Effect of B_(2)O_(3) enrichment on microstructural inhomogeneity of high strength steel weldments

The present work attributes the role of boron on the high strength steel submerged arc weld using an undermatching filler wire.Mild steel filler wire was used for welding in constant machine parameters setting to evaluate the joint strength due to the enrichment of boron.To change the chemical composition of the weld metal,boron trioxide powder was blended with virgin flux in various proportions(2.5%−12.5%),which led to an increase in boron weight percentage in the range of 0−0.0065.The results show that weld metals(WM)optical micrographs depict the various types of ferrites,pearlites and secondary phases like martensite-austenite(M-A).Acicular ferrite content was influenced by the boron trioxide addition.Heat affected zone(HAZ)micrographs were not showing appreciable changes with oxide enrichment.Hardness and toughness of weld metals showed the mixed trend with B_(2)O_(3) enrichment whereas,small reduction in ultimate tensile strength(UTS)and yield strength(YS)was observed.

Product Development of High Strength and Toughness Spring Flat Steel

With the continuous development of mechanical industry,higher requirements are put forward for the comprehensive properties of spring steel.The chemical composition and production process of spring flat steel are designed to meet the requirements of high strength and high toughness of spring flat steel,through the test,the product surface quality and internal quality all meet the national standards,the performance indicators to meet user requirements.

Development of Nb-V-Ti Hot-Rolled High Strength Steel With Fine Ferrite and Precipitation Strengthening

A hot-rolled steel with high yield strength of 700 MPa, good elongation of about 20% and low ductile-brittle transition temperature （DBTT） lower than -70℃ has been developed in laboratory. The results show that adopting finishing rolling temperature of around 800℃ is rational, and coiling temperature is between 400 and 500℃ The strength of developed 700 MPa hot-rolled high strength steel is derived from the cumulative contribution of fine grain size, dislocation hardening and precipitation hardening. The fine grain strengthening and precipitation hardening are the dominant factors responsible for such high strength, and good elongation and toughness are predominantly due to fine grain ferrite.

Research and development of hot-rolled ultra-high strength steel at Baosteel

The effects of the composition and cooling process on the microstructures and properties of hot-rolled ultra-high strength low alloy （HSLA） steel, complex phase steel and martensite steel were studied in the laboratory. And S700MC and MP1200 ultra-high strength steels were trial produced at the 1 880 mm hot-rolling line of Baosteel. Compared with conventional hot-rolled high strength products,the idea that water is alloy was applied in the newly developed hot-rolled ultra-high strength steel. By the use of the economical composition design and controlled cooling after hot-rolling effectively,ultra-high strength steel of different steel grades can be obtained.

Research on welding technology of hot-rolled extra-high-strength steel developed by Baosteel

In this study, the welding technology of the hot-rolled extra-high-strength steel, BS960QC, has been comprehensively investigated. Analysis has been made on the weldability ,the different welding procedures ,the mechanical properties, and the fatigue properties, and a set of recommendation guidelines have been proposed for evaluating the welded joints of the extra-high-strength steel. The research and results indicate that the hot-rolled extra-high-strength steel, BS960QC,has good weldability and an excellent adaptability to welding procedures. Further,the excellent mechanical properties and fatigue properties of the welded joints ,which can be achieved by using optimized welding procedures, can completely meet the technical requirements of the construction machinery industry.

Microstructural analysis of the softened zone in the welding joint of 100 kg class hot-rolled extra-high-strength steel

Using the Gleeble 3500 thermal-mechanical system to simulate thermal cycles with different peak temperatures, the hardness and microstructure in the heat-affected zones of two kinds of 100 kg class hot-rolled extra-high-strength steel were compared. When the peak temperature of the thermal cycle was 800℃ ,incomplete transformation occurred during quenching in both steels, and massive martensite and bainite grains were formed. The hardness was determined by the composition and distribution of the microstructure. The concentration of massive martensite was low, and hence the hardness was low,in steel #1. Conversely,the massive martensite content in steel #2 was high and uniformly distributed,resulting in a high hardness. These findings can provide a reference for improving the mechanical properties in the softened zone.

Research and Development of Cemented Carbide Multifacet Drill for Drilling High Strength Steel

Aim To research on a solid cemented carbide multi facet drill for drilling high strength steel. Methods Assimilating some features of multi facet drill edge structures, through systematic drilling experiments, a new type of solid cemented carbide drill was developed and the drill geometry was optimized. Results With the new type drill,the drilling force decreases by 10%-20%, the drilling productivity (drilled holes per hour) increases by 2-3 times, and the drilling precision and surface finish increase by one level. Conclusion The new type drill possesses excellent drilling performance.

