Mechanical and metallurgical properties of friction welded AISI 304 austenitic stainless steel

Owing to the superior properties, of stainless steel it is pertinent to make use of it in various automotive, aerospace, nuclear, chemical and cryogenic applications. It is observed that a wide range of dissimilar materials can be easily integrated by solid phase bonding techniques, such as friction welding and explosive bonding. This study mainly focuses on friction welding of AISI 304 austenitic stainless steel. The friction processed joints are evaluated for their integrity and quality aspects. Friction welding of austenitic stainless steel was carried out using a KUKA friction welding machine (Germany). As the friction time increased, the fully plastically deformed zone (region I) in the vicinity of the bond line becomes increased. In contrast, an increase in friction time will decrease the region (region II) where the grains are partly deformed and grown. Tensile test results indicated that, the joint strength is decreased with an increase of the friction time. The detailed fractographic observation confirmed that the rupture occurred mostly at the joint zone and partly through the base material.     

CO2 laser welding of zinc-coated steel sheets

Welding of zinc-coated steel sheets for the automotive industry has been investigated experimentally and theoretically, using a continuous wave 2 kW CO₂ laser. The specimens of 0.8, 1.0 and 1.2 mm thickness were welded as butt joint and lap joint. Argon gas was shielded co-axially to reduce the plasma and to protect the molten, pool from atmosphere. The mechanical tests of specimens were carried out to investigate the ductility of welds in butt joint and lap joint, using the Erichsen test, ball punch test and tensile shear test. The value of transverse weld pattern is higher than others. The fatigue life of longitudinal weld is superior, but that of circular weld pattern is inferior due to the high tensile residual stresses in the weld. The maximum Erichsen value was obtained as 96% and the deformability of zinc coated steel butt-welded was found to be 80% in the ball punch test. The high pressure formed by vaporization of zinc with the low boiling temperature during laser lap-joint welding splattered the molten pool and created porosities in the weld. The optimum gap was calculated to be 0.1 mm in the lap joint welding of zinc-coated steel sheet which was a good agreement with the experimental result.     

Microstructure and wear resistance of thermal sprayed steel coatings ion beam implanted with nitrogen

In the present study, the high-current-density nitrogen ion implantation technique is applied to enhance mechanical properties of thermal sprayed steel coatings. XRD measurements and optical microscopy of ion implanted coatings show clearly the presence of nitrogen solid solutions and precipitates of new phases in the surface layers of coatings. Phases formed are controlled by the temperature of ion beam processing, initial chemical composition and microstructure of coatings. Wear tests demonstrate that properly selected parameters of ion implantation dramatically improve wear and score-resistance of coatings. The influence of the microstructure and phase composition of nitrogen ion implanted layers on tribological properties is discussed.     

A study on tensile and fatigue properties of aged NAS 254N stainless steel at elevated temperatures

The effects of aging on tensile properties and fatigue crack growth behaviors of NAS 254N stainless steel was studied. Yield strength and ultimate tensile strength of the aged specimens were almost the same as the as-received (as-rec.). The fracture strain, however, was decreased significantly by the aging, and the fracture surface of the aged at room temperature (RT) test was intergranular. As test temperature increased, yield strength, ultimate tensile strength and elongation decreased. And a type of serration was observed at 550-650°C As strain rate decreased, yield strength and ultimate tensile strength decreased, but elongation increased. It was observed that tensile strength and strain had a sudden change at one point. And this critical temperatureT _cr was 550°C. The effect of aging time on the tensile strength and strain was also investigated. Tensile strength and strain decreased significantly beyond 100hrs. Fatigue crack growth rate at RT was enhanced by the aging at high stress intensity factor range. This is due to the occurrence of the intergranular fracture in the aged specimen. At 650°C, the fatigue crack growth behavior was almost the same without intergranular fracture.     

Effect of temperature on the charpy impact and CTOD values of type 304 stainless steel pipeline for LNG transmission

Stainless steel pipe of type 304 the with a wall thickness of 26.9 mm and the outer diameter 406.4 mm is welded by manual arc welding process. Mechanical properties and fracture toughness of type 304 stainless steel are investigated in the temperature ranging from room temperature to — 162°C. The results obtained are summarized as follows. The tensile strength noticeably increases as the temperature becomes lower while the yield strength is relatively insensitive to temperature. The Charpy impact energy and CTOD values become higher in the case that crack propagation direction is aligned to the transverse axis upon the rolling direction than longitudinal direction. The drop of fracture toughness is associated with the noticeable diminution of plastic component as temperature seduces from room temperature to — 162°C.     

