合金元素对双相不锈钢2101耐点蚀性能的影响

研究了合金元素对双相不锈钢2101耐点蚀性能的影响规律。结果显示,2101系列合金的浸泡点蚀腐蚀速率在1.9～7.0 g/（m^2.h）之间,与304不锈钢在同一数量级;Mo是提高2101系双相不锈钢耐腐蚀性的关键元素,而N对耐腐蚀性的影响不大;点蚀起源和Thermo-Calc计算结果显示2101成分体系中,铁素体相是耐点蚀性较弱相,提高铁素体相耐蚀性是提高合金整体耐蚀性的关键;当Cr含量固定在21.5%时,Mo作为铁素体形成元素将在铁素体相中富集,提高铁素体相的耐点蚀性能,从而提高合金整体耐蚀性。     

Effect of alloying elements on metadynamic recrystallization in HSLA steels

By means of interrupted torsion tests, the kinetics of metadynamic recrystallization (MDRX) were studied in a Mo, a Nb, and a Ti microalloyed steel at temperatures ranging from 850 °C to 1000 °C and strain rates from 0.02 to 2 s¹. Quenches were also performed after full MDRX. In contrast to the case of static recrystallization (SRX), the kinetics of MDRX are shown to be highly sensitive to a change of an order of magnitude in strain rate and are relatively insensitive to temperature changes within the range of values applicable to industrial hot-rolling practice. A similar algebraic dependence of the MDRX grain size on strain rate and temperature was found in the three steels. The kinetics of MDRX were slower in the Nb than in the Mo steel, and those of the Ti steel were slower than in the Nb and Mo steels. Above 900 °C and 950 °C, the retardation of MDRX in the Nb and Ti steels, respectively, is due to solute drag. Models predicting the start time for Nb and Ti carbonitride precipitation showed that MDRX is delayed below these temperatures by this mechanism. Comparison of the MDRX and precipitation start times in the Nb steel indicated that a temperature of “no-MDRX” could not be defined, in contrast to the well-definedT _nr (no recrystallization temperature) of SRX. By means of torsion simulations composed of multiple interruptions, it is shown that MDRX is retarded decreasingly as the accumulated strain is increased. This appears to be due to the promotion of precipitate coarsening by the continuing deformation.     

The effects of alloying elements on the susceptibility to stress-corrosion cracking of martensitic steels in salt water

The effects of a number of elements (C, Mn, Cr, Mo, Ni, Co, P, and S) on the stress-corrosion cracking (SCC) resistance in salt water of some quenched-and-tempered steels were investigated. Values of the threshold stress intensity for crack growth in salt water (K _Iscc) were measured using the cantilever beam test and precracked specimens. Values of the fracture toughness parameterK _Ix (an approximation ofK _Ic) were also determined. The steels were either Fe-C alloys to which alloying elements were added, or basically of AISI 4340-type composition in which alloying elements were varied. All steels in a series to show the effects of a given element were heat treated to the same yield strength, and generally the effects of an element were determined at two yield strength levels. The results show that only carbon and manganese are definitely harmful to SCC resistance.     

合金元素对双相钢形变及退火织构的影响

分析了双相钢冷变形过程中形变织构的演变规律以及合金元素对双相钢形变织构的影响规律。分析结果表明,虽然存在有少量珠光体,但双相钢冷变形织构与体心立方金属相近;非碳化物形成元素Si的加入对形变织构没有明显的影响;碳化物形成元素Cr和Nb导致形变织构在α取向线的{112}<110>取向位置上的取向密度增强。测试分析了双相退火过程中钢的织构演变规律。结果表明,退火时晶粒的取向将沿着α取向线向γ取向线位置转变,Si或Cr对晶粒取向改变的阻碍作用不明显,微合金元素Nb明显阻碍晶粒取向改变,退火织构仍保持很高的α取向线织构组分。对上述的实验结果进行了理论分析。     

合金元素对Cr-Mo钢第二类回火脆性影响研究综述

对于一些长期在中温条件下服役的Cr-Mo钢(2.25Cr1Mo),由于钢中P、S等有害杂质元素在服役过程中不断向晶界偏聚,降低了晶界结合力,致使该类钢出现第二类回火脆性这一关键问题.为了探寻降低这类Cr-Mo钢第二类回火脆性倾向的有效方法,提高材料安全服役可靠性,从溶质元素偏聚机制出发,总结分析了合金元素晶界偏聚及改善...     

