Failure of Welds

This is a picture to show what can happen when a weld fails in a pressure vessel. The picture is from ‘The efficient use of steam’ by P. M. Goodall.

Welds are often the source of failure in structures because the welding process has the possibility of introducing many different defects. In welding a localised area of material is heated and this necessarily leads to temperature gradients. This can cause large differences in the microstructure in the area of the weld.

Even when a good weld is possible it may not be simple to make the weld reproducibly due to differences in geometry of the structure and welding position (overhead, horizontal, sideways, etc.).

Failure of weld in all-welded watertube boiler

Blue Steel

Steel can change colour due to oxidation during heat treatment. I don’t know if this depends only on the thickness of the oxide, or if there is also some chemical difference. I tempered a high carbon alloy for 30 minutes at 300 Celsius (carbide free bainitic steel), and it changed into this purple colour.

There are a few web pages which give details of the Temper Colours - this one has a table with colours and hardnesses of various steel grades.

The surface colour depends on the oxide thickness, so is dependent upon alloy chemistry, temperature, time, surface finish and furnace environment.

There is also a page on wikipedia on the blueing of steel.

Airbus Delay

I knew the Airbus delays were caused by problems with the wiring of the aeroplane. But I was surprised by this statement in a BBC story.

Problems with the complex wiring required to allow different airlines to specify their own entertainment options and seating layout have meant the aircraft is being delivered about two years late.

Should the wiring of the entertainment system really be able to delay the whole plane? I can’t imagine it needs any hanger facility and therefore shouldn’t delay the manufacture of more planes (apart from CASH flow).

Couldn’t they have used WIFI? Can’t seat wiring be done Ad-hoc?

Early stages of precipitation - Copper precipitation

Last year I attended a conference on Early stages of Precipitation, which was a paralled session organised by the Royal Microscopical Society (Not to be confused with this other RMS).

George Smith (etal) reported that in the early stages of copper precipitation, precipitation can be accelerated by additions of Nickel, despite the fact that we do not expect Nickel to segregate from thermodynamic calculations (based on continuum assumptions). Atom probe results show that Nickel segregates to the boundary between the two phases, this was explained by consideration of pair-wise interaction energies. Modelling was performed using a Monte-Carlo scheme which reproduced the observed precipitation sequences based on interaction energies.

Nickel is friendly to both Cu and Fe, while Cu-Fe don’t get on together so well.

From this type of explanation we should be able to make a prediction of which alloying elements can similarly accelerate or diminish the formation of clusters/ nuclei.

To do this I would like to calculate or find a table of interaction energies.

Football Shirts

My friend went to the sports shop to buy a Liverpool F.C. football shirt here in Cambridge. However there were no Liverpool football shirts available, only ones for Manchester United, Chelsea, Arsenal and plenty of England shirts.

Mohs’ Hardness Scale

Friedrich Mohs introduced a popular hardness scale to quantify hardness, mainly to help in identification of minerals and gems.

Mohs’ Scale	Rosiwal-grinding-hardness	Material for comparison
		Graphite
1 Talcium	0.03
		Lead, tin
2 Gypsium, rock salt	1.25
		Aluminium, zinc, magnesium, copper, silver, gold
3 Calcite	4.5	Marble, brass, iron, nickel
4 Fluorspar	5
		Steels unhardened
5 Apatite	6.5
		Window glass
6 Feldspar	37
		Low-carbon steels, hardened
7 Quartz	120
		0.9% C steel, hardened; tungsten
8 Topaz	175
		Special Steels
9 Corundum	1000
10 Diamond	14000

There are pictures of Moh’s scientific instruments on the phase transformations group web page. Prof. Harry Bhadeshia photographed the equipment which is on display in Graz.

Steel Wires

Random bits of information about Steel wires.

