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58-548: The "HY" steels are designed to possess a high yield strength (strength in resisting permanent plastic deformation). HY-80 is accompanied by HY-100 and HY-130 with each of the 80, 100 and 130 referring to their yield strength in ksi (80,000 psi, 100,000 psi and 130,000 psi). HY-80 and HY-100 are both weldable grades, whereas the HY-130 is generally considered unweldable. Modern steel manufacturing methods that can precisely control time/temperature during processing of HY steels has made

116-404: A coil, are caused by the coiling process. When these conditions are undesirable, it is essential for suppliers to be informed to provide appropriate materials. The presence of YPE is influenced by chemical composition and mill processing methods such as skin passing or temper rolling, which temporarily eliminate YPE and improve surface quality. However, YPE can return over time due to aging, which

174-454: A depth of 2,250 feet (690 m). The first production submarines to use HY-80 steel were the Permit class . These reportedly had a normal operating depth of 1,300 feet, roughly two-thirds the crush depth limit imposed by the steel. USS  Thresher , the lead boat of this class, was lost in an accident in 1963. At the time, this unexplained accident raised much controversy about its cause and

232-461: A distinct upper yield point or a delay in work hardening. These tensile testing phenomena, wherein the strain increases but stress does not increase as expected, are two types of yield point elongation. Yield Point Elongation (YPE) significantly impacts the usability of steel. In the context of tensile testing and the engineering stress-strain curve, the Yield Point is the initial stress level, below

290-503: A ferrite stabilizer and can combine with carbon to form chromium carbides for increased strength of the material. Antimony, tin and arsenic are potentially dangerous elements to have in the compositional makeup due to their ability to form eutectics and suppress local melting temperatures. This is an increasing problem with the increased used of scrap in the making of steel in the electric arc furnace (EAF) process. The precise range of permitted alloy content varies slightly according to

348-404: A mechanical component, since it represents the upper limit to forces that can be applied without producing permanent deformation. For most metals, such as aluminium and cold-worked steel , there is a gradual onset of non-linear behavior, and no precise yield point. In such a case, the offset yield point (or proof stress ) is taken as the stress at which 0.2% plastic deformation occurs. Yielding

406-405: A need for improved steels for stronger pressure hulls. The strength of a submarine hull is constrained not merely by yield strength, but also fatigue strength. As well as the obvious need for a hull strong enough not to be crushed at depth, the cyclical effect of hundreds of dives over a submarine's lifetime mean that fatigue strength is also important. To provide sufficient resistance to fatigue,

464-446: A normal operating depth of "greater than 800 feet". Based on the reported operating depth of Thresher , it may be assumed that the normal operating depth of Seawolf is roughly double the official figure. HY-100 too was dogged by problems of weld cracking. Seawolf ' s construction suffered setbacks in 1991 and an estimated 15% or two years' work on hull construction had to be abandoned. Although later solved, these extra costs (and

522-412: A process known as bowing or ringing, in which a new ring of dislocations is created around the particle. The shearing formula goes as: and the bowing/ringing formula: In these formulas, r particle {\displaystyle r_{\text{particle}}\,} is the particle radius, γ particle-matrix {\displaystyle \gamma _{\text{particle-matrix}}\,}

580-464: A scale to measure strengths on another. Hardness testing can therefore be an economical substitute for tensile testing, as well as providing local variations in yield strength due to, e.g., welding or forming operations. For critical situations, tension testing is often done to eliminate ambiguity. However, it is possible to obtain stress-strain curves from indentation-based procedures, provided certain conditions are met. These procedures are grouped under

638-419: A variant of special treatment steel (STS), a homogeneous Krupp-type armor steel developed by Carnegie Steel in 1910 and commonly used for deck protection, with modifications in carbon and nickel and the addition of molybdenum , became known as "Low-carbon STS"; this steel showed the best combination of all the desirable properties. Low-carbon STS became the forerunner of HY-80, and was first used in 1953 for

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696-415: A variety of failures immediately after the weld or in service failures when put under load. In HY-80 steels the level of distortion is proportional to the level of weld heat input, the higher the heat input the higher levels of distortion. HY-80 has been found to have less in-plane weld shrinkage and less out-of-plane distortion than the common ABS Grade DH-36. The testing of HY-80 steel can be divided into

