Low temperature brazing of components of radioelectronic equipment with a focused light beam

The objective of this study was an evaluation of the influence of the type of coating on the working life of electrodes when spot welding interstitial free steels with heat immersion coatings of the Zn pure (GI) and Zn–Fe alloy (GA) types. To do so, the electrode life was determined and the behaviour of the Zn of the coating evaluated on the contact plate/electrode surface during its working life, using ESM/EDS. As a result, it was confirmed that the working life of electrodes when welding GA steel was much higher than with GI steel. The electrode life was shown to be dependent on the fusion point of the coating. With the GI steel, part of the zinc layer moves to the edge of the electrode/plate contact at the start of the working life of the electrode. With the GA steel, Zn displacement was not confirmed throughout the whole working life of the electrode, due to the high-fusion point of the coating.     

Combined pulsed effect of shielding gases and welding current in consumable electrode welding

Methods of improving the process of consumable electrode welding using different types of metal transfer in welding of steels by the combined pulsed effect of shielding gases and welding current are described. Special features of the microstructure of the metal of the welded joints in low-alloy steels are discussed.     

新型多功能全位置立向下焊条的开发

开发了一种新型全位置立向下焊条,采用有约束的配方均匀设计,对焊条配方进行了优化,采用GX-Ⅲ高温物性测试仪对焊条药皮的熔化特性进行了研究.结果表明,开发的全位置立向下焊条具有优良的工艺性能,焊缝成形美观,易脱渣,电弧稳定,飞溅率小等;该焊条具有较高的抗拉强度、屈服强度和较高的低温冲击韧性,能广泛应用于重要结构焊接.通过对焊接接头断口、金相组织以及焊缝成分和焊接接头横截面硬度分析表明了焊缝具有较高力学性能.形成了一整套开发全位置立向下焊条的新方法,该方法具有开发周期短、成本低、质量高的特点.     

Electrode degradation mechanism during resistance spot welding of zinc coated steel using Cu-TiB2 electrodes

1 INTRODUCTIONResistance spot welding(RSW) is the mostcommonly used method for joining steel sheets inthe automotive industry . In RSW, a weld isformed between two workpieces through meltingand coalescence of a small volume of the material atthe faying surfaces due to the resistance heatcaused by the passage of electric current when theworkpieces are held together under a large elec-trode force[1 ,2]. Over the past decade ,the require-ment of i mproved corrosion resistance in automo-bil…     

HSLA-100 steels: Influence of aging heat treatment on microstructure and properties

The structural steels used in critical construction applications have traditionally been heat-treated low-alloy steels. These normalized and/or quenched and tempered steels derive strength from their carbon contents. Carbon is a very efficient and cost-effective element for increasing strength in ferrite-pearlite or tempered martensitic structures, but it is associated with poor notch toughness. Furthermore, it is well known that both the overall weldability and weldment toughness are inversely related to the carbon equivalent values, especially at high carbon contents. The stringent control needed for the welding of these traditional steels is one of the major causes of high fabrication costs. In order to reduce fabrication cost while simultaneously improving the quality of structural steels, a new family of high-strength low-alloy steels with copper additions (HSLA-100) has been developed. The alloy design philosophy of the new steels includes a reduction in the carbon content, which improves toughness and weldability.     

火焰矫正对屈服强度900 MPa级低合金高强钢焊接接头组织与性能的影响

对屈服强度900 MPa级的高强度钢焊接接头进行加热温度为700℃的模拟火焰矫正,发现其焊接热影响过热区出现了大量的M-A组元,焊接接头强度基本不变,但焊接热影响区低温冲击韧性下降45.3%。结果表明:屈服强度900 MPa级高强钢高强钢宜采用机械矫正,若采用火焰矫正,需控制好加热温度。     

Arc welding technology for dissimilar joints

The most widely used metal underpinning modern industry is steel (carbon steel). Low-alloy steel designed to increase the strength and heat resistance of basic carbon steel and stainless steel to offer improved corrosion resistance and oxidation resistance are extensively used in the manufacture of thermal and nuclear power plants, chemical plants, etc. An extremely important and unavoidable practical requirement in modern steel construction technology is to be able to perform dissimilar welding of stainless steel to carbon and low-alloy steels (welding of dissimilar metals). This article profiles the basic principles and noteworthy features of dissimilar welding of stainless steel to carbon and low-alloy steels.     

