Low Strength Steel Research Articles

Friction Characteristics of Low and High Strength Steels with Galvanized and Galvannealed Zinc Coatings

As vehicle body structures become stronger and part designs more complex for lightweight, controlling frictional properties in automotive press forming has gained critical importance. Friction, a key factor in formability, is influenced by variables such as contact pressure, sliding velocity, sheet strength, and coatings. This study investigates the friction characteristics of steels with tensile strengths of 340 MPa and 980 MPa, under galvanized (GI) and galvannealed (GA) zinc coatings. Experimental results reveal that asperity flattening, a significant factor in determining friction, increases with contact pressure normalized by tensile strength, particularly for GI-coated steels. However, the relationship between friction and surface flattening deviates from conventional expectations, with the friction coefficient initially rising with increased flattening area up to ~20% before decreasing as flattening progresses. These findings suggest that traditional empirical formulas may not fully capture friction behavior under specific conditions. By understanding this inflection point, where friction reduces under high contact pressure, the study provides valuable insights for optimizing formability and improving sheet metal forming processes, especially in scenarios where precise friction control is critical for producing high-quality automotive parts.

Mechanical properties and microstructure evolution of 1800 MPa grade low alloy ultrahigh strength steel during quenching and tempering process

Mechanical properties and microstructure evolution of 1800 MPa grade low alloy ultrahigh strength steel during quenching and tempering process

Microstructure and mechanical properties of low cost co-free high strength steel fabricated by plasma arc-based directed energy deposition

Arc-based directed energy deposition (DED) is characterized by high efficiency and excellent manufacturing flexibility, making it a promising choice for fabricating large structural components. High power density plasma arc-based directed energy deposition (PA-DED) was employed to fabricate high strength steel (HSS) component with a new Co-free welding wire. The microstructure and mechanical properties of the component were investigated in detail. The results showed that the matrix microstructure consisted mainly of martensite and ferrite. Austenite was observed in the bottom and middle samples, and the bottom sample exhibited the highest austenite content. All the samples in different regions exhibited a pronounced {100} 〈001〉 cube texture. The vertical samples had worse tensile properties than horizontal samples, which would be contributed to the interlayer bands and preferred orientation. The horizontal-middle samples demonstrated the highest tensile strength (UTS: 1207.8 ± 14 MPa, EL: 15.91 ± 1.03%). All deposited samples showed strong plastic deformation characteristics, illustrating that the new Co-free HSS components manufactured by PA-DED might replace conventional high-alloy HSS components for industrial applications.

Calculation and experimental study of reactivity between CaO–BaO–Al2O3–CaF2–Li2O mould slag and low density and high strength steel

In the continuous casting of low-density and high-strength steel, minimising or eliminating steel–slag reactions is imperative to ensure stable slag properties and a smooth casting process. This study conducted steel–slag contact experiments at 1400 °C, based on thermodynamic calculations predicting the reaction trends of the proposed CaO–BaO–Al2O3–CaF2–Li2O mould slag with low-density and high-strength steel containing 8 wt-% Al. The changes in compositions, rheological, and solidification characteristics of slags pre- and post-reaction are analysed. The findings reveal that only Li2O reacts with Al in the steel, forming LiAlO2 rather than Al2O3. Reactivity is affected by component activity and the partial pressure of Li vapour at the reaction interface, established to vary between 0.154 and 0.253 atm. Within the current range of slag composition, increasing Al2O3 and reducing Li2O content in the slag inhibits the slag–metal reaction. Specifically, Li2O remains unreactive with Al when 2.5 wt-% < Li2O < 5 wt-% and Al2O3 > 27 wt-%. Conversely, the reaction occurs when Li2O > 4.5 wt-% and Al2O3 < 18 wt-%. In conclusion, low- and non-reactive mould slags suitable for casting low-density and high-strength steel are proposed, considering both reactivity and stable slag properties.

Investigating the effects of steel strength and tensile overload level on fatigue crack growth performance

Individual overloads (OLs) might significantly relax tensile residual stresses (RS) besides generating compressive RS in welded components and, thus, influence the fatigue performance of these components. This study seeks to investigate the effects of steel strength and OL level on the fatigue life performance of welded components. Welding calculations were first performed for different steel grades to predict welding RS (WRS). A series of numerical fatigue calculations were conducted using the elastic–plastic fracture mechanics approach based on FEM to comprehend the fatigue performance under various OL levels. The fatigue calculations were performed in the absence and presence of the WRS effect. The results showed that the higher-level OLs improved the fatigue performance of components made of higher-strength steel when the WRS effect was considered. In contrast, in the absence of the WRS effect, an improvement in fatigue performance was achieved from the higher-level OLs by lower-strength steel. Also, a remarkable RS relaxation with varying degrees was induced from the higher-level OLs for the applied steel grades. This variation in the degree of RS relaxation could be attributed to the difference in WRS distributions over the crack surface. The crack driving force and retardation effect were also used to support the study.

