Numerical simulation of residual stress and deformation for submerged arc welding of Q690D high strength low alloy steel thick plate

The finite element simulation software SYSWELD is used to numerically simulate the temperature field,residual stress field,and welding deformation of Q690D thick plate multi-layer and multi-pass welding under different welding heat input and groove angles.The simulation results show that as the welding heat input increases,the peak temperature during the welding process is higher,and the residual stress increases,they are all between 330–340 MPa,and the residual stress is concentrated in the area near the weld.The hole-drilling method is used to measure the actual welding residual stress,and the measured data is in good agreement with the simulated value.The type of post-welding deformation is angular deformation,and as the welding heat input increases,the maximum deformation also increases.It shows smaller residual stress and deformation when the groove angle is 40°under the same heat input.In engineering applications,under the premise of guaranteeing welding quality,smaller heat input and 40°groove angle should be used.

Relief of Residual Stresses in 800 MPa Grade High Strength Steel Weldments by Explosion Treatment and its Effect on Mechanical Properties

The explosion treatment technique has been used in the relief of residual stresses in 800 MPa grade high strength steel manual welded joints. The residual stresses on surface and through thickness of the weldment were measured for both as-welded and explosion-treated sample, the mechanical properties of welded joints under different conditions were also tested. The effect of explosion treatment on the fracture toughness of materials with a residual defect was investigated by crack opening displacement （COD） test. The results show that explosion treatment can reduce not only the surface residual stress but also the residual stress through thickness in the welded joints. The effect of explosion treatment on the mechanical properties and a residual defect in welded joint were inconspicuous.

ISOCHRONOUS STRESS-STRAIN CURVES OF LOW ALLOY STEEL CROSS-WELD-SPECIMEN AT HIGH TEMPERATURE

In this work, a parametric approach is presented and utilized to determine the creep properties of weldments; then the model of creep strain for cross weld specimen is given. On the basis of the experimental results, attempt has been made to establish equations of the isochronous stress-strain for weld joint that can predict the function of loading and service time in use of the creep data of base metal and weld metal.

PREDICTION OF FLOW STRESS OF HIGH-SPEED STEEL DURING HOT DEFORMATION BY USING BP ARTIFICIAL NEURAL NETWORK

The hot deformation behavior of TI (18W-4Cr-1V) high-speed steel was investigated by means of continuous compression tests performed on Gleeble 1500 thermomechan- ical simulator in a wide range of tempemtures (950℃-1150℃) with strain rotes of 0.001s-1-10s-1 and true strains of 0-0. 7. The flow stress at the above hot defor- mation conditions is predicted by using BP artificial neural network. The architecture of network includes there are three input parameters:strain rate,temperature T and true strain , and just one output parameter, the flow stress ,2 hidden layers are adopted, the first hidden layer includes 9 neurons and second 10 negroes. It has been verified that BP artificial neural network with 3-9-10-1 architecture can predict flow stress of high-speed steel during hot deformation very well. Compared with the prediction method of flow stress by using Zaped-Holloman parumeter and hyperbolic sine stress function, the prediction method by using BP artificial neurul network has higher efficiency and accuracy.

Charactersitics of Stress-strain Curve of High Strength Steel Fiber Reinforced Concrete under Uniaxial Tension

A whole of 110 specimens divided into 22 groups were tested with varying the volume fraction of steel fibers and the matrix strength of these specimens. The stress-strain behaviors of four types of steel fiber reinforced concrete （SFRC） under uniaxial tension were studied experimentally. When the matrix strength and the fiber content increase, the tensile stress and tensile strain vary differently according to the fiber type. The mechanisms of reinforcing effect for different types of fiber were analyzed and the stress-strain curves of the specimens were plotted. Some experimental factors for stress or strain of SFRC were given. A tensile toughness modulus Re0.5 was introduced to evaluate the toughness characters of SFRC under uniaxial tension. Moreover, the formula of the tensile stress-strain curve of SFRC was regressed. The theoretical curve and the experimental ones fit well, which can be used for references in construction.

Threshold Stress Intensity of Hydrogen-Induced Cracking and Stress Corrosion Cracking of High Strength Steel

The threshold stress intensity of stress corrosion cracking(SCC) for 40 CrMo steel in 3.5%NaCl solution decreased exponentially with the increase of yield strength.The threshold stress intensity of hydrogen-induced cracking during dynamical charging for 40 CrMo steel decreased linearly with the logarithm of the concentration of diffusible hydrogen.This equation was also applicable to SCC of high strength steel in aqueous solution.The critical hydrogen enrichment concentration necessary for SCC of high strength steel in water decreased exponentially with the increase of yield strength.Based on the results,the relationship between K_(ISCC) and σ_(ys) could be deduced.

Influence of Microstructures and Residual Stress on Fatigue Crack Propagation Rate of High Carbon Steels

The cold-work tool steels T10A and GCr15 have been studied with regard to the influence of austenitization temperature, tempering temperature and the residual stress on the crack propagation rate and the critical crack length. The kinds of fracture morphology have been studied too. The crack propagation rate is dependent strongly on the austenitization temperature, the tempering temperature and the surface compressional residual stress in specimens.

