A kind of chromic-nickel-free high-strength high ductility structural steel and manufacture method thereof
Technical field
The present invention relates to the composition design and the manufacture method thereof of metallurgy industry structure iron, refer in particular to the composition design and the manufacture method thereof of high strength, high-toughness structural steel.
Background technology
Structure iron is common steel alloy.Press chromium, nickel element content in the steel, we tentatively can be divided into and contain chromium nickel structure iron, Chrome-free nickel structure iron (Chrome-free nickel type structure iron mainly is divided into 8 classes such as manganese steel, silicon manganese steel, boron steel, manganese boron steel, manganese molybdenum boron steel, manganese vanadium boron steel, vanadium steel, silicomanganese molybdenum-vanadium steel) two big classes.High strength, high-toughness structural steel generally are meant the structure iron of intensity 〉=1200Mpa, impelling strength Aku 〉=60J.
(intensity 〉=1200Mpa, impelling strength Aku 〉=60J) are broad-spectrum structure iron for high strength, high-toughness structural steel, as (needle-valve body idol part is the precise part of a key of diesel fuel system, and the quality of its quality directly has influence on the performance characteristics and the work-ing life of locomotive to be used for oil engine needle-valve body idol part.Needle-valve body is up to 250~270kg/cm
2The oil pressure effect under, needle-valve in valve body with the frequency of thousands of bobs of per minute, reach the fuel oil purpose of supplying with uniform atomizing, be subjected to the cylinder operation Temperature Influence simultaneously, the head temperature of needle-valve body can reach 270~360 ℃, so require needle-valve body should have high surface hardness, high-wearing feature, good anti-tempered performance, good dimensional stability and contact fatigue property with steel; And because the manufacturing process elaborate of needle-valve body, technical process is long, also requires material to have good machinability and grinding performance and certain solidity to corrosion.) high strength chromium nickel converted steel (common high strength, high-toughness structural steel).
At present, (intensity 〉=1200Mpa, impelling strength Aku 〉=60J), be to contain chromium nickel structure iron are as high strength converted steel (R to satisfy the high strength, high-toughness structural steel of oil engine needle-valve body idol part service requirements
m〉=1200Mpa), the trade mark commonly used be 20Cr2Ni4A, 18Cr2Ni4WA, 15CrMn2SiMo etc. (see Table 1, table 2 composition, performance comparison.)。Its deficiency is: chromium nickel content height makes the material price costliness, and machinability is poor simultaneously, and working (machining) efficiency is low, also need implement complicated heat treatment technology in order to reduce remained austenite content, poor dimensional stability, anti-temper resistance instability is general only 200 ℃ of left and right sides tempering.Therefore, still can not adapt to oil engine to high-speed boosting, the needs that the high-power direction develops.
Several groups of chromium nickel of table 1 converted steel composition contrast (wt%)
Grade of steel |
C |
Mn |
Si |
Cr |
Ni |
V |
W |
Mo |
18Cr2Ni4WA |
0.13~ 0.19 |
0.30~ 0.60 |
0.20~ 0.40 |
1.35~ 1.65 |
4.00~ 4.50 |
-- |
0.80~ 1.20 |
-- |
20Cr2Ni4A |
0.17~ 0.24 |
0.30~ 0.60 |
0.20~ 0.40 |
1.25~ 1.75 |
3.25~ 3.75 |
-- |
-- |
-- |
15CrMn2SiMo |
0.13~ 0.19 |
2.00~ 2.40 |
0.40~ 0.70 |
0.40~ 0.70 |
-- |
-- |
-- |
0.40~ 0.50 |
