ASTM A194 Heavy Hex Nuts

Heavy hex nuts are fasteners that are thicker and wider than a standard finished nut of the same size.heavy hex nuts a194 2h 2hm 7 7m 8 8m They are used in conjunction with mating bolts to fasten components together by a combination of the threads’ friction and slight stretching of the bolt. These nuts have a greater bearing surface area and are a stronger option than regular nuts, which may fail in high-pressure or high-temperature applications. They can be manufactured from either a hot forging process or cold forging, and are typically made of an alloy steel that includes carbon, manganese, phosphorus, sulfur, silicon, and tin.

The ASTM A194 specification covers a variety of carbon and alloy steel nuts intended for use with bolts in high-pressure or high-temperature service.heavy hex nuts a194 2h 2hm 7 7m 8 8m It also covers austenitic stainless-steel nuts in the size range 1/4 through 4 in. and metric M6 through M100 nominal. This specification covers nuts of the following grades:

Grade 2HM heavy hex nuts are quenched and tempered alloy steel nuts that are 100% hardness tested.heavy hex nuts a194 2h 2hm 7 7m 8 8m They are usually paired with A193 Grade B7M bolts in applications where exposure to hydrogen sulfide gas can cause problems with embrittlement. They have a greater strength than other grades of hex nuts and are more resistant to dilation (widening or stretching).

All nuts shall be marked with the grade designation, followed by the symbol for the heat treatment process. Nuts shall be quenched and tempered at a temperature sufficient to achieve full tempering, which must include a minimum of 1h at the specified temperature. A final stress relief operation, at or above the minimum tempering temperature, may be done after forming, machining, and tapping operations.

In addition to the hardness tests required by 8.1.5, a proof load test shall be performed on one sample nut of each diameter and series, from each grade and heat number, after all production heat treatments. Proof loads prevail over hardness limits when a conflict exists.

Nuts that require proof loads exceeding 160 000 lbf or 705 kN shall, unless Supplementary Requirement S1 or S4 are invoked in the order, be subjected to cross-sectional hardness testing. Nuts machined from bar stock that has been heat treated in accordance with this requirement need not be reheat-treated, provided that they are identified by the actual heat analysis.

The ASTM A194 specification also requires that the nuts be tempered for a period of time at the specified temperature. This should include a minimum of 1h at the temperature, with the exception of Grade 8 nuts that must be carbide-solution treated by heating to a temperature at which chromium carbides can dissolve, followed by rapid cooling to prevent reprecipitation. A proof-load test, in accordance with 8.1.5, shall be conducted on the nuts after the carbide-solution treatment.

By:Ningbo Hope Fasteners Co., Ltd.