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

目的开发研究用于钻削高强度钢的整体硬质合金群钻钻型．方法吸收普通群钻钻型的经验，改变内外刃结构形式和参数，通过系统钻削试验优化钻刃结构及其几何参数，分析钻削效果．结果新钻型的钻削力降低１０％－２０％，钻削效率（单位时间钻孔数）提高２－３倍，加工精度和表面质量提高约１级．

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.

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 Al2O3 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-Al2O3 spinels were gradually changed into CaO-MgO-Al2O3 system inclusions surrounded by softer CaO-Al2O3 surface layers.By using high basicity slag which contained as much as 41%Al2O3 in the laboratory study,ratio of low melting temperature CaO-MgO-Al2O3 system inclusions was remarkably increased to above 80%.In the industrial experiment,during the secondary refining,the inclusions changed in order of 'Al2O3→MgO-Al2O3→CaO-MgO-Al2O3'.Through the LF and RH refining,most inclusions could be transferred to lower melting temperature CaO-Al2O3 and CaO-MgO-Al2O3 system inclusions.

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.

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 42CrMo, we have developed a 1300 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 ADF1 and commercial steel 42CrMo. The results showed that steel ADF1 has superior delayed fracture resistance to that of 42CrMo 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.

Complex Precipitation Mechanism of Ti-Nb-V Microalloyed Bainitic Base High Strength Steel

The addition of high Ti(>0.1%) in microalloyed bainitic high strength steel was designed, and the precipitation morphology of steels with different Ti, Nb, and V contents was studied by utilizing transmission electron microscopy(TEM). Based on the classical nucleation-crystal growth theory and the Johnson-Mehl-Avrami equation, the precipitation thermodynamic and kinetic model of second phase particles in austenite was established in the form of(Nbx,Vy,Tiz)C, and the complex precipitation mechanism of second phase particles was emphatically studied. The experimental results show that the complex precipitation particles could be divided into two categories: the coarser particles with about 100 nm grain size and the independent complex precipitation particles in the form of(Nb,V,Ti)C with 35-50 nm grain size. The latter has a better precipitation strengthening effect, and the calculated PTT curve shows a typical "C" shape. When the deformed storage energy is 3 820 J·mol^-1, the fastest precipitation temperature of calculated PTT curve is 925℃, and the calculated result is essentially consistent with experimental values. The increase of Ti content increased the nose point temperature and expanded the range of fastest precipitation temperature.

Microstructure and mechanical properties of high-strength low alloy steel by wire and arc additive manufacturing

A high-building multi-directional pipe joint(HBMDPJ)was fabricated by wire and arc additive manufacturing using high-strength low-alloy(HSLA)steel.The microstructure characteristics and transformation were observed and analyzed.The results show that the forming part includes four regions.The solidification zone solidifies as typical columnar crystals from a molten pool.The complete austenitizing zone forms from the solidification zone heated to a temperature greater than 1100℃,and the typical columnar crystals in this zone are difficult to observe.The partial austenitizing zone forms from the completely austenite zone heated between Ac1(austenite transition temperature)and1100℃,which is mainly equiaxed grains.After several thermal cycles,the partial austenitizing zone transforms to the tempering zone,which consistes of fully equiaxed grains.From the solidification zone to the tempering zone,the average grain size decreases from 75 to20μm.The mechanical properties of HBMDPJ satisfies the requirement for the intended application.

The welding application of high strength steels used in engineering machinery

With the rapid development of low alloy steel strength level,more problems caused by welding are exposed day by day.Recently,the efforts have been paid to improve or enchance the low toughness of heated affected zone and welded metal which can enchance the comprehensive mechanical properties that is the core scientific problems of its safe operation by researching crack initiation and crack propragation attracted a rapidly growing interest.This article focuses on the research status and progress of welding technology and joint microstructure and properties of advanced steel materials.The influence of shielding gas on the microstructure evolution of deposited metals,the effect heat input of welded joint performance,interpass temperature and alloy elements on welded joints microstructure and M-A constituent evolution and properties are reviewed in detail.And for the heat affected zone,the grain size and microstructure as well as the shape,size,and distribution of M-A constituent,have a significant impact on the impact toughness.This paper is an attempt to review the effect of different welding process parameters on welded metal and HAZ of HSLA steels.

Precipitation behavior of Ti in high strength steels

Precipitation behavior of Ti in high strength steels was investigated by means of the equilibrium solid solubility theory. The contributions of Ti content to yield strength were calculated. The calculated results were verified by the hot rolling experiment for C–Mn steel and C–Mn–Ti micro alloyed steel, respectively. The research results show that the precipitates are mainly Ti N at the higher temperature. With the decreasing temperature, the proportion of Ti C in precipitates increases gradually. When the temperature drops to 800 °C, Ti C will become predominant for the precipitation of Ti. When Ti content is less than 0.014%(mass fraction), Ti has little influence on the yield strength. When Ti content is in the range of 0.014%–0.03%(mass fraction), the yield strength of Ti micro alloyed steel is greatly increased, which leads to instability of the mechanical properties of the steel. Therefore, the design of Ti content in high strength steels should avoid this Ti content range. When Ti content is higher than 0.03%, the yield strength increases stably. In this experiment, when added Ti content was controlled in the range of 0.03%–0.05%, the contribution to the yield strength of Ti micro alloyed steel can reach about 92.44 MPa.

