超超临界机组用新型铁素体型耐热钢持久性能的预测研究

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	超超临界机组用新型铁素体型耐热钢持久性能的预测研究
	陈云翔
学位类型	博士
导师	杨柯 ; 单以银
	2012
学位授予单位	中国科学院金属研究所
学位授予地点	北京
学位专业	材料加工工程
关键词	铁素体型耐热钢持久性能性能预测多区时间-温度参数法 Cdm模型 Ferritic Heat Resistant Steels Creep-rupture Property Prediction Fo Properties Multi-region Ttp Method Cdm Model
摘要	"随着社会经济的发展，人们对环境及能源问题日益关注。近年来，很多国家都在大规模兴建超超临界火电机组，通过提高火电机组的发电效率来达到充分利用能源、防止环境污染的目的。为了满足超超临界火电机组的安全使用，发达国家开发了一批性能优异的新型铁素体型耐热钢，如T/P23、T/P24、T/P91、T/P92和T/P122钢等。但是，传统的持久性能预测方法仍然存在着很大的局限性。不论是早期使用的等温线外推法，还是之后出现的精度较高的时间-温度参数法，都容易高估新型铁素体型耐热钢的持久性能。为了分析现有持久性能预测方法高估新型铁素体型耐热钢的原因，本文首先从蠕变机制、蠕变损伤、断裂机制三个方面对新型铁素体型耐热钢进行研究、分析和讨论，得到如下主要研究结果：新型铁素体型耐热钢属于第二相粒子弥散强化耐热材料，其应力σ与稳态蠕变速率的关系图能反应出材料的蠕变机制（本文使用600℃下的T/P91钢为研究材料），可大致将之分为三个区域：当应力低于50MPa时，蠕变主要以空位扩散的方式进行；当应力高于130MPa时，蠕变主要以位错移动的方式进行，此时位错按Orowan机制绕过第二相粒子。当应力在50MPa和130MPa之间时，蠕变以位错移动的方式进行，此时位错主要以攀移的方式越过第二相粒子，但有其他变形机制同时起作用。 9~12%Cr系耐热钢的组织演变比2%Cr系耐热钢更为复杂。2%Cr系耐热钢的组织演变主要为第二相粒子的粗化，9~12%Cr系耐热钢的组织演变除了第二相粒子的粗化外，还有马氏体板条的粗化。结合显微硬度的测量，推测出材料强度的下降是造成9~12%Cr系耐热钢的σ-τ双对数曲线偏离线性关系的主要原因，但很可能不是造成2%Cr系耐热钢的σ-τ双对数曲线偏离线性关系的主要原因。在本文试验的应力范围之内，三种9~12%Cr系耐热钢的断裂机制不发生变化，均为韧性穿晶断裂。而2%Cr系耐热钢的代表材料T23钢高应力条件下为韧性穿晶断裂，低应力条件下变为脆性沿晶断裂。因此推测材料断裂机制的变化很可能是造成2%Cr系耐热钢的σ-τ双对数曲线偏离线性关系的主要原因。基于以上三个方面的分析结果，进一步研究和分析了近来倍受关注的多区时间-温度参数法和CDM模型，得到如下主要结论：对于新型铁素体型耐热钢，典型的时间-温度参数法Orr-Sherby-Dorn方程中的蠕变激活能Q值不会是一个常数。对于2%Cr系耐热钢可以近似地认为Q值为常数，不会产生很大的误差；对于9~12%Cr系耐热钢在高低应力区应使用不同的Q值，即所谓的多区时间-温度参数法。在600℃的高应力范围内，可采用CDM模型来模拟T/P91钢的蠕变曲线。如果不考虑各种蠕变损伤影响，则模拟计算得到的蠕变断裂时间要远长于试验结果。而考虑Laves相粗化（Dp）、溶质原子Mo贫化（Ds）、空洞形核长大（DN）三种蠕变损伤机制的影响后，模拟计算所得到的蠕变断裂时间与试验结果吻合较好。"
其他摘要	"With the development of social economy, the problems of environment and energy sources have attracted great public attentions. Many countries have built up a mass of ultra super critical (USC) power plants, because the enhancement of electricity generating efficiency can achieve the aim of protecting environment and saving energy sources. For withstanding the more severe service conditions in power plants, many advanced ferritic heat resistant steels have been quickly developed, such as T/P23, T/P24, T/P91, T/P92 and T/P122 steels. However, the conventional creep-rupture property assessment methods have shown big limitation. Both the early extrapolating method under constant temperature and the time-temperature-parameter (TTP) method showed a risk of over-estimating the creep-rupture property of advanced ferritic heat resistant steels. In order to analyze the reason of over-estimating by the conventional creep-rupture property assessment methods, this problem is studied in this deserattion from creep mechanism, creep damage mechanism and creep rupture mechanism, and the main results are listed as below: Advanced ferritic heat resistant steels are second phase particles strengthened steels, and creep mechanism can be analyzed (T/P91 steel at 600℃ in the desertation) based on the relationship of the minimum creep rate and applied stress σ. The creep data can be divided into three data sets. When the applied stress σ is lower than 50MPa, the creep is controlled by the migration of vacancies. When the applied stress σ is higher than 130MPa, the