Comparison of hole expansion ratios in a dual phase steel for holes prepared by conventional punching and fine piercing

Dual phase steels generally exhibit poorer stretch flangeability compared to lower strength steels. Stretch flangeability is normally evaluated using hole expansion testing, wherein a specimen with a 10 mm central hole is expanded using a conical punch till onset of cracking at the edge of the hole. The percentage increase in hole diameter is referred to as the hole expansion ratio (HER). In this study, hole expansion ratios of a DP 600 steel were evaluated. Holes were prepared on a standard 90 mm x 90 mm specimen using two different hole preparation conditions: i) conventional punching where the hole edge exhibits both fracture and shear regions and ii) fine piercing where the hole edge exhibits almost completely smooth shear. Hole expansion testing was carried out on these specimens as per standard ISO 16630. The specimens with holes produced by fine piercing exhibited lower values of HER in spite of having a hole edge with a smooth surface. The specimens with holes prepared by conventional punching exhibited higher HER values. The influence of strain hardening of the cut edge during hole preparation and the surface roughness of the cut edge on the HER are discussed.

A Review on Slit Steel Shear Walls: Development, Implementation, and Performance

Over centuries, natural phenomena have claimed a large number of lives and caused large amounts of damage. However, they were the reason for the development of knowledge and science. In engineering, there is no doubt that earthquakes were the driving force behind many design philosophies and advanced technologies. In this regard, steel plate shear walls (SPSWs) represent one of the technologies employed in both new constructions and existing structures to bolster lateral load resistance. In addition to its high elastic stiffness and strength, SPSWs often experience significant pinching during their hysteretic response unless heavily stiffened. Thus, numerous investigations have been performed recently to enhance the seismic behavior of SPSWs during severe ground shaking. The shear walls of steel plates have been studied in various ways, including stiffened and unstiffened steel plates, low yield strength steel plates, SPSWs perforated with circular holes or vertical slits, steel walls with stiffened and unstiffened openings. A stiffened SPSW panel dissipates significantly more energy than an unstiffened panel, as well as exhibiting a ductile and stable behavior. In view of its high elongation, the SPSW with low yield point has the best damping capacity. It has been demonstrated that steel walls perforated with circular holes have improved energy dissipation, in addition to allowing utilities to pass through their openings. Vertical slits on steel plate shear walls produce an exceptionally full hysteresis loop with improved performances. Slit steel walls (SSWs) can sustain a drift of over 3% while experiencing minimal hysteresis degradation. Additionally, a frame with a SSW can endure up to 6% drift without significant damage, surpassing expected ductility levels of a special moment frame, particularly with efficient slit geometry.

Effect of rolling reduction on microstructure, mechanical properties and fracture features of hot isostatically pressed 30CrMnSiNi2A low alloy ultrahigh strength steel

As a powder metallurgy (PM) defect, existence of prior particle boundaries (PPBs) often makes mechanical properties visibly deteriorated. Hot rolling has been found to be an effective method of destroying PPBs. In present study, five different rolling reductions are applied to explore the effects of rolling reduction on evolution of PPBs in PM 30CrMnSiNi2A steels. Microstructure, mechanical properties and fracture modes of five samples are systematically analyzed and compared. Increase of rolling reduction not only makes Al-rich PPBs refined but also makes continuous PPBs structure gradually transform to dispersed oxides and short chain fragments, which can be attributed to deformation of powder particles. Change on distribution of PPBs leads to the variation of fracture modes. A strength-ductility-toughness balance is achieved when the rolling reduction scales up to 60 %. Although increase of rolling reduction causes grain refinement, work hardening and improvement of PPBs, it promotes formation of edge cracks. Occurrence of edge cracks is strongly associated with PPBs inclusions and makes ductility and toughness deteriorated.