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 withcertain ductility and its correlation to microstructures,stress states,deformation history andstrain 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 workabsorbed in the stress-strain field.These are connected with the state function of triaxialstress.The deformation history and strain characteristic during deformation of material aredescribed by the flow line in which the deformation history and strain characteristic restrainthe crack initiation at stage Ⅱ and the crack propagation at stage Ⅲ.The strain hardeningrate may sensitively reflect the stress distribution and micro-fracture mechanism in the interi-or of material.

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.

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.

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 (0 to 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.

Microstructure, Impact Toughness and TEM Analysis in the CGHAZ of HQ130 High Strength Steel

Microstructure and impact toughness in the coarse grain heat-affected zone (CGHAZ) of HQ130 high strength steel were studied by using the weld thermo-simulation test. Fracture morphology and fine structure in the CGHAZ were analyzed by means of SEM, TEM and electron diffraction.Experimental results indicated that the impact toughness and hardness in the CGHAZ (Tm =1350℃) decreased with increasing cooling time (t8/5), and fracture morphology changed from dimple fracture into cleavage fracture. The reason for the toughness decrease is the formation of upper bainite. During application, the welding heat input should be strictly limited, to reduce brittleness in the CGHAZ of HQ130 steel.

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℃,M 7 C 3 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.

Effect of Quenching Parameters on Mechanical Property of Ultra High Strength Steel BR1500HS Based on Response Surface Methodology

Hot stamping of high strength steels is defined as a process in which blank is heated to the temperature of the austenite stabilization region for a definite time and then formed and quenched simultaneously in a mold with cooling channels. During this process,the processing parameters of austenite temperature and soaking time have strong effects on the mechanical properties such as quenching hardness,tensile strength and elongation. Hence,it is necessary to investigate the relationship between the mechanical properties and the two processing parameters. In this paper,the orthogonal experiment with two factors and five levels was applied, and the experimental data based on the orthogonal experiment was acquired. Based on the data,regression models were set up and the results of the analysis of variance( ANOVA) showed that it is reliable to predict the quenching hardness,tensile strength and elongation by the regression models. Besides,the optimal results of each single object were obtained based on response surface methodology( RSM),and global optimums was gained by employing ideal point method in which the quenching hardness,and tensile strength and elongation were considered simultaneously.

Study on welding process performance of HG70D high strength steel plate

In this paper,the performance of HG70 D welded joint of ultra-high strength steel plates is presented,and the performance of HG70 D and Q345 B welded joints is studied. The high strength steel plate HG70 D showed excellent weldability. Through the X-ray inspection of welded joints,tensile strength,impact test and bending performance test,the comprehensive performance of the joint was excellent. The macroscopic and microscopic metallographic analysises of the welded joints show that the welding seams included pearlite,sorbite,ferrite,etc. The influence of stress annealing temperature on HG70 D of high strength steel plate was analyzed by heat treatment.

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.

Behavior of High Strength Concrete Filled Square Steel Tube Stub Columns with Inner CFRP Tube Under Biaxial Eccentric Compression

This paper studies the contribution of CFRP(carbon fiber-reinforced polymer)to the mechanical behavior of high strength concrete-filled square steel tube(HCFST)under biaxial eccentric compression.The new type of composite member is composed of an inner CFRP tube and an outer steel tube with concrete filled in the two tubes.The finite element analysis was made by ABAQUS on the behavior of high strength concrete filled square steel tubular columns with inner CFRP circular tube subjected to bi-axial eccentric loading.The results obtained from the finite element analysis were verified with the experimental results.In addition,the load-deflection curves in the whole process were calculated and analyzed,which can be divided into three segments:Elastic phase,plastic phase,descending phase.Based on the load-deflection curves,the stresses analysis on the core concrete,CFRP tube and steel tube were conducted.The confinement effect of the CFRP tube improves the ductility of HCFST-CFRP stub column.CFRP ratio and eccentricity affect the ultimate bearing capacity of HCFST stub column.Finally,a calculation formula of ultimate bearing capacity was proposed in the paper.

Toughening mechanisms of a high-strength acicular ferrite steel heavy plate

An ultra-low carbon acicular ferrite steel heavy plate was obtained with an advanced thermo-mechanical control process-relaxed precipitation controlled transformation (TMCP-RPC) at Xiangtan Steel, Valin Group. The heavy plate has a tensile strength of approximately 600 MPa with a lower yield ratio. The impact toughness of the heavy plate achieves 280 J at ?40°C. The fine-grained mixed microstructures of the heavy plate mainly consist of acicular ferrite, granular bainite, and polygonal ferrite. The high strength and excellent toughness of the heavy plate are attributed to the formation of acicular ferrite microstructure. The prevention of blocks of martensite/retained austenite (M/A) and the higher cleanness are also responsible for the superior toughness.