CN1323907A - Relaxation-separation-phase change control technology for producing high-strength low-alloy steel - Google Patents
Relaxation-separation-phase change control technology for producing high-strength low-alloy steel Download PDFInfo
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Abstract
A technology for relaxing separating out and phase transition controlling for high strength low alloy steel controls the steel phase transition to finally obtain the superfine complex structure for reaching the aim of strengthening and malleablizing the base body by controlling the defective relaxation state in the structure and deformed crystal, during the time of final rolling to acceleration cooling as well as by controlling the physical metallurgy course of separating out behavior of the micro-alloy elements. The yield strength of the steel produced with the present ivnention can reach up to 800 MPa.
Description
The present invention relates to a kind of mechanical thermal treatment process that when making high-strength low-alloy steel, is adopted and corresponding alloy designs, belong to International Classification of Patents C21D8/02.
Microalloying and mechanical thermal treatment process (TMCP) are the important steps that obtains the high-performance low-alloy high-strength steel in the high-strength low-alloy steel production process, in mechanical heat treatment process, reach the purpose of thinning microstructure by austenite two stages deformation, simultaneously, microalloy element Nb, Ti, V, B etc. in TMCP technology to comprehensive thinning microstructure, the control phase transformation, precipitation strength etc. play an important role.At present, controlled rolling finish to gauge after-acceleration cooling and direct quenching technology have been used to online production, owing to removed the reheat quenching process from, and very useful to reducing cost.Usually tension and the comparable modifier treatment of yield strength by steel after the TMCP+ acceleration cooling/direct quenching technology improves about 20%.Direct quenching/acceleration cooling-tempering process also is to make the above rank high strength of 600MPa, effective, the feasible technology of high tenacity weldable steel.
But document (K.Okamoto, A.Yoshie, H.Nakao " Physical Metallugy of DirectQuenched SteelPlates and its Application for Commercial Processes andProducts ", Physical Metallugy of Direct Quenched Steels, Edited byK.A.Taylor, S.W.Thompson and F.B.Fletcher, The Minerals, Metals﹠amp; MaterialsSociety, 1993, P339) illustrate, all only pay attention at present being chosen in the recrystallization temperature district in TMCP+ direct quenching of extensively having adopted or the accelerated cooling process or non-recrystallization temperature district carries out ausrolling, or direct quenching or quicken to cool off after the two-phase region press working.And do not consider that always press working finishes the recovery and the evolution process of dislocation in the after strain crystal, deformation bands, subgrain etc., and influence that microalloy is separated out in relaxation process and effect, thereby can't give full play to intracrystalline microstructure configuration to improving the influence of final microstructure and property.
From the steel grade that has used both at home and abroad at present, the 700-800MPa level steel that has used mainly is the quenched and tempered steel of higher alloy content, and this Carbon Content Of Steel is higher, and the obdurability coupling is not enough, and welding property is relatively poor.Because alloy content is big, cost is higher, adopts modifier treatment to cause energy consumption very big.Also developed a collection of low-carbon bainite steel abroad, owing to only adopt conventional controlled rolling and controlled cooling and hardening and tempering process, so alloy content is still higher, cost is difficult to descend, and is as shown in table 1.
The external alloying constituent that adopts common controlled rolling and controlled cooling and hardening and tempering process of table 1
| Steel grade | WELTEN100 | HSLA100 naval plate | The TD bridge plate |
| Yield strength, MPa | ＞700 (modified) | ＞700 (modified) | ＞780 (directly quenching) |
| C measures (%) | 0.16 | ＜0.06 | ＜0.06 |
| Alloy content (is disregarded Mn, Si) % | 3.52 | 6.39 | 2.90 |
The objective of the invention is to propose a kind of special relaxation-separate out-the control mechanical thermal treatment process technology (TMCP+RPC) and the corresponding alloy designs of phase transformation.This technology is effectively utilized the effect of microalloy element on the basis that takes into full account alloy designs, Composition Control, hot-work (TMP) and process for cooling, control phase transformation by special mechanical thermal treatment process, thinning microstructure, reinforcement, malleableize matrix.The present invention propose especially to control after the finish to gauge tissue before begin to quicken to cool off and the intravital defective relaxed state of morphotropism, control microalloy element physical metallurgy processes such as the behavior of separating out, realize the phase transformation of control steel finally obtaining ultra-fine complex tissue.Make alloy content low, intensity is the low-alloy plate of moderate thickness steel of 600MPa after former controlled rolling and the modifier treatment, and yield strength reaches more than the 800MPa, reduces the cost of steel simultaneously.
