鞍钢TRIP钢的研制开发

介绍了鞍钢新型TRIP钢的研制开发过程。通过金相显微镜、扫描电镜和透射电镜对TRIP钢的微观组织进行观察,通过拉伸实验和汽车零件冲压对TRIP钢的基本力学性能和冲压性能进行了研究。结果表明,TRIP钢由铁素体、贝氏体和残余奥氏体组成,具有良好的强塑性和冲压成形性能。     

相变诱发塑性钢研究开发的进展

介绍了高强度低合金相变诱发塑性钢的研究现状,残余奥氏体形态、尺寸和体积分数对钢强塑性的影响以及为改善钢的热镀锌性能所进行的以铝代硅的成功开发;以热力学、动力学为工具进行的TRIP钢的成分设计以及相变塑性钢高速冲击拉伸性能的特点;800～1200MPa级微合金TRIP钢的研发和激光焊接试验以及具有优良焊接性能和热镀锌性能的新型相变塑性钢的开发进程.     

WYS700钢气体保护焊及激光复合焊试验研究

采用气体保护焊、激光焊以及激光复合焊等焊接方法对WYS700钢进行了试验研究,比较了不同焊接工艺,尤其是激光焊接工艺的焊接接头宏观形貌,并研究了不同焊接工艺下焊接接头的拉伸强度、弯曲性能、组织硬度等力学性能.结果表明:WYS700钢采用合适的焊接工艺,气体保护焊、激光焊及激光+MAG复合焊都能获得成形良好的接头,并且都能有效降低焊接热影响区的软化,获得较好的强度与塑性.激光+MAG复合焊在3 mm规格以上厚板的焊接中更能发挥高效大熔深优势.     

1800 MPa热成形钢与CR340LA低合金高强钢激光焊接性能

采用光纤激光焊接设备对1800 MPa级热成形钢与CR340LA低合金高强钢进行对接激光拼焊,研究了不同激光焊接功率和焊接速度下焊接接头的组织演变规律及热冲压成形性能,并对焊接接头的力学性能和硬度进行了分析。结果表明,3种焊接工艺下激光拼焊原板综合力学性能相差较小,由焊接接头造成的伸长率和抗拉强度的损失均在母材的28.3%和9.1%以内。激光焊接后焊缝区均为粗大、高硬度的马氏体结构;两侧热影响区组织主要为铁素体和马氏体,接头未出现明显的软化区。激光拼焊原板拉伸试样均断裂于CR340LA母材区,距离焊缝12 mm左右,且存在焊缝隆起现象。选取焊接功率和焊接速率分别为4000 W和0.18 m·s?1的焊接试样在高温下进行热冲压成形检测,未出现焊缝开裂,热成形后拼焊板具有良好性能,满足汽车激光拼焊板使用要求,拉伸结果表明,试样断裂位置与未热冲压成形前一致,均位于CR340LA母材区,拉伸过程中,焊缝向高强度母材侧偏移,在弱强度母材侧产生应力集中并缩颈断裂。      

Si-Mn系超高强度热成形淬火钢板的点焊性能

 采用不同的点焊工艺参数对研发的1700MPa级Si-Mn系热成形淬火钢板与低碳钢板DC04进行异种材料之间点焊,并对焊接接头的拉伸性能、显微硬度分布及微观组织特征等进行了分析。结果表明,焊接电流对点焊接头熔核直径和抗剪强度具有显著的影响,而焊接时间的影响相对较小。超高强度钢板侧的热影响区存在两个明显的软化区和硬化区,即在靠近母材处存在一个硬度明显低于母材的软化区,其组织为回火马氏体;在靠近熔核处存在一个硬度明显高于母材的硬化区,其组织为细小的马氏体。点焊接头熔核部位为柱状粗大马氏体组织,其硬度明显低于超高强度钢板母材且远高于低碳钢板母材。低碳钢板热影响区低的硬度和明显粗化的铁素体组织,使得点焊接头单向拉伸时均从低碳钢板的热影响区一侧破断。     

热处理对B1500HS钢激光拼焊板力学性能的影响

利用单轴拉伸试验机、扫描电子显微镜、能量色散谱仪、光学显微镜、维氏硬度仪等研究了热处理前后B1500HS钢激光拼焊板的淬火性能.结果表明:热处理前B1500HS钢拼焊板焊缝强度远高于母材区,硬度分布极不均匀;热处理后,B1500HS钢拼焊板的元素分布几乎没有变化,整体强度有了大幅的提高,但塑性下降程度较大,其中横向塑性最差,经维氏硬度测试,发现焊缝至母材区的硬度过渡平滑.硬度值平滑过渡使得应力和应变分布更加均匀,保证了母材和焊缝力学性能的良好连续性,可以显著提高B1500HS钢拼焊板的成形性能.      

