Heat treatment process for improving the comprehensive mechanical properties of 42CrMo forged parts with milled flats and avoiding cracking

Abstract

The present invention relates to a heat treatment process for improving the comprehensive mechanical properties of a flattened 42CrMo forging and preventing cracking. The process optimizes the dimensional design of the flattened portion during roughing, reduces stress concentration at a variable cross-section during quenching while ensuring the hardenability of the flattened portion, and reserves a processing allowance for ring cracking. During the quenching heating process, thermal stress is reduced by controlling the furnace entry temperature, heating at a limited speed, and preheating. Stepwise heating and heat preservation are used to ensure uniformity of the internal structure and composition of the forging, preparing for quenching and cooling. An air-water-air-liquid-air-liquid quenching and cooling method is designed to effectively ensure the quenching and cooling effect, reduce the quenching and cooling intensity, and avoid the risk of forging cracking. High-temperature tempering is performed at 570°C to 620°C to effectively remove quenching stress, improve the plastic toughness of the forging, and ensure that the comprehensive mechanical properties meet the requirements.

Description

Technical Field

[0001] The invention belongs to the technical field of heat treatment of metal materials, and in particular relates to a heat treatment process for improving the comprehensive mechanical properties of a flattened 42CrMo forging and preventing cracking. Background Art

[0002] In actual production, there are two main factors affecting the quality of 42CrMo forgings with an outer diameter of φ230mm, a local flattening thickness of 130mm, and a length of 300mm. On the one hand, due to the large difference between the local flattening thickness and the cross-sectional dimensions of the outer diameter, quenching cracking is very likely to occur during heat treatment, resulting in scrap. On the other hand, to avoid quenching cracking caused by the large difference between the local flattening thickness and the cross-sectional dimensions of the outer diameter, the quenching cooling force is weakened, resulting in extremely low impact energy and poor overall mechanical properties, which cannot meet the user's technical requirements. Therefore, based on actual production conditions, a heat treatment process method is urgently needed that can both prevent quenching cracking and improve overall mechanical properties. Summary of the Invention

[0003] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a heat treatment process for improving the comprehensive mechanical properties of milled 42CrMo forgings and avoiding cracking, which can achieve the goal of achieving excellent comprehensive mechanical properties while avoiding quenching cracking of milled 42CrMo forgings.

[0004] In order to achieve the above-mentioned object of the invention, the present invention adopts the following technical solutions:

[0005] A heat treatment process for improving the comprehensive mechanical properties of milled 42CrMo forgings and preventing cracking is carried out in accordance with the following process steps:

[0006] Step 1) Optimize the size design of the flattened part during roughing: first, increase the chamfer of the flattened part, and adjust the chamfer of the step from R10mm to R30mm; secondly, increase the ring crack allowance of the steps at both ends of the flattened part, and shorten the flattened length from 300mm to 230mm;

[0007] Step 2), quenching heating: furnace temperature ≤ 350℃, speed limit ≤ 50℃ / h, heat to 670-690℃, keep warm for 1h, continue to heat to 860-880℃, keep warm for 3-5h, cool down to 840-860℃ with the furnace, keep warm for 1-3h and then take out of the furnace;

[0008] Step 3), quenching cooling: 1) air cooling 250-300s; 2) water cooling 300-360s, initial water temperature 30-35°C; 3) air cooling 90-120s; 4) water-based liquid cooling 16-20min, initial liquid temperature 30-50°C, concentration 10-12%; 5) air cooling 60-80s; 6) water-based liquid cooling 16-20min;

[0009] Step 4) Tempering heating: the temperature in the furnace is ≤450℃, the temperature is raised to 570~620℃, kept at this temperature for 7~9h, and then taken out of the furnace and air-cooled;

[0010] Step 5) Semi-finishing: according to the user's drawing, the milling length is processed from 230mm to 300mm.

