Microstructure,Mechanical Properties,and Abrasive Wear Behaviour of Si‐Mn‐Cr‐B Cast Steel as a Function of Carbon Concentration

The microstructures, mechanical properties and abrasive wear behaviour of five kinds of Si‐Mn‐Cr‐B cast steels were studied. The steels investigated contained X wt.% C with X= 0.15, 0.25, 0.35, 0.45, 0.55, 2.5 wt.% Si, 2.5 wt.% Mn, 0.5 wt.% Cr, 0.004 wt.%B . The results showed that the A_c1temperatures increased and A_c3 and M_s temperatures decreased with increasing carbon concentration. From the continuous cooling transformation (CCT) curves, it was discovered that the incubation period of pearlitic transformation was prolonged and the transformation curves of pearlite and bainite were separated significantly with rising carbon concentration. At lower carbon concentration, the normalized structure of Si‐Mn‐Cr‐B cast steel consisted mainly of granular bainite and M‐A islands. The normalized microstructures of the cast steel changed from granular bainite gradually to needle‐like bainite, upper bainite, and lower bainite with rising carbon concentration. The tensile strength and hardness of Si‐Mn‐Cr‐B cast steel increased and impact and fracture toughness decreased with increasing carbon content. The wear testing results showed that the wear resistance of Si‐Mn‐Cr‐B cast steel improved with higher carbon content but was obviously unchanged beyond the carbon concentration of 0.45%. The best balance of properties of Si‐Mn‐Cr‐B cast steel is obtained at the carbon concentration range of 0.35 ‐ 0.45%C.     

High‐Interstitial Stainless Austenitic Steel Castings

Interstitial atoms are most effective in strengthening austenitic steels. In stainless grades, chromium strongly reduces the solubility limit of carbon. High‐nitrogen contents require costly pressure or powder metallurgy to dissolve N in the melt. The combination of both elements comes with a high‐interstitial solubility at normal pressure of air. Sand casting with 18 mass% Cr and Mn each and 0.85 mass% (C + N) were industrially produced. The investigation revealed: proof strength R_p0.2 = 457 [MPa], true fracture strength R = 1714 [MPa], fracture elongation A = 44%, notch impact toughness KV = 290 J combined with a DBTT of ?94°C, an impact wear resistance comparable to Hadfield steel X120Mn12 but combined with a good corrosion resistance. Deep freezing and cold working does not effect the low relative magnetic permeability. This unique combination of properties offers advantages in application.     

Effect of Carbon on Stainless Austenitic CrMnCN Steel Castings

The effect of up to 0.5 mass% C on a steel with 18 to 19 mass% Cr and Mn each and about 0.6 mass% N was investigated by tensile tests, notch impact tests and corrosion tests. The experimental results show that the solution anneal temperature and the sensitisation to intercrystalline corrosion depend on the carbon content which raise the strength and cold work hardening. Up to 1 mass% C+N the ductile to brittle transition temperature remains at about ?90 °C. Corrosion in diluted aqueous solutions of H₂SO₄, HCl and NaCl is described.     

Effects of Cr and V additions on the microstructure and properties of high-vanadium wear-resistant alloy steel

The effects of chromium and vanadium additions on the microstructure, hardness and wear resistance of high-vanadium alloy steel (containing 5–10 wt-% V and 2–10 wt-% Cr) were studied by means of optical microscopy, scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS), Vickers hardness and Rockwell-hardness tester & M-200 ring block wear tester. Researching results showed that the solidification structure of high-vanadium wear-resistant alloy steel was mainly consisted α-Fe (martensite), vanadium carbide (VC), M₃C and M₇C₃. Vanadium is mainly distributed over VC, and certain amount of vanadium exists in the matrix and M₇C₃ type eutectic carbide. Chromium is mainly distributed over the M₇C₃, and the matrix also contains a small quantity of chromium. It is found that the content of VC increases with the increase of vanadium content when carbon and chromium contents are constant. The change of micro- and macro-hardness was not obvious with the increase of vanadium content. The content of M₇C₃ type eutectic carbides increases gradually with the increase of chromium content when carbon and vanadium contents are constant. The micro- and macro-hardness increases with the increase of chromium content. The increase of vanadium content brings to the increase of wear resistance of alloy steel when carbon and chromium contents are constant. The change of chromium content had no obvious effect on wear resistance of high-vanadium alloy steel when carbon and vanadium contents. The increase of vanadium content brings to the increase of wear resistance of alloy steel when carbon and chromium contents are constant. The wear resistance of as-cast high-vanadium alloy steel is the best when the content of vanadium and chromium is 10 wt-% and 5 wt-% respectively.     

