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.

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.

Effect of Plastic Deformation and H_2S on Dynamic Fracture Toughness of High Strength Casing Steel

The effects of plastic deformation and H2 S on fracture toughness of high strength casing steel（C110 steel） were investigated. The studied casing specimens are as follows： original casing, plastic deformation（PD） casing and PD casing after being immersed in NACE A solution saturated with H2S（PD＋H2S）. Instrumented impact method was employed to evaluate the impact behaviors of the specimens, meanwhile, dynamic fracture toughness（JId） was calculated by using Rice model and Schindler model. The experimental results show that dynamic fracture toughness of the casing decreases after plastic deformation. Compared with that of the original casing and PD casing, the dynamic fracture toughness decreases further when the PD casing immersed in H2 S, moreover, there are ridge-shaped feature and many secondary cracks present on the fracture surface of the specimens. Impact fracture mechanism of the casing is proposed as follows： the plastic deformation results in the increase of defect density of materials where the atomic hydrogen can accumulate in reversible or irreversible traps and even recombine to form molecular hydrogen, subsequently, the casing material toughness decreases greatly.

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.

Effect of welding processes on mechanical and microstructural characteristics of high strength low alloy naval grade steel joints

Naval grade high strength low alloy(HSLA) steels can be easily welded by all types of fusion welding processes. However, fusion welding of these steels leads to the problems such as cold cracking, residual stress, distortion and fatigue damage. These problems can be eliminated by solid state welding process such as friction stir welding(FSW). In this investigation, a comparative evaluation of mechanical(tensile, impact,hardness) properties and microstructural features of shielded metal arc(SMA), gas metal arc(GMA) and friction stir welded(FSW) naval grade HSLA steel joints was carried out. It was found that the use of FSW process eliminated the problems related to fusion welding processes and also resulted in the superior mechanical properties compared to GMA and SMA welded joints.

Low temperature impact toughness of laser hybrid welded joint of high strength low alloy steel

High strength low alloy steel with 16 mm thickness was welded by using high power laser hybrid welding. Microstrueture was characterized by using optical microscopy, scanning electron microscopy （ SEM ） , transmission electron microscopy （TEM） and selected area electron diffraction （SAED）. Low temperature impact toughness was estimated by using Charpy V-notch impact samples selected from the upper part and the lower part at the same heterogeneous joint. Results show that the low temperature impact absorbed energies of weld metal are （202,180,165 J） of upper samples and （178,145,160 J） of lower samples, respectively. All of them increase compared to base metal. The embrittlement of HAZ does not occur. Weld metal primarily consists of refined carbide free bainite and a little granular bainite since laser hybrid welding owns the character of low heat input. Retained austenite constituent film ＂locates among the lath structure of bainitie ferrite. Refined bainitic ferrite lath and retained austenite constituent film provide better low temperature impact toughness compared to base metal.

Development of a New Kind of High Strength Spring Steel

A new kind of high strength, high toughness and high plasticity spring steel has been developed. The strength, the reduction of area and the elongation of the steel are all higher than those of the steel 60Si2CrVA. The decarburization resistance and the sag resistance are also higher than those of the steel 60Si2CrVA. It has good hardenability, and is suitable for making springs with big cross section. The bogie springs made of this kind of steel have passed 2×106 cycles without broken under the conditions of maximum stress of 906 MPa and the minimum stress of 388 MPa.

Study of welding technology on Baosteel high-strength heavy steel Bweldy620QL6

This study aims to conduct the weldability test for a high-strength structural steel, Bweldy620QL6, developed by Baosteel. This steel was subjected to welding,and the effects of two kinds of shielding gas,a binary gas of 80% Ar ＋ 20% CO, and ternary gas of 90% Ar ＋ 8% CO, ＋ 2% O2, on the performance of the welded joints of high-strength heavy steel were compared. The results show that Bweldy620QL6 has good weldability,and the joints obtained using binary gas and ternary gas meet common requirements.

