Investigation of the toughness behavior in cold-formed and welded high-strength steels using fracture mechanics concepts and notch impact test

doi:10.21203/rs.3.rs-4861472/v1

Download PDF

Research Article

Investigation of the toughness behavior in cold-formed and welded high-strength steels using fracture mechanics concepts and notch impact test

https://doi.org/10.21203/rs.3.rs-4861472/v1

This work is licensed under a CC BY 4.0 License

You are reading this latest preprint version

High-strength steels are increasingly utilized across various industrial sectors, notably in statically loaded components such as crane constructions. These steels are frequently subjected to cold forming during production, followed by welding. However, welding in cold-formed regions of structural steels often results in embrittlement, thereby elevating the risk of brittle fracture. Current standards like Eurocode 3 address this phenomenon by prescribing a minimum distance of five times the plate thickness for welding in cold-formed areas of structural steels with a minimum yield strength of 700 MPa. Failure to meet this minimum distance necessitates costly heat treatment processes.

This article investigates three steels with higher yield strengths ranging from 700 MPa to 1100 MPa, featuring diverse strengths and manufacturing variations, to elucidate the influence of embrittlement during cold forming and welding of high-strength steels utilizing concepts from fracture mechanics. The results indicate that embrittlement is not anticipated in the cold-formed and welded regions of high-strength steels. It is inferred that the absence of secondary recrystallization, attributed to the existing microstructure or fine grain size of the steels, mitigates the formation of coarse grains, thereby averting brittle fracture.

Fracture mechanics

cold forming and welding

high strength steels

Rhodes

2024

IIW

High-strength steels (HSS) are pivotal in modern engineering applications, particularly in construction, automotive, and aerospace industries, where exceptional mechanical properties, such as high tensile strength and durability, offer significant advantages. The microstructure of these steels typically consists of a mix of irregular ferrite, martensite, retained austenite, and bainite [1, 2]. Welding and cold forming are common manufacturing methods for these steels. The weldability of HSS is evaluated using various welding processes, such as gas-metal arc welding (GMAW) and laser welding [3–6]. Cold forming is also frequently employed to further enhance the strength of these materials [7]. Among different joining processes, welding is currently one of the most important and widely used methods for joining HSS. Thus, it is crucial to investigate the feasibility of cold-formed and welded steels.

However, cold forming can introduce challenges to subsequent welding processes due to structural changes induced by the forming process [1, 8]. The weldability can be different from that of non-cold-formed HSS [8–10], potentially leading to changes in material behavior, such as increased strength and hardness, alongside decreased fracture toughness and ductility. Older guidelines, such as DIN 4100:1968, DASt009:1973, and DIN 18800-1:1990, addressed this issue by restricting welding in these areas or requiring post-weld treatments. Current guidelines such as the Eurocode 3 [11] address this issue by restrict welding in cold-formed and welded areas due to the potential risk of coarse grain formation resulting from recrystallization processes. This associated reduction in toughness can increase the risk of brittle fracture. A critical degree of deformation is required to initiate recrystallization processes, which can vary depending on the material [12]. If a workpiece is cold-formed to its critical degree of deformation, the Eurocode state that welding is only permitted again after a minimum distance of five times the sheet thickness. If maintaining this distance is not feasible, cost-intensive post-weld-treatments, such as normalizing, are necessary [11]. Other guidelines from crane construction and train construction do not impose any restrictions on this issue [13, 14].

Understanding the toughness behavior of cold-formed and welded high-strength steels necessitates a thorough investigation grounded in fracture mechanics. Fracture mechanics provides a framework to analyze the propagation of cracks and predict the conditions under which materials fail. This approach is essential for developing reliable and safe structures, as it considers the inherent flaws and stress concentrators that may lead to failure.

This study aims to investigate the toughness characteristics of high-strength steels subjected to cold-forming and welding processes. By applying fracture mechanics concepts, the fracture toughness of these materials will be investigated. This investigation will involve experimental testing, including Charpy V-notch impact tests and fracture toughness tests. The objective is to determine the severity of the embrittlement.