Stainless Steels for Exhaust Lines

Exhaust lines of cars have been strongly evolving during the last decade to meet the various requirements of the automotive industry and the new environment regulations. This development tends to favour stainless steel grades to replace cast iron for the exhaust manifold and aluminized low carbon steel for pipes and mufflers. Among the various stainless steel grades, the proportion of ferritic grade increases for the hot part of the exhaust system as its price is lower and more stable than austenitic or refractory grades, and as it exhibits a better resistance to cyclic oxidation. A large and rapid development of stainless ferritic grades has been based on Ti and Nb stabilization. Adding niobium presents many advantages for corrosion resistance, deep‐drawability, and mainly creep resistance at high temperature. The paper is focused on stainless steel with 14 wt% chromium, stabilized with Nb. Intermetallic precipitation is studied after a 100 h holding time at different temperatures (sag tests). It is shown that, depending on the test temperature and on the chemical composition of the steel, Fe₂Nb or Fe₂Nb₃ intermetallic particles can precipitate, which affects the creep resistance: Fe₂Nb₃ being more stable at higher temperature. Some impacts on the alloy design dedicated to exhaust line application are presented as a conclusion of the study.     

Chromium Oxide Reduction from Slag by Silicon and Magnesium

Experimental and theoretical studies were performed in order to estimate the effect of the basicity of the slag as well as the amount of reducing agents on the reduction of chromium oxide from a slag in contact with molten steel at 1600 °C. The aim of this work was to compare the efficiency of magnesium and silicon as reducing agents of Cr₂O₃. The slag system contained CaO, MgO, SiO₂, CaF₂ and Cr₂O₃ together with Fe‐alloys (Fe‐Si or Fe‐Si‐Mg). The maximum Cr yield was about 81% with Fe‐44%Si‐9%Mg and 88% with Fe‐75%Si. That means that the reducing effect of Mg was much better than that of Si. Some experiments were conducted to study the effect of initial Cr in steel on the chromium oxide reduction reaction. Three initial Cr contents were tested (0.15, 2 and 4 mass%). It was found that chrome was partially bound into stable spinel phase MgO·Cr₂O₃ in the final slag. Thermodynamic estimations were made to determine the effect of process temperature, slag basicity and the amount of reducing agents in the slag on the Cr recovery. The efficiency of Cr reducing agents increased in the order: Si, Al, Ca and Mg. The Cr yield increased with slag basicity and amount of reducing agents.     

Studies on Nb Microalloying of 13Cr Super Martensitic Stainless Steel

The effect of Nb microalloying on microstructure, mechanical properties, and pitting corrosion properties of quenched and tempered 13?pct Cr-5?pct Ni-0.02?pct C martensitic stainless steels with different Mo and N contents was investigated. The microstructure, density, and dispersion of high-angle boundaries, nanoscale precipitates, and amount of retained austenite were characterized by using electron backscattered diffraction, transmission electron microscopy, and X-ray diffraction to correlate with properties. The results show that the combined effects of lowering nitrogen content in 13?pct Cr-5?pct Ni-1~2?pct Mo-0.02?pct C steels to 0.01?wt pct, and adding 0.1?pct Nb are to decrease the amount of Cr-rich precipitates, as Nb preferentially combines with residual carbon and nitrogen to form carbonitrides, suppressing the formation of Cr₂N and Cr₂₃C₆. Austenite grain refinement can be achieved by Nb microalloying through proper heat treatment. If the nitrogen content is kept high, then Cr-rich precipitates would occur irrespective of microalloying addition. The NbN would also occur at high temperature, which will act as substrate for nucleation of coarse precipitates during subsequent tempering, impairing the toughness of the steel. It was shown that the addition of Nb to low interstitial super martensitic stainless steel retards the formation of reversed austenite and results in the formation of nanoscale precipitates (5 to 15?nm), which contribute to a significant increase in strength. More importantly, the pitting corrosion resistance was found to increase with Nb addition. This is attributed to suppression of Cr-rich precipitates, which can cause local depletion of Cr in the matrix and the initiation of pitting corrosion.     

