CN102424934B

CN102424934B - Manufacturing method of steel forged component of 18CrNiMo7-6 large gear

Info

Publication number: CN102424934B
Application number: CN2011103642834A
Authority: CN
Inventors: 冯桂萍; 秋立鹏; 阚志; 王连海; 刘金鑫; 程丽杰; 薛井恒; 段永生; 郭晓俊; 马群; 赵敏; 陈明; 纪肖
Original assignee: FUSHUN SPECIAL STEEL SHARES Co Ltd
Current assignee: Fushun Special Steel Shares Co., Ltd.
Priority date: 2011-11-16
Filing date: 2011-11-16
Publication date: 2013-06-05
Anticipated expiration: 2031-11-16
Also published as: CN102424934A

Abstract

The invention discloses a manufacturing method of a steel forged component of an 18CrNiMo7-6 large gear. The process route comprises: electric furnace, LF (low frequency), VD (voltage detection), ingots of 9-27t, production with a 3500 quick forging machine, heat treatment, straightening and rough turning. The narrow composition scope of chemical elements such as C, Mn, Nb, Al and N with significant impact on the steel hardenability and grain size is strictly controlled to achieve dual purposes of narrow hardenability band, qualified grain size and grain size durability; the smelting process is strictly implemented to improve the steel purity; and the isothermal annealing and heat treatment with the furnace cooling speed controlled are adopted to achieve dual purposes of dehydrogenation and preparation of a structure with F and P. The invention has the advantages that the 18CrNiMo7-6 steel completely meeting technical requirements can be developed via improving the purity, ensuring the narrow hardenability band, realizing the grain size durability and adopting the unique heat treatment process, and the quality problems of manufacturing large gears such as difficulty in steel cutting, quenching cracks, coarse grains and white spots can be solved.

Description

18CrNiMo7-6 large gear steel forgings manufacture method

Technical field

The invention belongs to metallic substance and make the field, disclose a kind of large gear steel forgings manufacture method, be mainly used in the production of structural alloy steel 18CrNiMo7-6 Pinion Steel.

Background technology

18CrNiMo7-6 is the German trade mark, the former trade mark is 17CrNiMo6, fast development along with speed reduction unit machinery industry and wind-powered electricity generation industry, high ferro industry, 18CrNiMo7-6 is as the leading Material Used of gear or gear shaft key component, be high efficiency, the security operation of guaranteeing its product, the user constantly proposes Secretary to the quality of materials technical indicator, for reducing the large gear distortion, the forging hardenability band is reduced into 5HRC by original 7HRC, and proposes the requirement of banded structure; For improving machining efficient, require the steel condition of delivery to be organized as the F+P balanced weave; Be used for the weather resistance (namely be incubated 80h under 950 ℃ of pyroprocessing, grain fineness number reaches 8 grades～6 grades and do not grow up) that the wind power speed increaser Pinion Steel requires grain fineness number, have not yet to see the research work that the home and abroad bibliographical information is correlated with therewith.

18CrNiMo7-6 is the responsive steel grade of white point, adopts common dehydrogenation to be prone to white-spot defects (or the white point hysteresis phenomenon occurring).Owing to adopting the red annealing of sending after forging process for fuel, austenite structural transformation in process of cooling is insufficient, and residual austenite changes part, and hydrogen solubleness in austenite is maximum, As time goes on, and residual austenite generation martensitic transformation, form larger structural stress, crack.

The overall dimension Φ 750mm of the 18CrNiMo7-6 forging that 3500 tons of quick forging machines of present domestic employing are produced, the maximum outside diameter Φ 1250mm of hole cake forging.Application along with large ingot shape, easily exist be mingled with, the segregation problem of composition and tissue is more aobvious outstanding, the homogeneity of composition and tissue is the two large principal elements that affect finished product gear quenching hardness and distortion, therefore the user proposes requirements at the higher level to hardening capacity, be that hardenability band is not more than 5HRC, this is that common process is difficult to realize.