Relaxation involved in the present invention-separate out-control phase change technique is based on following ultimate principle:
1, make steel just enter non-recrystallization temperature district 950 ℃ the time by microalloying design.At this moment Nb, Ti, alloying elements such as B are poly-partially in deformed matrix to make recrystallize be difficult to carry out with separating out, like this when rolling, and distortion accumulation in the deformed austenite, the very fast rising of dislocation desity.After finish to gauge, have a large amount of distortion dislocations in the deformed austenite, the microalloy element precipitate of deformed belt and all size.
2, press the slow cooling of 1～2 ℃/s of air cooling cooling rate at finish to gauge distortion back steel plate, in this relaxation process, can take place in the distortion crystal to reply and the polygonization process, the distortion dislocation can rearrange or disappear, and forms the born of the same parents' shape substructure or the subgrain of 3-5 micron diameter in deformed austenite.NONEQUILIBRIUM SEGREGATION can take place and separate out on the cell structure border that these are made up of dislocation in Nb, Ti, trace elements such as B, and promptly deformation inductdion is separated out.
3, through after the above-mentioned relaxation-separate out-control phase transition process (RPC technology), greater than Ar
3The humidity province is carried out direct quenching or is quickened cooling.Because substructure and precipitate that the slow cooling stage forms, particularly those sizes lose the precipitated phase of coherence relation than big and matrix, can become the phase transformation vantage point, therefore when cooling, on them, can at first form cenotype, preferentially form intracrystalline acicular ferrite or bainite and original austenite grains is divided into different zones.When further bainite and martensitic transformation take place in cooling, the slat dimension of phase-change product is subjected to subgrain border and the early stage acicular ferrite that forms or the restriction of bainite, it is thinner, shorter that the lath that finally obtains is organized, and realized the super-refinement of tissue, and its process signal is as accompanying drawing 1.
Fig. 1 (a) handles steel cooling back tissue without RPC, and at this moment stave lengths runs through whole deformed austenite crystal grain substantially.(b) be because the relaxation stage intracrystalline forms the wide-angle substructure, restriction lath tissue is grown up and is caused refinement, (c) because the early stage acicular ferrite that occurs is cut apart the refinement that crystal grain causes final tissue, (d) during cooling on substructure and the precipitate nucleation site roll up, also cause refinement.
Present technique is will form acicular ferrite or bainite before bainite and martensitic transformation in deformed grains, the formation of this acicular structure will have two conditions usually, at first require steel grade bainitic transformation temperature lower, require to form in the deformed grains more tiny bainite forming core vantage point simultaneously.These two requirements only could realize when reaching certain state with separating out in the defective of deformed austenite intracrystalline.
Steel grade basal component scope such as table 2 that the present invention is selected.The total alloy content of steel grade is disregarded Mn, and Si is no more than 1.4%, and steel grade carbon equivalent＜0.4 is on Cromrile figure in the insensitive I of when welding HAZ cold crack district.
Table 2 steel grades scope (weight %)
| ?C | ?Mn | ?Si | ?P | S | ???Nb | ?Ti |
| ?0.03～0.07 | ?1.3～1.8 | ?0.15～0.5 | ?≤0.01 | ≤0.005 | ???0.03-0.10 | ?0.02-0.10 |
| ?B | ?Ni | ?Mo | ?Cu | |||
| ?0.0005～0.0025 | ?0.2～0.4 | ?0.05～0.35 | ?0.2～0.6 |
Implementing technical scheme of the present invention is: adopt relaxation-separate out-the control mechanical thermal treatment process technology of phase transformation, select steel billet 1200-1250 ℃ heating for use, start rolling temperature is 1150 ℃, at deflection more than 1000 ℃ is 50-80%, is 50～70% at 950 ℃ to deflection between the finishing temperature, and finishing temperature is 900-800 ℃ of scope.Roll back steel plate air cooling 10-100 second between finishing temperature to 700 ℃, then direct quenching or with the above cooling rate acceleration of 10 ℃/s cool to room temperature.Advantage of the present invention and effect are:
(1) adopt roll the back relaxation separate out control and fast cold after, the middle temperature transformation product can be realized super-refinement.The thermal analogy result shows, the sample that adopts RPC technology postcooling after the bainite bundle size after the phase transformation is than distortion immediately the bainite size of cooling samples reduce 8-10 doubly.
(2) the invention provides the production technology of a low cost, the energy-conservation and relative simple possible of technology.Steel grade alloy content (disregarding Mn, common element such as Si)≤1.4% is than generally lacking more than 50% with the alloy amount of intensity quenched and tempered steel.Energy-conservation, save man-hour, the modifier treatment that does not need to carry out second-heating can provide yield strength to reach the 800MPa level, has the high-strength low-alloy steel of good combination of strength and toughness and good weldability.
