High-Carbon Chromium Bearing Steel Tube

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Introduce High-Carbon Chromium Bearing Steel Tube

The most often used steel for making bearings and bearing parts is high carbon chromium bearing steel, which is a significant bearing steel category. The bearings performance and lifespan are directly influenced by the complexity of its manufacturing process.

What is the High-carbon chromium bearing steel tube?

The high-carbon chromium-bearing steel is a high-grade iron-carbon alloy steel. Its high chromium and carbon concentration is what makes it unique. In general, the chromium level ranges from 1% to 1.6%, whereas the carbon content ranges from 0.60 to 1.7%.

Good fatigue resistance, appropriate elasticity and toughness, high and consistent hardness following quenching and tempering, an easily controllable alloy composition, and a well-established heat treatment technique are all features of high-carbon chromium-bearing steel. It is extensively utilized both domestically and internationally in the bearing production sector.

⚑ Standards: ASTM A295, GB/T 18254, JIS G4805, DIN 17230

⚑ Grades:

USA	GB	JIS	EN
AISI 52100	GCr15	SUJ2	100Cr6

Chemical Composition (%)

Grade

As+Sn+Sb

GCr15

0.95-1.05

0.15-0.35

0.25-0.45

≤0.025

≤0.02

1.4-1.65

≤0.25

≤0.1

≤0.25

≤0.0012

≤0.05

≤0.005

≤0.04

≤0.075

≤0.002

GCr15A

≤0.02

≤0.0009

≤0.001

≤0.003

GCr15E

≤0.015

≤0.0006

≤0.001

≤0.0015

52100

0.93-1.05

0.15-0.35

0.25-0.45

≤0.025

≤0.015

1.35-1.6

≤0.25

≤0.1

≤0.3

≤0.0015

≤0.05

SUJ2

0.95-1.1

0.15-0.35

≤0.5

≤0.025

1.3-1.6

≤0.25

≤0.08

≤0.25

100Cr6

0.9-1.05

0.15-0.35

0.25-0.45

≤0.03

≤0.025

1.35-1.65

≤0.3

Hardness of High-carbon chromium-bearing steel grades

Grade	Hardness after Annealing
GCr15	179-207 HBW
52100	60-67 HRC
SUJ2	≤201 HBW
100Cr6	187–229 HBS

High-Carbon Chromium Bearing Steel Tube

Production Process of High-carbon chromium-bearing steel tubes

1. Raw materials + smelting

The smelting quality requirements for bearing steel are very high. It is necessary to strictly control the content of sulfur, phosphorus, hydrogen, etc., and the number, size, and distribution of non-metallic inclusions and carbides. Because the number, size, and distribution of non-metallic inclusions and carbides have a great impact on the service life of bearing steel, bearing failure is often caused by the expansion of microcracks generated around large inclusions or carbides.

✔ Raw materials: screened iron ore, scrap steel, alloy elements

2. Steelmaking methods:

✔ Electric arc furnace steelmaking: put the raw materials into the electric arc furnace, use the high temperature generated by the arc discharge to heat the materials to a molten state, and add alloy elements for synthesis

✔ Converter steelmaking: the raw material is molten iron, and high-pressure air or oxygen is blown into the molten iron in the furnace from the top, bottom, and side of the converter to remove unnecessary impurities and control the alloy composition

✔ Vacuum melting: in order to improve the purity of steel, especially in the production of high-quality bearing steel, vacuum smelting equipment is usually used to remove gas inclusions

3. Refining

✔ Electro-slag Remelting (ESR): Use the resistance heat generated when the current passes through the slag as a heat source for secondary refining to remove inclusions and gases in the molten steel and improve the internal quality and uniformity of the steel

✔ Vacuum degassing: Remove gases such as hydrogen, oxygen, and nitrogen from the molten steel in a vacuum environment to prevent these gases from forming pores or inclusions in the steel

4. Casting

✔ Continuous casting: Liquid steel passes through a continuous casting machine to form a continuous casting billet. The continuous casting process can reduce defects inside the steel and improve the uniformity of the material. At the same time, the shape and size of the continuous casting billet directly affect the subsequent forging and processing efficiency.

