CN118875186A - Processing Method of Large 35CrNi3MoV Shaft Forgings - Google Patents

Abstract

The present invention discloses a processing method for large-scale 35CrNi3MoV shaft forgings, including: smelting and ingot casting process, using the process route of arc furnace primary smelting → refining in refining furnace → vacuum treatment furnace degassing → ingot casting to smelt and cast the ingot; forging process, hot forging after the ingot solidifies and demolds, specifically including: first fire forging: ingot jaw pressing, chamfering, bottom cutting, and rounding; second fire forging: roughening, first WHF drawing and pressing square; third fire forging: roughening, second WHF drawing and flattening square; fourth fire forging: rounding, number stamping, forging steps, and finishing the finished product; as well as post-forging heat treatment process and performance heat treatment process. The present invention realizes the one-time qualified production of large-scale 35CrNi3MoV shaft forgings for the first time, fills the technical gap, and realizes a short-cycle, low-cost, high-efficiency and stable-quality manufacturing process.

Description

Processing method of large 35CrNi3MoV shaft forging

Technical Field

The invention belongs to the technical field of forging, and particularly relates to a processing method of a large 35CrNi3MoV shaft forging.

Background

For manufacturing large-scale forgings for main transmission and stress in metallurgical, nuclear, mining and power generation equipment, medium carbon medium alloy steel with the material of 35CrNi3MoV is generally selected, and the steel has good hardenability, good toughness and low-temperature impact toughness, and can completely meet the comprehensive mechanical properties required by stable operation of the large forgings under complex and severe working conditions. Because the 35CrNi3MoV steel has high supercooled austenite stability and large tissue genetic tendency in the whole hot working manufacturing process, coarse grains and uneven mixed crystals of the forging are often caused, and the high strength and high toughness of the forging are seriously affected.

The conventional manufacturing method is adopted to produce large shaft forgings, and due to the defects of large size, uneven inherent components of steel ingots, inclusion and the like, the forging process is repeatedly and uniformly heated and deformed for a long time, so that defects and tissue evolution are complex, the manufacturing period is long, the cost is high, and the product quality is unstable.

Disclosure of Invention

In order to solve part or all of the technical problems in the prior art, the invention provides a processing method of a large 35CrNi3MoV shaft forging, which comprises the following steps:

1. Smelting and ingot casting process

In the smelting and ingot casting process, a process route of 80 tons of electric furnace EBT primary smelting, 120 tons of refining furnace LF refining, vacuum treatment furnace VD degassing and steel ingot casting is adopted to smelt and cast steel ingots used for large 35CrNi3MoV shaft forgings, and the steel ingot chemical components are controlled to be ：C：0.30～0.45％、Mn：0.25～0.60％、Si：0.17～0.40％、P≤0.020％、S≤0.020％、Cr：1.10～2.00％、Ni：2.75～3.50％、Mo：0.30～0.50％、V：0.08～0.20％、Cu≤0.20％、Al≤0.015％、As≤0.020％、Sn≤0.015％、Sb≤0.0025％, according to the mass percent, wherein the steel ingot gas content is controlled to be less than or equal to 1.0ppm, [ O ] is less than or equal to 25ppm and [ N ] is less than or equal to 70ppm;

2. Forging process

Taking out the steel ingot after solidification and demolding of the steel ingot, loading the steel ingot into a heat preservation vehicle for hot forging at the surface temperature of not lower than 700 ℃, controlling the forging temperature range to 1265-850 ℃, controlling the shaft forging ratio to be greater than 5.0, and specifically performing the forging process:

a. First fire forging: steel ingot pressing jaw, chamfering, bottom cutting and rounding;

b. Second fire forging: upsetting, first WHF drawing and pressing in eight directions;

c. Third fire forging: upsetting, and drawing out and flattening the square by WHF for the second time;

d. fourth fire forging: pressing circles, marking, forging out steps and trimming out finished products;

3. Post-forging heat treatment step

After forging and forming the forging, air cooling to 300 ℃ of the surface temperature of the shaft body of the small shaft end of the forging, and then loading the forging into a heating furnace for carrying out heat treatment after forging, wherein the method specifically comprises the following steps:

a. Homogenizing temperature, fully supercooling the forge piece to 250-320 ℃, and preserving heat for 15h;

b. Heating the forging to 640-660 ℃ at a heating rate of less than or equal to 35 ℃/h, preserving heat for 10h, heating the forging to 890-950 ℃ according to the power of a heating furnace, preserving heat for 15-20 h, and discharging through air cooling;

c. Carrying out austenitizing low-temperature normalizing treatment and high-temperature normalizing treatment for the second time, carrying out air cooling on the forge piece to 250-320 ℃, then preserving heat for 20h, then heating to 640-660 ℃ at a heating rate of less than or equal to 35 ℃/h, preserving heat for 10h, then heating the forge piece to 850-900 ℃ according to the power of a heating furnace, preserving heat for 15-20 h, and carrying out air cooling and discharging;

d. Tempering, namely air-cooling the forge piece to 250-320 ℃ and preserving heat for 20 hours, then heating to 640-660 ℃ at a heating rate of less than or equal to 30 ℃/h, preserving heat for 50 hours, and discharging after furnace cooling to less than or equal to 150 ℃;

4. Performance heat treatment process

The forging piece after the forging post heat treatment process is provided with a heating furnace for performing performance heat treatment, and specifically comprises the following steps:

a. Quenching, wherein the forging is subjected to heat preservation for 5 hours at the temperature of 300-350 ℃, then heated to 640-660 ℃ at the heating rate of less than or equal to 50 ℃/h, heat preservation for 8 hours, then heated to 830-880 ℃ according to the power of a heating furnace, heat preservation for 10-18 hours, and oil-cooled until the surface temperature of the shaft body of the forging is less than or equal to 150 ℃;

b. and (3) carrying out high-temperature tempering treatment, wherein the forge piece is kept at the temperature of 200-300 ℃ for 5-10 h, then is heated to 570-650 ℃ at the heating rate of less than or equal to 30 ℃/h, is cooled to less than or equal to 200 ℃ at the cooling rate of less than or equal to 30 ℃/h after being kept for 20-35 h, and is discharged from the furnace.