Cold forming of metals defines a manufacturing process where the metal is shaped or deformed at a temperature significantly below its recrystallization temperature. These manufacturing processes can be classified according to DIN 8582 [15] by various methods such as rolling, drawing, bending or pressing. Unlike hot forming, which involves heating the metal to high temperatures above the recrystallisation temperature, cold forming is performed without or with very little addition of heat, relying instead on mechanical force to achieve the desired shape. It is a cost-efficient forming process which is also beneficial to increase the strength and hardness or improve the surface finishing.

However, cold forming also has limitations, such as the potential for increased internal stresses and a reduced ability to shape very thick or hard materials without cracking or failure. The structure of the material changes depending on the cold forming process employed. During elongation and rolling the structure is getting compressed and the grain is becoming longer. During the bending process, the grain at the inner side is compressed during the outside is stretched as illustrated in Fig. 1.

A combination of cold forming and welding is often necessary to meet required specifications of a part However, welding in cold-formed areas is frequently prohibited due to recrystallization processes, which can lead to coarse grain formation and subsequent brittle behavior. As a result, current guidelines, such as Eurocode 3 [11], restrict welding in cold-formed areas once a critical degree of deformation has been reached, unless post-treatment methods, such as normalizing, are employed.

2.1. Structural changes in for a welded structure

Arc welding of structural steels results in the local melting of the base material, forming a fusion zone of the weld seam along with the filler material. Adjacent to the melting zone, the base material undergoes various short-term temperature cycles, with temperatures decreasing as the distance from the melting zone increases. Close to the smelting zone are high temperatures and fall with increasing distance. These different temperature zones cause changes in the material structure (Fig. 2), which in turn affect the strength, hardness, and ductility of the material [16–18].

For cold-formed steels, the critical zone can be located right next to the heat-affected zone (HAZ) [17, 18]. Due to previously introduced structural changes, the grains in the recrystallization zone can continue to grow, leading to premature material failure.

As the temperature increases, small regions within the cold-worked structure become thermodynamically unstable. These regions, known as nuclei, are the first to transform into new grains. This process begins at lower temperatures within the annealing range. These nuclei are typically strain-free and form at locations such as grain boundaries, dislocations, and other defects within the material. Once nucleation has started, these new strain-free grains start to grow. They consume the deformed grains around them, reducing the dislocation density and internal stresses. The driving force for this growth is the reduction in free energy associated with the elimination of defects and dislocations in the crystal lattice.

The size of the crystals formed from the nuclei depends on the number of nuclei present. If cold forming is extensive, many nuclei are formed, which block each other from growing, leading to a fine-grain structure. Conversely, minimal cold forming results in the creation of only a few nuclei, which can grow due to the available space, resulting in a coarse-grain structure. Figure 3 illustrates the difference in the structure after cold forming and heating to a recrystallization temperature, which occurs during the welding process [17, 19].

This process occurs within the recrystallization temperature (T_S), which is not fixed but is approximately 40% of the melting temperature [12, 20]. For steel, this range is typically around 600°C and is not influenced by any phase transformations.

3.1. Notch impact test

The notch impact test is a standardized high strain rate test that determines the amount of energy absorbed by a material during fracture. It is used to compare the toughness of various specimen of the same geometrical dimensions. This test is widely used in various industries, including construction, automotive, and aerospace, because the production of samples and the execution of the test are both fast and cost-efficient. It is particularly important for evaluating materials that will operate in low-temperature environments, where the risk of brittle fracture is higher. Additionally, it is commonly referenced in various guidelines for steel production and component design.

The specimen for the notch impact test is typically a small bar with standardized dimensions (e.g., 55 mm x 10 mm x 10 mm for the Charpy test). A V-shaped notch is machined into the center of the specimen to act as a stress concentrator and promote fracture initiation at a specific point. The standard notch depth is 2 mm, with an angle of 45 degrees and a 0.25 mm radius at the base of the notch. During the test, a pendulum hammer strikes the specimen, and the energy absorbed by the specimen causes the hammer to swing to a lesser height after impact. The difference in the height of the pendulum before and after impact is used to calculate the energy absorbed by the specimen during the test. The standards for the notch impact test can be found in guidelines such as ASTM E23 [21] and ISO 148-1 [22].

