Forging control methods for consistent performance and weight of non-quenched and tempered steel connecting rod blanks

Abstract

This invention discloses a forging control method for ensuring consistent performance and weight of non-quenched and tempered steel connecting rod blanks. The process for forging connecting rod blanks using 38MnVS6 non-quenched and tempered steel round bars is as follows: sawing, induction heating, high-pressure water descaling, roll forging, flattening, pre-forging, final forging, edge trimming / punching, straightening, and cooling. The preheating temperature for induction heating is controlled at 1170±20℃, the pre-forging temperature is ≥1100℃, and the final forging temperature is ≥1050℃. By precisely controlling the bar temperature during the forging process, the method solves the problems of low mechanical properties after forging and slag shedding at the fracture surface after fracture of the non-quenched and tempered steel connecting rod blanks. It improves the lateral plastic elongation of the connecting rod, reduces impact energy, meets the weight deviation requirement of 70g without grouping, and significantly improves the machinability, fracture performance, weight consistency, and fracture surface quality of the connecting rod blank.

Description

Technical Field

[0001] This invention belongs to the field of automotive material forming technology, specifically relating to a forging control method for ensuring the consistency of performance and weight of non-quenched and tempered steel connecting rod blanks. Background Technology

[0002] As a crucial component in engine assembly, the connecting rod's performance directly impacts engine performance. Therefore, stringent requirements are placed on its mechanical properties. Specifically, the longitudinal tensile strength must be no less than 900 MPa, and its longitudinal elongation after fracture must be no less than 12%, while its transverse elongation after fracture must be no less than 5%. Furthermore, to improve production efficiency and reduce the need for grouping or non-grouping of processed weights, OEMs have imposed even higher requirements on the weight tolerance of connecting rods from forging suppliers, demanding that the connecting rod blank weight meet the requirement of 70g without grouping. Forging process parameters, especially forging temperature, are key factors affecting the consistency of forging quality and weight. Excessively high forging temperatures can cause overheating and burning; excessively low temperatures shorten forging time, narrow the forging temperature range, and increase forging difficulties. Moreover, excessively high final forging temperatures cause grains to continue growing at high temperatures after forging stops, resulting in coarse grains and reduced mechanical properties; excessively low final forging temperatures lead to poor plasticity, difficulty in deformation, increased internal stress, and even cracks in the forging. Precise control of the heating temperature range can reduce the impact of temperature fluctuations on the connecting rod thickness, thereby reducing weight deviation. Therefore, proper control of process parameters during forging can effectively ensure the quality of the connecting rod.

[0003] Currently, although research on connecting rod fracture technology has been carried out in China, the main equipment and materials still rely on imports from abroad, and the technology is still immature. Many problems exist in actual production, such as fracture defects such as tearing, failure to expand, flaking, and deformation of the fracture surface, which affect the stability of product quality. Furthermore, the influence mechanism of various factors on the fracture quality of connecting rods is still unclear, and the selection of fracture process parameters mainly relies on experience without theoretical support. Therefore, the localization of connecting rod blanks and research on connecting rod fracture technology are very urgent. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a forging control method for ensuring the consistency of performance and weight of non-quenched and tempered steel connecting rod blanks. While ensuring feasibility on existing production lines, the method clarifies the process and forging temperature range for 38MnVS6 non-quenched and tempered steel forged connecting rod blanks, resolving issues such as material defects and insufficient mechanical properties caused by excessively high or low forging temperatures, and meeting the requirement of a 70g weight deviation without grouping. Furthermore, while ensuring the consistency of performance and weight of the forged blanks meets the requirements, the method also addresses issues such as slag shedding / sharp steps on the fracture surface after connecting rod fracture.

[0005] To address the problems of unclear forging process, unstable performance and weight of forged blanks, and defects during fracture in existing technologies for non-quenched and tempered steel connecting rod blanks, this invention provides a forging control method for ensuring consistent performance and weight of non-quenched and tempered steel connecting rod blanks. The process for forging connecting rod blanks using 38MnVS6 non-quenched and tempered steel round bars is as follows (see...). Figure 1 The process involves sawing, induction heating, high-pressure water descaling, roll forging, flattening, pre-forging, final forging, edge trimming / punching, straightening, and cooling to obtain a qualified fracture-resistant connecting rod blank. The key features are: induction heating preheating temperature controlled at 1170±20℃, pre-forging temperature ≥1100℃, and final forging temperature ≥1050℃. By precisely controlling the material temperature during forging, the problems of low mechanical properties and large weight deviations in non-quenched and tempered steel connecting rod blanks after forging are solved, significantly improving the machinability, weight consistency, and fracture surface quality of the connecting rod blank.