754-425: Is a gradual failure mode which is normally not catastrophic , unlike ultimate failure . For ductile materials, the yield strength is typically distinct from the ultimate tensile strength , which is the load-bearing capacity for a given material. The ratio of yield strength to ultimate tensile strength is an important parameter for applications such steel for pipelines , and has been found to be proportional to

812-678: Is a real weldability concern that must be addressed in HY-80 steels. Hydrogen embrittlement is a high risk under all conditions for HY-80 and falls into zone 3 for the AWS method. HAC/HIC can occur in either the Fusion Zone or the Heat Affected Zone. As mentioned previously the HAZ and FZ are both susceptible to the formation of martensite and thus are at risk for HAC/HIC. The Fusion Zone HIC/HAC can be addressed with

870-429: Is considered secondary to their yield strength. Where this is required to meet a particular value, it is specified for each order. Notch toughness is a measure of tear resistance , a steel's ability to resist further tearing from a pre-existing notch. It is usually evaluated as the tear-yield ratio , the ratio of tear resistance to yield strength. Wrought HY-80 steels are produced by, amongst others, ArcelorMittal in

928-410: Is formed with the presence of oxides and the composition of the filler metal can increase the formation of these critical nucleation sites. The selection of the welding process can have a significant impact on the areas affected by welding. The heat input can alter the microstructure in HAZ and the fusion zone alike and weld metal/HAZ toughness is a key consideration/requirement for HY-80 weldments. It

986-482: Is holding at a temperature usually 200-400 °C. Despite its drawbacks, YPE offers advantages in certain applications, such as roll forming , and reduces springback . Generally, steel with YPE is highly formable. Seawolf-class submarine The Seawolf class is a class of nuclear-powered , fast attack submarines (SSN) in service with the United States Navy. The class was the intended successor to

1044-540: Is important to consider the totality of the weldment when selecting a process because thick plate generally requires multi-pass welds and additional passes can alter previously deposited weld metal. Different methods ( SMAW , GMAW , SAW ) can have a significant influence of the fracture toughness of the material. SAW as an example can temper previous weld passes due to its generally high heat input characteristics. The detailed hardness profiles of HY-80 weldments varies with different processes (gradients vary dramatically), but

1102-468: Is often difficult to precisely define yielding due to the wide variety of stress–strain curves exhibited by real materials. In addition, there are several possible ways to define yielding: Yielded structures have a lower stiffness, leading to increased deflections and decreased buckling strength. The structure will be permanently deformed when the load is removed, and may have residual stresses. Engineering metals display strain hardening, which implies that

1160-407: Is significantly lower than the expected theoretical value can be explained by the presence of dislocations and defects in the materials. Indeed, whiskers with perfect single crystal structure and defect-free surfaces have been shown to demonstrate yield stress approaching the theoretical value. For example, nanowhiskers of copper were shown to undergo brittle fracture at 1 GPa, a value much higher than

1218-447: Is still a concern that must be addressed with proper preheat and weld procedures to control the cooling rates. Slow cooling rates can be as detrimental as rapid cooling rates in the HAZ. Rapid cooling will form untempered martensite; however, very slow cooling rates caused by high preheat or a combination of preheat and high heat input from the weld procedures can create a very brittle martensite due to high carbon concentrations that form in

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1276-564: Is stronger than the HY-80 steel employed in previous classes, in order to withstand water pressure at greater depths. Seawolf -class submarines are larger, faster, and significantly quieter than previous Los Angeles -class submarines; they also carry more weapons and have twice as many torpedo tubes. The boats are able to carry up to 50 UGM-109 Tomahawk cruise missiles for attacking land and sea surface targets. The boats also have extensive equipment to allow shallow water operations. The class uses

1334-462: Is the magnitude of the Burgers vector , and ρ {\displaystyle \rho } is the dislocation density. By alloying the material, impurity atoms in low concentrations will occupy a lattice position directly below a dislocation, such as directly below an extra half plane defect. This relieves a tensile strain directly below the dislocation by filling that empty lattice space with

1392-401: Is the strain induced in the lattice due to adding the impurity. Where the presence of a secondary phase will increase yield strength by blocking the motion of dislocations within the crystal. A line defect that, while moving through the matrix, will be forced against a small particle or precipitate of the material. Dislocations can move through this particle either by shearing the particle or by

1450-420: Is the surface tension between the matrix and the particle, l interparticle {\displaystyle l_{\text{interparticle}}\,} is the distance between the particles. Where a buildup of dislocations at a grain boundary causes a repulsive force between dislocations. As grain size decreases, the surface area to volume ratio of the grain increases, allowing more buildup of dislocations at

