niag lasalle


A specialty steel product produced with an innovative process

StressProof® is produced using a proprietary process that draws the bar through a special die under heavy draft, then stress relieves it in a precisely controlled furnace.

Niagara LaSalle developed this groundbreaking process in 1938 and forever changed the economics of part production. In this modern age, uniformity in the machinability of a product is a crucial factor in improved productivity, and we not only met this critical need, but exceeded expectations.

The result is a steel bar product that meets stringent standards and provides a wide variety of benefits, including:

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  • Improved wearability without case hardening
  • Strength without heat treating
  • Exceptional surface quality
  • Excellent machinability
  • Extended tool life
  • Resistance to fatigue and stress
  • Balanced working
  • Minimized warpage and distortion
  • Controlled low stresses

StressProof® is electro-magnetically tested using eddy currents. Although it also can be induction hardened, it should be watched for quench cracks.

Niagara LaSalle is exceptionally responsive to the needs of our customers and puts a high priority on providing uniformity in the machinability of our products in order to improve productivity for you. Our exclusive StressProof® products not only meet the minimum properties of ASTM A311 but also have controlled low stresses, reliable machining and improved surface quality.

StressProof® offers reliability and significantly longer part life for every application. And, most importantly, help reduce your manufacturing costs.

You can rely on Niagara LaSalle for all of your steel bar needs. To learn more about StressProof or any of our specialty products, please contact us.

Facts about StressProof® Steel from Niagara LaSalle


Grade AISI 1144 was developed by the LaSalle Steel Company in the mid-1930s for the purpose of making StressProof®.


The original patent for StressProof® — both the steel product and method of manufacture — was based on cold drawing with heavy drafts. This was followed by the highest temperature stress relieving treatment possible to obtain a combination of properties, including strength, wear resistance, minimum warpage and excellent machinability.


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. The heavy draft stress-relieved Class B came into existence with the 1979 release of the specification.


Niagara LaSalle's proprietary 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. The results then become an integral part of the quality assurance program.


To assure surface quality, magnetic 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.


This specification was written in an attempt to cover StressProof® properties. It covers multiple grades and numerous conditions of stress-relieved cold drawn bars to meet minimum mechanical property requirements.


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 operation after all processing is completed.

Mechanical Property Tests
1 tension test every 50,000 lbs. or less of same lot for TENSILE, YIELD, ELONGATION/2", R/A
1 tension test for every 10,000 lbs. or less of same lot for TENSILE, YIELD, EL/2", R/A. If restraightened, then the same number of tests are again required.
Seam Depth Specification
No specification
Maximum seam depth of 0.010 up to 5/8" diameter. Thereafter 0.001 per each 1/16" of diameter, i.e., 1" dia.-0.016" max. depth of seam. Seams deeper than this are rejectable. This specification is 33% less than the standard for AISI 1144 grade.
Magnetic Testing
No specification
Every order is inspected for surface defects with a magnetic or roto bar tester. Seams deeper than that stated above are rejected.
Warpage Testing
No specification
One warpage test is taken of first bar produced by a new or reground specialty designed drawing die. If this test indicates stresses are out of specification, the die is not used.
Drawing Die Testing
No specifications
An optical comparator test is made of a mold from each new or reground die measuring the internal geometry of the die. Routine warpage tests are also conducted throughout the life of the die.
Carbon 0.40/0.48
Manganese 1.35/1.65
Phosphorus 0.040 Max.
Sulphur 0.24/0.33
Silicon 0.35 Max.
* AISI 1144 heats to be used for STRESSPROOF® are nitrogen treated, and contain nitrogen in quantities normally associated with steel produced by the electric furnace process.
To ASTM A311 Class B.
Tensile Strength
115,000 psi (Min.)
Yield Strength
100,000 psi (Min.)
Machining Characteristics
83% of 1212
8% Min. (7% Min. above 3 in.)
Reduction of Area
25% Min. (20% Min. above 2 in.)
Pearlite and ferrite
Rounds 1/4" through 4-1/2"
Hexagons 1/4" through 2"
(Tolerances, in decimals of an inch, provide for undersize variation only.)
1/4" to 1-1/2" incl. 0.004"
Over 1-1/2" to 2-1/2" incl. 0.005"
Over 2-1/2" to 4 incl. 0.006"
Over 4" to 4-1/2" incl. 0.007"
1/4" to 3/4" incl. 0.004"
Over 3/4" to 1-1/2" incl. 0.005"
Over 1-1/2" to 2" incl. 0.006"
  1. Standard "as drawn" finish is smooth, Accurate and dark in color.
  2. Ground and Polished with special close tolerances available on order.
Parts you are now heat treating from Rc 23 to Rc 30. A uniform material which provides exceptional quality for Production, maintenance or special machine parts.