CN101787492B - A method for manufacturing high-quality and large-scale mandrel blanks - Google Patents

Abstract

The present invention relates to a manufacturing technology for a high-quality large-size core rod, and belongs to the technical field of manufacturing processes for steel bar products. The present invention relates to a manufacturing technology for a large-diameter core rod (above 300 mm). The main points of the present invention are: adopting large-tonnage fast forging and realizing multiple forgings of large steel ingots to realize the forming of the core rod blank; the present invention adopts a reasonable process system to realize the effective improvement of the segregation and loose defects of the core rod, and achieves effective control of the microstructure. In the manufacturing process of the method of the present invention, the uniformity of the alloy structure of the steel ingot is strengthened before forging, and the cooling degree of the core rod blank after forging and the structure refinement heat treatment are strengthened after forging, thereby improving the various properties of the product core rod including hardness.

Description

A method for manufacturing high-quality and large-scale mandrel blanks

technical field

The invention relates to a method for manufacturing a high-quality and large-size mandrel, which belongs to the technical field of steel rod product manufacturing technology.

technical background

The mandrel works together with the roll to roll the perforated tube blank into seamless steel tubes of various sizes. According to the different rolling methods of steel pipes, it can be divided into floating mandrel, semi-limited mandrel and limited mandrel, among which the proportion of limited mandrel is the largest.

The production process of continuous rolling pipe with limited moving mandrel was developed under the condition that the production process of continuous rolling pipe with floating mandrel is difficult to solve the problem of producing steel pipes with an outer diameter of 177.8mm or more. The limited motion mandrel rolling mill was carried out in the mid-1960s and achieved gratifying results. In 1978, the world's first limited motion mandrel rolling mill (MPM) was designed and manufactured by Italy Insi Company. ) was completed and put into production at the Darmin Steel Pipe Plant in Italy, marking a breakthrough in the continuous rolling process; Craft equipment has jumped to a new peak. The continuous rolling tube technology with limited motion mandrel has become the mainstream in the development of hot-rolled seamless steel tube production technology.

In the process of rolling steel pipes by the continuous pipe mill, the mandrel directly squeezes the inner wall of the high-temperature tube billet. At this time, the mandrel bears huge extrusion force and strong thermal shock, and the instantaneous temperature of the mandrel surface can reach 700°C. Immediately after spraying water to cool, the temperature dropped sharply again. During the whole working process, the surface of the mandrel bears very complicated periodic extrusion stress, friction force, and high-intensity cold and heat shock. Under the action of periodic thermal load and mechanical load, thermal fatigue cracking is the most typical failure mode like other hot working dies. The peeling of the chromium layer on the surface of the mandrel, the hard spots in the structure of the tube blank, and the entry of external hard impurities into the working interface will cause mechanical scratches and grooves on the surface of the mandrel. In addition, the peeling off of the mandrel surface caused by local plastic deformation, thermal cracking and other factors is also a typical mandrel failure behavior.

Mandrels at home and abroad are generally made of H13 steel or its improved steel types, and the structure and properties of steel are the essential factors that determine the life of mandrels. The internal defects of steel destroy the continuity of the matrix, thereby reducing the life and performance of the mandrel; these defects mainly include various inclusions, eutectic carbides, segregation, etc. When the steel ingot is enlarged, the above problems will become more prominent. Moreover, today's high-purity H13 steel has less sulfide, and eutectic carbide becomes the main fracture source at this time. Therefore, the control of carbides in high-quality H13 steel is also a very important technology.

Contents of the invention

The purpose of the invention is to provide a method for manufacturing a high-quality large-size mandrel.

A method for manufacturing a high-quality large-size mandrel of the present invention is characterized in that it has the following processes and steps:

a. Design and select the chemical composition of the steel grade: the chemical composition and weight percentage of the steel grade are as follows: C0.30～0.38%, Si 0.70～1.00%, Mn 0.20～0.60%, Cr 4.50～5.50%, Mo 1.00～ 1.50%, V 0.80～1.10%, P<0.015%, S<0.005%, Fe balance, control the content of impurity elements. Put the ingredients into the smelting furnace for smelting. Make the alloy composition of the tapped steel close to the lower limit of the target value.

b. Electric furnace smelting: Melting is carried out according to traditional conventional methods. The batch prepared according to the above formula is poured into the electric arc furnace for melting, and the melting temperature is 1500-1550°C;

c. Vacuum refining and electroslag remelting: heat up desulfurization and vacuum degassing, improve the purity, adjust the alloy composition to the target value; put the smelted and poured electrode rods into the electroslag remelting device for electroslag remelting; The slag adopts the ternary slag system:

CaF2: Al2O3: CaO=60:20:20; the remelting speed is controlled at 10-20kg/min.

d. High-temperature homogenization treatment: heat the steel ingot after electroslag remelting to 1200-1280°C for high-temperature homogenization treatment, keep it warm for 15-20 hours, uniform structure, eliminate component segregation, and then bury it in sand for cooling.

e. Forging; heat the above steel ingot to a temperature range of 1100-1200°C for forging processing; forging is completed in 3-6 fires, the thick deformation of the pier is 30-60%, the elongation of the middle is 300%-600%, and finally One fire is drawn to the target size, and the forging ratio is kept at 4-8. The final forging temperature is between 1050°C and 900°C. Cool quickly to 200-400°C after forging.

f. High-temperature solid solution: after forging, the sample is kept at 950-1150°C for 2-4 hours and then air-cooled.

g. Spheroidizing annealing: Two-stage isothermal spheroidizing annealing is carried out after the steel is forged. Insulate at 830-880°C for 10 hours, then furnace cool;

Then keep it at 700-740°C for 3 hours, and cool in the furnace; the cooling rate is 20-40°C/h, when it is ≤400°C, it is air-cooled, and the annealing time is 15-18 hours, and finally a high-quality mandrel is obtained.

