阅读说明：本技术 含Cr、Mo合金耐热钢大型挤压厚壁制坯件的缓冷方法 (Slow cooling method for large-scale extruded thick-wall blank made of Cr and Mo alloy heat-resistant steel ) 是由 冯伟 邵忠伟 胡永平 周仲成 涂明金 郭运来 杜红强 黄艳丽 刘正伟 赵先锋 刘 于 2019-09-30 设计创作，主要内容包括：本发明公开了一种含Cr、Mo合金耐热钢大型挤压厚壁制坯件的缓冷方法,包括：坯料入炉、待料、保温、炉冷、出炉空冷；其中,坯料空冷至500℃以上入炉,坯料壁厚200mm～500mm,待料温度≥500℃,保温温度600-850℃,保温时间25h-55h,炉冷速度≤40℃/h。本发明解决了低合金、高合金各类制坯坯料由高温热态缓冷至室温产生表面硬度高、应力开裂及白点组织缺陷,避免坯料由高温冷却至室温时造成坯料表面过硬或报废的问题。(The invention discloses a slow cooling method for a large-scale extruded thick-wall blank made of Cr-Mo alloy heat-resistant steel, which comprises the following steps: charging blanks into a furnace, waiting for the blanks, preserving heat, cooling the furnace, and discharging from the furnace for air cooling; wherein, the blank is air-cooled to more than 500 ℃ and put into a furnace, the wall thickness of the blank is 200 mm-500 mm, the temperature of the blank is more than or equal to 500 ℃, the heat preservation temperature is 600-. The invention solves the defects of high surface hardness, stress cracking and white point organization caused by slowly cooling various blank blanks of low alloy and high alloy from a high-temperature thermal state to room temperature, and avoids the problem that the blank surface is too hard or scrapped when the blank is cooled from the high temperature to the room temperature.)

1. A slow cooling method for a large-scale extruded thick-wall blank made of Cr-Mo alloy heat-resistant steel is characterized by comprising the following steps of: charging blanks into a furnace, waiting for the blanks, preserving heat, cooling the furnace, and discharging from the furnace for air cooling; wherein, the blank is air-cooled to more than 500 ℃ and put into a furnace, the wall thickness of the blank is 200 mm-500 mm, the temperature of the blank is more than or equal to 500 ℃, the heat preservation temperature is 600-.

2. The slow cooling method for the large-scale extruded thick-wall blank made of the Cr-Mo alloy heat-resistant steel as claimed in claim 1, which is applied to a 15CrMo, P12 or P22 blank containing Cr-Mo alloy low alloy, the blank is cooled in air to 500 ℃ or more and then put into a furnace, the waiting temperature is not less than 500 ℃, the heat preservation temperature is 600-800 ℃, the wall thickness of the blank is 200-500 mm, and the average heat preservation time is as follows: the average heat preservation time is 25-40 h, the furnace cooling speed is less than or equal to 40 ℃/h, and the tapping temperature is less than or equal to 400 ℃ and then tapping and air cooling are carried out.

3. The slow cooling method for large-scale extruded thick-wall blanks made of Cr-Mo alloy heat-resistant steel as claimed in claim 1, wherein the method is applied to P91 or P92 blanks made of Cr-Mo alloy, the blanks are air-cooled to above 650 ℃ and then enter a furnace, the temperature of the blanks is more than or equal to 650 ℃, the heat preservation temperature is 700-850 ℃, the wall thickness of the blanks is 200-500 mm, the heat preservation time is 35-55 h, the furnace cooling speed is less than or equal to 30 ℃/h, and the tapping temperature is less than or equal to 300 ℃, and then the blanks are taken out of the furnace and air-cooled.

Technical Field

The invention relates to a hot working method for large-scale extrusion molding, in particular to a slow cooling method for a large-scale extrusion thick-wall blank of heat-resistant steel containing Cr and Mo alloy.

Background

The first 3.6 ten thousand tons of vertical extruders and 1.5 ten thousand tons of vertical blank-making machines in China successfully extrude at one time in 7 months in 2009, marks that the high-end forming and manufacturing technology in China obtains a major breakthrough, and breaks through the technical monopoly in the field of blank making and extrusion of large-sized workpieces abroad.

The steel ingot is used as the raw material for extrusion, and the processes of upsetting and perforating are carried out on a 150MN blank making press to provide the extrusion blank for a 360MN extruder, and the practice proves that: the quality of the pierced blank directly determines the surface quality of the extruded tube. The early-stage extrusion process generally adopts a 'blank making-extrusion' mode to form a tube blank at one time, and the formed tube blank has the phenomena of large wall thickness difference and serious surface quality defect.

However, for various blanks made of low alloy and high alloy, the defects of high surface hardness, stress cracking and white point texture are generated when the blanks are slowly cooled from a high-temperature thermal state to room temperature, and the blanks are cooled from the high temperature to the room temperature to cause the problems of over-hard surfaces or scrappage of the blanks.

