CN1273634C - Nb containing low-carbon low-alloyed steel with ultra-fine ferrite grain structure and method for producing same - Google Patents
Nb containing low-carbon low-alloyed steel with ultra-fine ferrite grain structure and method for producing same Download PDFInfo
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- CN1273634C CN1273634C CN 03129488 CN03129488A CN1273634C CN 1273634 C CN1273634 C CN 1273634C CN 03129488 CN03129488 CN 03129488 CN 03129488 A CN03129488 A CN 03129488A CN 1273634 C CN1273634 C CN 1273634C
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Abstract
The present invention relates to Nb containing and low carbon alloy steel of ultrafine ferrite grains. The Nb containing and low carbon alloy steel has the constituents by the mass percentage of 0.02% to 0.20% of C, 0.01% to 0.10% of Nb, less than 0.80% of Si, 0.007% to 0.025% of Ti, 0.0035% to 0.0083% of N, Fe and unavoidable impurities, wherein Fe and the unavoidable impurities account for the rest mass percentage. The manufacturing method comprising the following steps: the base materials are rapidly heated, and the temperature is preserved for austenizing the base materials; subsequently, the base materials are rapidly cooled to non austenite recrystallization zones; then, the base materials are rolled after rapid cooling; strain caused by the heavy pressure deformation in the non austenite recrystallization zones induces phase changes; through rapid cooling and heat preservation, issues are regulated and stabilized; the steps are circulated more than 3 times; finally, the temperature is cooled to the room temperature; thereby, the ultra refining of ferrite grains can be realized and ferrite grains which are small than 3.0 mum are obtained. The present invention is characterized in that the austenite /ferrite circular phase change (gamma<->alpha) can be realized through rapid heating and rapid cooling, and the combined action of the strain induced phase change is combined to realize the ultra refining of ferrite grains.
Description
Technical field
The present invention relates to a kind of low-carbon low-alloy steel manufacture method, particularly ferrite crystal grain refine to 3.0 μ m following contain Nb low-carbon low-alloy steel manufacture method.
Background technology
As everyone knows, low-carbon (LC) (high strength) low alloy steel is one of most important structural timber, is widely used among petroleum natural gas pipeline, ocean platform, shipbuilding, bridge, pressurized vessel, building structure, automotive industry, transportation by railroad and the machinofacture.
Low-carbon (LC) (high strength) low alloy steel performance depends on the process system of its chemical ingredients, manufacturing processed, and wherein intensity, toughness and weldability are the most important performances of low-carbon (LC) (high strength) low alloy steel, and its final decision is in the microstructure state of finished steel.The refinement ferrite grain size is unique measure that can improve intensity and toughness simultaneously and improve the weldability of steel, is the most important method for toughening of low-carbon (LC) (high strength) low alloy steel, is the target that the metallurgical engineer pursues for many years always.
(Thermo-mechanical controlprocess is handled in the novel heat machinery control that has developed since the eighties, abbreviation TMCP) steel has very big advantage than (high strength) low alloy steel of pair rolling attitude (as-rolled), these steel have very tiny ferrite/bainite tissue (its ratio depends on chemical ingredients and fabrication process condition), thereby demonstrate good intensity and toughness, niobium suppresses austenite recrystallization and grain growth in the controlled rolling process, often be added into and be used for improving intensity and low-temperature flexibility in the TMCP steel, the ferrite grain size scope of the minimum of commercial TMCP steel is at 3～5 μ m, and there is very big difficulty in the size that further reduces ferrite crystal grain.
The method that superfine crystal particle obtains roughly is divided into two classes, i.e. phase transition method and recrystallize method two classes.
If the method that will obtain ultra-fine ferrite crystal grain is carried out exhaustive division, phase transition method is included in the processing that surpasses under cold austenite (γ) state and phase transformation and austenite/ferrite dynamic phase trasnsition again and reaches at (γ+α) the processing and the phase transformation in two-phase zone.
The phase transition method common feature all is to suppress down and adopt in low temperature austenite region deformation processing (percentage pass reduction＞50%) with a passage.A kind of new controlled rolling technology that company of for example Japanese Nippon Steel adopts, promptly obtain the microstructure of superfine crystal particle by deformation induced ferritic dynamic phase trasnsition and dynamic recrystallization, low alloy steel to 0.1%C-1.0%Mn composition system adopts a kind of thermal deformation simulated experiment and actual rolling test subsequently, has obtained the superfine crystal particle less than 3 μ m.
