Critical level of intergranular fracture to affect the toughness of embrittled 2.25Cr-1Mo steels

In general, the low-temperature brittle fracture mode of unembrittled ferritic steel is transgranular cleavage. During temper embrittlement, impurity elements, such as sulfur (S), phosphorus (P), antimony (Sb), arsenic (As), and tin (Sn), segregate to prior austenite grain boundaries, which results in a decrease in the grain boundary cohesive strength. As a result, the brittle transgranular cleavage fracture mode changes to intergranular decohesion in association with the decrease in the critical fracture (stress (σ _F) as well as the fracture toughness (K). However, the appearance of intergranular facets on the fracture surface does not cause a decrease in the K and σ _F values. In this work, quenched and fully tempered 2.25Cr-1Mo steel (in an unembrittled condition that exhibits almost 100% brittle transgranular cleavage fracture) has been embrittled for 24, 96, and 210 h at 520 °C to produce different proportions of intergranular fracture. These unembrittled and embrittled steel specimens were tested to measure K (at −120 and −196 °C) and σ _F (at −196 °C). The experimental results and detailed fractographic observations show that the K and σ _F values decrease with an increase in the area fraction of intergranular fracture, provided that the area fraction of the intergranular facet on the brittle fracture surface exceeded a certain critical level, approximately 20–22%.     

Intergranular fracture on fatigue fracture surface of 2.25Cr-1Mo steel at room temperature in air

Low-alloy steels serving for a long time at high temperature (∼500 °C) are very sensitive to temper embrittlement due to segregation of various trace elements at prior austenite grain boundaries and/or carbide/matrix interfaces. This type of segregation in combination with various environmental effects can adversely affect the fracture resistance and fatigue crack propagation rate with subsequent change in the fracture morphology of low-alloy steels. The present work describes the effects of heat treatments on impurity element segregation and its subsequent effects on fatigue fracture behavior of 2.25Cr-1Mo steel under different environmental conditions and temperatures. It has been found that either prior impurity element segregation caused during the heat treatment or hydrogen-induced embrittlement due to the presence of water vapor in laboratory air alone cannot produce intergranular fracture on the fatigue surfaces of 2.25Cr-1Mo steel at room temperature in air. The occurrence of intergranular fracture on the fatigue surfaces results from the combined effect of impurity element segregation-induced grain boundary embrittlement and hydrogen-induced embrittlement, and that the proportion of intergranular fracture is a function of prior impurity element segregation provided that the grain boundary segregation level exceeds a certain critical value.     

2.25Cr-1Mo钢连铸圆坯端面缺陷分析和预防

通过对 2.25Cr-1Mo钢连铸圆坯锯切面出现的裂纹和“花样”缺陷进行了研究分析，发现这两种缺陷均属于解理断裂。通过对解理断裂机理的研究并结合实际情况，提出了防止解理断裂的措施：铸坯高温入坑、降低冷却速度；实施去应力退火，实现原子重排、推进位错行动并消除位错聚集。     

2.25Cr-1Mo不锈复合钢板厚壁容器的焊接

主要介绍了2.25Cr-1Mo不锈复合钢板的焊接工艺试验和工艺评定，阐明了2.25Cr-1Mo锈复合钢板焊接工艺的可行性，实践证明，该工艺能满足使用要求。     

2.25Gr-1Mo钢基于平衡晶界偏聚理论的连续脆化机理研究

和505℃.     

2.25Cr-1Mo钢回火过程中碳化物析出顺序的研究

采用化学相分析的方法研究了2．25Cr-1Mo钢粒状贝氏体组织在回火过程中碳化物的变化和析出顺序。结果表明，当回火参数为18140～22000时，试验钢中析出合金碳化物的类型为M2(CN)，M6C，M4C3，Cr9C3以及M23C6；合金碳化物的析出顺序为M2(CN)→M6C→M7C3，Cr7C3→M23C6，而且这些合金碳化物的变化过程是一系列重迭的阶段。     

Change in the ductility properties of 2.25 Cr-1 Mo steel during post-welding heat treatment

A major problem associated with the use of steels at elevated temperatures in the chemical, petrochemical and power industries, is not only that of hydrogen embrittlement and creep, but also the loss of ductility related to the content of low-alloy trace elements. This phenomenon is known as temper embrittlement. Temper brittleness is associated with embrittlement due to heat treatment, rather than that due to a long period of exposure to high temperatures under working conditions. Since Polish technical literature does not have a term describing this phenomenon, the authors will use the expression 'loss of ductility' or 'working brittleness'. This particular embrittlement is caused by the segregation of phosphorus, tin, antimony and arsenic on the grain boundaries of the primary austenite during prolonged working life, or a low rate of cooling of the steel within the temperature range of 550 to 350°C. It manifests itself in the lowering of the impact strength or in the rising of the brittle fracture transition temperature (Fig.1).     