Microstructure development in high-strength low-alloy steel welds

The reliability of steel welds becomes more critical issue with increasing steel strength,because brittle phases are more likely to form in the weld metals and heat-affected zone(HAZ) and thereby the toughness and ductility of the welds are degraded.Therefore,refinement of microstructure and minimization of the brittle phases are necessary to improve the reliability of the high-strength steel welds.In this presentation,microstructure formation that controls the toughness of weld metals and HAZ in high-strength low-alloy(HSLA) steel welds is reviewed and possible routes to the improvement of the weld microstructure and weld toughness are discussed.

Effect of Thermal Cycle on Microstructure and Fracture Morphology in HAZ of HQ130 Steel

The effect of different peak temperature(Tp) and cooling time (t8/5) on microstructure, hardness, impact toughness and fracture morphology in the heat-affected zone (HAZ) of HQ130 steel was studied by using weld thermo-simulation test. Experimental results indicate that the impact toughness and hardness decrease with the decrease of Tpor increase of t8/5 under the condition of a single thermal cycle. There is a brittle zone in the vicinity of Tp= 800℃, where the impact toughness is considerably low. There is a softened zone in the vicinity of Tp=700℃, where the hardness decreases but the toughness increases. In the practical application of multi-layer and multipass welding, the welding heat input should be strictly limited (t8/5≤20s) so as to reduce the softness and brittleness in the HAZ of-HQ130 steel.

EFFECTS OF THERMAL CYCLE ON MECHANICAL PROPERTIES AND FRACTOGRAPHY IN HAZ OF HQ130 STEEL

The effect of different peak temperature T_P) and cooling time (t_(8/5)) on hardness,impact toughness and fracture morphology in the heat--affected zone (HAZ) of HQ130steel was studied by using welding thermo--simulation test. Experimental results showthat the impact toughness and hardness decrease with the decrease of T_P or increase oft_(8/5) under the condition of a single thermal cycle. There is a brittle zone in the vicinityof T_P=800℃, where the impact toughness is considerebly low. There is softened zonein vicinity of T_P=700℃, Where the harkness decreases but the toughness increases. Inthe practical application of multi--layer and multi--pass welding, the welding heat inputshould be strictly limited (t_(8/5)≤20s) so as to reduce the softness and brittleness in theHAZ of HQ130 steel.

Effect of W on microstructure of high strength and toughness steels

The effect of W on the microstructure and the mechanical properties of ultrahigh strength low alloy steels was carried out. The microstructure of 30Cr3Si2Mn2NiMoNb and 30Cr3Si2Mn2NiMoNbW steels under quenched conditions were investigated by metallographic microscope, scanning electron microscope （SEM）, X-ray diffrac- tion （XRD）, and transmission electron microscope （TEM）. Thermodynamic cal- culation was also conducted. The results showed that the addition of W made undissolved carbides more and finer, which exerted strong pinning force on migrat- ing packet boundary and improved tensile strength significantly. M6C particles in 30Cr3Si2Mn2NiMoNb steel were disappeared above 1193 K, while the M6C particles in 30Cr3Si2Mn2NiMoNbW steel were disappeared above 1253 K, the calculation results were in agreement with the experimental.

Effect of Boron on CGHAZ Microstructure and Toughness of High Strength Low Alloy Steels

Effect of boron on the microstructure and impact toughness in the coarse-grained heat-affected zone（CGHAZ）of two high strength low alloy steels,boron-free and boron-containing,was investigated by means of weld thermal simulation test.The result shows that,for the boron-free steel,a microstructure consisting of grain boundary ferrite degenerates pearlite and granular bainite for longer t8/5（the cooling time from 800 to 500 ℃）,while lath bainite for shorter t8/5.For the boron-containing steel,granular bainite is dominant for a wide range of t8/5.Continuous cooling transformation（CCT）study on the CGHAZ indicates that the transformation start temperature decreases by about 50-100℃under different t8/5,for the boron-containing steel compared with the boron-free steel.The presence of boron suppresses the nucleation of ferrite at prior austenite grain boundaries and hence enlarges the range of t8/5for granular bainite transformation.However,the addition of boron deteriorates the impact toughness of CGHAZ,which may be due to a markedly increased fraction of martensite-austenite（M-A）constituents and decreased fraction of high angle grain boundaries.

