Economical Stainless Nitrogen Steels: Promising Substitutes of Light Alloys

Main process and mechanical properties of corrosion-resistant steels with a structure of nitrogen martensite are considered. Advantages of such steels over light (aluminum, titanium) alloys with respect to specific static and cyclic strength, process ductility in hot and cold state, and fracture toughness are determined. It is possible to organize wide-scale production of semiproducts and articles from such steels at Russian plants of quality metal products. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 7, pp. 9 – 13, July, 2005.     

Structure and Properties of Low-Alloy High-Nitrogen Martensitic Steels

Special features of structure formation and mechanical properties of low-alloy martensitic steels with superequilibrium content of nitrogen and low content of carbon are considered. Experimental data on the effect of the temperature of heating for hardening and tempering on the structure, strength, and ductility of these steels are presented. The advantages and disadvantages of the introduction of nitrogen into low-alloy martensitic steels instead of carbon are discussed. It is shown that steel 10Kh3A combines high strength with high ductility. This steel is considered as a material for heavily loaded parts and nonwelded structures instead of high-strength steels alloyed with Ni, Mo, V and other expensive and scarce elements.     

Springback prediction of TWIP automotive sheets

In an effort to reduce the weight of vehicles, automotive companies are replacing conventional steel parts with light weight alloys and/or with advanced high strength steels (AHSS) such as dual-phase (DP), twinning induced plasticity (TWIP), and transformation induced plasticity (TRIP) steels. The main objective of this work is to experimentally and numerically evaluate the macro-performance of the automotive TWIP sheet in conjunction with springback. In order to characterize the mechanical properties, simple tension and tension-compression tests were performed to determine anisotropic properties, as well as the Bauschinger, transient, and permanent softening behaviors during reverse loading. For numerical simulations, the anisotropic yield function Yld2000-2d was utilized along with the combined isotropic-kinematic hardening law based on the modified Chaboche model. Springback verification was performed for the unconstrained cylindrical bending and 2D draw bending tests.     

Überblick über die Entwicklung und Eigenschaften stickstofflegierter austenitischer Stähle für den chemischen Apparatebau

A review of the devolopment and the properties of nitrogen containing austenitic steels for chemical apparatus construction Addition of nitrogen results in increased strength austenitic steels and in increased austenite stability, so that the formation of undesirable phases is suppressed or at least delayed. This feature eliminates in particular the Structural stability problems encountered during welding. The increase of mechanical strength involves qualitatively all the properties related to strength, including fatigue strength and corrosion fatigue strength; it should be noted that this improvement has not been achieved at the expense of ductility, so that the steels are suitable for low temperature application as well. For these reasons it is recommended to include nitrogen alloyed steels in standardization projects.     

Low-Density Steels: The Effect of Al Addition on Microstructure and Properties

Density reduction of automotive steels is needed to reduce fuel consumption, thereby reducing greenhouse gas emissions. Aluminum addition has been found to be effective in making steels lighter. Such an addition does not change the crystal structure of the material. Steels modified with aluminum possess higher strength with very little compromise in ductility. In this work, different compositions of Fe-Al systems have been studied so that the desired properties of the material remain within the limit. A density reduction of approximately 10% has been achieved. The specific strength of optimal Fe-Al alloys is higher than conventional steels such as ultra-low-carbon steels.     

Characterization of the Trace Phosphorus Segregation and Mechanical Properties of Dual-Phase Steels

The segregation behavior of trace amount of phosphorus (P) and the mechanical properties of dual-phase (DP) steels have been systematically studied. The microstructure of DP steels is mainly composed of martensite, ferrite and nanoscale carbides. For the DP steels with different trace amounts of P (≤ 0.015 wt%), P has almost no effect on the mechanical properties. Atom probe technology (APT) analyses confirm that P segregation was only found at the precipitate/matrix interface. Moreover, the precipitates of (Ti, Mo) C are widely distributed in the ferrite, martensite and ferrite/martensite interface regions. The special segregation feature of P would not concentrate at specific regions such as ferrite/martensite interface and/or martensite lath interface, which reveals that trace amounts of P (≤ 0.015wt%) have almost no effect on the mechanical properties of DP steels. It is proved for the first time that the MC-type carbides of (Ti, Mo) C can reduce or eliminate the damage effect of P on the mechanical properties of steels, which provides a new way for the design of alloys to reduce P damage. This work will promote to increase the P content control standard in DP steels from 0.01 to 0.015 wt%, which will not change the mechanical properties, but greatly reduce the scrap rate and increase the energy efficiency of the manufacturing process.     