Effect of tempering on the toughness of a Cr- Mo bainitic steel

The effect of tempering on impact and fracture toughness properties of a Cr-Mo bainitic steel was studied in the quenched and stress relieved (Q & SR) condition. The lowest tempering parameter used resulted in considerable improvement in impact properties. Further tempering increased the upper shelf energy, had a minor effect on the transition temperature, and increased both the initiation fracture toughness (J_IC) and the tearing modulus(T). However, the effect on J_IC andT was much greater than the effect on the impact upper shelf energy. The results were discussed in light of the changes in microstructure and flow properties due to tempering.     

加载速率对结构钢力学性能和断裂韧度的影响

在常温下进行了常用建筑结构钢(16Mn和Q235B钢)动态拉伸和动态断裂韧度试验。试验结果表明，材料在动载下无论是屈服强度还是抗拉强度均有一定的提高，塑性有了一定的降低；由于缺口尖端区域温度的升高，常温下动载对于16Mn钢母材和焊缝的断裂韧度是有利的；Q235B钢常温下，焊缝的断裂韧度值较低，且动载对母材的断裂韧度影响较大，和静载相比动载下断裂韧度值降低了4倍有余，可以看出，Q235B钢的抗震性能较差。通过研究发现，对于低韧度水平的材料，研究动载下结构的断裂行为时．材料的强度也应该作为一个考虑因素。     

Low-temperature fracture toughness of a heat-treated mild steel

Specimens from a 0.14 % C mild steel were austenitized at 1000 °C for 1 h and thereafter furnace-cooled or isothermally transformed at 700 °C for 0.5,2, and 8 h. The microconstituents present in the as-received material were ferrite and pearlite and their amounts did not substantially change even after heat treatment. The impact energy of the as-received and the furnace-cooled materials increased from 4 to 89 J and from 4 to 108 J, respectively, when the temperature was changed from - 196 to 23 °C. For these materials, the failure mode was by ductile fracture at 0 and 23 °C and by quasicleavage fracture at - 196 and - 40 °C. The fracture toughness did not show any significant change with isothermal transformation time at 700 °C. The failure mode of the isothermally transformed materials was always by quasicleavage fracture.     

2.25Cr-1Mo与0Cr18Ni9钢焊接工艺研究

在筒体母材为2.25Cr-1Mo钢的大型压力容器生产制造过程中,常涉及到0Cr18Ni9不锈钢内构件与筒节2.25Cr-1Mo钢的焊接。阐述了采用药芯气体保护焊(FCAW)方法焊接该类异种钢的有关工艺要素。通过试验分析了如何调整工艺以改善焊接接头易出现脆化组织的情况,以使接头性能满足产品设计要求。     

回火温度对3Cr3Mo2NiW钢力学性能和断口形貌的影响

研究了3Cr3Mo2NiW钢力学性能和断口形貌随回火温度的变化。结果显示,随着回火温度的升高,试验钢的硬度降低,韧性增加,550 ℃回火时出现二次硬化现象;600 ℃以上回火,硬度明显降低,韧性大幅度增加;700 ℃回火态试样未冲断。淬火后,随着回火温度的升高,试验钢的基体组织逐渐转变为回火马氏体、回火屈氏体和回火索氏体。300~600 ℃温度区间内回火试样的断裂方式为准解理断裂,高温回火试样的断裂方式为韧性断裂,不同温度回火后得到的显微组织和碳化物对试样的冲击韧性有较大影响。     

X90管线钢的低温冲击韧性和断口形貌分析

采用系列温度冲击试验法测定了X90管线钢在-100~0℃的冲击吸收能量和剪切断面率,用扫描电镜观察了不同温度下试验钢的冲击断口形貌。结果表明,该管线钢具有良好的低温冲击韧性,-80℃时的冲击吸收能量可达219 J,韧脆转变温度ETT50为-78.5℃、FATT50为-83.5℃;冲击断口形貌在0、-20℃下以大而深的等轴状韧窝为主,在-40、-60、-80℃下以抛物线韧窝为主,且韧窝尺寸和深度开始减小,在-100℃以扇形解理花样为主。试验钢在-80~-40℃温度区间,冲击断口发生显著分离现象,导致冲击吸收能量与剪切断面率曲线斜率减小。     

