CN112029974B - Production process for improving flaw detection qualification rate of 27SiMn large-section forged material - Google Patents
Production process for improving flaw detection qualification rate of 27SiMn large-section forged material Download PDFInfo
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- CN112029974B CN112029974B CN202010852264.5A CN202010852264A CN112029974B CN 112029974 B CN112029974 B CN 112029974B CN 202010852264 A CN202010852264 A CN 202010852264A CN 112029974 B CN112029974 B CN 112029974B
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D7/00—Modifying the physical properties of iron or steel by deformation
- C21D7/13—Modifying the physical properties of iron or steel by deformation by hot working
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/005—Heat treatment of ferrous alloys containing Mn
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D6/00—Heat treatment of ferrous alloys
- C21D6/008—Heat treatment of ferrous alloys containing Si
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- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
Abstract
The invention provides a production process for improving the flaw detection qualification rate of a 27SiMn large-section forged material, which takes a 27SiMn continuous casting billet as a raw material and sequentially performs forging and heat treatment, and is characterized in that: the forging is carried out according to the size requirement of the finished product, the forging stop temperature is ensured to be more than 750 ℃, the obtained forging material is transferred into a furnace within 40min after the forging is finished, the surface temperature of the forging material in the furnace is ensured to be more than 635 ℃, and the temperature is directly raised to 660-680 ℃ after the forging is finished, so as to carry out annealing treatment. The flaw detection result of the 27SiMn large-section forged material produced by the process meets the 4-level requirement, and the economic loss caused by material modification or scrapping due to unqualified flaw detection is greatly reduced.
Description
Technical Field
The invention belongs to the field of large-section forged materials 27SiMn, and particularly relates to a process for improving the flaw detection qualification rate of large-section forged materials 27 SiMn.
Background
The large-section forged material 27SiMn is a forged round bar or square bar with the cross-section equivalent diameter of more than or equal to 250 mm. The large-section forging material 27SiMn is a main raw material of a hydraulic support which is a key bearing device for coal mining, is used for manufacturing a cylinder body, a plunger and the like of the hydraulic support, and has certain genetic influence on the service safety of subsequent parts due to the metallurgical quality. In recent years, with the upsizing of coal machinery, the demand of large-section forging materials is rapidly increased, and with the improvement of safe operation standards of China in the coal industry, the requirement of the coal industry on the flaw detection quality of the large-section forging materials is increasingly improved, from the past 2 grades to the current 3 grades or even 4 grades (the flaw detection standard executes steel forging ultrasonic detection method GB/T6402-2008), while under the condition of certain ingot blank specification and forging machine capability, the larger the section of the forging material is, the smaller the compression ratio is, and the defects such as loose and shrinkage cavity in the steel ingot are more difficult to improve.
At present, manufacturers generally adopt the following method to produce large-section forged materials 27 SiMn: after the forging pressing of the continuous casting billet is finished, in order to ensure the H expansion effect of the steel, the obtained forged material is cooled to 300 +/-20 ℃ in air, then transferred into a furnace, and heated to 660 and 680 for stress relief annealing; through researching the technological process of producing round bars with the maximum cross section diameter reaching 350mm by continuous casting billets (410mm by 530mm) according to the process, ultrasonic flaw detection positioning sampling and low-power acid corrosion inspection are carried out on forged materials which are unqualified for flaw detection, a large number of results show that flaw detection defects are mainly internal cracks, the forming reasons of the internal cracks are further analyzed, and the crack parts have large microscopic component segregation and large block pearlite structures from metallographic result observation; the C content at the crack is significantly higher than in other regions. Based on the method, the production process of the 27SiMn large-section forged material is improved.
Disclosure of Invention
The invention aims to overcome the technical problem of low flaw detection qualification rate of the 27SiMn large-section forged material generated in the prior art, and provides a production process for improving the flaw detection qualification rate of the 27SiMn large-section forged material, wherein the flaw detection result of the 27SiMn large-section forged material produced by the process meets the requirement of grade 4, and the economic loss caused by material modification or scrapping due to unqualified flaw detection is greatly reduced.