Further, in the above-described method for processing a large 35CrNi3MoV shaft forging, in the ingot smelting step:

The technological carbon distribution amount of the furnace charge is controlled to be more than or equal to 1.0%;

In the primary smelting process, the decarburization amount is controlled to be more than or equal to 0.20%, the molten steel in the oxidation period is uniformly boiled for more than 25 minutes, the temperature of the primary smelted steel is controlled to be 1660-1690 ℃, and the C, P content of the tapped molten steel is respectively controlled to be C:0.08 to 0.15 percent, and P is less than or equal to 0.005 percent;

in the refining process, ferrosilicon powder and carbon powder are adopted for diffusion deoxidation, the temperature is adjusted to 1650-1660 ℃ for vacuum treatment furnace VD degassing, and the vacuum is kept for at least more than 25min under the vacuum of less than or equal to 67 Pa;

The temperature of the casting steel is controlled between 1545 ℃ and 1555 ℃.

Further, in the processing method of the large 35CrNi3MoV shaft forge piece, the following steps are adopted:

in the first fire forging of the forging process, after the hot-cast steel ingot is charged in a heating furnace, the temperature is raised to 1255+/-10 ℃ at a heating rate of less than or equal to 70 ℃/h, and the temperature is kept for 12 hours; using a 125MN press, using an upper flat anvil and a lower V-shaped anvil to perform a first fire pressing jaw operation, and ensuring that the jaw center line is consistent with the steel ingot center line when the jaws are pressed; after finishing the jaw, cutting off the redundant riser material, rolling the clamp handle, turning the steel ingot, chamfering, cutting the bottom and rounding the steel ingot;

In the second fire forging of the forging procedure, returning the blank to the furnace, heating to 1255+/-10 ℃ according to the power of the heating furnace, and preserving heat for 20 hours; upsetting the blank by using a 125MN press, a drain pan and a spherical heading cap; after upsetting the steel ingot, performing first WHF drawing by adopting an upper wide flat anvil and a lower wide flat anvil, wherein full anvil strong pressing is adopted, the deformation of double-sided pressing is controlled to be 18-22%, 90 degrees are turned over after each pass is finished, half anvil is staggered, one pass is pressed, the pressing of each pass begins to be pressed from a riser end, the blank is compacted to be flat by multiple passes, and then chamfering is performed to enable the blank to be in eight directions;

In the third fire forging of the forging process, returning the blank to the furnace, heating to 1255+/-10 ℃ according to the power of the heating furnace, and preserving heat for 15 hours; upsetting the blank by using a 125MN press, a drain pan and a spherical heading cap; after upsetting the steel ingot, performing second WHF drawing by adopting an upper flat anvil and a lower flat anvil, wherein full anvil strong pressing is adopted, the deformation of double-sided pressing is controlled to be 18-22%, 90 DEG is turned over after each pressing pass, half anvil is staggered, one pressing pass is performed, pressing of each pass begins from a riser end, and the blank is compacted to be flat by multi-pass pressing;

In the fourth fire forging of the forging process, returning the blank to the furnace, heating to 1200+/-10 ℃ according to the power of the heating furnace, and preserving heat for 10 hours; and (3) using a 125MN press to press eight directions by using an upper flat anvil and a lower flat anvil, then stamping the anvil according to the size of the step material, forging out the shaft body and each step at two ends, and then correcting and rounding by using a forming circular arc anvil to finally form the forging piece.

Further, in the above processing method of a large 35CrNi3MoV shaft-like forging, if the small shaft end step of the forging cannot be formed in the fourth forging, the forging process further includes a fifth forging: returning the blank, heating to 1050+/-10 ℃ according to the power of the heating furnace, preserving heat for 7 hours, forging a small shaft end step after discharging, correcting rounding by using a forming circular arc anvil, and finally forming the forging.

As a specific embodiment, the processing method of the large 35CrNi3MoV shaft forging is used for manufacturing the forging with the external diameterThe forging process of the 35CrNi3MoV shaft forging for the large-scale generator comprises the following specific implementation steps of:

In the first fire forging of the forging process, a 125MN press is utilized, an upper 850mm flat anvil and a lower 850mm V-shaped anvil are used, the upper anvil and the lower anvil are aligned at the position of 100-150 mm of an upper ingot body along a steel ingot riser line, a light riser is started, the riser root and the shoulder of the ingot body are all pressed on a clamp handle material in a first circle, and the reduction is increased in a second circle; to press the jaw size to Cutting off redundant riser materials by using a lower chopper, and putting the round rolling forceps into an upsetting drain pan in the next firing time; turning over the steel ingot, and clamping the pressed steel ingotPliers handle for rounding steel ingot to 100mm double-side pressingThen cutting off the bottom of the steel ingot by using a lower chopper and then unloading;

In the second forging step, a 125MN press is used, A leak plate and a spherical heading cap, upsetting toThen adopting a wide flat anvil with 1700mm up and down to carry out first WHF drawing, wherein the circular arc angle R of the flat anvil is 150mm, the double-sided rolling reduction is controlled to be about 20%, full anvil strong pressing is adopted, the feeding amount of each anvil is more than 90% of the anvil width, the anvil receiving amount of 100-200 mm is needed between each anvil, the blank is compacted to be 1660mm x 1740mm in the flat direction through 6 times of rolling, then chamfering is carried out to enable the blank to be 1600mm x 4000mm in the eight direction, wherein the first WHF rolling reduction process parameters are controlled according to the following table:

In the third forging step, a 125MN press is used, A leak plate and a spherical heading cap, upsetting toAnd then adopting a flat anvil with the length of 1700mm from top to bottom to conduct second WHF drawing, controlling the double-sided rolling reduction to be about 20%, and drawing the blank to be a flattened square 1435mm multiplied by 1060mm through 11-pass rolling reduction, wherein the technological parameters of the second WHF rolling reduction are controlled according to the following table:

In the fourth fire forging of the forging process, a 125MN press is utilized, an upper flat anvil and a lower flat anvil are firstly adopted to press 1250mm in all directions, then, after the number of the anvil is printed according to the size of the step material distribution, each step at the shaft body and the two ends is forged, then, a forming circular arc anvil is used for correcting rounding, and the excess materials at the two ends are cut according to the required size in a gas mode, so that the final forming of the forge piece is carried out.

