Analyze Steel Tube Standard about DIN2391

Today I will simply expound what is DIN2391 standard and analyze some detail information in this standard.

The DIN2391 that is Germany standard specifies technical delivery conditions and dimensions about cold finished seamless precision steel tubes. Like this tube should have following requirements: exact dimensions and feasible a small wall thickness and a particular surface condition and specific mechanical properties. I will analyze that under different technical delivery conditions, compare different steel grades have the mechanical properties.

1.  What is steel grades in DIN2391.

The tube should be produced from electric steel or basic oxygen steel, but other processes like melting and casting can be up to manufacturer. The following list is Steel Grades information.

We can see that steel grades have two types:Grade A and Grade C. Grade A:St30si,st30al,st35, st45,st52. Without Grade A, other all steel grades called Grade C.

2. What is technical delivery conditions

Technical delivery conditions also called final supply conditions that have five conditions:BK(Cold finished-hard); BKW(Cold finished-soft); BKS(Cold finished and stress-relieved); GBK(Annealed); NBK(Normalized). Tubes that be in different final supply conditions can be applied in different fields.The following list is detail descriptions about final supply conditions.

After reading each description, we can that temperature and tubes’ cool-down time up to different final supply conditions.

3. What is mechanical properties

In common condition, the mechanical properties have following parts: Tensile strength(test the tube’s force that a structural beam to the point where it breaks), Yield strength(The stress the material can withstand without permanent deformation, Yield strength is the stress which will cause a permanent deformation of 0.2% of the original dimension), Elongation(After tensile fracture, the percentage of the total elongation to the original gauge length).Following list is Mechanical properties of tubes at ambient temperature information.

Above all we can see following conclusions:

1. Under the same material designation and BK, BKW,BKS,GBK final supply condition, the tensile strength and elongation have inverse proportion.For example, Under BK,BKW,BKS,GBK, Material ST 35, tensile strength data decrease step by step, but the elongation data increase gradually.

2. Under the same final supply conditions, the material carbon content have higher and the tensile strength date is higher. For example ST35 (C:0.17%) Mini tensile strength 480N/mm,ST45(C:0.21$) Mini tensile strength 580N/mm,ST52(C:0.22) Mini tensile strength 640N/mm.

So how to choose right tube to apply in your field, we can choose different material and through different final supply conditions to meet your needs and mechanical properties of tubes.