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.     

Methodology to parameterize and assess the burn-zinc technique in the resistance spot welding process

To minimize the detrimental effects of zinc during resistance spot welding of galvanized plates, a technique known as Burn-Zinc is usually employed. However, there is not much information and studies available in the current literature about when and how to use this technique. The objective of this paper is to assess and understand this technique. To do so, a methodology to determine the ideal burn-zinc parameters as a function of the plates was proposed. This methodology was evaluated by a series of welds by systematically varying current and pressure at compatible levels for zinc burning. High-speed filming, synchronized with electrical signals, was employed to visualize and to analyse results. Once the burn-zinc parameters were defined, new welds were performed with and without the burn-zinc application. The proposed experimental procedure was shown to be efficient for checking and parametrizing the burn-zinc technique. However, there was evidence that the application of burn-zinc does not always lead to a reduction in operating time.     

Brazing of UNS S32101 and UNS S32304 lean duplex stainless steels and UNS S32750 super duplex with AWS A5.3 BNi-7 (Ni–Cr–P) filler metal

Summary

Weld metals solidified in the ferritic-austenitic solidification mode (FA mode) have dual phases of ferrite and austenite in their as-solidified condition, where ferrite exhibits different morphologies depending on the chemical composition and welding conditions. This paper describes an investigation of the effect of the solidification and transformation sequence on the formation of final ferrite morphologies. Austenite is formed through either a eutectic reaction or peritectic reaction at the dendrite boundaries after the primary formation of ferrite. During the eutectic formation of austenite, the <100>_δ direction of the primary ferrite and the <100>_γ direction of the eutectic austenite are parallel to each other and lie along the growth direction of the primary dendrites. However, any specific lattice plane relationship between the two phases is not identified. During cooling after solidification, the austenite extends into the primary ferrite via solid-state transformation, and the final morphology of the ferrite is vermicular without any coherent orientation relationship between the primary ferrite and eutectic austenite. During peritectic formation of austenite, the Kurdjumov-Sachs orientation relationship is established between the primary ferrite and peritectic austenite, and the <100>_γ direction of the peritectic austenite is not parallel to the growth direction of the primary dendrites. During cooling after solidification, the primary ferrite transforms into austenite, and the final morphology of the ferrite is lathy, since the primary ferrite and peritectic austenite have a favourable coherent orientation.     

High-temperature Tensile Behavior in Coarse-grained and Fine-grained Nb-containing 25Cr-20Ni Austenitic Stainless Steel

In this study, tensile behavior of Nb-containing 25Cr-20Ni austenitic stainless steels composed of coarse or fine grains has been investigated at temperatures ranging from room temperature to 900 °C. Results show that the tensile strength of fine-grained specimens decreases faster than that of coarse-grained specimens, as the test temperature increases from 600 °C to 800 °C. The rapidly decreasing tensile strength is attributed to the enhanced dynamic recovery and recrystallization, because additional slip systems are activated, and cross-slipping is accelerated during deformation in fine-grained specimens. After tensile testing at 700-900 °C, sigma phases are formed concurrently with dynamic recrystallization in fine-grained specimens. The precipitation of sigma phases is induced by simultaneous recrystallization as the diffusion of alloying elements is accelerated during the recrystallization process. Additionally, the minimum ductility is observed in coarse-grained specimens at 800 °C, which is caused by the formation of M₂₃C₆ precipitates at the grain boundaries.     

Quantification of Compositional and Residual Stress Effects on Lattice Strain in Dual-phase Stainless Steels by Means of Differential Aperture X-ray Micro-diffraction

Residual stress is an important factor for evaluating the deformation and failure of engineering materials. Diffraction-based measurement assumes that the full measured lattice strain tensor contributes to residual stress according to Hookers Law. The present work focuses on the lattice strain determination of individual grains in a dual-phase stainless steel （DPSS） by means of differential-aperture X-ray micro-diffraction （DAXM）. The results show that the residual stress only takes part of the responsibility of the total measured lattice strain. In fact, the compositional variation inside the material was found to cause greater strain gradient in both ferrite （c~） and austenite （~） phases in DPSS. Therefore, quantification of compositional and residual stress effects on lattice strain was conducted in order to evaluate the true residual stress inside engineering materials.     

Effects of cryogenic and tempered treatment on the hydrogen embrittlement susceptibility of TRIP-780 steels

Cryogenic and Tempered (CT) treatments were performed on commercial TRIP 780 steels in order to reduce the hydrogen embrittlement (HE) susceptibility. The HE behavior was assessed immediately after cathodically hydrogen charging on both CT treated and untreated samples. Slow strain-rate tensile (SSRT) tests were conducted to evaluate their HE performance. It is shown that samples with CT treatments behave higher resistance to HE comparing with their untreated counterparts. Meanwhile, microstructure characterization and magnetization measurements were adopted to reveal the evolution of retained austenite (A_r) and its stabilization due to CT treatment. Moreover, hydrogen-induced cracking (HIC) accompanied with martensite phase transformation in TRIP steel was studied by electron backscattering diffraction (EBSD) technique and it was proved that cracks initiated from the fresh untempered martensite inherited from phase transformation of unstable A_r upon straining. Finally, results in this study demonstrate the relationship between A_r stability and HE susceptibility, and provide a possible solution to reduce HE susceptibility in TRIP steels.     

18-4-1及M42高速钢渗氮工艺研究

通过对M42及18-4-1高速钢氮化及碳氮共渗工艺的研究,得到了以下一些结果:1.高速钢经低氮势(N:H=1:4)长时间氮化,可以仅获得纯氮化扩散层,而不会出现明显化合物相。2.M42高速钢与18-4-1高速钢相比,相同条件下渗氮,渗层硬度高但层深较浅。3.高速钢在CH_4通入量少于3％的情况下进行氮碳共渗,可控制完全获得纯扩散层。氮碳共渗可以明显提高氮化渗速,增加渗层厚度,而对渗层硬度没有太大的提高。     

Failure Investigation of a Furnace Tube Support

A furnace tube support failed after 6 months service at 850 °C. The support was an HK alloy, a member of the heat-resistant cast alloy family (H-Series) steels. The H-series steels are widely used in the petrochemical industry for components requiring enhanced high-temperature properties. Microstructural changes occurring at high temperature clearly affect the mechanical properties. The property degradation in HK-40 steel furnace tube support subjected to high temperature was caused by the formation of sigma phase. The investigation included metallurgical analysis, materials characterization, and mechanical analysis.     

Deformation and fracture of high-temperature steels at different temperatures and loading rates

Charpy impact tests were conducted at different temperatures and loading rates. Temperature dependences of the crack initiation and propagation energies were determined for carbon steel 45, steels St. 3 and 15Kh2NMFA from the load-time curves obtained with due account of the impact test results. The effect of the loading rate on the temperature dependence of the impact toughness was analyzed within the range from 1 to 4.4 m/s. __________ Translated from Problemy Prochnosti, No. 1, pp. 29–34, January–February, 2009.