Strength of straight‐seam and spiral‐seam pipes in transmission gas and oil pipelines

It is shown that it is important to improve further the technology for welding oil and gas equipment produced from materials with high weldability (low-alloy steels) and working in the conditions of steep temperature gradients in the environment. The results of microstructural analysis, the tests of the impact bend strength of the specimens at different temperatures, and also the data obtained in the determination of the level of residual stresses of the third kind are used to show the possibility of increasing the parameters of the reliability of the welded oil and gas equipment produced from low-alloy steels.     

Methodological fundamentals of the evaluation of the weldability of structural materials using oil and gas pipes as an example

A method for evaluating weldability is proposed, and processes of welding petrochemical equipment with a wall thickness of 20–200 mm and pipelines produced from steels of almost all strength grades, starting with carbon and low-alloy steels, hot-rolled and normalized steels, steels strengthened by heat treatment and advanced low-carbon high-strength steels of the K65–K75 type, are outlined.     

Boride coatings on steel using shielded metal arc welding electrode: Microstructure and hardness

In the present study, shielded metal arc welding electrodes were produced for making boride coatings and low-carbon steel plates were surfaced with single-pass bead on-plate welds. The effects of the boron content in the electrode shield on the microstructure and hardness of the coatings were investigated. After deposition, microstructural analyses including metallographic examination, wavelength-dispersive X-ray (WDX), X-ray and microhardness measurements of the coatings were evaluated. From the results, it was seen that different boron contents formed primary and eutectic Fe₂B, and consequently had an effect on the hardness of the coating. As the amount of boron which was transferred from the electrode shield to the coating increased, the microstructure of the coating changed from the eutectic structure (α-Fe + F₂B) to primary Fe₂B with the eutectic of Fe₂B plus martensite, and the hardness increased. The present study has therefore shown that the shielded metal arc welding electrodes produced here for the first time can be used effectively and economically to produce boride coatings on SAE 1020 steel.     

Surface modification of resistance welding electrodes by electro-spark deposited composite coatings: Part II. Metallurgical behavior during welding

Electrodes with monolithic TiC_P/Ni coatings and multi-layer Ni/(TiC_P/Ni)/Ni coatings were used to resistance spot weld Zn-coated sheet steel to investigate metallurgical behaviour of the coatings during welding. Scanning electron microscopy, energy-dispersive X-ray analysis and X-ray diffraction were employed to characterize the microstructure of coatings, reactions of electrodes with Zn-coating and alloy layer formation. The results showed that molten Zn penetrated TiC_P/Ni coatings via the cracks that were present within as-coated TiC_P/Ni coating, starting from the first weld. Additional cracks continually formed in the coating during welding due to action of the welding force on the low toughness coating, resulting in formation of a granular loose overlay at the outer surface which were easily detached and stuck onto the work sheet. On the contrary, cracks could be rarely found within Ni/(TiC_P/Ni)/Ni coating until 100 welds or more were made, and much fewer cracks formed up to 400 welds, compared to the TiC_P/Ni coating. With Ni/(TiC_P/Ni)/Ni coating on the electrode surface, alloying between copper alloy and molten Zn as well as pitting (erosion) of the electrode tips were remarkably reduced, and hence, a slower growth rate of tip diameter was observed.     

Surface modified long-life electrode for resistance spot welding of Zn-coated steel

In order to increase the life of conventional copper electrodes in resistance spot welding of Zn-coated sheet steel, a multi-layer Ni/(TiC_P/Ni)/Ni composite coating was deposited onto the copper electrode top surface by electro-spark deposition. Scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction and micro-hardness tests were employed to characterize the microstructure and property of the coating. The results showed that the copper electrodes with a dense Ni/(TiC_P/Ni)/Ni coating slightly increased the resistance of the weld system and hence the welding current could be reduced to produce a weld with the same button size as that made by uncoated electrodes at a high welding current. The coating was gradually cracked during welding under the action of welding force, forming Ni/(TiC_P/Ni)/Ni composite islands which were strongly adherent to and further, punched into copper substrate. The coating could significantly reduce the alloying between copper electrode substrate and molten Zn. As a result, coated electrode showed a much longer life than an uncoated electrode even though the welding current for coated electrode was lower than that for uncoated one.     

