【摘要】：隨著汽車領域的不斷發(fā)展,除了在汽車安全性上的要求越來越高,節(jié)能減耗也逐漸成為一種新的發(fā)展趨勢,為了實現(xiàn)這個目標,迫切需要開發(fā)和應用高強鋼與超高強鋼。中Mn-TRIP鋼作為典型的第三代先進汽車高強鋼,開始受到越來越多的關注。本文以中頻感應熔煉爐冶煉出的四種不同成分的中Mn-TRIP試驗鋼為研究對象,通過連續(xù)冷卻轉變、形變熱模擬、中試熱軋和中間退火等試驗,研究了熱軋工藝參數(shù)和退火工藝參數(shù)對中Mn-TRIP鋼組織和性能的影響。首先在Gleeble3500熱力模擬試驗機上對試驗鋼的連續(xù)冷卻轉變規(guī)律進行了研究,得到了對應的連續(xù)轉變曲線;研究了形變熱模擬工藝對試驗鋼組織和性能的影響。結果表明:馬氏體相變在實驗的所有冷速條件下都可以發(fā)生,隨著冷速增加,馬氏體含量增加,不同成分的馬氏體組織形態(tài)存在一定差異;貝氏體相變只有在冷速比較低的情況下才有可能發(fā)生;在實驗條件下改變形變溫度和變形量的低溫大變形對試驗鋼的組織轉變影響不大。在此基礎上,根據試驗鋼組織和變形工藝參數(shù)之間的關系,確定了試軋工藝參數(shù)并開展了中試軋制試驗,對不同終軋溫度下試驗鋼組織和性能的變化規(guī)律進行了研究,結果表明:成分相同,隨著終軋溫度降低,原始奧氏體晶粒尺寸減小,形成的馬氏體束也較小,板條更細更短,馬氏體相變更完全;同時,終軋溫度越低,對應的抗拉強度反而越高,延伸率降低;在所有熱軋態(tài)試驗鋼中,1-3號試驗鋼的綜合力學性能最佳。中Mn-TRIP鋼熱軋后必須進行退火處理,以獲得更好的強度和塑性的匹配,也可為后續(xù)冷軋做好組織準備。因此,本文研究了不同成分的試驗鋼在退火后組織和性能的變化,發(fā)現(xiàn)在不同退火溫度下退火10h后,不同成分的試驗鋼組織中馬氏體的數(shù)量都有減少,分布也更加均勻,鐵素體數(shù)量減少,由XRD衍射圖譜還可發(fā)現(xiàn)退火后出現(xiàn)了一定數(shù)量的殘余奧氏體;同時,隨著退火溫度的升高,屈服強度先減小后增大,抗拉強度提高,而斷后延伸率降低,當退火溫度為620℃時,綜合力學性能最佳,強塑積最大可達31.5 GPa·%。
[Abstract]:With the continuous development of automobile field, in addition to the higher and higher requirements of automotive safety, energy saving and consumption reduction has gradually become a new development trend. In order to achieve this goal, it is urgent to develop and apply high-strength steel and ultra-high strength steel. As a typical third generation advanced automobile high strength steel, medium Mn-TRIP steel has been paid more and more attention. In this paper, four kinds of intermediate Mn-TRIP test steels with different compositions from intermediate frequency induction smelting furnace were studied. The experiments were carried out through continuous cooling transformation, deformation thermal simulation, pilot-scale hot rolling and intermediate annealing, etc. The effects of hot rolling process parameters and annealing process parameters on the microstructure and properties of Mn-TRIP steel were studied. At first, the continuous cooling transformation law of test steel was studied on Gleeble3500 thermal simulation machine, and the corresponding continuous transformation curve was obtained, and the effect of deformation thermal simulation technology on the microstructure and properties of test steel was studied. The results show that martensite transformation can take place under all the experimental cooling rates, and with the increase of cooling rate, the content of martensite increases, and the microstructure of martensite with different composition is different to a certain extent. Bainitic transformation can occur only when the cooling rate is low, and the change of deformation temperature and deformation amount at low temperature and large deformation have little effect on the microstructure transformation of the test steel. On this basis, according to the relationship between the microstructure and deformation parameters of the test steel, the parameters of the test rolling process were determined and the rolling tests were carried out. The variation of the microstructure and properties of the tested steel at different finishing rolling temperatures was studied. The results show that the grain size of the original austenite decreases, the martensite beam is smaller, the lath is thinner and shorter, and the martensite phase changes completely with the decrease of the final rolling temperature. At the same time, the lower the final rolling temperature, the higher the tensile strength and the lower the elongation. Among all the hot rolled test steels, 1-3 # test steel has the best comprehensive mechanical properties. Middle Mn-TRIP steel must be annealed after hot rolling in order to obtain a better match of strength and plasticity, and it can also be prepared for subsequent cold rolling. Therefore, the changes of microstructure and properties of different composition test steels after annealing are studied in this paper. It is found that after annealing for 10 h at different annealing temperatures, the number of martensite in different compositions of test steels decreases and the distribution of martensite is more uniform. The number of ferrite is reduced, and a certain amount of retained austenite can be found after annealing by XRD diffraction pattern. At the same time, with the increase of annealing temperature, the yield strength decreases and then increases, and the tensile strength increases, while the elongation at break decreases. When the annealing temperature is 620 鈩，

本文編號：2421022