The invention realizes the one-time qualification of the production of large 35CrNi3MoV shaft forgings for the first time, fills up the technical blank, and realizes the manufacturing process with short period, low cost, high efficiency and stable quality. Compared with the prior art, the processing method of the large 35CrNi3MoV shaft forging has the following advantages and beneficial effects:

(1) By making a proper smelting and ingot casting process scheme and adopting an ultra-pure low segregation smelting technology, effective process measures are adopted from the aspects of purity, homogeneity and compactness of the steel ingot, so that shrinkage holes, porosity, fewer inclusions, high component uniformity and low segregation in the steel are ensured, and the requirements of a large shaft forging on high purity and high homogeneity of the steel ingot are met;

(2) By formulating two upsetting and three drawing forging processes and adopting an axisymmetric low-stress uniform deformation forging technology, the low tensile stress in the forge piece is ensured, the compact forging penetration in the forge piece and the forging internal metallurgical defect are met, meanwhile, the forging temperature and the deformation of each firing are controlled, the internal cracks are avoided from being generated by forging, the original structure with controllable crystal grains is obtained, and the final qualification of the forge piece is ensured;

(3) Through heat treatment after forging and performance heat treatment, a uniform deep-cooling heat treatment technology is adopted to cut off and inhibit the tissue genetic effect, so that the forging finally obtains excellent mechanical properties.

Drawings

For a clearer description of embodiments of the invention or of the solutions of the prior art, the drawings which are required to be used in the description of the embodiments or of the prior art will be briefly described, it being apparent that the drawings in the description below are only some embodiments of the invention, and that other drawings can be obtained, without inventive effort, by a person skilled in the art from these drawings, in which:

FIG. 1 is a schematic flow chart of a processing method of a large 35CrNi3MoV shaft forging piece;

Fig. 2 is a schematic diagram of a forging morphology in each process step of the processing method of the large 35CrNi3MoV shaft forging of the present invention, wherein (a) is a schematic diagram of a steel ingot, (b) is a schematic diagram of a blank with a steel ingot pressing jaw, chamfering, bottom cutting and rounding, (c) is a schematic diagram of a blank with a steel ingot upsetting and a first WHF drawing and pressing eight directions, (d) is a schematic diagram of a blank with a steel ingot upsetting and a second WHF drawing and flattening directions, (e) is a schematic diagram of a blank with a steel ingot rounding, number stamping and forging steps, and (f) is a schematic diagram of a finished forging;

FIG. 3 is a schematic timing diagram of a post-forging heat treatment process in the method for processing large 35CrNi3MoV shaft forgings of the present invention;

FIG. 4 is a schematic timing diagram of a performance heat treatment process in the method for machining a large 35CrNi3MoV shaft forging of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions of the present invention will be clearly and completely described below with reference to specific embodiments of the present invention and corresponding drawings. It will be apparent that the described embodiments are only some, but not all, embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.

As shown in FIG. 1, the processing method of the large 35CrNi3MoV shaft forging comprises the following steps:

1. Smelting and ingot casting process

In the smelting and ingot casting process, a process route of 80 tons of electric furnaces EBT primary smelting, 120 tons of refining furnaces LF refining, vacuum treatment furnace VD degassing and steel ingot casting is adopted to smelt and cast steel ingots used for large 35CrNi3MoV shaft forgings.

According to the technical requirements of the large 35CrNi3MoV shaft forgings on flaw detection and comprehensive mechanical properties, the chemical components of steel ingots are strictly controlled, and particularly, the contents of impurity elements P, as, sn, sb causing tempering embrittlement, elements S reducing the toughness of steel and the like in the steel are strictly controlled. In addition, the 35CrNi3MoV steel has complex phase transition and large internal stress in the subsequent cooling process after forging, and particularly the H content in molten steel is strictly controlled, so that white spots caused by the concentration of the hydrogen content in the enrichment part of the forging piece are avoided, and flaw detection is not qualified.

Therefore, in the process of smelting and casting ingot, the chemical components of the steel ingot are controlled to be ：C：0.30～0.45％、Mn：0.25～0.60％、Si：0.17～0.40％、P≤0.020％、S≤0.020％、Cr：1.10～2.00％、Ni：2.75～3.50％、Mo：0.30～0.50％、V：0.08～0.20％、Cu≤0.20％、Al≤0.015％、As≤0.020％、Sn≤0.015％、Sb≤0.0025％, according to the mass percentage, and the gas content of the steel ingot is controlled to be less than or equal to [ H ] < 1.0ppm, [ O ] < 25ppm and [ N ] < 70ppm.

In addition, in the smelting and ingot casting process, the following technical points need to be controlled:

(1) And (3) furnace burden control: during the material mixing, the scrap steel and pig iron which meet the process requirements are preferably selected, the auxiliary materials are required to be cleaned and dried, the alloy is baked and dried in advance according to the process requirements, and elements such as Pb, sn, as, sb, bi and the like are controlled according to the internal control process requirements. Strictly according to the process ingredients, the process carbon content of the furnace charge entering the furnace is controlled to be more than or equal to 1.0 percent.

(2) Primary refining of 80 ton electric furnace EBT: charging, melting, slag discharging and temperature measuring are strictly carried out according to the operation rules, so that reasonable oxygen blowing fluxing and reasonable decarburization are realized. The decarburization amount is controlled to be more than or equal to 0.20%, P is removed at low temperature, slag is reasonably formed, molten steel in an oxidation period is uniformly boiled for more than 25 minutes, the purposes of degassing and removing impurities are achieved, and large boiling is strictly forbidden. The tapping adopts the operation of steel and slag, prevents the oxidizing slag from entering the refining ladle, and carbon powder can be sprayed in the furnace before tapping. The temperature of the primary refining steel is controlled between 1660 and 1690 ℃, and the C, P content in the tapping molten steel is respectively controlled to be C:0.08 to 0.15 percent and less than or equal to 0.005 percent of P.