Application of Hot Forming High Strength Steel Parts on Car Body in Side Impact

Lightweight structure is an important method to increase vehicle fuel efficiency. High strength steel is applied for replacing mild steel in automotive structures to decrease thickness of parts for lightweight. However, the lightweight structures must show the improved capability for structural rigidity and crash energy absorption. Advanced high strength steels are attractive materials to achieve higher strength for energy absorption and reduce weight of vehicles. Currently, many research works focus on component level axial crash testing and simulation of high strength steels. However, the effects of high strength steel parts to the impact of auto body are not considered. The goal of this research is to study the application of hot forming high strength steel（HFHSS） in order to evaluate the potential using in vehicle design for lightweight and passive safety. The performance of HFHSS is investigated by using both experimental and analytical techniques. In particular, the focus is on HFHSS which may have potential to enhance the passive safety for lightweight auto body. Automotive components made of HFHSS and general high strength steel（GHSS） are considered in this study. The material characterization of HFHSS is carried out through material experiments. The finite element method, in conjunction with the validated model is used to simulate the side impact of a car with GHSS and HFHSS parts according to China New Car Assessment Programme（C-NCAP） crash test. The deformation and acceleration characteristics of car body are analyzed and the injuries of an occupant are calculated. The results from the simulation analyses of HFHSS are compared with those of GHSS. The comparison indicates that the HFHSS parts on car body enhance the passive safety for the lightweight car body in side impact. Parts of HFHSS reduce weight of vehicle through thinner thickness offering higher strength of parts. Passive safety of lightweight car body is improved through reduction of crash deformation on car body by the application of HFHSS parts. The experiments and simulation are conducted to the HFHSS parts on auto body. The results demonstrate the feasibility of the application of HFHSS materials on automotive components for improved capability of passive safety and lightweight.

Effects of chromium on the corrosion and electrochemical behaviors of ultra high strength steels

The effects of chromium on the corrosion and the electrochemical behaviors of ultra high strength steels were studied by the salt spray test and electrochemical methods. The results show that ultra high strength steels remain martensite structures and have anodic dissolution characteristic with an increase of chromium content. There is no typical passive region on the polarization curves of an ultra high strength stainless steel, AerMet 100 steel, and 300M steel. However, chromium improves the corrosion resistance of the stainless steel remarkably. It has the slowest corrosion rate in the salt spray test, one order of magnitude less than that of AerMet 100 and 300M steels. With the increase of chromium content, the polarization resistance becomes larger, the corrosion potential shifts towards the positive direction with a value of 545 mV, and the corrosion current density decreases in electrochemical measures in 3.5wt% NaCl solutions. Because of the higher content of chromium, the ultra high strength stainless steel has a better corrosion resistance than AerMet 100 and 300M steels.

Effect of microstructure on the low temperature toughness of high strength pipeline steels

Microstructure observations and drop-weight tear test were performed to study the microstructures and mechanical properties of two kinds of industrial X70 and two kinds of industrial X80 grade pipeline steels. The effective grain size and the fraction of high angle grain boundaries in the pipeline steels were investigated by electron backscatter diffraction analysis. It is found that the low temperature toughness of the pipeline steels depends not only on the effective grain size, but also on other microstructural factors such as martensite-austenite （MA） constituents and precipitates. The morphology and size of MA constituents significantly affect the mechanical properties of the pipeline steels. Nubby MA constituents with large size have significant negative effects on the toughness, while smaller granular MA constituents have less harmful effects. Similarly, larger Ti-rich nitrides with sharp corners have a strongly negative effect on the toughness, while fine, spherical Nb-rich carbides have a less deleterious effect. The low temperature toughness of the steels is independent of the fraction of high angle grain boundaries.

Design of a low-alloy high-strength and high-toughness martensitic steel

To develop a high strength low alloy （HSLA） steel with high strength and high toughness, a series of martensitic steels were studied through alloying with various elements and thermodynamic simulation. The microstructure and mechanical properties of the designed steel were investigated by optical microscopy, scanning electron microscopy, tensile testing and Charpy impact test. The results show that cementite exists between 500℃ and 700℃, M7C3 exits below 720℃, and they are much lower than the austenitizing temperature of the designed steel. Furthermore, the Ti（C,N） precipitate exists until 1280℃, which refines the microstructure and increases the strength and toughness. The optimal alloying components are 0.19% C, 1.19% Si, 2.83% Mn, 1.24% Ni, and 0.049% Ti; the tensile strength and the V notch impact toughness of the designed steel are more than 1500 MPa and 100 J, respectively.