creep should be dominated by the glide of dislocations and dislocations would by-pass second phase particles by Orowan mechanism. When the applied stress σ is between 50MPa and 130MPa, the creep is also dominated by the glide of dislocations, but dislocations by-pass the second phase particles by climbing mechanism. Under this condition the creep may be simultaneously controlled by two different mechanisms. Compared with 2% Cr heat resistant steels, the microstructural evolution of 9~12% Cr heat resistant steels is more complicated. The microstructural evolution of 2% Cr heat resistant steels mainly consists of the coarsening of second phase particles, and that of 9~12% Cr heat resistant steels is composed of both the coarsening of second phase particles and the widening of martensitic laths. Through the measurement of Vicker’s hardness, it can be concluded that the decrease of material strength may be the main reason for the out of linear relationship between lgσ and lgτ for 9~12% Cr heat resistant steels, but this may not be the main reason for that between lgσ and lgτ for 2% Cr heat resistant steels. Under the stress range in this desertation, the creep rupture mechanism of three 9~12% Cr heat resistant steels did not change, and the creep rupture mechanism was a ductile intragranular fracture. However, under the high stress level the creep rupture mechanism of T23 steel, a representative 2% Cr heat resistant steel, was a intragranular ductile fracture, and under the low stress level the creep rupture mechanism of T23 steel was a brittle intergranular fracture. It can be concluded that the change of creep rupture mechanism may be the main reason for the out of linear relationship between lgσ and lgτ for 2% Cr heat resistant steels, but this may not be the main reason for that between lgσ and lgτ for 9~12% Cr heat resistant steels. Based on the analysis of three aspects above, in this desertation two creep-rupture property assessment methods, multi-region TTP method and CDM (continuum damage mechanics) model, were analyzed as below: In Orr-Sherby-Dorn method which is a representative TTP method, the activation energy Q is not a constant for all the advanced ferritic heat resistant steels. The activation energy Q can be approximately reckoned as a constant for 2% Cr heat resistant steels. The activation energy Q changes from a high value in short-term creep region to a low value in long-term creep region for 9~12% Cr heat resistant steels, which is so called multi-region TTP method. CDM model was used to simulate the creep curves of T/P91 steel under high stresses. When the influence of creep damage was neglected, the rupture time calculated by CDM model was longer than the experimental data. When the influences of the coarsening of Laves phase (Dp), the solute (Mo) depletion from the matrix (Ds) and cavity nucleation and growth (DN) were taken into account, the modeled creep curves were well in agreement with the experimental data."
文献类型	学位论文
条目标识符	http://ir.imr.ac.cn/handle/321006/64443
专题	中国科学院金属研究所
推荐引用方式 GB/T 7714	陈云翔. 超超临界机组用新型铁素体型耐热钢持久性能的预测研究[D]. 北京. 中国科学院金属研究所,2012.