In order to achieve the above purpose, the invention provides the following technical scheme:
a production process for improving the flaw detection qualification rate of a 27SiMn large-section forged material comprises the steps of using a 27SiMn continuous casting blank as a raw material, sequentially forging and performing heat treatment, performing forging according to the size requirement of a finished product, ensuring the forging stop temperature to be more than 750 ℃, transferring the obtained forged material into a furnace after the forging is finished, ensuring the surface temperature of the forged material when the forged material is put into the furnace to be more than 635 ℃, directly heating to 660-680 ℃ after the forged material is put into the furnace, and performing heat preservation to perform annealing treatment, thereby finally obtaining the forged material with the cross section equivalent diameter of more than or equal to 250 mm.
In the production process for improving the flaw detection yield of the 27SiMn large-section forged material, the heat preservation time of the annealing treatment is preferably according to D1(6-8) h/100mm, wherein D1Is the equivalent diameter of the forging.
In the production process for improving the flaw detection qualification rate of the 27SiMn large-section forged material, the obtained forged material is preferably transferred into a furnace, and the material waiting temperature in the furnace is between 635 and 680 ℃.
In the production process for improving the flaw detection qualification rate of the 27SiMn large-section forged material, preferably, after the annealing treatment is finished, the furnace is stopped, and the forged material is discharged after the furnace temperature is not higher than 200 ℃ by adopting a furnace-closing process.
In the production process for improving the flaw detection yield of the 27SiMn large-section forged material, the forging temperature is preferably 950 ℃ and 1020 ℃.
Preferably, the production process for improving the flaw detection qualification rate of the 27SiMn large-section forged material comprises the steps of heating the 27SiMn continuous casting billet to 1180-1260 ℃ before forging, and preserving heat for the time D2(0.22-0.25) min/mm +3h, wherein D2Is the equivalent diameter of the continuous casting billet.
Preferably, before forging, the production process for improving the flaw detection qualification rate of the 27SiMn large-section forged material comprises the steps of heating the 27SiMn continuous casting billet to 1240-1260 ℃, and preserving heat for the time D20.25min/mm +3 h.
The production process for improving the flaw detection yield of the 27SiMn large-section forged material preferably comprises the following specific operations: 3-pass drawing, wherein each pass of drawing adopts unilateral fractional reduction, the reduction rate of each pass in the first two passes is 20-25%, the reduction rate of the next pass is 8-12%, and finally chamfering and rounding are carried out.
According to the production process for improving the flaw detection yield of the 27SiMn large-section forged steel, preferably, the 27SiMn continuous casting slab comprises the following components: by weight percentage, 0.24 to 0.32 percent of C, 1.10 to 1.40 percent of Si, 1.10 to 1.40 percent of Mn, less than or equal to 0.035 percent of S, less than or equal to 0.035 percent of P, less than or equal to 0.030 percent of Cr, less than or equal to 0.030 percent of Ni, less than or equal to 0.20 percent of Cu, less than or equal to 0.15 percent of Mo, and the balance of Fe and inevitable impurities.
Compared with the closest prior art, the technical scheme provided by the invention has the following beneficial effects:
the invention adopts high temperature to stop forging, put into the furnace in time and combine the annealing process to improve the flaw detection quality of the steel, the flaw detection qualification rate meets the GB6402-2008 standard, the flaw detection meets the 4-grade requirement, the flaw detection qualification rate (GB/T6402-20084 grade standard) is improved to 100 percent from 50 percent of the original process, the economic loss caused by material modification or scrapping due to unqualified flaw detection is greatly reduced, and the production cost is reduced; the production process of the invention is adopted to process the 27SiMn large-section forged material, thereby accelerating the production rhythm, improving the production efficiency, realizing the aims of high product quality, quick delivery and low cost, meeting the industrial requirements of the produced product quality, having no adverse effect on the environment and the like, and having high popularization and application values.
