奥氏体化温度及冷却方式对20Mn2SiVB钢组织及性能的影响

通过各种试验手段,研究了20Mn2SiVB钢不同奥氏体化温度及不同冷却方式处理后其显微组织及其强度和塑性的变化,确定了最佳的热处理工艺。结果表明:900℃奥氏体化后风冷时钢的强塑性最好;在强塑性最佳时的微观组织是铁素体+粒状贝氏体。     

Design criteria for high-temperature steels strengthened with vanadium nitride

Fe-8-12Cr ferritomartensitic steels are widely used in the power generation, petrochemical and nuclear industries where they are subject to high operating temperatures and stresses. Resistance to creep deformation is therefore a critical materials property. One method of providing creep resistance is to precipitate a fine homogeneous distribution of vanadium nitride (VN) particles in the matrix. Maximizing this precipitation hardening effect requires a high nitrogen content, but this could cause gas bubble formation during conventional fabrication processes. It is therefore necessary to determine how much N can be added without encountering such problems. Phase stability calculations, using Thermo-Calc, were carried out to find high-N compositions to optimize the fraction of VN and the fabrication route for obtaining fine particles. Several experimental compositions, including nine high-nitrogen alloys, were fabricated as ingots; out of these, two exhibited porosity Thermo-Calc predicts that, in all of the high-nitrogen alloys, nitrogen gas is a stable phase around the solidus temperature. It is evident that porosity cannot simply be predicted from the presence of the gas phase on the equilibrium diagram. However, detailed analysis of the equilibrium phases predicted in these alloys, including their variation with composition, allowed a porosity criterion to be obtained. This criterion links porosity formation to the nature of the liquid-to-solid transformation. Further calculations were carried out to predict the dependence of gas phase evolution on both composition and pressure. Thermodynamic calculations are a valuable tool for the design of these industrially important alloys. Input from experimental data has enabled the refinement of the initial design criteria such that it should now be possible to propose compositions with high VN hardening but without the risk of porosity. This paper was presented at the International Symposium on User Aspects of Phase Diagrams, Materials Solutions Conference and Exposition. Columbus, Ohio, 18–20 October, 2004.     

Relationship between yield ratio and the material constants of the Swift equation

The relationship between the yield ratio and the material constants,b andN, of the Swift equation for hotrolled low carbon steels has been established. The yield ratio calculated by using the Swift equation agrees well with an experimentally obtained yield ratio. It was found that the yield ratio decreases with an increasing value ofN or with a decreasing value ofb. It was also found, however, that high yield strength is associated with small values of bothb andN. Therefore, to obtain both high yield strength and low yield ratio, a detailed microstructural control is needed to determine the optimum values ofb andN.     

Mechanical Properties of Reinforcing Steel and Fatigue Behavior in Corrosive Environment

Corrosion of reinforcing steel has a great impact on the mass reduction and high- and low-cycle fatigue. An experimental study showed that the mass loss, the fatigue limit and the life expectancy were reduced by approximately 1.50-3.00%, 20-40%, and 55-75%, respectively, according to the level of corrosion. Low-cycle strain controlled fatigue testing under ±1% and ±2.5% constant amplitude strain, indicated that the corroded steel bars exhibit gradual reduction in available energy, number of cycles to failure and the load-bearing ability. Formation of pits and notches took place on the corroded steel surface and stress concentration points were developed which are highly localized at imperfections and especially at the rib bases. The fatigue limit was reduced considerably since the existence of ribs and the formation of pits and notches combined with the mass loss led to reduction of the exterior hard layer of martensite and drastic drop in the energy density of the corroded specimens. Antiseismic design that does not take into account the maximum and cumulative plastic deformation demands and the strain history that a structure will suffer under severe ground motion could lead to unpredictable performance.     

Pitting corrosion behaviour of PM austenitic stainless steels sintered in nitrogen-hydrogen atmosphere

PM 304L and 316L stainless steel have been compacted at 400, 600 and 800 MPa and sintered in vacuum and in nitrogen-hydrogen atmosphere. Postsintered heat treatments (annealing solution and ageing at 375, 675 and 875 °C) have been applied. Pitting corrosion resistance has been studied using anodic polarization measurements and the ferric chloride test. Anodic polarization curves reveal that densities and atmospheres are relevant on anodic behaviour. Pitting resistance is higher for PM 316L and for higher densities and vacuum as sintered atmosphere. Ageing heat treatments at medium and high temperatures are detrimental to passivity although susceptibility to pitting corrosion barely changes. But heat treatments at 375 °C even show certain improvement in pitting corrosion resistance. The results were correlated to the presence of precipitates and mainly to the lamellar constituent which appears in some samples sintered in nitrogen-hydrogen atmosphere. The role of nitrogen on the samples sintered under nitrogen-hydrogen atmosphere and its relation to the microstructural features was described.     

不锈钢板镜面抛光技术

介绍一种适用于不锈钢抛光用的 ZH-1抛光乳化液,该液具有抛光、润滑、防锈和冷却等多种功能;讨论抛光工艺的操作条件,采用本技术用SUS321板抛制镜面板时,抛光速度可提高24倍,抛光质量可达 R_n<0.04μm。     

Stress corrosion behavior of pipeline steel(X52)welded joint

The resistance of pipeline steel joint welded by submerged arc welding to stress corrosion cracking (SCC) at its different regions in boiling mixed nitrate solution and in H_2S saturated solution at room temperature is examined by the constant-load tension method. The result shows that when tested in nitrate, the weld metal may be the weakest link of the joint if the welding material doesn't match well. The resistance to SCC of the joint in H_2S is very low, especially at the bond and coarse grain zone and is closely dependent on the metallurgical quality of base metal.     

304不锈钢在室温HCl+NaCl溶液中的应力腐蚀机理

304不锈钢在室温HCl+NaCl溶液中可发生活化态下的应力腐蚀开裂(SCC).XPS成分分析表明:在酸性氯化物溶液中,试样表面形成了一层富铬的吸附产物膜,应力腐蚀裂纹的形核与这层膜的形成和Cl一局部富集有关.     

Si对低碳贝氏体钢组织和性能的影响

Si在一定含量范围内,使低碳贝氏体钢中粒状贝氏体相对量、M—A岛体积分数、残余奥氏体量及其稳定性增加,从而提高钢的强度和韧性。在v_t=156℃/min冷速下,Si为1.62%时,钢的强韧性出现极大值;v_t=7.9和0.9℃/min时,Si>1.99%后,大量共析铁素体的析出降低了钢的强度和韧性,Si为1.99%时,强韧性最高,最佳Si含量为1.62—1.99%。     

Dry friction and wear characteristics of MoSi2 against ahoy steels

The dry friction and wear characteristics of three kinds of friction couples under different loads, MoSi2/45 tempered steel, MoSi2/45 quenched steel, and MoSi2/CrWMn steel, were investigated by using a friction and wear tester. SEM and X-ray diffraction were employed to analyze the microphotograph of the worn surface and the phase of worn pieces in order to reveal the wear mechanisms of MoSi2 material. The results show that MoSi2/CrWMn steel friction pair has good dry friction and wear properties under the load of 80 N, where the friction coefficient is 0.255 and the wear rate of MoSi2 is only 14.72 mg.km-1. But under the load of 150 N, it is MoSi2/45 tempered steel friction pair that has good tribological properties,MoSi2 under low loads is brittle fracture. With the increase of load, the main wear mechanism of MoSi2 against 45 quenched steel or CrWMn steel is adhesive wear. However, the wear mechanism of MoSi2 against 45 tempered steel is changed from oxidation-fatigue wear to adhesive wear.