✔ Mold casting: Liquid steel is introduced into a pre-designed mold to form the billet

5. Tube billet forging

✔ Hot forging: The billet is heated to a certain temperature and then forged. It is forged into the initial form required for bearing steel, such as round bars, bars, etc., by forging, extrusion, etc. During the forging process, the grains of the steel are refined, the structure becomes denser, and its mechanical properties are improved.

6. Tube Forming

✔ Hot rolling: The round steel is heated and fed into the hot rolling mill. Through multiple rolling passes, the tube billet is deformed and formed into the required tube size. The hot rolling process is usually suitable for larger steel tubes, which can better control the tube wall thickness and the dimensional tolerance of the tube.

✔ Cold rolling: The hot-rolled tube is usually rolled twice at room temperature to control the outer diameter and wall thickness. It is suitable for high-carbon chromium-bearing steel tubes with smaller tube diameters. The surface of the cold-rolled tube is smooth, and the dimensional accuracy is high, which is suitable for applications with high precision requirements.

Heat Treatment of High-carbon chromium-bearing steel tubes

Spheroidizing annealing

- Purpose: Reduce hardness, improve machinability, and obtain uniformly distributed fine-grained pearlite to prepare for the final heat treatmentAnnealing

- Structure:

✔ Fine-grained pearlite (average carbide diameter 0.5-1μm, minimum 0.2μm, maximum 2.5μm)

✔ Uneven coarse-grained pearlite (average carbide diameter 2.5-3.5 μm, minimum 0.5 μm, maximum 6 μm)

- Annealing temperature: 780-810℃

After special heat treatment, the annealing temperature of the forging should be reduced by 10-20℃

Quenching + low-temperature tempering

- Purpose: Make the steel have high and uniform hardness, good wear resistance, and high contact fatigue performance

Performance of High-carbon chromium-bearing steel tubes

- Hardness: High

- Wear resistance: High

When linear bearings are working, not only rolling friction but also sliding friction occurs between the rings, rolling elements, and cages, which causes the linear bearing parts to wear continuously. In order to reduce the wear of linear bearing parts, maintain the precision and stability of linear bearings, and extend the service life, bearing steel should have good wear resistance.

- Contact fatigue strength: High

Under the action of cyclic loads, the contact surface of linear bearings is prone to fatigue damage, that is, cracking and peeling, which is the main damage form of linear bearings. Therefore, in order to improve the service life of linear bearings, bearing steel must have high contact fatigue strength.

- Hot working performance: Good

Limitations of High-carbon chromium-bearing steel tubes

- High brittleness

Although high-carbon chromium-bearing steel tube has high hardness, it is also relatively brittle, especially after quenching. Although tempering can improve toughness to a certain extent, it still cannot completely eliminate its brittleness, which may lead to fracture under impact load.

Under extreme low temperature or impact load, brittle fracture or fatigue failure is prone to occur.

- Limited corrosion resistance

Compared with stainless steel, it is more susceptible to corrosion from moisture, salt water, chemical media, etc.

- Sensitive to heat treatment process

The hardness and mechanical properties of high-carbon chromium bearing steel tubes are highly dependent on the heat treatment process, so the operating conditions (such as heating temperature, cooling medium, tempering time, etc.) need to be strictly controlled during the heat treatment process.

Improper heat treatment may cause the steel tube to be too hard and brittle, or the hardness is not enough to meet the requirements.

- Poor low temperature performance

In a low-temperature environment, high-carbon chromium-bearing steel tube has poor toughness and impact resistance and is prone to brittle fracture, so it is not suitable for applications in extremely cold conditions.

Applications

Civil aviation bearings

High-speed train bearings

Special bearing equipment

Shield machine main cutter bearings

High-speed precision machine tool spindles