Solidification Cracking Susceptibility of Stainless Steels: New Test and Explanation
Solidification Cracking Susceptibility of Stainless Steels: New Test and Explanation
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DOI：
10.29391/2020.99.024
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发表时间：
2020-10
期刊：
影响因子：
2.2
通讯作者：
Kun Liu;P. Yu;S. Kou
中科院分区：
文献类型：
--
作者：
Kun Liu;P. Yu;S. Kou
奥氏体、铁素体和双相不锈钢对凝固裂纹的敏感性通过新的横向运动可焊性（TMW）试验进行了评估。重点是奥氏体不锈钢。304 L和316L最不感病，321极显著感病，310极感病。然而，一些321焊缝甚至比304 L焊缝更不易受影响。发现这321个焊缝具有更细的晶粒以更好地抵抗凝固裂纹。焊接过程中的淬火321表明，通过异质形核可以发生自发晶粒细化。对于304 L、316 L和310，基于柱状枝晶之间液体的连续性提出了对敏感性的新解释;不连续的孤立液体允许枝晶之间的结合早期发生，以更好地抵抗开裂。在304 L和316L中，枝晶边界液体是不连续的和孤立的，如淬火所揭示的。该液体可能通过快速反向扩散到α-枝晶（体心立方）和L + β-枝晶+ β-枝晶反应（在形成β-枝晶的同时消耗L）而耗尽。然而，在310中，树突被连续的液体分开，这阻止了它们之间的早期结合。反向扩散进入面心立方的枝晶要慢得多，并且L + β + β反应形成的β很少。淬火还揭示了在固化结束后很久在304 L和316L中形成的骨架/花边裂纹;因此，骨架/花边裂纹不抵抗固化开裂，正如几十年来广泛认为的那样。TMW测试进一步证明，更多的硫和较慢的焊接都可以增加敏感性。
The susceptibility of austenitic, ferritic, and duplex stain-less steels to solidification cracking was evaluated by the new Transverse Motion Weldability (TMW) test. The focus was on austenitic stainless steels. 304L and 316L were least susceptible, 321 was significantly more susceptible, and 310 was much more susceptible. However, some 321 welds were even less susceptible than 304L welds. These 321 welds were found to have much finer grains to better resist solidification cracking. Quenching 321 during welding revealed spontaneous grain refining could occur by heterogeneous nucleation. For 304L, 316L, and 310, a new explanation for the susceptibility was proposed based on the continuity of the liquid between columnar dendrites; a discontinuous, isolated liquid allows bonding between dendrites to occur early to better resist cracking. In 304L and 316L, the dendrite-boundary liquid was discontinuous and isolated, as revealed by quenching. The liquid was likely depleted by both fast back diffusion into -dendrites (body-centered cubic) and the L + + reaction, which consumed L while forming . In 310, however, the dendrites were separated by a continuous liquid that prevented early bonding between them. Back diffusion into -dendrites (face-centered cubic) was much slower, and the L + + reaction formed little . Quenching also revealed skeletal/lacy formed in 304L and 316L well after solidification ended; thus, skeletal/lacy did not resist solidification cracking, as had been widely believed for decades. The TMW test further demonstrated that both more sulfur and slower welding can increase susceptibility.