建筑维护系统用高耐蚀性铁素体不锈钢的研发与应用

研究了Mo、Nb、Ti对22.5%Cr铁素体不锈钢力学性能、耐腐蚀性能的影响,研究结果表明,Mo主要以固溶状态存在于铁素体不锈钢中,通过固溶强化提高了铁素体不锈钢的强度;在Ti/Nb双稳定铁素体不锈钢中,由于粗大TiN颗粒的形成和金属间化合物在晶界的析出,钢的韧性明显降低;在Nb单稳定铁素体不锈钢中,Nb以固溶状态和Nb(C,N)析出相存在于铁素体基体中,Nb(C,N)弥散分布于铁素体晶内,并作为σ相的形核质点,避免了σ相在晶界的析出,从而改善了钢的低温韧性。在此基础上研制出建筑维护系统用的高耐蚀性铁素体不锈钢B445R。测试结果表明,B445R在氯离子溶液中具有比316L更优越的耐点腐蚀性能,而且具有良好的成形性能和焊接性能,这些优点使其成为沿海地区建筑维护系统理想的装饰材料。     

退火温度对441铁素体不锈钢组织性能的影响

 为探索超纯铁素体不锈钢热轧板材在退火过程中组织和力学性能的演变,对441进行了900~1 050 ℃的退火试验,利用OM、SEM和TEM表征了441在退火过程中显微组织的变化规律,并通过拉伸试验和冲击试验研究了退火温度对力学性能的影响。结果表明,随着退火温度升高,轧制组织发生再结晶,且晶粒逐渐长大。退火后441热轧板材中存在3种析出相,初生(Ti,Nb)(C,N)、二次Nb(C,N)和Laves相。Laves相仅在900~950 ℃退火样品中大量析出,尺寸约为几百纳米。441的屈服强度随着退火温度的升高先减小再增大,抗拉强度逐渐降低,而伸长率逐渐升高。形变强化对材料的屈服强度具有最大贡献,固溶强化次之,析出强化最小。冲击试验结果显示,1 000 ℃退火后441具有最低的韧脆转变温度,第二相与晶粒长大对材料韧性均有显著的不良影响。     

Precipitation Strengthening by Nanometer-sized Carbides in Hot-rolled Ferritic Steels

The mechanical properties of the hot-rolled plates of Ti steel and Ti-Mo steel after isothermal transformation in a temperature range of 600 700 ℃ for 60 min have been tested, and the microstructures of the matrix and the characteristics of precipitated nanometer-sized carbides have also been examined by scanning electron microscopy and transmission electron microscopy. The precipitation regularity of nanometer-sized carbides has been studied by thermodynamic method and the contributions of corresponding strengthening mechanisms to the total yield strength have been calculated. The tensile strength of hot-rolled Ti-Mo ferritie steel can achieve 780 MPa with an elongation of 20.0% after being isothermally treated at 600 ℃ for 60 rain, and the tensile strength of Ti steel is 605 MPa with an elongation of 22.7%, according to the results of tensile tests. The critical nucleation size of （Ti,Mo）C is smaller than that of TiC at a given isothermal temperature, but the nucleation rate of （Ti, Mo）C is larger than that of TiC. The grainrefinement strengthening and precipitation strengthening contribute the main amount of the total yield strength. The major increase in yield strength with the decrease of isothermal temperature results from the contribution of precipi tation strengthening. The contribution of precipitation strengthening to the yield strength of the steels has been esti mated. The ferrite phase can be strengthened by about 400 MPa through precipitation strengthening in Ti-Mo steel isothermally treated at 600 ℃ for 60 rain, which is about 200 MPa higher than that of Ti steel under the same conditions.     

钛微合金化高强钢的组织性能及强化机制

 为了掌握钛微合金化高强钢的组织性能、第二相粒子特性和析出规律以及强化机制，采用光学显微镜、扫描电镜、透射电镜、拉伸试验机等设备并结合热力学计算，对高强度汽车车厢板进行了系统研究。研究结果表明，试验钢的显微组织类型主要为多边形铁素体+针状铁素体+少量索氏体，平均有效晶粒尺寸约为3.5 μm。钢中存在大量的球形TiC和少量的不规则形状Ti4C2S2及方形TiN析出物，析出顺序为TiN→Ti4C2S2→TiC。第二相析出物以TiC的沉淀强化效果最为显著，TiN和Ti4C2S2的沉淀强化效果十分微弱。试验钢中所有强化方式对试验钢的强度贡献大小顺序为细晶强化＞沉淀强化＞位错强化＞固溶强化＞晶格点阵强化，其中细晶强化和沉淀强化的强化效果最为显著，对屈服强度的贡献超过50%。     

