蠕变强度外推数据处理的EXCEL方法

蠕变强度是耐热钢和高温合金的重要力学性能指标之一。通常采用短时蠕变试验结果合理外推长时蠕变性能的方法获得蠕变强度。分析介绍了工程中常用的等温线法和时间-温度参数法外推蠕变强度的计算过程,利用EXCEL软件的趋势线、回归分析以及单变量求解功能实现了外推公式的拟合求解和蠕变强度的外推计算,为蠕变试验的数据处理和复杂外推计算过程的实现提供了一种简单、实用的操作方法。     

20CrNi4Mo螺栓用钢的高温持久性能

研究了新型螺栓用20CrNi4Mo钢的高温持久性能,在高温持久试验机上测定了该种螺栓用钢在350～450 ℃不同应力条件下的高温持久强度。用国际上普遍采用的等温线法、时间-温度参数法对试验数据进行拟合,得到了回归方程,并进行了外推估算。比对各种方法的拟合以及外推情况结果表明,拉森-密勒（L-M）参数法拟合及外推效果最好,因此,L-M参数法最适合于本文研究材料持久性能的预测。用L-M参数法外推20CrNi4Mo钢在工况温度为230 ℃、持久105 h时的强度极限,表明该螺栓用钢在此工况温度下应具有较好的持久性能。     

全磁无触点控温方法的应用

一、序言持久蠕变强度试验是衡量金属及合金材料高温性能中最常用的一个方法,它要求在固定的载荷与固定的温度下连续进行工作,有时长达数千个小时,这就必须有一个能连续长期工作并且温度衡定的电加热炉,根据持久蠕变试验的标准方法,要求电加热炉在整个试验中,炉膛温度的波动允许的误差如下表所示。     

铁素体-奥氏体异种钢接头高温失效原因的分析

通过用镍基合金、奥氏体和铁素体填充材料焊接的铁素体-奥氏体异种钢接头的蠕变断裂试验结果表明,材料之间的蠕变强度不匹配是异种钢接头高温运行中过早失效的主要原因。为了改善铁素体钢和奥氏体钢之间蠕变强度差别太大的问题,接入一段蠕变强度介于两者之间的过渡段,结果可使异种钢接头的蠕变断裂强度(寿命)达到铁素体同种钢接头的水平。     

TC4钛合金在200℃时的蠕变持久特性

研究了ＴＣ４钛合金在２００℃,１０００ｈ条件下的蠕变,持久特性,结果表明,该合金轧制棒材在２００℃和较低应力下具有蠕变饱和现象;１０００ｈ,残余变形量０．１％的蠕变强度为５６１ＭＰａ,１０００ｈ以内的持久强度极限为７７９．６３ＭＰａ,该值与试验持续时间无关。     

102钢(12Cr2MoWVTiB)持久强度统计分析

前言金属的高温持久强度是高温构件设计的主要指标。众所周知,金属材料的高温持久强度受化学成分、冶金工艺、热处理制度以及试验条件的影响。因而试验数据具有较大的分散性,只有应用统计分析方法来处理,才会得到满意的结果。特别是用短时间的试验数据,外推十万小时的持久强度必然会造成较大误差,如何正确评价材料的高温性能是关系到高温下工作部件的安全性和可靠性     

蠕墨铸铁缸盖蠕化率的超声波声速法检测

介绍了超声波声速法的适用范围,试验研究了利用超声波声速法进行蠕铁缸盖蠕化率的在线检测和产品检验的方法。通过试验得到了蠕化率与声速间的对应关系,回归性可达90%以上。采用穿透法可实现对蠕铁生产过程的在线检测,采用脉冲反射法可实现进行铸件本体材料的判断。     

蠕墨铸铁喂线蠕化处理工艺的研究

研究喂线蠕化处理工艺生产蠕墨铸铁的可行性,通过试验分析了蠕化芯线的化学成分及加入量对蠕化率的影响,确定了喂线蠕化的工艺参数.试验还通过对喂线法和冲入法的比较,体现出喂线工艺在生产中的优势.结果表明,喂线蠕化处理工艺可行,蠕化情况良好,蠕化率稳定.     

Al-Cu-Mn-Ti系耐热铸造合金高温蠕变性能研究

为探究新型耐热铸造铝合金Al-Cu-Mn-Ti的高温蠕变性能并探明合金有效热强化相，采用扫描电镜、EDS能谱分析、JMat-Pro材料仿真软件及蠕变持久性能测试等分析手段，对合金试样的显微组织、断口形貌和蠕变应变抗力进行了分析。结果表明，Al-Cu-Mn-Ti合金在250℃服役时合金中有效耐热相以θ′相为主，θ相、T相为辅，300℃时合金有效耐热相以T相、θ相为主；合金在300℃、100 MPa服役条件下测试，持久时间不超过40 h,且断裂方式呈塑性和脆性断裂同时发生；合金在250℃的蠕变强度极限达到了120 MPa,在300℃的蠕变强度极限达到了80 MPa。     