IMPROVEMENT ON SUSCEPTIBILITY OF ULTAR-HIGH STRENGTH STEEL TO STRESS CORROSION CRACKING BY HIGH TEMPERATURE QUENCHING

The effect of quenching temperature on the stress corrosion cracking of 30Cr3SiNiMoV ultra-high strength steel in 3.5% NaCl aqueous solution has been studied.The threshold K_(ISCC) may continuously increase with the quenching temperature raised from 870 to 1200℃ . All of the fractures are intergranular.The analyses of the segregation along prior austenitic grain boundaries,grain size and other microstructural factors reveal that the inerease of K_(ISCC) is mainly due to the coarsening of prior austenitic grains.

The relationship between microstructure and stress-strain behavior in tension in high strength pipeline steel

In this paper the relationship between microstructure and stress-strain behavior in tensile test of high strength pipeline steel was investigated.The steel with polygonal ferrite-bainite(PF + B) microstructure has a "round-house" type tensile stress-strain curve with low Y/T ratio,highly uniform elongation and high n-value,which means PF + B microstructure has the best deformability(i.e.Ideal stress-strain behavior) among the four microstructures.The steel with acicular ferrite-martensite&austenite(AF + MA) microstructure has a "continuous-yielding" type tensile stress-strain curve,whose deformability is worse than that of PF + B microstructure.Both the steels of polygonal ferrite-acicular ferrite(PF + AF) and polygonal ferrite-pearlite (PF+P) microstructure have "luders elongation" type tensile stress-strain curve with high Y/T ratio,low uniform elongation and low n-value,which means PF + AF and PF + P microstructures have the worst deformability among the four microstructures.

Support technology of deep roadway under high stress and its application

Roadway instability has been a major concern in the fields of mining engineering. This paper aims to provide practical and efficient strategy to support the roadways under high in-situ stress. A case study on the stability of deep roadways was carried out in an underground mine in Gansu province, China. Currently,the surrounding rock strata is extremely fractured, which results in a series of engineering disasters, such as side wall collapse and severe floor heave in the past decades. Aiming to solve these problems, an improved support method was proposed, which includes optimal bolt parameters and arrangement, floor beam layout by grooving, and full length grouting. Based on the modeling results by FLAC3D, the new support method is much better than the current one in terms of preventing the large deformation of surrounding rock and restricting the development of plastic zones. For implementation and verification, field experiments, along with deformation monitoring, were conducted in the 958 level roadway of Mining II areas. The results show that the improved support can significantly reduce surrounding rock deformation, avoid frequent repair, and maintain the long-term stability of the roadway. Compared to the original support, the new support method can greatly save investment of mines, and has good application value and popularization value.

1300 MPa High Strength Steel for Bolt with Superior Delayed Fracture Resistance

By the increase in Mo content,the addition of microalloying elements V and Nb and by reducing the contents of Mn,P and S based on the composition of steel 42 CrMo,we have developed a 1 300 MPa-grade high strength steel(ADF1)for bolts.The sustained load bending test,sustained load tensile test and stress corrosion cracking test have been carried out to evaluate the delayed fracture resistance of steel ADFl and commercial steel 42 CrMo.The results showed that steel ADF1 has superior delayed fracture resistance to that of 42 CrMo steel.It's concluded that the superior delayed fracture resistance of ADF1 is mainly due to the increase of tempering temperature,fine homogeneously distributed MC carbide and fine prior austenite grain size.

DUCTILE CRACK INITIATION AND STEADY-STATE PROPAGATION OF HIGH STRENGTH STRUCTURAL STEEL

The resistance to crack propagation at earlier stage for a high strength structural steel with certain ductility and its correlation to microstructures,stress states,deformation history and strain characteristics have been investigated.The resistance to crack propagation is mainly de- termined by the plastic constrain ahead of the crack tip,the elastic energy and plastic work absorbed in the stress-strain field.These are connected with the state function of triaxial stress.The deformation history and strain characteristic during deformation of material are described by the flow line in which the deformation history and strain characteristic restrain the crack initiation at stage Ⅱ and the crack propagation at stage Ⅲ.The strain hardening rate may sensitively reflect the stress distribution and micro-fracture mechanism in the interi- or of material.

Fatigue Behavior of High Speed Steel Roll Materials for Hot Rolling by Laser Impacting

The fatigue behavior of high speed steel （HSS） roll materials for hot rolling was researched under watercooling conditions by laser impacting. The microstructure of HSS sample and the morphologies of fatigue samples were observed by scanning electron microscope. The phase structure was detected by XRD. The morphology of situ oxide scale was observed by optical microscope, and the expansion coefficient was measured by TGA. The experiment results indicate that the cracks come into being at the carbide-matrix interface, but there are no cracks in the matrix after many times of laser impacting treatment, for the situ sample taken from the fractured roll surface, big carbides are more sensitive to the fatigue, and peel off prior to small ones. The relevant fatigue mechanisms are also discussed.

