Production method for improving macrostructure quality of 38CrMoAl forged piece

Abstract

This invention relates to a production method for improving the low-magnification quality of 38CrMoAl forgings. By controlling the ingot's demolding temperature to adjust its solid-liquid phase ratio, forging deformation is applied to the liquid phase region exhibiting positive chemical element segregation after selection and crystallization. The chemical element concentration in the liquid phase region decreases after being dispersed by external force. Then, normalizing treatment is performed to refine the grain size and transform the austenite structure into pearlite, resulting in another redistribution of chemical elements. Through the superposition of these two beneficial homogenization processes, the general spot-like segregation of the low-magnification structure is finally achieved. This invention improves the degree of chemical element segregation in the ingot by forging an incompletely solidified ingot and normalizing the intermediate billet, reducing the general spot-like segregation level of aluminum-containing steel and improving product quality.

Description

Technical Field

[0001] This invention belongs to the field of forging technology and relates to a production method for improving the low-magnification quality of 38CrMoAl forgings by reducing the general spot-like segregation. Compared with conventional production methods, it can improve the general spot-like segregation to no greater than level 1.0. Background Technology

[0002] GB / T 1979-2001 describes spot segregation as characterized by dark spots of varying shapes and sizes on the acid-soaked sample, regardless of whether the dark spots and bubbles coexist. These dark spots are collectively referred to as spot segregation. When the spots are dispersed across the entire cross-section, it is called general spot segregation.

[0003] It is generally believed that the main cause is poor crystallization conditions, resulting in component segregation due to slow cooling of the molten steel during the crystallization process.

[0004] 38CrMoAl is a nitriding steel used in products such as spindles, barrels, and cylinder liners after nitriding. Due to its high Al content and the larger the ingot size, the slower the cooling after casting, leading to more severe compositional segregation. When producing forgings using conventional methods such as forging and drawing or directly drawing the ingot, 38CrMoAl forgings often exhibit general spot-like segregation exceeding grade 3.5 in low-magnification microstructure, failing to meet customer requirements and resulting in product scrap. Therefore, there is an urgent need for a production method to improve the general spot-like segregation. Summary of the Invention

[0005] The purpose of this invention is to solve the problem of insufficient control of general spot segregation in conventional methods for producing 38CrMoAl forgings in the background art, and to propose a production method for improving the low-magnification quality of 38CrMoAl forgings by improving the general spot segregation of 38CrMoAl forgings.

[0006] To achieve the above objectives, the technical solution of this invention is as follows: a production method for improving the low-magnification quality of 38CrMoAl forgings, the production method comprising the following steps: Step 1) Preheat the steel ingot mold to 50-100℃ before casting. After casting the steel ingot, wait for the steel ingot mold to cool to 1050-1150℃, then transfer the steel ingot and steel ingot mold together to the forging workshop for demolding. Step 2) After demolding, measure the temperature of the tail end of the steel ingot from Step 1). When the steel ingot cools to a temperature range of 1200-1250℃, transfer it to a precision forging machine for forging. Forging starts from the tail end of the ingot, with a deformation of 5-8%; the forging speed is controlled at 4-5 m / min. Step 3) Use a precision forging machine to forge the billet from the tail end of the ingot, with a deformation of 8-10%; control the forging speed at 5-6 m / min; and ensure that the surface temperature of the forging is between 1180-1230℃ after forging. Step 4) The billet from Step 3) is fog-cooled to 650±10℃, transferred to an annealing furnace, and held at 650~750℃ for 1.5h for 100mm. Step 5) Transfer the billet from Step 4) to a heating furnace and hold it at 850-950℃ for 4 hours, then raise the temperature for 5 hours, and hold it at 1200℃±10℃ for 1.0-1.2 hours per 100mm section. Step 6) After reheating the billet from Step 5, forge it to the finished size using a precision forging machine.

[0007] The present invention has the following beneficial effects: The technical solution of this invention adjusts the solid-liquid phase ratio by controlling the demolding temperature of the steel ingot. After selection and crystallization, the liquid phase with positive chemical element segregation is subjected to forging deformation. After the liquid phase is dispersed by external force, the concentration of chemical elements is reduced. Then, normalizing treatment is carried out to refine the grain size and transform the austenite structure into a pearlite structure. The chemical elements are redistributed again. Through the superposition of two beneficial uniform chemical element processes, the general spot segregation of the low magnification structure is finally qualified.

