鋼胚在連鑄溫度的強度與延性

The Strength and Ductility of Steel at Continuous Casting Temperatures

陸木榮(Muh-Jung Lu) ； 林冠儒(Kuan-Ju Lin)

《鑛冶：中國鑛冶工程學會會刊》 35卷2期 (1991/06) Pp. 16-28

https://doi.org/10.30069/MM.199106_35(2).0002

摘要

在連鑄過程中，從模內凝殼的生成開始，經二次冷却，以至於最後鋼液完全凝固成鋼胚，鑄胚歷經了繁複的熱應力與機械應力的作用。一般咸信，鑄胚表面裂與內裂的生成主要是在鋼胚受應力時的熱延性與強度欠佳所致。為瞭解鋼胚裂縫的成因，並提供煉鋼廠澆鑄製程，二次冷却改善的參考，本計畫針對鑄胚的高溫機械性質做基礎研究，利用Gleeble動態熱機儀器來拉伸測試各鋼種（Group 10-50）在受力下連鑄溫度的強度與延性。結果顯示各鋼種皆存有二脆性區，（i）700℃〜900℃，（ii）近溶點區。兩區的SEM，EPMA破斷面分析顯示，在700℃〜900℃之脆性區，其脆斷原因在Ac_8以上為NbC/AIN之析出於晶界，導致沿晶界區域強度降低所致。在Ac_3以下則除了NbC/AIN之析出影響外，ferrite的生成是導致最低延性之主因。在近溶點區之脆斷，主要是由於P，S等元素的偏析現象，形成低溶點化合物存於柱狀晶間所致。另外應變率，試棒溶解與否，與Nb元素對延性的影響亦詳加討論。最後並測試鋼材在熱彎曲變形下之脆裂情形，做定性的比較。

並列摘要

During continuous casting, from the shell in the mould, through secondary cooling, and till the completely solidified slab, the strand has been experienced various thermal and stress cycles. The surface/internal cracks would form if the ductility and strength of slab are poor. To understand the cracking mechanism and improve the surface quality for casting practice, especially for secondary cooling, the hot ductility and strength of steel slabs were studied via reheated and in-situ melted and solidified tensile test method using GLEEBLE 1500. The results show there exists two temperature zones where embrittlement is noticed, i. e. , (I)700-900℃and(II)near the melting point. From SEM, EPMA analysis, in zone I, above Ac_3 embrittlement is caused by NbC/AlN ppts, along the grain boundary. Below AC_8, besides the NbC/A1N ppts, the pro-ferritt film along the grain boundary is the primary factor for minimum ductility. In zone II embrittlement is caused by residual film from P, S segregation. The effects of strain rate and Nb element on hot ductility are also discussed. Finally, the hot-bend test was performed for qualitative comparison.