Yield Strength Grade Research Articles

Impact Toughness and Softening of the Heat Affected Zone of High Heat Input Welded 390 MPa Yield Strength Grade TMCP Steel

The Charpy impact toughness of the heat affected zone (HAZ) of electro gas welded 390 MPa yield strength grade steel, manufactured by a thermo mechanically controlled process, was investigated. The effects of added Nb on the toughness of the steel and the factors influencing scatter in toughness are discussed in the present work. It was observed that adding Nb to the steel led to the deterioration of HAZ toughness. The presence of soluble Nb in the HAZ increased its hardenability and resulted in a larger amount of low toughness bainitic microstructure. Microstructural observations in the notch root area revealed the significant role of different microstructures in the area. In the presence of a larger amount of bainitic microstructures, the HAZ exhibited a lower Charpy toughness with a larger scatter in toughness. A softened zone with a lower hardness than the base metal was formed in the HAZ. However, theoretical analysis revealed that the presence of the zone might not be a problem in a real welded joint because of the plastic restraint effect enforced by surrounding materials. Key words: alloys, welding, toughness, impact test, niobium

Effects of Si on the Characteristics of FCA Multi-Layer Weld Metal with 460 MPa Yield Strength Grade Steels for Ships and Marine Structures

Effects of Si on the Characteristics of FCA Multi-Layer Weld Metal with 460 MPa Yield Strength Grade Steels for Ships and Marine Structures

Proposed Revisions to the Current Charpy V-Notch Requirements for Structural Steel Used in U.S. Bridges

AbstractThe purpose of the research presented in this paper is to reexamine the current Charpy V-notch (CVN) requirements for steel bridges in the United States using state-of-the-art applied fracture mechanics analysis. Proposed revisions to the current CVN requirements are introduced. It is shown that, in general, the typical fracture toughness implied by current minimum CVN requirements results in a trend of decreasing resistance to brittle fracture as the minimum specified yield strength grade increases. The results also show that fracture resistance for the current minimum CVN requirements for the three AASHTO temperature zones is inconsistent for different high-performance steel (HPS) grades. A realignment of the current CVN test temperatures and required notch energy is proposed by normalizing all grades to the crack tolerance associated with the AASHTO yield strength grade 36 ksi steel CVN requirements.

High Strength Offshore Steel with Excellent Weldability

A new high strength low alloy (HSLA) steel in 370MPa yield strength grade with low susceptivity to weld cold cracking has been developed for offshore engineering. The microstructure feature of base steel and weld heat affected zone (HAZ) has been investigated. The systematic studies showed that the developed steel exhibited high strength(yield strength≥370MPa)、high impact toughness and excellent weldability. The complex inclusions containing fine oxides in HAZ promoted the acicular ferrite formation in weld thermal cycle and resulted in desired mechanical properties of HAZ.

Microstructure and Property of 700MPa Ti Microalloyed High Strength Steel Produced by EAF-CSP

High strength steel ZJ700MC with yield strength grade of 700 MPa was successfully developed by Ti micro-alloyed technology in the EAF-CSP line at Zhujiang Steel. The composition design, smelting process, continuous casting and rolling process of the steel, as well as the mechanical properties of the hot-rolled product are introduced in the paper. An analysis on the strengthening mechanism of the high strength steel shows that the enhanced strength and toughness of the steel were caused by the refinement of ferrite grain and the precipitation strengthening of TiC.

The Development and Experimental Study on High Strength and Toughness Drill Pipe Steel

With the development of oil industry, the high strength-toughness drill pipe suited to the task of sour environment and ultra deep wells would be considered more and more important. A new drill pipe steel, which was designed with the proper decrease of C content and increase of Cr, Ni, Mo, Nb and V alloy element, was developed and studied in this study. Large deformation hot rolling technology was used to obtain ultrafine grains microstructure. The results showed that the yield strength of this new drill pipe steel had reached 150ksi with the impact toughness more than 150J, which can perfectly meet the “leak-before-break” crack principle. The new low-alloy carbon steel drill pipe in the controlled yield strength grade 150ksi showing excellent sulfide stress cracking resistance and strength-toughness have been developed. Based on the observation of scanning electron microscopy and transmission electron microscopy, several kinds of carbide particles including (Nb, Mo, V)C with nanometer scale, were distributed in tempered sorbite matrix. The objective of this work was to study the relationship between carbide precipitation and strength-toughness by optimizing element design, thermo mechanical control process and heat treatment of drill pipe steel.

