1. The definition of “high-strength steel” evolves with technological advancements relative to contemporary demands. Generally, alloy steels with yield strengths exceeding 1,370 MPa (140 kgf/mm²) and tensile strengths surpassing 1,620 MPa (165 kgf/mm²) are classified as ultra-high-strength steels. Based on alloying levels and microstructure, these are categorized as: - Low-alloy medium-carbon martensite-strengthened ultra-high-strength steel - Medium-alloy medium-carbon secondary precipitation-hardened ultra-high-strength steel - High-alloy medium-carbon Ni-Co-type ultra-high-strength steel - Ultra-low-carbon martensite age-hardened ultra-high-strength steel - Semi-austenitic precipitation-hardened stainless steel.

2. High Carbon Steel (High Carbon Steel) Commonly referred to as tool steel, with carbon content ranging from 0.60% to 1.70%, it can be quenched and tempered. Hammers, pry bars, and similar tools are manufactured from steel containing 0.75% carbon; Cutting tools like drills, taps, and reamers are made from steel with 0.90% to 1.00% carbon content.

After appropriate heat treatment or cold drawing hardening, high-carbon steel exhibits high strength and hardness, high elastic limit and fatigue limit (especially notch fatigue limit), and acceptable machinability. However, it has poor weldability and cold plastic deformation capability. Due to its high carbon content, it is prone to cracking during water quenching. Therefore, dual-liquid quenching (water quenching + oil cooling) is commonly used, while oil quenching is preferred for small-section parts. This type of steel is typically used after medium-temperature tempering or normalizing following quenching, or in a surface-hardened state. It is primarily used for manufacturing springs and wear-resistant components. Carbon tool steel is essentially high-carbon steel with minimal alloying elements. It represents a cost-effective tool steel grade offering good hot and cold workability with broad applicability. With carbon content ranging from 0.65% to 1.35%, it is specifically designed for tool manufacturing. High-carbon steel has a density of 7.81 g/cm³. It can be used in fishing tackle production.

Advantages:
1. Achieves high hardness (HRC 60–65) and excellent wear resistance after heat treatment.
2. Exhibits moderate hardness in the annealed state with good machinability.
3. Raw materials are readily available, resulting in low production costs.

High-carbon steel generally refers to steel with a carbon content greater than 0.6%. While heat treatment can achieve high hardness, it also results in increased brittleness.
High-strength steel has high comprehensive performance, not just high hardness. Generally, high-strength steel is alloy steel, which is steel with other metal elements added, such as manganese, chromium, nickel, etc., which can greatly improve the overall strength of the steel.

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