(3) the present invention is the compound action of comprehensive utilization microalloy element and lattice defect, makes the bainite and martensite microstructure ultra-fining treatment, realizes the thermomechanical treatment new technology of the high highly malleablized of micro-alloyed steel.
Further specify the present invention below in conjunction with embodiment.
Low alloy steel adopts vacuum oven to smelt, and steel ingot weight is 25kg, the chemical composition analysis result such as the table 3 of steel.The test steel is swaged into the 42mm heavy slab through 1200 ℃ of heating after heat.After the 6mm plate is arrived in two stages five passage controlled rollings, the rolling temperature and the draught of each passage see Table 4 to slab 1200 ℃ of heating.Steel plate air cooling relaxation 40s after 830 ℃ of finish to gauges treats that temperature to 750 ℃, is quickly cooled to room temperature with 20 ℃/s of speed of cooling then.In the operation of rolling, the high temperature recrystallization zone rolls 2 roads, total deformation 64%.Non-recrystallization zone rolls 3 roads, total deformation 60%.This composition experimental steel measured result shows that it is 950 ℃ that the recrystallize of experimental steel stops temperature, when cooling rate greater than 1 ℃/s, proeutectoid ferrite does not take place during cooling to be changed, what obtain is bainite and martensitic complex tissue, the test steel plate uses through after the tempering.Whole process is called controlled rolling+relaxation and separates out and control phase transformation+tempering (CR+RPC+T) technology.The sample stretching experiment is undertaken by GB228-87, and thickness of sample is sheet material original thickness (6.2-6.5mm).Because steel plate rolling thickness is 6mm, so impact specimen is of a size of half-width sample (5 * 10 * 55mm).The impact experiment temperature is respectively room temperature (21 ℃) ,-20 ℃ ,-40 ℃.
The chemical ingredients of table 3 steel (weight %)
S＜0.005％,P＜0.010％
| C | ?Mn | ?Si | ?Nb | ?Ti | ?Mo | ?Ni | ?Cu | ?B | |
| The embodiment steel | 0.036 | ?1.74 | ?0.16 | ?0.091 | ?0.08 | ?0.31 | ?0.25 | ?0.20 | ?0.0010 |
The rolling flow process of table 4
| Rolling pass | ????1 | ????2 | ????3 | ????4 | ????5 | Water-cooled |
| Every time thickness (mm) | ????23 | ????15 | ????11 | ????8 | ????6 | |
| Deformation rate (%) | ????44 | ????35 | ????27 | ????27 | ????25 | |
| Rolling temperature (℃) | ????1150 | ????1000 | ????930 | ????860 | ????830 | ????750 |
| Arrive the fast cold preceding air cooling relaxation time (s) after the finish to gauge: | ????40 | |||||
Fig. 2 (a) is for rolling the metallograph (800 *) of attitude tissue; (b) for rolling the stereoscan photograph (1800 *) of attitude tissue.
Fig. 3 is the electromicroscopic photograph (10000 *) that rolls attitude sample complex tissue.
Steel rolls attitude metallographic structure such as Fig. 2 after above-mentioned prepared.By Fig. 2 (a) as seen, carried out the subregions control of two stages during owing to hot rolling, after non-recrystallization zone was rolling, the austenite deformation grain form remained flattening deformation crystal grain in the steel; Phase-change organization is a granular bainite, ferrite bainite and martensitic mixture, and granular bainite in irregular shape is cut apart deformed austenite crystal grain, is lath of bainite and a small amount of shred shape martensite between the granular bainite.In the deformed austenite crystal grain that flattens, be divided into different bainite fields along its length, in flat die thickness direction, subregion is regardless of sometimes sometimes.
Electron microscopic observation shows that observed complex tissue is formed by thin lath under the low power, and the lath width is about 0.3 micron, and length is about the 4-6 micron.Typical case's photo such as Fig. 3.
The mechanical property of this composition soft steel after CR+RPC technology and temper sees Table 5, also listed congruent steel in the table without RPC technology, after the controlled rolling finish to gauge Direct Air-Cooled to room temperature, the mechanical property after 950 ℃ of modifier treatment again.
