CN104894353A - Nb-containing high-temperature carburized gear steel rolling method - Google Patents
Nb-containing high-temperature carburized gear steel rolling method Download PDFInfo
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Abstract
The invention discloses a Nb-containing high-temperature carburized gear steel rolling method, and belongs to the technical field of special steel rolling. The rolling method is characterized in that the casting blank reheating temperature is higher than the complete dissolving temperature of a Nb-precipitated phase, so Nb is fully re-dissolved in a matrix and is uniformly diffused; and rolling in an undercooled austenite most-unstable temperature range of 900-950DEG C for Nb precipitation is avoided, and the stay time in the temperature range is shortened. The method allows the Nb-containing precipitated phase to be reasonably distributed in rolled Nb-containing gear steel, and is in favor of pinning austenite crystal boundary in a subsequent carburizing process and preventing the growth of gear steel austenite crystal grains.
Description
Technical field
The invention belongs to special steel rolling technical field, in particular, provide a kind of rolling method containing Nb high temperature carburizing Pinion Steel.
Background technology
Current domestic conventional gear wheel carburization temperature is general not higher than 930 DEG C.If but carburizing temperature were brought up to 980 DEG C, the carburizing time of 50% could be shortened.Therefore the high temperature carburizing cycle is short, and production efficiency is high, energy-conserving and environment-protective, is the development trend of gear thermal processing technology, also for the production of Pinion Steel provides a direction.
Although Chinese patent CN102560255A discloses, one is novel adds Al high-temperature vacuum carburized gear steel.But there is technology to show to adopt Nb microalloying to be the Main way producing high temperature carburizing Pinion Steel.
When the crystal boundary moved runs into precipitated phase particle, be subject to the pinning effect of particle, effectively will stop Austenite Grain Growth.After the Nb content of steel grade is determined, at a certain temperature, the volume fraction of precipitated phase is fixing.According to Gladman formula, precipitate volume fraction is larger, and the size of precipitated phase is less, is more conducive to anchoring crystal boundary.Therefore will utilize Nb microalloy technology, improve gear wheel carburization temperature, the precipitated phase that must there is a large amount of small and dispersed between carburizing cycle could favourable anchoring austenite grain boundary.
Conventional art show Nb content composition be on the size of precipitated phase and the impact of distribution great.But rolling technology is the state-of-the-art technology of this invention to the size of precipitated phase and the function and significance of distribution.
Summary of the invention
The object of the present invention is to provide a kind of rolling method containing Nb high temperature carburizing Pinion Steel.At the process conditions, rolling containing Nb Pinion Steel, containing the distribution of Nb precipitated phase rationally, be more conducive to, at follow-up cementation process anchoring austenite grain boundary, preventing Pinion Steel Austenite Grain Growth.
The object of adding Nb in Pinion Steel is the precipitated phase obtaining small and dispersed, so that hinder grain coarsening in follow-up high temperature carburizing process.But this and do not mean that just must obtain in stocking small and dispersed containing Nb precipitated phase.Because before carburizing, wheel blank needs isothermal normalizing process (about 950 DEG C austenitizings, and at about 600 DEG C isothermals), if there is solid solution Nb, can fully separate out in the process, and the size of precipitated phase is more tiny.Therefore, in controlled rolling and controlled cooling process, key avoids the formation of thick precipitated phase.Accomplish following 2 points on request:
(1) strand reheats temperature range is complete solvent temperature to 1250 DEG C containing Nb precipitated phase, makes the abundant back dissolving of Nb to matrix and diffusion ratio is more even;
(2) avoid the nose warm area 900-950 DEG C of rolling of separating out at Nb, and reduce in this temperature range residence time.Therefore for the bar of different size, need to take different process control methods.
1, large scale rod bar (diameter > 30mm), Homogeneous cooling is more difficult, and the mode of high temperature finish rolling can be taked to produce.Concrete rate-determining steps is as follows: continuously cast bloom heating temperature range in process furnace is the complete solvent temperature to 1250 DEG C containing Nb precipitated phase, and rolling whole process temperature range 980 DEG C-1100 DEG C, rolls rear upper cold bed slow cooling.
