Project Description

AISI 4145/4145H steel Manufacturer and Exporter,supplied with round,square,flat,block,and shaft etc.

AISI 4145 Steel is defined as Cr-Mo series alloy steel as per USA standard ASTM A29.Like AISI 4130 steel, it is widely used in the oil and gas industry.Compared with AISI 4140 steel, AISI 4145 has a higher carbon content, which means higher strength and hardenability.

AISI 4145 steel is usually used in the quenched and tempered condition, and can be used for oil drill collars, shafts, spindles, and high-load control wheels, bolts, studs, gears, etc.

AISI 4145 Forged round steel with QT condition


Hot Forged Round bar:Φ80-Φ1000mm

Hot Rolled  Round bar:Φ16-Φ130mm

Hot Forged Square bar: Max Thickness:500mm

Flat bar/Blcoks:Thickness :120-800mm ,Width:120-1500mm

Surface FinishBlack-Forged Black-Rolled Turned   GrindingPolishedPeeledCold Drawn
Tolerance(0,+5mm)(0,+1mm)(0,+3mm)Best h9Best h11Best H11Best H11




  • Initial Forging Temperature:1180℃
  • Final Forging Temperature:850℃
  • Forging Ratio:above 4:1
  • Cooling Method After Forged: AISI 4145 Steel should be cooled as slowly as possible in sand after forged.


Is AISI 4145 Steel For Oil Drill Collars?

AISI 4145 steel has good comprehensive mechanical properties and corrosion resistance after heat treatment, and is the most widely used medium-carbon low-alloy steel in the international petroleum industry.

Due to its good strength and toughness and resistance to H2S corrosion, AISI 4145 Steel can be used as a drill collar material in the process of oil exploitation, and also be used for the production of oil drill pipes. Especially for its excellent resistance to corrosion in oil and gas environments, AISI 4145 steel is also used in the production of petroleum pipelines.

Is AISI 4145 Steel Corrosion Resistant?

AISI 4145 steel is mainly used in the production of oil drill collars, and can also be used in the production of oil casing, which are used in corrosive environments in oil fields.

The good structure of AISI 4145 steel (tempered sorbite) can improve the corrosion resistance. In addition, the alloying element Cr can be dissolved in F, which can improve the corrosion resistance, and the Mo element also helps to improve the corrosion resistance.

Can AISI 4145 Steel be Welded?

Calculated from the composition of AISI 4145, its CE is about 0.85,and its weldability is very poor.When welding AISI 4145 steel, preheating before welding and post-welding heat treatment are mandatory. Strict welding process for AISI 4145 can ensure the reliability of welding.

What is AISI 4145H?

When add “H”,this means that AISI 4145 steel is required to ensure hardenability.In fact, there is no difference in composition between AISI 4145H and AISI 4145 steel.

What is AISI 4145H MOD?

MOD means Modify.Therefore, AISI 4145H MOD is an improvement on the basis of AISI 4145 steel, which may be due to changes in composition or more stringent performance requirements.

AISI 4145H MOD Drill Collar

4145H MOD hollow bar

 AISI 4145 Steel Vs 50CrMo4 Steel

As a representative of medium carbon Cr-Mo series low alloy steel,AISI 4145 is derived from ASTM A29 American standard, while 50CrMo4 belongs to European standard EN10083.First of all, let’s take a look at their differences from their composition.please see the table below.

ASTM A2941450.43-0.480.15-0.35 0.75-1.0 ≤0.035≤0.040.8-1.10.15-0.25
EN1008350CrMo4 0.46-0.54≤0.40.5-0.8≤0.035≤0.0350.9-1.20.15-0.30

From the above table,the main difference between the elements is in C and Mn, and the other elements are generally very small.Due to these differences, 50CrMo4 steel is superior to AISI 4145 steel in terms of strength and hardenability,but its welding performance is relatively poor.

AISI 4145 steel is mainly used in the petroleum industry, such as drill collars, drill pipes, and petroleum pipelines.While 50CrMo4 is used for forgings that require higher strength or larger cross-section than 42CrMo4 steel, such as large gears for locomotive traction, supercharger transmission gears, rear axles, engine cylinders, 1200~2000m oil deep well drill pipe joints and fishing tools, etc.Sometimes 50CrMo4 steel can replace quenched and tempered steel with higher nickel content.


AISI 4145H steel adopts appropriate composition design and advanced production technology to obtain good mechanical properties, so that it can meet the performance requirements of 4145H steel in the process of oil drilling.

The production process of AISI 4145H steel:

Molten steel pretreatment →Converter→LF→RH→Continuous casting-continuous casting→Hot delivery→Heating→Hot rolling/Forging→Heat preservation→Straightening→Annealing→Grinding→Inspection→Delivery

In order to obtain a uniform and compact casting blank, in the molten steel smelting process, it undergoes magnesium-based powder spraying desulfurization treatment, stirring with inert gas, vacuum degassing treatment, and microalloying element V/Ti to treat the inclusions in the steel.

In the smelting process, attention should be paid to the matching of C and Cr, Mn, Mo and other elements. These means ensure that the alloying elements in the steel are uniform, and a more uniform ferrite structure can be obtained.

Controlled rolling and controlled cooling technology can help improve the mechanical properties of 4145H steel, make it have good mechanical properties, ensure the uniformity of hardness, and prepare for subsequent deep processing.


  • AISI 4145 Steel Annealing

The annealing process of AISI 4145 steel is complete annealing, which can completely recrystallize the structure of the steel to eliminate the defects in the structure after the material is forged or rolled.

According to various studies and demonstrations, the best annealing temperature for AISI 4145 is 820℃,and it will be cooled with the furnace after holding for an appropriate time. The final structure in the steel is ferrite and pearlite,and its surface hardness is about 200HBW.

  • AISI 4145 Steel Quenching & Tempering

AISI 4145 steel can obtain satisfactory overall performance through quenching and tempering heat treatment to meet the requirements of petroleum equipment.

Heating temperature and holding time are two important parts that affect the quality of quenching. The structure obtained after austenitization achieved by heating will affect the performance of the material after quenching.

For AISI 4145 steel, the appropriate quenching temperature is between 840-860ºC, and the holding time depends on the thickness of the material.

AISI 4145H Quenching Diagram

AISI 4145H Steel Quenching Diagram

Tempering process should be followed after quenching immediately.When 4145 steel is used as drill collar steel, it needs to be tempered at a high temperature of 560-630ºC to obtain tempered sorbite, and finally obtain good comprehensive mechanical properties.

AISI 4145H Steel Tempering Diagram

AISI 4145H Steel Tempering Diagram

  • AISI 4145H Steel Mechanical Property in Q&T Condition
Tensile Strength
Yield Strength
Charpy Impact

Actual Data