3.2. Fracture mechanics

Fracture mechanics provides a framework for understanding and predicting the behavior of cracked materials under various loading conditions. It integrates principles from materials science and mechanics to predict and analyze the failure of materials due to crack growth. Fundamental parameters like the stress intensity factor (K_IC), Crack Tip Opening Displacement (CTOD), and the J-integral offer critical insights into the mechanisms of crack initiation and growth. The ASTM E1820 [23] guidelines specify a standardized procedure for determining the fracture toughness of metallic materials, utilizing various types of standardized specimens, such as Single Edge Bend (SEB) specimens. The size of the samples depends on the analysis requirements, but the size ratios of the dimensions are specified in the standard.

Correct positioning of the notch is vital for the validity of the CTOD test. An incorrectly located fatigue crack may fail to sample the intended area, leading to invalid test results. Techniques such as polishing, etching, and metallurgical examination are employed to ensure precise notch placement. These methods are also useful post-test to confirm the test's validity, ensuring that the crack propagation occurred in the desired location and that the measured fracture toughness values accurately reflect the local material's behavior.

In ASTM E1921 [24], the reference temperature T₀ is determined within the transition temperature range for ferritic steels with a yield strength of 275–825 MPa. The T₀-temperature is characterized by the fracture toughness of a sample at which splitting cracks start due to elastic or plastic-elastic K_JC instabilities. Here, the variable J in K_JC denotes the definition of the crack opening mode. The tests prescribed in the standard are based on a three-point bending test, where the T₀-temperature is inferred from the K_JC values. To determine K_JC, several criteria must be met; if these criteria are violated, the results must either be completely discarded or partially censored to maintain the integrity of the data.

K_JC can be determined from tests that exhibit a complete cleavage fracture or significant pop-ins before a cleavage fracture at maximum force. Pop-ins are characterized by a sudden drop in force as the load increases while the crack opens simultaneously. K_JC can be calculated from the critical J-Integral (JC) using the material parameters Young's modulus (E) and Poisson's ratio (ν) according to Eq. 1:

\(\:{K}_{JC}=\sqrt{{J}_{C}*\frac{E}{1-{v}^{2}}}\) 1

In addition to determining individual fracture toughness parameters, the entire brittle-ductile transition range of the fracture toughness-temperature curve can be described using a Master Curve [25]. This concept, as used in ASTM E1921, represents the transition temperature and characterizes the fracture toughness behavior of ferritic steels with a yield strength of 275–825 MPa. The Master Curve method standardizes the fracture toughness (K_JC) for a 1-inch (2.54 cm) thick sample. According to this standard, the K_JC value of 100 MPa√m corresponds to the T₀-temperature, which marks the point where the material transitions from ductile to brittle behavior. The reference temperature T₀ is thus a crucial parameter, indicating the temperature at which the material exhibits a characteristic level of fracture toughness (100 MPa√m) [23, 26, 27].

To ensure sufficient strain restraint at the crack front during specimen breakage, the Master Curve includes a limitation defined by K_Jc(limit). This parameter ensures that the crack front experiences adequate constraint, which is crucial for valid fracture toughness measurements, as described in Eq. 2. The remaining ligament length b₀ is calculated using the difference between the specimen height W and the initial crack length a₀ [24, 26, 28].

\(\:{K}_{JC\left(limit\right)}=\sqrt{\frac{E*{b}_{0}*{\sigma\:}_{Y}}{30*(1-{v}^{2})}}\) 2

4.1. Testing material

In this study, the three high-strength fine-grained structural steels S700MC, S960QL and S1100 are analyzed. These steels are chosen to examine not only their strength characteristics but also their different delivery conditions and associated heat treatments. To produce standardized notched impact test specimens measuring 10x10 mm², these steels are utilized at a thickness of 12 mm.