Drawings
FIG. 1 is a metallographic photograph (100X) of a wrought material produced in comparative example 1;
FIG. 2 is a metallographic photograph (400X) of a wrought material produced in comparative example 1;
FIG. 3 is a metallographic photograph (100X) of a wrought material produced in example 1;
FIG. 4 is a metallographic photograph (400X) of a forged material produced in example 1.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived from the embodiments of the present invention by a person skilled in the art, are within the scope of the present invention.
The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings. It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.
The embodiment of the invention provides a production process for improving the flaw detection qualification rate of a 27SiMn large-section forged material, which comprises the steps of taking a 27SiMn continuous casting blank as a raw material, sequentially forging and performing heat treatment, performing forging according to the size requirement of a finished product, ensuring the forging stop temperature to be more than 750 ℃, preferably 800-.
The invention carries out ultrasonic flaw detection positioning sampling and low-power acid corrosion inspection on the forged material with unqualified flaw detection in the production process of a large-section forged material manufacturer, and a large number of results show that the flaw detection defects are mainly internal cracks; cracks form in the 27SiMn large-section forged steel. Analysis shows that when a manufacturer produces large-section forged steel, in order to ensure the H expansion effect of the steel, the manufacturer usually adopts supercooling at 300 +/-20 ℃ and then raises the temperature to 660-plus-680 ℃ for stress relief annealing, and internal cracks are mostly generated in the supercooling process at 300 +/-20 ℃, therefore, the invention researches the process and finally determines that the forming temperature of the internal cracks is usually below 635 ℃ or even lower, so that the invention improves the process, ensures that the forging stop temperature is above 750 ℃ (the service work is done for controlling the surface temperature of subsequent transfer steel to be above 635 ℃) in the production process, transfers the obtained forged steel into a furnace within 40min after forging is finished, ensures that the surface temperature of the forged steel is above 635 ℃ when the forged steel is put into the furnace, directly raises the temperature to 660-plus-minus-plus-minus-plus-minus-plus-minus-plus-minus-plus-temperature annealing treatment is directly carried out after the forging at the high-temperature forging is carried out, the method has the advantages that the higher forging stopping temperature is obtained, the transfer time is controlled, the temperature drop of the surface of the forged material is reduced, the mode of entering the furnace at the short time and the high temperature is adopted, the high-temperature material is matched, the high-temperature material is timely filled into a high-temperature furnace for H expanding annealing, the original internal cracks of the steel material caused by the tissue transformation in the cooling process below 635 ℃ can be effectively avoided, and the flaw detection qualification rate of the steel material is improved.
In a specific embodiment of the invention, the holding time of the annealing treatment is calculated according to D x (6-8) h/100mm, wherein D is the equivalent diameter of the forging material.
In the specific embodiment of the invention, the obtained forging material is transferred into a furnace, and the material temperature in the furnace is between 635-680 ℃. According to the research of the invention, the internal cracks of the 27SiMn large-section forging material are mostly formed below 635 ℃ or even lower, so the temperature of the forging material entering the furnace is increased to be above 635 ℃, the temperature of the forging material needs to be raised to the H expansion temperature in time after the forging material enters the furnace, the H expansion effect is ensured not to be superposed with the tissue transformation (the tissue transformation is at 635 ℃, the temperature of the forging material entering the furnace is controlled to be above 635 ℃, the stress cracking caused by the tissue transformation and the H expansion superposition can be reduced), the internal stress of the forging material is reduced, and the generation of the internal cracks is further prevented.
In the specific embodiment of the invention, after the annealing treatment is finished, the furnace is stopped, the furnace is taken out after the furnace temperature is reduced to less than or equal to 200 ℃ by adopting a furnace-closing process (stopping heat supply and adopting a furnace natural cooling mode for cooling), and the furnace is preferably taken out at 150 ℃. The invention adopts the annealing process to slowly cool the forging material in the furnace, thereby avoiding the cracking of the forging material caused by too high cooling rate.
