超高強度鋼易磷化退火製程開發

Optimization of Phosphating Reaction by Annealing Process of Ultra-High-Strength Steels

因強度要求，超高強度鋼較軟鋼添加相對較高含量之合金元素，然常於汽車白車身進行磷化反應後，發現超高強度鋼磷化有底材裸露之不良現象，顯見合金元素組成差異對磷化具影響性。因冷軋鋼片需經退火熱處理以進行機性調整，超高強度鋼所含之鉻元素親氧性較鐵元素高，易於退火時發生氧化反應，故抑制氧化鉻為提升超高強度鋼磷化反應之主要目標。本研究於退火爐區提升氮氫混合還原保護性氣氛，並鑑別鉻元素對冷軋超高強度鋼磷化反應影響，利用極表面分析氧化層與元素分佈，並於磷化反應時進行電化學檢測後，發現超高強度鋼磷化不良之原因，主要為氧化鉻阻礙底材鐵元素與化成液進行磷化反應。經提升退火區還原保護性氣氛後，明顯抑制超高強度鋼之鉻氧化反應，且磷化反應之表面電化學阻抗亦明顯下降，觀察製程改善後磷化反應結果，具良好連續鍍覆性、結晶性且無底材裸露現象。

To enhance steels strength, ultra-high-strength steels possess higher alloying-elements content then mild steels. After vehicle assembling, phosphating process was conducted but phosphating reaction was hard to occur on ultra-high-strength steels. It is obvious that additional alloying-elements act as an obstacle issue to restrain phosphating reaction of ultra-high-strength steels. Moreover, annealing heat treatment was used to adjust steels mechanical property, chromium element of ultra-high-strength steels was easily oxidized during annealing. To minimize the occurrence of chromium oxidation and enhance the phosphating reaction of ultra-high-strength steels would be the main target in this investigation. Increasing mixed nitrogen-hydrogen atmosphere content during annealing, act as process modified factor to restrain the chromium oxidation reaction of ultra-high-strength steels. After annealing process modification, the harmful effects of chromium oxidation on ultra-high-strength steels phosphating was eliminated. By observation on phosphating ultra-high-strength steels, continuous coated and uniform phosphating crystalline without substrate exposure could be detected.