The manufacturing method of the present invention is characterized in that: through reasonable metallurgical quality control technology and heat treatment technology, the composition and forging ratio are precisely controlled, and at the same time, the temperature of the heat treatment process is precisely controlled, effectively realizing the uniform control of the composition and structure. Finally, the component uniformity of the mandrel of the present invention exceeds the real level of the imported mandrel, and the uniformity of the structure reaches the level of the imported mandrel.

Description of drawings

Fig. 1 is the microstructural diagram of the electroslag process mandrel electroslag ingot of the present invention.

Fig. 2 is a microstructure diagram of the present invention after high-temperature homogenization.

Fig. 3 is the microstructure of the present invention after high-temperature solid solution and spheroidizing annealing.

Detailed ways

Specific embodiments of the present invention are now described below.

Embodiment: In this example, the composition and weight percentage of adopting steel grade are as follows:

The manufacturing process and steps of the large-scale mandrel in this example are as follows:

a. The proportion of alloying elements prepared according to the above formula is smelted in an electric arc furnace at a melting temperature greater than 1500°C, and then cast into a Φ900mm steel ingot and air-cooled;

b. Heating, desulfurization and vacuum degassing, adjusting the alloy composition to reach the target value; putting the electroslag ingot poured out of melting into the electroslag remelting device for electroslag remelting, and the liquid metal falls through the slag layer of the slag pool to the bottom In the water-cooled crystallizer, it is re-solidified into steel ingots; The remelting speed is controlled at 10-20kg/min.

c. Heat the steel ingot after electroslag remelting to 1250°C for high-temperature homogenization treatment, keep it warm for 18 hours, uniform structure, eliminate component segregation, and then bury it in sand for cooling.

d. Heat the above steel ingot to 1200°C, and then take it out of the furnace for forging; the forging is completed in 3-6 fires, the thick deformation of the pier is 30-60%, the middle drawing length is 300%-600%, and the last fire is drawn To Φ358.1×13200mm. The final forging temperature is around 1000°C. Cool quickly to 200-400°C after forging.

e. High-temperature solid solution: After forging, the sample is kept at 950-1150°C for 2-4 hours and then air-cooled.

f. Spheroidizing annealing after solid solution of the material. At 880°C×10h/furnace cooling +710°C×3h/furnace cooling ≤40°C/h, ≤500°C out of the furnace and air cooling. The annealing time is 15-18 hours, and finally a high-quality mandrel is produced.

After the core rod of the present invention is through above-mentioned heat treatment, carry out performance test and microscope detection, result is as follows:

(1) Quenching hardness: 53HRC; Tempering hardness: 47.5HRC

(2) Annealed hardness: HB 200-260

(3) The microstructure after high-temperature homogenization (as shown in Figure 2), after the high-temperature homogenization treatment of this process, the large-grain carbides have been completely eliminated, while there are large-grain pseudo eutectic carbide.

(4) The microstructure after high-temperature solid solution and spheroidizing annealing, as shown in Figure 3, the carbides are finely and evenly distributed on the ferrite matrix. In the present invention, the microstructure of electroslag process mandrel electroslag ingot is shown in Fig. 1

Claims (1)

1. the method for manufacture of a large size mandril is characterized in that having following process and step:

A. design and select the Chemical Composition of steel grade: the chemical ingredients and the weight percent of this steel grade are following: C0.30～0.38%, and Si 0.70～1.00%, and Mn 0.20～0.60%; Cr 4.50～5.50%, and Mo 1.00～1.50%, and V 0.80～1.10%; P＜0.015%; S＜0.005%, Fe surplus, control impurity content; Put into smelting furnace after the batching, carry out melting; The alloying constituent that makes tapping is near the target value lower limit;

B. electrosmelting: carry out melting by traditional ordinary method; To inject electric arc furnace by the admixtion of above-mentioned formulated and carry out melting, smelting temperature is 1500～1550 ℃;

C. vacuum refinement and esr: intensification desulfurization vacuum outgas, improve purity, the adjustment alloying constituent reaches target value; The electrode bar that smelting and pouring is gone out is put in the esr device, carries out esr; Electroslag adopts the ternary slag system:

CaF ₂: Al ₂O ₃: CaO=60: 20: 20; Remelt speed is controlled at 10-20kg/min;

D. high temperature homogenization is handled; Steel ingot behind the esr is heated to 1200～1280 ℃ carries out the high temperature homogenization processing, be incubated 15-20 hour, component segregation is eliminated by uniform formation, buries sand cooling then but;

E. forge; Above-mentioned steel ingot is heated in 1100～1200 ℃ of TRs forges processing; Forge and divide the 3-6 fire to accomplish, the mushrooming deformation amount is 30-60%, middle pulling amount 300%-600%, and last fire together pulls out to target size, and forging ratio remains on 4-8; Final forging temperature is between 1050 ℃-900 ℃; Be chilled to 200-400 ℃ after the forging soon;

F. high temperature solid solution: forge the back sample at 950～1150 ℃ of insulations, air cooling after soaking time 2-4 hour;

G. carry out Spheroidizing Annealing after the material solid solution: steel carry out the two-section type isothermal spheroidizing after forging; 830～880 ℃ of insulations 10 hours, stove was cold; Then 700～740 ℃ of insulations 3 hours, stove was cold; Speed of cooling is 20～40 ℃/h, the air cooling of in the time of≤400 ℃, coming out of the stove, and annealing time is 15-18 hour, finally makes plug.

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