Ultra-Pure Ferritic Stainless Steels-Grade,Refining Operation,and Application

The grades of ultra-pure ferritic stainless steels, especially the grades used in automobile exhaust system, were reviewed. The dependence of properties on alloying elements, the refining facilities, and the mechanism of the reactions in steel melts were described in detail. Vacuum, strong stirring, and powder injection proved to be effective technologies in the melting of ultra-pure ferritic stainless steels. The application of the ferritic grades was also briefly introduced.

Effect of cold-rolled annealing processes on microstructure and properties of ultra-pure ferritic stainless steel

In this study, the influence of annealing processes for cold-rolled sheets on the microstructure and mechanical performance of ultra-pure 430 ferritic stainless steel was investigated. Thermo-Calc calculation, organization observation, SEM detection,and tensile tests were used to discern the optimal annealing process. It is found that the microstructure is made up by the fine and uniform recrystallized ferritic grains after annealing. The optimum annealing process for ultra-pure 430 stainless steel is 950 ℃ for 90 s. After annealing, the stainless steel can obtain the optimum microstructure,recrystallization texture, and mechanical properties.

Low molybdenum ultra-pure ferritic stainless steel for solar water heaters

In order to meet the demands of service life and the synthetical performance/price ratio of stainless steel in the solar water heater industry, the low molybdenum ultra-pure ferritic stainless steel （FSS） B445J1M was developed at Baosteel. In this study, comparative studies were carried out on the mechanical properties, the formability and the corrosion resistance of B445J1M ,304 and 444 ,and the advantages and application fields of B445J1M were summarized.

Effect of Ni content on the weldability of middle-chromium hyperpure ferritic stainless steels 00Cr21Ti

Excellent weldability substantially contributes to the intrinsic quality of steels,while appropriate chemical composition plays a primary role in the essential weldability of steels.The poor weldability of ferritic stainless steels could be improved through modification with minor alloy elements while minimally increasing the cost.Therefore,studying the effect of minor alloy elements on the weldability of steels is of considerable importance.In this study,several steels of middle-chromium hyperpure ferritic stainless 00Cr21Ti with different Ni content(0.3%,0.5%,0.8%,and 1.0%)were developed,and their weldabilities of butt joint samples welded using the metal inert gas welding process,including the influence of welded joints on the microstructure,tensile performance,corrosion resistance,and fatigue property,were investigated.Results show that the steels with w(Ni)≥0.8%exhibit excellent mechanical properties compared with those with low-Ni content steels,further,their impact toughness at normal atmospheric temperature meets the industrial application standard and the fatigue property is similar to that of 304 austenitic stainless steel.Moreover,results show that the corrosion resistance of all the samples is almost at the same level.The results acquired in this study are supposed to be useful for the optimization of the chemical composition of stainless steels aiming to improve weldability.

Study on the simulated pickling of 443NT medium chrome ferritic stainless steel

The oxide scale structure of 443NT hot-rolled strips was analyzed. The pickling of 443NT stainless steel was simulated via the 6σ experimental design. The results indicate that parabolic relations exist between the pickling scores and some of the pickling influencing factors, such as the nitric acid density, the hydrofluoric acid density and the pickling temperature. Effective pickling of 443NT can be achieved by controlling the pickling processing parameters with the HNO3 density ranging from 80 g/L to 180 g/L ,the HF density from 20 g/L to 40 g/L and the pickling temperature from 45 ℃ to60 ℃.

Inclusions for Ultra-pure Ferritic Stainless Steels Containing 21% Chromium

As stabilizing elements added into ultra-pure ferritic stainless steels, niobium and titanium react with car- bon and nitrogen to form carbonitrides and have great effects on the ratio of equiaxed zone and the grain size of solidi- fication structure of ingots, which remarkably affect the quality of cold-rolled sheets. Combined with thermodynamic calculation, style and precipitation progress of inclusions in ultra-pure ferritic stainless steels were investigated by optical microscopy, scanning electron microscopy, transmission electron microscopy and energy dispersive spectros- copy. The results indicate that the inclusions are mainly Ti-Al-N- O system inclusions in ultra-pure ferritic stainless steels. Al2Oa starts to precipitate firstly and then TiOx and TiN precipitates sequently. The inclusions are mainly single TiN particles and complex inclusions with Al2O3-Ti2O3 as cores and covered with TiN under the condition of 0.31% titanium addition and mainly Al2O3 under the condition of 0.01% titanium addition. A few （Nb,Ti）N parti- cles precipitate because of no enough titanium to react with nitrogen when titanium addition is 0.01 %. In addition, fine Nb（C, N） particles with size of less than 500 nm precipitate at relatively low temperature.