18CrNiMo7-6 is bainitic steel, and according to its CCT curve, the F+P transformetion range is narrow, and fringe time is long, and the tissue that adopts isothermal normalizing technique to obtain is B or B+F+P mixed structure.

Address the above problem the key measures that should take two aspects: the thermal treatment process of formulating on the one hand science is to determine that can the 18CrNiMo7-6 steel obtain the core technology that F+P organized and went the white point effect, and reasonably chemical composition design is effective control method of hardening capacity and grain fineness number weather resistance on the other hand.To not finding the information of relevant valuable annealing process information and grain fineness number weather resistance assurance aspect in the literature search of home and abroad; The white point hysteresis phenomenon appearred in Fushun special steel limited-liability company in batches in adopting the prior art research and development, producing, can not guarantee the weather resistance of grain fineness number, and non-equilibrium and bainite structure often appears, banded structure and hardening capacity often have indivedual points to exceed specialized range.

Summary of the invention

For the 18CrNiMo7-6 steel, the difficult point of processing annealing process is namely will guarantee to obtain F+P, also wants simultaneously to guarantee to have the dehydrogenation function; The difficult point of chemical composition design is namely will guarantee grain fineness number and grain fineness number weather resistance, also wants simultaneously to guarantee narrow hardenability band; And grain fineness number and grain fineness number weather resistance also depend on the control of final forging temperature.

The present invention seeks to disclose a kind of 18CrNiMo7-6 large gear steel forgings manufacture method, by adopting the thermal treatment process of isothermal annealing, control speed of furnace cooling, reach dehydrogenation and obtain the dual purpose that F+P organizes; By strict control, hardenability of steel and grain fineness number there are chemical element C, Mn, Nb, the Al of great effect, the close limit of N, reach the dual purpose with narrow hardenability band and qualified grain fineness number and grain fineness number weather resistance; The strict implement smelting technology improves the purity of steel; Develop and reach the 18CrNiMo7-6 steel that client's technical quality requires fully, solution large gear steel difficult cutting, quenching crack, coarse grains and white point quality problems.

For achieving the above object, the present invention is by the following technical solutions:

1. operational path is: electric furnace → LF → VD → ingot casting 9t～27t → 3500 quick forging machine production → thermal treatment → alignings → rough turn comprise process for making, forging process and thermal treatment process;

2. concrete technology measure:

⑴ process for making

1. chemical composition design

According to the SEP1664 hardening capacity software for calculation of U.S. ASTMA255 and Germany, in conjunction with actual end quenching test result, use the mass data regression analysis, formulate 18CrNiMo7-6 chemical composition inner quality standard, see Table 1.

Table 1

2. eaf process

Batching is selected high-quality steel scrap, the pig iron (molten iron) 〉=30%; Tapping temperature 〉=1630 ℃, P≤0.010%, end point carbon is controlled by 〉=0.08%, and 3min before tapping～5min reduces and use oxygen intensity, increases and sprays carbon consumption, every stove 300kg～400kg; The steel final deoxygenation adds aluminium 2.5kg/t～3.0kg/t; Guarantee freeboard 〉=800mm, forbid lower oxidation sludge;

3. LF technique

Put in place and feed aluminium, whole process using carbon dust+Al grain diffusive deoxidation, first batch of add-on 20Kg～30Kg, white slag hold-time 〉=30min by 0.08%; According to the full aluminium result of sample 1 (considering in stove), by 0.06% hello aluminium, consider before vacuum to feed aluminium by 0.05% in stove, after assurance VD processes, aluminium content is greater than 0.02%, and all the other times are not fed aluminum steel as far as possible; Calculate by 0.03% and add Nb-Fe; Tapping temperature 〉=1690 ℃, S≤0.010%;

4. VD technique

Skim on a small quantity before entering tank, vacuum tightness≤100Pa, lower hold-time of vacuum 〉=20min; Add N-Cr after removing vacuum, N-Cr is baking fully, does not consider that in stove, N adds by 0.007% calculating, soft blow time 〉=30min;

5. cast

Ar protects cast, teeming temperature: 1585 ℃ ± 5 ℃, adopt mould cold greater than 9 tons of above steel ingots of ingot, mould cool time 84h;

⑵ forging process

1210 ℃ ± 10 ℃ of Heating Steel Ingots temperature, temperature keep 8h～10h by 1220 ℃ of controls of the upper limit; Twice upsetting pull of steel ingot opened and forged 1080 ℃ of temperature, guarantees the excision amount: ingot head 〉=15%, ingot butt 〉=5%; Intermediate blank is heated to 1180 ℃ ± 10 ℃, and soaking time is greater than 4h, 850 ℃ ± 20 ℃ of final forging temperatures.