[0006] The forging control method for ensuring consistent performance and weight of non-quenched and tempered steel connecting rod blanks involves setting strict temperature control ranges for each forging process (see [link]). Figure 2 The process steps and temperature control are as follows:

[0007] S1: When sawing and cutting the material, the angle of the end face of the material segment should be ≤2°;

[0008] S2: Induction heating, the temperature of the material section exiting the furnace is controlled at 1170±20℃, and the billet is not reheated before the entire forging process is completed;

[0009] S3: High-pressure water descaling ensures that the oxide scale removal rate on the surface of the heated bar stock is ≥90%;

[0010] S4: Roll-forged billet, drawn rod section;

[0011] S5: Flatten;

[0012] S6: Pre-forging, pre-forging temperature ≥1100℃, mold cavity temperature controlled at 120~300℃;

[0013] S7: Final forging, final forging temperature ≥1050℃, mold cavity temperature controlled at 120~300℃;

[0014] S8: Edge trimming / punching, edge trimming temperature ≥1000℃;

[0015] S9: Correction, correction temperature ≥950℃, to ensure the symmetry, straightness and geometric dimensions of the connecting rod; then cooling treatment to obtain the finished product.

[0016] Furthermore, the final cooling process of this invention involves controlling the airflow within a box furnace to achieve rapid and slow cooling. Specifically, the connecting rod blank, with a pre-cooling temperature ≥830℃, sequentially undergoes rapid cooling within the box furnace, slow cooling within the box furnace, slow cooling with external air, and cooling by stacking it in an insulated material frame. The rapid cooling within the box furnace is: cooling from ≥830℃ to 710±20℃ at a cooling rate of 1.5~2.5℃ / S; the slow cooling within the box furnace is: cooling from 710±20℃ to 580±20℃ at a cooling rate of 0.4~1.3℃ / S; the slow cooling with external air is: cooling from 580±20℃ to 480±20℃ at a cooling rate of 0.13~0.20℃ / S; and the cooling by stacking it in the insulated material frame is: cooling from 480±20℃ to room temperature.

[0017] In step S1 of this invention, the end face angle of the material segment should be ≤2°. The purpose is twofold: first, to ensure that the weight meets the requirements, reduce weight deviation, and ensure the consistency of the final blank weight; second, to ensure accurate positioning in the subsequent roll forging process, ensure that the metal flow meets the requirements during the material deformation process, and also to ensure the accurate positioning of the blank in the mold during the subsequent forging process.

[0018] In step S2 of this invention, the furnace exit temperature of the material segment is controlled at 1170±20℃. This temperature is the optimal temperature explored by the applicant through experiments. When the furnace exit temperature of the material segment is too high, the mechanical properties after forging are lower. This is because during the entire forging process, a high billet temperature leads to grain growth during forging, resulting in relatively coarse grain size after forging, thus causing lower strength and poorer plasticity. In addition, the higher the temperature, the more significant the volume expansion of the material. Since the cavity volume of the forging die is fixed, this will lead to a smaller volume of the billet after cooling, resulting in weight deviations and affecting the weight consistency of the product. On the other hand, a temperature that is too low will reduce the plasticity of the material, affect metal flow, and hinder metal filling in the die cavity during forging, potentially causing defects such as material shortages or folds.

[0019] In step S6 of this invention, the pre-forging temperature is ≥1100℃, and the mold cavity temperature is controlled between 120℃ and 300℃. The pre-forging temperature cannot be too low, as this will affect the plasticity of the material and the forming properties throughout the forging process. This temperature control also effectively controls the production cycle time, preventing excessive temperature drops due to long production cycles. Mold cavity temperature control: Because the mold itself has a low temperature, it significantly lowers the temperature of the billet upon contact, thereby reducing the billet's plasticity and affecting the metal's forming properties. Therefore, preheating of the mold cavity is necessary. Natural gas flame heating is used, which offers rapid heating and ease of operation. However, since the material itself generates heat during forging deformation, the mold preheating temperature does not need to be too high. Considering both efficiency and the impact on the billet temperature, the mold cavity preheating temperature is determined to be controlled between 120℃ and 300℃.

[0020] The principle of controlling the final forging temperature in step S7 of this invention is the same as that in step S6. Too low a final forging temperature will affect the plasticity of the material, thus affecting the performance of the blank; excessive temperature changes will also affect the consistency of product weight.

