锰含量对铸态球墨铸铁组织及性能的影响

通过强化孕育处理,细化石墨球,增加共晶团数目,以减轻锰在铸态组织中共晶团晶界处的偏析程度,可将锰量提高至超出常规的限度.如锰高达1.16%时,铸态可得到45~70%铁素体,使δ>10%.试验表明,可将锰视为强化合金元素,得到铸态混合型基体组织,从而显著提高球铁的强度.     

固溶处理对铸态FeMnSiCrNi合金形状记忆效应和力学性能的影响

微观分析证实固溶处理消除了铸态下粗大的枝晶组织，获得了多边形的单相奥氏体，消除了铸态枝晶组织对应力诱发ε马氏体长大的阻碍，变形后获得了数量更多的应力诱发ε马氏体，提高了合金的形状记忆效应。固溶处理后的铸态FeMnSiCrNi合金断裂由铸态时的脆性断裂转变为韧性断裂，合金断后伸长率显著增大，力学性能得到很大改善。     

Mg-Al-Zn-Sm耐热镁合金的组织与力学性能

利用光学显微镜、扫描电镜和X射线衍射仪分析了铸态和固溶态AZ61和AZ61-2Sm合金组织形貌和相组成,测试了其硬度和拉伸力学性能。结果表明,向AZ61合金中添加2%Sm后,铸态组织有所细化,β-Mg17Al12相数量减少和尺寸变小,同时生成小块状的高热稳定性相Al2Sm。经固溶处理后,β-Mg17Al12相完全固溶于α-Mg基体中,只存在Al2Sm相。铸态和固溶态室温拉伸力学性能与AZ61合金相当,而铸态高温拉伸力学性能却显著提高,经固溶后得到进一步提高,与铸态室温相当。     

Zr含量对Mg-5Zn-2Al镁合金组织与性能的影响

采用光学显微镜及拉伸试验机等手段,研究了Zr含量对Mg-5Zn-2Al合金铸态和热处理后显微组织及力学性能的影响.结果表明,Zr的加入使Mg-5Zn-2Al镁合金的铸态和热处理后的晶粒得到明显的细化.在铸态及热处理条件下,合金的抗拉强度与伸长率均呈现先上升后下降的变化趋势.对于铸态合金而言,Zr含量为0.6%时,Mg-5Zn-2Al合金的晶粒最为细小,并且其抗拉强度与伸长率均达到最大值,为215 MPa和12.563%.经热处理后,合金的抗拉强度较铸态得到了显著地提高.当Zr含量为0.6%时,合金的抗拉强度达到最大,为249 MPa.     

Cu对Mg-Zn-Y合金组织和力学性能的影响

以Mg93Zn6Y1合金作为研究对象,主要研究了Cu对铸态Mg93Zn6Y1合金组织和力学性能的影响。结果表明,Cu的引入使得Mg93Zn6Y1合金的铸态组织得到显著细化。铸态Mg91.5Zn6Y1Cu1.5合金中的共晶组织[α-Mg+I-Mg3Zn6Y相+MgZnCu相(Laves相)]呈连续网状分布在枝晶和晶界间。合金的室温和高温(200℃)力学性能均得到提高。室温和高温下,铸态Mg91.5Zn6Y1Cu1.5合金的抗拉强度和伸长率分别为178 MPa、3.8%和153 MPa、10.6%,相比基本合金,分别提高了10.5%、40.7%和26.4%、49.3%。     

退火处理对AlCoCuFeNi0.2高熵合金组织与性能的影响

利用电弧熔炼技术制备得到AlCoCuFeNi_(0.2)高熵合金,研究了铸态与900℃退火态高熵合金的组织、力学性能、磁学性能之间的差异。研究发现,铸态及900℃退火态合金都是BCC+FCC+有序BCC共存结构,BCC相是主相,组织都是典型的树枝晶组织,都具有优良软磁性能。900℃退火后,BCC相向FCC相转变,合金塑性显著改善,强度和硬度有所下降,饱和磁化强度得到提高。     

