不銹鋼高溫淬火溫降行為研究

Abstract

本研究提出得以合理預測高溫淬火過程中AISI 304不銹鋼直棒變形行為的表面熱傳條件。本研究使用長度6公尺，直徑分別為3公分與8公分的鋼棒，模擬1050°C不銹鋼棒於60°C環境的水平放置水淬過程。本研究在淬火過程的鋼棒的上、下表面使用不同的熱傳模型，其中兩者的熱傳係數為參考相關文獻結果決定。淬火的暫態熱傳過程使用計算流體力學軟體Ansys Fluent加以模擬，接著將暫態溫度場輸入有限元素分析軟體Ansys Mechanical以預測鋼棒暫態變形行為，並採用等向硬化模型描述淬火時鋼棒硬化的過程，其中鋼材的材料性質透過JMatPro軟體加以預測。利用本研究提出的模擬流程，改變鋼棒上、下表面的熱傳條件，可定量調整鋼棒的變形程度。本研究結果顯示，使用熱傳模型(300°C, 975°C) 並配合多線性或雙線性(使用應變為0.2的切線模量)的等向硬化模型，可成功重現長度6公尺、直徑8公分鋼棒在淬火過程中向上彎曲5公分的變形行為。

This study predicts the distortion of high-temperature AISI 304 stainless steel rods during quenching by proposing a proper heat transfer conditions for the surfaces of the rod. Six-meters-long steel rods with diameters of 30 mm and 80 mm heated up to 1050°C before a horizontal quenching in 60°C water is numerically studied. The heat transfer model employed in the simulation of the quenching process is distinctively defined for the upper and lower surfaces of the rod based on experimental evidences. The heat transfer coefficient (HTC) is determined using the HTC data proposed by various literature sources, ensuring a comprehensive and reasonable representation of the surface heat transfer. The transit heat transfer process is first simulated with Ansys Fluent, a computational fluid dynamics (CFD) software. The forecasted unsteady thermal field is then fed into Ansys Mechanical, a finite element analysis (FEA) software, to further calculate the induced distortion. To accurately capture the hardening effects of quenching, an isotropic hardening model is employed where JMatPro is used for estimating material properties under different conditions. With the proposed approach, the bending behavior of the steel rod can be favorably replicated in the quenching process. The numerical simulations indicate that the HTC curves of (300°C, 975°C) together with multilinear hardening model, or bilinear isotropic hardening model with E_0.2 is able to best describe a final distortion of 5 cm observed in the quenching process of steel rods with 80 mm diameter.