[0021] The temperature control principle of steps S8 and S9 in this invention is the same as that of step S6. It is set to ensure the continuous performance of the material, while also taking into account the temperature drop caused by the natural cooling of the billet under production cycle time.

[0022] In summary, precise control of forging temperature can: 1) ensure the formability of the material and avoid forging defects; 2) ensure uniform microstructure and relatively small grain size after grain deformation at this temperature, thus guaranteeing the mechanical properties of the forged blank; and 3) constrain the expansion rate and fluidity of the metal material by limiting the temperature range, ensuring the weight consistency of the forged blank and avoiding excessive dimensional differences after cooling due to large temperature variations.

[0023] The technical advantages of this invention are as follows: By precisely controlling the bar temperature during the forging process, it solves the problems of low mechanical properties after forging of non-quenched and tempered steel connecting rod blanks and slag shedding at the fracture surface after fracture. It improves the transverse plastic elongation of the connecting rod (≥5%), reduces the impact energy (meeting the requirement of 6-14J), and meets the weight deviation requirement of 70g without grouping. It significantly improves the machinability, fracture performance, weight consistency, and fracture surface quality of the connecting rod blank. Attached Figure Description

[0024] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0025] Figure 1 This is a flow chart of the forging process of the non-quenched and tempered steel connecting rod of the present invention;

[0026] Figure 2 This is a temperature control diagram for each stage of the forging process of the non-quenched and tempered steel connecting rod of the present invention.

[0027] Figure 3 The fracture morphology of the connecting rod blank prepared in Comparative Example 1 of this invention shows the fracture surface defects.

[0028] Figure 4 The fracture morphology of the expansion joint of the connecting rod blank prepared in Example 1 of the present invention. Detailed Implementation

[0029] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the scope of protection of the present invention.

[0030] The tensile test reference standard for this invention embodiment is GB / T228.2-2015, "Metallic materials, tensile testing, part 1: room temperature test method"; the impact test standard is generally GB / T 229—2007, "Metallic materials, Charpy pendulum impact test method".

[0031] Example 1:

[0032] The process control of the forging of 38MnVS6 connecting rod blanks in this invention is as follows:

[0033] S1: When using a saw to cut the material, the end face angle of the material segment should be ≤2°;

[0034] S2: Induction heating: The bar stock is rapidly heated to the set temperature (1170℃) and held at that temperature using induction heating. The temperature of the material segment exiting the furnace is controlled at 1172℃, and the billet is not reheated before the entire forging process is completed.

[0035] S3: High-pressure water descaling ensures that the oxide scale removal rate on the surface of the heated bar stock is ≥90%;

[0036] S4: Roll-forged billet, drawn rod section;

[0037] S5: Flattening: Flattening and deforming the billet after the rod part is drawn;

[0038] S6: Pre-forging: The flattened billet is picked up and placed into the preheated pre-forging die cavity. At this time, the pre-forging temperature of the billet is 1108℃, and the temperature of the die cavity is controlled at 120~300℃ to carry out pre-forging deformation.

[0039] S7: Final forging: The pre-forged billet is picked up and placed into the preheated final forging die cavity. At this time, the final forging temperature of the billet is 1060℃, and the die cavity temperature is controlled at 120~300℃ to carry out final forging deformation.

[0040] S8: Trimming / Punching, place the final forging in the trimming die to remove the forging flash, trimming temperature 1012℃;

[0041] S9: Correction: Correction temperature 962℃ to ensure the symmetry, straightness and geometric dimensions of the connecting rod; then cooling treatment (lower temperature before cooling is 904℃) to finally obtain the connecting rod blank.

[0042] The aforementioned cooling process achieves rapid and slow cooling within a box furnace by controlling the airflow. Specifically, the connecting rod blank sequentially undergoes rapid cooling within the box furnace, slow cooling within the box furnace, slow cooling with external air, and cooling by stacking it in an insulated material frame. Rapid cooling within the box furnace cools from ≥830℃ to 710±20℃ at a rate of 1.5–2.5℃ / s; slow cooling within the box furnace cools from 710±20℃ to 580±20℃ at a rate of 0.4–1.3℃ / s; slow cooling with external air cools from 580±20℃ to 480±20℃ at a rate of 0.13–0.20℃ / s; and cooling by stacking it in the insulated material frame cools from 480±20℃ to room temperature.