⑶ thermal treatment process

Steel diameter Ф＜350mm only walks II section in curve, and diameter Ф 〉=350mm walks curve I section+II section.

Steel diameter Ф=250mm(only walks II section in curve): H1(is soaking time at 890 ℃ of temperature) time 15h, H2(is soaking time at 650 ℃ of temperature) time is 40h; The every increase of steel diameter 100mm, the H2 time lengthens 25 hours; Hole cake forging final annealing technique is walked II section curve.

Advantage of the present invention and innovative point are:

⑴ improve purity

For guaranteeing 18CrNiMo7-6 large gear steel interior tissue, need the above large ingot shape of use 9t to produce, guarantee the processing ratio, and easily there is Inclusion Problem in large ingot smelting, the qualified rank of users specification regulation non-metallic inclusion should meet the regulation of table 2.

Table 2

For improving Molten Steel Cleanliness, close the following three link of key control process for making:

1. control the electric furnace steel tapping amount, freeboard 〉=800mm when guaranteeing the VD vacuum-treat so that the large argon gas of VD stirs, fully floats inclusion and gas;

2. LF white slag time 〉=30min, transfer aluminium before the VD vacuum, guarantees that VD processes rear aluminium content and reaches the control target, do not feed aluminum steel after VD as far as possible;

3. soft blow time 〉=30min, be as the criterion not reveal the molten steel face; Go out 1585 ℃ ± 5 ℃ of tank temperature, press 1580 ℃ of cast of lower limit temperature, rationally control pouring speed, adopt argon for protecting pouring.

Assay nonmetallic inclusionsin steel 100% conformance with standard regulation; The method of inspection adopts the extreme value analysis method of the high reliability of domestic initiation, proves that this technique satisfies standard-required fully.

⑵ guarantee narrow hardenability band

The user sees Table 3 to the requirement of end hardening capacity and the end hardening capacity contrast of European standard regulation, the distribution trend correlation curve is seen Fig. 2, European standard requires J9 point hardenability band≤10HRC, and users specification requires hardenability band≤5HRC, has certain difficulty from controlling.

Table 3

Fushun special steel limited-liability company is according to the SEP1664 hardening capacity software for calculation of U.S. ASTMA255 and Germany, in conjunction with actual end quenching test result, carry out the comparison comparative analysis of mass data, in the design mix process, both considered to make this material to obtain higher hardening capacity and narrow hardenability band, take into account again simultaneously large gear quenching crack sensitive question, the final best proportioning of determining appropriate chemical composition C, Mn, Cr, the alloying element contents such as Ni, Mo satisfies the user to the requirement of hardening capacity.

⑶ realize the grain fineness number weather resistance

Low-carbon (LC) Pinion Steel Examining Austenite Grain Size ordinary method has 2 kinds, cementing process and direct method.The cementing process general requirement is in 930 ℃ of insulation 6h, the cold rear Examining Austenite Grain Size of stove; Directly rule is incubated certain hour (soaking time general requirement 1h～4h scope), Examining Austenite Grain Size after shrend at 930 ℃ of temperature.And be used for wind power gear steel 18CrNiMo7-6, Secretary is proposed grain fineness number, it is grain fineness number blank sample, 950 ℃ of insulation 80h, be cooled to subsequently 860 ℃ of insulation 2h, quiet oil quenching, autstenitic grain size 〉=5 grade, this kind method is mainly simulated large gear for obtaining certain cementation zone, need at high temperature long-time carburizing, and crystal grain is not grown up.For reaching for wind power gear steel 18CrNiMo7-6 grain fineness number endurance test requirement, carry out the long-time grain fineness number test of 950 ℃ the longest insulation 100h, and to the grain fineness number trend analysis of growing up, reach a conclusion: 1. chemical composition should add the crystal grain thinning element, Nb adds by 0.03%, Al controls by 0.02%～0.04%, and the equivalent thickness of aluminium is between 0.030%-0.050%; 2. guarantee enough processing ratio and deflection, control final forging temperature at 870 ℃ ± 10 ℃; 3. the original structure of steel should be the F+P tissue.Use above-mentioned technology measure in actual production, guaranteed 950 ℃ under the autstenitic grain size 〉=6 grades of insulation 80h steel, satisfied the needs of the long-time carburizing of large gear high temperature to the grain fineness number weather resistance.