TRIP钢单向拉伸过程的组织转变特性

采用XRD和TEM研究了低碳低合金相变诱导塑性(TRIP)钢在单向拉伸状态下的组织转变特性.用Rietveld方法拟合分析了不同应变量下TRIP钢中残余奥氏体(RA)的含量.结果表明,试验中TRIP钢中RA转变量(RA-M)随塑性应变量的增大而增加.TRIP钢变形前的组织为铁素体、贝氏体和残余奥氏体,残余奥氏体主要以晶间薄片状、块状和位于铁素体晶内的细小颗粒状三种形态存在.经拉伸变形后,晶问块状或薄片状RA在应力作用下转变为孪晶结构的马氏体,铁索体晶内的细小颗粒状RA则未发现马氏体相变,但其周围会塞积高密度位错.     

热输入对DP600激光焊组织和力学性能的影响

摘要：为了研究DP600钢的焊接性能,采用5种不同的激光焊接工艺进行焊接试验。结果表明,焊接接头表面成形质量良好,随着热输入的增加,上下熔宽逐渐增大;熔融区均为板条状马氏体组织,当热输入高于33J/mm时热影响区组织为马氏体、铁素体和少量的回火马氏体;当热输入低于33J/mm时,热影响区组织为马氏体和铁素体。在低热输入条件下,回火时间很短,马氏体未发生分解;在高的热输入条件下,回火时间较长,马氏体分解显著,热影响区中出现M3C型碳化物,碳化物形貌以球状和片状为主。从熔融区到母材,显微硬度值逐渐降低;焊接接头静态拉伸失效位置均在母材,拉伸断口为韧性断口,DP600钢激光焊接接头不存在软化现象。     

热输入对DP600激光焊组织和力学性能的影响

为了研究DP600钢的焊接性能,采用5种不同的激光焊接工艺进行焊接试验。结果表明,焊接接头表面成形质量良好,随着热输入的增加,上下熔宽逐渐增大;熔融区均为板条状马氏体组织,当热输入高于33 J/mm时热影响区组织为马氏体、铁素体和少量的回火马氏体;当热输入低于33 J/mm时,热影响区组织为马氏体和铁素体。在低热输入条件下,回火时间很短,马氏体未发生分解;在高的热输入条件下,回火时间较长,马氏体分解显著,热影响区中出现M_3C型碳化物,碳化物形貌以球状和片状为主。从熔融区到母材,显微硬度值逐渐降低;焊接接头静态拉伸失效位置均在母材,拉伸断口为韧性断口,DP600钢激光焊接接头不存在软化现象。     

22MnB5钢激光焊接接头冷变形行为研究

采用金相显微镜、扫描电子显微镜、显微硬度仪和拉伸试验机对22MnB5钢激光焊接接头不同压下率下冷变形后接头进行检测。结果表明，随着冷轧压下率增加，塑性变形程度增加，焊缝宽度和硬度增加，激光焊缝显微组织为板条马氏体，焊接接头抗拉强度基本不变，22MnB5钢激光焊接接头具有良好的冷变形性，在冷轧压下率小于80%时，不会由于焊接接头和母材组织不匹配而出现断带等安全问题。     

热轧相变诱发塑性钢的热模拟实验

 利用Gleeble 1500热应力 应变模拟机研究了铌含量、热变形参数(终轧温度和卷取温度)对相变诱发塑性(TRIP)钢组织和性能的影响。实验结果表明：不含铌实验钢的残余奥氏体量、残余奥氏体相中的碳含量、宏观维氏硬度和抗拉强度与常规低碳硅锰系TRIP钢的水平相当;增加铌含量,残余奥氏体量和残余奥氏体相中的碳含量有所下降,而宏观维氏硬度和抗拉强度提高;铌含量为0014%、终轧温度为780 ℃、卷取温度为400 ℃时,残余奥氏体量、残余奥氏体相中的碳含量与宏观维氏硬度和抗拉强度具有最佳组合。     

Bake Hardening of Laser Welded Dual Phase Steel

The influence of bake hardening on the mechanical properties of laser welded dual phase steel was investigated. A remarkalbe increase of the hardness in the zone influenced by laser welding was observed. The fusion zone had a low carbon lath martensite microstructure. The laser weld region had a higher interstitial carbon content than the base material. The dual phase steel exhibited a clear bake hardening effect in both the as‐received and the laser‐welded conditions. The bake hardening effect is more pronounced in the prestrained laser welded condition. A pronounced decrease of the ductility was observed for prestrained laser welded DP steel.     

Nb含量对TRIP钢组织和性能的影响

利用Gleeble-1500热模拟机对不同Nb含量的TRIP钢的热轧过程进行了热模拟实验.研究了Nb含量对TRIP钢组织和性能的影响.实验结果表明：Nb的加入使得实验钢的组织得到细化,贝氏体量增多;增加Nb含量,残余奥氏体量和残余奥氏体含碳量有所降低,宏观维氏硬度值增加;Nb的质量分数为0.014%时,残余奥氏体量为19.2%、残余奥氏体含碳量为1.422%、宏观维氏硬度为258HV和抗拉强度为851 MPa.     

