Introduction

Characteristics

« Low alloy steel.

« Good strength, tenacity,corrosion and cutting properties.

Applications

Cr Mo steel for applications requiring high tensile and toughness values in the heat treated condition. The molybdenum addition preventsthe steel from being susceptible to temper brittleness. Used in Oil and Gas industry and Large Machinery Structural.

Physical Properties

Mechanical Properties

Heat Treatment

Annealing

Complete annealing: The steel is heated to about 850°C, held for a sufficient period of time and then slowly cooled to about 480°C with the furnace, followed by air cooling. This process can refine the grain, reduce the hardness, improve the plasticity and toughness, to facilitate the subsequent machining, can effectively eliminate internal stresses, so that the steel to obtain a stable organisation and properties.

Spheroidal annealing : for some need better cutting performance or for subsequent quenching to provide a more uniform organisation of the situation, can be used spheroidal annealing. Heating at a temperature between 750 - 770°C, holding and cooling slowly to spheroidise the carburites in the pearlite and obtain a uniform distribution of spherical carbides.

Normalising

The heating temperature is usually around 900°C. After holding, it is cooled in air. Normalising can refine the grain, make the organisation homogeneous, increase the strength and hardness of the steel, improve the cutting performance, reduce the surface roughness after machining, and eliminate the defects of overheated coarse crystal organisation and Weiss organisation of cast, forged and welded parts.

Hardening

Generally, the steel is first heated to 870 - 890°C for austenitising, so that the carbon is fully dissolved into the austenite, and then a suitable cooling method is selected according to the size and requirements of the parts. Oil cooling may be used for smaller sections, while water cooling may be required for larger sections to obtain a martensitic organisation, which significantly improves the hardness and strength of the steel, but the toughness and plasticity of the steel are reduced after quenching and there is a high degree of internal stress.

Tempering

Quenched steel must be tempered in time to remove internal stresses, reduce brittleness and adjust the balance between hardness and toughness.

1.Low Temperature Tempering: Tempering temperature between 150 - 250°C, the main purpose is to reduce the quenching stress, in maintaining high hardness and wear resistance at the same time, improve the toughness of the appropriate, applicable to the requirements of high hardness and wear-resistant parts, such as cutting tools, moulds and so on.

2.Medium Temperature Tempering: Tempering temperature of 350 - 500 ° C, can make the martensite decomposition, to get the tempered Torrite organisation, to improve the toughness at the same time, but still maintain high strength and hardness, suitable for the manufacture of parts subjected to high loads, impacts and medium-speed work, such as gears, spindles and so on.

3.high temperature tempering : tempering temperature of 500 - 650 ° C, get tempered Sohnite organisation, so that the steel has good overall mechanical properties, that is, strength, plasticity and toughness are better. Usually used in the manufacture of mechanical parts subjected to medium loads and medium speed work, such as automotive steering knuckles, rear half shafts and machine tools, gears, shafts and so on.

 Introduction

Equivalent Material & Chemical Composition

Characteristics

« The steel has good machinability with minimal machining distortion;

« Fatigue resistance is quite good, and it is a medium and other hardenable steel;

« 4140 has good strength and good overall mechanical properties after heat treatment;

« Good workability and high rate of material formation;

« The maximum operating temperature of 427 degrees Celsius.4140 strength, high hardenability, good toughness, quenching deformation is small, high temperature creep strength and lasting strength.

« degree and lasting strength

Applications

AISI 4140 is commonly used for a variety of applications in the oil and gas sector. Typical applications include components such as connection rods, collets, conveyor pins, gears, stem assemblies, pump shafts and tool holders

Physical Properties

Mechanical Properties

Heat Treatment

Quenching

 heating temperature 830 - 860 ℃, according to the workpiece to determine the holding time, generally 30 - 120 minutes, using oil cooling.

Tempering

temperature 550 - 650 ℃, holding time 1 - 3 hours, cooling mode for air-cooled or water-cooled.

 Normalising

heating to 850 - 900 ℃, holding time 30 - 90 minutes, cooling in the air naturally.

Annealing

complete annealing temperature 800 - 840 ℃, holding time 1 - 3 hours, slow cooling with the furnace; incomplete annealing temperature 770 - 800 ℃, holding time 1 - 3 hours, furnace cooling or air cooling. These processes are used to modify the properties of the steel for different applications.

Introduction

Equivalent Material & Chemical Composition

Characteristics

« It is a heat treatable, low alloy steel containing nickel, chromium and molybdenum. It is known for its toughness and capability of developing high strength in the heat treated condition while retain-ing good fatigue strength.

« But with high flake crake sensitivity and temper brittleness.

« It is not good at welding, before welding should preheat in high temperature, after welding must do stress relieving, applicate after quenched and tempered.

Applications

For permanently stressed components with large cross sections for automotive and mechanical engineering. For economic performance under severe dynamic stress, parts must be designed for optimum strength or toughness.

Physical Properties

Mechanical Properties

Heat Treatment

Quenching

Ordinary quenching: AISI4340 steel is usually heated to a certain temperature (such as around 800 ° C) for austenitization, and then rapidly cooled (such as quenching in oil). The quenching process promotes the transformation of steel structure from ferrite and pearlite to needle like martensite.

Double vacuum smelting and quenching: the microstructure of AISI4340 steel as quenched is mainly composed of Flat noodles and lamellar twin martensite, and the dislocation density in Flat noodles is high.

Tempering:

Effect of tempering temperature: With the increase of tempering temperature, the microstructure and properties of AISI4340 steel will change. For example, after tempering at 350 ℃, a large amount of carbides precipitate in AISI4340 steel produced by double vacuum smelting, and lamellar twinning martensite can still be observed; As the tempering temperature continues to increase, tempered martensite gradually forms.

Reason for property change: with the increase of tempering temperature, the lamellar twin martensite in AISI4340 steel produced by double vacuum smelting gradually decomposes and disappears, and the dislocation density in Flat noodles decreases, leading to the decrease of its strength, while the spheroidization of precipitated carbide is the main reason for the increase of plasticity.

Effect of different tempering temperatures: When heat treating the AISI4340 steel fan spindle, after quenching at 850 ℃ and tempering at 540 ℃, the mechanical properties of the spindle meet the technical requirements, including tensile strength of 1250 MPa, yield strength of 1140 MPa, elongation at break of 14.5%, section shrinkage rate of 55%, -40 ℃ impact absorption energy of 38.5-41.3 J, and surface hardness of 40-42 HRC3. The AISI/SAE 4340 steel was quenched and tempered at 300 ° C, 350 ° C, and 400 ° C, respectively. The results showed that the hardness and torsional resistance increased at different tempering temperatures.