⑷ the thermal treatment process of uniqueness

18CrNiMo7-6 is the responsive steel grade of white point; 18CrNiMo7-6 is bainitic steel, for improving machinability, requires the steel condition of delivery to be organized as the F+P balanced weave.Have anti-white point for solving the white point problem and obtain the F+P tissue, making, obtain the heat treatment cycle curve that typical F+P organizes the uniqueness of dual-use function.

Description of drawings

Below in conjunction with the drawings and specific embodiments, the present invention is elaborated.

Fig. 1 is 18CrNiMo7-6 large gear steel forgings heat treatment cycle curve figure, and wherein curve is divided into two sections: I section, II section;

Fig. 2 is that the user is to the end hardening capacity distribution trend correlation curve schematic diagram of the requirement of 18CrNiMo7-6 large gear steel forgings end hardening capacity and European standard regulation.

Embodiment

Embodiment 1

Heat (batch) number: 10203011386, hole cake trimmed size: external diameter 1129mm * internal diameter 442mm * height 291mm, forging ratio 11.8.

The fast forging finished hole cake → hole cake of forging of technical process: the electric furnace → LF → VD → ingot casting → fast forging forging of batch-type furnace heating → 3500 (technique is pulled out in two upsettings two) → intermediate blank annealing → intermediate blank blanking → batch-type furnace heating → 3500 is annealed.

⑴ process for making

1. chemical composition

18CrNiMo7-6 chemical composition standard sees Table 4.

Table 4

2. eaf process

Select steel scrap, the pig iron amount of allocating into 30%; 1670 ℃ of tapping temperatures, P content are 0.010%, end point carbon 0.010%, and 3min reduction oxygen intensity before tapping increases spray carbon consumption 378Kg; Final deoxygenation adds aluminium 162kg; Freeboard 810mm does not descend oxidation sludge.

2. LF technique

Put in place and feed aluminium, whole process using carbon dust+Al grain diffusive deoxidation, first batch of add-on 30Kg, white slag hold-time 30min by 0.08%; According to the full aluminium result of sample 1, feed aluminium by 0.06%.Feed aluminium by 0.05% before vacuum, add Nb-Fe by 0.03% calculating; 1700 ℃ of tapping temperatures, S:0.003%.

4. VD technique

Skim on a small quantity before entering tank, vacuum tightness≤100Pa, 20min of lower hold-time of vacuum.Add N-Cr after removing vacuum, N calculates by 0.007% and adds; Soft blow time 35min.

5. cast

Ar protects cast, teeming temperature: 1587 ℃; 27 tons of ingots of ingot shape, mould cool time 84h.

6. forging process

1210 ℃ ± 10 ℃ of Heating Steel Ingots temperature keep 10h; Twice upsetting pull of steel ingot, wide anvil production is adopted in pulling, opens 1080 ℃ of temperature, ingot head excision amount 18%, the ingot butt excision amount 5.5% of forging;

Intermediate blank is heated to 1180 ℃ ± 10 ℃, soaking time 4.5h, 860 ℃ ± 10 ℃ of finish-forging temperature.

7. thermal treatment process

The hole cake is heated to 890 ± 10 ℃ of insulations 20 hours, and per hour 70 ℃ cool to 660 ℃, are incubated 80 hours, and 30 ℃/h cools to 500 ℃ of air coolings of coming out of the stove.

