niag lasalle

Material Selection Hints

In the selection of steel for a particular application, a helpful guide to production, metallurgical or engineering personnel is experience. Over the years, steel users have developed a collective demand for a relatively few grades or chemistries. These steels have become widely used because they have given successful performance in service.

Niagara LaSalle's specialty steels have proved their value to steel users by eliminating costly secondary operations or by providing better reliability, uniformity, improved machinability and lower end costs.

When specifying a steel bar for the design or redesign of parts for original equipment, special machinery or maintenance and repair, there are a number of factors that must be considered to arrive at the best combination of properties with the greatest economy. Some of these are:

Design Requirements
Mechanical Properties
Thermal Treatments
Production Operations
Machinability
Size, Shape, Straightness, Finish and Tolerance
Availability
Cost

DESIGN REQUIREMENTS
The end use or the conditions under which the part will operate in service is a major factor in determining which grade of steel should be used.

MECHANICAL PROPERTIES
The mechanical property requirements which will enable the material to perform under service conditions must be given prime consideration. Wearability, freedom from distortion and warpage, surface hardness and fatigue life are only a few of the problems involved.

For example, in many parts strength is the first consideration. Unless the part has the required strength, other factors relating to manufacturing and production are of little consequence.

Various combinations of properties are available to today's cold finished steel bar user who may select carbon or alloy steel bars which have the properties in the bar and which require no heat treatment. These are Niagara LaSalle's specialty steels STRESSPROOF® FATIGUE-PROOF® and e.t.d.® 150®

The uniformity across the section, from bar to bar and lot to lot, of the newer specialty steels is important. Service reliability of a part is often improved. The quench cracks often found in quenched and tempered materials are eliminated since no further heat treatment is required. More uniform machinability and a combination of properties not generally available in other types of materials are also provided.

THERMAL TREATMENTS
Various heat treatments are available which provide steel bars with controlled properties and qualities important to the selection of steel. In addition to Niagara LaSalle specialty steels which require no further heat treatment the user may select conventional heat treatable steels or purchase heat treated in-the-bar stock. All of the following treatments offer varying degrees of strength and other properties.

Normalizing - used primarily to make the structures of the steel more homogeneous.

Stress Relieving - used to relieve residual stresses in bars that can cause warping and distortion or, following cold drawing, to obtain mechanical properties.

Annealing - improves machinability by controlling structure and hardness.

Elevated Temperature Drawing (e.t.d.®) - an exclusive process with Niagara LaSalle used to produce various combinations of properties not always available by other processes.

Electric Resistance Heating/Quenching and Tempering - In a revolutionary new process pioneered and patented by Niagara LaSalle, bars are heated while under tension by electrical resistance and immediately water quenched for full hardenability. They are then tempered under tension, again using DC current. These steels provide a bar with ultra-fine grain size and excellent bar-to-bar uniformity. The process can be applied to a wide range of carbon and alloy steels.

Niagara LaSalle has controlled roller hearth furnaces in use today to assure customers of better control of properties and qualities for furnace treated steel bars.

PRODUCTION OPERATIONS
The type of production equipment and the operations to be performed must also be carefully performed must also be carefully considered. For example, Niagara LaSalle's high strength specialty steels which require no heat treatment often eliminate the need for additional heat treat facilities, save floor space, cut investment in material in process, and eliminate or minimize secondary operations following heat treat. These in-process savings can be substantial and deserve careful consideration in selecting a steel.

It should be kept in mind that Niagara LaSalle offers an extension of your own production facilities by providing materials with qualities in the bar. Some of these are strength, straightness, different types of surface finishes, and dimensional accuracy as required as well as various thermal treatments.

MACHINABILITY
Since most parts are machined, machinability is a prime consideration in the selection of a steel. Machinability, measured in surface feet per minute, productivity, tool life and finish, is a most important consideration in the selection of steel. The use of the newer standard and special free machining steels such as Series 83®-420, LA-LED® and LA-LED®X usually make possible important increases in productivity and cost reduction. There have been many recent improvements in machinability and machinability techniques which are now available to the steel consumer.

SIZE, SHAPE, FINISH AND TOLERANCE
In selecting a steel for a given part, size is important. While a wide range of sizes are available, where possible, standard sizes and lengths should be specified.

Shape is usually predetermined. Cold finished steel bars come in round, square, flat, hexagon and special shapes. Most shafting and power transmission applications are made from round bar stock.

A number of surface finishes are available to the parts designer. The production method specified largely determines the finish, tolerance and accuracy which can be expected. The basic production methods are cold drawing, turning, grinding and polishing, or combinations of these.

AVAILABILITY
For maximum economy and best availability, the standard and special steel described in this book should be specified wherever possible. They are generally the most readily available from both mill and Steel Service Centers.

COST
Consider the various economic factors. The end or total cost should always be kept in mind. Frequently a higher priced material may actually be more economical. Production economies, elimination of operations, inventory levels, standardization of grades, larger quantity purchases, material handling, improved reliability, all affect cost and are not always taken into account in cost analyses. Wherever possible the standard grades (including Niagara LaSalle specialty steels), sizes, shapes, tolerances, accuracies and lengths should be specified for greatest economy and best availability.

CONCLUSION
The problems and possibilities relating to materials specifications for the manufacture of parts range from the simple to the complex. Of necessity, we can only suggest some of the areas to be considered. We hope these ideas will be helpful.