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, [TJC 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[TJC 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 [TJC 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[TJC 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[TJC 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%[TJC 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: [TJC 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 [TJC 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 [TJC STEEL](up to HRC62) is qualified.The maximum hardness of practical application is HRC55 (HRC58 for high frequency quenching).