8. production testing result:

The inclusion assay sees Table 5.

Table 5

Grain fineness number adopts 8 grades～6 grades of 930 ℃ of insulation 4h grain fineness numbers of direct method; 950 ℃ are incubated 80 hours, are cooled to subsequently 860 ℃ of insulation 2h, quiet oil quenching, 7 grades～6 grades of grain fineness numbers.

End hardening capacity assay sees Table 6.

Table 6

Table 6(is continuous)

Be organized as ferrite+perlite.

Mechanical properties test the results are shown in Table 7.

Table 7

Delivery hardness (HBW) 179,182,200,187.

Embodiment 2

Heat (batch) number: 10203022144, trimmed size φ 390mm, forging ratio 9.9; The fast forging of technical process: electric furnace → LF → VD → ingot casting → batch-type furnace heating → 2000 forged (technique is pulled out in a upsetting one) → steel annealing.

⑴ process for making

1. chemical composition

18CrNiMo7-6 chemical composition standard sees Table 8.

Table 8

2. eaf process

Select steel scrap, the pig iron amount of allocating into 30%; 1680 ℃ of tapping temperatures, P content are 0.0093%, end point carbon 0.072%, and 3min reduction oxygen intensity before tapping increases spray carbon consumption 400Kg; Final deoxygenation adds aluminium 150kg; Freeboard 820mm does not descend oxidation sludge.

3. LF technique

Put in place and feed aluminium, whole process using carbon dust+Al grain diffusive deoxidation, first batch of add-on 30Kg, white slag hold-time 33min by 0.08%; According to the full aluminium result of sample 1, feed aluminium by 0.06%; Feed aluminium by 0.05% before vacuum, add Nb-Fe by 0.03% calculating; 1692 ℃ of tapping temperatures, S:0.006%.

4. VD technique

Skim on a small quantity before entering tank, vacuum tightness≤100Pa, 25min of lower hold-time of vacuum.Add N-Cr after removing vacuum, N calculates by 0.007% and adds; Soft blow time 30min.

5. cast

Ar protects cast, teeming temperature: 1588 ℃; 15 tons of ingots of ingot shape, mould cool time 84h.

6. forging process

1210 ℃ ± 10 ℃ of Heating Steel Ingots temperature keep 10h; Twice upsetting pull of steel ingot, wide anvil production is adopted in pulling, opens 1080 ℃ of temperature, ingot head excision amount 16%, the ingot butt excision amount 5% of forging; In

Between base be heated to 1180 ℃ ± 10 ℃, soaking time 5.0h, 870 ℃ ± 10 ℃ of finish-forging temperature.

7. thermal treatment process

650 ℃ of guarantor 5h of steel heating are cooled to 290 ℃～320 ℃ and protect 8h, protect 5h for 680 ℃, 890 ℃ ± 10 ℃ insulation 10h are cooled to 290 ℃～310 ℃ and protect 12h, to 890 ℃ ± 10 ℃ insulation 15h, per hour 70 ℃ cool to 660 ℃, are incubated 78 hours, and 30 ℃/h cools to 500 ℃ of air coolings of coming out of the stove.

4. production testing result:

The inclusion assay sees Table 9.

Table 9

Grain fineness number adopts 7 grades of 930 ℃ of insulation 4h grain fineness numbers of direct method; 950 ℃ are incubated 80 hours, are cooled to subsequently 860 ℃ of insulation 2h, quiet oil quenching, 7 grades～6 grades of grain fineness numbers.

End hardening capacity assay sees Table 10.

Table 10

Be organized as ferrite+perlite.

Mechanical properties test the results are shown in Table 11.

Table 11

Delivery hardness (HBW) 202,196,192,187.

