耐热钢的高温松弛与蠕变关系的研究及应用

发布时间：2018-08-21 13:03

【摘要】：在现代工业中,高温、高压设备应用的日益广泛以及其逐渐向更高温度、更大压力方向发展的趋势迫使人们快速开发新的可适用材料,同时也使人们更为关注服役材料的安全性。持久性能是保证材料安全服役的重要指标,通常采用蠕变持久实验的方法来获得,但是该方法存在着周期长、材料需要量大、能耗高等缺点,制约着人们对材料蠕变性能的快速认知,进而降低新材料的研发速度。因此,迫切需要一种快速且准确的持久性能预测方法。应力松弛实验作为一种蠕变信息的快速获得方法,可以用于快速的分析材料的蠕变持久性能。基于此,本文以具有典型BCC和FCC晶体结构的数种耐热钢材料为研究对象,分别开展了应力松弛实验和蠕变持久实验,探讨了应力松弛过程中的蠕变速率(称为松弛蠕变速率,εSRT)与恒载荷蠕变的最小蠕变速率εmin)的关系及相关因素的影响作用,分析了稳态松弛蠕变和稳态恒载荷蠕变的变形机制,并提出了基于材料的应力松弛行为快速且高精度的预测持久性能的方法。研究发现,材料的松弛蠕变速率与最小蠕变速率的大小关系较为复杂,受材料、温度(T)和应力(σ)等因素影响作用较大。其中,材料因素的影响作用主要在于两种稳态蠕变阶段的微观组织差异,与材料晶体结构类型关系不大；当温度条件为T/Tm≥0.60且应力条件为σ/σ0.2≤0.40时,不同材料都表现出εmin与稳态εSRT大小相接近现象,超出这个条件范围的εmin与稳态εSRT大小关系则较为复杂。与此同时,本文也提出了稳态松弛蠕变速率与最小蠕变速率的相互转化模型,并在多种材料中得到了验证。通过分析数种材料在稳态松弛蠕变阶段和稳态恒载荷蠕变阶段的应力指数、表观激活能和表观激活体积的大小,本文认为：εmin与稳态εSRT大小相近现象的产生与幂律失效蠕变无关,而与位错攀移、粘滞性滑移和扩散蠕变等应力指数较低的幂律蠕变有关；稳态松弛蠕变过程中表观激活体积随应力降低而增大的现象表明低应力的稳态松弛蠕变行为对热激活运动依赖性较强。另外,Tm为熔点绝对温度,σ0.2为发生0.2%塑性应变时的屈服应力。在预测持久性能方面,传统的基于蠕变持久实验的断裂时间数据和最小蠕变速率数据的方法在预测结果上相差不大,但是仅采用时间相对较短的蠕变持久实验数据来预测的持久性能可能与真实蠕变数据差异较大,这意味着传统方法在高精度预测材料持久性能时较为依赖于长时间的蠕变持久实验数据。而通过应力松弛实验数据结合少量的高应力蠕变持久实验数据的方法可以高精度的预测材料的持久性能,其预测结果比仅采用短时间蠕变持久实验的传统预测方法具有更高的精度,并且与真实蠕变数据相差不大。
[Abstract]:In modern industry, the increasing application of high-temperature and high-pressure equipment and its trend towards higher temperature and greater pressure force people to develop new and applicable materials quickly. It also makes people pay more attention to the safety of service materials. The durability property is an important index to ensure the safe service of materials, which is usually obtained by creep rupture test. However, this method has many disadvantages, such as long period, large material requirement, high energy consumption, and so on. It restricts the rapid understanding of creep properties of materials, and then reduces the speed of research and development of new materials. Therefore, there is an urgent need for a fast and accurate durable performance prediction method. As a fast method to obtain creep information, stress relaxation test can be used to analyze the creep rupture properties of materials. Based on this, stress relaxation experiments and creep rupture tests were carried out on several heat-resistant steel materials with typical BCC and FCC crystal structures, respectively. The relationship between creep rate (called relaxation creep rate, 蔚 SRT) and minimum creep rate 蔚 min (constant load creep) and the influence of relative factors on creep rate during stress relaxation are discussed. The deformation mechanism of steady relaxation creep and steady state constant load creep is analyzed. A fast and high precision method for predicting the rupture performance based on the stress relaxation behavior of materials is proposed. It is found that the relationship between the relaxation creep rate and the minimum creep rate is more complex, which is influenced by the factors such as material, temperature (T) and stress (蟽). Among them, the effect of material factors is mainly due to the difference of microstructure between the two steady state creep stages, and has little relation to the crystal structure type of the material, when the temperature condition is T/Tm 鈮，

本文编号：2195818