Several groups of chromium nickel of table 2 converted steel performance and thermal treatment process contrast
The trade mark |
Thermal treatment process |
Tensile strength R
m(Mpa)
|
Yield strength R
e,Mpa
|
Elongation A% |
Relative reduction in area Z, % |
Impelling strength, Aku, J |
18Cr2Ni4W A |
For the first time quench 950 ± 15 ℃, for the second time quench 850 ± 15 ℃, 200 ± 20 ℃ of tempering |
≥1200 |
≥850 |
≥10 |
≥45 |
≥78 |
20Cr2Ni4A |
For the first time quench 880 ± 15 ℃, for the second time quench 780 ± 15 ℃, 200 ± 20 ℃ of tempering |
≥1200 |
≥1100 |
≥10 |
≥45 |
≥63 |
15CrMn2Si Mo |
Quench 860 ± 15 ℃ 200 ± 20 ℃ of tempering |
≥1200 |
≥900 |
≥10 |
≥45 |
≥63 |
From existing Chrome-free nickel type structure iron, the tensile strength of 7 class Chrome-free nickel type structure iron such as manganese steel, silicon manganese steel, boron steel, manganese boron steel, manganese molybdenum boron steel, manganese vanadium boron steel, vanadium steel generally can not surpass 1200Mpa, even intensity surpasses 1200Mpa, impelling strength yet very low (such as the ballistic work of spring steel generally below 20J) does not therefore belong to the category of high strength, high-toughness structural steel.Existing silicomanganese molybdenum vanadium class Chrome-free nickel type structure iron is aspect combination of strength and toughness, though good performance is arranged referring to (1) Yin Ruiyu " the modern progress-special steel of the quality of steel " volume two, metallurgical industry press, June nineteen ninety-five; (2) national standard: steel alloy handbook data storehouse electronic edition standard No. GB/T3077-1999:(3).Find: the Chrome-free nickel type structure iron that meets high strength, high-toughness structural steel performance index is the silicomanganese molybdenum-vanadium steel, it mainly comprises 20SiMn2MoV, 25SiMn2MoV, 37SiMn2MoV etc., the correlation data of steel grades, mechanical property and thermal treatment process sees table 1 and table 2 for details.), still, (still there is gap in the standard of intensity 〉=1200Mpa, impelling strength Aku 〉=62J) for the high strength that needs with oil engine needle-valve body idol part, the obdurability of high-toughness structural steel.
The no chromium nickel steel composition contrast of table 3 (wt%)
Grade of steel |
C |
Si |
Mn |
Mo |
V |
20SiMn2MoV |
0.17~0.23 |
0.90~1.20 |
2.20~2.60 |
0.30~0.40 |
0.05~0.12 |
25SiMn2MoV |
0.22~0.28 |
0.90~1.20 |
2.20~2.60 |
0.30~0.40 |
0.05~0.12 |
30SiMn2MoV |
0.27~0.33 |
0.40~0.70 |
1.60~1.90 |
0.40~0.50 |
0.15~0.25 |
37SiMn2MoV |
0.33~0.39 |
0.60~0.90 |
1.60~1.90 |
0.40~0.50 |
0.05~0.12 |
25SiMnMoV |
0.23~0.29 |
0.80~1.20 |
0.90~1.30 |
0.25~0.40 |
0.07~0.15 |
No chromium nickel steel performance of table 4 and thermal treatment process contrast
The trade mark |
Thermal treatment process |
Tensile strength R
m,Mpa
|
Yield strength R
e,Mpa
|
Elongation A % |
Relative reduction in area Z, % |
Impelling strength, Aku, J |
20SiMn2MoV |
Quench 900 ℃ 200 ℃ of tempering |
≥1380 |
-- |
≥10 |
≥45 |
≥55 |
25SiMn2MoV |
Quench 900 ℃ 200 ℃ of tempering |
≥1470 |
-- |
≥10 |
≥40 |
≥47 |
30SiMn2MoV |
Quench 900 ℃ 650 ℃ of tempering |
≥1000 |
≥800 |
≥12 |
≥50 |
≥78 |
37SiMn2MoV |
Quench 900 ℃ 650 ℃ of tempering |
≥980 |
≥835 |
≥12 |
≥50 |
≥63 |
25SiMnMoV |
Quench 900 ℃ 650 ℃ of tempering |
≥980 |
≥882 |
≥10 |
≥45 |
≥50 |
Chinese patent application CN95104296.3 discloses a kind of large section that high strength, high tenacity are provided of being applicable to structural part and steel plate, its chemical ingredients (weight %) is: carbon: 0.20~0.25%, silicon: 0.40~0.60%, manganese: 1.80~2.30%, molybdenum: 0.30~0.50%, tungsten: 0.40~0.60%, surplus is Fe.