T4与T6热处理对AM60-0.3Nd镁合金组织和力学性能的影响

通过对AM60-0.3Nd镁合金进行T4及T6热处理,研究了不同热处理工艺对合金组织和力学性能的影响。结果表明,AM60-0.3Nd镁合金经T4热处理后,晶粒尺寸由铸态时的90μm下降至20μm左右,铸态时沿晶界分布的网状β-Mg17 Al12相完全消失,Al-Nd中间化合物由点状、块状凝聚成球状,抗拉强度得到显著提高,达到262 MPa;经T6热处理后,晶粒尺寸由铸态时的90μm下降至30μm左右,β-Mg17Al12相重新析出而Al-Nd中间化合物的形态又转变为块状,硬度得到显著提高,达到75 HV。     

铸态锰钢的加工硬化性能

采用压缩试验方法,就合金元素对铸态锰钢的加工硬化性能的影响作了系统试验;试验结果表明,锰含量的降低,奥氏体的稳定性下降,因而铸态锰钢的加工硬化能力提高,适宜的N、Cr含量及N/Cr比使铸态锰钢的加工硬化能力显著提高,并对铸态锰钢的加工硬化机理作了重点分析探讨。     

Mg-5.0Y-3.0Nd-0.5Zr合金铸态组织和力学性能研究

对Mg-5.0Y-3.0Nd-0.5Zr镁合金进行熔铸和不同温度的均匀化退火,测试该合金的室温力学性能。并采用金相显微镜、扫描电镜等观察铸态和均匀化退火态组织。结果表明,添加Nd和Y能使镁合金的铸态组织得到细化,Nd和Y分别以Mg41Nd5和Mg24Y5化合物形式存在,均匀化退火后,试验合金抗拉强度和伸长率得到提高。其中450℃的均匀化退火效果最好,合金的抗拉强度比铸态时的提高了24.5%,伸长率提高了116.7%。     

激光重熔镍铝青铜组织、腐蚀及空蚀行为研究

镍铝青铜(NAB)是制备船用螺旋桨的重要材料。针对铸态NAB组织粗大且不均匀,影响螺旋桨使用寿命的问题,采用激光重熔(LSM)对铸态NAB表面进行改性处理。结果表明,LSM显著细化了铸态组织,LSM NAB重熔区组织为细小柱状晶,柱状晶长轴垂直于熔池界面,热影响区组织为晶粒较为粗大的等轴晶及柱状晶。LSM NAB的硬度可达285~325 HV,较铸态提高50%~70%。电化学测试结果显示,LSM NAB与铸态NAB在3.5%Na Cl溶液中的电极反应过程类似,但LSM NAB的阴极过程较铸态缓慢,因此腐蚀速率低于铸态NAB。超声振动空蚀实验结果表明,由于硬度的提高和组织的均匀化,LSM NAB空蚀失重率可降至铸态的3/5,且表面发生均匀损伤,无铸态表面较大的空蚀坑。     

NODULARIZATION OF CARBIDE IN AS-CAST WEAR-RESISTANT MANGANESE STEEL

The needle-like and network carbides in as-cast high carbon wear-resistant manganese steelswill be nodularized and dispersed,by a large majority,in austenite aider modifying treatmentwith Mg system agents.The impact toughness of the steels is significantly improved and thehardness is also increased to a certain extent.As a result,the steels can be used in as-castedstate without any heat treatment and their wear resistance can be greatly enhanced.     

Temporärer Korrosionsschutz von Spannstählen in unverpressten Hüllrohren

Temporary corrosion protection of prestressing steels in non‐injected ducts Prestressing steels may be subjected to corrosive conditions during the manufacturing process at building sites. Due to this a risk of hydrogen induced stress corrosion cracking of the steels may arise. Tests under practical conditions in a prestressed concrete beam were carried out where non‐injected ducts were treated with preheated scavenging air to prove this method being able to protect the prestressing steels against corrosion. The results yielded sufficient corrosion protection by this measure and therefore it may be an interesting alternative in comparison to corrosion protection by film forming agents which contain inhibitors.     

