Papers by Keyword: HSLA

Abstract: The microstructure and hardening behavior of HSLA steels with different microalloying element/carbon (M/C) atomic ratios, namely high M/C steel (H-M/C) and low M/C steel (L-M/C), were investigated in the present study. A dual precipitation morphology of nanosized carbides, namely interphase precipitation carbides and random precipitation carbides, was found at the same ferrite grain of both kind of steels, and these precipitates are believed to provide the main strengthening ability within ferrite. Of the two steels with different M/C atomic ratios, the ferrite matrix of H-M/C steel showed a rising trend in micro-hardness with increasing isothermal holding times from 5 min to 60 min at 650°C to 700°C. This higher strengthening ability occurring within ferrite grains after holding at longer times can be ascribed to the higher austenite decomposition rate occurring in the H-M/C atomic ratio steel. Therefore, the hardening mechanisms in both kinds of steel are also discussed in the present study.

Abstract: An artificial neural network (ANN) model has been developed for the analysis and simulation of the correlation between the chemical composition and mechanical properties of high strength low alloy (HSLA) steel X70. The input parameters of the model consist of the base metal chemical composition (C, Si, Mn, the sum of Cr+Cu+Ni+Mo, the sum of Nb+Ti+V, carbon equivalent CEpcm) and the yield strength (YS). The outputs of the ANN model include the ultimate tensile strength (UTS) of the test material. Scatter plots, correlation coefficient (R) and mean relative error (MRE) were used to assess the performance of the developed neural network. Interestingly, the model output is efficient to calculate the mechanical properties of high strength low alloy steels, especially the ultimate tensile strength as a function of chemical composition and yield strength of the used material. The obtained results are in a good agreement with experimental ones, with high correlation coefficient and low mean relative error. The predictions accuracy of the developed model also conforms to the results of mean paired T-test.

Abstract: A new generation of low-carbon microalloyed High Strength Low Alloy (HSLA) steels has been developed to utilize a combination of single-phase ferritic microstructures and optimized interphase precipitation to provide high level strength and exceptional formability. The interphase precipitation reaction is a transient process lending itself strongly to take advantage of in-situ characterization techniques. The austenite/ferrite interface kinetics during isothermal transformation at 1003 K is measured using HT-CSLM, the pre-exponential effective mobility constant was found to be mobility 0.822 (m J)/(mole s). The V interphase precipitation is characterised using TEM at isothermal transformation temperatures of 923 and 973 K as having inter-sheet spacing of 22±7 and 32±9 nm respectively. Interphase precipitation inter-sheet-spacing is simulated using a revised Quasi-Ledge model and qualitatively predicts the observed trends observed for inter-sheet spacing. The results of in-situ characterisation and modelling suggest that it is possible to optimize the strengthening potential of the precipitation processes by controlling the thermal processing of microalloyed HSLA.

Abstract: The weld overlay technology of high strength low alloy steel (HSLA) and austenitic stainless steel is widely applied in such fields as petroleum, chemical industry and energy, and its service environment is of high temperature and corrosion. As the matching performance is often poor for both austenitic stainless steel and high strength low alloy steel, cavities and crackles occur easily at the joints, which cause brittle fractures with dangerousness to some extent. So in the present study, the metal-inert gas welding (MIG) is used to clad the austenitic stainless steel to HSLA. In the experimental group, 4mm buffer layer (E309L) and 8mm cladding layer (E347L) were successively cladded on the substrate (Q345B), while 12mm cladding layer was directly deposited on the substrate in the control group. The hot corrosion tests were done, and through the scanning electron microscope (SEM), we observed the cross-sectional morphology. By the X-ray diffraction (XRD), we analyzed ingredients of the corrosion products. The corrosion products in the experimental group mainly consist of iron and nickel oxides, while the products are mainly iron complex compound and salt in the control group. The SEM results show the area near the welding seam of the specimens without buffer layer had been corroded severely. However, only a slight corrosion occurs adjacent to the welding seam. This demonstrates that the buffer layer can protect the specimens from being corroded.

Abstract: Dual phase (DP) steels belong to the group of high-strength low-alloy (HSLA) steels. Our study focuses on the causes of crack formation of sheets, which are designed for deep drawing, of DP780-grade dual phase steel. Also, a series of heat treatment experiments were performed regarding the effect of intercritical annealing temperature on the structure and mechanical properties of the finished product (in this case a rolled sheet).

