Serves to support vehicle weight, absorb bumps and locate axle to the vehicle
During the serves cycle, leaf spring must not exceed certain level of stress to avoid settling or premature failure. Therefore, the choice of chemical composition of the spring steel should be such to get sufficient harness to bear the required level of stress. Spring steel flats are available in various chemical compositions of alloy steel. The most common ones are -
| GRADE | C | Si | Mn | S | P | Cr | V |
| EN 45A | 0.55-0.65 | 1.70-2.10 | 0.70-1.00 | 0.040 Max | 0.040 Max | - | - |
| 55 Si7 | 0.55-0.60 | 1.50-1.80 | 0.70.1.00 | 0.045 Max | 0.045 Max | - | - |
| 60 Si7 | 0.55-0.65 | 1.50-2.00 | 0.80-1.00 | 0.040 Max | 0.040 Max | - | - |
| 65 Si7 | 0.60-0.68 | 1.50-1.80 | 0.70-1.00 | 0.050 Max | 0.050 Max | - | - |
| 55 Si Cr7 | 0.50-0.60 | 0.70-1.00 | 0.50-1.80 | 0.025 Max | 0.025 Max | 0.20-0.40 | - |
| 60 Si Cr7 | 0.57-0.65 | 1.50-1.80 | 0.70-1.00 | 0.030 Max | 0.030 Max | 0.20-0.40 | - |
| 65 Si Cr7 | 0.60-0.68 | 1.50-1.80 | 0.00-1.00 | 0.050 Max | 0.050 Max | 0.20-0.40 | - |
| 50 Cr V4 | 0.47-0.55 | 0.15-0.40 | 0.70-1.00 | 0.035 Max | 0.035 Max | 0.90-1.20 | 0.10-0.20 |
Other grades can be used according to customer requirements.
The desired grade of spring steel, of required width and thickness is cut to specification. Than passing through the processes that are industry recognized and ultimate, quality leaf springs are produced without variation.
Gandhara is on record as being the first Leaf Spring manufacturing plant to run the heat treatment cycle on Compressed Natural Gas (CNG). Not only being an Eco-friendly fuel, CNG also has an undisputed edge over other fuels such as LDO / Furnace Oil used to run the heat treatment cycle in producing quality. The hardening and tempering furnaces run on CNG, controls the de-carbonization limits of the finished product to minimum, thereby giving more value for money to its customers.
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2% Withal 200% |
2% Wital 200% |
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| Microstructure |
Tempered |
Tempered |
| De-Carbonized Layer Hardness |
0 - 0.1mm |
0.1 - 0.3mm |
| Surface |
HRC 38(BHN - 364) |
HRC 32(BHN - 302) |
| Core |
HRC 45(BHN - 430) |
HRC 45(BHN - 430) |
The above record has been validated through a test conducted by Process & Product Development Centre (A Government of Pakistan Society, Ministry of Industry).
Hardness Testing
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Range of hardness after heat treatments : |
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| 50Cr4V2 | 409 to 485 HB | |
| 60Cr4V2 | 432 to 485 HB | |
| 55Si7 | 378 to 432 HB | |
| 60Si7 | 363 to 435 HB | |
| 65Si7 | 363 to 432 HB | |
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Variation in hardness of any one leaf does not vary by more than 7% of the range specified above. Hardness Testing does according to IS: 1500 : 1983. |
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Load Testing
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Downward load test load applied to test stress equal to 90% of the yield stress of the spring leaf material in its heat treated condition. All Leaf Springs are tested for minor and major defects. |
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Spring Rates below |
Tolerance on Normal Loaded Rate |
Tolerance on Normal Loaded Height |
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4.5 KN/25 mm |
+5 % |
+3 mm |
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Spring Rates above |
+7 % |
+5 mm |
