5140 alloy steel Structural 5140 alloy steel chemical composition

5140 steel is medium carbon modulation steel, cold heading die steel. The steel
is moderate in price, easy to process, and can obtain certain toughness,
plasticity and wear resistance after proper heat treatment. Normalizing can
promote tissue spheroidization and improve the cutting performance of blanks
with hardness less than 160HBS. Tempered at a temperature of 550~570℃, the
steel has the best comprehensive mechanical properties. The hardenability of
this steel is higher than that of S45C steel, and it is suitable for surface
hardening such as high frequency quenching and flame quenching.

Heat Treatment
AISI/SAE/ASTM 5140 Steel Heat Treatment
Heat treatment specification: quenching at 850℃, oil cooling; tempering at
520℃, water cooling, oil cooling
5140 surface quenching hardness is 52-60HRC, flame quenching can reach 48-55HRC
Nitriding treatment
1.7035 is a nitridable steel, and the elements it contains are conducive to
nitriding. 40Cr can obtain higher surface hardness after nitriding treatment,
the highest hardness of 40Cr after nitriding treatment can reach 72~78HRA, and
the core hardness can reach 43~55HRC.
Nitriding workpiece process route: forging – annealing – roughing –
quenching and tempering – finishing – stress relief – rough grinding –
nitriding – fine grinding or grinding. Since the nitrided layer is thin and
brittle, a high-strength core structure is required, so quenching and tempering
heat treatment should be performed first to obtain tempered sorbite to improve
the mechanical properties of the core and the quality of the nitrided layer.
Weldability of 5140 steel:
It is easy to segregate during crystallization, and is sensitive to
crystallization cracks (a kind of thermal cracks), and it is easy to crack in
arc craters and concave parts of welds during welding. The carbon content is
high, and it is easy to obtain a hardened structure (martensitic structure)
that is sensitive to cold cracks during rapid cooling. When the cooling rate of
the superheated zone is large, it is easy to form hard and brittle high-carbon
martensite to embrittle the superheated zone.
Welding process points
1. Generally, welding is carried out in the annealed (normalized) state.
2. The welding method is not limited.
3. Use larger line energy to appropriately increase the preheating temperature.
Generally, the preheating temperature and interlayer temperature can be
controlled between 250 and 300 °C.
4. The welding material should ensure that the composition of the deposited
metal is basically the same as that of the base metal, such as J107-Cr.
5. Quenching and tempering heat treatment should be carried out in time after
welding. If it is difficult to carry out the quenching and tempering treatment
in time, intermediate annealing or holding for a period of time at a
temperature higher than preheating can be carried out to eliminate diffusible
hydrogen and soften the structure. For products with complex structure and many
welds, an intermediate annealing can be performed after a certain number of
welds have been welded.

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