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鈰對工程機械用700 MPa級高強鋼焊接性能的影響

Effect of cerium on welding performance of 700 MPa high-strength steel used in construction machinery

  • 摘要: 針對工業生產700 MPa級高強度調質態鋼板,通過Gleeble3500熱模擬機進行模擬焊接試驗,利用光學顯微鏡、硬度儀、場發射掃描電鏡等設備對比研究了稀土Ce對高強鋼焊接熱影響區(HAZ)顯微組織、晶粒度和力學性能的影響。研究結果表明,焊接熱輸入為25 kJ·cm?1和50 kJ·cm?1時,無稀土鋼焊接熱影響區沖擊功分別為84.8 J和24.5 J,Ce質量分數為0.0018%的鋼焊接熱影響區沖擊功分別為110.0 J和112.0 J,因此鋼中加入適量Ce能夠有效改善鋼板焊接韌性。對比分析兩種實驗鋼焊接熱影響區晶粒尺寸和顯微組織可以看出,隨著焊接熱輸入值增大,高強鋼焊接熱影響區顯微組織均逐漸從馬氏體、下貝氏體轉變為上貝氏體和粒狀貝氏體組織,且奧氏體晶粒尺寸明顯增大。但相同焊接熱輸入下,含Ce鋼焊接熱影響區晶粒尺寸顯著減小,組織更加細小,且脆性的上貝氏體組織減少,從而顯著提高了700 MPa級高強鋼的焊接性能。

     

    Abstract: As the use of high-strength thick plates is increasing in marine engineering, bridge engineering, petroleum pipelines, and other fields, the required performance level of thick welded plates is also increasing. Oxide metallurgy technology, which is used to improve the toughness of heat-affected zones by controlling the formation and dispersion of high-melting-temperature oxide particles in steel, has attracted increasing attention by researchers in recent years. The effect of cerium on the welding performance of industrial quenched and tempered high-strength steel was investigated. Using a Gleeble 3500 thermal simulator, the coarse-grained heat-affected zones of high-strength steel were simulated with different cerium contents. The microstructures, austenite grains, and mechanical properties of the heat-affected zone were investigated by using optical microscopy, scanning electron microscopy equipped with energy dispersive spectrometry, and hardness testing. The results show that when the heat inputs are 25 kJ·cm?1 and 50 kJ·cm?1, the impact energies of the heat-affected zone of Ce-undoped steel are 84.8 J and 24.5 J, respectively. When the mass fraction of Ce is 0.0018%, the impact energies of the heat-affected zone are 110.0 J and 112.0 J, respectively. The different degrees of toughness of the two experimental steels indicate that the appropriate content of rare earth element can effectively improve welding performance. By comparing and analyzing the microstructures and prior-austenite grain sizes of the two experimental steels, it can be seen that with increases in the welding heat input, the microstructure of the heat-affected zone of the high-strength steel gradually transforms from martensite and lower bainite to upper bainite and granular bainite, and the average size of the prior-austenite grains in the heat-affected zone obviously increases. However, at the same welding heat input, the size of the prior-austenite grains in the heat-affected zone of Ce-doped high-strength steel is significantly smaller. The observed microstructure of Ce-doped steel is finer with a reduced content of brittle upper bainite, which significantly improves the welding performance of 700 MPa high-strength steel.

     

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