Chrome Molybdenum Steel Round Bar

Chrome molybdenum steel round bar, also known as medium-temperature hydrogen-resistant steel, is an alloy of chromium (Cr), molybdenum (Mo), iron (Fe), and carbon (C). It has good hardenability and can be deep quenched instead of the anti-saw lock surface quenching on the market. Due to its special high-quality performance, it is often used to manufacture some high temperature and high pressure resistant valves and pressure vessels, such as chromium molybdenum steel safety valves, chrome-molybdenum steel gate valves, screwdriver bits, bicycles, etc.

Properties of chrome molybdenum steel round bar:

1. Good hardenability, deep hardening can be carried out, instead of surface hardening for anti-saw locks on the market

2. Less tendency to temper brittleness

3. Good processability at high temperature, beautiful after processing

4. Good weldability

5. The impact absorption performance is good, the hammer will have a sense of rebound when it hits it, and it cannot be destroyed violently

Advantages of chrome molybdenum steel round bar:

1. Good processability

2. Good impact absorption performance

3. Easy to weld

The basic characteristics of chromium molybdenum steel round bar:

heat resistance

The addition of chromium, molybdenum, phosphorus and other elements effectively improves the high-temperature oxidation resistance and high-temperature strength of steel. The mechanism of action is as follows: chromium mainly exists in cementite (Fe3C), and chromium dissolved in cementite improves Lower the decomposition temperature of carbides, prevent the occurrence of graphitization, and improve the heat resistance of steel. Molybdenum has a solid solution strengthening effect on ferrite and can also improve the stability of carbides, so it is beneficial to improve the high temperature strength of steel. The addition of an appropriate amount of vanadium can make the steel maintain a fine-grained structure at a higher temperature, and improve the thermal stability and strength of the steel.

Hydrogen corrosion resistance

Elements such as chromium and molybdenum improve the stability of carbides, prevent the decomposition of carbides, and reduce the chance of carbides and precipitated carbon and hydrogen reacting to form methane. The addition of vanadium can make the steel maintain a fine grain structure at a higher temperature, which greatly increases the stability of the steel to hydrogen under high temperature and high pressure.

Temper Brittleness

The temper brittleness of chrome-molybdenum steel refers to the phenomenon that the impact toughness will decrease when it is operated in the temperature range of 370°C-595°C for a long time. And our commonly used hydrogen equipment just works in this temperature range for a long time. According to the experimental research, among the chromium-molybdenum steels commonly used in pressure vessels, the tendency of temper embrittlement with a Cr content of 2%-3% is the most serious. P, Sb, Sn, As, Si, Mn and other elements have a great influence on temper brittleness. Embrittlement is reversible, and severely embrittled materials can be debrittled by proper heat treatment.

High brittle and hard tendency, prone to delayed cracks

Due to the addition of chromium, molybdenum, vanadium and other alloying elements, the critical cooling rate of steel is reduced and the stability of supercooled austenite is improved. If the welding cooling rate is faster, the transformation from austenite to pearlite is not easy to occur in the superheated zone of the heat-affected zone, and it will transform to martensite at a lower temperature to form a hardened structure. Under the combined action of complex residual stress and diffusive hydrogen in welded joints, hydrogen-induced delayed cracks are easily produced in the hardened structure in the weld zone and heat-affected zone.

The following are common national standards

Chinese standard:

GB/T 3077-2015 "Alloy Structural Steel" specifies a series of technical requirements for alloy structural steel, including chemical composition and mechanical properties.

British Standard:

Hot-rolled alloy steel products (BS EN 10083-1): This standard specifies a range of hot-rolled alloy steel products for the manufacture of machine parts

American standard:

Alloy Structural Steel Grades (ASTM A29/A29M): This standard covers a range of alloy structural steels, which may include chrome-molybdenum round bars.

Low- and High-Strength Low-Alloy Structural Steels (ASTM A572/A572M): This standard specifies a family of low-alloy and high-strength low-alloy structural steels used in buildings, bridges, and other engineering.

Japan

Alloy structural steel materials (JIS G4053): This standard specifies a series of alloy structural steel materials suitable for machine parts, bearings, etc.

Alloy Steel Round Bars Standard Diameter Tolerances (Inches)

Molybdenum Round Bars Standard Length Tolerances (Inches)