Basic knowledge of forged (rolled) steel balls?

In the steel ball industry, how do forged (rolled) steel balls differ from cast steel balls? What are the basics of the forged (rolled) steel ball production process? Let's delve into the world of steel balls and explore its mysteries.

1. Forged (rolled) steel ball production process

Forging (rolling) steel balls is essentially a high-temperature deformation process. Forging steel balls, in particular, requires suitable temperatures (including initial and final temperatures), die deformation transitions, suitable forged ball materials, and appropriate heat treatment methods.

The production line uses qualified round steel directly fed into the heating system for heating.

=> Hot blanking (blank length varies depending on specifications)

=> Air hammer forging (or other air hammer equipment)

=> Isothermal holding

=> Quenching heat treatment

=> Holding and tempering process

=> Hardness testing - surface testing

=> Product Storage

II. Heating Methods

Currently, there are three heating methods: The first is the traditional coal-fired reverberatory furnace, which is simple to operate and suitable for a variety of materials, especially carbon steel, mild steel, and inferior materials such as mill scrap. However, its disadvantages are high heat consumption, typically 3.2%-4.0%, and deep decarburization on the surface of the steel balls. The second is the gas-fired furnace (natural gas, coal gas, heavy oil, etc.). It is characterized by high labor efficiency and moderate heat consumption, typically 1.2%-2.5%. However, the disadvantage is that strict mastery of the characteristics of the gas furnace and its safe operation are required. The third is the electric furnace, which is characterized by fast heating, high output, environmental friendliness, low labor intensity, and low heat consumption, typically 0.8%-1.5%. However, the disadvantage is that strict operating procedures must be followed and the heating sensor should be replaced promptly.

3. Heat Treatment

This is a critical aspect of forged steel ball production, directly impacting whether the balls will break or not. A stable heat treatment process can achieve the hardness range required by customers while also increasing the hardened layer of the steel balls, which is beneficial for wear resistance during grinding. Tempering is also necessary. Without post-treatment, the work is only half done; both are essential.

4. Improper forging (rolling) steel ball processing. The most common defects include the following:

1. Large grains: Large grains are typically caused by excessively high initial forging temperatures and insufficient deformation, excessively high final forging temperatures, or deformation falling within the critical deformation zone. Therefore, it is crucial to properly control the heating temperature of forged (rolled) steel balls.

2. Grain non-uniformity: Grain non-uniformity refers to the presence of coarse grains in some areas of the forging and smaller grains in others. The main causes of grain non-uniformity are uneven deformation across the billet, resulting in varying degrees of grain breakage, deformation falling within the critical deformation zone in a localized area, localized work hardening of high-temperature alloys, or localized coarse grains during quenching.

3. Chilling: Low temperatures or rapid deformation during forging (rolling) can cause the softening caused by recrystallization to outpace the strengthening (hardening) caused by deformation, resulting in the retention of some cold-deformed microstructure within the forging after hot forging. This structure increases the strength and hardness of the forging, but reduces its plasticity and toughness. Severe chilling can lead to forging cracks.

4. Cracks: Cracks are typically caused by internal stresses resulting from high tensile, shear, or additional tensile stresses during forging. Cracks typically occur on the surface or core of the steel ball. There are two main sources of cracking: inherent structural defects in the steel material, such as porosity or deep scratches caused by rolling; and cracks caused by the quenching temperature during heat treatment, typically resulting from high-temperature quenching.