But there is following deficiency in above-mentioned existing Chrome-free nickel type structure iron technology:
20SiMn2MoV, 25SiMn2MoV steel all adopt lower carbon content and relative high manganese content (2.20~2.60%), its objective is the deficiency that remedies intensity with manganese, but the manganese too high levels can tend to make austenite crystal thick in converted steel, cause flexible on the low side, so these two kinds of steel only are applicable to the less demanding purposes of impact toughness value.The carbon content of 30SiMn2MoV, 37SiMn2MoV steel employing 0.27~0.39% is come proof strength, but the converted steel carbon content is unfavorable for carburizing greater than 0.30%, and low simultaneously silicon, manganese content make the intensity of above-mentioned two steel can not reach more than the 1280Mpa far away.25SiMnMoV and invention steel have comparatively approaching carbon, silicone content, but manganese content is low excessively, are unfavorable for improving carburizing steel core portion perviousness, and the carbon that this steel is low relatively, silicon, manganese content have determined the strength level that it is lower.
More than the chemical ingredients of five steel determined its tissue, determining its mechanical property again indirectly, this mechanical property all can not satisfy the requirement of oil engine needle-valve body idol part.
Summary of the invention
The objective of the invention is to design a kind of high strength, high-toughness structural steel that does not contain chromium, nickel element, substitute existing high strength chromium nickel converted steel, it adopts cheap silicomanganese as main element, design and implement concrete technical scheme by the alloying composition, make steel reach the mechanical property of oil engine needle-valve body idol part requirement: yield strength 〉=1170MPa, tensile strength 〉=1274MPa, unit elongation 〉=9%, relative reduction in area 〉=45%, impelling strength 〉=62J.Solve chromium nickel converted steel and cost an arm and a leg, machinability is poor, and working (machining) efficiency is low, and defectives such as anti-tempering ability satisfy the requirement of diesel locomotive needle-valve body steel better.
The present invention adopts cheap Si, Mn as main element, uses no or little noble element, and the size of austenitic homogeneity and grain fineness number is controlled in control and optimize Si, Mn content, makes the finished steel performance reach the good toughness and tenacity of coupling.Make the invention steel have more stable anti-tempering ability, good machinability simultaneously.
Chromic-nickel-free high-strength high ductility structural steel of the present invention, its chemical element composition (weight %): carbon: 0.24~0.30%, silicon: 1.10~1.40%, manganese: 1.30~1.70%, molybdenum: 0.40~0.60%, vanadium: 0.20~0.35%, aluminium: 0.015~0.050%, copper≤0.30%, sulphur≤0.012%, phosphorus≤0.020%, all the other are iron and inevitable impurity.
Further, this structure iron is organized as ferrite+globular pearlite.
Wherein, carbon: be the principal element that improves hardness of steel, guarantee the necessary certain carbon content of certain intensity, but carbon be unfavorable to plasticity, simultaneously unfavorable to carburizing greater than 0.30% carbon content, control 0.24~0.30% carbon content is comparatively reasonable.
Manganese: replace carbon, chromium to keep intensity with manganese.Manganese is the principal element that can significantly improve hardening capacity, and manganese can suppress the formation of bainite in the cementation zone simultaneously; But manganese has the austenitizing of promotion grain growth shortcoming in steel, the content of manganese is controlled at 1.30~1.70% can bring into play good effect in steel of the present invention.
Silicon: silicon can reduce the concentration gradient of carbon in steel, promotes the carbon diffusion under austenitic state, and it can suppress separating out of carbide, helps the formation of cementation zone, and 1.10~1.40% improve toughness when can play solution strengthening.
Molybdenum: molybdenum act on highly significant in the steel, it not only can improve the hardening capacity of part cementation zone and heart portion, obviously suppresses the formation of non-martensite, can also improve piece surface hardness.But molybdenum element belongs to noble element, and the molybdenum of steel adding 0.40~0.60% of the present invention is most economical effective content.
