X90级管线钢应变时效行为

针对高级管线钢应变时效问题,对X90级直缝埋弧焊管管体不同预应变及时效前后的组织和力学性能进行了对比,研究了应变时效对X90级管线钢组织和力学性能的影响。结果表明：不同应变时效前后X90级管线钢的显微组织和冲击韧性变化不明显;应变时效后拉伸曲线由拱顶型连续曲线转变为吕德斯型屈服曲线,屈服强度增加,屈强比升高;预应变量越大,屈服强度和屈强比升高越显著,且横向性能受到预应变量的影响比纵向要大,而200~250 ℃温度区间时效对屈服强度和屈强比影响较小。     

铸造低合金钢的生产

通过对低合金钢中合金元素作用的介绍,针对低合金钢铸造性能特点,提出低合金钢铸造过程应注意的事项,尤其是要加强熔炼过程及铸件在后道工序热割处理过程的控制,是有效提高铸件质量,降低生产成本,提高市场竞争力的有力措施.     

Microstructural characterization and surface properties of zinc phosphated medium carbon low alloy steel

The present study concerns an in-depth investigation of the influence of process parameters on zinc phosphating of medium carbon steel to have an understanding of nucleation and growth mechanism and the microstructures developed thereafter. Furthermore, the wear and corrosion behavior of phosphated steel were evaluated in details. Phosphating was carried out in zinc phosphate bath (6–8% ZnPO₄) using 0.43 wt.% Fe as catalyst at 90 °C with variable time ranging from 60 s to 1800 s followed by water rinsing and oil sealing. The microstructural evolution with time was recorded to understand the nucleation and growth phenomena. The morphology of coating was both plate and needle shaped. The microhardness of the coated layer is significantly lower than that of as-received steel. Fretting wear behavior against hardened steel ball showed that phosphating reduced the wear resistance which was possibly attributed to the presence of phosphate needles causing an increased coefficient of friction and the reduced hardness of the phosphate layer. Corrosion potential of the phosphated steel shifted towards noble direction as compared to the as-received one. The study of the corrosion rate also shows that the rate is considerably reduced by phosphating. Pitting corrosion resistance was also found to be increased (in terms of increased critical potential for pit formation) due to phosphating as compared to as-received steel.     

Solidification cracking in low alloy steel welds

Abstract

The high solidification cracking susceptibility of low C steel weld metals was investigated using pure Fe model alloys containing 0–0·23%C, 0–5%Ni and 0–0·0144%B. In addition, a few Fe–C–Ni ternary alloys were also tested. Solidification cracking susceptibility was tested using longitudinal varestraint and transvarestraint tests. Cracking was evaluated using crack length and brittleness temperature range criteria. The Fe–C alloys showed high cracking tendency in two regimes, the first in the ultralow carbon range of 0·03–0·05%C and the second in a narrow band close to 0·1%C. The cracking was much more than that attributable to solute segregation. In Fe–Ni and Fe–B alloys, cracking was a function of alloy content. Solidification cracking due to C and Ni was higher in the ferritic mode of solidification compared to the austenitic, unlike in stainless steels, where the ferritic mode provides high resistance to cracking. In Fe-C-Ni ternary alloys, cracking could be better related to composition in terms of a variable coefficient for C in the Ni equivalent. In the vicinity of 0·1%C, cracking was attributable to shrinkage due to solid state transformation from δ to γ in the brittle temperature range, and is similar to that occurring during continuous casting of steel. However, this factor did not appear to play a role in cracking in the ultralow C range of 0·03–0·05%C.     

Electroslag cladding of low alloy steel with stainless steel

Abstract

Cladding of a low alloy steel slab with stainless steel was carried out using a modified electroslag remelting technique. It is shown that the thickness of the cladding that can be achieved via electroslag remelting is dependent on the fill ratio used. The effect of power input on the joint profile obtained is reported. A combination of low fill ratio and relatively low power input is essential to minimise penetration of the base slab by the liquid metal. A satisfactory joint profile and defect free joint can be obtained via the optimisation of these process parameters. The clad product was successfully forged and rolled, which indicates satisfactory strength of the clad joint.     

Ultrafine grain refinement in a low alloy steel

The phenomenon of grain refinement was studied in a steel containing 0.15% C, 0.32% Si, 1.4% Mn, and 0.43% V. Initial austenite grain size was found to be 50 μm, determined by quenching the specimen in an iced brine solution from 1150 °C. Transformational grain refinement (TGR) was applied to give a reasonable refinement in the grain size. A rolling reduction of about 67% was given to specimens at 900 °C, which was followed by air cooling. Cold rolling and recrystallization of these specimens gave refinement of grains down to 1 μm size was obtained. The electron backscattered diffraction (EBSD) technique was used to determine low- and high-angle grain boundaries that are effectively used to determine the substructure contribution at various stages of recrystallization.     