The S700MC is a hot-rolled steel according to DINE EN 10149-2 [29] with a ferritic structure. Micro-alloy elements such as Mn, Ni, or Mo contribute to its excellent formability. On the other hand, S960QL is a quenched and tempered steel with a fine grain structure. Despite having similar delivery conditions to S960QL, S1100 cannot be designated as QL under DIN EN 10025-6 [30] as this standard only covers strengths up to 960 MPa. Both quenched and tempered steels, S960QL and S1100, exhibit a lamellar bainitic-martensitic microstructure. The low Carbon Equivalent Value (CEV) of S700MC enhances its weldability without requiring pre-heating. In contrast, S960QL and S1100 necessitate pre-heating before welding to prevent issues like hardening and cold cracking. The chemical composition was determined using optical emission spectrometry and is shown in Table 1.

Table 1

Chemicals composition of the test materials
	C [%]	Mn [%]	Si [%]	Al [%]	Nb [%]	V [%]	Ti [%]	Mo [%]	Cr [%]	Cu [%]	Ni [%]	CEV [%]
S700MC	0,066	1,86	0,023	0,054	0,049	0,005	0,132	0,022	0,03	0,013	0,03	0,391
S960QL	0,163	1,10	0,256	0,093	0,028	0,001	0,003	0,591	0,614	0,017	0,034	0,591
S1100	0,158	0,855	0,219	0,051	0,018	0,02	0,002	0,375	0,484	0,012	1,27	0,562

The mechanical characteristics investigated through tensile tests, as shown in Table 2, provide an initial indication of the formability of the steels. It is evident from the data that the elongation decreases significantly with increasing strength.

Table 2

Material properties of the test material
	yield strength [MPa]	tensile strength [MPa]	elongation without necking [%]	elongation at break [%]
S700MC	788	840	9,3	17,6
S960QL	1009	1049	5,5	12,8
S1100	1189	1398	3,5	10,3

4.2. Cold forming

In this article, two cold forming processes, bending and elongation, were investigated. The elongation process involved stretching the material using a tensile machine with a maximum test force of 2,000 kN. Given the high strength of the steels and their large dimensions, such a high test force was necessary to deform the material. The elongation of the plate was achieved by pulling a 12 mm thick sheet measuring 700 mm x 1000 mm until the defined strain was reached. To ensure a straight stop, edges were milled, and the sheets were mounted perpendicularly to the test direction to achieve an even force distribution during testing. Retroreflection stripes were applied at defined distances along the edges to measure elongation. During the process, the shift of the retroreflectors was measured using a laser, while the machine itself recorded the force. This method enabled the recording of the force-strain diagram throughout the entire process. The strain rate was adjusted to achieve both high strain just before necking and low strain conditions. The objective was to investigate the effects of cold forming by elongation and the subsequent development of coarse grain after welding.

Due to the different strain rates determined from the tensile tests, each material had specific maximum strain rates before necking occurred. Specifically, S700MC was tested at a strain rate of 3–9%, S960QL at 5%, and S1100 at 3%. Further elongation beyond these points led to necking and subsequent fracture.

Cold forming through bending was conducted using a folding machine, setting the inner radius to 56 mm, which was measured post-bending.

4.3. Welding of the cold formed steels

The elongated and bent specimens were joined using Gas Metal Arc Welding (GMAW). To investigate the deformed zone, a deformed sheet was joined with an unformed sheet of the same material. To ensure a straight line of the Heat Affected Zone (HAZ) and sufficient filler material for a stable connection, a HV-joint with an opening angle of 40° was employed. In this configuration, the straight side was the deformed side. To achieve consistent results between the sheets, welding was conducted using a robotic welding system.

The elongated plates were welded in the PA-position, while the bent plates were welded in the PC-position. The shielding gas used was M21 (18% CO2 and the remainder argon) to protect the weld seam. T_8 − 5-times were measured directly in the melt using PT100 resistance. Preheating of the first layer was not necessary for S700MC. However, the higher-strength steels, S960QL and S1100, were preheated to 100°C. The intermediate and cover layers were then welded at 120°C. T_8 − 5-times where between 8 and 10 seconds.