Vanadium, aluminium all belong to the crystal grain thinning element.Aluminium, v element cooperate further crystal grain thinning with above-mentioned element, increase hardening capacity, and improve obdurability.But experience shows that too much vanadium is unfavorable to toughness, and too much aluminium easily increases the chance that steel inclusion produces, and therefore, 0.20~0.35% vanadium and 0.015~0.050% aluminium are the suitable content of steel of the present invention.
Simultaneously, sulphur, phosphorus, lead, antimony, bismuth should reduce its content as far as possible under technical qualification permission situation, to reduce the poly-partially of original austenite crystal prevention place, improve toughness.Residual element and gas content are controlled at suitable low levels level, make steel have quite high purity, are dissolved in and reach the best proportioning content of ideal between carbon in the austenite and each element, thereby lay a good foundation for the homogeneity and the obdurability that improve material.
The manufacture method of chromic-nickel-free high-strength high ductility structural steel of the present invention, it comprises the steps:
1) smelts, pours into a mould ingot, arc melting routinely, refinery practice, cast ingot;
2) rolling, 1100~1180 ℃ of hot rolling Heating temperatures, 1 hour 50 minutes~2 hours 10 minutes heat-up time, conventional silicomanganese molybdenum-vanadium steel soaking time is greater than 1 hour 20 minutes,
Technical solution of the present invention prolongs 30~50 minutes, to guarantee the steel billet homogeneous heating; 850~900 ℃ of finishing temperatures are rolled the back and are cooled off with 40~80 ℃/h speed of cooling;
3) stocking annealing, 720 ± 10 ℃ of annealing temperatures, soaking time 8~10 hours, with the speed of cooling that is not more than 30 ℃/h be as cold as≤450 ℃ come out of the stove.The conventional structure steel is lower than A for the elimination internal stress only need be heated to
C1The low temperature of (600~700 ℃), cold or the air cooling of stove gets final product behind even heat penetration, the technical program adopts 720 ± 10 ℃ of higher annealing temperatures, can shorten annealing time, to obtain globular pearlite+ferritic balanced weave is the best, can reduce simultaneously steel hardness and guarantee cutting ability, further crystal grain thinning.
Further, adopt electroslag remelting technique to improve the steel clarity in the step 1), improve the tissue of strand;
The present invention of cast ingot postcooling preferably substituted annealing in cold 16~24 hours with mould, prevented the tendency of ingot cracking, was not electroslag remelting process down together even the small cracking of steel ingot appearance also can not influence.
Step 2) it is cold that the hot rolling postcooling adopts case.
Again, bar is through ℃ tempering modifier treatment of 870~920 ℃ of oil quenching+200~350, and metallographic structure is a tempered martensite, has good mechanical property: yield strength 〉=1170MPa, tensile strength 〉=1274MPa, unit elongation 〉=9%, relative reduction in area 〉=45%, impelling strength 〉=62J.
In steel ingot or steel billet cooling, adopt slow cooling or annealing process to prevent steel ingot or steel billet cracking.
Beneficial effect of the present invention:
1. steel of the present invention reduces and has produced cost without chromium nickel and tungsten noble element, is the resource-conserving material, meets the trend of Sustainable development.
2. steel matter of the present invention is even, and hardness is moderate, has good machinability.
3. steel of the present invention has good hardening capacity and anti-tempered performance, can stand 250~350 ℃ of low-temperaturetemperings, so thermal treatment process is simple and direct, and quality is easy to control.
4. steel of the present invention is quenched and is had good comprehensive matching mechanical property: yield strength 〉=1170MPa, tensile strength 〉=1274MPa, unit elongation 〉=9%, relative reduction in area 〉=45%, impelling strength 〉=62J after the tempering.
Embodiment
Certain Iron And Steel Company implements patent of the present invention, smelts 26 electroslag heat (batch) numbers, its preparation method employing four step rule technical process: the first step: electric arc furnace just refines → the ladle furnace vacuum refinement → water the electrode ingot; Second step: esr; The 3rd step: rolling the becoming a useful person of rolling mill (blooming mill) hot-work; The 4th step: stocking annealing.