Microstructures and mechanical properties of C-Mn-Cr-Nb and C-Mn-Si-Nb ultra-high strength dual-phase steels

The microstructures and mechanical properties of C-Mn-Cr-Nb and C-Mn-Si-Nb ultra-high strength dual-phase steels were studied by scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, and tensile test. The results show that Si can promote the transformation of austenite （γ） to ferrite （α）, enlarge the （α＋γ） region, and increase the aging stability of martensite by inhibiting carbide precipitation. Adding Cr leads to the formation of retained austenite and martensite/austenite （M/A） constituents, as well as the decomposi- tion of martensite during the overaging stage. Both of the steels show higher initial strain-hardening rates and two-stage strain-hardening characteristics. The C-Mn-Si-Nb steel shows the higher strain-hardening rate than the C-Mn-Cr-Nb steel in the first stage; however, there is no significant difference in the second stage. Although the tensile strength and elongation of the two steels both exceed 1000 MPa and 15%, respectively, the comprehensive mechanical properties of the C-Mn-Si-Nb steel are superior.

Delayed Fracture Behavior of CrMo-Type High Strength Steel Containing Titanium

The delayed fracture behaviors of CrMo-type high strength steels containing different amount of titanium(0to 0.10%)were studied.The steels were quenched at 880℃ and tempered from 400℃ to 650℃,and a wide range of tensile strength was obtained.The sustained load tensile test was carried out by using notched tensile specimens in Walpole solution.The experimental results showed that with higher strength,the Ti-microalloyed steels show higher resistance to delayed fracture compared with non-microalloyed steel due to titanium beneficial role and microstructure changes.The undissolved TiC is uniformly distributed as strong hydrogen traps,retarding or preventing the diffusion and accumulation of hydrogen to lower-interaction energy sites,such as prior austenite and martensite lath boundaries in stress concentration area.Meanwhile,the grain refining effect of titanium is also an important factor to improve the delayed fracture resistance of Ti-microalloyed steels.The characteristics of delayed fracture remain nearly the same with titanium addition.

Study on non-metallic inclusions in Al killed high strength alloy steel refined by high basicity and high Al_2O_3 content slag

Laboratory and industrial studies were carried out to investigate non-metallic inclusions in high strength alloy steel refined by high basicity and high Al_2O_3 slag.It was found that the steel/slag reaction time largely affected non-metallic inclusions.With the reaction time increased from 30 min to 90 min in laboratory study,MgO-Al_2O_3 spinels were gradually changed into CaO-MgO-Al_2O_3 system inclusions surrounded by softer CaO-Al_2O_3 surface layers.By using high basicity slag which contained as much as 41%Al_2O_3 in the laboratory study,ratio of low melting temperature CaO-MgO-Al_2O_3 system inclusions was remarkably increased to above 80%.In the industrial experiment,during the secondary refining,the inclusions changed in order of 'Al_2O_3→MgO-Al_2O_3→CaO-MgO-Al_2O_3'.Through the LF and RH refining,most inclusions could be transferred to lower melting temperature CaO-Al_2O_3 and CaO-MgO-Al_2O_3 system inclusions.

Ultra-high cycle fatigue behavior of high strength steel with carbide-free bainite/martensite complex microstructure

The ultra-high cycle fatigue behavior of a novel high strength steel with carbide-free bainite/martensite （CFB/M） complex microstructure was studied. The ultra-high cycle fatigue properties were measured by ultrasonic fatigue testing equipment at a frequency of 20 kHz. It is found that there is no horizontal part in the S-N curve and fatigue fracture occurs when the life of specimens exceeds 10^7 cycles. In addition, the origination of fatigue cracks tends to transfer from the surface to interior of specimens as the fatigue cycle exceeds 10^7, and the fatigue crack originations of many specimens are not induced by inclusions, but by some kind of ＂soft structure＂. It is shown that the studied high strength steel performs good ultra-high cycle fatigue properties. The ultra-high fatigue mechanism was discussed and it is suggested that specific CFB/M complex microstructure of the studied steel contributes to its superior properties.

Effect of microstructure on corrosion behavior of high strength martensite steel-A literature review

The high strength martensite steels are widely used in aerospace,ocean engineering,etc.,due to their high strength,good ductility and acceptable corrosion resistance.This paper provides a review for the influence of microstructure on corrosion behavior of high strength martensite steels.Pitting is the most common corrosion type of high strength stainless steels,which always occurs at weak area of passive film such as inclusions,carbide/intermetallic interfaces.Meanwhile,the chromium carbide precipitations in the martensitic lath/prior austenite boundaries always result in intergranular corrosion.The precipitation,dislocation and grain/lath boundary are also used as crack nucleation and hydrogen traps,leading to hydrogen embrittlement and stress corrosion cracking for high strength martensite steels.Yet,the retained/reversed austenite has beneficial effects on the corrosion resistance and could reduce the sensitivity of stress corrosion cracking for high strength martensite steels.Finally,the corrosion mechanisms of additive manufacturing high strength steels and the ideas for designing new high strength martensite steel are explored.

