Carbon Steels Machining Processes

Carbon structural steel such as Q235, Q345. (Q:yield strength, Q235 is σs=235MPa.). We generally adopt Q235 as substitute of S235J2, and adopt Q355 as substitute of S355J2. 

They are widely used as welded and riveted steel structural parts, and a few are used to make various machine parts. 

Q235 has good ductility and toughness, and is easy to formed and welded. It is mostly used as reinforcement and steel structural parts, and also used as rivets, railway spikes and various mechanical parts, such as bolts, tie rods, connecting rods, etc.

The main constituent elements of Q345 steel is basically the same as that of 16Mn steel. But Q345 is added V, Ti, Nb. The comprehensive mechanical properties of Q345 steel should be better than that of 16Mn steel.

For example, the grades C45, 65Mn. The numbers 45 and 65 represent 0.45% and 0.65% carbon content.

High-quality carbon structural steel is mainly used to manufacture mechanical parts, and is generally used after heat treatment.

Common steel grades and uses:

C20, good plasticity and weldability, used for parts with low strength requirements and carburized parts, such as hoods, welding containers, small shafts, nuts, washers and carburized gears;

C45, 40Mn have good comprehensive mechanical properties after quenching and tempering, and are used for mechanical parts with large force, such as gears, connecting rods, machine tool spindles, etc..

40Cr is one of the most widely used steel grades, is an alloy structural steel. 40Cr’s main features: After quenching and tempering treatment, 40Cr has good comprehensive mechanical properties, low temperature impact toughness and low notch sensitivity, good hardenability, high fatigue strength can be obtained during oil cooling, and parts with complex shapes are prone to cracks during water cooling. After tempering or quenching, the machinability is good, but the weldability is not good, and cracks are easy to occur. It should be preheated to 100 ~ 150℃ before welding. 40Cr can also have the treatments of carbonitriding and high-frequency surface quenching.

After quenching and tempering, 40Cr is used to manufacture medium-speed and medium-load parts, such as machine tool gears, shafts, worms, spline shafts, thimble sleeves, etc. 

After quenching and tempering and high frequency surface quenching, 40Cr is used to manufacture parts with high surface hardness and wear resistance, such as gears, shafts, main shafts, crankshafts, mandrels, sleeves, pins, connecting rods, screws and nuts, intake valves, etc. 

After quenching and medium-temperature tempering, 40Cr is used to manufacture heavy-duty, medium-speed impact parts such as oil pump rotors, sliders, gears, spindles, collars, etc. 

After quenching and low-temperature tempering, 40Cr is used to manufacture heavy-duty, low-impact parts, wear-resistant parts, such as worm, spindle, shaft, collar, etc. 

The 40Cr carbonitriding part is used to manufacture transmission parts with larger size and higher low temperature impact toughness, such as shafts and gears.

For example T12 steel. The carbon content is 1.2%.

Carbon tool steel has high strength, hardness and good wear resistance, and is suitable for the manufacture of various low-speed cutting tools.

Common steel grades and uses:

T7, T8 make parts that withstand a certain impact and require toughness, such as sledgehammers, punches, chisels, woodworking tools, scissors.

T9, T10, T11 manufacture tools that require high hardness and high wear resistance with low impact, such as taps, small drills, dies, hand saw blades.

T12, T13 make tools that are immune to impact, such as files, scrapers, razors, measuring tools.

For example, the grade ZG200-400 represents the cast steel with yield stengthσs=200MPa and tensile strengthσb=400MPa. 

It is mainly used to manufacture relatively important mechanical parts with complex shapes and high requirements on mechanical properties, but it is difficult to form by forging and other methods in the process, such as gearbox casings of automobiles, couplers and couplings of locomotives and vehicles.