The first step, electric arc furnace smelting cast ingot
Adopt the white slag method, in 20~100 tons electric arc furnace, carry out molten steel and just refine, smelt the qualified substantially steel of composition, on AC system ladle refining furnace (capacity and electric furnace are complementary), carry out the refining of molten steel, remove obnoxious flavour and inclusion in the steel, the vacuum and the degassing; Cast electrode billet, cold 16~24 hours of electrode circle ingot mould (according to steel ingot billet size control mould cool time), the demoulding enters next procedure.
Generally adopt annealing process for the silicomanganese molybdenum-vanadium steel: steel ingot advances stove for about 600 ℃, is not more than the heat-up rate to 650 ℃ of 100 ℃/h ± 10 ℃ insulation 8 hours, and the cooling rate that is not more than 50 ℃/h is come out of the stove to about 450 ℃.
Second step, esr
1. preparation starting material
Slag charge will fully toast T 〉=600 ℃, storing time T 〉=4 hour.The striking agent is by proportioning Ti0
2: CaF
2=1: 1, lumpiness is even, is difficult for excessive.
2. melting is prepared
The crystallizer inner wall smooth is smooth, and waterworks is normal, places Dummy plate and striking agent.Settle crystallizer, the lifting consumable electrode.
3. reflow operation:
3.1 slag system: CaF
2: Al
2O
3=70: 30, striking agent, the melt cinder starting the arc.The quantity of slag: 70Kg.
3.2 energisingization slag technology:
Change slag: voltage 56~62V, electric current 2000~5000A, 20 minutes time
Electricity system: voltage 61~65V, electric current 12500~13500A
Bind: voltage 56~62V, electric current progressively reduces, time 〉=30 minute
3.3 normal remelting
Holding current is stable, and fluctuation range is controlled at ± 200A.
3.4 sampling, feeding
The length that should keep consumable electrode during sampling guarantees the feeding time, and the rising electrode cuts off high-voltage when getting glass sample, send high-voltage after the sampling earlier, back decline electrode, sampling back feeding begin to keep normal process regulation power in 2~3 minutes, change the feeding technology electric current then over to.
4. the demoulding: mould demoulding after cold 45 minutes, advance coldly behind stay-warm case slow cooling 〉=48 hour to send annealing furnace annealing.The general ambiguous time of silicomanganese molybdenum-vanadium steel is 36 hours, and technology of the present invention is according to different crystallizer size block cover half cool time 〉=48 hours, prevents that the influence of electroslag ingot cracking from producing.
5. electroslag ingot annealing: adopt 250~400 ℃ and advance stove, rise to 650~720 ℃, be incubated 10~12 hours, be cooled to≤450 ℃ of air coolings of coming out of the stove with≤30 ℃/h cooling rate with≤50 ℃/h heat-up rate.The annealing soaking time of general silicomanganese molybdenum-vanadium steel is 8 hours, and technical solution of the present invention has increased by 2~4 hours, has stipulated stove and tapping temperature simultaneously, with the assurance is to obtain the stabilized uniform annealed structure.
The 3rd step: rolling bar
Adopt rolling mill (blooming mill) hot-work rolling method, earlier qualified steel ingot rolling-cogging become billet, again billet hot-work is rolling to the finished product bar,
Breaking down, breaking down cogging technics rolling-cogging routinely, blooming mill hot-work is made billet with Rolling from Ingot:
1. process furnace heating process: 900 ℃ of insulations of steel ingot charging temperature 20~40 minutes; Be warming up to 1250~1260 ℃ in 3 hours 30 minutes; Be incubated 2 hours 30 minutes~3 hours; (conventional silicomanganese molybdenum-vanadium steel breaking down cogging soaking temperature is about 1290 ℃, and soaking time 1 hour 50 minutes, technical solution of the present invention are compared soaking temperature with prior art and reduced by 30~40 ℃, and soaking time prolongs 50~80 minutes, makes the full and uniform diffusion of steel ingot).