Disclosure of Invention

The invention aims to provide a slow cooling method for large-scale extruded thick-wall blanks made of Cr-Mo alloy heat-resistant steel, which solves the problems of high surface hardness, stress cracking and white point tissue defects caused by slow cooling of various blanks made of low alloy and high alloy from a high-temperature thermal state to room temperature, and avoids the problems of over-hard surface or scrapping of the blanks when the blanks are cooled from the high temperature to the room temperature.

The technical scheme is as follows:

a slow cooling method for a large-scale extruded thick-wall blank made of Cr-Mo alloy heat-resistant steel comprises the following steps: charging blanks into a furnace, waiting for the blanks, preserving heat, cooling the furnace, and discharging from the furnace for air cooling; wherein, the blank is air-cooled to more than 500 ℃ and put into a furnace, the wall thickness of the blank is 200 mm-500 mm, the temperature of the blank is more than or equal to 500 ℃, the heat preservation temperature is 600-.

Further, the method is applied to 15CrMo, P12 or P22 blanks containing Cr and Mo low alloy, the blanks are air-cooled to more than 500 ℃ and then are put into the furnace, the temperature of the blanks is more than or equal to 500 ℃, the heat preservation temperature is 600-800 ℃, the wall thickness of the blanks is 200-500 mm, and the heat preservation time is as follows: the average heat preservation time is 25-40 h, the furnace cooling speed is less than or equal to 40 ℃/h, and the tapping temperature is less than or equal to 400 ℃ and then tapping and air cooling are carried out.

Further, the method is applied to P91 or P92 blanks containing Cr and Mo high alloy, the blanks are cooled in air to above 650 ℃ and then enter a furnace, the temperature of the blanks is more than or equal to 650 ℃, the heat preservation temperature is 700-850 ℃, the wall thickness of the blanks is 200-500 mm, the heat preservation time is 35-55 h, the furnace cooling speed is less than or equal to 30 ℃/h, and the tapping temperature is less than or equal to 300 ℃, and then the blanks are discharged from the furnace and cooled in air.

The invention has the technical effects that:

1. the invention solves the defects of high surface hardness, stress cracking and white point organization caused by slowly cooling various blank blanks of low alloy and high alloy from a high-temperature thermal state to room temperature, and avoids the problem that the blank surface is too hard or scrapped when the blank is cooled from the high temperature to the room temperature.

By the slow cooling method, the internal stress of the blank is eliminated, the surface hardness is reduced, the internal structure of the blank is optimized, the hydrogen diffusion effect is achieved, and the stress cracking and white point structure limitation are avoided.

2. The economic benefit and the social benefit are obvious.

The quality of the surface of the tube blank extruded after the blank slow cooling machine is adopted for heating is greatly improved, and the surface cracks and the wall thickness difference of more than 10mm are reduced from 70 percent to 20 percent. The raw material loss cost, energy cost, labor cost and other auxiliary costs caused by the wall thickness difference and the grinding of the tube blank are about 30.08 ten thousand yuan/year. Before the blank slow cooling machine is not used for heating, the scrapped tube blank accounts for 1.3 percent (year) of surface cracks and wall thickness differences, after the blank slow cooling is adopted, the surface cracks and the wall thickness differences caused by blank-free reasons directly generate tube blank scrapping, and the economic loss of the direct year is recovered as follows: 3760 pieces × 1.3% × 6550 yuan × 8 ton

Therefore, the total saving value of the extruded tube blank after the blank is processed by the slow cooling machine is about 256.13+30.08-3760 pieces multiplied by 0.07 ten thousand yuan to 23.01 ten thousand yuan.

The invention lays a solid foundation for the extrusion of the novel technology to break through the quality problem of the extruded blank, and provides support for the innovation of the extrusion mode of the large-caliber seamless steel pipe.

Drawings

FIG. 1 is a slow cooling process diagram of a Cr-Mo-containing low alloy 15CrMo, P12 and P22 blank in the invention;

FIG. 2 is a slow cooling process diagram of Cr-Mo containing high alloy P91, P92 billet in the invention.

Detailed Description

The following description sufficiently illustrates specific embodiments of the invention to enable those skilled in the art to practice and reproduce it.

The slow cooling method for the large-scale extruded thick-wall blank made of Cr-and Mo-containing alloy heat-resistant steel comprises the following steps: charging blanks into a furnace, waiting for the blanks, preserving heat, cooling the furnace, and discharging from the furnace for air cooling; wherein, the blank is air-cooled to more than 500 ℃ and put into a furnace, the wall thickness of the blank is 200 mm-500 mm, the temperature of the blank is more than or equal to 500 ℃, the heat preservation temperature is 600-.

In order to improve the surface quality of the extruded tube blank, the extrusion procedure adopts a mode of blank making, machining and extrusion; the process flow is as follows: steel ingot blank making, perforating, heating, extruding and tube blank annealing.