1508-675: The Los Angeles class , and design work began in 1983. A fleet of 29 submarines was to be built over a ten-year period, but that was reduced to 12 submarines. The end of the Cold War and budget constraints led to the cancellation of any further additions to the fleet in 1995, leaving the Seawolf class limited to just three boats. This, in turn, led to the design of the smaller Virginia class . The Seawolf class cost about $ 3 billion per unit ($ 3.5 billion for USS  Jimmy Carter ), making it

1566-514: The Skate -class , which were the first nuclear submarines, with the then-conventional hull shape. The later Skipjack class , although of the new Albacore 'teardrop' hull form, also used these earlier steels. Such boats had normal operating depths of some 700 feet (210 m), and a crush depth of 1,100 feet (340 m). Bureau of Ships conducted a research program for developing higher strength steel for ship and submarine construction. During testing,

1624-605: The sonic layer depth . World War II submarines operated at a total depth of rarely more than 100 metres. With the development of nuclear submarines , their new independence from the surface for an air supply for their diesel engines meant that they could focus on hidden operation at depth, rather than operating largely as surface-cruising submersibles. The increased power of a nuclear reactor allowed their hulls to become larger and faster. Developments in sonar made them able to hunt effectively at depth, rather than relying on visual observations from periscope depth . All these factors drove

1682-433: The strain hardening exponent . In solid mechanics , the yield point can be specified in terms of the three-dimensional principal stresses ( σ 1 , σ 2 , σ 3 {\displaystyle \sigma _{1},\sigma _{2},\sigma _{3}} ) with a yield surface or a yield criterion . A variety of yield criteria have been developed for different materials. It

1740-414: The HAZ. Preheating should be considered to allow diffusible hydrogen to diffuse and to reduce the cooling temperature gradient. The slower cooling rate will reduce the likelihood of martensite formation. If the preheat temperature is not high enough the cooling temperature gradient will be too steep and it will create brittle welds. Multipass welds require a minimum and maximum inter-pass temperature with

1798-428: The HY-80 and is also an austenite stabilizer. Manganese – Cleans impurities in steels (most commonly used to tie up sulfur) and also forms oxides that are necessary for the nucleation of acicular ferrite. Acicular ferrite is desirable in HY-80 steels because it promotes excellent yield strength and toughness. Silicon – Oxide former that serves to clean and provide nucleation points for acicular ferrite. Chromium – Is

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1856-643: The USA, forgings and castings in HY-80 by Sheffield Forgemasters and castings in HY80 by Goodwin Steel Castings in the UK. Yield strength In materials science and engineering , the yield point is the point on a stress–strain curve that indicates the limit of elastic behavior and the beginning of plastic behavior. Below the yield point, a material will deform elastically and will return to its original shape when

1914-563: The added weldability challenges created by enhanced stress concentrations in connective joints. Carbon – Controls the peak hardness of the material and is an austenite stabiliser, which is necessary for martensite formation. HY-80 is prone to the formation of martensite and martensite's peak hardness is dependent on its carbon content. HY-80 is an FCC material that allows carbon to more readily diffuse than in FCC materials such as austenitic stainless steel . Nickel – Adds to toughness and ductility to

1972-420: The applied stress is removed. Once the yield point is passed, some fraction of the deformation will be permanent and non-reversible and is known as plastic deformation . The yield strength or yield stress is a material property and is the stress corresponding to the yield point at which the material begins to deform plastically. The yield strength is often used to determine the maximum allowable load in

2030-525: The categories of destructive and non-destructive evaluation. A variety of destructive tests from Charpy V-notch to explosion bulge can be performed. Destructive testing is not practical for inspecting completed weldments prior to being placed in service; therefore, NDE is preferred for this case. Non-destructive evaluation includes many techniques or methods: visual inspection, X-ray, ultrasonic inspection, magnetic particle inspection and eddy-current inspection. The ultimate tensile strength of these steels

2088-458: The construction of USS  Albacore , a small diesel research submarine. Albacore tested its eponymous teardrop hull shape, which would form a pattern for the following US nuclear classes. Although the operating depths of submarines are highly secret, their crush depth limits can be calculated approximately, solely from knowledge of the steel strength. With the stronger HY-80 steel, this depth increased to 1,800 feet (550 m) and with HY-100