2. blooming mill rolling technology: rolling technology routinely, blooming mill becomes billet with qualified steel ingot rolling-cogging;
3. steel billet advanced the burial pit cooling more than 36 hours, and cold blank carries out sand stripping finishing.(conventional silicomanganese molybdenum-vanadium steel rolls the general annealing process that adopts in back, and the laggard burial pit slow cooling of technical solution of the present invention regulation steel billet whole stake cooling in heap is more than 36 hours, prevent to ftracture and reduce the content of hydrogen in the steel).Rolling mill hot-work with billet rolling to bar;
4. rolling mill process furnace heating process: 1100~1180 ℃ of Heating temperatures, 1 hour 50 minutes~2 hours 10 minutes heat-up time, the square billet male and female face temperature difference≤40 ℃ of steel billets are come out of the stove.
5. common process is rolling, 800~900 ℃ of finishing temperatures.
6. it is cold that steel roll back employing case, 40~80 ℃/h of speed of cooling.Conventional silicomanganese molybdenum-vanadium steel rolls back wind sheltering cooling in heap, and the present invention preferably adopts case cold, can effectively prevent the steel cracking.
The 4th step: stocking annealing
Softening annealing temperature: 720 ± 10 ℃; Soaking time 〉=8~10 hour, with the speed of cooling that is not more than 30 ℃/h be as cold as≤450 ℃ come out of the stove.
The chemical ingredients of table 3 embodiment rod iron, wt%
Embodiment |
C |
S |
P |
Mn |
Si |
V |
Ni |
Cu |
Al |
Mo |
1 |
0.24 |
0.002 |
0.012 |
1.70 |
1.38 |
0.31 |
0.07 |
0.30 |
0.039 |
0.52 |
2 |
0.25 |
0.002 |
0.012 |
1.53 |
1.40 |
0.30 |
0.07 |
0.10 |
0.035 |
0.50 |
3 |
0.25 |
0.012 |
0.020 |
1.48 |
1.30 |
0.20 |
0.11 |
0.13 |
0.015 |
0.60 |
4 |
0.26 |
0.002 |
0.010 |
1.34 |
1.21 |
0.31 |
0.07 |
0.19 |
0.035 |
0.51 |
5 |
0.27 |
0.003 |
0.013 |
1.62 |
1.22 |
0.35 |
0.08 |
0.20 |
0.040 |
0.40 |
6 |
0.28 |
0.004 |
0.008 |
1.30 |
1.12 |
0.23 |
0.06 |
0.12 |
0.045 |
0.55 |
7 |
0.29 |
0.003 |
0.012 |
1.45 |
1.15 |
0.28 |
0.07 |
0.09 |
0.029 |
0.53 |
8 |
0.30 |
0.002 |
0.009 |
1.43 |
1.10 |
0.26 |
0.08 |
0.11 |
0.050 |
0.48 |
The mechanical property of table 4 embodiment rod iron
Embodiment |
Thermal treatment process |
Tensile strength Rm (Mpa) |
Yield strength Re, Mpa |
Elongation A% |
Relative reduction in area Z, % |
Impelling strength, Aku.J |
1 |
Quench: 890 ± 10 ℃, be incubated 45 minutes, oil cooling; Tempering: 280 ± 20 ℃, be incubated 150 minutes, air cooling. |
1400 |
1280 |
14.5 |
52.5 |
84 |
76 |
72 |
2 |
1610 |
1380 |
14.0 |
52.6 |
90 |
84 |
75 |
3 |
1360 |
1240 |
14.5 |
54.0 |
94 |
72 |
66 |
4 |
1380 |
1260 |
16.0 |
51.0 |
68 |
70 |
70 |
5 |
1470 |
1350 |
17.0 |
55.0 |
96 |
80 |
96 |
6 |
1350 |
1230 |
16.5 |
52.5 |
72 |
65 |
72 |
7 |
1480 |
1360 |
14.2 |
51.5 |
88 |
89 |
98 |
8 |
1460 |
1340 |
14.0 |
50.5 |
77 |
65 |
80 |
Implement the Steel Bar During that the present invention produces, be applied to the fuel injection valve for internal combustion engines needle-valve body through domestic certain petrol pump factory's deep processing, every performance all meets service requirements.The demand of fuel injection valve for internal combustion engines needle-valve body material has been satisfied in example evidence, the present invention.