The effect of nitrogen on the cold forging properties of 1020 steel

We have studied the effect of nitrogen on the cold forging properties of a low carbon steel as a function of temperature. Five AISI 1020 steels with nitrogen contents from 12 to 180 ppm were examined by tensile testing from 25 to 371 °C. Yield strength, tensile elongation (ductility), ultimate tensile strength (UTS), strain hardening exponents and strength coefficients were determined. The influence of nitrogen on the mechanical property behavior of this low carbon steel exhibits trends as expected—when nitrogen content increases, the strength of the steel increases and the ductility decreases. Likewise, as the temperature increases, the strength of the steel generally decreases; however, the ductility initially decreases, then exhibits an increasing trend. Additionally, there is an intermediate temperature range for these alloys where anomalous behavior is observed. Serrated stress–strain curves seen in this temperature range are indicative of dynamic strain aging. It is probable that this anomalous mechanical property trend is due to dynamic strain aging.     

Improved Ferritic–Austenitic Stainless Steel

Abstract

For the efficient operation of chemical process plant it is of paramount importance to ensure as far as possible that the periods of closurefor maintenance and repair are minimised.

The arduous conditions encountered in many chemical plants as a result of progressive trends towards. higher yields, etc., have therefore highlighted the need for greater strength and pitting resistance than can be obtained in conventional austenitic stainless steels. This paper describes the development of ferritic/austenitic high chromium duplex cast stainless steels and demonstrates how, by addition of nitrogen and close control of composition, certain inherent drawbacks of duplex alloys can be overcome. The nitro gen-containing steel has an attractive combination of mechanical properties, corrosion resistance, ductility, weldability and castability, and has received application in a wide range of aggressive environments.     

Solubility of Nitrogen in Superaustenitic Stainless Steels During Air Induction Melting

The amount of nitrogen contained in super austenitic stainless steels (SASS) influences their properties significantly. The effect of maximum amount of nitrogen in the highly alloyed Cr and Ni SASS containing further additions of Mo and Mn is studied. The calculated nitrogen contents of the experimental alloys are compared with the actual nitrogen contents obtained in the alloys produced using induction melting furnace. The actual nitrogen content of the alloys is always lower than the calculated value, and this discrepancy is due to the presence of positive interaction parameters of Ni, Cu, and Si in the alloy. However, the yield of nitrogen in the liquid SASS is improved significantly with additions of Mn and Mo contents. The construction of multicomponent phase diagrams for SASS is demonstrated using Thermo-Calc software. SASS containing more nitrogen exhibited a very high strength without loss of toughness.     

Ultrahigh-strength steels for aerospace applications

The ultrahigh-strength steels used in aerospace applications are primarily alloys developed 25 or more years ago, which would seem to illustrate the conservatism of alloy producers. However, the now widespread use of AF1410, which was developed in the mid-1970s, suggests that new alloys will be adopted for aerospace applications if their mechanical properties are markedly superior to incumbent alloys. Given the excellent properties of the secondary hardening steels such as AF1410, it would appear that the greatest need is for alloys with yield strengths of 1,725 MPa and higher, which have improved fracture toughness and resistance to stress-corrosion cracking. Control of sulfide-type inclusions, coupled with low sulfur levels, may be a means of achieving quite reasonable toughness at high strength levels. Improving resistance to stress-corrosion cracking appears to be a more difficult problem, but it is hoped that a general solution for the case of intergranular fracture by stress-corrosion cracking will arise from ongoing fundamental studies of the effects of segregating impurities and alloying additions on grain boundary cohesion.     