Influence of electrospark alloying on the heat resistance of steels

Conclusions The high-temperature oxidation of electrospark coatings on R9K5, 5KhNV, and 50 steels obtained by electrospark alloying with standard (T15K6, VK8, VK6M) and carbide-, nitride-, and boride-base tungsten-free alloys was investigated by the differential thermal analysis method. It was shown that in increase in heat resistance the refractory compound-base electrode materials used for production of coatings are in the order (by base component) boride-carbidenitride. A significant factor increasing the high-temperature oxidation resistance of the coatings is the increase in their coverage. With a high coating coverage on carbon steel its high-temperature oxidation resistance approaches that of die steel. Therefore, in a number of cases, replacement of expensive alloy steels with carbon steels is possible.Translated from Poroshkovaya Metallurgiya, No. 3(303), pp. 69–74, March, 1988.     

Effects of alloying elements upon austenite decomposition in Low-C steels

The kinetics of austenite decomposition were studied in high-purity Fe-0.1C-0.4Mn-0.3Si-X (concentrations in weight percent;X represents 3Ni, 1Cr, or 0.5Mo) steels at temperatures between 500 °C and 675 °C. The transformation stasis phenomenon was found in the Fe-C-Mn-Si-Mo and Fe-C-Mn-Si-Ni alloys isothermally transformed at 650 °C and 675 °C but not in the Fe-C-Mn-Si and Fe-C-Mn-Si-Cr alloys at any of the temperatures investigated. The occurrence of transformation stasis was explained by synergistic interactions among alloying elements. The paraequilibrium model was applied to calculate the metastable fraction of ferrite in each alloy. This fraction was shown to coincide with cessation of transformation in the Mo alloy transformed at 600 °C. Transformation stasis was found in both the Ni and the Mo alloys isothermally reacted at 650 °C and 675 °C. The interactions among Mn, Si, and Mo, as well as interactions among Mn, Si, and Ni, appear to decrease the threshold concentrations for transformation stasis in Fe-C-Mn-Si systems. Segregation of Mn and Mo to the α/yγ boundary, assisted by the presence of Si, was suggested to enhance the solute draglike effect (SDLE) and lead to transformation stasis. In the Ni alloy, a lower driving force for ferrite formation resulting from the Ni addition could be responsible for the occurrence of transformation stasis.     

Influence of alloying elements on the thermal contraction of peritectic steels during initial solidification

Abstract

A modified SSCT (submerged split chill tensile) test was used to measure the contraction forces occurring during the solidification of steels with a carbon content of between 0·05 and 0·2 wt-% at constant Mn (1·55%) and Si (0·3%) contents. Further test series were performed with varying Si, V, Cr, Mn, Ni and Nb contents at a constant C content of 0·1%. Any cracks generated were detected, counted and measured. The total crack length allows conclusions to be drawn about the influence of alloying elements on crack susceptibility. The measured results match very well with results calculated from hot tearing criteria. Besides the steel composition, the superheat of the melt proved to be the most important factor in crack formation caused by contraction.     

Effect of texture and microstructure on resistance to cracking of high-strength hot-rolled Nb-Ti microalloyed steels

Significant texture gradient in the through-thickness direction was observed in high-strength hot-rolled 560 and 770 MPa Nb-Ti microalloyed steels, characterized by polygonal ferrite and ferrite bainite microstructures, respectively. {113}〈110〉 was the most intense deformation texture in the two high-strength grades of Nb-Ti steels and was dominant in the midthickness region compared to 10 and 25 pct depth below the surface. The recrystallization texture of austenite, {100}〈001〉, transformed into {100}〈011〉 component in the ferrite and indicated an increase in the intensity with increase in depth for the Nb-Ti microalloyed steels. The {100}〈011〉 texture has a detrimental effect on the edge formabiity of steels. However, the midthickness plane contained considerable intensity of desired texture, {332}〈113〉, which is expected to offset the undesirable {100}〈011〉 texture resulting in superior edge formability and impact toughness of Nb-Ti steels, consistent with experimental observations.     