Effects of micro-alloying and production process on precipitation behaviors and mechanical properties of HRB600

Effects of micro-alloying elements and production process on microstructure,mechanical properties and precipitates of 600 MPa grade rebars were studied by using pilot test,metallographic observation,tensile test,thermodynamic calculation and transmission electron microscopy. The results show that the tested steels are composed of ferrite and pearlite,in which the content range of pearlite is 33%-45%. For vanadium microalloyed steel,interphase precipitation strengthening effect of V can be promoted and the yield strength of tested steels can be increased with increasing V content and decreasing finishing rolling temperature. The temperature of terminated cooling should be more than 700 °C when the water cooling is used. When niobium is added to the steel,more coarse( Nb,V) C,N precipitates are generated at high temperature,so that the solid solubility of precipitated phases of vanadium is reduced and the precipitation strengthening effect of vanadium is weakened.     

439铁素体不锈钢的研制

439是在430不锈钢基础上降低C＋N含量，添加Nb、Ti等稳定化元素发展起来的新型不锈钢材料，已逐步代替304不锈钢应用于电梯面板等行业。为开发满足用户使用要求的439不锈钢，试验室研究了成分、热处理制度对439不锈钢性能的影响，结果表明：Ti、Nb稳定化元素的添加对改善439不锈钢综合性能比较有利、热轧439退火再冷轧可明显改进深冲性能。生产试制结果表明，宝钢生产的439冷轧产品完全能满足用户对材料的性能要求。     

TTS443高铬铁素体不锈钢的开发

针对304(Crl8-Ni8型)奥氏体不锈钢和430(Cr17型)铁素体不锈钢的特性,通过试验和分析Cr、Cu、Nb、Ti等合金元素对铁基合金材料性能的影响,开发出一种高铬铁素体不锈钢-TTS443(/%:O.010C、21Cr、0.40Cu、0.25Nb、0.20Ti、O.012N) 。该钢种的耐蚀性能与304奥氏体不锈钢相当,具有良好的成形性与焊接性能,TTS443铁素体不锈钢是304奥氏体不锈钢理想代替材料。     

Effect of Ti Additions on Micro‐Alloyed Nb TRIP Steel

In the present study, the influence of Ti‐additions on the mechanical properties of Nb‐microalloyed TRIP steel is investigated. Ti micro‐alloying additions to multi‐phase Nb TRIP steel result in a substantial increase of the yield strength and a reduction of strain hardening. The increase of the yield strength can be attributed mainly to grain refinement with a relatively small contribution of precipitation hardening. Based on general principles and well‐known models of alloying strengthening, metallurgical reasons for the observed mechanical behavior of the steel can be formulated. The contribution of precipitation hardening is relatively small as Ti‐addition result in the formation of coarse (Nb,Ti)(C,N) particles. The addition of Ti to a Nb‐microalloyed TRIP steel leads to a pronounced enhancement of precipitation kinetics of (Nb,Ti)(C,N), thereby increasing their phase fraction. The precipitates coarsen and tend to form groups of aggregates of particles rather than single isolated particles with increasing intercritical annealing time. In addition, Ti‐addition to Nb‐microalloyed TRIP steel has a direct influence on the chemical composition of the precipitates, which become Ti‐rich.     

铌与钛对铁素体不锈钢析出和成形性的影响

研究了铌、钛对铁素体不锈钢析出相、织构和成形性的影响。结果显示:添加铌、钛后的析出相主要是TiN和(Nb,Ti)C,其析出尺寸分别为4μm和200 nm;同时,铌、钛的添加抑制了冷轧薄板α纤维织构的生长,促进了γ纤维织构强度的增加。添加稳定化元素铌、钛后,冷轧薄板的平均r值由1.05增加到1.46,起皱高度也由29.1μm下降到18.9μm,薄板成形性能的改善同再结晶织构的变化密切相关。     

Investigation on the cold-strip breakage of SUS445J2 ultra-pure ferritic stainless steel during rolling process

In this work,the cause of the cold-strip breakage of SUS445J2 ultra-pure ferritic stainless steel was investigated using optical microscopy,energy dispersive spectroscopy,and electron backscatter diffraction technique.Results show that during cold rolling,the breakage of the stainless steel strip was mainly caused by massive niobium-rich(Nb-rich)carbides present in the center of the strip.Furthermore,cracks initiated at these carbides in the central layer.The massive carbide precipitates resulted from the segregation and enrichment of Nb,titanium(Ti),and carbon(C)in the central layer during the subsequent solidification stage of SUS445J2 stainless steel.Additionally,the banded structure and coarse ferrite grains in the central layer reduced the plasticity of the material,causing cracks to propagate along these grains and finally leading to cold-strip breakage.By reducing the solidification cooling rate of the billet,increasing the pouring temperature,discretizing Nb,Ti,and C enrichment via electromagnetic stirring,and forming equiaxed crystals in the central layer,the precipitation of harmful massive Nb-rich carbides in the central layer could be effectively avoided.     