To fill the 12 mm plate, four layers were required, comprising of two filler layers and two cover layers. An additional layer was applied on the opposite side without preheating to ensure good root protection. To maintain strength and avoid degradation, steels were welded with filler materials of the same grade: Union X77 for S700MC and ED-FK1000 for the quenched and tempered steels (S960QL and S1100). Detailed welding parameters are provided in Table 3.

Table 3

Welding parameters
material	parameter	root layer	filler layer 1	filler layer 2	cover layer 1	cover layer 2
S700MC	speed [cm/min]	25,5	40,8	51	51	51
	voltage [V]	17,7	23,7	23,7	23,7	23,7
	current [A]	170	290	290	290	290
S960Ql and S1100	speed [cm/min]	25,5	40,8	51	51	51
	voltage [V]	17,7	26,8	26,8	26,8	26,8
	current [A]	150	260	260	260	260

To verify the welding process, hardness tests via Ultrasonic Contact Impedance (UCI) were performed at the weld seams. Typically, the weld seam exhibits a characteristic hardness distribution. In structural steels, a loss of strength is common in the softened zone, which cannot be entirely avoided. Following this, there is a slight increase in hardness until the material returns to its normal strength comparable to the base material. Figure 4 illustrates the measurements taken on S700MC and S1100 after the welding process.

4.4. Positioning and extracting of the specimen

The specimens were extracted from the welded plates with a slight excess length. To accurately determine the notch position, the Heat Affected Zone (HAZ) was etched using 10% nitric acid (Nital) to make it visible. Due to this excess length, the notch was positioned in the recrystallization zone at the center of the specimen. Figure 5 demonstrates the notch position at the example of the straight sheet.

For the elongated sheets, samples could be taken along the entire length. In the case of bent sheets, samples were extracted from the area of greatest deformation, typically at the radius. This was achieved by cutting the sheets in half. Notched bar impact bending samples were then taken from the left side, while fracture mechanics samples were taken from the right side. The maximum size of the fracture mechanics samples was set at 10 mm to facilitate testing and ensure accurate evaluation.

4.5. Fracture mechanics

The CTOD (Crack Tip Opening Displacement) tests were conducted following ASTM E 1820 [23] and ASTM E1921 [24] standards, using SEB (Single Edge Bend) specimens with dimensions as recommended in these guidelines, as depicted in Fig. 6.

Initially, the specimens were pre-cracked under a stress ratio of 0,1, and the required force was determined accordingly. It took between 70.000 to 100.000 cycles to propagate the crack to a length of 0,4 to 0,7 times the specimen width (W). Following this, 1 mm deep side notches were milled into the specimens.

The tests were conducted in a temperature-controlled chamber using the single temperature method at -66°C. The span of the bend roller (S) was set to 80 mm. To ensure gradual loading and prevent impact, the force was applied slowly from the top at a rate of 0,3 mm/min. The stamp descended from above at the same rate of 0,3 mm/min until reaching a cut-off limit of 5 mm, controlled by path control. The test would automatically stop if a fracture was detected, defined by a 90% drop in force. Throughout the test, an extension sensor measured the displacement.

After fracture, annealing colors were generated on the specimen to aid in examining the residual fracture surfaces. To induce a brittle residual fracture surface, the samples were cooled in liquid nitrogen and subsequently fractured by impacting with a hammer. This helps to preserve the fracture surfaces in a brittle state, enabling detailed examination and analysis of the fracture characteristics. Images of the fractured surfaces were captured and analyzed using IC Measure software to determine the proportion of fatigue fracture versus residual fracture.