(3) LF refining in a 120 ton refining furnace: the ferrosilicon powder and carbon powder are adopted for diffusion deoxidation, alloying operation is carried out according to the technological requirements, the pressure and flow of argon are controlled, and the alloy components are ensured to be uniform in place. The refining process can make the reducing slag deoxidize and desulfur as soon as possible, and ensure the non-metallic inclusion in the molten steel to float up fully to the maximum. Ensuring proper slag alkalinity, slag quantity and molten steel temperature. And adjusting the temperature to 1650-1660 ℃ to carry out vacuum treatment furnace VD degassing.

(4) Vacuum treatment furnace VD degasification: after the molten steel is subjected to high vacuum treatment, oxygen in the molten steel is removed by utilizing a carbon-oxygen reaction, and gases such as H, O, N and impurities in the molten steel are diffused and float out of the molten steel by utilizing generated CO bubbles, so that the effect of purifying the molten steel is achieved. And keeping the vacuum at less than or equal to 67Pa for at least 25 min. After vacuum treatment, the molten steel is kept stand and is stirred for more than 25 minutes by utilizing argon gas, so that the floating of inclusions in the steel is further ensured.

(5) Pouring steel ingot: during casting, the prepared ingot mould and other auxiliary tools are cleaned and dried in advance, and the operation is strictly performed according to the casting technological rules, so that the casting quality of the steel ingot is ensured. Particularly, the key links of molten steel drainage, casting time, casting temperature, casting speed control, whole argon protection casting and the like are paid attention to. The tapping temperature is controlled at 1545-1555 ℃. Finally, the casting is completed, adding proper amount of heating agent as soon as possible.

Through the measures in the smelting and ingot casting process, the chemical components of the steel ingot meet the standard requirements, and in the finished steel ingot product, [ H ]:0.5ppm, [ O ]:15ppm, [ N ]:55ppm, wherein the coarse system and the fine system of inclusions A, B, C, D in the steel are controlled to be 0-0.5 level, and DS is controlled to be less than or equal to 0.5 level.

2. Forging process

And taking out the steel ingot after solidification and demoulding according to the steel ingot solidification and cooling process requirements, and loading the steel ingot into a heat preservation vehicle for hot-feeding forging at the surface temperature of not lower than 700 ℃, wherein the schematic diagram of the steel ingot is shown in (a) of fig. 2.

For large 35CrNi3MoV shaft forgings, the ultrasonic flaw detection requirement is strict, the weight of forging blanks reaches about 60 tons, and the utilization rate of forging steel ingots is controlled to be about 70%. For producing large shaft forgings, the used steel ingot has large size, and the defects of inherent segregation, gas, inclusion, shrinkage cavity, looseness and the like are more obvious, and during forging, according to the simulated casting result of the ingot, the deposition cone part of the water gap is cut off by about 7%, the riser part is cut off by about 18%, and the fire loss is about 5%. In order to meet the requirement of ultrasonic flaw detection of the forging, the forging process has excellent internal quality, and the design principle of the forging process takes the core part of the compacted steel ingot, the loose and dispersed inclusions of the forged core part as an essential target. Therefore, in the forging process of the processing method of the large 35CrNi3MoV shaft forgings, an effective forging process method is designed by adopting a 125MN press, so that the forgings are fully deformed, the grain structure is fully and uniformly refined, the heating and heat preservation temperature of each fire is effectively controlled, the forging temperature range is controlled to 1265-850 ℃, and the shaft body forging ratio is controlled to be more than 5.0.

And taking out the steel ingot after solidification and demoulding according to the steel ingot solidification and cooling process requirements, and loading the steel ingot into a heat preservation vehicle for hot-feeding forging at the surface temperature of not lower than 700 ℃, wherein the schematic diagram of the steel ingot is shown in (a) of fig. 2. In the forging process, a 125MN press is adopted for forging for multiple times, the forging temperature range is controlled to 1270-850 ℃, the shaft-body forging ratio of the rotor body is controlled to be more than 3.5, the forging is enabled to be fully deformed, the grain structure is fully and uniformly refined, the core of the steel ingot is compacted, and therefore the core is forged to be loose and dispersed for inclusion, the solid integral rotor body forging with excellent internal quality is obtained, and the ultrasonic flaw detection requirement is met.

The specific process of the forging procedure is as follows:

a. first fire forging: steel ingot pressing jaw, chamfering, bottom cutting and rounding. After the hot-delivered steel ingot is loaded in a heating furnace, the temperature is raised to 1255+/-10 ℃ at a temperature rising speed of less than or equal to 70 ℃/h, and the temperature is kept for 12h; using a 125MN press, using an upper flat anvil and a lower V-shaped anvil to perform a first fire pressing jaw operation, and ensuring that the jaw center line is consistent with the steel ingot center line when the jaws are pressed; after the jaw is pressed, the excess riser material is cut off, the clamp handle is rolled, the steel ingot is turned around, and chamfering, bottom cutting and rounding operations are carried out on the steel ingot. After the first fire forging is finished, the hot state of the oxygen lance is utilized to clean the surface defects of the blank such as cracks, indentations and the like. The schematic diagram of the ingot pressing jaw, chamfering, bottom cutting and rounding is shown in fig. 2 (b).

B. Second fire forging: upsetting, drawing and pressing in eight directions by a first WHF (wide anvil strong pressing forging) method. Returning the blank to the furnace, heating to 1255+/-10 ℃ according to the power of the heating furnace, and preserving heat for 20 hours; upsetting the blank by using a 125MN press, a drain disc and a spherical heading cap, so that the sectional area of the steel ingot blank is increased through axisymmetric deformation, the forging ratio is increased for subsequent WHF drawing, the inner holes of the steel ingot are effectively pressed, the cast structure is crushed, the segregation is improved, the transverse performance of the shaft forging is improved, and the anisotropy of the mechanical performance is reduced; after upsetting the steel ingot, performing first WHF large reduction drawing by adopting an upper wide flat anvil and a lower wide flat anvil, wherein full anvil strong pressing is adopted, double-sided reduction deformation is controlled to be 18-22%, the steel ingot is overturned by 90 degrees after one pass is pressed, half anvil is staggered, one pass is pressed, the reduction of each pass starts to be pressed from a riser end, the integral deformation of a forge piece is effectively covered, the deformation uniformity of the blank is ensured, the blank is compacted to be flat by multiple passes of reduction, and then chamfering is performed to enable the blank to reach eight directions. After the second fire forging is finished, the hot state of the oxygen lance is utilized to clean the surface defects of the blank such as cracks, pits, folds and the like. A schematic diagram of the ingot in the eight directions of upsetting, first WHF elongation and compaction is shown in fig. 2 (c).