C-HRA-5钢焊接接头高温短时拉伸及持久强度预测

持久强度对于评价C-HRA-5钢焊接接头在复杂工况条件下的使用寿命具有极其重要的意义.通过不同温度下的高温短时拉伸试验,基于Larson-Miller参数,利用状态函数和全微分的特征,建立了C-HRA-5钢焊接接头持久强度预测的数学模型,外推10万小时的持久强度.结果表明:C-HRA-5钢焊接接头在650℃时强度和塑性最好,在700℃时呈现典型的微孔聚集性断裂,随着温度的升高,第二相颗粒和夹杂物增多,位错的塞积群增多,焊接接头的力学性能降低.700℃时外推拟合公式为lgσ=2.76018-0.13151 lgτ,外推10万小时的持久强度为σ973105=116.0203 MPa,高于ASME SA-213标准的要求.     

Creep Behavior and Life Assessment of a Novel Heat-Resistant Austenite Steel and Its Weldment

In the present study, creep activation energy for rupture was obtained as 221-348 kJ/mol for 22Cr15Ni3.5 CuNbN due to the precipitation-hardening mechanism. The extrapolation strength of creep rupture time of 10~5 h at 923 K for22 Cr15 Ni3.5 CuNbN is more valid(83.71 MPa) predicted by the Manson-Haferd method, which is superior to other commercial heat-resistant steels. The tensile creep tests ranging from 180 to 240 MPa at 923 K were conducted to investigate creep deformation behavior of welded joint between a novel heat-resistant austenite steel 22Cr15Ni3.5 CuNbN and ERNiCrCoMo-1 weld metal. Apparent stress exponent value of 6.54 was obtained, which indicated that the ratecontrolled creep occurred in weldment during creep. A damage tolerance factor of 6.4 in the weldment illustrates that the microstructural degradation is the dominant creep damaging mechanism in the alloy. Meanwhile, the welded joints perform two types of deformation behavior with the variation in applied stress, which resulted from the different parts that govern the creep processing. Also, the morphology evolution of the fracture surfaces confirms the effects of stress level and stress state.     

Al-Zn-Mg-Cu铝合金变温双级蠕变时效模型

针对Al-Zn-Mg-Cu合金变温双级蠕变时效过程,建立了一种考虑蠕变应变与屈服强度的本构框架,通过实验数据的简单拟合方法获得了模型参数。模型不仅以简单的形式具备了处理蠕变时效过程中的应力松弛、强化响应和温度变化的能力,而且能够应用到有限元软件中模拟构件的蠕变量、屈服强度和回弹。模型结果不仅能够适应不同外加应力下实测的蠕变应变曲线,且有限元模拟结果与实测结果能够很好地吻合。     

Microstructural stability and creep rupture strength of the martensitic steel P92 for advanced power plant

Japanese 9% Cr steel containing 0.5% Mo and 1.8% W (P92) has been investigated. Quantitative microstructural analyses using TEM of thin foils and extraction double replicas have been carried out after different austenitization and tempering treatments and after creep deformation at 600 and 650°C. Statistical quantitative analyses were undertaken to determine the dislocation density within the martensite laths, the width of the martensite laths/subgrains and the size and distribution of the carbide and carbonitride precipitates. Correlation of the results of the microstructural investigation with the creep rupture properties allowed the stability of the microstructure during the high temperature exposure to be assessed. The consequences of microstructural changes for the extrapolation of creep rupture data to design lifetimes are considered. Taking into account the strengthening mechanisms which remain effective in long term testing, the 100000 h stress rupture strength of P92 at 600°C is estimated at 115 MPa.     

螺杆泵性能测试综合软件系统设计

根据螺杆泵试验台的硬件组成及试验过程,利用VB6.0和DLL技术开发了用于螺杆泵性能测试的综合软件系统。研制的软件系统包括基础数据设置模块、数据实时采集模块、数据分析处理及曲线绘制模块、数据存档及报表生成模块。采用最小二乘法对试验点性能数据进行多项式拟合,以获得非试验点性能数据的预测值,提高螺杆泵性能测试的试验效率。利用VC++6.0将多项式拟合程序封装在标准DLL文件中,提升程序的通用性和可移植性。现场试验证明,该软件系统运行稳定,能满足对螺杆泵性能测试的功能要求,并能对试验数据进行准确、快速的分析与处理。     

T91/P91钢持久性能的统计分析及可靠性预测

利用Z参数方法分析了T91/P91(9Cr--1Mo--V--Nb)钢高温持久性能数据的统计分布规律. 结果表明:形状、热处理工艺等不同的T91/P91钢的高温持久性能数据交替重叠地分布在以应力σ--TTP(时间--温度参数)关系主曲线为中心的数据带中, 而表征T91/P91钢持久性能数据分散性的Z参数服从正态分布. 基于Z参数法对材料高温持久性能的可靠性分析结果, 提出了T91/P91钢的σ--TTP--可靠度R曲线、 σ--断裂时间t_r--R曲线和许用应力[σ]--温度T--R曲线.预测结果与NRIM及ECCC公开的实验数据均符合良好.     