High Strain Low Cycle Fatigue and Anti-Seismic Behavior of HRB400 QST Reinforced Steel Bars

Based on the failure model of building structural steels under earthquake loading, High strain low cycle fatigue properties of HRB400QST (yield strength grade 400MPa, Quenched and Self Tempered) reinforced steel bars with diameters of 20mm and 16mm(unmachined) and HRB400V-N MA(microalloying)with diameters of 16mm (unmachined) were investigated. Based on the tests of total strain controlling, cycle strain response character of three kinds of steel bars and the relationship between cyclic stress and strain were researched. Hollomon and Coffin-Manson formulas were used to induce fatigue life formulas of three kinds of steel bars, and then the values of σa·Δεt were gained when Nf =100, calculated results show that the high strain low cycle fatigue properties of HRB400V-N MA rebars tested are much better than HRB400QST steel bars. Rupture surface scan reveals that surface hardened layer will reduce the cyclic toughness, and is bad for the anti-seismic performance.

Fracture toughness of a high-strength beryllium at room temperature and 300� C

The fracture toughness of a high yield strength grade of hot-pressed beryllium block was determined at room temperature and 300° C. Fatigue cracks were generated in doublecantilever beam specimens by a reversed loading method. Room temperature fracture toughness values from specimens with electric discharge machined notches fell within the scatter band of values from specimens with fatigued precracks. Load—displacement records generated from test on specimens with machined notches exhibited the expected linearity. However, the records were nonlinear from tests on specimens with long cracks formed by repeated propagation and arrest. Evidence points to a crack-closure phenomenon rather than plasticity as the source of the nonlinearity. The fracture toughness data show that specimen orientation or test temperature have little effect. By contrast, reported ductility values for this material are very sensitive to both these variables. The mean value of the fracture toughness ranged from 9.0 MPa m1/2 (8.1 ksi in. 1/2) at 23° C to 10.8 MPa m1/2 (9.7 ksi in. 1/2) at 300° C. These values are among the lowest ever reported for beryllium.

Metallurgical aspects in cold rolled high strength steel sheets

Cold rolled high strength steel sheets with yield strength from 300 to 500 N/mm2 have been developed by using conventional equipment for producing commercial cold rolled steel sheet, that is, cold rolling, box annealing, and temper rolling. Effective alloying elements for strengthening are carbon, silicon, manganese, phosphorus, niobium, etc. The sheets up to 400 N/mm2 yield strength grade are easily produced by selecting appropriate chemical compositions. The sheets with higher yield strength grade than 450 N/mm2 are obtained by introducing the new idea that the steel with more than 2 pct manganese is annealed between A1 and A3 transformation temperatures, and moderately temper rolled. Increase of tensile strength does not affect deep drawability while it deteriorates stretch-forming and stretch-flanging properties. As for electric resistance spot welding, shear tension strength increases in proportion to tensile strength, but cross tension strength hardly increases or tends to decrease. These sheets have been applied to door beams and bumper reinforcements.

Hydrogen-Assisted Cracking by Microscopic Plasticity Mechanisms

The recently proposed model for hydrogen-assisted cracking (hydrogen “embrittlement”) which states that such cracking in steels occurs by hydrogen diffusing into the metal ahead of the crack and lowering the local resistance to plastic flow has been further substantiated in other steels.The term hydrogen “embrittlement” was coined long before electron fractography, and it is based on the observation that many steels that normally show considerable ductility when tested in the absence of hydrogen, frequently lose this macroscopic ductility when the steels contain hydrogen and are maintained under a high stress. Electron fractography has shown that, while this macroscopic plasticity is minimized, it still persists on the microscopic scale. This plasticity may be seen in Figs. 1 and 2, for two different steels. Figure 1 is from the fracture surface of a 13Cr-8Ni-Mo steel and Fig. 2 is from a 250 ksi yield strength grade of maraging steel.

Fatigue crack growth characteristics of rotor steels

Room temperature fatigue crack growth rate data were generated for Ni-Mo-V (ASTM A469, Cl-4), Cr-Mo-V (ASTM A470, Cl-8) and Ni-Cr-Mo-V (ASTM A471, Cl-4 and a 156,000 psi yield strength grade) rotor forging steels. Testing was conducted with WOL type compact toughness specimens and the results presented in terms of fracture mechanics parameters. Data show that the Ni-Cr-Mo-V steels exhibit slower fatigue crack growth rates at a given stress intensity range ( ΔK) than do the Ni-Mo-V steels. In addition, the Cr-Mo-V steel was found to exhibit slower growth rates than the other alloys at ΔK levels below 40 ksi √in but somewhat foster rates at ΔK levels in excess of 45 ksi √in. The fatigue crack growth rate properties of the alloys studied conform to the generalized fracture mechanics crack growth rate law where d a/d N = C 0 ΔK R . It was noted that the fatigue crack growth rate parameters n and C 0 tend to decrease and increase, respectively, with increasing material toughness, K ic .