THE VALENCE ELECTRON STRUCTURES OF MARTENSITE IN LOW ALLOY ULTRAHIGH-STRENGTH STEELS AND THEIR INFLUENCE ON STRENGTH AND TOUGHNESS

Ⅰ. THE VALENCE ELECTRON STRUCTURES OF MARTENSITE IN LOW ALLOY ULTRAHIGH-STRENGTH STEELS AND THE SEGREGATION OF C-ME IN MARTENSITEThe valence electron structures ofmartensite in 30CrMnSiNi2A and Gc-4 steels can be established based on Refs. [1—3]. To be brief, only σ, nA and ncD are listed in Table 1, which are the values of electron structures of martensite in 30CrMnSi2A and Gc-4 steels.

Effect of Post-weld Tempering on the Microstructure and Mechanical Properties in the Simulated HAZs of a High-Strength-High-Toughness Combination Marine Engineering Steel

The effects of tempering temperatures on the microstructure and mechanical properties of the simulated coarse-grain heataffected zone(CGHAZ) and inter-critical heat-affected zone(ICHAZ) were investigated for a high-strength-high-toughness combination marine engineering steel.The results demonstrate that the microstructure of the simulated CGHAZ and ICHAZ after tempering is characterized by tempering sorbites and coarse grain in the simulated CGHAZ.As tempering temperature increases,the tensile strength of the simulated CGHAZ and ICHAZ decreases and the Charpy absorbed energy of the simulated ICHAZ at-50℃increases remarkably,but the impact toughness of the simulated CGHAZ is not improved.After tempering at 550℃,the coarse flake carbides,which distribute at the prior austenite grain and martensite lath boundaries,deteriorate the impact toughness of the simulated CGHAZ.With the increase in tempering temperature,the morphology and the size of the carbides gradually change from coarse flake to fine granular,which is beneficial to the improvement of impact toughness.However,the coarse-grain size of the simulated CGHAZ and the M23 C6-type carbide precipitated along the grain boundaries weakens the enhancing effect of carbides on impact toughness.

440 MPa级高强钢焊条熔敷金属组织与低温冲击韧性研究

为满足440 MPa级高强钢对焊接材料的需求,研制了三种焊条,并进行了熔敷金属焊接试验,使用光学显微镜、扫描电镜和透射电镜等手段研究了熔敷金属组织与低温冲击韧性.结果表明,随着Mn,Ni,Cr和Cu含量的增大,熔敷金属的-40℃平均冲击吸收功从35.7 J逐渐增至96.3 J,低温冲击韧性逐渐提高;随着Mn,Ni,Cr和Cu含量的增大,虽然熔敷金属中M23C6型碳化物含量逐渐增大,但是熔敷金属的CCT曲线逐渐右移,相变温度逐渐降低,使得针状铁素体含量逐渐增加,铁素体板条尺寸逐渐减小和板条间交织状分布趋势逐渐增强,M-A组元含量及尺寸逐渐减小,是低温冲击韧性逐渐提高的主要原因;含Cu熔敷金属中夹杂物外层会形成CuS,针状铁素体形核更容易,有利于低温冲击韧性提高.