Mechanical properties and corrosion resistance evaluation of superduplex stainless steel UNS S32760 repaired by GTAW process

Superduplex stainless steels (SDSSs) are alloys widely used in the exploration and production of oil. They are used in marine and offshore components such as heat exchangers, umbilicals, sea water injection lines and various other equipment that requires high corrosion resistance with elevated mechanical strength values. These characteristics are due to its fine two-phase microstructure composed of similar proportions of austenite and ferrite and the alloying elements of Cr, Ni, Mo, N and W. However, during welding, and also in the stages of fabrication and pipe assembly, the presence of defects may occur that requires the need for repair procedures to be carried out on the welded joint. This study aims to characterise the microstructure, mechanical properties, nitrogen content and critical pitting temperature (CPT) of a SDSS pipe, UNS S32760, in certain regions of a welded joint, where the gas tungsten arc welding process was performed, with the completion of two sequential repair procedures. The results show that there is a decrease in the value of the CPT at the root of the weld, though there are not substantial variations in the mechanical properties analysed.     

Al— Be alloys: Multipurpose metallic composite materials

The article is devoted to composite materials created on the basis of the technology of light alloys and developments of the All-Russia Institute of Aircraft Materials concerning beryllium alloys with a high modulus of elasticity. The competitiveness of such composite materials is determined by the high level of the specific strength properties, which exceed, in some cases, the characteristics of powder materials of a similar composition and approach the properties of titanium alloys and steels.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 9, pp. 23 – 26, September, 1996.     

Overview of Lightweight Ferrous Materials: Strategies and Promises

Reducing the density of steels is a novel approach for weight reduction of automobiles to improve fuel efficiency. In this overview article, strategies for the development of lightweight steels are presented with a focus on bulk ferrous alloys. The metallurgical principles of these steels and their mechanical properties of relevance to automotive applications are discussed. Some of the engineering aspects highlighting the possible problems related to mass production of these steels are also considered. Application prospects of these steels vis-à-vis standard automotive steels are shown.     

Herstellung und Eigenschaften stickstofflegierter,korrosionsbeständiger Stähle und Sonderstähle mit niedrigen Kohlenstoffgehalten

Production and properties of nitrogen alloyed, corrosion resistant steels and special steels with low carbon contents Alloying with nitrogen has favourable influence in particular on the mechanical properties of CrNiMo steels (X 2 CrNiMoN 17 12, materials No. 1.4406, X 2 CrNiMoN 17 13 5, materials No. 1.4439 und X 2 CrNiMoN 22 5, materials No. W.-Nr. 1.4462). This comes to bear when ambient temperature and low temperature strength and toughness are concerned. With respect to the corrosion behaviour the data concerning the effect of nitrogen are contradictory. It has become clear that nitrogen improves pitting corrosion resistance; this applies, however, only to pit initiation but not to pit growth. Stress corrosion cracking is not delayed by nitrogen but different results have been obtained with different media: while the duplex steel X 2 CrNiMoN 22 5 is attacked considerably faster than the corresponding nitrogen-free steel in 42% boiling magnesium chloride solution the time-to-failure of both steels are comparable in 30% boiling MgCl₂-solution. The nitrogen alloyed steels can be welded by all known welding procedures, provided fully austenitic welding rods are used.     

The fracture toughness of bulk metallic glasses

Stiffness, strength, and toughness are the three primary attributes of a material, in terms of its mechanical properties. Bulk metallic glasses (BMGs) are known to exhibit elastic moduli at a fraction lower than crystalline alloys and have extraordinary strength. However, the reported values of fracture toughness of BMGs are highly variable; some BMGs such as the Zr-based ones have toughness values that are comparable to some high strength steels and titanium alloys, whereas there are also BMGs that are almost as brittle as silicate glasses. Invariably, monolithic BMGs exhibit no or low crack growth resistance and tend to become brittle upon structural relaxation. Despite its critical importance for the use of BMGs as structural materials, the fracture toughness of BMGs is relatively poorly understood. In this paper, we review the available literature to summarize the current understanding of the mechanics and micromechanisms of BMG toughness and highlight the needs for future research in this important area.     