[0011] Due to the adoption of the above technical solution, the present invention has the following advantages:

[0012] 1. By optimizing the size design of the flattened part during roughing, the stress concentration at the variable cross section during quenching is effectively reduced while ensuring the hardenability of the flattened part, and a ring crack processing allowance is reserved;

[0013] 2. During the quenching heating process, thermal stress is reduced by controlling the furnace temperature, speed-limited heating, and preheating; step-by-step heating and heat preservation are used to ensure that the internal structure and composition of the forging are homogenized, preparing for quenching cooling;

[0014] 3. The air-water-air-liquid-air-liquid quenching cooling method is designed to effectively ensure the quenching cooling effect and reduce the quenching cooling intensity to avoid the risk of forging cracking;

[0015] 4. High temperature tempering at 570℃~620℃ can effectively remove quenching stress, improve the plasticity and toughness of forgings, make the comprehensive mechanical properties meet user requirements, and improve product delivery rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Design diagram before and after size optimization of the flattened area.

[0017] Figure 2 Heat treatment process curve of milled 42CrMo forgings. DETAILED DESCRIPTION

[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0019] Example 1: Take a 42CrMo forging with an outer diameter of φ230mm, a length of 8m, and a local flattening of 130mm in thickness and 300mm in length at a position 2m away from the riser end as an example. The heat treatment process steps are as follows:

[0020] Step 1) Optimize the size design of the flattened part during roughing: 1) Increase the chamfer of the flattened part and adjust the chamfer of the step from R10mm to R30mm; 2) Increase the ring crack allowance of the steps at both ends of the flattened part and shorten the flattened length from 300mm to 230mm;

[0021] Step 2), quenching heating: furnace temperature ≤ 350℃, speed limit ≤ 50℃ / h, heat to 670-690℃, keep warm for 1h, continue to heat to 860-880℃, keep warm for 4h, cool down to 840-860℃ with the furnace, keep warm for 2h and then take out of the furnace;

[0022] Step 3), quenching cooling: 1) air cooling 280s; 2) water cooling 320s, initial water temperature 35℃; 3) air cooling 100s; 4) water-based liquid cooling 20min, initial liquid temperature 45℃, concentration 12%; 5) air cooling 70s; 6) water-based liquid cooling 18min into the tempering furnace;

[0023] Step 4) Tempering heating: furnace temperature ≤ 450℃, heat to 580~600℃, keep warm for 8h, then take out of furnace and air cool;

[0024] Step 5) Semi-finishing: according to the user's drawing, the milling length is processed from 230mm to 300mm.

[0025] Comparison example:

[0026] The heat treatment process adopts the non-optimized milling flatness size design and air-liquid-air-liquid-air-liquid quenching cooling method.

[0027] The products of the embodiment and the reference example were tested, and the results are shown in Table 1 below.

[0028] Table 1 Mechanical properties test data of the products of the embodiment and the control example

[0029] The present invention is based on the product size characteristics, optimizes the size design of the flattened part during roughing, and adopts an air-water-air-liquid-air-liquid quenching cooling method. It not only effectively ensures the quenching cooling effect and reduces the quenching cooling intensity to avoid the risk of cracking and scrapping of forgings, but also obtains better comprehensive mechanical properties, which fully demonstrates the significant superiority of the present invention.

Claims

1. A heat treatment process for improving the comprehensive mechanical properties of flattened 42CrMo forgings and preventing cracking, characterized in that: Follow the following process steps: Step 1) Optimize the size design of the flattened part during roughing: first, increase the chamfer of the flattened part, and adjust the chamfer of the step from R10mm to R30mm; secondly, increase the ring crack allowance of the steps at both ends of the flattened part, and shorten the flattened length from 300mm to 230mm; Step 2), quenching heating: furnace temperature ≤ 350℃, speed limit ≤ 50℃ / h, heat to 670-690℃, keep warm for 1h, continue to heat to 860-880℃, keep warm for 3-5h, cool down to 840-860℃ with the furnace, keep warm for 1-3h and then take out of the furnace; Step 3), quenching cooling: 1) air cooling 250-300s; 2) water cooling 300-360s, initial water temperature 30-35°C; 3) air cooling 90-120s; 4) water-based liquid cooling 16-20min, initial liquid temperature 30-50°C, concentration 10-12%; 5) air cooling 60-80s; 6) water-based liquid cooling 16-20min; Step 4) Tempering heating: the temperature in the furnace is ≤450℃, the temperature is raised to 570~620℃, kept at this temperature for 7~9h, and then taken out of the furnace and air-cooled; Step 5) Semi-finishing: according to the user's drawing, the milling length is processed from 230mm to 300mm.

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