Wear and corrosion resistance of alumina dies for isothermal semi-solid processing of steel

The tool wear of high-purity alumina (Al₂O₃) dies applied in semi-solid extrusion of steel X210CrW12 under near-isothermal conditions at 1250–1350 °C is investigated. Results show excellent wear resistance of the Al₂O₃ dies against semi-solid steel and scale under experimental conditions. Minor chemical interaction was observed at the die inlet which, in contrast to the die land, is in contact with scale formed on the billet during pre-heating. This effect is attributed to the appointed billet pre-heating procedure. A tribochemical interaction mechanism between alumina dies and semi-solid steel is presented. This paper contributes to the evaluation of a self-heating ceramic tool concept for steel thixoextrusion introduced previously. Results lead to the conclusion that the targeted benefit of applying corrosion resistant but thermal shock-sensitive ceramics as die materials for the semi-solid processing of steel is achieved.     

Nano structured surface modification of tool steel and its beneficial effects in mechanical properties

The industrial beneficial effects of nano-structured surface modification of tool steel (SKD 61) have been studying. Ultrasonic cold forging technology (UCFT) is one of severe plastic deformations for the improvement of mechanical properties by making nano-structure on surface. The basic mechanism of UCFT and experimental device for treatment of trimmer knives (SKD 61) are presented. Test results of UCFT treated knives in cold steel milling line and analysis why the improved service life is achieved are explained.     

Some investigations on microstructure and mechanical properties of submerged arc welded HSLA steel joints

This paper investigates the influence of the submerged arc welding (SAW) process parameters (welding current and welding speed) on the microstructure, hardness, and toughness of HSLA steel weld joints. Attempts have also been made to analyze the results on the basis of the heat input. The SAW process was used for the welding of 16 mm thick HSLA steel plates. The weld joints were prepared using comparatively high heat input (3.0 to 6.3 KJ/mm) by varying welding current (500–700 A) and welding speed (200–300 mm/min). Results showed that the increase in heat input coarsens the grain structure both in the weld metal and heat affected zone (HAZ). The hardness has been found to vary from the weld centre line to base metal and peak hardness was found in the HAZ. The hardness of the weld metal was largely uniform. The hardness reduced with the increase in welding current and reduction in welding speed (increasing heat input) while the toughness showed mixed trend. The increase in welding current from 500 A to 600 A at a given welding speed (200 mm/min or 300 mm/min) increased toughness and further increase in welding current up to 700 A lowered the toughness. Scanning electron microscopy of the fractured surfaces of impact test specimen was carried out to study the fracture modes. Electron probe micro analysis (EPMA) was carried out to investigate the variation in wt.% of different elements in the weld metal and HAZ.     

汽车板拉伸试验机测控系统设计与实现

介绍了汽车板拉伸试验机测控系统的软硬件结构和应用实例.试验机中横梁上下移动采用直流伺服系统控制完成.数据测量链由工业PC机、信号放大器、A/D卡、力传感器和引伸计组成.测控软件选用VC++6.0编写,包含测量链标定、标定结果验证和数据采集等功能模块.试验结果与钢厂样品出货清单的力学性能值一致.     

Quantification of wear,strain and heat energy consumption rates for sliding steel ball against diamond-like carbon coatings

Abstract

In this work, we evaluated the different energy consumption rates associated with the total frictional energy for a ball sliding on a flat surface. The energy generated by the sliding two bodies in contact is dissipated into the materials in various forms. The wear consumption energy for a steel ball against a diamond-like carbon surface was evaluated by the wear coefficient of the wear volume–energy input equation. The strain energy generated in the steel ball as a result of being made to slide under a certain load was calculated using the Hertzian theory. The chemical reaction energy was estimated based on iron oxidation. Finally, the frictional energy dissipated as heat was obtained by subtracting the wear and the strain energies from the total frictional energy.