"Strengthened steel shot" is essentially achieved through special chemical composition and heat treatment processes, resulting in higher hardness, better toughness, and fatigue resistance, making it more wear-resistant and with a longer service life than ordinary steel shot.

The differences in chemical composition between strengthened steel shot from different manufacturers and grades mainly lie in the following key elements. Subtle adjustments to these elements directly determine the final performance of the steel shot:

1. Core Differentiating Elements These are alloying elements actively added to alter the internal structure and properties of the steel.

* **Carbon**:

* **Role**: The most critical element. Determines the **base hardness** of the steel shot. Higher carbon content results in greater hardness potential, but may also increase brittleness.

* **Difference**: Ordinary steel shot may have a lower carbon content (e.g., 0.2%-0.5%). **Strengthened steel shot typically has a higher carbon content (generally 0.7%-1.2% or even higher)** to ensure high hardness can be achieved through heat treatment. Different hardness grades (e.g., HRC 40-50, 50-60, ...) For steel shot (60-67), carbon content is the primary adjustment parameter.

* **Silicon (Si):**

* **Function:** An important strengthening element. It significantly improves the strength, hardness, and elastic limit of steel, while also enhancing fatigue resistance. It also refines the microstructure during heat treatment and improves tempering stability.

* **Difference:** Ordinary steel shot has a lower silicon content. **Strengthened steel shot typically has a deliberately increased silicon content (e.g., 0.4%-1.5%), which is one of the key factors in its "strengthening," making it less prone to breakage and deformation under repeated impacts.

* **Manganese (Mn):**

* **Function:** Improves hardenability (making the hardness more uniform inside and outside the steel shot cross-section), strength, and wear resistance. It can combine with sulfur, reducing the harmful effects of sulfur's hot brittleness.

* **Difference:** Strengthened steel shot usually also has a higher manganese content than ordinary steel shot to ensure sufficient hardenability, allowing even larger shot cores to be strengthened.

### 2. Important Alloying Elements These elements are commonly used in high-performance or special-purpose strengthened steel shot.

* **Chromium** (Cr)**:

* **Function**: Significantly improves hardenability, hardness, wear resistance, and corrosion resistance. It is a hallmark element of alloy steel shot.

* **Difference**: Ordinary carbon steel shot has a very low chromium content. **Mid-to-high-end reinforced steel shot (often called "alloy steel shot" or "chromium alloy steel shot") contains added chromium (e.g., 0.2%-1.5% or higher).** High-chromium steel shot (such as stainless steel shot) contains even higher levels of chromium (typically >10%) and is mainly used for corrosion protection or special surface treatments.

* **Molybdenum (Mo)** and **Nickel (Ni)**:

* **Function**: Molybdenum significantly improves hardenability, strength, and high-temperature performance, and reduces temper brittleness. Nickel improves toughness, strength, and fatigue resistance.

* **Difference**: These are elements that may be added to **high-end reinforced steel shot**, used to manufacture top-tier products requiring extremely high toughness and extremely long service life (such as steel shot used in aerospace and heavy machinery). They are more expensive.

### 3. Impurity Elements Requiring Control

The lower the concentration of these elements, the better; their levels also differentiate quality.

* **Sulfur (S)** and **Phosphorus (P)**:

* **Function**: Harmful impurities. Sulfur causes hot brittleness, and phosphorus causes cold brittleness; both severely impair the toughness of steel, making the steel shot brittle under impact.

* **Difference**: High-quality strengthening steel shot has extremely strict control over sulfur and phosphorus (typically requiring below 0.03%, and premium quality requiring below 0.015%). Ordinary or low-quality steel shot may have higher levels.

* **Oxygen (O)** and **Inclusions**:

* **Function**: Non-metallic inclusions such as oxides in molten steel are the origin of fatigue cracks and significantly reduce the fatigue life of steel shot.

* **Differences:** Strengthened steel shot produced using advanced processes such as **vacuum degassing and ladle refining** has extremely low gas and inclusion content, resulting in a highly pure internal structure. This is one of the fundamental reasons why its durability far surpasses that of ordinary cast steel shot. Ordinary steel shot is mostly produced through simple casting and contains many inclusions.

### Summary Table of Chemical Composition Differences

| Chemical Elements | Role in Strengthened Steel Shot | Main Differences from Ordinary/Low-Quality Steel Shot |

| **Carbon (©)** | Provides basic hardness | **Higher content** (typically >0.7%) to match the target hardness grade. |

| **Silicon (Si)** | Improves strength, hardness, elasticity, and fatigue resistance | **Intentionally added and increased in content**, it is one of the core elements for "strengthening". |

| **Manganese (Mn)** | Improves hardenability and strength | Typically higher content to ensure uniform cross-sectional properties. |

| **Chromium (Cr)** | Improves hardenability, wear resistance, and corrosion resistance. **A hallmark of mid-to-high-end products:** Contains almost no ordinary steel shot. | | **Molybdenum/Nickel:** Significantly improves toughness, hardenability, and overall performance. | **Elements selected for high-end products:** High cost, superior performance. | | **Sulfur/Phosphorus:** Harmful impurities, reduce toughness. | **Strictly controlled, extremely low content** (high-quality <0.015%). | | **Gases/Inclusions:** Crack initiation, reduces fatigue life. | **Extremely low content through refining processes, resulting in a purer internal structure. |

 Conclusion

The so-called "strengthening" in chemical composition mainly manifests in:

1. **Higher carbon, silicon, and manganese content** to achieve high hardness and strength.

2. **Possible addition of alloying elements such as chromium, molybdenum, and nickel** to further improve hardenability, toughness, and wear resistance.

3. Extremely low levels of sulfur, phosphorus impurities, and oxide inclusions ensure high purity and high toughness.

Therefore, when selecting reinforced steel shot, it is crucial to consider not only the hardness index but also, and perhaps more importantly, its chemical composition report. A report specifying strictly controlled C, Si, Mn, and Cr contents, as well as extremely low S and P contents, is the most direct proof of high-quality reinforced steel shot. Furthermore, its manufacturing process (such as smelting and heat treatment) is equally important as the chemical composition, jointly determining the final superior performance.