The high carbon content and chromium content of martensitic steels enable them to maintain their martensitic structure after heat treatment. The transformation of their structure causes volume changes and produces stress, thereby improving hardness and reducing plasticity. This feature is particularly important for the impact of welded joints, so it is easy to cause cracks in the heat affected zone after welding. The excellent high hardness of martensitic steel makes it more excellent in application fields. The representative steel type SUS440C is widely used.

What is SUS440C and what is its chemical component element carbon and chromium content.

The SUS440C stainless steel brand is high chromium and carbon magnetic stainless steel. The material structure is martensite. It has high ultimate tensile strength, reasonable corrosion resistance, and strong hardness and wear protection. After a heat treatment process, stainless steel 440C can provide durable indentation and wear protection in many other stainless steel alloys. The quality of all discussions is due to the very high carbon content. These rugged qualities make stainless steel 440C primarily suitable for use with valve components and ball bearings. The carbon content of 440C stainless steel exceeds 420A stainless steel, so 440C can obtain higher hardness after treatment.

Chemical composition of SUS440C stainless steel:

Carbon C: 0.95~1.20

Silicon Si: ≤ 1.00

Manganese Mn: ≤ 1.00

Sulfur S ：≤0.030

Phosphorus P: ≤ 0.040

Chromium Cr: 16.00 ～ 18.00

Nickel Ni: allowable content ≤ 0.60

Molybdenum Mo: ≤ 0.75 can be added

What are the other standard equivalent materials for SUS440C?

In the JIS standard, the equivalent material is referred to as SUS 440C section steel.

In DIN standards, the equivalent material is referred to as 1.4125 steel.

In the UNS standard, the equivalent material is referred to as S44000 section steel.

How can I increase the hardness of SUS440C to 55HRC?

SUS440C heat treatment process: quenching+tempering

When tempered at 440°C, a Rockwell hardness of 60 HRC can be obtained. Temper for at least one hour. Tempering above 400 ° C is not recommended as this can lead to reduced corrosion resistance and impact performance.

Temperature [° C] 150 200 250 300 350

Hardness [HRC] 60 59 57 56 56

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