Nb 对双相不锈钢激光熔覆组织及性能的影响研究

采用激光熔覆技术,在基体45#钢板上熔覆了含Nb的双相不锈钢涂层。采用扫描电子显微镜(SEM)和能谱分析仪(EDS)对涂层的微观组织和元素组成进行了表征分析,测试了涂层沿深度方向上的显微硬度,在20℃条件下进行了UMT摩擦磨损试验,并在3.5 wt.%的NaCl水溶液中进行电化学测试。结果表明:在双相不锈钢合金粉中添加Nb进行激光熔覆,所制备的熔覆层中碳化物由Cr和Nb的碳化物组成,同时Cr含量显著降低;熔覆层中添加Nb后,其硬度和耐磨性比未添加Nb的熔覆层有显著提高,Nb含量为1.4%的时候效果最好;随着Nb含量的增大,自腐蚀电位逐渐增大,自腐蚀电流密度逐渐降低,说明Nb含量越高熔覆层的耐蚀性越好。综上所述,当熔覆层中Nb含量为1.4%的时候,其耐磨性和耐蚀性最好。     

Microstructural and crystallographic relationships in directionally solidified NbCr2Nb and CrCr2Nb eutectics

The present paper describes processing, microstructures and phase relationships in directionally solidified Cr₂NbNb and Cr₂NbCr eutectics. Both of these eutectics, and the stoichiometric Laves phase Cr₂Nb, were directionally solidified using cold crucible Czochralski crystal growth with growth rates from 1 to 15 mm/min. Cr₂NbNb had a rod/ribbon-type structure and Cr₂NbCr had a lamellar structure. The crystallographic oreintation relationships between both Cr and Nb and the Cr₂Nb Laves phase in the individual eutectics were characterized using transmission electron microscopy. Inter-phase orientation relationships in these eutectics were complicated by the transformation of Cr₂Nb from the C14 to the C15 crystal structure on post-solidification cooling. Twins were observed in the C15 Cr₂Nb phase in both the single phase and eutectic samples. The relationship between the twins, the C14–C15 transformation, and the eutectic morphology is also discussed.     

Composition Control of CaO‐MgO‐Al2O3‐SiO2 Inclusions in Tire Cord Steel ‐ a Thermodynamic Analysis

The effect of oxide component content on the low melting point zone (LMP) in the CaO‐MgO‐Al₂O₃‐SiO₂ system has been analysed using FactSage software. The contents of dissolved elements [Si], [Mg], [O] and [Al] in liquid steel in equilibrium with the LMP inclusions in the CaO‐MgO‐Al₂O₃‐SiO₂ system have been calculated. The results show that the CaO‐MgO‐Al₂O₃‐SiO₂ system has the largest LMP zone (below 1400°C) when the Al₂O₃ content is 20% or the MgO content is 10%. The LMP zone becomes wide with the increase in CaO content (within the range of 0~30 mass%) and the decrease in SiO₂ (from 25 to 5 mass%). To obtain the LMP (below 1400°C) inclusions, the [Mg], [Al] and [O] contents must be controlled within the range of 0.2~2 ppm, 1.0~2.0 ppm and 60~100 ppm, respectively.     

三种耐蚀塑料模具钢的耐磨性和磨损机理

通过M200环-块磨损试验机和扫描电镜研究了具有良好耐腐蚀性能的3种塑料模具钢STAVAX (%:0.37C、13.40Cr、0.31V)、M330(%:0.36C、12.88Cr、0.15Mo)和N702(%:0.05C、16.30Cr、4.00Cu、4.00Ni、0.34Nb)的磨损性能和磨损表面形貌。结果表明,STAVAX、M330和N702钢在淬、回火后HRC值分别为55、53和44,磨痕宽度分别为2.61 mm、2.74 mm和7.41 mm。STAVAX和M330钢组织为基体+细球状碳化物,具有较高的耐磨性,而N702钢的基体相对较软,无第二相碳化物,在试验过程中其基体极易磨损,形成大量疲劳裂纹,易导致块状或片状剥落,耐磨性较低。     

Effect of Cr2O3 Addition on Sintering Behavior of Novel Chromite-Based Ladle Filler Sand

