45# Steel- SCALE STEEL.

​45# steel is carbon structural steel with carbon content of 0.45%. It is characterized by cheap price, good cutting performance, high hardness after quenching, [SCALE STEEL]good strength and toughness and certain wear resistance after quenching and tempering treatment. It is widely used in the manufacture of structural parts and medium and low grade plastic molds.
"45# steel" is a popular name, the symbol is generally[SCALE STEEL] written as "45#".Actually GB standard steel number is "45", it is not a serial number, read as "45# steel" is not very accurate.
Chemicals
The similar grades of 45 steel are S45C(JIS) and 1045(AISI).In addition, China's metallurgical technology standards have SM45 marks specifically [SCALE STEEL]indicated the use of plastic mold.Compared with 45 steel, SM45 steel has lower phosphorus and sulfur content and better steel purity.

Standards GB/T 699 Grades 45
C 0.42~0.50 Cr ≤0.25
Si 0.17~0.37 Ni ≤0.30
Mn 0.50~0.80 Cu ≤0.25
P,S P S
(45) ≤0.035 ≤0.035
(45A) ≤0.030 ≤0.030
(45E) ≤0.025[SCALE STEEL] ≤0.020
Standards YB/T 094 AISI JIS G4051
Grades SM45 1045 S45C
C 0.42~0.48 0.43~0.50 0.42~0.48
Si 0.17~0.37 -- 0.15~0.35
Mn 0.50~0.80 0.60~0.90 0.60~0.90
P ≤0.030 ≤0.030 ≤0.030
S ≤0.030 ≤0.050[SCALE STEEL] ≤0.035

Mechanical Property（GB/T 699-1999）
Sample Size（mm） 25
Suggested Heat Treatment（℃） Normalizing 850
Quenching 840
Tempering 600
Mechanical Property Tensile StrengthMPa ≥600
Yield Strength MPa ≥355
Elongation%[SCALE STEEL] ≥16
Reduction of Area% ≥40
Impact Test Value J ≥39
HBS Before Heat Treatment ≤229
Annealing ≤197
Note: For steel larger than 80mm, the elongation and section shrinkage after fracture are allowed to be reduced by 2% and 5% respectively compared with the above table.

Heat Treatment and Hardness
Recommended quenching process specification: [SCALE STEEL]quenching temperature is 820~860℃, water or oil cold, hardness ≥50HRC.
The recommended tempering process specification: tempering temperature is 500~560℃, air cooling, hardness is 25~33HRC.
Tempering in this temperature range is a tempering treatment.The strength, plasticity and toughness of 45 steel are well balanced by tempering and tempering, and the comprehensive performance is good, which can adapt to the environment of alternating load.
After tempering and tempering, 45 steel has [SCALE STEEL]low surface hardness and no wear resistance.So commonly used quenching and tempering + surface hardening to improve the surface hardness of parts.

Relationship between Temperature and Hardness under Tempering Treatment:
Tempering
Tem Quenching Unit（℃）
200 300 400 500 550 600

HRC 57 55 50 41 33 26 22

Note: ① quenching is water quenching at 840℃.(2) 45 steel after quenching without tempering, hardness is greater than HRC55 [SCALE STEEL](up to HRC62) is qualified.The maximum hardness of practical application is HRC55 (HRC58 for high frequency quenching).