First, in 980 DEG C of-1100 DEG C of temperature ranges, the solid solution capacity of Nb is higher, and the incubation period of separating out is as shown in Figure 1 long, is not easy to produce a large amount of strain induced precipitate.Secondly, in 980 DEG C of-1100 DEG C of temperature ranges, the dislocation that in finish to gauge process, deformation produces also is eliminated than being easier to.Therefore, in follow-up process of cooling, the forming core point of precipitated phase is less, is not easy to separate out in austenite.
2, for small-sized bar (diameter≤30mm), the mode of high temperature finish rolling or Low Temperature Finish can be taked to produce.High temperature finish rolling is identical with the mode of production of large gauge.The concrete rate-determining steps of Low Temperature Finish is as follows: continuously cast bloom heating temperature range in process furnace is the complete solvent temperature to 1250 DEG C containing Nb precipitated phase, roughing and in roll temperature range 980 DEG C-1100 DEG C, by wearing water, finishing temperature being reduced to 850 DEG C-900 DEG C, rolling rear upper cold bed slow cooling.
First, roughing and in roll temperature and control more than 980 DEG C, the solid solution capacity of Nb is higher, and the incubation period of separating out is long, is not easy to produce a large amount of strain induced precipitate phases.When final rolling temperature scope 850 DEG C-900 DEG C., the precipitation phasor of strain inducing is very little, and at this temperature, alligatoring is not serious.
The present invention is the back dissolving of control Nb and precipitation strictly, can give full play to Nb precipitated phase anchoring austenite grain boundary in high temperature carburizing process, stops Austenite Grain Growth.Therefore add a small amount of Nb and namely can reach raising carburizing temperature, the consumption of Nb can be saved thus, reduce the cost of steel.
Accompanying drawing explanation
Fig. 1 is containing the dynamic precipitation PTT curve of Nb precipitated phase.
Grain morphology after the 1050 DEG C of finish to gauge simulation carburizings of Fig. 2 large gauge SAE8620H-NbTi bar.
Grain morphology after the 980 DEG C of finish to gauge simulation carburizings of Fig. 3 large gauge SAE8620H-NbTi bar.
Grain morphology after the 950 DEG C of finish to gauge simulation carburizings of Fig. 4 large gauge SAE8620H-NbTi bar.
Precipitated phase after the 1050 DEG C of finish to gauges of Fig. 5 large gauge SAE8620H-NbTi bar.
Precipitated phase after the 980 DEG C of finish to gauges of Fig. 6 large gauge SAE8620H-NbTi bar.
Precipitated phase after the 950 DEG C of finish to gauges of Fig. 7 large gauge SAE8620H-NbTi bar.
Precipitated phase after the 1050 DEG C of finish to gauge simulation carburizings of Fig. 8 large gauge SAE8620H-NbTi bar.
Precipitated phase after the 980 DEG C of finish to gauge simulation carburizings of Fig. 9 large gauge SAE8620H-NbTi bar.
Precipitated phase after the 950 DEG C of finish to gauge simulation carburizings of Figure 10 large gauge SAE8620H-NbTi bar.
Grain morphology after the carburizing of Figure 11 small dimension 20CrMnTi-Nb bar 1050 DEG C of finishing temperature Imitatings.
Grain morphology after the carburizing of Figure 12 small dimension 20CrMnTi-Nb bar 850 DEG C of finishing temperature Imitatings.
Grain morphology after the carburizing of Figure 13 small dimension 20CrMnTi-Nb bar 930 DEG C of finishing temperature Imitatings.
Embodiment
Embodiment 1
Embodiment 1 continuously cast bloom chemical composition mass percent is: C:0.19%, Si:0.25%, Mn:0.80%, P:0.015%, S:0.030%, Cr:0.50%, Ni:0.55%, Mo:0.16%, Al:0.02%, Nb:0.02%, Ti:0.02%, surplus is Fe.
The technical process of the present embodiment SAE8620H-NbTi Pinion Steel is electrosmelting → LF refining → continuous casting → strand heating → rolling → wear water → cold bed cooling → cold shears → steels strapping → warehouse-in of listing of weighing.