In the embodiment of the invention, the forging temperature is 950-1020 ℃.
In the specific embodiment of the invention, before the forging, the 27SiMn continuous casting slab is heated to 1180-1260 ℃, and the temperature is kept for the time D2(0.22-0.25) min/mm +3h, wherein D2The equivalent diameter of the continuous casting billet; further preferably, the upper limit heating is adopted, specifically the heating is carried out to 1240-1260 ℃, and the heat preservation time is according to D20.25min/mm +3 h. According to the metallographic observation result of the research of the invention, the crack part has larger microscopic component segregation, and a massive pearlite structure appears; the C component at the crack is obviously higher than other areas, and Si, Mn elements and the like in the forging material are easy to segregate, therefore, the 27SiMn continuous casting blank is heated to 1180-.
In an embodiment of the present invention, the forging operation is as follows: and (2) adopting a high-temperature high-pressure flat square forging mode (namely a high-temperature high-pressure forging mode), arranging 3 times of drawing, wherein each time of drawing adopts single-side fractional pressing, the pressing rate of the first two times is 20-25%, the pressing rate of the next time is 8-12%, and finally chamfering and rounding.
In a specific embodiment of the invention, the 27SiMn continuous casting slab comprises the following components: by weight percentage, 0.24 to 0.32 percent of C, 1.10 to 1.40 percent of Si, 1.10 to 1.40 percent of Mn, less than or equal to 0.035 percent of S, less than or equal to 0.035 percent of P, less than or equal to 0.030 percent of Cr, less than or equal to 0.030 percent of Ni, less than or equal to 0.20 percent of Cu, less than or equal to 0.15 percent of Mo, and the balance of Fe and inevitable impurities.
Example 1
A production process for improving the flaw detection qualification rate of 27SiMn large-section forged materials,
the generation process flow of the 27SiMn large-section forging material comprises the following steps: a converter, continuous casting billet heating, forging to form a material, annealing treatment, ultrasonic flaw detection, physical and chemical detection and customer sending after qualification;
in the embodiment, a 27SiMn continuous casting slab (with a length of 4-5m) with a width of 410mm and a height of 530mm is selected, and according to GB/T3077-: in terms of weight percentage, the weight percentage of the active carbon is,
the specific process steps are as follows:
the first step is as follows:
heating a continuous casting blank: according to the heating process of the conventional carbon alloy, the heat preservation temperature is executed according to the upper limit, namely the 27SiMn continuous casting billet is heated to 1240 and 1260 ℃, and the heat preservation is carried out for 5 hours, so as to reduce the adverse effect caused by element segregation;
the second step is that:
forging into a material: forging under high pressure by using a 20MN quick forging machine to increase the compactness of the material; meanwhile, the length of the finished product is controlled to be 5-6m, the forging stop temperature is ensured to be more than or equal to 800 ℃, and the risk of stress cracking is reduced;
during forging, the forging temperature is 1020 ℃, one end is firstly pressed, and the pressing is carried out from the middle to the end part:
the forging method comprises the following steps that in the first pass, the height is 530mm to 360mm, the blank is turned over for 90 degrees, the width is 410mm and is expanded to about 510mm, in the second pass, the width is 335mm, the height is 420mm, in the third pass, the height is 335mm, then the width and the height are both repaired to 335mm, 340mm of octagon and 345mm of hexagon are sequentially turned over, the forging temperature is 960 ℃, the forging temperature of the other end is started, the forging temperature of the other end is 960 ℃, the forging temperature of the other end is also 960 ℃, the forging is also carried out from the middle to the end, the same forging mode is adopted, and the temperature at the end of forging is 890 ℃; and finally, throwing the circle, wherein the temperature after the circle throwing is 850 ℃, the total time consumption is 32 minutes, and forging to obtain a round bar-shaped forging material with the diameter of 330 mm.