Developing novel filler sands has garnered significant interest in improving the ladle's free-opening rate and enhancing the cleanliness of high-Mn and high-Al steel. Laboratory studies explore the effect of adding Cr₂O₃ powder on the sintering behavior of chromite-based filler sands. Furthermore, interfacial phenomena are examined between the sands and the steel grades, varying in Mn contents. The results demonstrate that adding Cr₂O₃ power plays a role in inhibiting the liquid phase formation in the sand. With a 16% addition, the steel (Mn mass% = 30) reacts with the sand, leading to the shape of a spinel phase, specifically (Mn, Fe, Mg)O·(Al, Cr)₂O₃, which facilitates the separation of the liquid phase. The reduction of FeO to Fe by Mn, Al, and C in steel, especially Al, is hindered by adding Cr₂O₃, resulting in a suitable sintering degree that ultimately benefits ladle free-opening. SiO₂ is crucial for forming the liquid phase during the sintering process. The SiO₂ content of the sand should be about 20% to achieve optimal sintering effects. Chromite sand for casting is not suitable for the steels. The mixed sand presented in the current study demonstrates potential as a suitable filler sand for the steel (20 ≤ Mn mass% ≤ 30).     

Wear Protection by Fe‐B‐C Hard Phases

Four as‐cast iron alloys with (mass%) 1B + 3C, 2B + 2C, 3B + 1C and 4B + 1C were investigated in respect to their microstructure by optical and scanning electron microscopy with EDX and ESBD and by microprobe analysis. The microhardness of eutectic Fe₃(C,B) increased with the B/C ratio and raised the resistance to scratching by Flint particles. The low melting range of the castings was used for the powder metallurgical production of a metal matrix composite by liquid phase sintering of admixed hard particles in an Fe‐B‐C base material. Abrasive wear tests showed that the eutectic carborides in the base material raised the wear resistance even more than the admixed particles.     

Microstructure and Tribological Properties of AlCoCrFeNiTi0.5 High-Entropy Alloy in Hydrogen Peroxide Solution

Microstructure and tribological properties of an AlCoCrFeNiTi_0.5 high-entropy alloy in high-concentration hydrogen peroxide solution were investigated in this work. The results show that the sigma phase precipitates and the content of bcc2 decrease during the annealing process. Meanwhile, the complex construction of the interdendrite region changes into simple isolated-island shape, and much more spherical precipitates are formed. Those changes of microstructure during the annealing process lead to the increase of hardness of this alloy. In the testing conditions, the AlCoCrFeNiTi_0.5 alloy shows smoother worn surfaces and steadier coefficient of friction curves than does the 1Cr18Ni9Ti stainless steel, and SiC ceramic preserves better wear resistance than ZrO₂ ceramic. After annealing, the wear resistance of the AlCoCrFeNiTi_0.5 alloy increases coupled with SiC counterface but decreases with ZrO₂ counterface.     

Corrosion resistance of high-strength austenitic chromium–nickel–manganese steel containing nitrogen

The corrosion resistance of high-strength Cr–Ni–Mn austenitic steel containing nitrogen and copper is compared with that of Cr18Ni9 and Cr18Ni10N chromonickel steel by means of the Zive MP2 electrochemical system. The polarization curves and electrochemical characteristics of the alloys are determined in general, pitting, and intercrystallite corrosion by various media: aqueous solutions of NaCl (3%); FeCl₃ 6H₂O (100 g/L); H₂SO₄ (0.5 M); H₂SO₄ (0.5 M) + injected H₂S; and H₂SO₄ (0.5 M) + KSCN (0.01 M). The corrosion rates are calculated. The results indicate that all the steel samples are corrosion-resistant: they exhibit high resistance to intercrystallite corrosion and also to pitting and general corrosion in chloride-bearing media. No pitting corrosion is observed when Cr–Ni–Mn steel of balanced composition containing nitrogen (and especially steel containing both nitrogen and copper) is immersed in sea water, even when the steel’s nickel content is low. This steel outperforms traditional Cr18Ni9 steel in terms of strength and corrosion resistance, even in an acidic medium (0.5 M H₂SO₄).     