Effect of rare earth elements on the thermal cracking resistance of high speed steel rolls

The effect of rare earth elements on the thermal cracking resistance of high speed steel (HSS) rolls was investigated. Laser rapid heating was used for thermal fatigue experiments. Thermal cracks and microstructure were observed using metalloscopy and scanning electron microscopy. The results showed that thermal cracks initiated from the interface between the matrix and eutectic carbides (including M6C and M7C3 type carbides),and propagated along the interface between the two phases. MC type carbides enriched with vanadium could prevent the propagation of thermal cracks. The presence of rare earth elements decreased the quantity of big eutectic carbides,and proportionally increased spherical and rod-shaped MC type carbide content. HSS0 (0.00% RE) had approximately three times the thermal cracking density of HSS3 (0.12 wt.% RE). Rare earth elements were shown to significantly improve the microstructure and thermal cracking resistance of HSS rolls.     

合金元素对铁素体不锈钢耐应力腐蚀开裂性能的影响

通过42%沸腾氯化镁U型弯曲试验,结合扫描电子显微镜、X射线衍射分析,研究了合金元素Ni、Cu、Mo对铁素体不锈钢耐氯化物应力腐蚀开裂性能的影响规律。结果表明,Ni、Cu元素能够提高铁素体不锈钢应力腐蚀开裂的敏感性,单独添加Mo元素不会降低铁素体不锈钢耐应力腐蚀开裂的能力,但是钢中Mo、Cu元素同时存在时,应力腐蚀开裂的敏感性大大增加。钢中析出的ε-Cu在氯离子环境中形成点蚀,引起了铁素体不锈钢应力腐蚀开裂。     

Influence of alloying elements on the strain rate and temperature dependence of the flow stress of steels

After a short introduction to the theoretical background of thermally activated glide of dislocations, a constitutive model is presented, which describes the temperature and strain-rate dependence of the flow stress. The properties of this constitutive equation were estimated for several plain carbon steels in normalized conditions, for quenched and tempered low-alloy steels, as well as for some high-strength low-alloy (HSLA) steels based on the temperature dependence and strain-rate sensitivity of the flow stress at temperatures 81 K≤T≤398 K and strain rates 5 · 10⁻⁵ s⁻¹≤ε≤1 · 10⁻² s⁻¹. The constitutive equation enables the extrapolation of flow-stress data to higher strain rates (ε≲10⁺⁴ s⁻¹), which are in good agreement with the results obtained from high strain-rate deformation tests. The influence of solute-alloying elements on the thermal stress, the activation enthalpy, and the constitutive parameters will be discussed. This article is based on a presentation given in the symposium entitled “Dynamic Behavior of Materials-Part II,” held during the 1998 Fall TMS/ASM Meeting and Materials Week, October 11–15, 1998, in Rosemont, Illinois, under the auspices of the TMS Mechanical Metallurgy and the ASM Flow and Fracture Committees.     

Influence of alloying elements on the strain rate and temperature dependence of the flow stress of steels

After a short introduction to the theoretical background of thermally activated glide of dislocations, a constitutive model is presented, which describes the temperature and strain-rate dependence of the flow stress. The properties of this constitutive equation were estimated for several plain carbon steels in normalized conditions, for quenched and tempered low-alloy steels, as well as for some high-strength low-alloy (HSLA) steels based on the temperature dependence and strain-rate sensitivity of the flow stress at temperatures 81 K≤T≤398 K and strain rates 5·10⁻⁵ s⁻¹≤ε≤1·10⁻²s⁻¹. The constitutive equation enables the extrapolation of flow-stress data to higher strain rates (ε<~10 ⁺⁴s⁻¹), which are in good agreement with the results obtained from high strain-rate deformation tests. The influence of solute-alloying elements on the thermal stress, the activation enthalpy, and the constitutive parameters will be discussed. This article is based on a presentation given in the symposium entitled ‘Dynamic Behavior of Materials-Part II,” held during the 1998 Fall TMS/ASM ASM Meeting and Materials Week, October 11–15, 1998, in Rosemont, Illinois, under the auspices of the TMS Mechanical Metallurgy and the ASM Flow and Fracture Committees.     