The recrystallize rule is utilized the recrystallize after martensite and bainite are suppressed down, has successfully developed the superfine crystal particle ferritic structure.
Above method all adopts in low temperature supercooled austenite district or metastable martensite, bainite district are suppressed rolling (percentage pass reduction＞50%) down with a passage.So high percentage pass reduction and low deformation temperature will cause huge deformation drag and high mill load, are difficult to realize in actual production; Its next passage is suppressed down the ununiformity of deformation, the ununiformity that will cause final phase transformation/recrystallized structure, deformed belt, the original austenite crystal prevention zone of strain high concentration, mechanical twin band that position in deformed set such as high density dislocation tangle, form ultra-fine crystalline substance by strain-induced transformation/recrystallize easily, and other position grain-size thicker (5 μ m～10 μ m), cause the ununiformity of tissue, therefore realize that the difficulty of the big test specimenization of industrial production is bigger.
Summary of the invention
What the object of the present invention is to provide a kind of ultra-fine ferrite crystal grain contains Nb low-carbon low-alloy steel and manufacture method thereof, obtains super-refinement, the ferrite crystal grain of＜3.0 μ m contain the Nb low-carbon low-alloy steel.
For achieving the above object, technical solution of the present invention is:
The manufacture method that contains the Nb low-carbon low-alloy steel of ultra-fine ferrite crystal grain of the present invention comprises the steps,
A. contain the Nb low-carbon low-alloy steel, its component is,
C 0.02％～0.20％
Nb 0.01％～0.10％
Si ＜0.80％
Ti 0.007％～0.025％
N 0.0035％～0.0083％
Surplus Fe and unavoidable impurities,
It more than is mass percent;
B. heating: above-mentioned base material rapid heating, rate of heating 〉=10 ℃/s are to Ac
3+ 30 ℃～50 ℃;
C. insulation: make the base material austenitizing;
D. cooling fast: the fully instant cooling fast in back of austenitizing, speed of cooling 〉=10 ℃/s are to austenite non-recrystallization district;
E. rolling: quick cooled base material is rolled, and finishing temperature is Ar
3Near the point, every time draft 〉=15%, accumulative total draft 〉=40%;
F. cool off, be incubated, be quickly cooled to Ar after rolling
1-10～30 ℃, tissue is adjusted, and makes it stable;
G. the above-mentioned steps that circulates, number of times 〉=3 time.
H. be cooled to room temperature.
Further, also contain Mn 1.0%～2.0% in the component that contains the Nb low-carbon low-alloy steel of ultra-fine ferrite crystal grain of the present invention.
In addition, soaking time is that sufficient to guarantee is organized austenitizing among the described step b, shortens as much as possible guaranteeing to organize under the prerequisite of austenitizing.
Described step b adopts induction heating or energising direct heating.
The speed of cooling of described steps d is 10 ℃/s～30 ℃/s.
The cooling temperature of described steps d is to Ar
3+ 30 ℃～60 ℃.
The rolling accumulative total of described step e draft is controlled at 45%～55%, and percentage pass reduction is controlled at 15%～25%.
The present invention is based on by quick induction heating or test specimen energising direct heating, the up-quenching that is rapidly heated (up-quenching) technological process and acceleration controlled chilling and realize austenite/ferrite circulating phase-change (γ α), and be combined in austenite non-recrystallization district accumulative total and depress the acting in conjunction of the strain-induced transformation that deformation causes greatly and realize the ferrite crystal grain super-refinement, obtain the ferrite crystal grain of＜3.0 μ m.