The continuously cast bloom of the present embodiment to be cross dimensions be 200mm × 200mm, rolling diameter is the bar of Φ 60mm.Roll control technique is as follows:
In process furnace, soaking temperature is 1200 DEG C, and be greater than the complete solvent temperature 1150 DEG C containing Nb precipitated phase, heat-up time is 4h.Start rolling temperature 1130 DEG C, in roll temperature 1080 DEG C, finishing temperature is controlled as 1050 DEG C, 980 DEG C and 950 DEG C.Temperature on cooling table is 930 DEG C, 890 DEG C and 870 DEG C.
By the bar isothermal normalizing process (940 DEG C of austenitizings, and at 650 DEG C of isothermal 2h) under above three finishing temperature techniques, and be processed into the sample of 10 × 10 × 10mm.Then carry out the test of simulation carburizing and quenching, simulation carburizing quenching process is: sample heats up with stove, and 800 DEG C of insulations 1 hour, is then heated to 950 DEG C of insulations 4 hours, then carries out shrend.The metallograph of its austenite crystal as shown in figs 2-4.As can be seen from the figure, finishing temperature is the sample of 1050 DEG C and 980 DEG C, and its autstenitic grain size can remain on more than 8.0 grades, does not find mixed crystal phenomenon.And finishing temperature is the sample of 950 DEG C, there is mixed crystal in local austenite crystal abnormal growth.This shows, for large gauge containing Nb high temperature carburizing Pinion Steel bar finishing temperature control more than 980 DEG C, have utilize keep austenite crystal tiny.
Fig. 5-Fig. 7 is the precipitated phase transmission electron microscope photo of stocking.As can be seen from the figure, along with the reduction of finishing temperature, thick precipitated phase (100-200nm) volume fraction increases.These precipitated phases consume a large amount of Nb, and thick precipitated phase can not play anchoring crystal boundary.Thick precipitated phase is many, causes the volume fraction of the tiny precipitated phase of energy anchoring crystal boundary to reduce.Therefore the nose warm area (900-950 DEG C) that finishing temperature is in precipitated phase is unfavorable for controlling grain coarsening.
Fig. 8-Figure 10 is precipitated phase transmission electron microscope photo after simulation carburizing.Containing Nb precipitated phase Dispersed precipitate after the sample carburizing of 1050 DEG C of finish to gauges, the mean sizes of precipitated phase is 13 ± 4nm, as shown in Figure 8.Precipitated phase after the sample carburizing of 980 DEG C of finish to gauges is also Dispersed precipitate, and the mean sizes of precipitated phase is 17 ± 11nm, as shown in Figure 9.The thick precipitated phase of more than 50nm has been there is in precipitated phase.And as shown in Figure 10, be divided into two classes at its precipitated phase of sample of 950 DEG C of finish to gauges: the thick precipitated phase of a class to be mean sizes be 70nm, another kind of for mean sizes be the thin precipitated phase of 12nm.The precipitation of thick precipitated phase, result in the dilution of Nb around it, and making does not have thin precipitated phase to separate out around, therefore result in local grain abnormal growth, mixed crystal occurs.
Embodiment 2
Embodiment 2 continuously cast bloom chemical composition mass percent is: C:0.18%, Si:0.23%, Mn:0.90%, P:0.015%, S:0.023%, Cr:1.06%, Al:0.02%, Nb:0.03%, Ti:0.04%, surplus is Fe.
The technical process of the present embodiment 20CrMnTi-Nb Pinion Steel is electrosmelting → LF refining → continuous casting → strand heating → rolling → wear water → cold bed cooling → cold shears → steels strapping → warehouse-in of listing of weighing.
The continuously cast bloom of the present embodiment to be cross dimensions be 200mm × 200mm, rolling diameter is the bar of Φ 30mm.Roll control technique is as follows:
In process furnace, Heating temperature is 1200 DEG C, and be greater than the complete solvent temperature 1180 DEG C containing Nb precipitated phase, heat-up time is 3.5h.Start rolling temperature 1130 DEG C, in roll temperature 1080 DEG C, finishing temperature is controlled as 1050 DEG C, 850 DEG C and 930 DEG C.Temperature on cooling table is respectively 830 DEG C, 780 DEG C and 800 DEG C.