The mechanical property of table 5 experimental steel after different tempering systems
| Mechanical property | Yield strength (MPa) | Tensile strength (MPa) | Unit elongation (%) |
| 650 ℃ of tempering 1.5h of example steel | ????820 | ????860 | ????15 |
| 675 ℃ of tempering 1.5h of example steel | ????770 | ????795 | ????17 |
| With the congruent 950 ℃ of modifier treatment of example steel (600 ℃ of tempering 1h) | ????600 | ????650 | ????19 |
By table as seen, after 1.5 hours, it is all preferable to test steel mechanical property through 650 ℃ and 675 ℃ of tempering, and yield strength σ s is between 770-820MPa, and unit elongation δ is greater than 15%.Show and utilize technology of the present invention can obtain the low alloy steel of yield strength greater than the 800MPa level.In addition by table as seen, through controlled rolling but without RPC and the steel plate that quickens cooling control, even after adopting 600 ℃ of tempered modifier treatment, its mechanical property is far short of what is expected by the steel plate of RPC prepared, and σ s only is the 600MPa magnitude.The tensile strength of two kinds of technologies and the contrast of yield strength are as seen, the steel plate tensile strength of CR-RPC-T explained hereafter, yield strength is all comparable through the high 200MPa of modifier treatment steel, and promptly the performance of the comparable congruent modifier treatment steel of CR+RPC+AC prepared rigidity energy improves about 30%.
Claims (2)
1, a kind of mechanical heat treatment technics of making high-strength low-alloy steel, it is characterized in that, adopt relaxation-separate out-the control method of phase transformation, select 1200-1250 ℃ of heating of low alloy steel steel billet for use, 1150 ℃ of start rolling temperatures, deflection is 50-80% more than 1000 ℃, is 50～70% at 950 ℃ to deflection between the finishing temperature, and finishing temperature is 900-800 ℃ of scope.Roll back steel plate air cooling 10-100 second between finishing temperature to 700 ℃, then direct quenching or with the above cooling rate acceleration of 10 ℃/s cool to room temperature.
2, low alloy steel according to claim 1, it is characterized in that the composition of low alloy steel (weight percent) is C:0.03～0.07%, Mn:1.3～1.8%, Si:0.15～0.5%P :≤0.01%, S :≤0.005%, Nb:0.03～0.10%, Ti:0.02～0.10%, B:0.0005～0.0025%, Ni:0.2～0.4%, Mo:0.05～0.35%, Cu:0.2～0.6%.
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN100368582C (en) * | 2003-01-28 | 2008-02-13 | 鞍钢股份有限公司 | Ultra-low-carbon bainite steel and producing method thereof |
| CN102251178A (en) * | 2011-06-21 | 2011-11-23 | 北京科技大学 | Preparation method for low-alloy steel keeping constant hardness under thermal disturbance |
| CN102851471A (en) * | 2012-09-27 | 2013-01-02 | 攀枝花学院 | Heat treatment method for rapidly obtaining fine ferrite grains by low carbon alloy steel |
| CN103147000A (en) * | 2013-03-20 | 2013-06-12 | 钢铁研究总院 | Polygonal ferrite-acicular ferrite two-phase steel plate/belt and production method thereof |
| CN103627980A (en) * | 2013-11-25 | 2014-03-12 | 首钢总公司 | Low-temperature X80HD (High Density) large-deformation pipeline steel with great wall thickness and production method thereof |
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2001
- 2001-04-29 CN CN 01115650 patent/CN1123642C/en not_active Expired - Fee Related
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN100368582C (en) * | 2003-01-28 | 2008-02-13 | 鞍钢股份有限公司 | Ultra-low-carbon bainite steel and producing method thereof |
| CN102251178A (en) * | 2011-06-21 | 2011-11-23 | 北京科技大学 | Preparation method for low-alloy steel keeping constant hardness under thermal disturbance |
| CN102251178B (en) * | 2011-06-21 | 2012-12-05 | 北京科技大学 | Preparation method for low-alloy steel keeping constant hardness under thermal disturbance |
| CN102851471A (en) * | 2012-09-27 | 2013-01-02 | 攀枝花学院 | Heat treatment method for rapidly obtaining fine ferrite grains by low carbon alloy steel |
| CN103147000A (en) * | 2013-03-20 | 2013-06-12 | 钢铁研究总院 | Polygonal ferrite-acicular ferrite two-phase steel plate/belt and production method thereof |
| CN103627980A (en) * | 2013-11-25 | 2014-03-12 | 首钢总公司 | Low-temperature X80HD (High Density) large-deformation pipeline steel with great wall thickness and production method thereof |
| CN103627980B (en) * | 2013-11-25 | 2016-01-20 | 首钢总公司 | Low temperature large wall thickness X80HD gross distortion pipe line steel and production method thereof |
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