How Much Do You Know 40Cr Bolts

1Introduction of 40Cr Bolts:

are the standard steel grade of China GB. 40Cr steel is one of the most widely used steels in machinery manufacturing. After quenching and tempering treatment, it has good comprehensive mechanical properties, good low temperature impact toughness and low notch sensitivity. The hardenability of 40Cr steel is good.It can be hardened to 28~60mm deep when water quenching is done.It can be hardened to 15~40mm deep when oil quenching is done. This steel is also suitable for cyanidation and high frequency quenching in addition to common quenching and tempering. The cutting performance is good. When the hardness is 174~229HB, the relative machinability is 60%. The steel is suitable for making medium plastic molds.






Bolt: Mechanical parts, cylindrical threaded fasteners with nuts. A type of fastener consisting of a head and a screw (a cylinder with an external thread) is required to be fitted with a nut for fastening the two parts with through holes. This type of connection is called a bolted connection. If the nut is unscrewed from the bolt, the two parts can be separated, so the bolt connection is a detachable connection.

At present, the standard parts on the market mainly include carbon steel, stainless steel and copper.

  1. Classification of 40Cr Bolts:

According to the way of connection, it is divided into ordinary and reamed holes. According to the shape of the head, there are hexagonal heads, round heads, square heads, countersunk heads, etc. The hexagonal head is the most commonly used. Generally, the countersunk head is used where the connection is required.

Ordinary bolts can be divided into three grades A, B, and C according to the production precision. Grades A and B are refined bolts, and grade C is thick bolts. For the connection bolts for steel structures, unless otherwise specified, they are generally ordinary C-class bolts. There are differences in the methods of different grades. Generally, the corresponding processing methods are as follows:Grade A and B bolts are machined by lathe, the surface is smooth and the size is accurate. The material grade is 8.8. The production and installation are complicated.The price is relatively high. They are rarely used.

Grade C bolts are made of unprocessed round steel.They are not accurate enough to have a material performance rating of 4.6 or 4.8. The deformation is large when the shear connection is made.But the installation is convenient.The production cost is low.It is mostly used for the temporary connection of the tensile connection or the installation.

  1.  Use of 40Cr Bolts

There are many names for bolts. Everyone’s name may be different. Some people call them screws.Some are called bolts.And some people call them fasteners. Although there are so many names,the meanings are the same and they are bolts. Bolts are a general term for fasteners. Bolts are tools that use the physics and mathematical principles of the circular rotation and friction of the bevel of an object to progressively fasten the components of the object.

  1. Different Gride for 40Cr Bolts 

According to the relevant standards, the performance grades of carbon steel and alloy steel bolts are more than 10 grades. They are grade 3.6, 4.6, 4.8, 5.6, 6.8, 8.8, 9.8, 10.9, 12.9. Among which the bolts of grade 8.8 and above are made of low or medium carbon alloy steel. Carbon steel is heat treated (quenched, tempered), commonly known as high-strength bolts.And the rest is commonly referred to as ordinary bolts. The bolt performance grade label is composed of two parts. They represent the nominal tensile strength value and the yield ratio of the bolt material. According to the class of steel performance,stainless steel bolts are classified into.A1-50, A1-70, A1-80, A2-50, A2-70, A2-80, A3-50, A3-70, A3-80, A4-50  A4-70, A4-80, A5-50, A5-70, A5-80, C1-50, C1-70, C1-110, C4-50, C4-70, C3-80, F1-45, F1- 60. The first letter and number represent the group of stainless steel. And the second and third digits represent 1/10 of the tensile strength.

  1. Common Surface Treatment Methods for Bolts

Bolts generally need to be surface treated. There are many types of surface treatments for bolts. Generally, blue, electroplated, oxidized, phosphatized, non-electrolytic zinc sheet coatings are commonly used. Among them, plating is the most extensive. For fasteners, not only is it required to have a certain degree of corrosion resistance, but also the interchangeability of the threads must be ensured.It can also be called screwing.

Comparison: The lowest cost of blue is the worst. The galvanizing cost is higher and the anti-corrosion effect is better. Chrome plating is costly but best preserved. The blue surface is blue. The galvanized surface is silver-gray.And the chrome finish is reflective.

  1. Inspection of Bolts

For large-volume use bolts, the relevant inspections are carried out in the warehouse.

The hardness of the bolts can be tested.Bolt torsion torque can be tested.The corresponding salt spray test can be done.The appearance should have no obvious defects. Threads can be tested with standard pass gauges. For other inspection items,please refer to the general specifications for common bolt threads and screws.

  1.  Calculation for Thread Size and Length

The thread size has a distinction between a preferred specification and a non-preferred specification. In general, the second series of non-preferred threads are not used. For  example,M14 bolts are not preferred. For the interchangeability of bolts, not all sizes of bolts are available. There are also series of bolt lengths, which are divided into full thread and non-full thread. The length of the nut 0.3d should be excluded when calculating the bolt length.

8.40Cr bolts sent to Finland

Just in June, we received a purchase order from the Finnish customer about 40Cr bolts.And soon we arranged the production according to the customer’s drawings. Below is a picture of the bolts we sent to Finland.

40Cr bolts

Eternal Bliss Alloy Casting & Forging Co, Ltd.

Technical Dept.


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