High Strength Low Alloy (HSLA) Steels in Building Construction

Majority of the buildings,including industrial buildings,are constructed using either structural steel (plates and structural shapes) or deformed bar steel reinforced concrete.Such buildings,however,must be designed to be safe and serviceable during construction and during use and occupancy.These objectives can be easily achieved by the use of steels having superior mechanical properties,ductility,weldability,fire resistance,etc.Over the years,the steel industry has made improvements in steel making technologies resulting in high strength low alloy (HSLA) steels with superior steel properties well suited for building construction.First part of this paper presents the structural design considerations,and the constructional considerations associated with the building structures in general,and steel structures in particular.This second part of the paper looks at the acceptance criteria for HSLA steels for North American building codes and construction.The third part of the paper presents the structural properties of currently available HSLA steels for building construction.The discussion focuses on hot-rolled structural steel shapes as well as deformed steel bars for concrete reinforcement.The paper argues that Niobium microalloying is the key to achieving superior properties in such steels.     

Microstructure-Property Relationship of High Strength Low Alloy Steels During Tensile Testing at High Strain Rates

The influence of strain-rate on the room temperature mechanical properties of Dual-Phase and Transformation Induced Plasticity (TRIP) steels was investigated.The results showed that both plastic strain,and strength properties increased with increasing strain rates at high strain rates.At strain rates lower than approximateil 1s-1 the properties no longer have an advantageous proportionality to strain rate and remain strain rate neutral.Possible explanations are offered for trends exhibited,in terms of thermal and athermal considerations,in relation to the respective microstructures of the two steels.     

A Flow Stress Model for High Strength Steels with Low Carbon Bainite Structure

Two kinds of steels(YP960 and YP690)with low carbon bainite structure were designed,and their flow stress and strain hardening exponents were studied.The results showed that,when Hollomon relation was applied to describe the flow stress,there were significant errors between the experimental and calculated points in specimens tempered below 400 ℃,while a high precision was observed in samples tempered above 400℃.Whereas,the modified Voce relation could effectively predict the flow stress as well as the strain hardening exponent at different tempering temperatures,which was verified by unbiased estimators such as maximum relative error(MRXE)and average absolute relative error(AARE).Besides,the modified Voce relation was also applied to estimate the maximum uniform strain,and the correlation coefficients(R)between the experimental data and calculated maximum uniform strain were more than 0.91.The high correlation coefficients indicated that the modified Voce relation could effectively predict the uniform deformation ability of high strength steels with low carbon bainite structure at different tempering temperatures.     

Apparent Morphologies and Nature of Packet Martensite in High Carbon Steels

The apparent morphologies of packet martensite in eight high carbon steels were researched by using optical microscope, scanning electron microscope, and transmission electron microscope. It was found that the apparent morphologies, substructures, and habit plane of packet martensite in high carbon steels are entirely different from that in low carbon steels; the substructures of packet martensite in high carbon steels possess fully twinned structure, while the substructures of individual coarse martensite plates in these steels bear both fully and partially twinned structures. The formation reason for apparent morphologies, substructures and two habit planes （i. e, { 111 }, and { 225}r） of high carbon martensite were discussed in detail.     

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.     

Thermomechanical Control Process and Its Effect on Structure and Properties of High Strength Low Alloy Steels

Low carbon steels microalloyed with small amount of carbide and/or nitride forming elements such as Nb,Ti and V with Thermomechanical controlled processing (TMCP) can give fine grained ferrite structure with high strength and superior toughness.The present study was aimed at identifying rolling parameters as well as microstructural characterization for accomplishing high yield strength and high charpy impact property at-60℃ by controlling hot rolling parameters and microstructure Grain size distribution was also monitored and related to mechanical properties of steel.     