焊接热循环峰值温度对1000 MPa级超高强钢热影响区组织性能的影响

为研究1 000 MPa级超高强钢焊接热影响区(HAZ)不同区域的组织性能,采用焊接热模拟技术制备了试验钢在不同热循环峰值温度下的试样,通过夏比冲击试验研究了HAZ不同区域的冲击韧性。结果表明:在亚临界区(SCHAZ)、临界区(ICHAZ)和细晶区(FGHAZ),样品冲击吸收能量、裂纹扩展能量和动态冲击韧度较大,断口上形成较大面积的脚跟形纤维区和剪切唇,微观可看到大小不一的韧窝,样品冲击韧性较好;在粗晶区(CGHAZ),样品各项冲击数据均急剧下降,断口呈宏观脆性断裂,几乎全为放射区,微观下显示准解理断裂特征,表明裂纹扩展时受到的阻力减小,裂纹萌生后稳定扩展的时间减少,失稳扩展较快,样品的冲击韧性恶化,CGHAZ为HAZ中的韧性谷区;组织分析表明,粗大的晶粒和粗大的马氏体板条是导致CGHAZ脆化的主要原因。该结论为探究1 000 MPa级超高强钢在水电工程中的优选研制及工程应用奠定了理论基础。

钢纤维形状和养护制度对超高性能混凝土强度及韧性的影响

热养护和掺加异形钢纤维是提高超高性能混凝土(UHPC)强度并改善韧性的有效技术手段。研究了养护制度(标准养护28 d、90℃蒸汽养护2 d、90℃热水养护2 d)和钢纤维形状(平直形、波纹形、端钩形)对UHPC立方体抗压强度、单轴抗压强度、抗折性能的影响,采用ASTM C1018、JSCE-SF4、修正的Post-Crack Energy Ratio(PCER)三种韧性表征方法对UHPC弯曲韧性进行评价,并借助三维光学扫描仪定量表征了掺加不同形状钢纤维的UHPC断裂面粗糙度。结果表明,相较于28 d标准养护,2 d热水养护和2 d蒸汽养护均能在一定程度上提高UHPC力学性能,且对UHPC抗折性能的提升较为显著。与掺平直形钢纤维的UHPC相比,掺端钩形钢纤维的UHPC的抗折强度和PCER韧性指标分别提升46.26%~58.82%和32.77%~39.81%,断裂面粗糙度提高41.67%;粗糙度参数与弯曲韧性具有良好的指数关系,可用于UHPC韧性的表征。此外,单轴抗压强度与立方体抗压强度存在线性关系,相关系数为0.83~0.93。采用ASTM C1018和PCER方法计算出的韧性结果与采用4 mm挠度处荷载-位移曲线包围的面积和抗折性能指标结果基本一致,提出的PCER方法引入初始弯曲韧度比来表征UHPC达到峰值挠度前的弯曲韧性,使得计算结果更为准确。

氮含量与终轧温度对钛微合金化高强钢CGLC700低温冲击韧性的影响

针对钛微合金化高强钢CGLC700低温冲击韧性差的问题,通过热力学计算与高温原位观察,采用电子背散射衍射、透射电镜、扫描电镜和光学显微镜对含Ti高强钢的夹杂物、第二相粒子、断口形貌和低温冲击韧性等进行了研究。结果表明,含Ti高强钢低温冲击韧性差的原因与钢中大尺寸脆性夹杂物和Ti(C,N)、TiN析出相有关。将钢中w[N]从0.0049%降低至≤0.0035%时,可以有效降低钢中脆性夹杂物的数量和尺寸,从而提高钢材冲击韧性;终轧温度从885~895℃降低至875~885℃,可以促使纳米级TiC第二相粒子析出和大角度晶界的生成,并降低有效晶粒尺寸,从而明显改善钢材的低温冲击韧性;同时降低氮含量至≤0.0035%与终轧温度在875~885℃时,钛微合金化高强钢中平均晶粒尺寸从3.1μm降至2.7μm,小尺寸有效晶粒占比高,大尺寸夹杂物及数密度降低,大角度晶界中占比增长了16.6%,钢材低温冲击功可以从14.75 J提高到37.35 J。