Oxidation behavior of 2.25Cr-1Mo steel with prior tempering at different temperatures

The oxidation behavior of a normalized 2.25Cr-1Mo steel tempered previously for 10 hr at different temperatures between 873 and 1023 K has been studied up to a maximum duration of 1000 hr in air at 773–973 K. The oxidation resistance of the steel was found to decrease significantly with the temperature of tempering. Tempering of this steel is reported to cause microstructural changes involving precipitation of Cr as carbides and a decrease in the effective (free) Cr contents, that could influence the oxidation resistance of the Cr-containing alloys. Relative compositions across the thickness of the oxide scales, as analyzed by SEM/EDX and SIMS, suggest that a less Cr-rich (and less protective) and thicker scale on the steel formed because previous tempering caused extensive depletion of free Cr.     

2.25Cr-1Mo钢TIG堆焊Fe_3Al合金的研究

通过TIG堆焊工艺试验,建立了填充金属Al含量与Fe-Al合金堆焊层中Al含量之间的对应关系,研究了Al含量对堆焊层裂纹倾向、显微组织、力学性能以及断裂特征的影响规律,确定了获得Fe3Al合金堆焊层所要求的焊丝中Al含量范围,为研制开发Fe3Al堆焊焊丝提供了依据。     

2.25Cr-1Mo钢相变塑性的实验研究

试验测定了2.25Cr-1Mo钢贝氏体相变的相变塑性变形,并观测了相变塑性变形随相变进程的演化规律.根据试验结果确定了相变塑性模型.试验测定了应力对2.25Cr-1Mo钢贝氏体最大转变量和相变动力学参数的影响系数.     

12Cr2Mo1R钢的韧脆转变机理

利用夏比冲击试验测定了12Cr2Mo1R钢的韧脆转变温度,并通过SEM、XRD、光学显微分析等方法对该钢在低温下的韧脆转变机理进行了探讨。结果表明,12Cr2Mo1R钢的韧脆转变温度（FATT₅₀）约在－95 ℃左右,在低温环境下12Cr2Mo1R钢中的位错运动受到抑制,造成位错在碳化物前发生塞积,萌生微裂纹,最终在外力作用下发生穿晶脆性断裂,符合Stroh位错塞积理论。     

逆转变奥氏体对中Mn钢低温冲击断裂过程的影响

对超低碳7%Mn钢进行了不同温度的回火处理,测定了组织中的逆转变奥氏体含量及其在-60、-100 ℃下的冲击吸收能量,并观察了冲击断口附近的显微组织,进而讨论了逆转变奥氏体含量及稳定性对试验钢低温冲击断裂过程的影响。结果表明:逆转变奥氏体对试验钢低温韧性的影响具有两面性,一方面能够通过相变缓解裂纹尖端的应力集中,改善钢的低温韧性,另一方面,当其稳定性较低时易于在应力作用下大量发生马氏体相变,导致钢低温韧性降低。冲击断口附近产生明显塑性变形的区域都较小,表明在冲击断裂过程中难以通过大范围的TRIP效应实现韧化。     

淬火冷速对大型核电压力容器用钢显微组织和力学性能的影响

采用光学显微镜和力学性能测试等研究了淬火冷速对大型核电压力容器用SA508-3钢显微组织及力学性能的影响,尤其对落锤冲击性能的影响。结果表明:随着冷速的增加,SA508-3钢的显微组织由宽大的上贝氏体+粒状贝氏体组织向细小下贝氏体+马氏体组织转变。淬火冷速对SA508-3钢的常/高温强度影响不大,而对冲击韧性的影响显著,尤其对零塑性转变温度(NDTT)的影响显著。低冷速下的NDTT只能达到≥-13.3℃,而高冷速下的NDTT大幅度降低,达到≤-48.3℃。     

加氢反应器用2.25Cr-1Mo-0.25V钢锻件的持久性能

研究了高温持久对2.25Cr-1Mo-0.25V钢断口及显微组织的影响.对热处理态试样的常温、高温及相同温度、不同载荷下的高温持久强度进行分析,并通过扫描电镜(SEM)对持久试样的断口及微观组织进行观察.结果表明,随着加载应力的增加,持久时间显著降低,持久试样断裂后,断口形貌的韧窝中有富Mo析出相,且随着持久断裂时间的...