By the bar isothermal normalizing process (920 DEG C of austenitizings, and at 620 DEG C of isothermal 1h) under above three finishing temperature techniques, and be processed into the sample of 10 × 10 × 10mm.Then carry out the test of simulation carburizing and quenching, simulation carburizing quenching process is: sample heats up with stove, and 800 DEG C of insulations 1 hour, is then heated to 1000 DEG C of insulations 6 hours, then carries out shrend.The metallographic of its austenite crystal as shown in figures 11-13.As can be seen from the figure, finishing temperature is the sample of 1050 DEG C and 850 DEG C, and its autstenitic grain size can remain on more than 8.0 grades, does not find mixed crystal phenomenon.And finishing temperature is the sample of 930 DEG C, there is mixed crystal in austenite crystal abnormal growth.This shows, the Nb high temperature carburizing Pinion Steel bar that contains for small dimension adopts high temperature finish rolling or Low Temperature Finish, keeps austenite crystal tiny when being all conducive to carburizing.But when the nose warm area of finishing temperature at precipitated phase, when being unfavorable for carburizing, keep Austenite Grain Refinement.
Above two embodiments show: in process furnace, Heating temperature is higher than the complete solvent temperature containing Nb precipitated phase, avoids the formation of thick precipitated phase, be conducive to controlling grain growth in cementation process in the operation of rolling.Particularly, for large scale rod bar, adopt high temperature finish rolling, namely finishing temperature control is more than 980 DEG C; For small-sized bar, adopt high temperature finish rolling or Low Temperature Finish.Low Temperature Finish refer to roughing and in roll and all control more than 980 DEG C, and finish to gauge controls below 900 DEG C.
Claims (1)
1., containing a rolling method for Nb high temperature carburizing Pinion Steel, it is characterized in that: for the bar of different size, need to take different technique; The processing parameter of concrete control is as follows:
(1) large scale rod bar of diameter > 30mm: continuously cast bloom heating temperature range in process furnace is the complete solvent temperature to 1250 DEG C containing Nb precipitated phase, and rolling whole process temperature range 980 DEG C-1100 DEG C, rolls rear upper cold bed slow cooling;
(2) small-sized bar of diameter≤30mm: take high temperature finish rolling or Low Temperature Finish
High temperature finish rolling: continuously cast bloom heating temperature range in process furnace is the complete solvent temperature to 1250 DEG C containing Nb precipitated phase, and rolling whole process temperature range 980 DEG C-1100 DEG C, rolls rear upper cold bed slow cooling;
Low Temperature Finish: continuously cast bloom heating temperature range in process furnace is the complete solvent temperature to 1250 DEG C containing Nb precipitated phase, roughing and in roll temperature range 980 DEG C-1100 DEG C, by wearing water, finishing temperature being reduced to 850 DEG C-900 DEG C, rolling rear upper cold bed slow cooling.
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| CN110129653A (en) * | 2019-05-21 | 2019-08-16 | 柳州钢铁股份有限公司 | A kind of production method of soft 20CrMnTi round steel |
| CN110218949A (en) * | 2019-07-12 | 2019-09-10 | 东北大学 | The method of carburizing temperature and the case-carbonizing method of mild steel are improved using microalloying |
| CN111570513A (en) * | 2020-05-25 | 2020-08-25 | 江苏联峰实业有限公司 | Fine-grain gear steel and preparation method thereof |
| CN112322997A (en) * | 2020-11-13 | 2021-02-05 | 江苏联峰能源装备有限公司 | High-temperature carburized automobile gear steel and production process thereof |
| CN112570451A (en) * | 2020-11-26 | 2021-03-30 | 宝钢特钢韶关有限公司 | 20CrMnTi steel and production method thereof |
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Cited By (6)
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| CN110129653A (en) * | 2019-05-21 | 2019-08-16 | 柳州钢铁股份有限公司 | A kind of production method of soft 20CrMnTi round steel |
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| CN112570451A (en) * | 2020-11-26 | 2021-03-30 | 宝钢特钢韶关有限公司 | 20CrMnTi steel and production method thereof |
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Address after: 100041 Shijingshan Road, Shijingshan District, Shijingshan District, Beijing Patentee after: Shougang Group Co. Ltd. Address before: 100041 Shijingshan Road, Shijingshan District, Shijingshan District, Beijing Patentee before: Capital Iron & Steel General Company |
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