Cf53 Steel Camshaft: What Are the Effects of Normalizing Process on Its Mechanical Properties?

1. Preface

Camshaft is one of the key parts in the valve train of internal combustion engine.

It is used to control the valves to open and close in time according to a certain working sequence and valve phase, and ensure that the valves have sufficient lift.

It plays a decisive role in the performance of the whole valve train.

In a four stroke engine, the rotational speed of the camshaft is 1 / 2 of the crankshaft, so the rotational speed of the camshaft is very high and needs to bear a large torque.

During operation, there is a high periodic contact stress and a fast relative sliding speed between the cam surface and the rocker arm or tappet, which requires that the camshaft has sufficient toughness and rigidity, and the cam surface has good wear resistance and impact resistance.

2. Research background

The product of model M belongs to marine large-scale diesel engine.

The camshaft material of this product model is Cf53 steel.

During the tensile performance test of the camshaft body in the early stage, the yield strength is low.

After the supplier adjusts the heat treatment process, the yield strength is qualified and the tensile strength is low (see Table 1).

Table 1 mechanical property test of Cf53 steel camshaft

ProjectRm/MPaRp0.2/MPa
Standard value710~850≥400
First test717358
Second test685408

In addition, in daily production, the camshaft made of Cf53 steel (equivalent to 55 steel) has the problem of low hardness (< 200 HBW).

In view of the above quality problems, we conducted investigation and analysis on the production site of the supplier company of M-type camshaft in the early stage, and put forward improvement measures for the adjustment of process parameters such as normalizing equipment, normalizing temperature and cooling speed.

See Table 2 for the process adjustment scheme.

Table 2 adjustment scheme for heat treatment process of Cf53 steel camshaft

ProjectHeat treatment facilitiesProcess route  Cooling method
Before adjustment  Trolley furnace  820 ℃ normalizingForced air cooling 
After adjustment  Push plate normalizing wire840 ℃ normalizingStrong wind cold

In this post, the physical and chemical properties of the body material of the improved Cf53 steel camshaft are analyzed, and the effect of normalizing process on the mechanical properties of the Cf53 steel camshaft is studied, so as to provide a reasonable process plan for improving the comprehensive properties of the camshaft.

3. Material analysis

3.1 Chemical composition

The chemical composition of the camshaft was inspected, and the results are shown in Table 3, which meet the requirements of material specification: Steel camshaft (enterprise standard) Q / WCG 610.22.

Table 3 chemical composition of cf53 steel camshaft (mass fraction) (%)

ProjectCSiMnCrNiPS
Standard value0.52~0.570.15~0.350.60~0.80≤0.35≤0.30≤0.025≤0.035
Detection value0.5610.2410.7490.2120.0110.0090.010

3.2 Mechanical properties

The tensile properties at room temperature were tested on the tensile testing machine in the physical and chemical laboratory (see Fig. 1).

Cf53 Steel Camshaft: What Are the Effects of Normalizing Process on Its Mechanical Properties? 1

Fig. 1 Tensile property test

And detects the hardness of the camshaft test bar.

See Table 4 for mechanical property test results of camshaft test rod.

Table 4 mechanical property test results of camshaft body

ProjectHeat  treatmentRm/MPaRp0.2/MPaA(%)Z(%)HardnessHBW
Standard valuenormalizing  710~850≥400≥16≥40214~252
1 # sample normalizing  7914291842222
2 # samplenormalizing  7534091947226

The inspection indexes meet the requirements of material specification: Steel camshaft (enterprise standard) Q / WCG 610.22.

The mechanical property test results of Cf53 steel camshaft after process adjustment are compared with those before process adjustment (see Table 1), and the mechanical property, especially the tensile strength (RM), is greatly improved.

3.3 Metallographic structure of body

Fig. 2a shows the structure of cam shaft center of model m after corrosion with 4% nitric acid alcohol.

There is an elongated area with a diameter of 1.5 mm at the center position B with completely different display colors.

The metallographic structure is shown in Fig. 2b.

The structure characteristics of area B are obviously different from that of area A, forming regional segregation.