Initial Oxidation of a 9%CrMo‐ and a 12%CrMoV‐Steel

For the oxidation and high temperature corrosion resistance of 9‐12% Cr steels, the rapid formation of a dense protective Cr‐rich oxide scale is important. The initial oxidation processes were investigated on a 9%CrMo‐steel and a 12%CrMoV‐steel. Auger spectroscopic studies in the first hours showed a non‐uniform oxidation and effects of surface segregation and microstructure. Grain boundaries and martensite laths provide sufficient Cr to the surface for chromia formation, in other areas formation of SiO₂ may prevent Fe‐oxide growth. For up to 100 hours the oxidation kinetics is largely controlled by diffusion of the selectively oxidized elements Cr, Mn and Si in the steel, only gradually the transition to control by diffusion in the oxide occurs. Thickness and composition of the scale, and also the diffusion profiles in the steel were determined after 10 and 100 hours oxidation by SNMS, revealing important effects of surface treatments, such as electropolishing, polishing, grinding or sandblasting. Strong surface deformation favours the formation of Cr‐rich scales and of flat Cr‐depletion minima. Also the effects of different oxidation atmospheres, H₂‐H₂0, N₂‐H₂‐H₂0 and N₂‐O₂ were investigated and described. The kinetics of the oxide growth and the possibilities to obtain protective scales by pre‐oxidation are discussed.     

445J2超纯铁素体不锈钢和316L超低碳奥氏体不锈钢在溴化锂溶液的点蚀分析

445J2铁素体不锈钢由于高的导热率、低的热膨胀系数以及良好的耐蚀性能使得其作为溴冷机中一些部件的良好候选材料,本文采用电化学测试方法对比研究了445J2超纯铁素体不锈钢(/%:0.01C,22.5Cr, 1.9Mo, 0.27Nb, 0.20Ti, 0.09Al, 0.36Cu, 0.015P,0.001S,0.015N)和316L奥氏体不锈钢(/%:0.002C,16.8Cr, 10.19Ni, 2.02Mo, 0.025P,0.0008S)在20～60℃0.1～1M的溴化锂溶液中的点蚀行为,并采用扫描电镜(SEM)和能谱分析仪(EDS)对电化学结果进行表征。结果表明,随着LiBr温度和浓度的升高,两种钢腐蚀电流密度增大,点蚀电位降低,耐点蚀性变差;氧化物和硫化物夹杂会引起两种钢的点蚀;高含量的Cr以及Mo、Ti、Nb、Al等合金元素使445J2钢具有优异的耐点蚀性能。     

Sintered Composites Based on Stainless Steel

The effect of the amount of chromium carbide addition on the properties of composites based on stainless steel of the austenitic class and their structure formation during sintering in a vacuum are studied. Compositions with 10, 15, 20, 25, and 30% Cr₃C₂ and also a content of 5% MoSi₂ addition are investigated. It is established that an increase in Cr₃C₂ content from 10 to 30% for all composites leads to an increase in hardness and wear resistance, but to some reduction in strength, and in some case a reduction in corrosion resistance.     

Nb对铸造双相耐热钢高温氧化的影响

摘要：为探究Nb对双相耐热钢高温抗氧化性能的影响规律，采用扫描电镜、能谱分析和XRD等分析测试手段研究了1000和1100℃下含Nb双相耐热钢高温氧化性能。结果表明，双相耐热钢氧化层结构为氧化外层(MnCr2O4)→氧化内层(Cr2O3)→Si的内氧化层；Nb的加入加速双相耐热钢的表层氧化膜生长，降低了其抗氧化性能；随着Nb含量的增加，表层基体内部形成富Nb相，促进Si的沿晶界氧化而抑制Si的界面氧化，Cr2O3层和Si的内氧化层厚度均增加。在对高温抗氧化性能要求高的情况下，本双相耐热钢中Nb的质量分数应控制在0.8%以下。     

Desilicating Zircon with Plasma Heating and Phase Equilibrium Analyses

Desilicated zirconia has a great variety of applications. The maximum SiO₂ content in desilicated zirconia is <7 mass%. The present techniques to produce zirconia are always accompanied by many drawbacks. So the authors have developed a new plasma process. Desilicated zirconia (88.6 ~ 96.9 mass% ZrO₂) and magnesia‐stabilized zirconia (> 91.54 mass% ZrO₂, < 5.39 mass% MgO) were produced successfully from zircon using a 150 kW plasma rotating furnace. The effects of time and carbon content on the desilication degree were investigated. The mixture treated in the plasma furnace included condensed phases Zr, ZrC, ZrN, ZrO₂, C, Si, SiC, SiO₂ and gaseous phases SiO, O₂, N₂, CO. The established phase equilibrium diagrams of the Si‐C‐N‐O and Zr‐C‐N‐O systems suggest that the formation of Si₃N₄ is thermodynamically impossible, and the formation of ZrC and ZrN is thermodynamically possible in the central high‐temperature region of the plasma furnace. Experimental results supported the analyses.