claim 1, characterized in that: The process for determining the heat treatment of the batch number of the material is as follows: The crankshaft blank is loaded into a suspended quenching furnace, heated to 840℃ for 260 minutes, held for 130 minutes, cooled to 835℃ for 22 minutes, held for 44 minutes, and then vertically placed into a quenching tank to cool to room temperature. It is then placed into a suspended tempering furnace, heated to 600℃ for 300 minutes, held for 350 minutes, and then water-cooled before being unloaded into the material box.

4. The heat treatment process for improving the heat treatment quality of tempered crankshaft blanks according to claim 1, characterized in that: The tail roll batch number is determined by the following tempering process: The crankshaft blank is loaded into a suspended quenching furnace, heated to 840℃ for 260 minutes, held for 130 minutes, heated to 850℃ for 22 minutes, held for 44 minutes, and then vertically placed into a quenching tank to cool to room temperature. It is then placed into a suspended tempering furnace, heated to 580℃ for 300 minutes, held for 350 minutes, and then water-cooled before being unloaded into the material box.

5. A heat treatment process for improving the heat treatment quality of quenched and tempered crankshaft blanks according to any one of claims 1 to 4, characterized in that: The quenching tank contains a quenching agent.

6. The application of the heat treatment process for improving the heat treatment quality of tempered crankshaft blanks as described in claim 5, characterized in that: The crankshaft blank for the 6DM2 engine is quenched and tempered using the aforementioned heat treatment process; The crankshaft blank material is 42CrMo.

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