Automobiles and New Steel Products

Raising fuel efficiency and complying with legal regulations related to safety and durability are pressing issues in the automotive industry. Steelmakers must supply materials that help to meet these goals while reducing users' costs as well. Described below are new steel products that answer the needs of automobile manufacturers in several specific ways.

Lightweight Steel Sheets

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Formable High-Strength Steel Sheets

These sheets, used for the outer panels of automobiles, offer both high strength and good workability – properties which until now were difficult to combine in a single product. They can be thin due to their high strength, and their thinness saves weight. The new sheets resist denting by flying pebbles and are stiff enough to prevent noise and vibration when the vehicle is running. They are now available in several types: sheets for general forming, with good bendability; low-yield ratio sheets with high strength and high ductility; sheets for deep drawing, with high Lankford value; and sheets of bake-hardening type for deep drawing, their strength rising when paint-baked. These products are offered in a range of tensile strength from 35 to 100 kgf/mm². Coated and one-side coated high-strength steel sheets are also on the market.

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Plastic-Sandwiching Steel Sheets

In this product, a plastic sheet is sandwiched between two steel sheets. A type recently supplied to one automobile maker, consisting of a 0.6-mm 280 plastic sheet between two 0.2-mm steel sheets, is only half the weight of the usual 1-mm steel sheet and yet has the same rigidity. It is used for trunk-lid panels and air-cleaner covers.

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Pure aluminium has good corrosion resistance and working and forming properties but poor machining characteristics and low mecha­nical strength. By adding other elements to aluminium, its strength and machining characteristics can be improved. Such a combination of two or more elements, at least one of which is metallic, is called an alloy and the predominant metal in the system is referred to as the base metal.

Silicon, copper, zinc and magnesium are common alloying elements and are often added to aluminium in substantial proportions. Iron, manganese, nickel, chromium, titanium, antimony, cadmium, cerium, lithium, beryllium and molybdenum are also added in smaller proportions with various beneficial effects.

Titanium, tungsten, cerium and molybdenum all contribute to grain refinement of cast aluminium. Manganese and antimony are often added to improve corrosion resistance. Cobalt and nickel affect strength and workability while cadmium and tin increase hardness in heat treatable alloys.

The market penetration of ZA alloys has been aided by the fact that traditional high volume foundry metals have significant shortcomings that detract from their inherent advantages: cast iron has high energy and machining costs, protective finishes are nearly always required and there are industry environmental prob­lems; bronze has high material and energy costs and the environmental problem of lead for many important alloys; aluminium has limitations in strength, bearing properties and finishing along with moderately high energy costs. Of course, each of these classic materials does have distinct advantages in given applications.

In contrast, the zinc casting alloys have advantages that are highly attractive to foundries:

excellent casting properties;

low energy consumption;

pollution free melting and casting;

excellent machinability;

lower material cost and density than bronze.

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A Wonder Metal

The story of titanium is extraordinary. To begin with, it was discovered twice. A British scientist, William Gregor, found it first and called it menachanite, and six years later, in 1797, M. H. Klaproth, a German chemist, also found it and gave it its present name.

For many years, titanium was of interest only to research chemists – it was considered too brittle to be of any practical value. Yet it was the impurities with which it was usually associated (it forms compounds easily with nearly every known element) that made it brittle.

It cost the chemists in many countries endless efforts to isolate pure titanium and even more to start producing it commercially. In 1948 the world stock of pure titanium was only ten tons. Today the output is much larger.

Titanium has one surprising property – it is completely inert in biological media, something the medical community was quick to notice. It is being used to make artificial joints and many other things necessary in surgery at the Priorov Central Institute of Traumatology and Orthopedics. Titanium instruments do not corrode, and are thirty per cent lighter than instruments made of stainless steel.

Titanium's high standard of corrosion resistance, lightness, tensile strength, and the ease of forging, rolling and stamping are finding it more and more uses. Titanium alloys are very useful in mechanical engineering, and for chemical and refractory apparatus. Titanium helped Russian design engineers to surmount the sound and heat barriers in supersonic and high-altitude aircraft designing. On earth, it shows good work at chemical plants, in the pulp-and-paper and food industries. Moreover, it is still a source of surprise for the investigator.

A group of researchers under the leadership of Prof. I. Kornilov produced a material that has a kind of "memory", as the following experiment shows: a thin bent strip of the new alloy was clamped to a stand, a 500-gram weight hung on the free end. A current was passed through for several seconds, which heated the strip to more than 100°C. As if commanded by an enigmatic force, it straightened out like a tight spring and lifted the load. When the current was switched off, the strip gradually went back to its original shape. The cycle was repeated a number of times, and the strip always "remembered" its original shape surprising phenomenon of direct conversion of thermal energy into mechanical is seen with the naked eye.

The explanation is in the crystalline modifications of titanium-nickel alloy which, changing with the temperature, also changes back again.

That is why the material has a "memory^” and special acoustic properties. At room temperature, the alloy called titanium nickeloid becomes soft, ductile and does not produce the characteristic metallic sound when struck. However when it is heated to a certain temperature, it becomes hard, resilient and ringing.

There will undoubtedly be some unusual applications for this phe­nomenon in the future — even at this early stage it is clear that titanium-nickeloid-based alloys will be useful in many areas. For instance, in sensitive pickups which are activated by a change in temperature, in acoustics for sound absorption, etc, etc.

Titanium and its alloys are coming out in the commercial field – they have already made quite a name for themselves as structural materials.

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1 Titanium was discovered twice.

2 Pure titanium is found in nature.

3 Titanium forms compounds with many elements.

4 To isolate pure titanium isn't difficult.

5 Titanium is light, strong and corrosion resistant.

6 It is active in biological media.

7 Titanium can be used in surgery.

8 Titanium alloys can't be used as structural materials.

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What is plastic memory? 2 In what cases is this memory un­desirable? 3 What phenomena does the change in mechanical properties of polymers result from?

Plastic Parts That Remember

Thermoplastics can be bent, pulled, or squeezed into various useful shapes. But eventually–especially if you add heat – they return to their original form. This is known as plastic memory. Plastic memory offers some interesting design possibilities.

Thermoplastics never forget. You deform them; and after a while, depending on temperature, they move back toward their original shape.

When most materials are bent, stretched, or compressed, they somehow alter their molecular structure or grain orientation to accom­modate the deformation – permanently. Not so with polymers. Polymers temporarily assume the deformed shape but always maintain internal stresses that want to force the material back to its original shape. Usually, this desire to change shape is called plastic memory.

This so-called memory is often undesirable. Sometimes people prefer that thermoplastic parts forget their original shape and stay put–especially when the parts must be formed, machined, or rapidly cooled. However, this memory, or instability, can be used advantageously.

The time/temperature-dependent change in mechanical properties results from stress relaxation and other viscoelastic phenomena typical of polymers. When the change is an unwanted limitation, it is called creep. When the change is skillfully adapted to the overall design, it is called plastic memory.

Most plastic parts can be produced with a built-in memory. That is, the tendency to move into a new shape is included as an integral part of the design. So then, after the parts are assembled in place, a small amount of heat can make them change shape.

Seals, gaskets and seamless covers for tubing and wiring are typical examples.

In other applications, plastic parts can be deformed during assembly, then allowed to return to their original shape. In this case, parts can be stretched around obstacles without permanent damage.

Potential memory exists in all thermoplastics. Polyolefins, neoprene, silicone, and some other polymers can be given a memory either by radiation or by a chemical change.