Das Verhalten von Großbaustählen in Meerwasser

Behaviour of construction steels in seawater The chemical composition of steel has a considerable bearing on their corrosion in seawater. Systematic laboratory studies have shown that addition of Si, Cr and Cu, but also Al and P yields considerable improvements of the sea water resistance of construction steels. Long term tests in natural seawater (in harbours, bays and straits) close to the surface and at depth up to 90 m have revealed that the seawater resistance of steels containing about 1% Si, 3% Cr and 1% Cu may be 3 to 6 times (depending on exposure conditions) the resistance of unalloyed construction steel. This behaviour may be attributed to the fact that by forming sulfates Si and Cr inhibit the growth of bacteria which would enhance corrosion, and to the fact that Si, Cr and Cu give rise to the formation of a dense rust layer which slows down the exchange phenomena between seawater and corrosion products. The use of such steels may constitute an alternative to the use of unalloyed steels with an appropriate corrosion protection system.     

Temporärer Korrosionsschutz von Spannstählen mit filmbildenden Mitteln

Temporary corrosion protection of prestressing steels with film forming coatings Prestressing steels may be subjected to corrosive conditions during the manufacturing process at building sites. Due to this a risk of hydrogen induced stress corrosion cracking of the steels may arise. Electrochemical investigations and constant load tests have been carried out to show the suitability of different film forming coatings to be applied as temporary corrosion protection measures. The results indicated the applicability of two agents involved in the investigations without any risk for post tensioning purposes.     

The interphase precipitation reaction in HSLA steels

An in-depth study of the interphase precipitation reaction in model vanadium steels has shown that the reaction may not just be confined to HSLA steels, but may be part of a general class of banded microstructures which are common to both eutectoid and eutectic systems. A new mass transport theory has been developed in which the interphase precipitation reaction in Fe-C-V steels is treated as a generalized type of cooperative growth. In addition to predicting the spacings of sheets of interphase precipitates and the precipitate sizes in steels, this theory is providing new insights into the origin of banded structures occurring in eutectic systems at solid-liquid interface boundary velocities faster than those required for coupled growth, but slower than those required to produce the extended metastable solid solution.     

Corrosion resistance of low‐nickel duplex stainless steel rebars

The use of stainless steel bars in reinforced concrete structures may be an effective method to prevent corrosion in aggressive environments where high amounts of chlorides may penetrate in the concrete cover. For an estimation of the service life of structures where stainless steel bars are used, the chloride threshold for these rebars should be defined, and the influence of chemical composition and metallurgical factors that may affect the corrosion resistance (strengthening, welding, etc.) should be assessed. To reduce the cost of stainless steel reinforcement, duplex stainless steels with low nickel content have been recently proposed as an alternative to traditional austenitic steels, even though, few results are available regarding their corrosion performance in chloride contaminated concrete. This paper deals with the corrosion resistance of low‐nickel duplex stainless steel rebars (1.4362 and 1.4162) as a function of the chloride content. Comparison is made with traditional austenitic steels. An attempt to define a chloride threshold for the different stainless steels is made by comparing the results of several test procedures both in concrete and in solution.     

