AISI 1045 Steel/C45 Steel

Is AISI 1045 mild steel?

No, 1045/C45 steel is a medium carbon structural steel with good cold and hot workability, good mechanical properties, low price, and wide sources, so it is widely used. Its biggest weakness is that workpieces with low hardenability, large section size, and high requirements should not be used.

The quenching temperature of 1045/C45 steel is A3+(30~50) ℃. In actual operation, the upper limit is generally taken. Higher quenching temperatures can speed up workpiece heating, reduce surface oxidation, and improve work efficiency. 

To homogenize the austenite of the workpiece, the sufficient holding time is required. If the actual charging amount is large, it is necessary to extend the holding time appropriately. 

Otherwise, insufficient hardness may occur due to uneven heating. However, if the holding time is too long, the defects of coarse grains and oxidation decarburization will also occur, which will affect the quenching quality. 

We believe that if the furnace loading is greater than the provisions of the process document, the heating and insulation time should be extended by 1/5.

Because the hardenability of 1045/C45 steel is low, a 10% brine solution with a high cooling rate should be used. After the workpiece is filled with water, it should be quenched, but not cooled. If the workpiece is cooled in brine, it may crack. 

This is because when the workpiece is cooled to about 180 ℃, the austenite rapidly transforms into martensite, causing excessive structural stress. Therefore, when the quenched workpiece is rapidly cooled to this temperature zone, the slow cooling method should be adopted. 

As the outlet water temperature is difficult to master, it must be operated by experience. When the workpiece in the water stops shaking, the outlet water can be cooled by air (oil cooling is better). 

In addition, the workpiece should be dynamic rather than static when entering the water. It should move regularly according to the geometric shape of the workpiece. The static cooling medium plus the static workpiece will lead to uneven hardness and stress, leading to large deformation and even cracking of the workpiece.

The hardness of quenched and tempered parts of 1045/C45 steel should reach HRC56~59, which may be lower if the section is large, but not lower than HRC48. Otherwise, it means that the workpiece has not been completely quenched, and sorbate or even ferrite structure may appear in the structure. This structure is still retained in the matrix through tempering, which cannot achieve the purpose of quenching and tempering.

For high-temperature tempering of 1045/C45 steel after quenching, the heating temperature is usually 560~600 ℃, and the hardness is required to be HRC22~34. Because the purpose of quenching and tempering is to obtain comprehensive mechanical properties, the hardness range is relatively wide. 

However, if the drawing has hardness requirements, the tempering temperature shall be adjusted according to the drawing requirements to ensure the hardness. If some shaft parts require high strength, the hardness is required to be high; However, some gears and shaft parts with keyways need to be milled and inserted after quenching and tempering, so the hardness requirements are lower. 

As for the tempering and heat preservation time, it depends on the hardness requirements and the size of the workpiece. We believe that the hardness after tempering depends on the tempering temperature and has little to do with the tempering time, but it must be back penetrated. Generally, the tempering and heat preservation time of the workpiece is more than one hour.

Physical Properties of AISI 1045

What is 1045 steel used for?

1045/C45 steel is widely used in machinery. When it is not heat treated, HB ≤ 229; Heat treatment: normalizing; Impact energy: Aku ≥ 39J; It has high strength, good plasticity, and toughness. 

1045/C45 steel plate is qualified if its hardness is greater than HRC55 (up to HRC62) after quenching and before tempering. After heat treatment, it can reach HRC42-46 after tempering, which can not only ensure its good mechanical properties but also obtain the surface hardness requirements. 

It is used to make small sections of quenched and tempered parts with large loads and large normalized parts with small stress, As well as the surface hardened parts with low requirements on the central strength, such as pins, guide pillars, watch needles, and other components.

Welding AISI 1045 steel

1045 steel is suitable for hydrogen welding and argon arc welding, but not suitable for gas welding. Preheating is required before welding, and stress relief annealing shall be carried out after welding.