Characteristics of SEN clogging and adhesive behavior of oxide inclusion during continuous casting of Ti-stabilized ultra-pure ferritic stainless steels

Submerged entry nozzle(SEN)clogging during continuous casting of Ti-stabilized ultra-pure ferritic stainless(Ti-UPFS)steels was systematically investigated via cross-sectional analysis and acid dissolution treatment.The SEN deposit profile was characterized as occurring in three major layers:(1)an eroded refractory layer;(2)an initial adhesive layer comprised an Al_(2)O_(3)-ZrO_(2) composite sub-layer and a dense Al_(2)O_(3)-based deposit sub-layer;and(3)a porous multiphase deposit layer mainly consisting of MgO·Al_(2)O_(3),CaO-Al_(2)O_(3),and CaO-TiOx.The MgO·Al_(2)O_(3)-rich inclusions did not adhere directly to the eroded refractory but were entrapped during the deposit growth.Results of inclusion characterization in the tundish revealed that the MgO·Al2O3-rich particles present in the tundish served as the primary source of clogging deposits.Furthermore,a novel cavity-induced adhesion model by circular approximation was established to explain the effects of complex inclusion characteristics and refractory material type on adhesion force.A high number of small MgO·Al_(2)O_(3) inclusions were expected to accelerate the buildup of clogging deposits.Improving the modification of MgO·Al_(2)O_(3)-rich inclusions in the size range of 2-4μm by Ca treatment was crucial to minimizing the risk of SEN clogging during the continuous casting of Ti-UPFS steels.

Comparison of feasibility,microstructure and performance of hybrid laser arc,activated flux tungsten inert gas and friction stir welding for thick plate of innovative ultra-pure ferritic stainless steel

An innovative grade of ferritic stainless steel,ultra-pure 18Cr–2Mo thick plate,was designed and produced for special industrial application.In order to maintain its mechanical properties after joining,three advanced joining methods,hybrid laser arc welding,activated flux tungsten inert gas welding and friction stir welding,were selected and conducted to connect the thick plates.The feasibility of three joining methods,the microstructure and mechanical properties were compared,and the results have demonstrated that the sound joint was successfully produced using the selected parameters through friction stir welding.The obtained hardness and impact toughness of the weld zone were satisfying.In terms of activated flux tungsten inert gas welding,the crack will be created due to microstructural brittleness.And as for hybrid laser arc welding,the weld zone is narrow,and the addition of wire during welding for the top weld metal area leads to higher formation ratio of low-angle grain boundaries,which is beneficial to performance of the joint.However,there is still a weak area in the fusion line of the welded joint.The result has illustrated that the welding of innovative ultra-pure ferritic stainless steel thick plate by friction stir welding is feasible.

稳定化元素对443铁素体不锈钢组织和性能的影响

通过金相、SEM和EBSD技术,研究了稳定化元素对443铁素体不锈钢组织和性能的影响。结果表明:单钛稳定443钢中液相析出的TiN可以作为等轴晶有效形核质点,铸还等轴晶率明显高于双稳定443钢的;单钛稳定443钢冷轧产品组织均匀性及抗皱性能均较好,柱状晶导致的(112)<110>不利织构明显减弱;由于NbC的析出,锯钛双稳定性元素增强了沉淀相与基体之间的粘附性,有效提高了材料的韧性;锯钛双稳定443钢中Nb元素可以提高钝化膜中Cr元素有效浓度,并且Nb元素还能增加钝化膜稳定性,从而显著提高443钢的耐点蚀性;由于Nb的晶界偏聚效应,铌钛双稳定443钢的再结晶晶粒尺寸较小。

钛含量对443超纯铁素体不锈钢凝固组织的影响

通过真空感应炉浇注不同钛含量的443超纯铁素体不锈钢铸锭,并分析研究不同钛含量对443超纯铁素体不锈钢铸锭凝固组织的影响。试验结果表明:443超纯铁素体不锈钢凝固过程中先从液相中析出高温铁素体,随着温度降低析出TiN和NbC。钛含量越高凝固组织的等轴晶率越高、晶粒尺寸越小,在[Ti]为0.3%时,铸锭组织全部为等轴晶,等轴晶率为100%,平均尺寸达到0.56 mm,晶粒球化率为0.85。

Distribution of TiN inclusions in Ti-stabilized ultra-pure ferrite stainless steel slab