4.6. Notch impact test

For the notch impact test, a hammer with a energy of 300 J was applied. The specimens were V-notched according to DIN EN ISO 148 [22], with standard dimensions of 10x10x55 mm³ and a notch depth of 2 mm. The tests were conducted in alcohol baths cooled down to temperatures as low as -90°C. To reach even lower temperatures, nitrogen at -196°C was used. Higher temperatures were achieved by annealing the specimens in a furnace for a minimum of 10 minutes, ensuring uniform temperature throughout the sample. Immediately after removal from the temperature-controlled medium, the notch impact tests were performed. The resulting data pairs were plotted on a temperature-impact strength diagram. Typically, an S-curve characteristic of structural steels was fitted using an arctangent function. This fit was utilized to determine the characteristic value of T_27J-temperatures, which represent the temperature at which the impact energy reaches 27J.

5.1. Notch impact tests

The following diagrams in Fig. 7 present the results of the notched bar impact tests, comparing the unwelded base material with the welded and cold-formed conditions. Each diagram includes a description of the respective conditions. The impact energies depicted correspond to one specimen per data pair, and the curves were determined using the arctangent function.

When comparing the specimens elongated through different processes, it is observed that the high shelf of the base material exhibits greater impact energy compared to the welded conditions, which show consistent values. The loss of the higher shelf in impact energy should not be considered too critical, as it generally indicates a high level of ductility in the material. However, the lower shelf and transition temperature seem similar across all conditions except for the 3% elongation. This observation might be influenced by the larger number of samples tested at lower temperatures from the 3% elongated sheet, which naturally shifts the curve fit downwards and extends the transition region to higher temperatures. Individual data points from the welded conditions are consistently at the same level across the temperature range.

Similarly to the S700MC, a loss of impact energy at the high shelf was detected in the elongated and welded condition of S960QL. However, the T_27J-temperatures remained comparable across these conditions. No loss of ductility was detected in the investigated area of the cold-formed and welded condition as illustrated in Fig. 8.

Figure 9 shows that the investigated conditions of S1100 (unwelded base material and 3% elongated and welded) do not exhibit any signs of losing ductility in the cold-formed and welded conditions. Although there is again a slight decrease in the high shelf after welding, the transition area and the characteristic T_27J-values remain unchanged.

5.2. Master Curves

The following diagrams in Fig. 10 and Fig. 11 present the results of the fracture mechanics tests plotted as master curves for S700MC and S960QL. The investigation includes three conditions: non-welded base material, welded base material, and bent condition. The master curves are calculated out of 6 specimens exclusively from tested temperatures of -66°C. Additional specimens are included to compare the trends observed in the master curves.

The different conditions of S700MC show only a minor deviation. The T₀-temperatures of the welded and non-welded base material are very similar. After bending and welding, the T₀-temperatures increase marginally. However, there is no clear drop in toughness due to embrittlement observed in the investigated area. The samples tested at higher temperatures also reflect the trend of the master curve.

The base material exhibits minimal scattering. In contrast, the welded samples display greater scatter, especially in the bent areas. This variability may arise from slight notch displacement or, despite robotic welding, incomplete repeatability in production conditions. Additionally, one sample had to be limited due to exceptionally high toughness.

However, the T₀-temperatures decrease after welding and further decrease after cold forming. This temperature reduction can be attributed to the re-tempering of the previously tempered microstructure in the investigated area. Despite these changes, no embrittlement is observed in the investigated areas. For the bent condition, the fracture toughness was so high that it was necessary to limit one value (marked in red) to include it in the master curve. Despite ASTM E1921 not being standardized for S960QL, the master curve exhibited consistent behavior across all tested temperatures.

In conclusion, the investigated high-strength steels (S700MC, S960QL, S1100) demonstrate consistent impact toughness and fracture resistance across base, welded, and cold-formed conditions. The observed minor variations in mechanical properties are well within acceptable limits for structural applications, affirming the suitability of these steels for demanding engineering environments where welding and cold forming are integrated processes.

