MA 组元对焊接热影响区粗晶区断裂行为的影响

将高强钢焊接热影响区中硬化组织ＭＡ组元视作局部硬化区（ＬＨＺ），采用二维有限元数值方法讨论了含ＬＨＺ材料的断裂机理．结果表明，含细长ＭＡ的热影响区比含块状ＭＡ的热影响区更容易产生裂纹．这一结果在高强钢焊接影响区ＣＴＯＤ试验中得到证实。

700MPa级高强耐候钢中MA组元的变化规律及其对性能的影响

采用热模拟试验和工业试验研究了卷取温度、冷却速度等工艺参数对700MPa级高强耐候钢中的MA组元和力学性能的影响。结果表明，随着卷取温度的提高，钢中的MA组元数量降低，尺寸减小；随着冷却速度的提高，MA组元分布更加弥散，但数量略有增加。工业试制结果表明，钢带在600-610℃卷取时可有效降低MA组元数量，细化MA组元尺寸，并可获得较高的屈服强度和良好的塑性。

EFFECT OF LOCAL HARD ZONE ONFRACTURE INITIATION OF WELD HAZ

The effect of the local hard zone (LHZ) distributed in the coarse grained HAZ (CGHAZ) has been analyzed by 2-dimensional FEM on a mechanical model of the weld CGHAZ. The existence of the LHZ elevates considerably the stress in LHZ and causes the discontinuity of strain at the boundary between the LHZ and the matrix. The stress distribution in the LHZ is strongly affected by the shape of the LHZ. In a slender LHZ almost the whole region in the LHZ is exposed to elevated stress, whereas in the massive LHZ only the edge region sustains high stress. The longer the LHZ becomes, the more the highly stressed area, and the peak stress in the LHZ grows even under the same volume fraction of the LHZ. These results indicate that the slender LHZ brings about unstable fracture at a lower load level than the blocky LHZ. This tendency was confirmed by CTOD test results on the weld CGHAZ of a high-strength steel. The CGHAZ with elongated M-A constituents fractures at apparently lower critical CTOD than the CGHAZ with massive M-A constituents. In conclusion, the control of the shape of the M-A constituent has a striking effect on the toughness improvement of CGHAZ.

冷却工艺对低焊接裂纹敏感性钢组织的影响

采用弛豫控制析出+加速冷却(RPC+ACC)和超快速冷却+加速冷却(UFC+ACC)2种不同冷却工艺试制低裂纹敏感性钢板,结合显微硬度、SEM及TEM技术分析了冷却工艺对显微组织及力学性能的影响。结果表明:RPC+ACC工艺试样的屈服强度和抗拉强度比UFC+ACC工艺高170 MPa和65 MPa,而且维持了相同的冲击韧性。获得含有大量位错胞的板条贝氏体组织,且不同尺寸的板条贝氏体被亚结构或位错墙分割,出现相互交错排列是RPC+ACC冷却工艺提高强度的主要机制。