Structure and Mechanical Properties of High-Strength Structural Steels (original) (raw)
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A R C H I V E S 5/2 Structural and strength characteristics of wear-resistant martensitic steels
The paper presents structural, strength and impact resistance characteristics of a construction materials group. These are low-alloy steels of martensitic type structure, showing very high strength moduli, high wear resistance in the dynamic load conditions, and good weldability. Subject of the studies has been the most commonly used group of Hardox steels (Hardox 400 and Hardox 500), as well as the Polish equivalents of those materials (HTK 700 and HTK 900). It has been shown that despite similarity of chemical composition and production processes, the steels differ somewhat in structure, which influences their strength and usability (an operating experiment has been performed). Unfavourable structural changes in welded joints deteriorate their operating properties in the heat-affected zones, and cause clear drop in the wear resistance, despite the application of welding procedures recommended by a producer. The work presents synthesis of knowledge on that modern and still not well recognized group of steels, documented with results of own studies.
Metallurgical and Materials Transactions A-physical Metallurgy and Materials Science, 1999
A series of dual-phase (DP) steels containing finely dispersed martensite with different volume fractions of martensite (V m) were produced by intermediate quenching of a boron- and vanadium-containing microalloyed steel. The volume fraction of martensite was varied from 0.3 to 0.8 by changing the intercritical annealing temperature. The tensile and impact properties of these steels were studied and compared to those of step-quenched steels, which showed banded microstructures. The experimental results show that DP steels with finely dispersed microstructures have excellent mechanical properties, including high impact toughness values, with an optimum in properties obtained at ∼0.55 V m. A further increase in V m was found to decrease the yield and tensile strengths as well as the impact properties. It was shown that models developed on the basis of a rule of mixtures are inadequate in capturing the tensile properties of DP steels with V m>0.55. Jaoul-Crussard analyses of the work-hardening behavior of the high-martensite volume fraction DP steels show three distinct stages of plastic deformation.
Metallurgical and Materials Transactions A, 2001
A series of high-martensite dual-phase (HMDP) steels exhibiting a 0.3 to 0.8 volume fraction of martensite (V m), produced by intermediate quenching (IQ) of a vanadium and boron-containing microalloyed steel, have been studied for toughness and fatigue behavior to supplement the contents of a recent report by the present authors on the unusual tensile behavior of these steels. The studies included assessment of the quasi-static and dynamic fracture toughness and fatigue-crack growth (FCG) behavior of the developed steels. The experimental results show that the quasi-static fracturetoughness (K ICV) increases with increasing V m in the range between V m ϭ 0.3 and 0.6 and then decreases, whereas the dynamic fracture-toughness parameters (K ID , K D , and J ID) exhibit a significant increase in their magnitudes for steels containing 0.45 to 0.60 V m before achieving a saturation plateau. Both the quasi-static and dynamic fracture-toughness values exhibit the best range of toughnesses for specimens containing approximately equal amounts of precipitate-free ferrite and martensite in a refined microstructural state. The magnitudes of the fatigue threshold in HMDP steels, for V m between 0.55 and 0.60, appear to be superior to those of structural steels of a similar strength level. The Parislaw exponents (m) for the developed HMDP steels increase with increasing V m , with an attendant decrease in the pre-exponential factor (C).
Structure and Mechanical Properties of High Strength Steel 960QL Weldments
Defect and Diffusion Forum, 2022
The structure and the mechanical properties of the high-strength structural martensitic steels used in manufacturing the mechanism parts subjected to significant cyclic dynamical loads are considered. All the steels have a similar martensitic-bainite structure and a high stability of their mechanical properties. At the same time, their structures are found to contain secondary phases, which can degrade their functional properties. 03Kh11N10M2T maraging steel exhibits fairly high impact toughness for this class of steels despite a brittle character of fracture during bending impact tests.
Archives of Metallurgy and Materials, 2015
The paper presents results of dynamic tensile investigations of high-manganese Fe-20 wt.% Mn-3 wt.% Al-3 wt.% Si-0.2 wt.% steel. The research was carried out on a flywheel machine, which enables to perform dynamic tensile tests and impact bending with a linear velocity of the enforcing element in the range of 5÷40 m/s. It was found that the studied steel was characterized by very good mechanical properties. Strength of the tested materials was determined in the static tensile test and dynamic deformation test, while its hardness was measured with the Vickers hardness test method. The surface of fractures that were created in the areas where the sample was torn were analyzed. These fractures indicate the presence of transcrystalline ductile fractures. Fractographic tests were performed with the use of a scanning electron microscope. The structure was analyzed by light optical microscopy. Substructure studies revealed occurrence of mechanical twinning induced by high strain rates. A detailed analysis of the structure was performed with the use of a transmission scanning electron microscope STEM.