Eurocode 3 maintains regulations concerning welding in cold-formed areas due to concerns over potential structural integrity compromises, necessitating meticulous implementation procedures. Nonetheless, this study did not discern a diminution in material toughness within the examined areas of the series of high-strength steels (HSS) across various processing conditions. The absence of observable grain coarsening in the recrystallisation zone suggests that contemporary HSS are inherently resistant to such microstructural transformations und the given circumstances. Furthermore, none of the investigated materials or processing configurations exhibited definitive indications of embrittlement subsequent to undergoing cold forming and welding procedures. These findings align with prior research, reinforcing the robustness of HSS under these manufacturing conditions [1, 17, 31, 32]. Guidelines for crane construction, such as DIN EN 13001-3-1[13], and welding standards for railway vehicles and components, like DIN EN 15085-3[14], do not impose restrictions indicating embrittlement in cold-formed and welded areas.

The authors declare that they have no conflict of interest.

Acknowledgements

The research project IFG Nr. 01IF21558N / P 1508 “Zähigkeit kaltgeformter geschweißter Bereiche in höchst- und ultrahochfesten Stählen” from the Research Association for steel Application (FOSTA), Düsseldorf, is supported by the Federal Ministry of Economic Affairs and Climate Action the German Federation of Industrial Research Associations (AiF) as part of the programme for promoting industrial cooperative research (IGF) on the basis of a decision by the German Bundestag.

Funding Open Access funding enabled and organized by Projekt DEAL.