Characterisation of precipitates formed in 26% Cr super ferritic stainless steel

In this study, a newly designed super ferritic stainless steel, 26Cr–4Mo–2Ni, was developed and heated to 800°C for different durations to study the precipitation behaviour of various intermetallic phases, which determined its final mechanical and corrosion resistance properties. The types, numbers and distribution of typical precipitates were investigated. Besides TiN and Nb(C,N), which are common phases formed in Ti- and Nb-stabilised ferritic stainless steel, the Laves, chi (χ) and sigma (σ) phases were also detected in the grain boundary and grain interiors, depending on the aging times . The study focused on the morphology and regularity of these intermetallic precipitates. And the effect of precipitation on the mechanical properties and the corrosion resistance were discussed.     

Precipitation behavior and its effect on strengthening of an HSLA-Nb/Ti steel

The precipitation behavior of a commercial high-strength low-alloy (HSLA) steel microalloyed with 0.086 wt pct Nb and 0.047 wt pct Ti has been investigated using transmission electron microscopy (TEM) and mechanical testing. The emphasis of this study is to compare an industrially hot-rolled steel and samples from a laboratory hot torsion machine simulation. From TEM observations, the Ti and Nb containing precipitates could be grouped according to their size and shape. The precipitates in order of size were found to be cubic TiN particles with sizes in the range of 1 μm, grain boundary precipitates with diameters of approximately 10 nm, and very fine spherical or needle-shaped precipitates with sizes on the order of 1 nm. The needlelike precipitates were found on dislocations in ferrite and constituted the dominant population in terms of density. Thus, they appear to be responsible for the precipitation strengthening observed in this steel. Aging tests were carried out at 650°C to evaluate the precipitate strengthening kinetics in detail. The strengthening mechanisms can be described with a nonlinear superposition of dislocation and precipitation hardening. The mechanical properties of torsion-simulated material and as-coiled industrial material are similar; however, there are some microstructural differences that can be attributed to the somewhat different processing routes in the laboratory as compared to hot strip rolling.     

钛强化对700MPa高强耐候钢性能的影响及改进

针对10和14mm厚规格700MPa级高强度耐候钢屈服强度和抗拉强度偏低的情况,利用金相显微镜和扫描电镜进行了组织观察,调查了炼钢和热轧工艺过程控制情况,研究了碳化钛的固溶和析出强化对力学性能的影响。结果表明,加热制度执行不够导致碳化钛未完全固溶,冷却温度控制偏高导致钛析出物粗化是造成性能不合的主要原因。通过成分优化及工艺制度调整,实现了碳化钛的充分固溶,提高了钛析出强化效果,解决了力学性能不合的问题。     

超快速冷却条件下Ti 微合金钢中纳米碳化物及其强化作用

具有较高强度的Ti微合金钢已广泛应用于国民经济及国防工业的各个领域.针对超快速冷却条件下（轧制冷却速度高达64 ℃/s）的Ti微合金钢,采用无损电解提取技术获得Ti微合金钢中的纳米碳化物. 在此基础上,运用化学相分析、X射线小角散射及透射电镜综合分析纳米碳化物的物理化学特征,并考察其强化作用. 结果表明:Ti微合金钢中存在大量纳米尺寸的Fe_xC、TiC析出物,其平均粒度分别为76.06 nm和133.95 nm;同时,超快速冷却条件强化了Fe_xC的析出行为,使得其析出强化增量达到243.8 MPa,而TiC的析出强化增量仅为63.1 MPa;然而,钢中每增加0.01 %（质量分数）的TiC析出物（＜40 nm）却可大幅贡献强化增量77.1 MPa,远高于Fe_xC析出物（＜40 nm）的强化贡献量. 因此,强化TiC的析出行为在提高钢屈服强度方面具有重要潜力.      