The third step:
annealing treatment: naturally cooling the forging material in the air, controlling the material temperature in the furnace according to 650 ℃, strictly controlling the transfer time to be less than or equal to 40min, feeding the forging material into the furnace, controlling the surface temperature of the naturally cooled forging material when the forging material is fed into the furnace to be 724 ℃, directly heating to 660 and 680 ℃ for annealing after the forging material is fed into the furnace, controlling the heat preservation time according to the effective dimension D8 h/100mm, cooling to 150 ℃ according to the annealing process after the heat preservation is finished, and discharging the forging material out of the furnace and air cooling to room temperature.
Examples 2 to 12
Examples 2 to 12 Using substantially the same production process as in example 1, round bar-shaped forged materials having a diameter of 330mm were similarly forged, and only the surface temperatures of the forged materials when they were charged into the furnace were different: in examples 2 to 12, after completion of forging, the forged materials obtained in examples 2 to 12 were transferred to a furnace and annealed, and when charged into the furnace, the forged materials in examples 2 to 12 had surface temperatures of 719 ℃, 711 ℃, 699 ℃, 657 ℃, 710 ℃, 708 ℃, 686 ℃, 692 ℃, 716 ℃, 742 ℃ and 713 ℃, respectively.
Examples 13 to 18
Examples 13 to 18 substantially the same production process as in example 1 was employed, and forging parameters were adjusted according to a conventional forging process to obtain a round bar-shaped forged material having a diameter of 340mm, and the surface temperatures of the forged material at the time of charging were different: in examples 13 to 18, after completion of forging, the forged materials obtained in examples 13 to 18 were transferred to a furnace and annealed, and the surface temperatures of the forged materials in examples 13 to 18 were 695 ℃, 733 ℃, 763 ℃, 730 ℃, 709 ℃ and 702 ℃ respectively.
The charging temperature trace distribution of the wrought materials obtained in examples 1 to 18 is shown in Table 1 below:
TABLE 1 statistics of charging temperature of forged materials obtained in examples 1 to 18
The invention carries out flaw detection on the forged materials with phi of 330mm obtained in examples 1 to 12 and the forged materials with phi of 340mm obtained in examples 13 to 18 according to the GB/T6402-2008 standard, wherein the flaw detection results of 18 forged materials in total meet the 4-grade requirement, and the flaw detection qualification rate is 100 percent; in order to avoid the influence of steel timeliness on flaw detection, the invention carries out repeated flaw detection on the obtained forged material after 7-10 days, meets the 4-grade requirement and has the flaw detection qualification rate of 100 percent.
Comparative example 1
Comparative example 1 adopts the same continuous casting billet heating and forging material forming operation as that of example 1, only the annealing treatment process is different, in comparative example 1, the forging material obtained after the forging is finished is overcooled at 300 +/-20 ℃ and then is transferred into a furnace, the temperature of the material in the furnace is controlled according to 650 ℃, the temperature is increased to 660 + 680 ℃ for stress relief annealing, the heat preservation time is controlled according to the effective size D8 h/100mm, the temperature is reduced to 150 ℃ according to the annealing process after the heat preservation is finished, and the material is taken out of the furnace and cooled to room temperature by air.
The 18 pieces of forged materials with the specification of phi 340mm obtained by the method of the comparative example 1 are subjected to flaw detection according to the GB/T6402-2008 standard, the flaw detection results of most forged materials are 3-grade or even 2-grade, the flaw detection qualification rate of part of the forged materials is 55 percent, after 7-10 days, the obtained forged materials are subjected to repeated flaw detection, stress cracks occur, and the whole furnace cannot be used after exceeding the standard.
