Heavy vehicle chassis: Which type of steel should you use ?

According to an industry report by Tech Sci Research, India's commercial vehicle market is expected to grow at a CAGR of 5.6% between FY2023 and FY2027. In FY2021, the country's commercial vehicles industry was valued at about $4 billion. This included a fleet of more than 1.6 million buses, of which 170,000 are public transport buses servicing 70 million people daily. Other types of heavy vehicles include goods vehicles, vehicle carriers, agricultural vehicles, trucks, cranes, and special vehicles.

The chief driver behind the growth of this segment is the use of heavy vehicles by end-use industries such as public transportation, construction, road transport, utilities, and others.

The manufacture of heavy motor vehicles (HMV) presents unique challenges. These include the need for raw and intermediate materials with a wide range of material properties, including higher yield strength, durability, fatigue-life, impact resistance, corrosion resistance, and high life-cycle cost, among others. In particular, heavy-duty HMV chassis need to be able to withstand sudden shock, twists, vibrations, and other stresses regularly, unlike chassis used in LMVs or two-wheelers.

It is thus important to carefully curate and select the right mix of steel types for the manufacture of HMV chassis. Let’s take a closer look.

Heavy vehicle chassis - Components and type of steel used

These are the different components that collectively form the chassis:

1. The frame of the chassis

2. Engine

3. Suspension system

4. Steering system

5. Braking system

6. Wheels and tires

7. Transmission system – clutch, gearbox, etc.

Chassis frame

The frame is the most important part of any vehicle, as it provides support and strength for the other components. The frame is made out of high-strength steel(HSS).

This type of steel has good resistance to wear, fatigue, and corrosion, and is stronger than low-alloy high-strength steel, but is not as strong as advanced high-strength steel (AHSS).

Engine

The steel used to make the engine block is more important than that used to make the pistons, and cylinder head, since it holds all other parts together.

As the engine is the main source of power for an HMV's drivetrain system, high-strength low alloy or HSLA steels are the ideal choice. HSLA steels have a higher yield strength than standard steels, which means they can be used under rough conditions without fracturing or cracking. This makes them a good fit for automotive applications where there's a lot of shock loading on the engine block.

As an alternative, an engine block can also be made from cast iron, which is a hardy, heavy-duty alloy of iron and carbon. It has a higher melting point than plain iron, which makes it stronger.

Suspension

The steel that is predominantly used to make suspension systems (such as leaf springs) for heavy automobiles is carbon-chromium spring steel (AISI 5160). It is renowned for its toughness, high yield strength, pliability, resilience, and high fatigue life. These physical qualities make this steel grade suitable for suspension applications.

Apart from carbon-chromium spring steel, four alternative materials are also popularly used for HMV suspensions -

• Carbon steel (good strength and durability but lower corrosion resistance compared to other alloys)

• Stainless steel (better durability and corrosion resistance but expensive compared to carbon steel alloys)

• High alloy steel (high strength, good corrosion resistance, and good ductility, but relatively expensive)

• Cast iron (relatively inexpensive high-strength alloy but is very heavy in weight, and has poor resistance to wear when compared with stainless steel or carbon steel)

Steering system

The type of steel used in the steering system varies depending on what type of vehicle it is for. For example, a sports car might use a different type of steel than an SUV would.

Broadly, there are three types of steel commonly used in steering systems: mild steel, stainless steel, and aluminum alloyed steel.

Braking system

The most common type of steel used for brake discs is stainless steel (an alloy of chromium and steel).

The braking system in heavy motor vehicles uses four different types of steel -

Cast iron is used in the brake drums, shoes, and linings

Bearing steel is used in the bearing races and bearings

Stainless steel is used in drums and shoes

High-strength steel is specifically used in linings and brake shoes

Wheels and tyres

Wheels and tyres can be made from different types of steel depending on their purpose -

Stainless steel – This type of steel is more expensive than carbon steel but has better corrosion resistance, compared to carbon steel. It also has better wear resistance than carbon steel but is lower than alloy steel (which is made from iron and other metals). Stainless steel is resistant to rusting, so it is often used on wheels and in tyres.

Alloy steels – These types of steels are made by combining several different types of metal into one composite metal which leads to higher strength and greater resistance to wear.

Transmission

The transmission system of heavy vehicles is made up of various components including the flywheel, clutch, gearbox and gears, collars, and drive shafts. Various types of steel are utilised for the transmission system as each of these components serves a different purpose, with a wide range of operational constraints.

In the transmission, clutch systems, and differential systems - carbon-steel alloys, cast iron, and forged steel are typically used.

Advanced high-strength steel (AHSS) viz. AISI 1045 is most commonly used for transmission systems because it has a higher yield strength than other types of steel. In India, AHSS grades that are typically used in transmission systems include IS 2062:2011 E250A & IS 15961:2012 YS550

Manufacturing HMV chassis is a complex process involving the selection and production of different steel alloys. Automobile MSMEs can control their manufacturing costs by partnering with a single, one-stop supplier like JSW One Platforms to purchase a wide variety of steel grades under one roof. Choose from a large selection of products, including IS-certified coils, sheets, wire rods, and color-coated steel.

You can place an online order and have your materials delivered hassle-free. Get in touch!