Experimental and numerical investigation on out-of-plane ultimate strength of high-strength steel arches

This study presents an experimental investigation on the out-of-plane ultimate strength of high-strength-steel (HSS) I-section arches, which has not been reported previously. Fourteen I-section HSS arches having different yield strengths, cross-sectional dimensions, slendernesses, and rise to span ratios were tested under three-point symmetrical vertical loading. The corresponding out-of-plane deformation modes and strengths are identified. Subsequently, in order to predict the out-of-plane capacities of HSS arches, a finite element analyses is carried out, which takes into consideration residual stresses and initial geometrical imperfections. This analysis demonstrates a strong alignment with the experimental results, confirming the accuracy of finite element model and experimental results. Furthermore, the study comprehensively analyzes the influence of yield strength of steel, rise-span ratio, and slenderness on the ultimate bearing capacity of HSS arches. Through a parametric analysis, design formulas for the out-of-plane bearing capacity of HSS arches subjected to arbitrary compression forces combined with arbitrary bending moments are formulated. It is found that the out-of-plane ultimate strength of HSS arches is significantly influenced by the yield strength of the steel. Compared to a low strength steel (LSS) arch, the out-of-plane ultimate bearing capacity of the HSS arch increases with an increase in yield strength in the plastic stage, and the ultimate lateral displacement of the HSS arch decreases with an increase in yield steel strength due to the lower ductility of HSS. In addition, after reaching the out-of-plane ultimate bearing load of arch, the load-displacement curve of the HSS arch drops faster than the LSS arch. It is also found that the proposed design formulas can effectively predict the out-of-plane bearing capacity of HSS arches.

Effect of tempering temperature on stress corrosion resistance of a low alloy high strength steel with high vanadium content

The stress corrosion resistance of a low alloy high strength steel with high vanadium content, tempered at different temperatures, was examined by electrochemical measurements and slow strain rate tensile test under different environments. Combined with scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM), the results show that three different tempering temperatures had an influence on the microstructure of this steel as well as its electrochemical behavior and stress corrosion sensitivity. With the increase of tempering temperature, the ferrite grains coarsened, the average dislocation density lowered as well as the number of vanadium carbide also decreased, though the size of vanadium carbide increased. However, the interface distortion between vanadium carbide and matrix exacerbated, resulting in the increase of the local dislocation density. Therefore, the corrosion potential and impedance decreased, meantime, the stress corrosion sensitivity aggravated.

Effect of welding state on the re-precipitation behavior of Cu-rich and NiAl nanoparticles in HAZ of 1100 MPa grade low carbon ultra-high strength steel

The influence of multi-layer multi-pass welding and post-weld heat treatment (PWHT) on the co-precipitation behavior of Cu-rich and B2–NiAl, microstructural characteristics, grain size and mechanical properties of the coarse grain heat affected zone (CGHAZ) were systematically investigated for low-carbon ultra-high-strength steel with different Ni/Cu ratio. The results show that the CGHAZ microstructure of both high (1.5Cu) and low (2.0Cu) Ni/Cu ratio steel are composed of LB and GB, the grain size increases from 10.1 ± 1.1 μm and 9.5 ± 0.7 μm to 32.1 ± 1.0 μm and 32.2 ± 2.7 μm, and the nanoparticles are dissolved and subsequently re-precipitated during the welding process, with an average radius 1.56 nm and 1.71 nm, respectively. The hardness profile of the joint shows softening at CGHAZ and the tensile strength reaches 1218 MPa and 1056 MPa respectively. After PWHT, the re-precipitated behavior of the nanoparticles was enhanced, with average radius of 1.53 nm and 1.55 nm, and the number density increases from 1.55 × 1023 m−3 and 1.06 × 1023 m−3 to 4.01 × 1023 m−3 and 3.33 × 1023 m−3, respectively. The co-precipitation evolution mechanism shows that the typical core-shell structure is transformed into individual 9 R–Cu and B2–NiAl particles, and a large number of small-sized B2–NiAl particles were re-precipitated during the aging process. The strengthening mechanism shows that martensite strengthening and grain size strengthening are weakened in the as-welded CGHAZ, and only part of the nanoparticles was re-precipitated leading to the softening of CGHAZ during welding. After PWHT, a large number of small-sized nanoparticles were re-precipitated to restore the contribution of precipitation strengthening, while small-sized nanoparticles interacted with dislocations and entangled near the M-A constituents to promote the formation of microvoids and microcracks, thus seriously deteriorating the ductility.