As everyone knows; when ferritic structure by up-quenching to the austenite phase region; promptly be heated to the austenite phase region with the rate of heating that is exceedingly fast; because rate of heating is very fast; ferrite crystal grain can not grown up substantially, and the chemical ingredients of ferritic phase does not change substantially yet, thereby causes the huge phase driving force of α → γ; greatly improve the nucleation rate of austenite nucleus, the refine austenite grain-size.Secondly, the austenite nucleus of forming core have four crystal degrees to, i.e. (111), (111), (111)), (111), and these four crystal degrees are high-angle boundaries to the crystal boundary that intergranule forms, therefore can cut apart former ferrite crystal grain effectively at the ferrite crystal boundary or at the austenite crystal that ferrite intracrystalline forming core is grown up, form tiny and uniform austenite crystal, as shown in Figure 1.Equally, when the austenite through deformation is as cold as the ferrite phase region by quick mistake, because huge γ → α phase driving force (comprising that chemical driving force, deformation substructure and deformation make effects such as austenite grain boundary useful area increase), greatly increased the nucleation rate and the nucleation site of ferrite nucleus, thus greatly refinement ferrite crystal grain.In addition, the ferrite crystal grain of forming core have (110) and (110) two crystal degrees to, and these 2 crystal degrees also are high-angle boundaries to the crystal boundary that intergranule forms, therefore the ferrite crystal grain that forming core is grown up at austenite grain boundary or in austenite crystal also can be cut apart original austenite grain effectively, form tiny and uniform ferrite crystal grain, as shown in Figure 2.Tiny austenite crystal is by (〉=15 ℃/s) be cooled to Ar of fast coolings
3Near+30 ℃～60 ℃ temperature spots, and Ar
3Carry out deformation near+30 ℃～60 ℃ temperature spots,, can obtain superfine little ferrite crystal grain by strain-induced transformation.Promptly ought be in Ar
3In the time of near+30 ℃～50 ℃ temperature spots, when tiny austenite crystal was deformed, serious plastic flow was at first brought out crystal grain and is elongated along rolling direction.Because austenite crystal is tiny, strain mainly concentrates on original austenite crystal prevention near zone, mechanical twin circle near zone, the quantity that the deformed belt of intracrystalline forms is then less, and this has reduced the ununiformity of strain distribution greatly, and strain is distributed among the crystal grain equably.In contrast, when thick austenite crystal deformation, strain distribution is extremely inhomogeneous, and main concentrating is distributed among the part crystal grain, concentrates to be distributed among the intracrystalline deformation band; During secondly tiny austenite crystal deformation, strain stores can be higher; On the contrary, during thick austenite crystal deformation, strain stores can be relatively low.Continuation along with deformation, the increase of accumulative total dependent variable, at austenite grain boundary, twin boundary near zone, because coordination does not retrain and different slip system starts simultaneously mutually to intergranule, dislocation with as " source " of dislocation and the crystal boundary generation complex interactions of " well ", on original austenite crystal prevention, annealing twin circle, form a large amount of steps, this step is the best nucleation site of ferrite crystal grain, because the energy barrier of forming core is minimum on step, dislocation in the austenite crystal is also assembled in some zone in addition, forms the deformed belt tissue.Along with austenite plastic deformation degree strengthens (accumulative total draft 〉=40%) unceasingly, it (is that deformation makes Ar that the strain inducing dynamic phase trasnsition will take place effectively
3Move on the some temperature, γ → α phase transformation is taken place at the austenite phase region).At Ar
3On the transition temperature, superfine little ferrite crystal grain changes by the dynamic γ of strain inducing → α, mainly forms on the crystal boundary that is elongated, form the austenite crystal of a large amount of steps, mechanical twin circle, deformed belt.After phase transformation finished, just the ferrite crystal grain that comes from austenitic transformation was in and is higher than Ar
3In the some temperature range, promptly be in the austenite phase region, this ferrite is unsettled, will very fast disappearance with the austenitic answer of deformation, and promptly the ferrite that forms by strain-induced transformation reverses by α → γ again and is deformed into austenite.So change ground generation repeatedly by γ → α and the α → γ that moves in circles, conformal alternating temperature degree is near Ar
3Point, austenite/ferrite crystal grain can be by continuously refinement.Finally, superfine little uniform ferrite crystal grain forms.The crystal grain that forms in this has and more waits shape shaft rather than extended shape in stage, subsequently by cooling off (speed of cooling 〉=10 ℃/s) to Ar fast
1Below the point, and the short period of time insulation, make uniform crystal particlesization, finish first round circulating phase-change refinement and strain-induced transformation refinement; Repeat above-mentioned circulating phase-change refinement and strain-induced transformation refinement subsequently, when cycle index reached more than 3 times or 3 times, cycle index was different and different with alloying constituent, and whole test specimen tissue is＜3.0 μ m ultra-fine ferrite crystal grains.In addition, need that also steel is carried out little titanium and handle, promptly Ti content is controlled at 0.007%～0.025% in the steel, and between best 0.01%～0.02%, Ti/N is controlled between 2.0～3.0, and in the inhibition up-quenching process or the operation of rolling, ferrite/austenite crystal is grown up.