Basic model for primary and secondary creep in copper

A model for primary and secondary creep is established. The starting point is a combination of basic models for tensile stress-strain curves and for secondary creep. The derived model can describe experimental creep strain curves for Cu 50 p.p.m. P in the temperature interval 75-250 °C with the same precision as the variation in the experimental creep strain curves for identical conditions. No fitting parameters are involved in this representation. The model has also been applied successfully to creep specimens with round notches, where multiaxial stress states are present. One main aim of deriving a basic creep model is to improve the accuracy of extrapolation. That this is possible has been demonstrated for creep tests with estimated secondary creep rates down to 5 × 10⁻²² s⁻¹. In conventional creep rupture testing strain rates down to 1 × 10⁻¹² s⁻¹ can be recorded. As a background, a summary of empirical methods for the extrapolation of creep strain data is given.     

The effect of W and N addition on the mechanical properties of 10Cr steels

The effect of W and N on the creep properties and microstructural degradation in 10Cr steels was studied. Creep testing was performed to determine the creep rupture strength and minimum creep rate. Transmission electron microscopy was used to observe the microstructural degradation during the creep deformation. W and N which were added to the 10Cr steel increased the creep rupture strength and decreased the minimum creep rate. As W and N were added, the thermal stability of the subgrain and carbide was improved, thus the growth of the subgrain and carbide during creep deformation was restricted. In W added steel, the Laves phase played an important role in increasing creep rupture strength. But the impact toughness was rapidly degraded by the addition of W after aging at 600°C for 5000 hours. So one must evaluate more accurately the effect of the Laves phase on long term creep and impact properties. In N added steel, V(C, N) was precipitated in the lath boundary and within the lath. The size of the precipitates was 20–50 nm. The increase of creep rupture strength in N added steel may be due to the precipitate of the V(C, N). Future tests are required to clarify the effect of N on creep and impact properties.     

Modelling creep rupture strength of ferritic steel welds

Abstract

Recent changes in the design of steam turbine power plant have necessitated the replacement of bolted flanges with welded joints. The design process therefore requires a knowledge of the creep rupture strength of the weld metal consumed in the welding process. This paper presents a method which can be used to estimate the creep rupture strength of ferritic steel weld metals, from a knowledge of the creep strength of wrought plates. The method is validated using published data.     

Study on gas metal arc welding procedure of stainless steel

Summary

This paper describes an investigation of the creep rupture properties of welded joints produced from W-containing 9Cr-Mo-W steel. The creep rupture properties of the HAZ are also studied using simulated HAZ specimens subjected to PWHT (post-weld heat treatment). The effect of W on the creep rupture strength of the welded joints is examined.

Creep rupture tests of GTA (TIG) welded joints are conducted. The longest creep rupture time is around 20 000 hours. In the creep rupture tests, the welded joints rupture in the base metal at higher applied stresses, rupturing in the low-ductility fine-grained HAZ adjacent to the base metal at lower applied stresses.

When the welded joints rupture in the base metal, their creep rupture strength is as high as that of the base metal. When the welded joints rupture in the HAZ, however, their creep rupture strength is lower than that of the base metal. The cracking which occurs in the HAZ is TYPE IV cracking which tends to affect the welded joints of ferritic heat-resistant steel. TYPE IV cracking is the type which occurs in the fine-grained HAZ at a lower stress than the creep rupture strength of the base metal without being associated with any heavy deformation.

In the creep rupture tests, the simulated HAZ specimens heated to a temperature around Ac1 and Ac3 give a lower creep rupture strength than that of the base metal. The simulated HAZ specimens heated to the Ac3 temperature give the lowest creep rupture strength.

A comparison of the creep rupture strengths of welded joints produced from 9Cr-Mo-W steel and 9Cr-1 Mo-Nb-V (mod. 9Cr-Mo) steel suggests that W improves the creep rupture strength of both welded joints and base metal.     

一种具有极高屈强比的高强钢的室温蠕变特性

利用MTS万能试验机研究了屈强比为99.7%的高强钢在不同加载应力条件下的室温蠕变行为,并对不同蠕变条件下的组织演变特征进行了分析。结果表明:在低于屈服强度的应力作用下,试验钢表现出明显的室温蠕变,且蠕变曲线呈现出以稳态阶段为主的双阶段室温蠕变特征。从蠕变曲线的拟合结果可知,曲线符合对数规律,并且蠕变速率随着蠕变时间的增加逐渐降低,其可相差两个数量级。在不同的室温蠕变条件下,该高强钢在室温蠕变过程中组织变化不明显,晶粒都以细小晶粒为主,多数为5 μm以下,且晶界都是以15°以下的小角晶界为主,而大角晶界多集中于50°~60°。