Effect of alloying additions on secondary hardening behavior of Mo-containing steels

The effect of alloying additions on secondary hardening behavior in Fe-Mo-C steels has been investigated by means of the successive alloying additions of Cr, Co, and Ni. The Cr additions promote M₃C cementite formation. The Ni additions destabilize the cementite formation, while the Co additions retard dislocation recovery and present the necessary sites for M₂C formation which provides the secondary hardening. Professor Kwon is jointly appointed at the Center for Advanced Aerospace Materials.     

Clean steels for steam turbine rotors—their stress corrosion cracking resistance

This work presents the results of a comprehensive study concerning stress corrosion crack growth rates in steam turbine rotor steels exposed to hot water. The effects of stress intensity, temperature, and dissolved gases in the water have been investigated. Special attention has been given to the influence of impurities and alloying elements in the steel such as P, S, Mn, Si, Mo, and Ni, and to the effect of yield strength and fracture toughness on the growth rates of stress corrosion cracks. The results of this study clearly show that there exists a threshold stress intensity of about 20 MNm^−3/2 above which the invariably intergranular stress corrosion cracks grow at a constant, stress-independent velocity. This plateau stress corrosion crack growth rate isnot affected by the oxygen and carbon dioxide concentration in the water. The temperature and the yield strength of the steel have a strong influence on the growth rate of stress corrosion cracks. In contrast, there isno effect of the steel composition within the range investigated, neither of the impurity elements such as P and S, nor of the major alloying elements such as Mn, Si, Mo, and Ni. Steels with low fracture toughness due to temper embrittlement do not exhibit faster stress corrosion crack growth rates in water than nonembrittled steels. No direct relationship between intergranular temper embrittlement and intergranular stress corrosion crack growth in water can be demonstrated.     

Influence of alloying elements on the kinetics of strain-induced martensitic nucleation in low-alloy, multiphase high-strength steels

Low-alloy multiphase transformation-induced-plasticity (TRIP) steels offer excellent mechanical properties in terms of elongation and strength. This results from the complex synergy between the different phases, i.e., ferrite, bainite, and retained austenite. The precise knowledge of the austenite-to-martensite transformation kinetics is required to understand the behavior of TRIP steels in a wide array of applications. The parameters determining the stability of the metastable austenite were reviewed and investigated experimentally, with special attention paid to the effect of the chemical composition, the temperature, and the size of the austenite particles. The results show that the stability and rate of transformation of the austenite particles in TRIP steels have a pronounced composition dependence: austenite particles transform at a faster rate in CMnSi TRIP steel than in TRIP steels in which Si is fully or partially replaced by Al and P. The results clearly support the view that (1) both a high C content and a submicron size are required for the room-temperature stability of the austenite particles and (2) the effect of the chemical composition on the transformation is due to its influence on the intrinsic stacking-fault energy. In addition, the composition dependence of the Md ₃₀ temperature was derived by regression analysis of experimental data. The influence of the size of the retained austenite particles on their Ms ^σ temperature was studied by means of a thermodynamic model. Both the analysis of the transformation-kinetics data and the microstructural analysis by transmission electron microscopy revealed the very limited role of autocatalysis in the transformation.     

浅谈耐高温用铁素体型钢铁材料

耐高温材料的开发和材料高温下安全服役的实现一直是材料领域关注的热点问题。简要阐述了钢铁材料强度性能随温度变化的一般规律、材料强度在高温下的主要损失机理,并详细介绍了几种代表性的耐高温用途的铁素体型钢铁材料的合金化思想和强化机制,可为今后针对其他应用条件,开发新型耐高温钢铁材料、改善现有材料耐高温性能提供技术经验借鉴。