The invention has the advantages that: eliminate the low temperature deformation that a passage is suppressed down (percentage pass reduction＞50%), reduce mill load greatly and improved template, make on the ordinary hot milling train and realize that by common controlled rolling ultra-fine crystalline substance becomes possibility, eliminated a passage and suppressed down the ununiformity of the tissue that ununiformity caused of deformation, it is possible that industrial production big test specimen is changed into; Production control simultaneously is comparatively simple, is a kind of production method of practicable superfine grain steel sheet, has very strong adaptability, higher economical efficiency and technical perspective.
Description of drawings
Fig. 1 for former ferrite crystal grain by the different crystal degree to austenite crystal cut apart synoptic diagram.
Fig. 2 for original austenite grain by the different crystal degree to the ferrite austenite crystal cut apart synoptic diagram.
Fig. 3 is a process flow diagram of the present invention.
Fig. 4 forms synoptic diagram for superfine crystal particle of the present invention.
Fig. 5 is the metallographic microstructure figure of embodiment of the invention B.
Embodiment
Embodiment A～the E that contains the Nb low-carbon low-alloy steel of ultra-fine ferrite crystal grain of the present invention sees Table 1.
See also Fig. 3, Fig. 4 again, the Ultrafine Grained Steel board manufacturing process is as follows: the laboratory vacuum induction furnace smelting, after molten steel component reaches target component, begin casting immediately, and the pouring temperature of molten steel is 1560 ℃～1580 ℃.Steel ingot forges into thick 70mm steel billet for the simulation hot rolling at 1150 ℃, hot rolling adopts Gleeble 1500 thermal analogy machines to simulate the actual operation of rolling, the heat-up rate of steel billet is controlled between 15 ℃/s～30 ℃/s, be heated between 1000 ℃～1050 ℃, insulation 5min (t1), make the steel billet complete austenitizing, and then be cooled to 800 ℃～850 ℃ with 10 ℃/s～30 ℃/s speed of cooling, carry out controlled rolling subsequently, the accumulative total draft is controlled between 40%～55%, percentage pass reduction is controlled between 15%～25%, and finishing temperature is controlled between 750 ℃～800 ℃.Roll the back and be cooled to about 400 ℃～450 ℃, insulation 2min (t0) with 10 ℃/s～30 ℃/s speed of cooling; Carry out the circulation second time as shown in Figure 4 subsequently, just soaking time t2 is 1min behind the up-quenching; So circulation is 3～5 times, and the steel billet grain-size of acquisition is all below 3.0 μ m, as shown in Figure 5.
Among Fig. 4, Ar
1Be the end temp of austenite to ferrite/perlitic transformation, Ar
3Be the starting temperature of austenite to ferritic transformation, Tnr is an austenite non-recrystallization temperature, Ac
3Be the equilibrium temperature of ferrite to the austenitic transformation end.