低碳钢时效现象剖析

为了解决时效影响冷轧产品性能这一问题,从时效条件,时效影响因素,时效引起的产品性能变化等方面进行了分析,并结合宝钢生产实际,提出了解决时效问题的一些方法。     

一种低碳低合金钢的纳米压痕表征

对具有两种不同组织状态的一种低碳低合金钢进行了纳米压痕表征．结果表明,在双相组织试样中,马氏体的硬度高于铁索体的70％以上．在纳米压痕实验过程中,由于马氏体相的尺寸较小并被软的铁素体基体所包围,当压痕深度超过40nm时,纳米压痕硬度呈现出明显的基底效应．由于在铁索体一奥氏体两相区加工过程中发生C元素向奥氏体的分配,双相组织试样中的马氏体中富集了数倍于钢的名义含量的C元素．结果导致双相组织试样中马氏体的平均纳米压痕硬度比同一钢的全马氏体组织试样高出30％以上．此外,还讨论了C的富集分配对马氏体Poisson比和Young’s模量的可能影响．     

ZG35CrMo低合金强度钢的焊接

分析了35CrMo铸钢的焊接性能以及焊接参数,如焊接材料、预热温度和焊后热处理方案等的选择。采用合理的焊接工艺,可使焊缝质量达到设计要求。     

低合金钢焊接工艺优化系统

在焊接领域内多方位的开发和研制计算机辅助焊接系统具有重大的技术和经济意义。本文采用Ｃ＋＋语言自行设计了低合金钢焊接工艺优化系统，系统涉及到了３种焊接方法和１２种低合金钢母材以及多种焊接材料。采用Ｃ－ＷＯＲＴＨＹ作为菜单生成工具，使系统具有由鼠标和热键自由控制的彩色窗口和菜单。     

Effect of aging time at low aging temperatures on the corrosion of aluminum alloy 6061

The effect of heat treatment in the underaged, peak aged and overaged conditions in the temperature range 140–225 °C on the corrosion characteristics of Al–Mg–Si–Cu alloy (AA6061) was investigated. Potentiodynamic polarization testing in neutral NaCl solution and immersion testing in acidified NaCl solution were applied to investigate the corrosion behavior of the alloy. The results showed significant dependence of the dominant corrosion form and the electrochemical corrosion parameters on the aging conditions. Maximum changes were noted for the peak aged condition. The results were discussed in terms of changes in precipitate type, size, volume fraction and distribution.     

Model for inclusion formation in low alloy steel welds

Abstract

Oxide inclusion formation in low alloy steel welds is described with a model as a function of weld metal composition and process parameters. The model was developed by coupling thermodynamic and kinetic considerations. Thermodynamic calculations considered the effect of the alloying elements and kinetic equations allowed, describing oxide formation during weld cooling. The model showed that weld cooling rate influences the inclusion characteristics and therefore must be taken into consideration. This inclusion model is capable of predicting the composition, size, number density, and oxidation sequence of inclusions and was verified with published data. The inclusion model was coupled with numerical heat transfer and fluid flow models to extend the model to a wide range of welding process conditions.     

低钨含量W-Ni-Fe三元合金的预应变时效

研究了钨含量为36％，Ni与Fe质量比为7／3和9／1的两种W—Ni—Fe三元合金的预应变时效硬度变化规律，用X射线衍射鉴定了时效后两种合金的物相组成，并用透射电镜观察其微观结构。结果表明：Ni与Fe质量比为7／3的W—Ni-Fe三元合金在800℃下进行预应变时效时，硬度随时间增加而单调降低；相同条件下Ni与Fe质量比为9／1的W—Ni—Fe三元合金时效初期硬度下降，但随时间延长硬度又逐步提高。X射线衍射物相鉴定和透射电子显微分析发现：Ni与Fe质量比为7／3的合金在预应变时效过程中没有明显沉淀析出物，其时效硬度下降是固溶度降低、残余应力消除以及回复与再结晶的结果；而Ni与Fe质量比为9／1的合金经预应变时效后析出了细小弥散的β相，其硬度变化存在两种机制，一种是固溶度降低、残余应力消除和回复与再结晶引起软化，另一种是细小A相沉淀析出导致弥散强化。     

Phase composition and crack resistance of alloy boride layers on steel

Conclusions  

Redistribution of alloy elements in aging of austenitic chrome-manganese steel containing nitrogen

Conclusions In interrupted decomposition of the austenite of chrome-manganese steel containing nitrogen in the 600–900°C range the alloy element content in the nitride phase formed changes. The quantity of chromium increases while that of iron decreases significantly. The manganese content in the nitride is low and remains approximately constant.The residual austenite in the grains which have undergone interrupted decomposition is gradually depleted of chromium and nitrogen.The growth of pearlitelike colonies consisting of transformed austenite and type M₂N nitride is controlled simultaneously by the mechanisms of grain-boundary and three-dimensional diffusion.Institute of Metallurgy and Metals Technology, Sofiya, Peoples Republic of Bulgaria. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 11, pp. 60–61, November, 1988.