2146-515: The cost to manufacture more economical. HY-80 is considered to have good corrosion resistance and has good formability to supplement being weldable. Using HY-80 steel requires careful consideration of the welding processes, filler metal selection and joint design to account for microstructure changes, distortion and stress concentration. The need to develop improved steels was driven by a desire for deeper-diving submarines. To avoid detection by sonar , submarines ideally operate at least 100 metres below

2204-462: The grain edge. Since it requires a lot of energy to move dislocations to another grain, these dislocations build up along the boundary, and increase the yield stress of the material. Also known as Hall-Petch strengthening, this type of strengthening is governed by the formula: where The theoretical yield strength of a perfect crystal is much higher than the observed stress at the initiation of plastic flow. That experimentally measured yield strength

2262-459: The hull must be designed so that the steel always operates below its endurance limit ; that is, the stress due to pressure at depth remains less than the fatigue strength for an indefinite number of cycles. US submarines post-WWII, both conventional and nuclear, had improved designs compared to the earlier fleet submarines . Their steel was also improved and was the equivalent of "HY-42". Boats of this construction included USS  Nautilus , and

2320-468: The impurity atom. The relationship of this mechanism goes as: where τ {\displaystyle \tau } is the shear stress , related to the yield stress, G {\displaystyle G} and b {\displaystyle b} are the same as in the above example, C s {\displaystyle C_{s}} is the concentration of solute and ϵ {\displaystyle \epsilon }

2378-400: The lattice energy and move the atoms in the top plane over the lower atoms and into a new lattice site. The applied stress to overcome the resistance of a perfect lattice to shear is the theoretical yield strength, τ max . The stress displacement curve of a plane of atoms varies sinusoidally as stress peaks when an atom is forced over the atom below and then falls as the atom slides into

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2436-410: The material), a larger stress must be applied. This thus causes a higher yield stress in the material. While many material properties depend only on the composition of the bulk material, yield strength is extremely sensitive to the materials processing as well. These mechanisms for crystalline materials include Where deforming the material will introduce dislocations , which increases their density in

2494-410: The material. This increases the yield strength of the material since now more stress must be applied to move these dislocations through a crystal lattice. Dislocations can also interact with each other, becoming entangled. The governing formula for this mechanism is: where σ y {\displaystyle \sigma _{y}} is the yield stress, G is the shear elastic modulus, b

2552-647: The maximum stress, at which an increase in strain occurs without an increase in stress. This characteristic is typical of certain materials, indicating the presence of YPE. The mechanism for YPE has been related to carbon diffusion, and more specifically to Cottrell atmospheres . YPE can lead to issues such as coil breaks, edge breaks, fluting, stretcher strain, and reel kinks or creases, which can affect both aesthetics and flatness. Coil and edge breaks may occur during either initial or subsequent customer processing, while fluting and stretcher strain arise during forming. Reel kinks, transverse ridges on successive inner wraps of

2610-470: The mechanical properties, weldability and service life/performance of the material/weldment. Alloying elements, weld procedures and weldment design all need to be coordinated and considered when looking to use HY-80 steel. HY-80 and HY-100 are covered in the following US military specifications: The alloy content will vary slightly according to the thickness of the plate material. Thicker plate will be more restrictive in its compositional alloy ranges due to

2668-436: The more advanced ARCI Modified AN/BSY-2 combat system, which includes a larger spherical sonar array, a wide aperture array (WAA), and a new towed-array sonar. Each boat is powered by a single S6W nuclear reactor , delivering 45,000 hp (34 MW) to a low-noise pump-jet . As a result of their advanced design, however, Seawolf -class submarines were much more expensive. The projected cost for 12 submarines of this class

2726-619: The most expensive United States Navy fast attack submarine and second most expensive submarine ever, after the French Triomphant -class nuclear-powered ballistic missile submarines . The Seawolf design was intended to combat the threat of advanced Soviet ballistic missile submarines such as the Typhoon class , and attack submarines such as the Akula class in a deep-ocean environment. Seawolf -class hulls are constructed from HY-100 steel, which

2784-403: The new HY-80 steel used was looked at suspiciously, especially for theories about weld cracking having been the cause of the loss. HY-100 steel was introduced for the deeper diving Seawolf class , although two of the preceding HY-80 Los Angeles class, USS  Albany (1987) and USS  Topeka (1988), had trialled HY-100 construction. USS  Seawolf is officially claimed to have

