SUS 403麻田散鐵不銹鋼經熱機處理之機械及超音波特性研究

Study on Mechanical and Ultrasonic Properties of SUS 403 Martensitic Stainless Steel after TMT Treatments

黃昭然(Chao-Jan Huang)

指導教授 ： 許正勳

大同大學/工程學院/材料工程學系所/碩士(2007年)

摘要

SUS 403麻田散鐵不銹鋼可用於高應力組件，是一種常用的核電廠材料。本研究乃針對SUS 403麻田散鐵不銹鋼晶粒粗大的缺失採用熱機處理(Thermal mechanical treatment，TMT )製程，並配合超音波特性之檢測，探討其晶粒細化、機械性質(抗拉強度、延性、衝擊韌性等)與超音波特性之關係，以尋求提昇機械性質之最佳化熱機處理製程條件，並直接利用超音波音速變化來評估晶粒大小。
實驗結果顯示，麻田散鐵系403不銹鋼在1010℃沃斯田鐵化2hrs後可以使碳化物重新固溶於基地，使硬度值增加。隨著輥軋量的增加，403麻田散鐵不銹鋼之晶粒也隨之變小，輥軋量愈大，晶粒愈小(rolled 20%為20~60µm，rolled 40%為10~20µm)，此時材料之機械性質也隨晶粒細化而變好。
回火300℃至600℃時有碳化物析出，由於在500℃回火時出現二次硬化之現象，使材料之硬度、抗拉強度在此溫度時最高，但衝擊值、伸長率則最低。回火於600℃時麻田散鐵分解成肥粒鐵，因此硬度、抗拉強度在此溫度最低，而衝擊值、伸長率受肥粒鐵鈍化之影響而增加。
在超音波特性方面，由實驗結果得知超音波之音速與輥軋量成反比，回火溫度成正比。超音波音速之衰減係數與輥軋量成正比，而與回火溫度成反比。特別是在400℃至500℃區間可由超音波之音速v(rolled 20%為5888~5894m/s、rolled 40%為5886m/s)及衰減係數α(rolled 20%為0.130054 dB/mm、 rolled 40%為0.134408 dB/mm)判定SUS403不銹鋼之回火脆性現象。

關鍵字

麻田散鐵不銹鋼 ； 熱機處理 ； 晶粒大小 ； 機械性質 ； 超音波特性

並列摘要

SUS 403 martensitic stainless steels is commonly used in high stress parts such as nuclear power plant. This research has used thermal mechanical treatment (TMT) to improve the disadvantages of coarse grain size of SUS 403 stainless steels. In general, finer grain sizes have several advantages on mechanical properties, such as increasing ultimate tensile strength, ductility, hardness and impact toughness. Also, the degree of grain fineness can result in the difference in ultrasonic responses because the sound waves traveling in the material interact with grain boundaries which show up the variation of ultrasonic velocity and ultrasonic attenuation. Thus, the purpose of this study is to explore the possibility that grain size refinement of SUS 403 by TMT processing and the relationship between its mechanical properties and ultrasonic characteristics.
It was found that the as-received SUS 403 was composed of ferrite and martensite phases with high chromium alloy carbides at grain boundary. After austenitization at 1010℃ for 2hrs, the carbides was dissolved into matrix. In addition, the grain sizes were refined with the increase of the rolled amount. The average grain size is 60~100µm for 20% rolled material and 10~20µm for 40% rolled material as compared to the as-received (>100µm). Moreover, the mechanical properties consisting of tensile strength, ductility, hardness and impact toughness were all improved when the grain sizes were refined.
From the experimental results, it was also found that the carbides reappeared after tempering at 300℃~600℃. In particular, tempering at 500℃, fine alloy carbides were precipitated from martensite resulting in secondary hardening of this material. However, elongation decreased. Higher temperature tempering (>600℃) could increase impact toughness and ultimate tensile strength but hardness decrease. It is because martensite was decomposited to form ferrite.
In the case of ultrasonic properties, it was found that ultrasonic velocity decreased and ultrasonic attenuation increased with the refinement of grain size. Moreover, it was found that the second hardening occurred at the ultrasonic velocity of 5888~5894m/s for 20% rolled material and of 5886m/s for 40% rolled material; and its ultrasonic attenuation is 0.130054dB/mm for 20% rolled material and 0.134408dB/mm for 40% rolled material, respectively.

並列關鍵字

ultrasonic ； Martensite stainless steels ； TMT

參考文獻

1. J.A. Wert, “Grain Refinement and Grain Size Control in Superplastic

3. S. C. Lee, J. M. Suen, “Ultrasonic Nondestructive Evaluation of Matrix

4. H.J.Meyer, “Inspection of Gray Iron Castings by Ultrasonic

edition, Edward Arnold, London, 1995, p.251.

Guidestandard Practices and Procedures for Steels”, American Society