Special features of the formation of welded joints in vertical laser-arc welding of low-alloy steels

ABSTRACT

Investigations were carried out into the special features of the technology of vertical laser-arc welding of large structures made of high-strength and low-alloy steels with a variable welding gap and a large root face.

The parameters of the conditions of vertical laser-arc welding of root passes in the low-alloy steel 30–40 mm thick with a root face of 10 mm (welding speed, the amplitude and frequency of transverse oscillations, the intensity of welding current, arc voltage, laser radiation power) resulting in the formation of high-quality welded joints are determined. The experimental results show that the laser radiation power, required for producing continuous penetration of the root face, depends on the thickness of the parent metal: for the metal thickness of 14–30 mm the sufficient laser radiation power is 3.8 kW, for a thickness of 40 mm it is no less than 4.6 kW to penetrate a depth of 5 mm.

The welded joints have a fine-dispersed acicular structure of the martensitic – bainitic type. The experimental results were used to develop a technology of welding of low-alloy steels of different thickness using robotic equipment.     

Impact of liquid metal embrittlement cracks on resistance spot weld static strength

ABSTRACT

Advanced high strength steels used in automotive structural components are commonly protected using zinc coatings. However, the steel/zinc system creates the potential for liquid metal embrittlement (LME) during welding. Although LME cracks are known to form, limited research has found any detrimental impact of LME cracks on weld strength. In this work, a comparison of zinc coated and uncoated advanced high strength steel joints showed LME decreased strength in welds from transformation induced plasticity type microstructures and an 1100?MPa ultimate tensile strength by 43.6%. LME cracks were observed to propagate until final fracture. However, only cracks located in the periphery of the weld area were found contribute to a loss in strength.     

Study of hyper-interfacial bonding of ultrafine-grained steels

To obtain so-called super-steels providing a good combination of high strength and high toughness, efforts are being made to develop ultrafine-grained steels involving intense grain size refinement with retention of a mild steel-equivalent low-alloy composition in order to lessen their environmental impact and reduce total life cycle costs.^1-5 Within this context, it is imperative to develop suitable welding and joining technologies for structural applications of ultrafine-grained steels; a number of previous studies have addressed their welding characteristics.^6-8 Developed ultrafine-grained steels, however, face a number of important problems such as grain coarsening, HAZ softening and microstructural changes due to the thermal effect of the welding process itself. Such microstructural changes are predicted to exert a significant effect on joint characteristics, particularly deterioration of welded joint performance in ultrafinegrained steels as steels subjected to a high degree of grain size control. Microstructural changes in the joints of ultrafine-grained steels, however, have not yet been satisfactorily investigated.     

Calculating the static cracking resistance of the fusion zone of 15Kh2NMFA steel and austenitic deposits

Abstract

In this paper the method and apparatus used to measure the arc force produced during welding with covered electrodes were studied and developed. The factor which caused the main error of measurement was revealed, and the experimental results were corrected. The arc force of typical electrodes under different welding conditions was measured and the factors affecting the force were also investigated. Furthermore, the effects of such components of the electrode coatings, as marble, feldspar and fluorspar, on the arc force were studied, and the origin of the arc force in MMA welding with covered electrodes was preliminarily analysed.     

