低合金钢焊缝的针状铁素体微观组织
Acicular ferrite microstructure of weld metal for low-alloy steel
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摘要: 针对X70管线钢多道焊焊缝金属,利用Gleeble1500热模拟机进行了热模拟试验,对焊缝金属中初生针状铁素体组织及其与非金属夹杂物之间的关系以及经历二次热循环后感生形核的针状铁素体组织进行了SEM及TEM分析。结果表明,针状铁素体边界存在着一层富碳的薄膜,其长大既存在切变转变的特征,同时也伴随着C原子的扩散过程。共感生成的二次针状铁素体是在初生针状铁素体基体的高密度位错处形核并以一定的速度迅速长大到有限的尺寸。初生针状铁素体和共感形核针状铁素体都是在奥氏体晶内形核、长大,都具有细化奥氏体晶粒、提高多道焊焊缝金属和焊接热影响区韧性的作用。Abstract: For understanding the microstructure acicular ferrite(AF), the thermal simulation test of weld metal in X70 pipe-line steel was carried out with GLEEBLE 1500.SEM and TEM were used to analysis the relations between the inclusions and the AF, and the C concentration distribution along AF boundary and the characteristics of sympathetic AF sufferred from secondary heat cy cling.The results show that there exits a layer of thin C-riched film along the AF boundary, and both the shear mechanism and the C diffusion were occurred during AF growth.The sympathetic AF nucleated on the site of high density dislocation of the primary AF and grown into specific size rapidly.Both the AF and sympathetic AF were nucleated and grown-up in the austenite grain, and were good to fine-grained strengthening effect in the multi-pass weld metal and HAZ.
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Key words:
- low-alloy steel /
- weld metal /
- acicular ferrite /
- microstructure
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