Retained Austenite and Tempered Martensite Embrittlement in Medium Carbon Steels

Electron microscopy, diffraction and microanalysis, X-ray diffraction, and auger spectroscopy have been used to study quenched and quenched and tempered 0.3 pct carbon low alloy steels. Some in situ fracture studies were also carried out in a high voltage electron microscope. Tempered martensite embrittlement (TME) is shown to arise primarily as a microstructural constraint associated with decomposition of interlath retained austenite into M₃C films upon tempering in the range of 250 °C to 400 °C. In addition, intralath Widmanstätten Fe₃C forms from epsilon carbide. The fracture is transgranular with respect to prior austenite. The situation is analogous to that in upper bainite. This TME failure is different from temper embrittlement (TE) which occurs at higher tempering temperatures (approximately 500 °C), and is not a microstructural effect but rather due to impurity segregation (principally sulfur in the present work) to prior austenite grain boundaries leading to intergranular fracture along those boundaries. Both failures can occur in the same steels, depending on the tempering conditions.     

Chi-Carbide in Tempered High Carbon Martensite

Martensite in an Fe-1.22C alloy was tempered at 523, 573, and 623 K and examined by transmission electron microscopy (TEM) and Mössbauer effect spectroscopy (MES) to identify the morphology and type of carbide formed at the beginning of the third stage of tempering. Carbides formed in three morphologies: on twins within the martensite plates, in the matrix of twin-free areas of the martensite plates, and along the interfaces of the martensite plates. Chi-carbide (χ), as identified by selected area diffraction (SAD), was associated with each carbide morphology in specimens tempered at 573 K. Cementite (θ) together with chi-carbide was observed in specimens tempered at 623 K. Small amounts (about 2 pct) of retained austenite were observed by MES of specimens tempered at 523 K. The transformation of the 25 pct retained austenite in as-quenched specimens was related to the χ-carbide formed at the martensite plate interfaces during tempering. The MES results also show the presence of χ-carbide in the specimen tempered at 523 K and yields parameters indicative of a mixture of χ and θ carbides for the specimens tempered at 573 K and 623 K. MES measurements of the magnetic transition temperatures of the carbides show diffuse transitions but suggest thatχ is the dominant carbide in the tempering temperature range examined.     

Fatigue Strength and Crack Initiation Mechanism of Very-High-Cycle Fatigue for Low Alloy Steels

The fatigue strength and crack initiation mechanisms of very-high-cycle fatigue (VHCF) for two low alloy steels were investigated. Rotary bending tests at 52.5?Hz with hour-glass type specimens were carried out to obtain the fatigue propensity of the test steels, for which the failure occurred up to the VHCF regime of 10⁸ cycles with the S-N curves of stepwise tendency. Fractography observations show that the crack initiation of VHCF is at subsurface inclusion with ??fish-eye?? pattern. The fish-eye is of equiaxed shape and tends to tangent the specimen surface. The size of the fish-eye becomes large with the increasing depth of related inclusion from the surface. The fish-eye crack grows faster outward to the specimen surface than inward. The values of the stress intensity factor (K _I ) at different regions of fracture surface were calculated, indicating that the K _I value of fish-eye crack is close to the value of relevant fatigue threshold (??K _th ). A new parameter was proposed to interpret the competition mechanism of fatigue crack initiation at the specimen surface or at the subsurface. The simulation results indicate that large inclusion size, small grain size, and high strength of material will promote fatigue crack initiation at the specimen subsurface, which are in agreement with experimental observations.     

低合金高强度中厚板生产技术

Q345B中厚板生产中，提高板坯表面及内在质量要注重化学成分设计．合理制定加热、轧制规范，轧制厚规格钢板时还应进行正此处理．以满足性能要求。     

含钒低合金高强钢的沉淀析出行为

介绍了含钒低合金高强钢沉淀析出的形成,分析了碳氮化钒的一般析出、相间析出和纤维状析出的典型形貌、析出模型等,给出了最新的研究现状,探讨了含钒低合金高强钢的应用前景。     