Claims

1. 18CrNiMo7-6 large gear steel forgings manufacture method, operational path is electric furnace → LF → VD → ingot casting 9t～27t → 3500 quick forging machine production → thermal treatment → alignings → rough turn, manufacturing process comprises process for making, forging process and thermal treatment process, it is characterized in that:

Described process for making:

1. 18CrNiMo7-6 chemical composition (%) inner quality standard: C0.16～0.19, Mn0.55～0.65, Si0.20～0.30, S≤0.005, P≤0.015, Ni1.55～1.65, Cr1.65～1.75, Mo0.25～0.30, Al0.02～0.04, N0.008～0.015;

2. electric steelmaking process: batching is selected high-quality steel scrap, the pig iron or molten iron 〉=30%; Tapping temperature 〉=1630 ℃, P≤0.010%, end point carbon is controlled by 〉=0.08%, and 3min before tapping～5min reduces and use oxygen intensity, increases and sprays carbon consumption, every stove 300kg～400kg; The steel final deoxygenation adds aluminium 2.5kg/t～3.0kg/t; The high-quality lime satisfies the above specification of quality CaO of one-level 〉=90%, raw burn rate≤10%, and activity 〉=300ml guarantees freeboard 〉=800mm, forbids lower oxidation sludge;

3. LF stove refinery practice: put in place and feed aluminium, whole process using carbon dust+Al grain diffusive deoxidation, first batch of add-on 20kg～30kg, white slag hold-time 〉=30min by 0.08%; ,, consider before vacuum to feed aluminium by 0.05% in stove by 0.06% hello aluminium comprising the full aluminium result in stove according to sample 1, after assurance VD processes, aluminium content is greater than 0.02%, and all the other times are not fed aluminum steel as far as possible; Calculate by 0.03% and add Nb-Fe; Tapping temperature 〉=1690 ℃, S≤0.010%;

4. VD treatment process: skim on a small quantity before entering tank, vacuum tightness≤100Pa, lower hold-time of vacuum 〉=20min; Add N-Cr after removing vacuum, N-Cr is baking fully, does not consider that in stove, N adds by 0.007% calculating, soft blow time 〉=30min;

5. pouring technology: Ar protects cast, teeming temperature: 1585 ℃ ± 5 ℃, adopt mould cold greater than 9 tons of above steel ingots of ingot, mould cool time 84h;

Described forging process:

1210 ℃ ± 10 ℃ of Heating Steel Ingots temperature, temperature keep 8h～10h by 1220 ℃ of controls of the upper limit; Twice upsetting pull of steel ingot opened and forged 1080 ℃ of temperature, guarantees the excision amount: ingot head 〉=15%, ingot butt 〉=5%; Intermediate blank is heated to 1180 ℃ ± 10 ℃, and soaking time is greater than 4h, 875 ℃ ± 25 ℃ of final forging temperatures;

Described thermal treatment process:

Steel diameter Ф＜350mm is heated to 890 ℃ ± 10 ℃, and insulation cools to 650 ℃ ± 10 ℃ with 30 ℃/h, and insulation cools to 500 ℃ with 30 ℃/h, the air cooling of coming out of the stove;

Diameter Ф 〉=350mm is heated to 650 ℃ ± 10 ℃, insulation 5h, cool to 280 ℃～320 ℃, insulation 8h is heated to 680 ℃ ± 10 ℃, insulation 5h is heated to 890 ℃ ± 10 ℃, soaking time 10h, cool to 280 ℃～320 ℃, insulation 12h is heated to 890 ℃ ± 10 ℃, insulation cools to 650 ℃ ± 10 ℃ with 30 ℃/h, insulation, cool to 500 ℃ with 30 ℃/h, the air cooling of coming out of the stove;

When steel diameter Ф=250mm, be heated to 890 ℃ ± 10 ℃, soaking time 15h cools to 650 ℃ ± 10 ℃ with 30 ℃/h, and insulation 40h cools to 500 ℃ with 30 ℃/h, the air cooling of coming out of the stove; The every increase of steel diameter 100mm, 650 ℃ ± 10 ℃, soaking time lengthens 25h;

Hole cake forging final annealing technique is to be heated to 650 ℃ ± 10 ℃, and insulation 40h cools to 500 ℃ with 30 ℃/h, the air cooling of coming out of the stove.