There is a patent on using Scifer in composite structures, where about 10% metal fibres are added. “Carbon fiber prepreg and carbon fiber reinforced resin composite, US Patent Issued on September 6, 1994″ Inventor(s), Shouaki Ide, Akira Shimamoto, Toshiaki Yutori, Masahiko Uchimura. Patent No. 30264 filed on 1993-04-05

There is a 2001 paper about dissolution of cementite during drawing of pearlitic wire. K. Honoa, M. Ohnumaa, M. Murayamaa, S. Nishidaa, A. Yoshieb and T. Takahashia, Scripta Materialia
Volume 44, Issue 6 , 1 April 2001, Pages 977-983. “Cementite decomposition in heavily drawn pearlite steel wire”

doi:10.1016/S1359-6462(00)00690-4

Press release about uses of Scifer from find articles.com

Kobe Steel starts ultrafine ’scifer’ wire R&D - research and development
American Metal Market, April 5, 1991 by Minoru Inaba
Find More Results for: “scifer steel “
Kobe’s superfine wire…
Japanese steelmakers…

Kobe Steel starts ultrafine ’scifer’ wire R&D

TOKYO — Kobe Steel Co. Ltd. has begun research efforts involving unidentified U.S. and Japanese companies to develop industrial applications for a family of patended ultrafine “scifer” steel wires ranging from 15 to 100 microns in diameter.

Despite the fact that they are as fine as spider thread (7 to 8 microns) and human hair (70 to 80 microns), the scifer wires, according to Kobe executives, have a tensile strength twice as great as that of piano wire and an elasticity three times as great as aramid fiber.

Shunji Omae, deputy general manager of steel wire rod and bar sales at Kobe, said the company and local customers have found commercial fine wires in sports equipment, such as fishing wire, golf clubs and skis.

He said Kobe recently began joint efforts in the United State and Japan to cultivate industrial applications for the wires, including computers, communications, aircraft and medical uses.
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The scifer wire is said to be composed of 97 percent steel, 2.9 percent silicon and manganese and 0.1 percent carbon. The material is available for 43 cents per kilogram.

After a “special” heat-treatment process that Kobe calls the key step needed to make scifer wire, the steel becomes a ferrite-matrix composite containing martensite. The grain size is said to be 20 angstroms in diameter, or one-5,000th that of ordinary steel.

The heat-treated wire can be drawn out of its final form by a factor of 10,000, Omae said.

Kobe rated 25-micron scifer wire at 475 [kgf/mm.sup.2] in tensile strength, 20,000 [kgf/mm.2] in elastic modulus, 4 percent in elongation and 53 percent in reduction of area.

The 100-micron scifer was rated at 400 [kgf/mm.2] in tensile strength, 20,000 [kgf/mm.2] in elastic modulus, 4.5 percent in elongation and 55 percent in reduction of area.

In short, Omae said, the ultrafine wires are strong and, at the same time, elastic.

Kobe is offering them in the form of straight wires, plated wires with some conductive characteristics, twisted cables and as an extra reinforcement in fiber-reinforced plastic and fiber-reinforced rubber.

Fishing rod maker Daiwa Seiko has put on sale a fishing wire consisting of two 7-to-16-micron scifer wires twisted together.

Golf club maker Homma is producing wood clubs that take advantage of the scifer wire’s good elasticity to give the clubs good control in addition to ball-carrying strength. Scifer clubs are priced at $719 to $2,156 apiece.

Before the next winter season, ski maker Ogasaka will introduce scifer skis said to be just as elastic or smooth as glass-fiber skis and yet much superior in responsiveness and shock absorption. Scifer skis will sell for $783 per set.

Saying scifer wire might be following a similar path taken by carbon-reinforced plastics in terms of development of applications, Kobe’s Omae said he was hoping to see a wide variety of industrial applications develop for the ultrafine wires.

Possible applications, some of which were said to be actually pursued jointly with American and Japanese customers, include plated wires for supercomputers, communications wires, high-frequency applications, precision springs, probes and extra reinforcement for carbon-reinforced plastics.

COPYRIGHT 1991 Reed Business Information
COPYRIGHT 2004 Gale Group

My First Diffusion Bond

These 1 cm x 1 cm samples of high carbon steel stuck together during austenitisation, the bonded surfaces were not prepared in any way to make them clean, so had large oxide layers.

The samples on the right were tested in 3 point bending using a small metal rod for a fulcrum and two human fingers to supply a load. With a load estimated to be several kg the samples broke apart at the bond.

Dr. Shirzadi advises that better results could be obtained by cleaning oxides from the surface, and using a load of around 10 MPa to press the samples together.