提高低合金高强度钢强韧性的措施

本文通过对提高低合金高强度钢强韧性措施的探讨,结合舞钢的具体生产情况,提出了提高低合金高强度钢强韧性的工艺方法。     

Isochronal Phase Transformations of Low‐Carbon High Strength Low Alloy Steel upon Continuous Cooling

Aimed to acquire optimum comprehensive properties for the oil and gas pipeline steels, thermal treatment should be controlled to achieve ideal microstructures. Effects of cooling rates on transformation kinetics and microstructures of the low‐carbon high strength low alloy (HSLA) steel were investigated to obtain an optimized thermal treatment technology. Dilatometric measurements, light microscopy, scanning electron microscopy, and transmission electron microscopy were employed in present work. The transformed microstructures contained polygonal ferrite + pearlite, acicular ferrite (AF), and bainitic ferrite (BF) due to the cooling rates increasing from 5 to 3000°C min^?1, in present investigated HSLA steel. The result shows that, the increase of cooling rate accelerates AF transformation and refines the steel's matrix. The morphology of martensite/austenite structures transformed from islands in AF to films in BF with the increase of cooling rate.     

碳含量和组织类型对低合金钢耐蚀性的影响

 研究了碳含量不同和显微组织不同的低合金钢的耐腐蚀性能和腐蚀行为,并和商业耐候钢09CuPCrNi做了相应的比较。在碳含量比较低的情况下,组织类型对试验钢的耐蚀性影响不大;碳含量比较高时,单相贝氏体钢的耐蚀性优于由铁素体、渗碳体(珠光体)等构成的复相组织钢。轧后水冷时,不同碳含量的钢耐蚀性差别不大;轧后空冷时,碳含量低的钢的耐蚀性优于碳含量较高的钢。用扫描电镜对锈层进行观察,可以看出耐蚀性较好的试样在腐蚀后期形成了较致密的内锈层。碳的质量分数分别为0.03%和0.1%的钢水冷后的平均腐蚀速率相差很小,但从微观角度看其点蚀发展趋势不同。加速腐蚀5个周期后,w(C)为003%的水冷钢中蚀坑尺寸不再增加,而w(C)为01%的钢中蚀坑尺寸仍有增加趋势。     

Influence of Ti on Weld Microstructure and Mechanical Properties in Large Heat Input Welding of High Strength Low Alloy Steels

The influence of Ti on weld microstructure and mechanical properties in large heat input welding of high strength low alloy steels is investigated.The results indicate that a moderate amount of Ti is still effective for grain refinement even under larger heat input and a large amount of acicular ferrite(AF)is formed in the weld metal when Ti content is within 0.028%-0.038%.With increasing Ti content,proeutectoid ferrite in the weld metal decreases,whereas bainite and M-A constituent increase.The type of inclusion in the welds varies from Mn-Si-Al-O to TiMn-Al-O and finally to Ti-Al-O as Ti content increases from 0up to 0.064%.As for adding 0.028%-0.038% Ti,high weld toughness could be attained since most inclusions less than 2μm which contain Ti2O3 provide the effective nuclei for acicular ferrite formation.However,the toughness of the weld metals severely reduces when Ti content is over the optimum range of 0.028%-0.038%.     

近年来低合金高强度钢的进展

 从洁净钢生产、薄板坯连铸连轧无头轧制、薄带铸轧以及以快速冷却为核心的TMCP工艺等几个方面介绍了HSLA钢生产工艺技术的最新发展,并系统介绍了汽车用钢、船舶及海洋工程用钢、管线钢、建筑结构钢、核电用钢、压力容器用钢、工程机械用钢及集装箱用钢等行业所用的HSLA钢品种开发方面新进展。认为未来HSLA钢将向高强、高性能和低成本方向发展,对HSLA钢的发展有指导作用。     

低合金高强度钢开发与研究的新进展

介绍了低合金高强度钢开发与研究的新进展,并对当前国内低合金高强度钢生产存在的总理２进行了分析,同时对低合金高强度钢的市场需求进行了预测。