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The differences between 304 and 45# steel shaft

In mechanical design and processing, we need to choose the right materials to fully utilize their characteristics and ensure that the equipment operates well and stably. Each material has its own advantages and disadvantages, which requires us to identify and utilize its strengths while controlling its weaknesses. Directly using the most expensive material is not the optimal solution.

Experienced engineers will come up with the optimal solution for the cost-effectiveness of material selection.

Today, we will provide a case study on the commonly used materials 304 and 45 # steel encountered in our factory,

For example, the shaft of the feeder precision cnc machining  is made of 45 # steel. Although the surface is coated with anti rust paint, it is still prone to rusting. I originally planned to use 304 instead. So we evaluated its differences. Simply for rust prevention, switching to 304 is completely fine and easy to use; But if there are requirements for load-bearing, wear-resistant, high-strength, and precision fitting, 304 is not as good as 45 # and has shortcomings.

1. The advantages of switching to 304

Rust prevention can be directly applied to damp, damp, and slightly acidic or alkaline environments, without rusting. There is no need to perform blackening, galvanizing, or oil coating maintenance, which is much more worry free.

Corrosion resistance, long service life, outdoor, water mist, and humid workshop conditions, much more durable than 45 # bare shaft.

2. The fatal flaw of 304 compared to 45 # (which many people overlook)

Low hardness, not wear-resistant. After quenching and tempering, the hardness can reach HB220~280; 304 is originally soft and cannot be quenched as a whole without quenching. It is easy to grind and wear quickly, and the shaft diameter is prone to decrease and the gap becomes larger.

The strength and rigidity are not as good as shafts of the same thickness as 45 #. 304 has poorer bending and torque resistance than 45 #, and is prone to bending under heavy load, long axis, and cantilever conditions. Easy to bite, stick to the knife, and fit tightly. 304 stainless steel has high plasticity and is prone to cold welding. It is also prone to bite and cannot be removed after prolonged fitting with bearings and sleeves.

The material cost is much higher than 45 # due to its higher price.

Simply from a theoretical analysis, there are other options:

2.1. Continue to use 45 # steel+surface treatment quenching and tempering+blackening/chrome plating/hard chrome plating/quenching, which not only maintains strength and hardness, but also prevents rust and wear, with a lower cost than 304.

2.2. Changing to 2Cr13/4Cr13 stainless steel can be quenched and hardened, with hardness, wear resistance, and strength close to 45 #. It is also rust resistant and used specifically for shafts.

2.3. Use 304 cold processing rods instead. 304 cold processed rods are much better than ordinary hot-rolled 304, but still cannot replace quenched and tempered 45 #; Only suitable for light load, low speed, and rust proof working conditions, heavy load wear resistance is still not sufficient.

3. The improvement of 304 cold processing rod compared to ordinary 304

The strength and hardness are significantly increased by cold drawing deformation strengthening, and the tensile strength and yield strength are both increased. The hardness can reach around HB200, which is much harder than annealed soft 304.

High straightness and outer diameter accuracy, precise rod tolerance, good roundness, can be directly used as the optical axis, eliminating the need for precision machining and rounding.

Good surface finish does not require additional grinding, making the appearance and assembly more comfortable.

Whether the rust prevention ability remains unchanged or the standard 304 corrosion resistance, it does not rust in humid and humid environments, solving the pain point of your original 45 # rust.

4. Shortcomings still exist (hard wounds that cannot be bypassed)

The hardness is still much lower than that of quenched and tempered 45 #: HB240-280, and even high-frequency quenching to HRC45+cold drawn 304: quenching hardening cannot be achieved, and even cold drawing cannot increase the wear resistance hardness. Long term friction with the shaft sleeve and bearing is still prone to wear.

Still prone to sticking and biting, the austenitic material characteristics of stainless steel have not changed. When combined with copper sleeves and bearing steel, it is prone to fuzzing, locking, and pulling during long-term operation, making it more prone to jamming than 45 #.

Compared to 45 # with the same shaft diameter, it is more prone to bending and fatigue deformation under heavy load, cantilever, and frequent reciprocating force.

5.Cost effective first choice: Continuing with 45 # tempering+hard chrome plating, the hardness, wear resistance, and strength are fully retained, rust prevention is thorough, the cost is lower than 304, and the most commonly used shaft type.

Be sure to use stainless steel material: Choose 2Cr13 cold drawn rod for quenching and tempering, with a hardness of HRC40+. It is wear-resistant, strong, and rust resistant, making it more suitable for use as a load-bearing shaft than 304 cold drawn rod.

Just want to save trouble and replace it directly: use a 304 cold processed precision drawing rod to accept moderate wear resistance, cannot be overloaded, only seeking no rust, qualified assembly, completely usable.

Why did the company ultimately choose 304 instead of 45 #? Let's make a simple mnemonic, I believe readers will guess the reason. Save money in a dry indoor environment with 45#

Moisture requires rust prevention and wear resistance, directly 2Cr13

Long term immersion in water, seaside, and minor chemical treatments, only 304 can be used