TiB_2-ZrB_2/Ni涂层电极点焊镀锌钢板失效过程分析

目的了解TiB_2-ZrB_2/Ni涂层电极点焊镀锌钢板时的失效机理。方法通过扫描电镜(SEM)、X射线衍射仪(XRD)、显微硬度测试等表征方法,研究TiB_2-ZrB_2/Ni涂层点焊电极点焊镀锌钢板时表面结构、物相及性能的变化。结果 TiB_2-ZrB_2/Ni涂层电极对提高点焊电极寿命有很大帮助,点焊电极寿命可提高5倍左右。涂层使点焊电极表面的硬度得以明显提高,减缓了点焊电极端部塑性变形的进程。ZrB_2-TiB_2/Ni涂层在一定程度上减缓了钢板镀层与点焊电极产生合金化反应的进程。结论 ZrB_2-TiB_2/Ni涂层电极由于具有一定的塑性,点焊过程中涂层不会出现完全脱落现象。涂层作用一直持续至电极失效,电极失效的形式主要表现为塑性变形。     

Advances in Replacements for Cadmium Plating in Aerospace Applications

This paper examines some of the problems associated with the replacement of cadmium plating for the protection of aircraft components and fasteners manufactured from steel. It reviews the range of coatings which are available commercially and are currently being considered as alternatives to cadmium plating. Results of research being undertaken into the corrosion behaviour and galvanic compatibility of electrodeposited zinc alloy coatings and aluminium-magnesium alloy coatings are presented. Other aspects of coating performance are also considered including frictional properties, effects of coatings on fatigue strength, hydrogen embrittlement of steels and the repair of damaged coatings. It is concluded that although the corrosion performance of cadmium plating may be achieved with several coating systems, no one coating is likely to be acceptable as a replacement for cadmium for all aerospace applications.     

Characteristics and Verification of a Low Hydrogen Embrittling Zinc-Nickel Electroplate,Developed for Corrosion Protection of High Strength Steels

A coating process is outlined that gives low hydrogen embrittling zinc-nickel binary alloy electroplate for sacrificial corrosion protection of high strength steels, and the physical properties of the coatings produced are presented. The highly corrosion resistant zinc-nickel binary alloy coatings produced by the new process comply fully with the ASTM test requirements for control of hydrogen embrittlement. They are an alternative to the cadmium coatings currently employed for the corrosion protection of high strength steels. The results of hydrogen embrittlement tests and of structural analyses are discussed in light of the structure of the zinc-nickel coating, and of its efficiency in allowing labile hydrogen to diffuse out of the coated high strength steels.     

Method for the evaluation of the low-cycle fatigue strength of welded joints using the J-integral energy criterion

Summary

The purpose of this study was to investigate effects of aluminium in the Zn coating on electrode life in welding galvanized steel sheet. Three hot‐dip galvanized and one electro‐galvanized steel sheet types were prepared for this study. Aluminium content in the coatings varied within the range 0.26–0.87 mass% for the three types of hot‐dip galvanized sheet.

The approach used here included EDX, AEX analysis of the coating layers, electrode life tests and EPMA analysis of electrodes after 900 spots were welded.

The results were as follows:

1. The electrode lives of HDG materials were changed at approximately 0.3–0.4 mass% Al content in Zn coating. Materials with low‐Al coating content showed over three times longer electrode lives than materials with high‐Al coating content.

2. Although the thickness of Al oxide layers was in proportion to the Al content in Zn coatings, the obvious correlation between electrode life and thickness of Al oxide layers was not observed.

3. In the case of low‐Al coating content, it was observed that Fe‐Zn alloy grew from the steel‐coating interface to the Zn coating. It was considered that, in the initial stage of welding, the content of Fe in Zn coating increased immediately.

4. In the case of high‐Al coating content, Fe‐Al alloy was observed at coating‐steel interfaces instead of Fe‐Zn alloy. It was known that Fe‐Al alloy suppresses the Fe‐Zn alloying reaction. Zn coating was not alloyed with Fe in initial stages of welding.

5. From these results, it was concluded that aluminium in coatings affected electrode life by changing the melting point of coating layers between the electrode and the steel. The melting point of low‐Al content coating layers rose because of the diffusion of Fe into the Zn coating. This phenomenon decreased electrode wear and electrode life was long. In contrast, the melting point of high‐Al content coating layers remained low. This phenomenon caused electrode alloying easily and also increased electrode wear. As a result, electrode life became shorter.