45 steel is a carbon structural steel with a carbon content of 0.45%. It is characterized by low price, good machining performance, high hardness after quenching, good toughness and certain wear resistance after quenching and tempering. It is widely used in the manufacture of structural parts and low-grade plastic molds.
Let's take a look at 45 steel.
"45 steel" is a popular name, and the symbol is generally recorded as "45#". In fact, the GB standard steel number is "45", which is not a sequence number, and it is not very accurate to read "45 steel".
The similar grades of 45 steel are S45C (JIS) and 1045 (AISI). In addition, the SM45 grade in my country's metallurgical technical standards specifically indicates the use of plastic molds. Compared with 45 steel, SM45 has lower phosphorus and sulfur content and better steel purity.
>>Ingredient Specifications
Standard | GB/T 699 | Grade | 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 |
Classified by Phosphorus and Sulfur | P | S | |
45 | ≤0.035 | ≤0.035 | |
45A | ≤0.030 | ≤0.030 | |
45E | ≤0.025 | ≤0.020 | |
Standard | YB/T 094 | AISI | JIS G4051 |
Grade | 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 | ≤0.035 |
>>mechanical property（GB/T 699-1999）
Sample blank dimension（mm） | 25 | |
Recommended heat treatment（℃） | normalizing | 850 |
quenching | 840 | |
tempering | 600 | |
Mechanical properties | tensile strength MPa | ≥600 |
Yield Strength MPa | ≥355 | |
Elongation % | ≥16 | |
reduction of area % | ≥40 | |
Impact energy J | ≥39 | |
HBS | not heat-treated steel | ≤229 |
annealed steel | ≤197 |
Note: For steels larger than 80mm, the elongation after fracture and the reduction in area are allowed to be reduced by 2% and 5% respectively compared with the above table.
>>Heat treatment and hardness
Recommended quenching process specification: quenching temperature is 820~860℃, water cooling or oil cooling, hardness ≥50HRC.
Recommended tempering process specification: tempering temperature is 500~560℃, air cooling, hardness is 25~33HRC.
Tempering in this temperature range is quenching and tempering. Quenching and tempering makes the strength, plasticity and toughness of 45 steel get a better balance, the comprehensive performance is good, and it can adapt to the alternating load environment.
The surface hardness of 45 steel after quenching and tempering is low, and it is not wear-resistant. Therefore, quenching and tempering + surface quenching is commonly used to improve the surface hardness of parts.
The relationship between tempering temperature and hardness is shown in the following table:
tempering temperature | After quenching | （℃） | |||||
200 | 300 | 400 | 500 | 550 | 600 | ||
Hardness HRC | 57 | 55 | 50 | 41 | 33 | 26 | 22 |
Note: ① Quenching is water quenching at 840°C. ② 45 steel is qualified if the hardness is greater than HRC55 (up to HRC62) after quenching and before tempering. The highest hardness in practical application is HRC55 (induction quenching HRC58).