Further, the forged material obtained in example 1 was used as a sample in the present invention, and the metallographic structure was examined as shown in fig. 3 and 4, and the metallographic structure of the forged material obtained in comparative example 1 was examined as shown in fig. 1 and 2, which indicates that the forged material obtained in example 1 had a more dense and uniform structure.
Comparative example 2
Comparative example 2 Using substantially the same production process as in example 1, a round bar-shaped forged material was obtained also in a gauge of 330mm, but the surface temperature of the forged material in this comparative example 2 was different when it was charged into the furnace: comparative example 2 after the completion of forging, the resulting forged material was transferred to a furnace and annealed, and the surface temperatures of the forged material of comparative example 2 were 600 ℃, 630 ℃ and 580 ℃, respectively.
18 pieces of forged materials with the specification of phi 340mm (6 pieces of forged materials with the furnace entry surface temperature of 600 ℃, 630 ℃ and 580 ℃) obtained by the method of the comparative example 2 are subjected to flaw detection according to the GB/T6402-2008 standard, the flaw detection results of the 18 pieces of forged materials are different, part of the flaw detection results of the forged materials with the furnace entry temperature of 630 ℃ are 4 grades, the flaw detection results of the forged materials with the furnace entry temperatures of 600 ℃ and 580 ℃ have the condition of 2-grade flaw detection, the flaw detection qualification rate is lower, and after 7-10 days, repeated flaw detection is carried out, the 18 pieces of forged materials have stress cracks with different degrees, and the flaw detection is totally unqualified.
The above description is intended to be illustrative of the preferred embodiment of the present invention and should not be taken as limiting the invention, but rather, the invention is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
Claims (1)
1. The utility model provides a promote production technology of 27SiMn large cross-section forging stock qualification rate of detecting a flaw to 27SiMn continuous casting billet is the raw materials, forges and heat treatment in proper order, its characterized in that:
the 27SiMn continuous casting slab comprises the following components: by weight percentage, 0.24 to 0.32 percent of C, 1.10 to 1.40 percent of Si, 1.10 to 1.40 percent of Mn, less than or equal to 0.035 percent of S, less than or equal to 0.035 percent of P, less than or equal to 0.030 percent of Cr, less than or equal to 0.030 percent of Ni, less than or equal to 0.20 percent of Cu, less than or equal to 0.15 percent of Mo, and the balance of Fe and inevitable impurities;
before forging, firstly heating the 27SiMn continuous casting slab to 1240-1260 ℃, and preserving heat for the time according to D2(0.22-0.25) min/mm +3h, wherein D2The equivalent diameter of the continuous casting billet;
performing forging according to the size requirement of a finished product, ensuring the forging stop temperature to be more than 750 ℃, after the forging is finished, naturally cooling the forging material in the air, strictly controlling the transfer time to be less than or equal to 40min when the material temperature in the furnace is between 635-680 ℃, transferring the obtained forging material into the furnace, ensuring the surface temperature of the forging material when the forging material is put into the furnace to be more than 635 ℃, directly heating to 660-680 ℃ after the forging material is put into the furnace, and preserving heat for annealing treatment, and finally obtaining the forging material with the cross section equivalent diameter of more than or equal to 250 mm;
the holding time of the annealing treatment is in accordance with D1(6-8) h/100mm, wherein D1Is the equivalent diameter of the forging stock;
after the annealing treatment is finished, stopping the furnace, discharging the furnace by adopting a furnace closing process until the furnace temperature is less than or equal to 200 ℃, and air-cooling the furnace to room temperature;
the forging temperature is 950-1020 ℃;
the forging operation comprises the following specific steps: pressing one end from the middle to the end, then pressing the other end, and similarly pressing the other end from the middle to the end; the two ends of the steel tube are forged in the same mode, the steel tube is drawn out in 3 times, each drawing is conducted through unilateral fractional reduction, the reduction rate of each time in the first two times is 20-25%, the reduction rate of the next time is 8-12%, and finally chamfering and rounding are conducted.
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