C. Third fire forging: upsetting and drawing out the flattened square by a second WHF method. Returning the blank to the furnace, heating to 1255+/-10 ℃ according to the power of the heating furnace, and preserving heat for 15 hours; upsetting the blank by using a 125MN press, a drain disc and a spherical heading cap, so that the sectional area of the steel ingot blank is increased through axisymmetric deformation, the forging ratio is increased for subsequent WHF drawing, the inner holes of the steel ingot are effectively pressed, the cast structure is crushed, the segregation is improved, the transverse performance of the shaft forging is improved, and the anisotropy of the mechanical performance is reduced; after upsetting the steel ingot, performing second WHF drawing by adopting an upper flat anvil and a lower flat anvil, wherein full anvil strong pressing is adopted, the deformation quantity of double-sided pressing is controlled to be 18-22%, 90 DEG is turned after each pass is finished, half anvil is staggered, each pass is pressed, the pressing of each pass begins to be pressed from a riser end, the integral deformation of a forge piece is effectively covered, the deformation uniformity of the blank is ensured, and the blank is pressed to be flat by multiple passes of pressing. And after the third fire forging is finished, the hot state of the oxygen lance is utilized to clean the surface defects of the blank such as cracks, pits, folds and the like. A schematic diagram of the ingot upsetting, second WHF elongation flattening, is shown in fig. 2 (d).

D. Fourth fire forging: pressing round, marking, forging steps and trimming to obtain the finished product. Returning the blank to the furnace, heating to 1200+/-10 ℃ according to the power of the heating furnace, and preserving heat for 10 hours; and (3) using a 125MN press to press eight directions by using an upper flat anvil and a lower flat anvil, then stamping the anvil according to the size of the step material, forging out the shaft body and each step at two ends, and then correcting and rounding by using a forming circular arc anvil to finally form the forging piece. The schematic diagram of the blank for rounding, stamping and forging the steps of the steel ingot is shown in (e) of fig. 2, and the schematic diagram of the finished forging is shown in (f) of fig. 2.

3. Post-forging heat treatment step

For large 35CrNi3MoV shaft forgings, after long-time high-temperature heat preservation and forging deformation, most of forged tissues of the forgings are coarse crystal tissues, and the tissue genetics are extremely strong. The unbalanced original structure of the coarse grains is martensite, bainite and the like, the coarse grains are re-austenitized under a certain heating condition, the phenomenon of original coarse grains is inherited and recovered, and if the final heat treatment is directly carried out, the original coarse crystal state is reserved due to the inheritance of the structure, so that the mechanical property of the forge piece is reduced, and grass-like waves appear during ultrasonic flaw detection. Therefore, the necessary post-forging heat treatment is carried out firstly, the heat stress is eliminated, the uneven structure in the forging process is adjusted and improved, austenite grains are thinned, the structure inheritance is effectively cut off, the structure preparation is made for the final performance heat treatment, the detectability of ultrasonic flaw detection is improved, and the subsequent machining cutting performance is improved. As shown in fig. 3, the post-forging heat treatment step specifically includes:

a. homogenizing temperature, fully supercooling the forging to 250-320 ℃, preserving heat for 15h, ensuring that the core of the forging is also reduced below the lower bainite transformation temperature, and finishing tissue transformation;

b. Heating the forging to 640-660 ℃ at a heating rate of less than or equal to 35 ℃/h, preserving heat for 10h, heating the forging to 890-950 ℃ according to the power of a heat treatment heating furnace, preserving heat for 15-20 h, and discharging through air cooling;

c. carrying out austenitizing low-temperature normalizing treatment and high-temperature normalizing treatment for the second time, carrying out air cooling on the forge piece to 250-320 ℃, then preserving heat for 20h, then heating to 640-660 ℃ at a heating rate of less than or equal to 35 ℃/h, preserving heat for 10h, then heating the forge piece to 850-900 ℃ according to the power of a heat treatment heating furnace, preserving heat for 15-20 h, and carrying out air cooling and discharging;

d. tempering, namely cooling the forge piece to 250-320 ℃ in air, preserving heat for 20 hours, heating to 640-660 ℃ at a heating rate of less than or equal to 30 ℃/h, preserving heat for 50 hours, cooling to less than or equal to 150 ℃ in a furnace, and discharging.

4. Performance heat treatment process

For large 35CrNi3MoV shaft forgings, fine grains, high low-temperature impact toughness and high room-temperature tensile strength are required to meet the performance requirements of the final forgings. Therefore, in the performance heat treatment process, martensite and bainite structures are obtained as targets, the whole section of the forging is quenched through controlling the quenching heating temperature and the heat preservation time, so that martensite or martensite and lower bainite structures are obtained, the homogenization of the whole structure and the mechanical properties of the forging is realized, and the quenching process has a large cracking risk due to high carbon equivalent of the forging, and the oil cooling mode is adopted in the quenching of the performance heat treatment.

As shown in fig. 4, the performance heat treatment process specifically includes:

a. Quenching, wherein the forging is subjected to heat preservation for 5 hours at the temperature of 300-350 ℃, then heated to 640-660 ℃ at the heating rate of less than or equal to 50 ℃/h, heat preservation for 8 hours, then heated to 830-880 ℃ according to the power of a heating furnace, heat preservation for 10-18 hours, and oil-cooled until the surface temperature of the shaft body of the forging is less than or equal to 150 ℃;

b. and (3) carrying out high-temperature tempering treatment, wherein the forge piece is kept at the temperature of 200-300 ℃ for 5-10 h, then is heated to 570-650 ℃ at the heating rate of less than or equal to 30 ℃/h, is cooled to less than or equal to 200 ℃ at the cooling rate of less than or equal to 30 ℃/h after being kept for 20-35 h, and is discharged from the furnace.

Further, in the forging step of the method for processing a large 35CrNi3MoV shaft-like forging of the present invention, if the small shaft end step of the forging cannot be formed in the fourth forging, the forging step further includes a fifth forging: returning the blank, heating to 1050+/-10 ℃ according to the power of the heating furnace, preserving heat for 7 hours, forging a small shaft end step after discharging, correcting rounding by using a forming circular arc anvil, and finally forming the forging.

