Self-similar and self-affine characteristics of microstructural images of HSLA steel

Abstract

This paper reports a procedure based on discrete Fourier transformation adopted for verifying statistical self-affinity and self-similarity in microstructural images of high strength low alloy steel. The procedure is first applied on synthetic images based on fractional Brownian motion to show the degree of self-similarity in them and finally, applied on microstructural images of three different magnifications. Effects of length scales on power spectral estimates of the microstructural images captured by scanning electron microscopy have been discussed. Importance of appropriate image resolutions and characteristic length for fractal based quantification of microstructural images is highlighted.     

锰对一种HSLA钢的组织和性能的影响

把一种含碳量为0．06％的低碳钢,通过真空感应熔炼把锰的含量由1．3％提高到2．0％,通过对未提高锰含量和提高锰含量之后的钢的组织和性能的比较,分析锰对一种低合金高强度钢的强化机理,并初步确定锰的强化方式,为综合分析合金元素对高强度低合金钢组织和性能的影响奠定基础。     

Effect of heat treatments on the hydrogen embrittlement susceptibility of API X-65 grade line-pipe steel

Delayed failure tests were carried out on hydrogen charged API X-65 grade line-pipe steel in as received (controlled rolled), normalized, and quenched and tempered conditions. The resistance to hydrogen embrittlement was found in the order of controlled rolled > quenched and tempered > normalized. The fracture mode in the hydrogen embrittled steel was ductile.     

Evaluating the deterioration of electrodes when increasing the number of pulses in the welding time using galvanised IF and HSLA steels and assigning mechanical properties in the spot welds

ABSTRACT

Resistance spot welding is the most important method in the industry of self-supporting or monocoque body joinery because of its automation, its speed, the flexibility of welding parts with a complicated shape, and it is economical because it does not require a filler metal, and it is also possible to apply pre-heating and post-heating pulses to improve the weldability of the spot weld, which is defined as the ability of the structure to adequately protect passengers against injuries in the event of a collision, and this mainly depends on the integrity and mechanical performance of the weld button. In order to extend the lifetime of vehicles, galvanized steels are produced. However, zinc coatings have increased the difficulty of weldability, with higher currents being required in the process, since there is less resistance at the weld interface due to improved electrical conductivity. This work investigates the effect of galvanizing on the reduction of the lifetime of the electrodes, for this reason, it follows that there is a loss in the mechanical properties in the weld buttons as the number of spot welds increases. The main aim of this study is to correlate the electrode wear with the mechanical properties of the weld buttons. The experiment procedure consists of making 1,000 spot welds; and every twenty-fifth spot weld after the first was examined by means of stereoscopy, hardness tests, unbuttoning tests and shear stress tests. In terms of electrode wear, the face was evaluated using impressions on carbon paper, optical microscopy and X-ray spectroscopy.     

高强度低合金钢焊缝金属的组织及其影响因素

HSLA钢焊缝金属组织主要是由先共析铁素体、侧板条铁素体和针状铁素体组成,针状铁素体具有良好的韧性和强度配比,是HSLA钢焊缝金属最希望得到的组织。从合金元素、焊接参数和夹杂物三个方面对针状铁素体组织的形成进行阐述,以期为HSLA钢的使用及配套焊丝的开发等相关研究提供一定的借鉴。     

低合金高强度抗H2S应力腐蚀钻材钢的研究

“ＰＵ－１”低合金高强度抗Ｈ２Ｓ应力腐蚀钻材钢具有良好的综合力学性能和抗Ｈ２Ｓ应力腐蚀性能。对“ＰＵ－１”钢和焊缝合金断裂行为的研究结果表明,“ＰＵ－１”钻材钢抗Ｈ２Ｓ应力腐蚀性能和焊接性能较好,应用于结构钢构件具有显著的经济和社会效益。     

Rolling and Coiling Technology for the Production of Thin Strip on a Casting Rolling Line

One aim of the casting rolling plant is the production of hot strip with low thicknesses [1]. Results form an ECSC project [2], dealing with the introduction and optimisation of the new rolling and coiling technology for thin strip production at ThyssenKrupp Stahl are presented. Several series of hot rolling with different mild steels were performed. The strips were produced by two‐step (ferritic) rolling, as well as by austenitic rolling. In both cases direct application and hot‐dip galvanising of the strips were tested. The thinnest strip thickness achievable was 0.8 mm. Industrial trials were also carried out successfully with HSLA and dual phase steels.     

Fuzzy Modeling of Strength-Composition-Process Parameter Relationships of HSLA Steels

The effect of composition and process parameters on the mechanical properties of high-strength low-alloy (HSLA) steels is modeled by the application of fuzzy systems viz. Sugeno and Mamdani types. The fuzzy inference systems are found to be capable of interpreting the metallurgical relations between composition and process variables and yield strength described through some if-then rules. The predictability of the fuzzy inference systems is found to be moderate.     

低合金高强钢微观组织转变机制

摘要：通过高温激光共聚焦显微镜原位观察低合金高强钢（Q345R）在热循环过程中微观组织演变规律,并结合扫描电镜和纳米压痕,研究不同类型铁素体形核、长大机制及硬度。结果表明,铁素体可在晶界、亚晶界及夹杂物上形核,多边形铁素体及链状晶界铁素体主要在晶界上形核,而侧板条铁素体可在晶界及亚晶界上形核,而针状铁素体则主要在夹杂物及已形成的铁素体上形核,且奥氏体晶界及晶内亚结构尺寸控制了铁素体尺寸;讨论了夹杂物特征参数对针状铁素体形核的影响规律,Al、Mg、Ca、S等元素的含量达到一定比值且尺寸在5μm以下的复合夹杂物更容易成为针状铁素体的诱导核心;硬度实验结果表明,不同类型铁素体组织硬度存在差别,针状铁素体硬度最大可达到4GPa。     

低碳低合金高强钢的连续转变行为及其相变模型

用DIL805型热膨胀仪研究了低碳低合金高强钢(HSLA)奥氏体连续冷却过程的相变规律,用膨胀法结合金相法建立了实验钢奥氏体的连续冷却转变曲线(CCT),随着冷却速度的增加,实验钢的组织分别发生了铁素体转变、珠光体转变、贝氏体转变和马氏体转变。建立了相变点-冷却速度以及相变量-冷却速度之间的数学方程,并回归计算了拟合度较高的相变模型。结果表明,计算值与试验值之间能很好的吻合,证明了该相变模型的可行性。