The method comprises the steps of cooling a high-temperature blank manufactured by a 150MN blank manufacturing machine to room temperature to prepare for subsequent machining, wherein the purpose of slow cooling of the blank is to cool the high-temperature blank to the room temperature, ensure the hardness of the blank to meet the requirement of subsequent machining, and simultaneously prevent the blank from generating cracks due to overlarge internal stress and prevent the blank from generating tissue defects such as white spots and the like in the blank. Secondly, the blank making is carried out on the first 150 blank making machines in China, and the forming method is different from the traditional forging and has the characteristics of quick forming and large deformation. In terms of mechanism, because the components and the forming method of the blank are different from those of the traditional forged piece, the components determine different tissues, the deformation capability is different, and the internal stress and the hydrogen diffusion capability of the blank after deformation are different; the different deformation modes and the different deformation energy inside the blank result in different recrystallization temperature and recovery time.

As shown in FIG. 1, the slow cooling process of the Cr and Mo containing low alloy 15CrMo, P12 and P22 billet is shown.

A slow cooling process for Cr and Mo-containing low alloy 15CrMo, P12 and P22 blanks. The method aims at large-scale extrusion thick-wall blank, the forming mode of the workpiece is different from that of common forging, and the method is independently developed by breaking through foreign technology blockages for the first time in our factory. Because of different forming methods, the annealing slow cooling method is naturally different from the dehydrogenation annealing after the common forging. The slow cooling method comprises the following steps: the method comprises the steps of charging a blank into a furnace, waiting for charging, preserving heat, cooling the furnace, discharging and air cooling, wherein the blank is charged into the furnace when the blank is air cooled to more than 500 ℃, the waiting temperature is more than or equal to 500 ℃, the average preserving temperature is 600-800 ℃, the wall thickness of the blank is 200-500 mm, and the average preserving time is as follows: the average heat preservation time is 25-40 h, the furnace cooling speed is less than or equal to 40 ℃/h, and the tapping temperature is less than or equal to 400 ℃ and then tapping and air cooling are carried out.

As shown in FIG. 2, it is a slow cooling process diagram of Cr and Mo-containing high alloy P91 and P92 billets in the invention.

The invention relates to a slow cooling process for Cr and Mo-containing high-alloy P91 and P92 billets. The high alloy P91 and P92 alloy is steel for an ultra supercritical power station, the steel type is introduced from abroad, a slow cooling method of the steel type is not available in a heat treatment manual, the forming mode of the steel type is special, the components and the forming method are different from the traditional forged piece, the components determine different tissues and structures, the deformation capability is different, and the internal stress and the hydrogen diffusion capability are different after the blank is deformed; the different deformation modes and the different deformation energy inside the blank result in different recrystallization temperature and recovery time. The slow cooling method comprises the following steps: comprises charging blank into furnace, waiting for charging, heat preservation, furnace cooling and discharging from furnace air cooling. Air cooling the blank to above 650 ℃, charging into a furnace, keeping the temperature of the blank to be more than or equal to 650 ℃, keeping the temperature at 700-850 ℃, keeping the wall thickness of the blank at 200-500 mm, keeping the temperature for the following time: the heat preservation time is 35h-55h, the furnace cooling speed is less than or equal to 30 ℃/h, and the tapping temperature is less than or equal to 300 ℃, and then the steel plate is tapped for air cooling.

In small-batch trial production, three furnaces are respectively selected for test verification according to three materials of high alloy and low alloy, according to the production condition, 15CrMo, P12 and P22 low alloy blanks (3-5 furnaces respectively) of a certain contract are selected, and P91 and P92 high alloy blanks (3-5 furnaces respectively) of a certain contract are selected for an extrusion blank slow cooling test. See table 1 specifically:

TABLE 1 batch wall thickness selection and Process execution

And (4) after the blank is discharged from the furnace, detecting white spots, wherein no white spots are generated. The surface hardness of the blank is detected before the blank is processed, the hardness of P91 is 160-170 HB, and the hardness of P92 is 168-180 HB. On the other hand, the blank machining process is tracked and observed, and the metal cutting is normal and no crack is generated in the blank machining process. For further examination and verification, the high-alloy tube blank and the low-alloy tube blank are respectively subjected to physical and chemical detection, the detection items comprise macrostructure, metallographic phase test and mechanical property test, the test meets the technical index requirements, and the details are shown in tables 2 and 3.

TABLE 2 macrostructure test results

TABLE 3 Performance and high magnification tissue test results

According to the small-batch trial production condition: after the blank is slowly cooled according to the process, the blank has moderate hardness and is suitable for machining; the blank and the tube blank have no cracks and white spots; the performance of the subsequent tube blank is qualified. Further verifies the rationality of the calculation principle of the slow cooling temperature and the heat preservation time. Practice proves that the method can meet the technical requirements, and at present, the method is popularized and used, can achieve the expected effect, and ensures the product quality.

The terminology used herein is for the purpose of description and illustration, rather than of limitation. As the present invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, it should also be understood that the above-described embodiments are not limited by any of the details of the foregoing description, but rather should be construed broadly within its spirit and scope as defined in the appended claims, and therefore all changes and modifications that fall within the meets and bounds of the claims, or equivalences of such meets and bounds are therefore intended to be embraced by the appended claims.