Metallurgical and Mechanical Characterization of Laser Spot Welded Low Carbon Steel Sheets

This paper aims at investigating metallurgical and mechanical characterization of low carbon steel laser spot welds. Microstructural examinations, microhardness tests and quasi‐static tensile‐shear tests were preformed. Mechanical properties of the welds were described in terms of peak load and failure mode. The effects of laser spot welding parameters including pulse frequency, laser energy, welding speed, pulse width and welded circle diameter, on low carbon steel laser spot weld performance were studied using the Taguchi design of experiment method. It was found that the effective laser pulse energy is the controlling factor in the determination of mechanical strength of laser spot welds.     

Weldability of Low Carbon Transformation Induced Plasticity Steel

Transformation induced plasticity （TRIP） steel exhibited high or rather high carbon equivalent （CE） because of its chemical composition, which was a particularly detrimental factor affecting weldability of steels. Thus the weldability of a TRIP steel （grade 600） containing （in mass percent, %） 0.11C-1. 19Si-1.67Mn was extensively studied. The mechanical properties and impact toughness of butt joint, the welding crack susceptibility of weld and heat affected zone （HAZ） for tee joint, control thermal severity （CTS） of the welded joint, and Y shape 60° butt joint were measured after the gas metal arc welding （GMAW） test. The tensile strength of the weld was higher than 700 MPa. Both in the fusion zone （FZ） and HAZ for butt joint, the impact toughness was much higher than 27 J, either at room temperature or at -20 ℃, indicating good low temperature impact ductility of the weld of TRIP 600 steel. In addition, welding crack susceptibility tests revealed that weldments were free of surface crack and other imperfection. All experimental results of this steel showed fairly good weldability. For application, the crossmember in automobile made of this steel exhibited excellent weldability, and fatigue and durability tests were also accomplished for crossmember assembly.     

Partial Inverse Grain Size Dependence of Strength in High Mn Steels Microalloyed With Nb

 Two steels without and with Nb addition were chosen to investigate the effects of Nb on the microstructures and the mechanical properties of Fe-Mn-Al-Si steels. The results revealed that Nb refined the grains markedly and both TRIP and TWIP effects occurred during deformation process. The Nb containing steel possesses higher yield strength and much lower tensile strength, the latter being explained by the suppression of TRIP effect due to the increase of stacking fault energy. This indicates grain refining is secondary for strengthening of steels when TRIP or TWIP effect exists during the deformation of low carbon and high Mn steels.     

Microstructures and Mechanical Properties of Fe-Mn-（Al, Si） TRIP/TWIP Steels

The mechanical properties and microstructure of two low carbon high manganese steels with 23.8% （No. 1） and 33% （No. 2） （mass percent） of manganese were investigated. The results showed that No. 1 steel possesses high strength and high plasticity, and No. 2 steel has a relatively high strength and extraordinary plasticity. The No. 1 steel exhibits both TRIP （transformation induced plasticity） and TWIP （twin induced plasticity） effects during the deformation; while only TWIP effect appeared under the same deformation condition for No. 2 steel. The comparison between the microstructures and mechanical properties of two steels was made, and the strengthening mechanisms were also analyzed.     

Investigation of modern fabricated pattern welded Damascus steel

Work on modern fabricated pattern welded Damascus steel by two of the best Russian bladesmiths was investigated. The main mechanical properties were measured, macro and microstructure were examined, and EDAX, mass-spectroscopy, and fractography tests were performed. The effect of heat treatment on both macrostructure and hardness was studied. It was shown that mechanical properties of pattern welded Damascus steel was on a level with standard tool plain carbon and low alloyed steels.     

Effects of Holding Temperature for Austempering on Mechanical Properties of Si-Mn TRIP Steel

A new type of high strength steel containing a significant amount of stable retained austenite was obtained by austempering immediately after intercritical annealing. This sort of low carbon steel only contains alloying elements of silicon and manganese rather than nickel and chromium. Its mechanical properties were enhanced considerably due to strain-induced martensite transformation and transformation-induced plasticity (TRIP) of retained austenite when it was strained at temperatures between Ms and Md, because retained austenite was moderately stabilized due to carbon enrichment by austempering. Austempering was carried out at different temperatures and 400℃ was found to be optimal. Tensile strength, total elongation and strength-ductility balance reached the maximum values and the product of tensile strength and total elongation exceeded 30 135 MPa % when the TRIP steel was held at 400℃ and strained at 350℃.     

高强TRIP钢的动态力学性能

将Si-Mn系双相钢（DP钢）作为对比钢种,分析研究了高应变速率下600 MPa级Si-Mn系TRIP钢及含Al、Ni的1000 MPa级TRIP钢的显微组织及其动态力学性能.对DP钢而言,其抗拉强度随着应变速率的增大而升高,断裂延伸率则由于绝热温升的作用也呈上升趋势;对TRIP钢而言,随着应变速率的增大,其抗拉强度不断增大,断裂延伸率先减小后增大,但无法达到其静态拉伸时的塑性水平,这是由于在动态拉伸条件下奥氏体向马氏体的渐进式转变被抑制造成的.此外,在相同应变速率下测得的TRIP钢的绝热温升始终比DP钢高,而这部分高出的热量应当来自于在动态变形条件下TRIP钢中发生TRIP效应后释放的相变潜热.