Abstract: Mechanical and fracture properties of 20MnMoNi55 grade high strength low alloy (HSLA) steel welds have been studied. The weld joints were made using Gas Tungsten Arc Welding (GTAW), Shielded Metal Arc Welding (SMAW) and Pulse Gas Metal Arc Welding (P-GMAW) methods on conventional V-groove (V-Groove) and Narrow groove (NG-13). The base metal and weld metal were characterised in terms of their metallurgical, mechanical and fracture toughness properties by following ASTM procedures. The J-Integral fracture test was carried out using compact tension C(T) specimen for base and weld metal. The fracture toughness and tensile properties of welds have been correlated with microstructure. In conventional V-groove welds prepared by P-GMAW shows the improvement in initiation fracture toughness (J_IC) as compared to the weld prepared by SMAW. Similar improvements in tensile properties have also been observed. This is attributed to reduction in co-axial dendrite content due to lower heat input during P-GMAW process as compared to SMAW. In the narrow groove P-GMA weld prepared at f value of 0.15 has shown relative improvement of J_IC as compared to that of the weld prepared by SMAW process.

Abstract: The use of CSP^® thin slab casting followed by direct thermomechanical rolling is well placed for the production of low-carbon Nb microalloyed steels. In this process thin slabs of between 48 and 90 mm thickness are cast and directly hot rolled to hot strip typically between 1 and 12 mm thick. To obtain optimum strength and toughness property combinations in a direct rolling process, hot rolling has to compact the dendritic as-cast microstructure and to achieve a fine-grained microstructure. This affords a two-stage rolling strategy with start rolling above the recrystallization stop temperature and finish rolling in the non-recrystallization temperature range. Temperature and deformation in the first stand should be as high as possible in order to delete the initial as-cast microstructure by complete recrystallization. Based on these considerations, SMS Siemag further developed the CSP^® concept including features allowing isothermal rolling in the first stands of the finishing mill. The present contribution gives the results of a laboratory study of this innovative approach. The report concludes with resulting new plant configurations for improved high strength and API linepipe grade production.

Abstract: 360MPa grade heavy plate with high performance was developed through TMCP technology. By means of tensile and charpy impact tests and optical microscopy, the effects of processing parameters on final microstructure and properties of the steel have been studied, such as start rolling temperature in austenite non-recrystallization region and cooling rate. In order to obtain better mechanical properties, the optimization of the rolling process in an experiment rolling mill has been carried out. It has been found that the tensile strength of HSLA heavy plate are significantly improved by decreasing the start rolling temperature and increasing of the cooling rate, but the impact properties present the reverse law.

Abstract: Fatigue crack growth properties of Bisplate 80, a high strength low alloy (HSLA) steel, with extensive weld repair have been studied. Fatigue cracking becomes relevant if extensive abrasive wear damage is repaired through welding because of the change in material properties. In this study, extended compact tension (E-CT) specimens of Bisplate 80 with and without weld repair, and with and without a buffer layer between the weld and parent material are used to evaluate the fatigue crack growth behaviour. Fatigue crack growth rates are closely monitored at the interface regions between the weld, buffer layer and parent metal. Detailed SEM observations are also conducted at those locations. It is expected that the experimental results can provide useful information on the optimum weld repair conditions of HSLA.

Abstract: In all application fields for hot rolled strip products for direct processing, e.g. construction and engineering but also crane and truck industry, there is a strong customers demand for grades with increased strength levels and well balanced formability. At voestalpine Stahl GmbH these requirements were met with the development of the high strength microalloyed steel grade ALFORM700M and the ultra high strength steel grade ALFORM900M with a minimum yield strength (YS) of 700 MPa and 900 MPa, respectively. In the present paper investigations on the steel grades ALFORM700M and ALFORM900M are introduced. To explain the evolution of the obtained complex microstructures consisting of bainitic ferrite, bainite and martensite alloy design and industrial production process is discussed on the base of dilatometric experiments and TEM investigations. The formation of precipitates is studied by using a numerical model, chemical methods and mechanical testing after heat treatment. Mechanical and mechanic-technological properties of the two steel grades are compared. Furthermore, some processing aspects as weldability an bending behaviour are highlighted. Finally, some typical applications for this high and ultra high strength steel grades are presented.