B443超低碳氮铁素体不锈钢的研究

为开发价格昂贵的SUS304奥氏体不锈钢的替代产品,试验研究了不同含量C N和Nb,Ti稳定化对B443系列铁素体不锈钢再结晶组织、力学性能、点蚀电位的影响.试验结果表明,Nb,Ti双稳定化提高了B443铁素体不锈钢的再结晶温度和点蚀电位.在试验室研究基础上,宝钢不锈钢分公司试制了B443NT超低碳氮铁素体不锈钢.该产品不仅具有与SUS304相当的耐腐蚀性能,而且具有优良的深拉伸性能和满意的焊接性能,可用于运输、建筑、厨具等众多行业.     

Effect of Ti Addition on Yield Strength of Low-Mo Fire-Resistant Steel at Elevated Temperatures

Herein, a series of low-Mo (0.2 wt%) fire-resistant steels with varying amounts of Ti (0.008–0.13 wt%) are investigated to study the effects of Ti on yield strength at elevated temperatures. At room temperature (RT), precipitation strengthening by nanoscale TiC precipitates is found to be the major factor for the enhanced strength. The amount of TiC precipitates and both the yield and tensile strengths increase monotonically with the Ti content. However, the yield strength ratio (YS at 600 °C divided by YS at RT) of the steel with the highest Ti content (0.13 wt%) is significantly reduced to 0.6. In contrast, the YS ratio of the steels with Ti content in the range of 0.008–0.087 wt% remains above 0.7 and increases with Ti content. The difference between the steels lies in the B content and the resultant bainite volume fraction. The steel with 0.13 wt% Ti does not contain B and has only 4% bainite, whereas the other steels contain 20 ppm B and approximately 60% bainite. Hence, a microstructure with a sufficient fraction of bainite is required to ensure strength at elevated temperatures. The properties can be further improved by Ti precipitation strengthening.     

汽车排气系统高温端用B441铁素体不锈钢研制

为了开发满足排气系统高温端零件使用要求的不锈钢产品,在实验室研究了化学成分、热处理制度对B441不锈钢性能的影响.结果表明,稳定化元素Nb、Ti的添加对改善B441不锈钢的综合性能有利.生产试制结果表明,生产的B441铁素体不锈钢产品具有优良的常温力学性能和耐高温性能,能够满足汽车排气系统高温端使用要求.     

罩式退火铌微合金化汽车钢的强化机理

 通过比较相同冷轧与罩式退火工艺下Mn-Si系和铌微合金化2种汽车用低合金高强钢的显微组织与力学性能,研究微量铌在冷轧罩式退火低合金高强钢中的强化机理。利用OM、SEM、TEM和拉伸试验机分别对2种钢的显微组织与力学性能进行了表征。对比分析表明：相对热轧板来说,2种钢冷轧退火板的铁素体晶粒和第二相析出物的尺寸都有所长大,导致了强度降低。相对Mn-Si钢而言,铌微合金化钢热轧板和冷轧退火板中的铁素体晶粒和第二相析出物尺寸更细小,细小第二相析出物的数量也更多,在相同的伸长率水平下明显提高了强度。冷轧罩式退火板的强化机理分析表明,铌微合金化低合金高强钢的主要强化方式是细晶强化和NbC的沉淀强化;研究认为添加质量分数为0.025%的铌时细晶强化更强烈。     

以Nb为中间层AgCuTi为钎料连接炭/炭复合材料与不锈钢

在连接温度为900℃、保温时间10 min的条件下,以Nb为中间层,采用AgCuTi钎料对炭/炭复合材料与不锈钢进行连接.利用扫描电镜和X射线衍射对接头界面组织进行分析.实验结果表明,以Nb为中间层、AgCuTi为钎料能很好地连接炭/炭复合材料与不锈钢;连接过程中,钎料中的Ti向炭/炭复合材料界面区聚集并形成含TiC的...     

CSP流程钛微合金化高强钢的第二相粒子析出行为

采用光学显微镜、扫描电镜、透射电镜、物理化学相分析等方法并结合热力学计算,分析了CSP工艺生产的钛微合金化高强钢的析出物特征及析出规律.研究发现:屈服强度700 MPa级高强钢中存在大量球形的纳米级TiC和Ti(C,N)粒子及少量不规则形状、100 nm以上的Ti₄C₂S₂粒子,TiN在连轧前完成析出,TiC主要在卷取和空冷时析出.不含钼钢和含钼钢(0.1% Mo)中MC相的质量分数为0.049%和0.043%,由于钼的加入,含钼钢中Ti的析出量较少,但析出粒子更为细小,并定量得到了不含钼钢和含钼钢的析出强化效果分别为126 MPa和128 MPa.