In order to clarify and control the silver defect on surface of cold-rolled sheet of the Ti-stabilized ultra-pure ferrite stainless steel, the distribution of TiN inclusions on the cross section of hot-rolled plate was studied using automated scanning electron microscopy/energy-dispersive X-ray spectroscopy inclusion analysis (ASPEX 1020 system). It was found that the number density decreases sharply from the surface to the center of the hot-rolled plate, whereas the average size increases. Then, the distribution of TiN inclusions on the cross section of continuously cast slab was investigated. Similarly, numerous small-sized TiN inclusions were generated at the subsurface of the slab. The average size rapidly increased and the number density dramatically decreased from the subsurface to 1/4 thickness, while from 1/4 thickness to 1/2 thickness, the increase in average size and the decrease in number density were slight. Thermodynamics results showed that TiN inclusion was formed below the liquidus temperature, which indicated that TiN inclusions could not be formed during secondary refining. Considering the microsegregation of solute elements and the equilibrium of TiN formation during solidification, TiN precipitated in the mushy zone when the solid fraction was close to 0.2. The growth of TiN was analyzed based on the diffusion-controlled growth model. With the increase in cooling rate, the time for TiN growth decreased and the size of TiN inclusions was diminished, which revealed the size distribution of TiN inclusions in the cast slab qualitatively.

热输入对超薄443铁素体不锈钢组织性能的影响

针对443铁素体不锈钢焊接接头存在粗晶组织与性能脆化等问题进行研究,采用光学显微镜(OM)、扫描电子显微镜(SEM)分析了不同焊接方法焊后接头组织和性能的变化.采用钨极氩弧焊(TIG)、脉冲钨极氩弧焊(P-TIG)和脉冲激光焊(P-LBW)三种焊接方法进行焊接,分析了不同热输入对超薄443铁素体不锈钢焊接接头微观组织、拉伸性能和杯突性能的影响规律.结果表明,焊接热输入是影响该铁素体不锈钢焊接接头组织和性能的重要因素,采用脉冲焊接方法来细化组织可以有效提高焊接接头综合性能.

拉-拉循环载荷下443铁素体不锈钢产热规律及疲劳性能预测

采用红外热像法研究了443铁素体不锈钢在疲劳试验过程中表面温度场的变化规律,提出了采用ΔT-Nf曲线预测疲劳寿命的方法。结果表明:温升极限值ΔT=3.18℃,即当ΔT>3.18℃时,试样发生疲劳断裂,与实测温升值3.49℃相比,误差为8.89%。利用ΔT-Nf曲线预测443铁素体不锈钢在5×106循环次数下的疲劳强度为277.97MPa,与传统方法测得结果284.45MPa相对误差为2.28%。

退火温度对443超纯铁素体不锈钢冷轧板性能的影响

采用电子背散射衍射(EBSD)技术和拉伸试验等研究了退火温度对443超纯铁素体不锈钢冷轧板微观组织、织构和力学性能的影响。结果表明:随着退火温度从880℃升高到980℃,晶粒尺寸增大,平均晶粒尺寸从32.5μm增大到64.3μm。随着退火温度升高,{111}织构增强,{111}<112>织构强度由6.6增加到10.3。不同退火温度下试验钢的屈服强度、抗拉强度和硬度变化不显著。经过930℃退火,伸长率和综合力学性能最佳,组织均匀。

443高铬铁素体不锈钢耐蚀性能评价

通过盐雾试验、电化学试验和应力腐蚀试验,并结合扫描电镜,对比研究了443超纯铁素体不锈钢和304奥氏体不锈钢的耐腐蚀性能。结果表明:碳、氮间隙元素极低的高铬443超纯铁素体不锈钢点腐蚀速率小于304奥氏体不锈钢,具有比304更优异的耐氯离子腐蚀性能;同时,443不锈钢不具有晶间腐蚀敏感性,而304具有严重的晶间腐蚀敏感性;304不锈钢有可能发生应力腐蚀断裂,443不锈钢没有这种危险。可见,443超纯铁素体不锈钢是304奥氏体不锈钢理想的替代材料,可用于电梯、建筑装饰、厨具等众多行业。

冷轧工艺对443铁素体不锈钢抗皱性能影响

以443铁素体不锈钢为研究对象,研究了冷轧工艺对其表面抗皱性能的影响。结果表明,冷轧采用二轧程的生产工艺可以明显改善表面抗起皱性能;一轧程冷轧板芯部存在明显的晶粒簇,沿着轧向成条状分布,晶粒呈非等轴状,尺寸偏大,而二轧程冷轧板芯部组织分布均匀;一轧程冷轧板表层和芯部除了γ纤维再结晶外还保留强烈的{112}<110>织构,且γ纤维再结晶织构的强度小于二轧程;冷轧采用二轧程工艺可以有效消除原始柱状凝固组织带来的不利影响,弱化α纤维变形织构,使得微观晶粒取向分布更加均匀。