Afkhami S, Björk T, Larkiola J (2019) Weldability of cold-formed high strength and ultra-high strength steels. J Constr Steel Res 158:86–98
Spindler H, Klein M, Rauch R, Pichler A (2005) ‘HIGH STRENGTH AND ULTRA HIGH STRENGTH HOT ROLLED STEEL GRADES – PRODUCTS FOR ADVANCED APPLICATIONS’, (2005)
Kah P, Pirinen M, Suoranta R, Martikainen J (2013) ‘Welding Ultra High Strength Steels’ AMR 849:357–365
Guo W, Li L, Dong S, Crowther D, Thompson A (2017) Comparison of microstructure and mechanical properties of ultra-narrow gap laser and gas-metal-arc welded S960 high strength steel. Opt Lasers Eng 91:1–15
Guo W, Li L, Crowther D, Dong S, Francis JA, Thompson A (2016) ‘Laser welding of high strength steels (S960 and S700) with medium thickness’. J Laser Appl, 28, (2)
Guo W, Liu Q, Francis JA et al (2015) Comparison of laser welds in thick section S700 high-strength steel manufactured in flat (1G) and horizontal (2G) positions. CIRP Ann 64(1):197–200
Ritakallio P, Björk T (2014) Low-temperature ductility and structural behaviour of cold‐formed hollow section structures – progress during the past two decades. Steel Constr 7(2):107–115
Cosham A, Hopkins P, Palmer A (2004) ‘An Experimental and Numerical Study of the Effect of Pre-Strain on the Fracture Toughness of Line Pipe Steel’. 2004 International Pipeline Conference, Calgary, Alberta, Canada, Oct. 04–08, pp. 1635–1652
Bal CS, Kumar A (2008) Radionuclide therapy for hepatocellular carcinoma: indication, cost and efficacy. Trop gastroenterology: official J Dig Dis Foundation 29(2):62–70
Ma J-L, Chan T-M, Young B (2015) Material properties and residual stresses of cold-formed high strength steel hollow sections. J Constr Steel Res 109:152–165
‘DIN EN (1993) -1-8:2010-12 Eurocode_3: Bemessung und Konstruktion von Stahlbauten_- Teil_1–8: Bemessung von Anschlüssen; Deutsche Fassung EN_1993-1-8:2005_+ AC:2009&#8217
Klocke F (2017) Fertigungsverfahren 4. Springer Berlin Heidelberg, Berlin, Heidelberg
‘DIN EN 13001 -3-1:2019-03, Krane_- Konstruktion allgemein_- Teil_3 – 1: Grenzzustände und Sicherheitsnachweis von Stahltragwerken; Deutsche Fassung EN_13001-3-1:2012 + A2:2018&#8217
‘DIN EN 15085-3:2023-07, Bahnanwendungen_- Schweißen von Schienenfahrzeugen und -fahrzeugteilen_- Teil_3: Konstruktionsvorgaben; Deutsche Fassung EN_15085-3:2022 + A1:2023&#8217
‘DIN 8582 2003-09, Fertigungsverfahren Umformen_- Einordnung; Unterteilung, Begriffe, Alphabetische Übersicht&#8217
Radaj D (1988) Wärmewirkungen des Schweißens: Temperaturfeld, Eigenspannungen, Verzug. Springer Berlin Heidelberg, Berlin, Heidelberg
Röhrs K (2005) Untersuchungen zum Schweißen in kaltgeformten Bereichen von Feinkornbaustählen. Shaker, Aachen. 1st edn.)
Ruge J (1991) Handbuch der Schweisstechnik. Springer-, Berlin. 3rd edn.)
Haake H, Kauczor E (1964) Metall unter dem Mikroskop. Springer Berlin Heidelberg, Berlin, Heidelberg
Gottstein G (2001) Physikalische Grundlagen der Materialkunde. Springer Berlin Heidelberg; Imprint; Springer, Berlin, Heidelberg
‘Test Methods for Notched Bar Impact Testing of Metallic Materials’
‘DIN EN ISO 148- 1:2017-05, Metallische Werkstoffe_- Kerbschlagbiegeversuch nach Charpy_- Teil_1: Prüfverfahren (ISO_148-1:2016); Deutsche Fassung EN_ISO_148-1:2016&#8217
‘ASTM E 1820 (2024) Test Method for Measurement of Fracture Toughness&#8217
‘ASTM E (1921) Test Method for Determination of Reference Temperature, T0, for Ferritic Steels in the Transition Range’
Wallin K (1999) The master curve method: a new concept for brittle fracture. IJMPT 14(2/3/4):342
Hesse A-C (2023) ‘Zur Bruchzähigkeit strahlgeschweißter hochfester Feinkornbaustähle’ (Shaker, Düren, 1st edn.)
Nagel G, Blauel J-G (1999) Evaluation of the standard master curve for fracture toughness determination. Nucl Eng Des 190(1–2):159–169
Wallin K (2011) Fracture Toughness of Engineering Materials: Estimation and Application. EMAS Publishing, Warrington
‘DIN EN 10149- 2:2013-12, Warmgewalzte Flacherzeugnisse aus Stählen mit hoher Streckgrenze zum Kaltumformen_- Teil_2: Technische Lieferbedingungen für thermomechanisch gewalzte Stähle; Deutsche Fassung EN_10149-2:2013’
‘DIN EN 10025-6:2023-06, Warmgewalzte Erzeugnisse aus Baustählen_- Teil_6: Technische Lieferbedingungen für Flacherzeugnisse aus Stählen mit höherer Streckgrenze im vergüteten Zustand; Deutsche Fassung EN_10025-6:2019 + A1:2022&#8217
Werner T, Nitschke-Pagel T, Dilger K (2023) Entwicklung der Rekristallisationskorngröße an kaltumgeformten hochfesten Stählen. Stahlbau 92(10):658–663
Halbritter J (2000) Beurteilung der Schweißeignung in kaltumgeformten Bereichen bei Einsatz hochfester Feinkornbaustähle. Stahlbau 69(4):292–294

Download PDF

Reviewers agreed at journal
23 Aug, 2024
Reviewers invited by journal
23 Aug, 2024
Editor invited by journal
20 Aug, 2024
Editor assigned by journal
15 Aug, 2024
First submitted to journal
15 Aug, 2024

You are reading this latest preprint version

Investigation of the toughness behavior in cold-formed and welded high-strength steels using fracture mechanics concepts and notch impact test

Status:

Version 1

Abstract

Figures

1. Introduction

2. Cold forming and welding

2.1. Structural changes in for a welded structure

3. Determination of ductility

3.1. Notch impact test

3.2. Fracture mechanics

4. Experimental procedure

4.1. Testing material

4.2. Cold forming

4.3. Welding of the cold formed steels

4.4. Positioning and extracting of the specimen

4.5. Fracture mechanics

4.6. Notch impact test

5. Results

5.1. Notch impact tests

5.2. Master Curves

6. Conclusions

Declarations

References

Status:

Version 1