[0008] The technical solution of this invention improves the degree of chemical element segregation in the steel ingot by forging the incompletely solidified steel ingot and simultaneously normalizing the intermediate billet, thereby reducing the general spot segregation level of aluminum-containing steel and improving product quality. Detailed Implementation

[0009] The present invention will be further described and illustrated below with reference to specific embodiments.

[0010] Example 1: Steel grade: 38CrMoAl; Ingot weight: 5900kg; Forging specifications: φ300mm; The smelting process uses a 40-ton electric furnace combined with a 40-ton vacuum refining furnace, and the forging process uses an RF70 precision forging machine. The specific steps are as follows: Step 1) Before casting, preheat the ingot mold for the 5900kg steel ingot to 50-100℃. After electric furnace smelting and vacuum refining, cast the ingot and measure the temperature at the tail end of the ingot mold in time. When the ingot mold cools down to 1050-1150℃, transfer the steel ingot and the ingot mold together to the forging workshop for demolding. Step 2) After demolding, measure the temperature of the tail end of the steel ingot from Step 1). When the steel ingot cools to a temperature range of 1200-1250℃, transfer it to the precision forging machine for forging. Start forging from the tail end of the ingot and forge to φ650mm. Control the forging speed to 4-5m / min. Step 3) Forge the billet from step 2) starting from the tail end of the ingot using a precision forging machine until it reaches φ590mm; control the forging speed at 5-6m / min; ensure the surface temperature of the forging is between 1180-1230℃ after forging. Step 4) Transfer the billet from Step 3) to the annealing chamber for cooling. Cool it using a fan spray method. When the billet temperature is cooled to 650±10℃, transfer it to the annealing furnace and hold it at a furnace temperature of 650~750℃ for 1.5h per 100mm. Step 5) Transfer the billet from Step 4) to a heating furnace and hold it at 850-950℃ for 4 hours, then raise the temperature for 5 hours, and hold it at 1200℃±10℃ for 1.0-1.2 hours per 100mm section. Step 6) After reheating the billet from Step 5, forge it to a finished size of φ300mm using a precision forging machine.

[0011] The forgings were produced according to the above method. After subsequent annealing and inspection, the surface quality of the forgings was good. The ultrasonic testing met the GB / T4162-2008 Class B standard. The low magnification microstructure is shown in the table below. Φ300 Furnace Ingot No. 1 0.5 1 0 0.5 none / Φ300 Furnace Ingot No. 2 0.5 1 0 1 none /

Claims

1. A production method for improving the low-magnification quality of 38CrMoAl forgings, characterized in that: The production method includes the following steps: Step 1) Preheat the steel ingot mold to 50-100℃ before casting. After casting the steel ingot, wait for the steel ingot mold to cool to 1050-1150℃, then transfer the steel ingot and steel ingot mold together to the forging workshop for demolding. Step 2) After demolding, measure the temperature of the tail end of the steel ingot from Step 1). When the steel ingot cools to a temperature range of 1200-1250℃, transfer it to a precision forging machine for forging. Forging starts from the tail end of the ingot, with a deformation of 5-8%; the forging speed is controlled at 4-5 m / min. Step 3) Use a precision forging machine to forge the billet from the tail end of the ingot, with a deformation of 8-10%; control the forging speed at 5-6 m / min; and ensure that the surface temperature of the forging is between 1180-1230℃ after forging. Step 4) The billet from Step 3) is fog-cooled to 650±10℃, transferred to an annealing furnace, and held at 650~750℃ for 1.5h for 100mm. Step 5) Transfer the billet from Step 4) to a heating furnace and hold it at 850-950℃ for 4 hours, then raise the temperature for 5 hours, and hold it at 1200℃±10℃ for 1.0-1.2 hours per 100mm section. Step 6) After reheating the billet from Step 5, forge it to the finished size using a precision forging machine.