THE DISSOLUTION AND PRECIPITATION OF BORON CONSTITUENT AND THEIR EFFECTS ON THE PROPERTIES OF 40MnB STEEL

采用定量相分析,硼自射线照象等技术,对不同含硼量的中碳钢40 MnB,在高温加热及冷却过程中,M_(23)(C,B)_6的溶解、析出行为及对钢性能的影响进行了研究。发现析出的M_(23)(C,B)_6的数量及粒度随着钢中的含硼量增加及冷却速度的减小而增加;含硼量不同的钢具有一个相同的临界冷却速度,在这一冷速下,M_(23)(C,B)_6,的析出量达到饱和。M_(23)(C,B)_6的溶解、析出对淬透性和韧性有很大影响。含硼量较低的钢,在相同条件下M_(23)(C,B)_6的析出量较小,且易于溶解,故钢具有较好的综合性能,并对热履历的变化不敏感。提出了一些稳定钢性能的建议。     

Selektive Korrosion an Verbindungsschweißen von Stählen

Selective corrosion at welded assemblies of steels The paper deals with the possible selective corrosion phenomena at the most important types of weld assemblies of steels, viz. those of unalloyed ferritic ship building steels, austenitic manganesechromium steals, aluminium-killed boiler steels an well as chemically resistant ferritic and austenitic chrom-nickel steels. With unalloyed ship building steels, a strong corrosion element is liable to occur between not fully descaled plates and scaleless welding material, where the latter is particularly liable to be attacked. But even where scalefree plates are welded, a local element may be set up, depending on the killing intensity and on the filler metals, between plate and welding material in such a way that, again, the welding material is liable to be dissolved first. In the case of austenitic manganese-chromium steels, exposed to sea water, intercrystalline corrosion takes place at a certain distance from the weld as a result of chrome-carbide segregation. In the case of welded assemblies of aluminium-killed steels, intercrystalline fissuration is particularly liable to occure in a more or less marked decarbonised zone at the transition. With ferritic chromium steals and austenitic chrom-nickel steels, the welds are decisively influenced by the segregation of chrome-carbides at the grain boundaries which results in a proneness to intercrystalline grain decomposition. Measures are discussed by which the segregation of chrom-carbides during welding can be avoided. Finally, mention is made of the effect of delta-ferrite on the corrosion behaviour of austenitic welding material.     

Resistance to Oxidation at Elevated Temperatures of a Number of Alloy Steels

Abstract

A wide range of steels, extending from a plain carbon steel to high chromium-nickel, austenitic types and some nickel-based alloys, have been subjected to a cyclic oxidation test in natural gas combustion products at various temperatures. Resistance to oxidation can be expressed in terms of a breakdown temperature which provides a convenient parameter by means of which the behaviour of steels and alloys may be compared. On this basis, the beneficial effects of additions of chromium of up to 30% are confirmed, as are additions of silicon and/or aluminium to chromium steels. Cobalt, copper, molybdenum, vanadium, tungsten, niobium, titanium and nitrogen have comparatively little effect. Manganese appears to be detrimental when added to chromium steels and carbon can be in some circumstances. Nickel can enhance oxidation resistance in some circumstances but is detrimental in others. The presence of sulphur in free-machining, stainless steels appears to counteract the effect of a higher-thannormal manganese content.     

Pitting and sulphide inclusions in steel

Pits are initiated at sulphide inclusions (usually MnS) in both carbon steels and stainless steels. In carbon steels, the attack starts in the matrix close to the sulphide inclusion which is more noble than the matrix. Some sulphides, termed “active”, initiate attack more easily than others, termed “inactive”. Active and inactive sulphides in carbon steels may be distinguished by a so-called micro-corrosion test (MCT). In stainless steels, the attack starts in the sulphide inclusion proper, which is less noble than the surrounding oxide film, and then spreads to the active metal below the sulphide inclusions. The propagation of a pit is, in principle, the same in both types of steel and depends upon the formation of a concentration cell in which the pit solution has a higher salt content, a higher acid content and a lower oxygen content than the surrounding bulk of the solution. The detrimental effect of S upon the corrosion properties of steels is counteracted by metals which form sulphides less soluble than FeS. These sparingly soluble sulphides may either be present in the steel (examples: TiS, CrS and VS) or form during the corrosion process (examples: the sulphides of W, Mo, Ni, Co, Zn, Cd, Sn, Pb, Cu, Ag, Bi and Hg). Of the latter metals, Cu is of particular importance.