Dynamic recrystallization behavior and kinetics of high strength steel

The dynamic recrystallization behavior of high strength steel during hot deformation was investigated.The hot compression test was conducted in the temperature range of 950-1150 °C under strain rates of 0.1,1 and 5 s-1.It is observed that dynamic recrystallization(DRX) is the main flow softening mechanism and the flow stress increases with decreasing temperature and increasing strain rate.The relationship between material constants(Q,n,α and ln A) and strain is identified by the sixth order polynomial fit.The constitutive model is developed to predict the flow stress of the material incorporating the strain softening effect and verified.Moreover,the critical characteristics of DRX are extracted from the stress-strain curves under different deformation conditions by linear regression.The dynamic recrystallization volume fraction decreases with increasing strain rate at a constant temperature or decreasing deformation temperature under a constant strain rate.The kinetics of DRX increases with increasing deformation temperature or strain rate.

Properties of High Strength Steel Fiber Reinforced Concrete under Compression

This paper mainly discusses the properties of high strength steel fiber reinforced concrete under compression. Steel fibers with volume content of 1% do not display significant effect on the strain at peak stress and the area of the ascending portion of

Stress Corrosion Cracking of Pipeline Steels

This paper provides a review of the differences between high pH and near-neutral pH stress corrosion cracking of pipeline steels, influencing factors, and mechanisms. The characteristics and historical information on both forms of SCC are discussed. The prospect for research in the future is also presented.

Experimental study on stress-strain-temperature models for structural steel

For the research on steel structure in fire,it is very important to determine the properties of structural steel at elevated temperature.Up to now,the high-temperature properties of material is believed to be related to only temperature state,which is not precise enough to simulate the behavior of steel structures under different combinations of heating,cooling,loading,and unloading.To analyze the influence of the temperature-load history on the steel properties,a series of tests were carried out under different temperature-load paths about steel Q235,which is widely used in steel structures in China.In this paper,the method to set the temperature-load paths was introduced;the variety regulation of steel properties changing with temperature was analyzed under different paths;according to experimental results,the formulas of elastic modulus and yield strength at elevated temperature were fitted,and the stress-strain-temperature 3D relationships of structural steel under different paths were presented.

The Adhesion Improvement of Cubic Boron Nitride Film on High Speed Steel Substrate Implanted by Boron Element

Cubic boron nitride(c-BN) films were deposited on W6Mo5Cr4V2 high speed steel(HSS) substrate implanted with boron ion by RF-magnetron sputtering. The films were analyzed by the bending beam method, scratch test, XPS and AFM. The experimental results show that the implantation of boron atom can reduce the internal stress and improve the adhesion strength of the films. The critical load of scratch test rises to 27.45 N, compared to 1.75 N of c-BN film on the unimplanted HSS. The AFM shows that the surface of the c-BN film on the implanted HSS is low in roughness and small in grain size. Then the composition of the boron implanted layer was analyzed by the XPS. And the influence of the boron implanted layer on the internal stress and adhesion strength of c-BN films were investigated.

Experimental Study on Mechanical Properties of Q690 High-Strength Steel after High Cycle Fatigue Damage

Through the static tensile test of Q690 high-strength steel, the relevant mechanical parameters are obtained and the maximum fatigue load is determined. The fatigue life is measured by the fatigue test under the load. According to the fatigue cumulative damage method, the number of fatigue pre-damage vibration is designed in proportion. Then the fatigue pre-damage test is carried out on the high-strength steel, the stress-strain curve and the variation of residual mechanical property reduction coefficient with fatigue damage were drawn. The results show that: compared with the undamaged specimens, the yield strength and tensile strength of Q690 steel are less affected by fatigue damage, but the elongation changes more significantly, and the elastic modulus is not significantly affected. Finally, through the change of mechanical properties of Q690 high-strength steel with different fatigue damage, it provides a scientific basis for the performance evaluation of existing Q690 high-strength steel structure after fatigue damage.

基于MMC模型的Q460C高强结构钢延性断裂性能研究

为研究Q460C高强结构钢的延性断裂性能,对处于不同应力状态的9个试件进行了单调加载断裂试验。采用修正加权平均(MWA)法获得了Q460C钢材直至断裂的全过程真实应力-真实应变曲线,通过编写MATLAB优化程序校准了VGM和MMC断裂预测模型的参数。借助VUMAT子程序将相关参数代入ABAQUS/Explicit求解器模拟各试件的断裂行为,评估了两种断裂模型对各试件断裂预测的相对精度。通过对已有文献中两个圆周缺口试件的断裂模拟,验证了该文校准的MMC模型参数对Q460钢断裂预测的普适性。研究结果表明:采用MMC模型进行数值模拟得到的荷载-位移响应与试验结果吻合度较好,尤其是对纯剪和剪拉试件的断裂模拟;带应力软化的MMC模型可准确且形象地再现各试件的起裂和裂缝扩展;该文校准的MMC断裂模型参数对Q460钢材断裂行为预测具有相对较好的适用性。