2842-743: The next lattice point. where b {\displaystyle b} is the interatomic separation distance. Since τ = G γ and dτ/dγ = G at small strains (i.e. Single atomic distance displacements), this equation becomes: For small displacement of γ=x/a, where a is the spacing of atoms on the slip plane, this can be rewritten as: Giving a value of τ max {\displaystyle \tau _{\max }} τ max equal to: The theoretical yield strength can be approximated as τ max = G / 30 {\displaystyle \tau _{\max }=G/30} . During monotonic tensile testing, some metals such as annealed steel exhibit

2900-406: The peak values for hardness remains constant among the different processes. This holds true for both HAZ and weld metal. Given the compositional differences between the base material and the composite zone of the weld it is reasonable to expect that there will be potential Distortion due to non-uniform expansion and contraction. This mechanical effect can cause residual stresses that can lead to

2958-416: The post-Soviet peace dividend) were a factor in reducing the planned 29 Seawolf submarines to just three constructed. The final microstructure of the weldment will be directly related to the composition of the material and the thermal cycle(s) it has endured, which will vary across the base material, Heat Affected Zone (HAZ) and Fusion Zone (FZ). The microstructure of the material will directly correlate to

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3016-434: The purpose to maintain yield strength and to prevent cracking. The preheat and inter-pass temperatures will depend on the thickness of the material. Generally, HY-80 is welded with an AWS ER100S-1 welding wire. The ER100S-1 has a lower Carbon and Nickel content to assist in the dilutive effect during welding discussed previously. An important function of the filler metal is to nucleate acicular ferrite . Acicular ferrite

3074-411: The strength of bulk copper and approaching the theoretical value. The theoretical yield strength can be estimated by considering the process of yield at the atomic level. In a perfect crystal, shearing results in the displacement of an entire plane of atoms by one interatomic separation distance, b, relative to the plane below. In order for the atoms to move, considerable force must be applied to overcome

3132-435: The term Indentation plastometry . There are several ways in which crystalline materials can be engineered to increase their yield strength. By altering dislocation density, impurity levels, grain size (in crystalline materials), the yield strength of the material can be fine-tuned. This occurs typically by introducing defects such as impurities dislocations in the material. To move this defect (plastically deforming or yielding

3190-1306: The thickness of the sheet. The figures here are for thicker sheets, 3 inches (76 mm) and over, which are the more restrictive compositions. A further steel, HY-130, also includes vanadium as an alloying element. Welding of HY-130 is considered to be more restricted, as it is difficult to obtain filler materials that can provide comparable performance. (550 MPa) (690 MPa) (900 MPa) E {\displaystyle E} ( GPa ) ν {\displaystyle \nu } G = E / 2 ( 1 + ν ) {\displaystyle G=E/2(1+\nu )} (GPa) K = E / 3 ( 1 − 2 ν ) {\displaystyle K=E/3(1-2\nu )} (GPa) ρ {\displaystyle \rho } (kg/m) k {\displaystyle k} (W/mK) c p {\displaystyle c_{p}} (J/kgK) k / ρ c p {\displaystyle k/\rho c_{p}} (m/s) α {\displaystyle \alpha } (K) T m e l t {\displaystyle T_{melt}} (K) HIC or HAC - hydrogen induced or hydrogen assisted cracking

3248-479: The use of a proper filler metal, while the HAZ HIC/HAC must be addressed with preheat and weld procedures. Low hydrogen practice is always recommended when welding on HY-80 steels. It is not possible to autogenous weld HY-80 due to the formation of untempered martensite. Use of filler metals is required to introduce alloying materials that serve to form oxides that promote the nucleation of acicular ferrite. The HAZ

3306-530: The yield stress is increased after unloading from a yield state. Yield strength testing involves taking a small sample with a fixed cross-section area and then pulling it with a controlled, gradually increasing force until the sample changes shape or breaks. This is called a tensile test. Longitudinal and/or transverse strain is recorded using mechanical or optical extensometers. Indentation hardness correlates roughly linearly with tensile strength for most steels, but measurements on one material cannot be used as

3364-607: Was $ 33.6 billion, but construction was stopped at three boats when the Cold War ended. USS  Jimmy Carter is roughly 100 feet (30 m) longer than the other two boats of her class, due to the insertion of a section known as the Multi-Mission Platform (MMP) which allows launch and recovery of remotely operated underwater vehicles (ROV) and Navy SEALs . The MMP may also be used as an underwater splicing chamber for tapping of undersea fiber optic cables . This role

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