本文選題：熱作模具鋼　切入點：熱疲勞　出處：《湖北工業(yè)大學(xué)》2015年碩士論文

【摘要】：當(dāng)今社會,隨著科技的發(fā)展,模具被運用到越來越多的領(lǐng)域,各國的模具行業(yè)正在飛速向前發(fā)展,模具儼然已經(jīng)成為國民經(jīng)濟的重要產(chǎn)業(yè)了。鑒于熱作模具工作環(huán)境的惡劣性和復(fù)雜性而常常會伴隨著熱疲勞損傷失效破壞現(xiàn)象的發(fā)生,作為熱作模具鋼來說必須具有較高的高溫強度、高的紅硬性和回火穩(wěn)定性、良好的延展性和韌性、高的導(dǎo)熱系數(shù)、低的熱膨脹系數(shù)、良好的化學(xué)熱穩(wěn)定性等性能特點。針對熱作模具鋼嚴重的熱疲勞失效,許多科技工作者對熱作模具鋼的熱疲勞失效機理、止裂和修復(fù)技術(shù)給予了高度的關(guān)注,研究了不同的方法來進行止裂修復(fù)模具或延緩熱疲勞裂紋擴展,從而提高模具使用壽命。而脈沖電流處理技術(shù)作為近幾年來興起的一種對模具鋼疲勞損傷止裂修復(fù)的技術(shù)而逐漸被大量推廣應(yīng)用,此技術(shù)環(huán)保,無污染,節(jié)省能源,操作簡便迅速,安全,高效,值得大力推廣。本文首先采用實際實驗與數(shù)值模擬有限元相結(jié)合的方法對帶有預(yù)制切口的HG1鋼試樣通入脈沖電流處理,研究結(jié)果表明:施加的脈沖電流使預(yù)制切口尖端熔化變成橢圓形,發(fā)生鈍化現(xiàn)象,增大了切口尖端處的曲率半徑,,起到了部分修復(fù)的作用,同時還消除了一部分切口尖端的應(yīng)力集中,達到了止裂修復(fù)的目的,為后面實驗研究熱循環(huán)到300次后施加一次脈沖電流的這個最佳時機提供了理論依據(jù)。其次,本文還研究了對熱疲勞循環(huán)過程中的試樣施加一次脈沖電流處理后裂紋擴展的情況,采用Uddeholm熱疲勞法中的損傷因子來對裂紋情況進行標準評價,它是一種借助計算機圖像處理功能,采用Visual Basic編程處理,依據(jù)圖像中不同顏色的灰度值不同,針對熱疲勞后試樣的表面裂紋和深度裂紋進行計算機輔助評價分析的方法,通過這種對熱疲勞裂紋的評定方法再結(jié)合顯微硬度的變化情況,研究得出:施加一次脈沖電流處理在本實驗條件下對熱疲勞裂紋可以起到止裂修復(fù)的作用,且熱循環(huán)到300次后施加一次脈沖電流這個時機最優(yōu),同時,熱循環(huán)到3000次后試樣截面發(fā)生了軟化,表層到心部的硬度呈現(xiàn)先降低后升高且次表層硬度最低的趨勢。
[Abstract]:In today's society, with the development of science and technology, mould is applied to more and more fields. Mould has become an important industry of the national economy. Because of the bad and complex working environment of hot work mould, it is often accompanied by the phenomenon of thermal fatigue damage and failure. As a hot working die steel, it must have high high temperature strength, high red hardness and tempering stability, good ductility and toughness, high thermal conductivity, low thermal expansion coefficient, In view of the severe thermal fatigue failure of hot work die steel, many scientific and technological workers have paid great attention to the mechanism of thermal fatigue failure, crack arrest and repair technology of hot work die steel. Different methods for crack arrest and repair die or for delaying thermal fatigue crack propagation are studied. In order to improve the service life of the mould, pulse current treatment technology, as a kind of fatigue damage prevention and repair technology developed in recent years, has been widely used, which is environmentally friendly, pollution-free and energy saving. The operation is simple, rapid, safe and efficient, and it is worth popularizing. Firstly, the method of combining practical experiment with numerical simulation finite element method is used to treat the HG1 steel sample with prefabricated notch by pulse current. The results show that the applied pulse current causes the tip of the prefabricated notch to melt into an ellipse, resulting in passivation, which increases the radius of curvature at the tip of the notch and plays a partial role in repairing it. At the same time, the stress concentration at the tip of a part of the notch is eliminated, and the purpose of crack prevention and repair is achieved, which provides a theoretical basis for the later experimental study on the optimal time of applying a pulse current after 300 cycles. Secondly, In this paper, the crack propagation of the specimen during thermal fatigue cycle is also studied. The damage factor of Uddeholm thermal fatigue method is used to evaluate the crack situation. It is a method of computer aided evaluation and analysis of surface cracks and depth cracks of samples after thermal fatigue according to the gray value of different colors in the image by using Visual Basic programming with the help of the function of computer image processing. Through the evaluation method of thermal fatigue crack and the change of microhardness, it is found that the application of single pulse current treatment can prevent the crack from repairing under the experimental conditions. At the same time, the cross section of the specimen softened after 3000 cycles, and the hardness of the surface to the center decreased first and then increased, and the hardness of the subsurface layer was the lowest.
【學(xué)位授予單位】：湖北工業(yè)大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TG142.45;TG156.7

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1 賀榮翠;脈沖電流處理對HG1鋼熱疲勞裂紋擴展的影響研究[D];湖北工業(yè)大學(xué);2015年

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