Pull-out capacities of screw connections in thin steel battens exposed to bushfire conditions

External building envelopes made of cold-formed steel (CFS) claddings are commonly used in bushfire prone areas due to their non-combustible properties. However, their designs should ensure safety under the combined action of enhanced wind suction loading and elevated temperatures experienced during bushfires. Although numerous studies have investigated the critical pull-out failures in CFS batten screw connections under wind suction loading at ambient temperature, the pull-out failure behaviour of batten screw connections under bushfire conditions has not been investigated. The main objective of this study is to examine the pull-out failure mechanisms and capacities of screw connections in CFS battens under wind suction loading at elevated temperatures. Two hundred and sixteen small-scale tests were conducted on CFS battens made of three commonly used thicknesses and both high (G550) and low (G300) strength steels. Tests were conducted at six different temperatures using three types of screw fasteners to investigate the critical localised pull-out failures of batten screw connections. The results of these tests were utilised to develop applicable design equations and capacity reduction factors for the pull-out capacities of batten screw connections under the combined action of wind suction loading and elevated temperatures. The findings of this study will help design and build structures safely in bushfire-prone regions.

Optimizing the hydrogen embrittlement resistance by Cu addition in a low carbon high strength steel

This study used the electrochemical hydrogen permeation test and the slow strain rate tensile (SSRT) test to examine the impact of Cu addition on hydrogen embrittlement (HE) in a low carbon high strength steel. The following method explains how Cu alloying affected HE resistance. (i) Cu alloying refined the prior austenite grain size, which increased the effective area of grain/packet/block/lath boundaries and mitigated the strain localization, and thus provided additional reversible hydrogen traps, homogenized the hydrogen distribution and suppressed local accumulation of hydrogen at boundaries. (ii) Cu alloying promoted the Cu-rich precipitates, which had strong binding energy with hydrogen. Also, the “incoherent” fcc Cu-rich precipitates contrary to the “slightly coherent” Cu-rich with an energy-poor trap strongly trapped hydrogen and enhanced the HE resistance.

Flexural Behavior of High-Strength Steel and Ultra-High-Performance Fiber-Reinforced Concrete Composite Beams

The flexural performance of steel and concrete composite beams can be further enhanced by utilizing advanced construction materials such as ultra-high performance fiber-reinforced concrete (UHPFRC) and high-strength steel. In this paper, the concept of critical elastic moment resistance is proposed and the equation for its estimation is derived. It was found that the high yield strength of steel calls for a narrow UHPFRC top layer to reach the critical state, whereas this ideal condition is not realistic for composite beams with normal-strength steel and UHPFRC. Small-scale composite beams composed of both high-strength and low-strength steel materials were tested under four-point bending to verify the critical state and performance of different types of connectors. The headed studs and plate connectors were first tested through small-scale push-out tests and then implemented in the composite beam with different spacing. The connection utilizing headed studs with 150 mm spacing performed the best among the three tested specimens in helping reach the critical elastic moment resistance. Finite element analyses of the composite beam were performed based on the estimated material properties under axial and biaxial stress conditions and the results align with the experiment results.

Hot Stamping of Heavy-Gaged - Full Development and the Effect of Press Hardening Process on the Microstructure and Mechanical Properties of 22MnB5 + NbMo Alloyed

For saving mass, to improve the payloads and the durability of commercial vehicles, it is necessary to increase the thickness range of PHS - Press Hardening Steel, replacing low strength steel grades on structural and saving parts. This work presents the industrial development of Heavy-Gaged PHS-Press hardening Steel (4-8mm) starting from the alloy design concept, especially adding niobium to promote a fine and homogeneous microstructure. The development included hot forming simulations, in order to achieve martensitic microstructure through the thickness, correlating with cooling rates and mechanical characteristics, after quenching, as well as welding qualification and fatigue evaluation. Furthermore, were presented the characterization of 22MnB5(Nb+Mo) steel after industrial hot stamping that were evaluated mechanical properties, using the Vickers 10Kgf and the relationship between the microstructure and the thermodynamic aspects.

Thermal cycle method’s applicable conditions for predicting residual stresses in low-strength steel weldments induced by arc welding

The present study purposes to systematically investigate the viability of the fast computation method “thermal cycle method (TCM)” for simulating welding residual stresses (WRS) in transforming and non-transforming low-strength steel weldments under various restraint conditions. Both experimental and finite element analysis were performed. Comparison of the predicted WRS with the measurements reveals that TCM is completely not suitable to assess WRS in the transforming low-strength steel weldments with low restraint degrees in numerical simulation. Nevertheless, that is feasible overall when the constraint degree is high, although this method reduces the accuracy of the calculated longitudinal residual stress to some extent in base material (BM). For non-transforming single-phase low-strength steels, no matter how much the restraint degree of the weldment is, it is trustworthy using TCM instead of the commonly applied moving heat source to calculate WRS for reducing the computational time. Based on the current work, the application conditions of TCM for the assessment of WRS in the low-strength steels induced by arc welding are systematically clarified.