The method for processing the large 35CrNi3MoV shaft forging according to the invention is described in detail below with reference to specific examples. The following examples are used for manufacturing and processing 35CrNi3MoV shaft forgings for large-scale generator projects, and the forging products are required to have the following dimensions: outer diameter ofThe grain size is required to be more than or equal to 5 grades, the ultrasonic flaw detection is required to not allow a nonmetallic dense area with the equivalent diameter of more than or equal to phi 2.0mm to exist, and the single defect with the equivalent diameter of more than phi 3.0mm to exist, and the bottom wave reduction is required to be less than or equal to 4.4dB. The forging has strict flaw detection requirement, large control difficulty of grain structure, forging blank weight up to 60 tons and minimum shaft-to-body forging ratio of 5.

The processing method of the large 35CrNi3MoV shaft forgings is carried out according to the smelting ingot casting process, the forging process, the post-forging heat treatment process and the performance heat treatment process, and the specific implementation process of the forging process is as follows:

in the first fire forging of the forging process, a 125MN press is utilized, an upper 850mm flat anvil and a lower 850mm V-shaped anvil are utilized, the upper anvil and the lower anvil are aligned at the position of 100-150 mm of an upper ingot body along a steel ingot riser line, a light riser is started, the riser root and the shoulder of the ingot body are all pressed on a clamp handle material in a first circle, the reduction is started to be increased in a second circle, the uniform rotation angle of a jaw of an operating machine and the reduction of each hammer are controlled, and the center line of the jaw is ensured to be consistent with the center line of the steel ingot; to press the jaw size to Cutting off redundant riser materials by using a lower chopper, and properly rolling a clamp handle to ensure that the next firing time can be put into an upsetting drain pan; turning over the steel ingot, and clamping the pressed steel ingot by an operating machinePliers handle, double-side rolling reduction is controlled to be 100mm, and steel ingot is rounded to beThen cutting the bottom of the steel ingot by using a lower chopper and then taking off the machine, utilizing the thermal state of the oxygen lance to clean cracks blank surface defects such as indentation.

In the second forging step, a 125MN press is used,A leak plate and a spherical heading cap, upsetting to aboutAnd then, adopting a wide flat anvil with 1700mm up and down to carry out WHF drawing for the first time with a large rolling reduction, wherein the arc angle R of the flat anvil is 150mm, the rolling reduction of the two sides is controlled to be about 20%, full anvil forced pressing is adopted, the feeding amount of each anvil is more than 90% of the width of the anvil, the anvil receiving amount of 100-200 mm is needed between each anvil, after turning over for 90 degrees after each pass is finished, half the anvil is misplaced, one pass is pressed, and the rolling reduction of each pass begins to be pressed from a riser end, so that the integral deformation of a forge piece is effectively covered. The blank was compacted to a square 1660mm x 1740mm by 6 passes of reduction, and then chamfered to achieve a square of about 1600mm x 4000mm. After the blank is taken off the machine, the defects of cracks, pits, folds and the like on the surface of the blank in the drawing process are completely cleaned by an oxygen lance in a thermal state. The first WHF reduction process parameters were controlled as in table 1 below:

Table 1 first WHF reduction process parameters

In the third forging step, a 125MN press is used,A leak plate and a spherical heading cap, upsetting to aboutAnd then adopting a flat anvil with the length of 1700mm up and down to carry out second WHF drawing, controlling the double-sided rolling reduction to be about 20%, wherein specific parameters and notes of the second WHF drawing are consistent with those of the first WHF drawing. And will not be described in detail herein. The blank was drawn into a flattened square 1435mm×1060mm by 11 passes of reduction. After the blank is taken off the machine, the defects of cracks, pits, folds and the like in the drawing process are completely cleaned by an oxygen lance in a full thermal state. The second WHF reduction process parameters were controlled as follows in table 2:

TABLE 2 second WHF reduction Process parameters

In the fourth fire forging of the forging process, a 125MN press is utilized, an upper flat anvil and a lower flat anvil are firstly adopted to press 1250mm in all directions, then, after the number of the anvil is printed according to the size of the step material distribution, each step at the shaft body and the two ends is forged, then, a forming circular arc anvil is used for correcting rounding, and the excess materials at the two ends are cut according to the required size in a gas mode, so that the final forming of the forge piece is carried out. If the small shaft end step of the forging cannot be formed, forging by a fifth fire after forging by a fourth fire, returning the blank to the furnace, heating to 1050+/-10 ℃, preserving heat for 7 hours, discharging, forging the small shaft end step, correcting and rounding by using a forming arc anvil, and finally forming the forging.

The specific implementation processes of the smelting ingot casting process, the post-forging heat treatment process and the performance heat treatment process in the above embodiment of the present invention are the same as those described above, and will not be repeated here.

According to the embodiment of the invention, 2 large 35CrNi3MoV shaft forgings (the sample A and the sample B) are processed and produced for chemical component detection and mechanical property detection, and all detection results meet the technical requirements, specifically:

(1) Chemical component detection

The chemical component detection is performed by sampling at two ends of the shaft body of the sample A and the sample B respectively, and the detection results are shown in the following table 3:

TABLE 3 chemical component detection results (mass percent,%)

In the table above, X1 refers to the tangential sampling position of the shaft body in the direction of the forging water gap, X2 refers to the tangential sampling position of the shaft body in the direction of the forging riser, and specifically refer to (f) in fig. 2.

(2) Mechanical property detection

Mechanical property detection is carried out by respectively sampling in the axial direction of the shaft head, the radial direction of the shaft body and the longitudinal direction of the central hole of the sample A and the sample B, and the detection results are shown in the following table 4:

TABLE 4 mechanical property test results

In the table above, L1 refers to the axial sampling position of the shaft head in the direction of the forging water gap, L2 refers to the axial sampling position of the shaft head in the direction of the forging riser, X1 refers to the tangential sampling position of the shaft body in the direction of the forging water gap, X2 refers to the tangential sampling position of the shaft body in the direction of the forging riser, and M1 refers to the longitudinal sampling position of the center hole of the forging, and specifically, refer to (f) in fig. 2.

