Systematic investigation of acicular ferrite formation on laboratory scale

By increasing the amount of acicular ferrite (AF) in the microstructure, steel toughness can be improved significantly. The steel composition, cooling rate, non-metallic inclusions and austenite grain size have a strong influence on the formation of AF. The present paper describes and compares two approaches to study AF formation in a titanium-deoxidised high-strength low-alloyed steel and its influencing factors on laboratory scale: route A simulates the formation of AF after heat treatment; route B simulates the formation directly after solidification of the melt. The formation of AF is essentially influenced by the former processing, which also changes the optimum cooling parameters substantially. (Ti,Mn)_xO_y and (Ti,Al,Mn)_xO_yS_z are the predominant active inclusion types in the investigated steel.     

薄板坯连铸连轧高强度低合金钢的控轧控冷工艺

针对FTSR工艺生产的700 MPa级高强度低合金(HSLA)钢进行了控轧控冷(TMCP)工艺试验研究,分析了不同控制轧制和控制冷却工艺对钢带力学性能和组织的影响规律。结果表明:热轧钢带强度与精轧阶段控制轧制道次积累变形量呈现显著正相关;层流冷却方式对钢带性能影响不显著,但间隔冷却模式能够改善钢带通宽方向性能不均匀性;控制冷却终点温度由600 ℃提高至670 ℃,钢带显微组织随温度升高而发生粗化,但析出相析出更充分,钢带强度持续升高。     

Neutron diffraction measurements of residual stresses in a 50 mm thick weld

Residual stresses were determined through the thickness of a 50 mm thick ferrite steel weld plate using neutron diffraction. Whereas the limiting penetration depth for iron-based alloys is about 25 mm in the most typical neutron diffractometers, we significantly enhanced the penetration depth up to 50 mm with 2 mm spatial resolution by using the neutron wavelength of 2.39 Å. The selected wavelength minimizes the total neutron cross-section and beam attenuation, thereby, maximizes the neutron fluxes at depth. Two-dimensional mapping of the residual stresses shows that significant amounts of the tensile longitudinal stresses (over 90% of yield strength) were developed along the heat-affected zone of the weld.     

A design of experiments assessment of moisture content in uncured adhesive on static strength of adhesive-bonded galvanized SAE1006 steel

As part of a cooperative research program to develop and implement crash-resistant toughened adhesives targeted for future vehicles, this paper summarizes a study of the influence of pre-exposure of uncured adhesive and steel sheets in a humid and elevated temperature environment on quasi-static strength of bonded hot dipped galvanized SAE1006 steel joints.In this study, we use a DOE (design-of-experiment) program called DEXPERT to design the experiment and to analyze the effects of exposure temperature, exposure time, curing temperature and curing time on joint strength of adhesive-bonded galvanized SAE1006 steel. Prior to adhesive curing, the adhesive and galvanized steel coupons were pre-exposed to various relative humidity levels and temperatures. The experimental results were then analyzed by DEXPERT and the relative contributions of each factor on variance in joint strength were calculated. It was found that curing temperature is the most influential factor affecting the strength of adhesive-bonded galvanized SAE1006 steel joints. The curing of a joint at 180 °C can increase the robustness of the process and provides the greatest strength regardless of the variation of other factors. The joint strength curing at 150 °C shows a strong sensitivity to the curing time, while the adhesive cannot cure at 130 °C at all under all conditions. It has also been found that the pre-exposure of adhesive and steel for an hour can slightly decrease the joint strength at high temperature and humidity. Therefore, the effect of long time exposure of the uncured adhesive and steel still needs to be further investigated.     

New polymer/steel solution for automotive applications

Dry and wet steel/polymer adhesion was investigated using pull-off test and dielectric measurements. The influence of the composition of a hexafluorotitanic acid based surface treatment (Patent WO9607772A1) was also studied. It was noticed that when manganese or organic phase was missing from surface treatment, breaking force level decreases and steel surface was not protected from water effects. After ageing and drying, a complete recovery in breaking force was noticed except for treatment without the organic phase.     

高层建筑用钢的发展

近年来，我国各大城市高层建筑发展迅猛，为充分利用有限的土地资源、发展钢结构建筑、急需大量建筑材，为此本文重点好国内外建筑用钢的发展，指出了高强度、高性能、大型化、功能化是建筑用钢发展的主要方向。     

多道次热轧形变中混晶的细化规律研究

本文用定量金相的方法研究了多道次热轧形变条件下混晶奥氏体的细化规律。研究结果表明:形变在高温再结晶区进行时,起始奥氏体大晶粒或未再结晶晶粒明显细化,而小晶粒细化缓慢;形变在部分再结晶区进行时,主要是小晶粒或已再结晶晶粒细化,随温度下降,起始奥氏体大晶粒或未再结晶晶粒变得更难实现再结晶细化。此外,还研究讨论了产生上述结果的原因。     

Mechanism of effects of warm prestressing (WPS) on apparent toughness of notched steel specimens Part II: Calculations and analyses

Based on the experimental results of Part I of present work, this paper describes results of FEM calculations and analyses in details which identified that the effect of tensile-warm pre-stressing (WPS) on improvement of the apparent toughness of notched specimens results from three factors i.e. the residual compressive stress, macroscopic blunting of the original notch, and prestrain-deactivating cleavage initiation. The effects of three factors are separated and is effective for each at various extents of prestressing specified with a prestress-ratio, P₀/P_gy, defining the prestressing load P₀ as a fraction of general yield load P_gy. For values of prestress-ratio lower than 1.0, the residual compressive stress acts as the main factor. Between 1.0 to 1.5 of prestress-ratio values, in addition to the residual compressive stress the macroscopic blunting plays increasing role. The effect of the prestrain-deactivating cleavage initiation presents at the prestress-ratio P₀/P_gy1.2. In the case of compressive-warm prestressing, the apparent toughness is deteriorated due to the residual tensile stress. The effects of complex cycles of WPS, with various steps of loading and unloading different in signs, are determined mainly by the loading step just before the fracturing step.     

细长钢材的在线称量技术

本文介绍了以钢轨为例的细长钢材的在线称量技术方案。对称量设备的工艺布置和结构、称量过程和控制系统、称量仪表系统进行了较为详细的描述。该技术方案适用于成捆的钢轨、钢管、棒村等多种细长物料的称量。