Background
The martensite heat-resistant steel has higher strength and hardness, and good high-temperature oxidation resistance and smoke corrosion resistance, and is widely applied to high-temperature component materials of thermal power generation equipment. In recent years, more than 1000 300MW subcritical boilers, more than 600-660 MW supercritical (super) boilers and more than 100 MW super supercritical (super) boilers have been put into operation in China in succession. However, in the long-term service process of the thermal power generating unit, the martensite heat-resistant steel and other high-temperature components are damaged by one or more factors such as creep, fatigue, corrosion and the like, and various changes can be generated on the structure. The failure of high-temperature components of the unit in the long-term operation process is one of the main factors influencing the safe and economic operation of the power plant, and whether the high-temperature components are safely and stably operated or not directly relates to the safety of the whole power plant. Therefore, the service life of the thermal power generating unit is managed in advance according to the tissue damage state of the material by analyzing the tissue damage degree of the martensite heat-resistant steel boiler pipeline and other power station high-temperature component materials in the long-term service process, and the method has very important significance for ensuring the safe operation of the thermal power generating unit.
At present, detection means commonly used for predicting the service life of the in-service power generation equipment material are generally based on means such as hardness, room temperature and high temperature tensile property detection, oxide scale detection and the like, and have certain defects in the aspects of detection reliability and accuracy.
Disclosure of Invention
The invention aims to provide a more accurate and effective method for evaluating the residual life of a martensite heat-resistant steel high-temperature component based on tissue damage characteristic parameter analysis.
In order to solve the technical problems, the technical scheme of the invention provides a method for evaluating the residual life of martensite heat-resistant steel, which is mainly characterized in that according to the corresponding trend relation between the width of a martensite lath of a martensite heat-resistant steel sample and the material life loss rate obtained by analysis under a Transmission Electron Microscope (TEM), the residual life of the service high-temperature component is calculated by micro-damage sampling of the martensite heat-resistant steel high-temperature component in the service process and the tissue damage characteristic parameter analysis of the sample.
The method comprises the following specific steps:
carrying out endurance tests on the martensite heat-resistant steel sample under different working conditions, and sampling at different time under different working conditions;
calculating the service life loss rate of the martensite heat-resistant steel according to the test data;
measuring the sampling, and measuring the average width of the martensite lath as a tissue damage characteristic parameter;
establishing a corresponding trend relation between the tissue damage characteristic parameters and the life loss rate;
locally sampling the martensite heat-resistant steel in service, measuring the width of the locally sampled martensite lath, and calculating the residual life according to the corresponding relation between the tissue damage characteristic parameter and the life loss rate.
The endurance test is a 5-grade stress endurance test of a martensite heat-resistant steel sample at a service temperature under a laboratory condition, and the longest test time is 3.3 ten thousand hours; at each stress, the test was stopped for test times of 3000 hours, 5000 hours, 10000 hours and 20000 hours, respectively, and intermediate sampling was performed.
Establishing a life loss rate model: the corresponding permanent fracture time of the sample under the same temperature and stress conditions (i.e. the actual life of the sample under the temperature and stress) is defined as taIf the actual endurance test time is t, the actual life loss rate corresponding to the test time t is m ═ t/ta. According to the above definition, for the original state sample, t is 0, and the life loss rate is 0; for a permanent fracture specimen, t ═ taThe life loss rate at the time of breakage of the specimen was 1.
Obtaining tissue damage characteristic parameters: according to the original state test sample and the martensite heat-resistant steel test samples under different stresses and test time, the martensite structure morphology in the test sample is observed under a Transmission Electron Microscope (TEM), and a TEM morphology photograph of 10 martensite lath structures is taken under a magnification of 10 k. And directly measuring the width of each martensite lath in each picture under related image processing software, and averaging the width measurement values of all the martensite laths to obtain the width of the martensite lath under the corresponding test condition of the sample.
Establishing a corresponding relation between the tissue damage characteristic parameters and the material life loss rate: and according to the obtained width values of the martensite laths in the samples under different test conditions, the service life loss rate of the samples is taken as an abscissa and the width value of the martensite laths is taken as an ordinate, and the corresponding trend relation of the width of the martensite laths along with the service life loss rate is obtained, so that a service life loss model of the martensite heat-resistant steel samples in the endurance test process is established.