(3) In addition, through detection, the grain sizes of the large 35CrNi3MoV shaft forgings processed and manufactured by the embodiment of the invention at the X1 and X2 positions are respectively 7.0 and 7.0, and the technical requirement that the grain size is more than or equal to 5 levels is met. Moreover, the ultrasonic detection result of the whole forging piece does not find out the defects of record and exceeding standard.

In conclusion, the invention realizes the one-time qualification of the production of the large 35CrNi3MoV shaft forge piece for the first time, fills the technical blank, and realizes the manufacturing process with short period, low cost, high efficiency and stable quality. Compared with the prior art, the processing method of the large 35CrNi3MoV shaft forging has the following advantages and beneficial effects:

(1) By making a proper smelting and ingot casting process scheme and adopting an ultra-pure low segregation smelting technology, effective process measures are adopted from the aspects of purity, homogeneity and compactness of the steel ingot, so that shrinkage holes, porosity, fewer inclusions, high component uniformity and low segregation in the steel are ensured, and the requirements of a large shaft forging on high purity and high homogeneity of the steel ingot are met;

(2) By formulating two upsetting and three drawing forging processes and adopting an axisymmetric low-stress uniform deformation forging technology, the low tensile stress in the forge piece is ensured, the compact forging penetration in the forge piece and the forging internal metallurgical defect are met, meanwhile, the forging temperature and the deformation of each firing are controlled, the internal cracks are avoided from being generated by forging, the original structure with controllable crystal grains is obtained, and the final qualification of the forge piece is ensured;

(3) Through heat treatment after forging and performance heat treatment, a uniform deep-cooling heat treatment technology is adopted to cut off and inhibit the tissue genetic effect, so that the forging finally obtains excellent mechanical properties.

It should be noted that, herein, relational terms such as "first" and "second", and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. In this context, "front", "rear", "left", "right", "upper" and "lower" are referred to with respect to the placement state shown in the drawings.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and are not limiting thereof; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims (5)

1. A processing method of a large 35CrNi3MoV shaft forging is characterized by comprising the following steps:

1. Smelting and ingot casting process

In the smelting and ingot casting process, a process route of 80 tons of electric furnace EBT primary smelting, 120 tons of refining furnace LF refining, vacuum treatment furnace VD degassing and steel ingot casting is adopted to smelt and cast steel ingots used for large 35CrNi3MoV shaft forgings, and the steel ingot chemical components are controlled to be ：C：0.30～0.45％、Mn：0.25～0.60％、Si：0.17～0.40％、P≤0.020％、S≤0.020％、Cr：1.10～2.00％、Ni：2.75～3.50％、Mo：0.30～0.50％、V：0.08～0.20％、Cu≤0.20％、Al≤0.015％、As≤0.020％、Sn≤0.015％、Sb≤0.0025％, according to the mass percent, wherein the steel ingot gas content is controlled to be less than or equal to 1.0ppm, [ O ] is less than or equal to 25ppm and [ N ] is less than or equal to 70ppm;

2. Forging process

Taking out the steel ingot after solidification and demolding of the steel ingot, loading the steel ingot into a heat preservation vehicle for hot forging at the surface temperature of not lower than 700 ℃, controlling the forging temperature range to 1265-850 ℃, controlling the shaft forging ratio to be greater than 5.0, and specifically performing the forging process:

a. First fire forging: steel ingot pressing jaw, chamfering, bottom cutting and rounding;

b. Second fire forging: upsetting, first WHF drawing and pressing in eight directions;

c. Third fire forging: upsetting, and drawing out and flattening the square by WHF for the second time;

d. fourth fire forging: pressing circles, marking, forging out steps and trimming out finished products;

3. Post-forging heat treatment step

After forging and forming the forging, air cooling to 300 ℃ of the surface temperature of the shaft body of the small shaft end of the forging, and then loading the forging into a heating furnace for carrying out heat treatment after forging, wherein the method specifically comprises the following steps:

a. Homogenizing temperature, fully supercooling the forge piece to 250-320 ℃, and preserving heat for 15h;

b. Heating the forging to 640-660 ℃ at a heating rate of less than or equal to 35 ℃/h, preserving heat for 10h, heating the forging to 890-950 ℃ according to the power of a heating furnace, preserving heat for 15-20 h, and discharging through air cooling;

c. Carrying out austenitizing low-temperature normalizing treatment and high-temperature normalizing treatment for the second time, carrying out air cooling on the forge piece to 250-320 ℃, then preserving heat for 20h, then heating to 640-660 ℃ at a heating rate of less than or equal to 35 ℃/h, preserving heat for 10h, then heating the forge piece to 850-900 ℃ according to the power of a heating furnace, preserving heat for 15-20 h, and carrying out air cooling and discharging;

d. Tempering, namely air-cooling the forge piece to 250-320 ℃ and preserving heat for 20 hours, then heating to 640-660 ℃ at a heating rate of less than or equal to 30 ℃/h, preserving heat for 50 hours, and discharging after furnace cooling to less than or equal to 150 ℃;

4. Performance heat treatment process

The forging piece after the forging post heat treatment process is provided with a heating furnace for performing performance heat treatment, and specifically comprises the following steps:

a. Quenching, wherein the forging is subjected to heat preservation for 5 hours at the temperature of 300-350 ℃, then heated to 640-660 ℃ at the heating rate of less than or equal to 50 ℃/h, heat preservation for 8 hours, then heated to 830-880 ℃ according to the power of a heating furnace, heat preservation for 10-18 hours, and oil-cooled until the surface temperature of the shaft body of the forging is less than or equal to 150 ℃;

b. and (3) carrying out high-temperature tempering treatment, wherein the forge piece is kept at the temperature of 200-300 ℃ for 5-10 h, then is heated to 570-650 ℃ at the heating rate of less than or equal to 30 ℃/h, is cooled to less than or equal to 200 ℃ at the cooling rate of less than or equal to 30 ℃/h after being kept for 20-35 h, and is discharged from the furnace.

