STRESSPROOF® is made by a patented process which consists of drawing the bar through a special die under heavy draft, then stress relieving it in a precisely controlled furnace.

When Niagara LaSalle developed STRESSPROOF® in 1938, it changed the economics of part production. Because for the first time, users could get an improved wearability without case hardening, strength without heat treating, plus excellent machinability and tool life.

STRESSPROOF® is electro-magnetically tested using eddy currents. Other benefits include resistance to fatigue and stress, balanced working and minimum warpage and distortion. STRESSPROOF® can also be induction hardened, but should be watched for quench cracks.

The Only Steel Bar Pretested for Machinability

Consistent quality is becoming increasingly important to steel users over a wide range of products. This is particularly true in the case of the uniformity of machinability of cold finished steel bars, because of the ever greater automation in the machine shop. The present new generation of computer-controlled machine tools is less tolerant of differences in tool life, emphasizing the need for materials that are dependable performers.

Niagara LaSalle has recognized this need for product uniformity, since it has worked in the field of machining for many years in close contact with production machine shops. Through the years, the desirability of having available a quick and inexpensive machinability test that could be used as a routine quality control check was often discussed. Finally, several years ago, after much painstaking research, Niagara LaSalle did develop a new machinability test ideally suited for quality control purposes and the monitoring of certain specialty products where uniform machinability is important.

Niagara LaSalle's machining test is different from most other tests now in use in that it is basically a "go/no-go" test, which is an integral part of the machining cycle used to prepare the standard tension test specimen needed for releasing every lot of STRESSPROOF® produced. When this machining procedure is done with a modern computer-controlled lathe, the test is simple, accurate, and inexpensive to carry out. (See Charts 1 and 2, page 22.)

It is recognized that this test will not pick up every conceivable problem associated with machining, particularly those related to residual stresses or surface problems. However, the test is very sensitive to effects associated with the basic nature of the steel, such as tensile properties, hardness, metallographic differences in structure and inclusions, and variations in chemical composition.

It has also been proven that this new test correlates well with the Taylor test, across a broad spectrum of chemistries and strength levels. Niagara LaSalle has conducted thousands of tests on STRESSPROOF® alone. Field feedback has shown that the test will pick up substandard batches and is sensitive not only to single but also multiple factors known to influence day-to-day production machining performance.

It is strongly felt that in our modern computer age, uniformity in machinability of a product has become a key factor in improved productivity, and Niagara LaSalle will continue to be responsive to the needs of its customers.

STRESSPROOF not only meets the minimum properties of ASTM A311, but it also has controlled low stresses, reliable machining, and improved surface quality. Result is longer part life with less manufacturing costs.

Facts

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FACT: THE GRADE 1144 MODIFIED Grade AISI 1144 was originated by the LaSalle Steel Company in the mid-1930's for the purpose of making STRESSPROOF.

FACT: THE PATENT The original patent for STRESSPROOF, "the steel product and method of manufacture", was based on cold drawing with heavy drafts, i.e., higher-than-normal drafts. This was followed by the highest temperature stress relieving treatment possible to obtain a combination of properties… strength, wear resistance, minimum warpage, and excellent machinability.

FACT: HIGH TEMPERATURE STRESS RELIEVING The importance of high temperature stress relieving to obtain maximum ductility, minimum warpage and excellent machinability is a major part of the original patent. The stress relieving temperature selection is based on 60 years of experience and thorough documentation.

FACT: PATENTED DRAWING DIES Niagara LaSalle's patented drawing dies have always been the most critical part of producing STRESSPROOF. Therefore, a warpage test is always performed on the first bar drawn through either a new or reground die. Warpage tests are also regularly made as part of a standard quality assurance procedure. Niagara LaSalle is the only mill to use a warpage test. The results then become an integral part of the quality assurance program.

FACT: SURFACE QUALITY To assure surface quality, comparitor or roto bar testing for seams on every order is a part of the STRESSPROOF manufacturing process. To further improve quality, Niagara LaSalle reduced the standard seam depth tolerance for STRESSPROOF from 0.0015 per each 1/16" to 0.0010 per each 1/16". This can mean a savings of 3% in material weight purchased.

FACT: MACHINABILITY ASSURANCE Machinability testing of all STRESSPROOF is regularly done as a part of the Niagara LaSalle Quality Assurance Program. Niagara LaSalle is the only mill in the world to use a machining test as part of a production and quality assurance program.

FACT: ASTM A311 SPECIFICATION This specification was written in an attempt to cover STRESSPROOF properties. This specification is very broad in that it covers eight grades and four conditions of stress relieved cold drawn bars to meet minimum mechanical property requirements.

FACT: MECHANICAL PROPERTY TESTING Mechanical property (tension) testing at Niagara LaSalle uses the largest sampling plan in the industry. A minimum of one test (tensile, yield, elongation, R/A) is made for every 50,000 lbs. or less. Mechanical property testing is always the final production operation after all processing is completed.

Specifications

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Chemistry

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Mechanical Properties

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