The design of advanced performance high strength low-carbon martensitic armour steels
Materials Science and Engineering: A, 2008
Neither a higher hardness nor higher mechanical properties (yield strength, ultimate tensile strength, impact energy, and %elongation) appear to be exclusive or even reliable criteria for predicting the ballistic performance of martensitic armour steels, as shown in our previous work [K. Maweja, W.E. Stumpf, Mater. Sci. Eng. A (February), submitted for publication]. An alternative design methodology for tempered martensitic armour steels is, therefore, proposed which is based on the effect of retained austenite on the ratio of the yield to ultimate tensile strength (YS/UTS), the microstructure of the tempered martensite and its martensite start temperature M s. This approach was developed using 6 mm thick armour plates and later was successfully applied to the design of eight experimental armour steels with plate thicknesses ranging from 4.7 to 5.2 mm and tested by the standard R4 (5.56 mm rounds) ballistic test. Article Outline 1. Introduction 2. Materials and experiments 2.1. Chemical composition and manufacturing 3. Results of the ballistic testing 3.1. The ballistic parameter (BP) 3.2. Microstructure 3.3. The martensite start temperature of the steel 4. An improved design scheme for advanced performance armour steels 4.1. The chemical composition of the steel and its tempering treatment 4.2. The microstrural-based design procedure for low-carbon martensitic plates with thickness less than 8.5 mm 5. Conclusion Table 5. Optimum heat treatment and microstructures High performance armour plates High strength components Category Group 1 Groups 2 Austenitisation 870-950 °C for 20-60 min 800-860 °C for 20-60 min Quenching medium Water at room temperature Water or oil
Effect of microstructure on the impact toughness transition temperature of direct-quenched steels
Materials Science and Engineering: A, 2018
A sufficient level of toughness at low temperatures is paramount for the use of structural steels intended for arctic applications. Therefore, it is important for the steel industry to identify the factors that control brittle fracture toughness. In this study, the quantitative effect of microstructure on the impact toughness transition temperature has been investigated with 18 different thermomechanically rolled and direct-quenched low-carbon ultra-high-strength steels with varying martensite and bainite contents. The steels were produced by altering their chemical composition, the finish rolling temperature and the total reduction of the prior austenite grains in the non-recrystallisation temperature regime, i.e. austenite pancaking, and characterised in terms of microstructural constituents, grain size distributions and texture as well as by using Charpy-V impact and tensile testing. It is shown for the first time that the impact toughness transition temperatures T 28J and T 50 closely follow a dynamic reference toughness, defined by yield strength and the size of the coarsest grains in the effective grain size distribution at 80th percentile. Decreasing the area fraction of {100} cleavage planes oriented within 15°of the macroscopic fracture plane by increasing austenite pancaking is also shown to improve T 28J. The best toughness is achieved with the lowest finish rolling temperatures that are nevertheless high enough to avoid the subsequent formation of granular bainite, which weakens both the toughness and strength. The results show that it is perfectly possible to produce untempered ultra-high-strength martensitic and martensitic-bainitic structural steels with adequate low-temperature toughness when the grain size is properly controlled.
Modern high strength steels under high strain-rate regimes
EPJ Web of Conferences
In order to properly design critical infrastructures and buildings in steel (bridges, high-rise building, off-shore, cranes, etc.), certain requirements concerning to mechanical resistance and robustness under exceptional actions have to be carefully fulfilled. An acceptable level of safety must be assured to avoid human loss, environmental pollution and material damage. These structures can be subjected to severe accidental loading such as blast or impact. In this context it is fundamental to adequately know the behaviour of structural steel under high strain rate. Modern high strength steels are quenched and selftempered steels. These steels have several layers with differentiated microstructures (martensitic in the cortical part and ferritic in the core). The behaviour of the single layer at high strain rate regimes have to be accurately studied. The paper collects and discusses the tensile results at high strain rate obtained on samples of homogeneous layers of S690QL and S960QL...
Fatigue Properties of Wear Resistant Martensitic Steel
2014
In the automotive industry about 60% of mass of the car continue to represent structural elements, formed of steel plates of increasing strength while maintaining good plastic characteristics and susceptibility to stamping. Constructors seek to reduce the mass of cars and semi-trailers and it is possible through the use of fine-grained and quench and tempered high strength steels. An important factor that guarantees safety of use is the knowledge about safe operation life. In order to answer to this question are needed relevant studies including fatigue tests. The article presents the results of fatigue tests in the range of low and high cycle fatigue of wear resistant quenched and tempered martensitic steel on example of Hardox steel 400 and 450. There is also discussed the influence of grain size on the shape of fatigue curves. Obtained results of wear resistant martensitic steels are compared with the results of fatigue tests of S355J2 structural steel.