[0043] The performance of the continuously cast billets was tested. The connecting rod billets weighing 70g were not grouped. Other test indicators are shown in Table 3.

[0044] Comparative Example 1 (High Temperature):

[0045] The forging process control of the 38MnVS6 connecting rod blank is shown in Table 1, and the rest is the same as in Example 1. The weight of the connecting rod blank partially fails to meet the requirements, with fluctuations exceeding 70g. Other testing indicators are shown in Table 2.

[0046] Table 1 Temperature settings for Example 1 and Comparative Example 1

[0047]

[0048]

[0049] Tables 2 and 3 show the strength, elongation, and impact performance of the blanks obtained at the forging temperatures of the comparative example and Example 1, respectively. The forged connecting rod blanks were then machined and subjected to fracture treatment (the process mainly included: drilling oil holes—laser marking—rough boring of the large and small end holes, grinding the end face, drilling and tapping—cooling, laser grooving, fracture treatment, bolt tightening, and bushing installation in the small end hole—fine boring of the large and small end holes, grinding the end face—deburring—flaw detection—cleaning—finished product weighing—fracture surface inspection). Figure 3 The fracture morphology of the fracture surface defect of the connecting rod obtained at the forging temperature in Comparative Example 1 is presented. Figure 4 The fracture surface morphology of the connecting rod obtained at the forging temperature in Example 1 after fracture is given.

[0050] In Example 1 and Comparative Example 1, the induction heating temperatures of the round bar stock differ, with Comparative Example 1 being higher than that of Example 1. Correspondingly, the temperatures for pre-forging, final forging, trimming, and correction in Comparative Example 1 are also higher than those in Example 1. Comparing Comparative Example 1 and Example 1 reveals that when the temperature is too high, the transverse and longitudinal strength of the connecting rod blank is relatively low, and the transverse elongation does not reach 5%. This invention, by controlling the temperature during the forging process of the 38MnVS6 connecting rod blank, can achieve improved and effective control of the connecting rod blank's performance. Furthermore, as... Figure 3-4 The connecting rod obtained in Example 1, after being processed and fractured, has a better fracture surface quality than that of Comparative Example 1, and there is no slag shedding or sharp steps.

[0051] Table 2: Performance test results of the connecting rod blank prepared in Comparative Example 1 of the present invention

[0052]

[0053] Table 3: Performance test results of the connecting rod blank prepared in Example 1 of the present invention

[0054]

[0055] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made using the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A forging control method for ensuring consistent performance and weight of non-quenched and tempered steel connecting rod blanks, characterized in that, The process steps and temperature control for forging connecting rod blanks using 38MnVS6 non-quenched and tempered steel round bars are as follows: S1: When sawing and cutting the material, the angle of the end face of the material segment should be ≤2°; S2: Induction heating, the material outlet temperature is controlled at 1170±20℃; S3: High-pressure water descaling ensures that the oxide scale removal rate on the surface of the heated bar stock is ≥90%; S4: Roll-forged billet, drawn rod section; S5: Flatten; S6: Pre-forging, pre-forging temperature ≥1100℃; S7: Final forging, final forging temperature ≥1050℃; S8: Edge trimming / punching, edge trimming temperature ≥1000℃; S9: Correction, correction temperature ≥950℃, to ensure the symmetry, straightness and geometric dimensions of the connecting rod; then cooling treatment to obtain the finished product; The cooling process is as follows: the connecting rod blank has a temperature ≥830℃ before cooling, and then passes through rapid cooling in a box furnace, slow cooling in a box furnace, slow cooling with air outside the furnace, and cooling by stacking in an insulated material frame. The rapid cooling inside the box furnace is as follows: cooling from ≥830℃ to 710±20℃ at a cooling rate of 1.5~2.5℃ / S; The slow cooling inside the box furnace is as follows: cooling from 710±20℃ to 580±20℃ at a cooling rate of 0.4~1.3℃ / S; The slow cooling of the air outside the furnace is: cooling from 580±20℃ to 480±20℃ at a cooling rate of 0.13~0.20℃ / S; The insulation material is stacked and cooled from 480±20℃ to room temperature.

2. The forging control method as described in claim 1, characterized in that, The billet is not reheated before the entire forging process is completed.

3. The forging control method as described in claim 1, characterized in that, The temperature of the mold cavity in step S6, pre-forging, is controlled at 120–300°C.

4. The forging control method as described in claim 1, characterized in that, The temperature of the mold cavity in the final forging step S7 is controlled between 120 and 300°C.

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