Seismic performance of steel reinforced ultra high-strength concrete composite frame joints

To investigate the seismic performance of a composite frame comprised of steel reinforced ultra high-strength concrete （SRUHSC） columns and steel reinforced concrete （SRC） beams, six interior frame joint specimens were designed and tested under low cyclically lateral load. The effects of the axial load ratio and volumetric stirrup ratio were studied on the characteristics of the frame joint performance including crack pattern, failure mode, ductility, energy dissipation capacity, strength degradation and rigidity degradation. It was found that all joint specimens behaved in a ductile manner with flexural-shear failure in the joint core region while plastic hinges appeared at the beam ends. The ductility and energy absorption capacity of joints increased as the axial load ratio decreased and the volumetric stirIup ratio increased. The displacement ductility coefficient and equivalent damping coefficient of the joints fell between the corresponding coefficients of the steel reinforced concrete （SRC） frame joint and RC frame joint. The axial load ratio and volumetric stirrup ratio have less influence on the strength degradation and more influence on the stiffness degradation. The stiffness of the joint degrades more significantly for a low volumetric stirrup ratio and high axial load ratio. The characteristics obtained from the SRUHSC composite frame joint specimens with better seismic performance may be a useful reference in future engineering applications.

Experimental research on behavior of 460 MPa high strength steel I-section columns under cyclic loading

To investigate the seismic behavior of I-section columns made of 460 MPa high strength steel （HSS）, six specimens were tested under constant axial load and cyclic horizontal load. The specimens were designed with different width-to-thickness ratios and loaded under different axial load ratios. For each specimen, the failure mode was observed and hysteretic curve was measured. Comparison of different specimens on hysteretic characteristic, energy dissipation capacity and deformation capacity were further investigated. Test results showed that the degradation of bearing capacity was due to local buckling of flange and web. Under the same axial load ratio, as width-to-thickness ratio increased, the deformation area of local buckling became smaller. And also, displacement level at both peak load and failure load became smaller. In addition, the full extent of hysteretic curve, energy dissipation capacity, ultimate story drift angle decreased, and capacity degradation occurred more rapidly with the increase of width-to-thickness ratio or axial load ratio. Based on the capacity of story drift angle, limiting values which shall not be exceeded are suggested respectively for flange and web plate of 460 MPa HSS I-section columns when used in SMFs and in IMFs in the case of axial load ratio no more than 0.2. Such values should be smaller when the axial load ratio increases.

Experimental investigation of axially loaded steel fiber reinforced high strength concrete-filled steel tube columns

An experimental study on the compressive behavior of steel fiber reinforced concrete-filled steel tube columns is presented. Specimens were tested to investigate the effects of the concrete strength, the thickness of steel tube and the steel fiber volume fraction on the ultimate strength and the ductility. The experimental results indicate that the addition of steel fibers in concrete can significantly improve the ductility and the energy dissipation capacity of the concrete-filled steel tube columns and delay the local buckling of the steel tube, but has no obvious effect on the failure mode. It has also been found that the addition of steel fibers is a more effective method than using thicker steel tube in enhancing the ductility, and more advantageous in the case of higher strength concrete. An analytical model to estimate the load capacity is proposed for steel tube columns filled with both plain concrete and steel fiber reinforced concrete. The predicted results are in good agreement with the experimental ones obtained in this work and literatures.

Investigation of Surface Damage in Forming of High Strength and Galvanized Steel Sheets

Powdering/exfoliating of coatings and scratching galvanized steels and high strength steels （HSS）, are the main forms of surface damage in the forming of which result in increased die maintenance cost and scrap rate. In this study, a special rectangular box was developed to investigate the behavior and characteristics of surface damage in sheet metal forming （SMF） processes. U-channel forming tests were conducted to study the effect of tool hardness on surface damage in the forming of high strength steels and galvanized steels （hot-dip galvanized and galvannealed steels）. Experimental results indicate that sheet deformation mode influences the severity of surface damage in SMF and surface damage occurs easily at the regions where sheet specimen deforms under the action of compressive stress. Die corner is the position where surface damage initiates. For HSS sheet, surface damage is of major interest due to high forming pressure. The HSS and hot-dip galvanized steels show improved ability of damage-resistance with increased hardness of the forming tool. However, for galvannealed steel it is not the forming tool with the highest hardness value that performs best.