Characterization of LC/HC-FeMn alloys and their melting mechanism in the molten iron

Low density high strength steel has become an important lightweight structural material for future civilian and military vehicles due to its combination of less weight and high strength and toughness. However, due to extremely high amount of Mn content (∼25%), the fast melting of ferromanganese in molten steel is extremely important. Two grades of commercial FeMn alloy were used in this study: LC-FeMn and HC-FeMn, respectively. Compared with LC-FeMn, HC-FeMn contains more MnO and MnS inclusions. The density of HC-FeMn (6550 kg/m3) are lower than LC-FeMn (7110 kg/m3). The liquidus temperature of HC-FeMn (1389 °C) are higher than LC-FeMn (1219 °C). After being inserted into the molten iron for 6 s, an initial size of 4 mm HC-FeMn melted to be 3.1 mm, while the same size of LC-FeMn became 0.45 mm. The adding the cold ferromanganese alloy to the molten iron resulted in the formation of a solid shell on the surface. The solid shell thickness of the cold alloy reaches its maximum value after 1 s in the molten pool, 2.09 mm for LC-FeMn and 1.86 mm for HC-FeMn respectively. The solid shell was expected to melt completely within about 3 s.

Enhancement of the resistance to hydrogen embrittlement by tailoring grain boundary characteristics in a low carbon high strength steel

In this work, the feasibility of using “grain boundary engineering” to reduce the susceptibility to hydrogen embrittlement in a low carbon low alloy steel was examined. By adding Cu element, the fraction of random grain boundary (RGB) exhibited the highest value in the steel with 1%Cu, while the fraction of special grain boundary (SGB) showed a monotonical decline. The slow strain rate tensile (SSRT) test revealed that the elongation loss presented an increase with Cu addition increasing from 1 % to 3 %. This can be explained in terms of hydrogen diffusion, hydrogen trap and crack propagation. The steel with 1%Cu had a higher fraction of high angle grain boundary (HAGB), which contributed to a higher density of hydrogen traps and a lower hydrogen diffusion rate. Moreover, the steel with 1%Cu had the highest fraction of SGB (∑3, ∑5, ∑7 and ∑≥9), which was beneficial to the resistance to crack propagation. Under the combined effect of RGB and SGB, a higher resistance to hydrogen embrittlement was achieved in the steel with 1%Cu.

Mechanism of Development of Damage of Low-Strength Pipe Steel Due to Hydrogenation Under Operation

Mechanism of Development of Damage of Low-Strength Pipe Steel Due to Hydrogenation Under Operation

Fatigue tests and design of Q460 CHS-CHS T-joints under axial loading and in-plane bending

Previous research has primarily focused on stress concentration factors (SCFs) and fatigue life of tubular joints made from low-strength steel (nominal yield strength of 235–360 MPa). The fatigue behavior of high-strength tubular joints remains insufficiently studied. In this study, a total of sixteen CHS-CHS T-joints fabricated from Q460 steel were designed, eight of which were subjected to axial load and eight of which were under in-plane bending. Static and fatigue tests were conducted to analyze the distribution of hot spot stress, fatigue crack propagation, and fatigue failure modes. The experimental results showed that the crack initiation consistently occurred at location of maximum hot spot stress for all specimens. The maximum SCFs were concentrated at the saddle (90°) for specimens under axial loads and around the position of 22.5° for those under in-plane bending. The modified SCF design formula for in-plane bending was proposed based on regression analysis. Prior to crack initiation, all specimens exhibited a relatively slow stiffness degradation due to cumulative damage from fatigue loading. Through least squares analysis of the test data, the fatigue design Srhs-N curve for Q460 CHS-CHS T-joints was developed. The proposed Srhs-N curve is capable of accurately predicting the fatigue life of Q460 CHS-CHS T-joint subject to axial loads and in-plane bending. Comparison with previous research and existing design guidelines shows that under the same stress amplitude level, the fatigue lives of CHS-CHS T-joints subjected to axial loading of Q460 steel are comparable to that of low-strength steel (WFG36Z). Under in-plane bending, the fatigue lives for Q460 steel are higher than that for low-strength steels (C350L0, t < 4 mm).