Table 1
| The steel sample | C(％) | Si(％) | Mn(％) | P(％) | S(ppm) | Al s(％) | Nb(％) | N(ppm) | Ti(％) | Cr(％) | Cu(％) | Ni(％) | Mo(％) | REM (ppm) | Average GS (μ m) |
| Embodiment A | 0.070 | 0.43 | 1.40 | 0.009 | 32 | 0.030 | 0.020 | 50 | 0.013 | / | 0.26 | / | / | / | 2.5 |
| Embodiment B | 0.032 | 0.25 | 1.68 | 0.011 | 10 | 0.027 | 0.038 | 41 | 0.012 | 0.19 | 0.25 | 0.45 | 0.10 | / | 2.8 |
| Embodiment C | 0.130 | 0.18 | 1.15 | 0.011 | 42 | 0.021 | 0.016 | 39 | 0.014 | / | 0.29 | 0.24 | / | 38 | 2.0 |
| Embodiment D | 0.050 | 0.51 | 1.43 | 0.011 | 28 | 0.033 | 0.030 | 45 | 0.016 | 0.23 | 0.27 | 0.22 | / | 26 | 2.3 |
| Embodiment E | 0.09 | 0.36 | 1.25 | 0.010 | 21 | 0.024 | 0.025 | 28 | 0.010 | 0.10 | / | / | / | 30 | 2.5 |
Claims (7)
1. the manufacture method that contains the Nb low-carbon low-alloy steel of ultra-fine ferrite crystal grain comprises the steps,
A. the composition that contains the Nb low-carbon low-alloy steel is:
C 0.02％～0.20％
Nb 0.01％～0.10％
Si ＜0.80％
Ti 0.007％～0.025％
N 0.0035％～0.0083％
Surplus Fe and unavoidable impurities,
It more than is mass percent;
B. heating: the heating of above-mentioned base material, rate of heating 〉=10 ℃/s are to Ac
3+ 30 ℃～50 ℃;
C. insulation: make the base material austenitizing:
D. cooling fast: the fully instant cooling fast in back of base material austenitizing, speed of cooling 〉=10 ℃/s are to austenite non-recrystallization district;
E. rolling: quick cooled base material is rolled, and finishing temperature is Ar
3Near the point, every time draft 〉=15%, accumulative total draft 〉=40%;
F. cool off, be incubated, be quickly cooled to Ar after rolling
1-10～30 ℃, tissue is adjusted, and makes it stable;
G. the above-mentioned steps that circulates, number of times 〉=3 time;
H. be cooled to room temperature.
2. the manufacture method that contains the Nb low-carbon low-alloy steel of ultra-fine ferrite crystal grain as claimed in claim 1 is characterized in that, contains the Nb low-carbon low-alloy steel and also contains Mn 1.0%～2.0%.
3. the manufacture method that contains the Nb low-carbon low-alloy steel of ultra-fine ferrite crystal grain as claimed in claim 1 is characterized in that, soaking time is to guarantee to organize the time of austenitizing among the described step c.
4. the manufacture method that contains the Nb low-carbon low-alloy steel of ultra-fine ferrite crystal grain as claimed in claim 1 is characterized in that, described step b adopts induction heating or energising direct heating.
5. the manufacture method that contains the Nb low-carbon low-alloy steel of ultra-fine ferrite crystal grain as claimed in claim 1 is characterized in that, the speed of cooling of described steps d is 10 ℃/s～30 ℃/s.
6. the manufacture method that contains the Nb low-carbon low-alloy steel of ultra-fine ferrite crystal grain as claimed in claim 1 is characterized in that, the cooling temperature of described steps d is to Ar
3+ 30 ℃～60 ℃.
7. the manufacture method that contains the Nb low-carbon low-alloy steel of ultra-fine ferrite crystal grain as claimed in claim 1 is characterized in that, the rolling accumulative total of described step e draft is controlled at 45%～55%, and percentage pass reduction is controlled at 15%～25%.
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| Application Number | Priority Date | Filing Date | Title |
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| CN 03129488 CN1273634C (en) | 2003-06-24 | 2003-06-24 | Nb containing low-carbon low-alloyed steel with ultra-fine ferrite grain structure and method for producing same |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN 03129488 CN1273634C (en) | 2003-06-24 | 2003-06-24 | Nb containing low-carbon low-alloyed steel with ultra-fine ferrite grain structure and method for producing same |
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| CN1273634C true CN1273634C (en) | 2006-09-06 |
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Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN105838862A (en) * | 2016-05-26 | 2016-08-10 | 中国科学院金属研究所 | Method for refining grains of maraging stainless steel by cyclic phase transformation |
| CN107815526A (en) * | 2017-11-30 | 2018-03-20 | 攀钢集团攀枝花钢铁研究院有限公司 | Microalloy containing Nb builds Steel Bar and its production method |
| CN107723435B (en) * | 2017-11-30 | 2023-06-06 | 贵州大学 | Method and device for obtaining refined full pearlite structure in hypoeutectoid steel wire rod |
| CN114807549A (en) * | 2022-04-27 | 2022-07-29 | 昆明理工大学 | Thermal deformation method for refining hot work die steel grains |
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