Calculating the residual life: obtaining long-term service t by adopting a structure analysis means according to a service life loss model of a martensite heat-resistant steel sample in a endurance test processsThe width of the martensite lath of the martensite heat-resistant steel after the time is partially sampled, the corresponding service life loss rate m is determined according to the width of the martensite lath, and the actual service time is tsThen, the remaining life tr=ts/m-ts。
According to the method for evaluating the residual life of the martensite heat-resistant steel, the structure damage comprises the change of the internal structure of the material under the comprehensive action of temperature, stress and time.
The method for evaluating the residual life of the martensite heat-resistant steel is suitable for thermal power generating units which run for a long time and heat-resistant steel high-temperature parts with martensite structures, such as various boiler pipelines and the like.
The method can be used for accurately calculating the residual service life of the martensite heat-resistant steel high-temperature component of the thermal generator set after long-term operation, and provides more accurate basis for the safe operation and service life management of the thermal generator set.
The invention has the following beneficial effects:
the method tracks the change of the service life of the material through the change of the tissue damage characteristic parameters, and has the advantage of easy quantification.
The method calculates the residual service life of the high-temperature component of the service unit by establishing the corresponding trend relation between the material tissue damage characteristic parameter and the service life loss rate, and has the advantage of intuition.
The invention is suitable for martensite heat-resistant steel high-temperature components of thermal generator sets with various parameters.
Examples
The method takes a Transmission Electron Microscope (TEM) as a detection means, and carries out quantitative analysis on the tissue damage characteristic parameters of samples from different tissue damage states to a material life termination (fracture) state, so as to establish the corresponding relation between the width of a martensite lath of the martensite heat-resistant steel material and the life loss rate of the sample. And obtaining the width of the martensite lath of the martensite heat-resistant steel T91 boiler pipeline in the service state by sampling the micro-loss of the martensite heat-resistant steel T91 boiler pipeline in the long-term service process, obtaining the service life loss rate of the martensite heat-resistant steel T91 boiler pipeline according to the corresponding trend relationship, and calculating the residual service life of the martensite heat-resistant steel T91 boiler pipeline of the service unit.
The method comprises the following specific steps:
1) carrying out high-temperature endurance tests at service temperature and under different stress conditions under laboratory conditions;
2) carrying out quantitative analysis on tissue damage characteristic parameters on samples in different tissue damage states until the material service life is stopped (broken) by adopting a Transmission Electron Microscope (TEM);
3) establishing a corresponding relation between the width of a martensite lath and the service life loss rate of a martensite heat-resistant steel T91 boiler tube sample;
4) sampling the micro-loss of the boiler pipeline T91 in the service process to obtain the width of the martensite lath of the martensite heat-resistant steel in the state;
5) and calculating the residual service life of the martensite heat-resistant steel T91 boiler pipeline of the service unit according to the corresponding trend relation between the tissue damage parameter and the service life loss rate obtained under the laboratory condition.
According to the steps, the martensite refractory steel T91 boiler pipe local micro-loss sampling during the field service process is adopted in the embodiment, and the martensite lath width value inside the T91 boiler pipe sample is analyzed. And obtaining the service life loss rate of the T91 boiler pipeline made of the service heat-resistant steel according to the corresponding relation between the structure damage characteristic parameters of the corresponding martensite heat-resistant steel T91 material and the service life loss rate of the material, and further calculating the residual service life of the T91 boiler pipeline.
A T91 reheater pipeline of a certain thermal generator set which is in service for 12 ten thousand hours for a long time is sampled, the tissue damage state of the martensite heat-resistant steel T91 pipe sample after 12 ten thousand hours of long-term service is observed and measured through a Transmission Electron Microscope (TEM), and the width of a martensite lath, namely the tissue damage characteristic parameter is 520 nm. According to the relation between the width of martensite laths in the martensite heat-resistant steel T91 boiler tube and the service life loss rate of a sample, the service life loss rate m of the T91 boiler tube after 12 ten thousand hours of long-term service is obtained to be 0.48, and the residual service life T of the T91 reheater tube in service can be calculatedrIs 13 ten thousand hours.