Cf53 Steel Camshaft: What Are the Effects of Normalizing Process on Its Mechanical Properties? 2

Fig. 2 macro structure and metallographic structure of cam axis after corrosion

Fig. 3 shows the metallographic structure of area a of cam shaft center of model M.

The metallographic microstructure is evaluated according to GB / T 13320-2007 metallographic structure rating diagram and evaluation method of steel die forgings.

The core structure is pearlite + ferrite, with uniform grain size.

The structure rating is grade 2.

According to GB / T 6394-2002 method for determination of average grain size of metals, the actual grain size of austenite is grade 8, which meets the technical requirements.

Fig. 4 shows the metallographic structure of area B of the cam shaft center of model M.

The core structure is mainly pearlite, with a small amount of ferrite distributed, and the pearlite grain is relatively uniform.

Cf53 Steel Camshaft: What Are the Effects of Normalizing Process on Its Mechanical Properties? 3

Fig. 3 metallographic structure of area 4 of cam shaft center

Cf53 Steel Camshaft: What Are the Effects of Normalizing Process on Its Mechanical Properties? 4

Fig. 4 metallographic structure of area B of cam shaft center

The central region of camshaft bar is the last crystallization position, and the content of C, S, P and other elements is high.

The W C of Cf53 steel is 0.52% ~ 0.57%, and the segregation region of the core component is close to the eutectoid point component, so the pearlite structure is mainly formed, and only a small amount of ferrite structure is formed.

The center segregation is rated as grade 1 according to GB / T 1979-2001 structural steel macrostructure defect rating diagram, which is within the allowable range of technical requirements.

Therefore, the segregation area of the cam shaft center should be controlled, the purity of the molten steel should be improved, the reasonable pouring process should be adopted, and the large forging ratio should be adopted during the forging and rolling of the bar blank.

Since severe segregation will have a significant impact on the quality of steel, the inspection of segregation defects should be reasonably controlled during the incoming inspection of bar materials to ensure the quality of billet.

3.4 Metallographic structure of surface induction hardening layer

See Table 5 for the surface induction hardening layer depth and hardness test results of cam peach tip, base circle and support Journal (see Fig. 5).

Cf53 Steel Camshaft: What Are the Effects of Normalizing Process on Its Mechanical Properties? 5

Table 5 detection results of camshaft induction paint fire layer

 

Peach tip

Base circle

Bearing journal

Quench-hardened case/mm

Hardness

HRC

Quench-hardened case/mm

Hardness

HRC

Quench-hardened case/mm

Hardness

HRC

Criterion

1.5~5.5

59~63

1.5~3.5

≥55

1.5~3.5

≥55

Test

5.0

61.2

3.5

63.4

3.5

63.2

Meet the standard requirements.

The metallographic structure of the induction hardening layer is shown in Fig. 6.

The structure is evaluated according to QC / T 502-1999 metallographic inspection of automotive induction hardening parts.

The structure is fine needle martensite, rated as grade 4, and meets the requirements of standard 20200718.

Cf53 Steel Camshaft: What Are the Effects of Normalizing Process on Its Mechanical Properties? 6

Fig. 6 metallographic structure of induction hardening layer

3.5 Conclusion

Through physical and chemical analysis of the M-type camshaft made of Cf53 steel after process adjustment, the following conclusions are drawn.

1) The chemical composition of camshaft of model M meets the requirements.

2) The mechanical properties (tensile strength, yield strength, elongation, reduction of area and hardness) of camshaft can be improved by increasing normalizing cooling speed.

3) The metallographic structure of the camshaft body of model M meets the requirements.

There is a level 1 central segregation area at the center of the camshaft body, with a diameter of 1.5mm distributed along the center line of the camshaft.

4) The metallographic structure of induction hardening layer of M-type camshaft meets the requirements.

4. Improvement suggestions

1) The supplier shall solidify the normalizing process of Cf53 steel M-type camshaft according to the process of this adjustment and trial production, and improve the relevant process documents.

2) The inspection of segregation defects shall be reasonably controlled to ensure the quality of the billet when the bar material enters the factory.

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