2. The method for processing a large 35CrNi3MoV shaft forging according to claim 1, wherein in the ingot smelting step:

The technological carbon distribution amount of the furnace charge is controlled to be more than or equal to 1.0%;

In the primary smelting process, the decarburization amount is controlled to be more than or equal to 0.20%, the molten steel in the oxidation period is uniformly boiled for more than 25 minutes, the temperature of the primary smelted steel is controlled to be 1660-1690 ℃, and the C, P content of the tapped molten steel is respectively controlled to be C:0.08 to 0.15 percent, and P is less than or equal to 0.005 percent;

in the refining process, ferrosilicon powder and carbon powder are adopted for diffusion deoxidation, the temperature is adjusted to 1650-1660 ℃ for vacuum treatment furnace VD degassing, and the vacuum is kept for at least more than 25min under the vacuum of less than or equal to 67 Pa;

The temperature of the casting steel is controlled between 1545 ℃ and 1555 ℃.

3. The method for processing the large 35CrNi3MoV shaft forging according to claim 1, which is characterized in that:

in the first fire forging of the forging process, after the hot-cast steel ingot is charged in a heating furnace, the temperature is raised to 1255+/-10 ℃ at a heating rate of less than or equal to 70 ℃/h, and the temperature is kept for 12 hours; using a 125MN press, using an upper flat anvil and a lower V-shaped anvil to perform a first fire pressing jaw operation, and ensuring that the jaw center line is consistent with the steel ingot center line when the jaws are pressed; after finishing the jaw, cutting off the redundant riser material, rolling the clamp handle, turning the steel ingot, chamfering, cutting the bottom and rounding the steel ingot;

In the second fire forging of the forging procedure, returning the blank to the furnace, heating to 1255+/-10 ℃ according to the power of the heating furnace, and preserving heat for 20 hours; upsetting the blank by using a 125MN press, a drain pan and a spherical heading cap; after upsetting the steel ingot, performing first WHF drawing by adopting an upper wide flat anvil and a lower wide flat anvil, wherein full anvil strong pressing is adopted, the deformation of double-sided pressing is controlled to be 18-22%, 90 degrees are turned over after each pass is finished, half anvil is staggered, one pass is pressed, the pressing of each pass begins to be pressed from a riser end, the blank is compacted to be flat by multiple passes, and then chamfering is performed to enable the blank to be in eight directions;

In the third fire forging of the forging process, returning the blank to the furnace, heating to 1255+/-10 ℃ according to the power of the heating furnace, and preserving heat for 15 hours; upsetting the blank by using a 125MN press, a drain pan and a spherical heading cap; after upsetting the steel ingot, performing second WHF drawing by adopting an upper flat anvil and a lower flat anvil, wherein full anvil strong pressing is adopted, the deformation of double-sided pressing is controlled to be 18-22%, 90 DEG is turned over after each pressing pass, half anvil is staggered, one pressing pass is performed, pressing of each pass begins from a riser end, and the blank is compacted to be flat by multi-pass pressing;

In the fourth fire forging of the forging process, returning the blank to the furnace, heating to 1200+/-10 ℃ according to the power of the heating furnace, and preserving heat for 10 hours; and (3) using a 125MN press to press eight directions by using an upper flat anvil and a lower flat anvil, then stamping the anvil according to the size of the step material, forging out the shaft body and each step at two ends, and then correcting and rounding by using a forming circular arc anvil to finally form the forging piece.

4. The method of working a large 35CrNi3MoV shaft-like forging as recited in claim 3, wherein if the small shaft end step of the forging cannot be formed in the fourth forging, the forging process further comprises a fifth forging: returning the blank, heating to 1050+/-10 ℃ according to the power of the heating furnace, preserving heat for 7 hours, forging a small shaft end step after discharging, correcting rounding by using a forming circular arc anvil, and finally forming the forging.

5. The method for manufacturing a large 35CrNi3MoV shaft forging as recited in any one of claims 1 to 4, for manufacturing a machined size of an outer diameterThe 35CrNi3MoV shaft forging for the large-scale generator with the length of 11000mm is characterized in that the specific implementation process of the forging procedure is as follows:

In the first fire forging of the forging process, a 125MN press is utilized, an upper 850mm flat anvil and a lower 850mm V-shaped anvil are used, the upper anvil and the lower anvil are aligned at the position of 100-150 mm of an upper ingot body along a steel ingot riser line, a light riser is started, the riser root and the shoulder of the ingot body are all pressed on a clamp handle material in a first circle, and the reduction is increased in a second circle; to press the jaw size to Cutting off redundant riser materials by using a lower chopper, and putting the round rolling forceps into an upsetting drain pan in the next firing time; turning over the steel ingot, and clamping the pressed steel ingotPliers handle for rounding steel ingot to 100mm double-side pressingThen cutting off the bottom of the steel ingot by using a lower chopper and then unloading;

In the second forging step, a 125MN press is used, A leak plate and a spherical heading cap, upsetting toThen adopting a wide flat anvil with 1700mm up and down to carry out first WHF drawing, wherein the circular arc angle R of the flat anvil is 150mm, the double-sided rolling reduction is controlled to be about 20%, full anvil strong pressing is adopted, the feeding amount of each anvil is more than 90% of the anvil width, the anvil receiving amount of 100-200 mm is needed between each anvil, the blank is compacted to be 1660mm x 1740mm in the flat direction through 6 times of rolling, then chamfering is carried out to enable the blank to be 1600mm x 4000mm in the eight direction, wherein the first WHF rolling reduction process parameters are controlled according to the following table:

In the third forging step, a 125MN press is used, A leak plate and a spherical heading cap, upsetting toAnd then adopting a flat anvil with the length of 1700mm from top to bottom to conduct second WHF drawing, controlling the double-sided rolling reduction to be about 20%, and drawing the blank to be a flattened square 1435mm multiplied by 1060mm through 11-pass rolling reduction, wherein the technological parameters of the second WHF rolling reduction are controlled according to the following table:

In the fourth fire forging of the forging process, a 125MN press is utilized, an upper flat anvil and a lower flat anvil are firstly adopted to press 1250mm in all directions, then, after the number of the anvil is printed according to the size of the step material distribution, each step at the shaft body and the two ends is forged, then, a forming circular arc anvil is used for correcting rounding, and the excess materials at the two ends are cut according to the required size in a gas mode, so that the final forming of the forge piece is carried out.