Effects of Rare Earth Metal addition on the cavitation erosion-corrosion resistance of super duplex stainless steels

Austenitic stainless steels such as AISI 316L have been used in equipment in which fluid flows at high speeds which can induce cavitation erosion on metallic surfaces due to the collapse of cavities, where the collapse is caused by the sudden change of local pressure within the liquid. Usually AISI 316L is susceptible to cavitation erosion. This research focuses on developing a better material to replace the AISI 316L used in equipment with high speed fluid flow, such as impellers. The effects of Rare Earth Metal (REM) additions on the cavitation erosion-corrosion resistance of duplex stainless steels were studied using metallographic examination, the potentiodynamic anodic polarization test, the tensile test, the X-ray diffraction test and the ultrasonic cavitation erosion test. The experimental alloys were found to have superior mechanical properties due to interstitial solid solution strengthening, by adding high nitrogen (0.4%), as well as by the refinement of phases and grains induced by fine REM oxides and oxy-sulfides. Corrosion resistance decreases in a gentle gradient as the REM content increases. However, REM containing alloys show superior corrosion resistance compared with that of other commercial alloys (SAF 2507, AISI 316L). Owing to their excellent mechanical properties and corrosion resistance, the alloys containing REM have high cavitation erosion-corrosion resistance.     

Cu和Cr对耐候钢的力学性能及耐蚀性能的影响

研究了不同Cu和Cr含量对低合金高强耐候钢的力学性能及耐腐蚀性能的影响规律。结果表明,Cu元素含量对合金的强度影响较为明显,随Cu含量增加,合金的屈服强度逐渐提高;随Cr含量增加,合金屈服强度也略有上升,但强化效果不明显。Cu和Cr的加入均会提高合金的韧脆转变温度,但冲击功的绝对值仍保持在较高的水平。Cu和Cr元素的加入,增加了锈层的致密度,使得合金的耐腐蚀性能得到明显提升。     

Structure-property correlation of two Cu-bearing high-strength low-alloy steels

Structure and mechanical properties of two copper bearing high-strength low-alloy steels (HSLA)—one similar to HSLA 80 and the other to HSLA 100—are studied in different aging conditions. Elemental copper precipitates of nanometer size have been found to play an important role in the formation of different types of microstructures and in enhancing the strength and toughness of the alloys. Other alloying elements such as Ti, Nb, and V result in fine precipitates of carbides and nitrides, which improve the mechanical strength.     

含镍TRIP钢的组织与力学性能研究

采用Thermo-Calc热力学计算软件、Gleeble-3500热模拟试验机、X射线衍射仪等研究了两相区(780～820℃)等温处理对含镍TRIP钢组织和力学性能的影响。结果表明,Thermo-Calc软件的计算结果和试验结果符合较好。该成分的试验钢具有较好的力学稳定性,经过不同的热处理工艺,均能达到比较理想的强韧性配合,抗拉强度达到1 000 MPa,延伸率达到20%以上,其中强塑积最大值达到24 036 MPa%。     

高锰氮双相不锈钢25Cr-2Ni-10Mn-xW-N的组织和性能研究

研究了钨含量对新型高锰氮双相不锈钢25Cr-2Ni-xW-10Mn-N(x=1.5,3.0,4.5)的显微组织、力学性能以及耐腐蚀性能的影响。结果表明:该系不锈钢固溶处理后具有典型的铁素体+奥氏体双相组织,随着固溶温度的增加,铁素体含量上升。随着钨含量的增加,σ相析出增加,铁素体体积分数增大,耐点蚀性增强,屈服强度上升,断裂延伸率和冲击韧性降低。此类钢作为结构材料具有广阔的应用前景。